Ghost Proposal_Darin Gaytan by Darin Gaytan

Southern California Aircraft Design Presents

Ghost

Next Generation Strategic Bomber

Darin Gaytan Member # 279164 USC Co-Lead Aircraft Performance

Michael Zarem Member # 416621 USC Co-Lead Mission Capability

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Jorge E. Montoya Member # 436282 USC Configuration Structure & Payload

Alan Liu Member # 437297 USC Stealth Engineering Aircraft Sizing

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Azadeh Keyvani Member # 280596 UCLA Weight Engineering Pilot Situational Awareness

Sean Keil Member # 407969 USC Systems Architecture C4ISR Integration

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Andrew Levinson Member # 457142 USC Combat Effectiveness Ordnance

Keith Homlund Member # 413045 USC Aerodynamics (CFD) Airfoil Optimization

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Richard Boles Member # 437301 USC Propulsion Stability & Control

Geoff Legg Member # 438075 USC Aerodynamics (CFD) High Lift Mechanism

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____________________ Dr. Geoff Spedding Member # 233796 USC Chairman & Project Advisor

Dr. Charles A. Radovich Member # 189769 USC Faculty Advisor

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Nomenclature – canopy/windshield drag coefficient – empennage drag coefficient – leading/trailing edge slat/flap coefficient – fuselage drag coefficient – landing gear drag coefficient – interference drag coefficient – miscellaneous drag coefficient typically caused by speed brakes, struts, inlet drag, antennas, gaps, and the like – nacelle/pylon drag coefficient – store(s) drag coefficient – trim drag coefficient – wing drag coefficient – Airplane lift coefficient – Maximum airplane lift coefficient including flap effects – Mission Fuel Fraction – Empty Weight – Weight of Fuel used during mission – Airplane weight at takeoff

Acronyms AAM – Air-to-Air Missile AC – Alternating Current ACM – Air Cycle Machine AESA – Active Electronically Scanned Array AEW&C – Airborne Early Warning & Control AFDX – Avionics Full-Duplex Switched Ethernet AMCAS – Advanced Multi-band Communications Antenna System ATC – Air Traffic Control BPR – Bypass Ratio C4ISR – Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance CDS – Countermeasures Dispensing System CFRP – Carbon Fiber Reinforced Plastic DAS – Distributed Aperture System DC – Direct Current DRFM – Digital Radio Frequency Memory DSM – Design Structure Matrix EHF – Extremely High Frequency EISS – Enhanced Integrated Sensor Suite ELINT – Electronic Intelligence EMI – Electromagnetic Interference EMP – Electromagnetic Pulse EMR – Electromagnetic Radiation EO – Electro-Optical EOTS – Electro-Optical Targeting System

EPLRS – Enhanced Position Location Reporting System ESDU – Engineering Sciences Data Unit EW – Electronic Warfare EWS – Early Warning System FC – Fiber Channel FCS – Future Combat System FLIR – Forward Looking Infrared FRP – Federal Radio Navigation Plan GATS – Global Position System Aided Target System Gbps – Gigabit per Second GPS – Global Positioning System HF – High Frequency IFF – Identification Friend or Foe IR – Infrared IRST – Infrared Search and Track ISR – Intelligence, Reconnaissance, and Surveillance JIAWG – Joint Integrated Avionics Working Group JSF – Joint Strike Fighter / F-35 KVA – Kilovolt-Ampere LPI/LPD – Low Probability-of-Interception/-Detection LRE – Launch and Recovery Element LWR – Laser Warning LUR – Line Replaceable Unit MADL – Multifunction Advanced Data Link Mbps – Megabits per Second MCE – Mission Control Element MIDS JTRS– Multifunctional Information Distribution System Joint Tactical Radio System MWNT – Multi-Walled Carbon Nanotubes NATO – North Atlantic Treaty Organization NLF – Natural Laminar Flow POFACETS – Physical Optics Radar Cross Section Prediction and Analysis Application RAM – Radar Absorbing Materials RCS – Radar Cross Section RF – Radio Frequency RFP – Request for Proposal RMP – Radar Modernization Program SAM – Surface-to-Air Missile SAR – Specific Air Range [Preliminary Sizing] SAR – Synthetic Aperture Radar [Systems] SATCOM – Satellite Communications SCAD – Southern California Aircraft Design SCF – Specific Fuel Consumption SIGINT – Signals Intelligence SINCGARS – Single Channel Ground and Airborne Radio System SRW – Soldier Radio Waveform TACAN – Tactical Air Navigation TR – Transmit/Receive TSFC – Thrust Specific Fuel Consumption UHF – Ultra High Frequency UV – Ultraviolet VHF – Very High Frequency

Dedication & Acknowledgement We at Southern California Aircraft Design (SCAD) understand that this project would not have been possible without the generous guidance and help of our friends, family, peers, and mentors. Dr. Geoff Spedding, Dr. Charles Radovich, and Mr. Mark Page of USC’s Aerospace and Mechanical Engineering Department were instrumental in providing critical and relevant feedback during the development of this project. Their expertise and experience in aeronautical design and the aeronautical industry established a cornerstone from which we were able to build what proved to be an exciting and challenging aircraft. Mr. Sina Golshany of the Boeing Company for providing insight and guidance throughout the entire project. His contributions reinforced and tested our ideas by encouraging better discussion within the team. Mr. Christopher Penny, a Support Engineer at CDadapco, and Mr. Ahmed Al Makky, a PhD student at Warwick University’s Centre for Scientific Computing, both provided exceptional instruction in the use of Star CCM+ CFD analysis tool. We would like to recognize current and former students Mark Alphonso, Supachai Anuyouthapong, Sanjeev Datta, Kirsten Gradel, Jen Lee, John Roehrick, Si Shen, Bahram Peace, Sahil Kabra, and Zhipeng Wang that contributed invaluable advice and experience, which was greatly appreciated. Additionally, a very special thanks is dedicated to the faculty and staff at USC and UCLA whose contributions are too numerous to name. Samantha Graves and Silvana Martinez -Vargas provided excellent, patient, and creative support in our never-ending search for sufficient meeting space and time, for which we thank them. Like all projects in work and life, there exist unplanned and unexpected setbacks. We at SCAD wish for the speedy and full recovery of our former teammate and recent USC graduate, Todd Erickson. Our hearts go out to his family and friends during this difficult time. In closing, we would like to dedicate this year’s project to Ying Wu. Her contributions are responsible for the visually improved graphic output of the radar cross section analysis. Our condolences to her family and to her friends, of which she had many.

Executive Summary With the aging fleet of United States Air Force (USAF) bombers at its lowest total number since the 1930s1 and with the total number of aircraft capable of completing a mission more than 1,000 nm into enemy territory from the last air-to-air refueling station limited to just 16,2 the USAF is no longer capable of mounting full-scale air campaigns or rapid-response long-range strikes against heavily defended targets. The USAF needs an advanced long-range strategic bomber that is capable of deploying from the US or advanced US-allied air bases on short notice to strike entrenched targets in highly defended airspace with a price tag that will allow purchase in significant numbers even with a declining defense budget. SCAD firmly believes that Ghost answers the USAFâ&#x20AC;&#x2122;s need and the request by the American Institute of Aeronautics and Astronautics for a Next Generation Strategic Bomber. The primary focus of Ghost is to provide a long-range, defensible, and autonomous aircraft that meets the needs of the USAF today and can adapt easily to any unforeseen need in the future. Thus, Ghost is designed to maximize range, payload variety, and survivability in any combat situation. Ghost utilizes a flying wing configuration, modular payloads, a removable cockpit module, and advanced communications. With an unrefueled combat range of 8,000 nm with a 30,000 lb payload, SCAD stands firmly behind the ability of Ghost to provide a low-cost solution to the USAFâ&#x20AC;&#x2122;s need for the next generation in long range strategic strike capabilities.

Table of Contents Nomenclature ....................................................................................................................................................... 3 Acronyms .............................................................................................................................................................. 3 Dedication & Acknowledgement ...................................................................................................................... 5 Executive Summary ............................................................................................................................................. 6 1.0 Introduction.................................................................................................................................................... 9 1.1 Request for Proposal Interpretations .................................................................................................... 9 1.2 Requirements Matrix .............................................................................................................................. 10 1.3 Design Process & Methodology........................................................................................................... 11 2.0 Mission Profile & Range ............................................................................................................................ 12 2.1 Key Mission Profile ................................................................................................................................ 12 2.2 Range Analysis......................................................................................................................................... 12 3.0 Preliminary Sizing ........................................................................................................................................ 16 3.1 Mission Analysis and Preliminary Weight Estimations .................................................................... 16 3.2 Preliminary Drag Polars ......................................................................................................................... 17 3.3 Constraint Diagram ................................................................................................................................ 18 4.0 Stealth Considerations in Configuration Design .................................................................................... 19 5.0 Configuration Description ......................................................................................................................... 21 5.1 Configuration Selection ......................................................................................................................... 21 5.2 Wing .......................................................................................................................................................... 23 5.3 Body .......................................................................................................................................................... 25 5.3.1 Payload Bays .................................................................................................................................... 25 5.3.2 Cockpit Module ............................................................................................................................... 26 5.3. Power ....................................................................................................................................................... 27 6.0 Aerodynamics ............................................................................................................................................... 32 6.1 Airfoil Selection ....................................................................................................................................... 32 6.2 Airplane Drag Estimation ..................................................................................................................... 34 6.3 Wave Drag Estimation ........................................................................................................................... 35 6.4 High Lift Systems.................................................................................................................................... 36 6.5 Detailed Drag Polars .............................................................................................................................. 37 6.6 3D CFD .................................................................................................................................................... 38 7.0 Propulsion ..................................................................................................................................................... 39 7.1 Engine Technology Tradeoffs .............................................................................................................. 39 7.1.1 Supersonic configuration â&#x20AC;&#x201C; the F135........................................................................................... 39 7.1.2 Transonic configuration ................................................................................................................. 40 7.2 Engine Characteristics/Optimization.................................................................................................. 42 8.0 Systems Architecture & Integration ......................................................................................................... 45 8.1 AESA Radar ........................................................................................................................................... 46 8.2 Integrated CNI/EW and EO Systems ............................................................................................... 48 8.2.1 Communication/Navigation/Identification............................................................................... 48 8.2.2 Electronic Warfare and Defense ................................................................................................. 52 8.2.3 Electro-Optical ............................................................................................................................... 55 8.2.3.1 EO Targeting System ................................................................................................................. 56 8.2.3.2 EO DAS ....................................................................................................................................... 57 8.2.3.3 EISS and ISR ............................................................................................................................... 58 8.3 Interfacing ................................................................................................................................................ 59 8.4 Avionics Cooling & Environmental Control System (ECS) ........................................................... 60

8.4.1 Cockpit Environmental Control System ..................................................................................... 61 8.5 Cockpit Design ........................................................................................................................................ 62 8.6 Unmanned Configuration...................................................................................................................... 63 8.6.1 Remote and Autonomous Operations ........................................................................................ 63 8.6.2 Future C4ISR Capabilities ............................................................................................................. 66 8.7 Power Generation ................................................................................................................................... 67 8.8 Nuclear Capability................................................................................................................................... 67 9.0 Stealth ............................................................................................................................................................ 69 9.1 Radar Evasion.......................................................................................................................................... 69 9.2 Infrared Signature ................................................................................................................................... 75 9.3 Visual, Smoke, Contrails, and Acoustic .............................................................................................. 76 10.0 Structure ...................................................................................................................................................... 77 10.1 Materials Selection ................................................................................................................................ 77 10.2 Component Description and Analysis .............................................................................................. 78 10.2.1 Wing Structure and Analysis ....................................................................................................... 78 10.2.2 Fuselage Primary and Support Structures ................................................................................. 79 10.2.3 Landing Gear Well, Payload Bay, and Missile Bay Structures ............................................... 80 10.2.4 Cockpit and Fuel Module Structure........................................................................................... 80 11.0 Stability & Control .................................................................................................................................... 81 12.0 Weight Justification & Analysis .............................................................................................................. 82 12.1 Detailed Weight Analysis..................................................................................................................... 82 12.2 Class III Weight Estimation ............................................................................................................... 83 12.3 Center of Gravity Analysis .................................................................................................................. 83 13.0 Performance ............................................................................................................................................... 86 13.1 Takeoff Performance ........................................................................................................................... 86 13.2 Climb Performance .............................................................................................................................. 86 13.3 Max Speed .............................................................................................................................................. 87 13.4 Payload-Range ....................................................................................................................................... 87 13.5 Mission Performance ........................................................................................................................... 88 13.5.1 Intercontinental Refueling ........................................................................................................... 88 13.5.2 Unmanned Extended Loiter with Aerial Refueling ................................................................ 90 13.6 Landing Trajectories ............................................................................................................................. 93 14.0 Cost .............................................................................................................................................................. 93 14.1 Unit Price per Airplane ........................................................................................................................ 93 14.2 Operating Cost Breakdown ................................................................................................................ 95 14.0 Software Used Description ...................................................................................................................... 96 14.1 Advanced Aircraft Analysis (AAA) ................................................................................................... 96 14.2 Star CCM+ v7 ....................................................................................................................................... 96 14.3 GasTurb 11 ............................................................................................................................................ 96 14.4 Physical Optics Radar Cross Section Prediction and Analysis Application (POFACETS) ..... 96 14.5 DesignFOIL .......................................................................................................................................... 97 14.6 Ansys CFX ............................................................................................................................................. 97 15.0 References................................................................................................................................................... 98

1.0 Introduction 1.1 Request for Proposal Interpretations The 2011-2012 American Institute of Aeronautics and Astronautics (AIAA) Graduate Team Aircraft Design Request for Proposal (RFP) calls for a new, affordable, long-range, penetrating strategic bomber with anticipated entry into service date of 2020-2025. The RFP states, “…shall be an optionally manned aircraft…” “…additional unrefueled range beyond [4,000 nm] is highly desirable…up to or beyond 5,000 nm.” “All aspect broadband stealth features…and self-protection…are expected” “…Fully integrated with current and anticipated C4ISR infrastructure…” “…imperative that unit cost does NOT become prohibitive…” The problem with an optionally manned vehicle is that during “unmanned mode” the cockpit is taking up valuable space and contains unnecessary equipment. As a response to this problem, Ghost is integrated with a modular cockpit that is capable of being removed and replaced with mission optimized equipment, which is discussed in §5.3.2. Based on the distance of potential targets to forward US air bases, discussed in §2.2, the range of Ghost is 8,000 nm. Analysis shows that all of the desirable targets are within Ghost’s unrefueled combat range. These potential targets are located in regions such as the Middle East, Eastern Asia, and Eurasia. Ghost is designed to utilize highly advanced active and passive stealth features to allow persistence in heavily defended areas. These features, discussed in Ch. 9, help improve the stealth ability of Ghost by reducing Radar Cross Section (RCS), infrared signature, visual detection, acoustic footprint, and contrail formation. For example, extensive analysis has been performed to measure the RCS of the configuration’s surface using a numerical MATLAB code. This RCS was compared to that of highly stealth aircraft such as the B-2 and modifications to the configuration’s surfaces were made to reduce radar signature beyond that of the B-2. The communication system of Ghost was designed to take advantage of current and future command, control, communications, computers, intelligence, surveillance, and reconnaissance (C4ISR) infrastructure with the use of advanced multiband systems that allow high bandwidth communications with satellites, other manned or unmanned aircraft, and ground stations. One such system featured on Ghost is Raytheon’s Enhanced Integrated Sensor Suite (EISS) that images and

pinpoints stationary or moving targets with superior accuracy and near real-time speed at altitudes up to 60,000 ft.3 Ghost was designed to be affordable by using systems that are currently available or in development in other programs, thus reducing overall development costs which drives a reduction in per unit cost. Future costs of the program were also considered in that Ghost implements a modular payload system that allows for a wide variety of missions to be performed, which normally would require several different aircraft to complete. Because of this ability, Ghost can replace the aging and maintenance heavy fleet of B-52s, B-1s, and B-2s, reducing the United States Air Force overhead cost.

1.2 Requirements Matrix Parameter

Requirement

Ghost

Section

2 Removable modular cockpit to interchange between manned and unmanned “modes” 30,000 lbs

§5.3.2, §8.6.1, §13.5.2 §5.3.1

8,000 nm

§2.2

RFP General Requirements Manned Crew

Unmanned Ability

Optionally manned

Payload

20,000 lbs ≤ X ≤ 50,000 lbs min 4,000 nm; >5,000 nm preferred Compatible with current and anticipated C4ISR infrastructure

Range C4ISR Stealth Features

All-aspect broadband stealth features

Self-Protection Features

Variety of self-defense features

Air-to-Air Engagement

Capable of carrying & deploying air-to-air missiles Capable of performing a nuclear strike Flexibility for future modifications

High bandwidth systems such as Raytheon’s EISS, AMCAS, Harris MADL, MIDS JTRS, SINCGARS and others Minimal RCS, radar absorbent material, deception countermeasures, fiber optic towed decoy Defense Management System, AN/ALE-47 countermeasures dispensing system, decoy flare, chaff, self-sealing fuel tank, electronic countermeasures 4 Air-to-Air Missiles AIM-9 & -120 family

Affordability

<<$1.2 billion per platform

Aerial Refueling

Must allow aerial refueling

B83 nuclear bomb, AGM-129 ACM, avionics EMP shielding, fly-by-light system Modular payload system allows for a variety of modifications $271.6 million (50 units); $236.4 million (100 units) Capable via flying boom

Entry into Service

2020-2025

Nuclear Capability Platform Flexibility

Ch. 8 Ch. 9

Ch. 8 §5.3.1 §8.8 §8.6.1, §8.6.2 §14.1 §13.5.1 --

1.3 Design Process & Methodology The general design philosophy of Ghost has been substantially influenced by methodology presented by Jan Roskam4, Dan Raymer5, Ed Heinemann6, and Bill Sweetman.7,8 It should be noted that these methods are often quite extensive and cover technical aspects of the analysis in great detail. The majority of calculations performed and referenced within this proposal use published graphs and tables in order to determine the constants and parameters, often consisting of multiple timeconsuming iterations. While the theoretical backgrounds of these methods are discussed in various parts of this proposal, many of the mathematical models and statistical data used in the design process are not presented in their entirety in the interest of brevity. Design Structure Matrix (DSM), a modern method of development management, was used in order to determine the optimum design process. This method, described by Eppinger et al.9, is used to organize interrelated tasks in the design process in a way that minimizes feedback cycles and determines possible parallel analyses. The PSM 32 code, developed by Blitzkrieg Software, was utilized to implement the DSM in the routine process of developing Ghost. Utilizing this code, the entire design process was re-ordered based on the degree of dependency of each sub-process on the outputs of others. As a result, the design approach presented by Roskam has been slightly modified so as to allow for additional parallel processes, as dictated by specific needs of the Ghost concept, and consequently, improved development speed. Lastly, the POFACETS v4.0 program10 coded by by Dr. David Jenn of the Naval Postgraduate School and Major Filippos Chatzigeorgiadis of the Hellenic Air Force was run in MATLAB and used iteratively to analyze and compare the RCS among various configurations. An RCS measurement of the B2-Spirit was used as a baseline against which the final configurations were compared and expected to improve upon. The particular importance of the radar signature from RCS is that it is by far the most prominent signature and provides the observer with the greatest amount of useful information at the greatest distance. Without controlling the radar signature, it is impossible to achieve stealth.11 As a result, RCS became the major driving factor during the down select of the design process.

2.0 Mission Profile & Range 2.1 Key Mission Profile Several historical missions were considered for the initial sizing of Ghost. The first mission profile considered was based on the first successful combat role flown by the USAF B-2 during the 1999 strategic bombing campaign led by NATO. This mission profile would have consisted of a near-5,000 nm trip from Whiteman AFB, MO to the target in Kosovo, a strategic bombing run, and a near-5,000 nm return trip, with aerial refueling in both directions. The second mission profile considered was based on bombing sorties flown by the B-52, fighter-bombers, and the B-2 during conflicts in Iraq and Libya over the last decade. This mission would have consisted of short cruise lengths, a significantly longer loiter over target, and easy access to aerial refueling tankers. The above missions are typical of modern bombing sorties from which a mission profile can be extracted for the preliminary sizing of Ghost. In the selected mission, Ghost leaves a USoperated base with a full payload, travels to its target, loiters, and returns to base without dropping ordnance (considering a go-ahead was not given for sizing design purposes). Figure 1 shows the mission profile used to aid in the sizing of Ghost.

Figure 1 The mission profile of Ghost : 1 – Takeoff 2 – Climb 3 – Cruise 4 – Loiter 5 – Return Cruise 6 – Decent 7 – Landing

2.2 Range Analysis The RFP outlines a minimum unrefueled combat range of 4,000 nm, with a strong preference for greater range capability extending up to or beyond 5,000 nm. To determine the range needed for Ghost, a survey of US DoD Joint Air Bases in North America, the Pacific, Asia, and Europe, was conducted alongside a similar survey of potential targets in Eurasia, the Middle East, Eastern and South Asia. First, the coordinates of each location were recorded. Then a great circle analysis was performed to find the flight distances from each base to each target. The central angle, ̂, was found using, ̂

(

)

(1) 12

where

is the latitude of the standpoint (base) or the fore-point (target), and

is the difference

in longitude between the standpoint and fore-point. The great circle distance, , was found using Ě&#x201A; where

(2)

is the sphere great circle radius of the earth at 6,372.8 km. The great circle distance was

multiplied by two and ten percent was added to account for a roundtrip, uncertainties in wind, Coriolis effect, and other miscellaneous effects. Figure 3 shows the results of the range analysis of distance to every target from every forward US air base sampled. To find the most effective combat range, several potential scenarios were considered. The first was where Ghost was able to operate out of the nearest forward air base used by the USAF. The second scenario was that the closest air base used by the USAF was either destroyed or simply did not have the available aircraft and only the second closest air base was considered. The final scenario took into account how the USAF currently deploys the B-2, which is from a handful of bases with specialized hangars that exist primarily on U.S. soil. Figure below shows the results of that analysis.

Figure 3 Histogram of the required range from base to target with all Base-to-Target combinations considered.

Figure 2 3D Histogram of the required range from base to target using the closest bases, 2nd closest bases, and bases equipped with hangars built for the B-2.

From this analysis, it was noted that with a range of 7,500 nm, Ghost would be capable of operating from existing B-2 hangars and hit all potential targets without refueling. Furthermore, if Ghost were to operate out of any forward air base used by the USAF, 92.5% of all potential targets were within range with a single aerial refueling. This was noted because it would free up aerial tanker resources for other aircraft. The last consideration was loiter time which is proportional to range. With more loiter time, especially for an unmanned mission, the bomber is capable of staying out near station for longer periods awaiting directives typically driven by time-critical intelligence. Additionally, more loiter time gives the bomber the ability to wait and strike the target at the best

window of opportunity, if enemy defenses are too hostile at a given point in time. As a result, a final design range of 8,000 nm was chosen. A summary of the analysis is presented in Table 1 and 2. Table 1. US Air Bases used for Range Analysis. B-2-capable operating bases highlighted in orange. Two refuel locations are shown along with the required combat radius for nearest re-fueling tankers.

Location

Runway Length (ft)

Edwards

Edwards, CA

8,000 min./ 15,024 max.

MacDill

Tampa, FL

11,421

Whiteman

Knob Noster, MO

7,310 min. / 12,400 max.

Ellsworth

Rapid City, SD

13,497

Pearl Harbor

Honolulu, HI

3,000 min. / 12,300 max.

Andersen

Guam

10,558 min. / 11,185 max.

Gunsan, South Korea

9,000.

Bishkek, Kyrgyzstan

13,780

Abu Dhabi, UAE

12,012

Diego Garcia

12,003

Aviano

Pordenone, Italy

9,800

RAF Alconbury

Cambridgeshire, UK

4,000 min. / 8,250 max.

RAF Fairford

Over the Atlantic Ocean

Gloucestershire, UK Nearest USAF Refuel Base RAF Mildenhall, UK

9,993 Distance from Nearest Refuel AB 338 nm

Over the Mediterranean

RAF Mildenhall, UK

658 nm

DoD Joint Air Base

North America

Pacific Ocean

Eastern Asia Kunsan

Central Asia Manas

Western Asia Al Dhafra

Indian Ocean Naval Support Facility Diego Garcia

Europe

Refuel Location

Table 2. Combat ranges for targets from nearest AB, 2nd nearest AB, and AB from which B-2 has operated are shown.

Potential Target

Nearest Air Base

2nd Nearest Air Base

Air Base that B-2s Operate

1,096 nm 2,548 nm 2,333 nm 3,026 nm 2,371 nm 2,829 nm 2,548 nm 1,089 nm 2,857 nm 3,342 nm 1,942 nm

1,711 nm 3,002 nm 3,251 nm 3,166 nm 2,493 nm 2,933 nm 3,002 nm 4,180 nm 2,858 nm 4,441 nm 3,091 nm

4,797 nm 3,154 nm 3,555 nm 3,166 nm 2,647 nm 3,809 nm 3,154 nm 4,180 nm 3,870 nm 4,588 nm 3,210 nm

1,628 nm 760 nm 1,517 nm 739 nm 419 nm 2,061 nm 1,878 nm 1,234 nm 1,520 nm 1,108 nm 1,537 nm 1,770 nm 938 nm 1,985 nm 1,390 nm

1,755 nm 3,124 nm 2,227 nm 2,920 nm 2,879 nm 2,905 nm 3,110 nm 2,473 nm 2,508 nm 2,438 nm 2,320 nm 4,972 nm 3,855 nm 3,962 nm 4,676 nm

5,213 nm 5,520 nm 5,642 nm 5,483 nm 4,981 nm 4,735 nm 4,837 nm 5,408 nm 4,311 nm 5,556 nm 5,108 nm 5,045 nm 5,370 nm 5,416 nm 4,246 nm

1,988 nm 1,738 nm

3,306 nm 2,871 nm

3,335 nm 2,871 nm

1,172 nm 2,401 nm 2,698 nm 683 nm 585 nm 2,187 nm 1,818 nm 1,251 nm

4,129 nm 3,787 nm 4,482 nm 4,341 nm 4,194 nm 3,179 nm 3,689 nm 4,695 nm

4,797 nm 5,151 nm 4,482 nm 4,341 nm 4,194 nm 5,605 nm 3,689 nm 4,764 nm

Eastern Europe and Eurasia Warsaw, Poland Moscow Air Defense Center, Russia Novorossiysk Naval HQ, Russia Severomorsk Naval HQ, Russia Submarine Bases near St. Petersburg, Russia Tatischevo Air Base, Russia Tula, Russia Vladivostok Naval Base, Russia Volgagrad, Russia Ural Military Complexes, Vorkuta, Russia Sevastopol Naval Base, Ukraine

Middle East Kandahar, Afghanistan Bushehr Fighter Base, Iran Military/Industrial Complexes, Tehran, Iran Shiraz Fighter Base, Iran Strait of Hormuz, Iran Tabriz International Airport, Iran Sulaymaniyah International Airport, Iraq Islamabad International Airport, Pakistan Karachi International Airport, Pakistan Ouch, Pakistan Center of Punjab Region, Pakistan Jizan, Saudi Arabia Riad International Airport, Saudi Arabia Yanbu, Saudi Arabia Mukalla International Airport, Yemen

Northern Africa Benghazi, Libya Tripoli, Libya

Eastern Asia Beijing Capital Intl. Airport, China Chongqing Air Base, China Suixi Air Base, China Tuchengzi Air Base, China Yantai SW Air Base, China Yinchuan/Xincheng AB, China Zhangzhou Air Base, China Piung-Yang Intl. Airport, North Korea

3.0 Preliminary Sizing 3.1 Mission Analysis and Preliminary Weight Estimations Building upon the results from Chapter 2, a mission analysis was performed using the methodology presented by ESDU Performance Data Items 73018 12, 7301913, and 7401814, combined with Roskam’s low order statistical weight estimation methods.15 Initial cruise altitude of 45,000’ and cruise Mach 0.85 were selected based on those of the B-2 and B-1. The B-2 cruises at 40,000’ at Mach 0.8516 and the B-1 cruises at 50,000’ at Mach 0.9.17,18 An altitude of 45,000’ provides the best of what B-2’s altitude can offer (in terms of detection avoidance) and can provide a better scanning area for the bomber’s sensors. Roskam suggests a TSFC range of 0.5 to 0.9 lb/lb-hr for military bombers at cruise.19 Considering the technology level in the timeframe of 2020 20, a cruise TSFC was estimated as 0.6 lb/lb-hr for the purposes of this study. Table 3 presents the results for Ghost. Table 3. Preliminary Mission Analysis Results.

Mission Segment

Altitude (ft.)

Mach

Distance (nm.)

Time (min.)

TSFC (lb/lb-hr)

ΔWF used (lb)

0a-Warm up

0.19

2,750

0b-Taxi Out

0.19

2,700

1-Takeoff

0-150

0.12

0.23

1,350

2-Climb

150-45,000

0.66

0.50

5,000

3-Cruise

45,000

0.85

3750

360

0.60

50,500

4-Loiter

45,000

0.80

400

0.60

5,800

5- Cruise

45,000

0.85

3750

360

0.60

40,000

6- Descent

45,000-200

0.2

0.28

1,700

7- Land/Taxi

200-0

0.19

1,300

Using statistical trends of military bombers obtained from Roskam21, data sheets on the B122,B-223, and B-5224 as well as the results for the mission analysis, initial estimations for empty, takeoff, and required fuel weight of the aircraft were performed. Table 4 presents the results of this analysis. Note that these results only reflect the statistical trends in military bombers and are later corrected in Ch. 12 using higher order methods of estimating

Table 4. Summary of initial weight analysis

120,800 lb 267,000 lb 0.597 111,100 lb

weight.

3.2 Preliminary Drag Polars Using the 2nd order regression methods presented by Roskam25,26, as well as the results obtained from the preliminary weight and mission analyses of Ghost, initial empirical drag polars were obtained in order to complete preliminary performance sizing. ESDU Performance Data Item 7301927 was consulted to choose the critical parameters with the highest influence on fuel burn, range, and endurance. Three parameters were chosen to determine an optimal lift coefficient region for the aircraft when operating at cruise. ESDU 73019 suggests CL/CD3/2 to be maximized, which corresponds to the maximum Specific Air Range (SAR). SAR represents the sensitivity of the air range of the aircraft to its takeoff gross weight and, therefore, the amount of fuel burned during cruise. CL corresponding to maximum CL0.5/CD maximizes the range at constant altitude. As it can be seen from Figure 4b, the SAR is maximized if the aircraft is operating at a lift coefficient of 0.45, which is significantly lower than the lift coefficient corresponding to maximum L/D (0.65). However, one could observe that the CL/CD curve in Figure 4b is relatively flat around a lift coefficient of 0.58; therefore, the reduction in maximum L/D as a result of optimizing the aircraft for maximum SAR is minimal. To optimize the aircraft for maximum range at a specific altitude, the cruise CL would be 0.37, which is the lowest CL of the three. Therefore, an optimal region can be defined for the cruise CL of the aircraft, leaving it up to the pilot or mission planner to choose the appropriate CL during cruise, whether they want to minimize fuel burn (0.45), maximize range (0.37), or maximize endurance (0.65).28

(a)

(b)

Figure 4. Results of the preliminary aerodynamic projections. (a) Preliminary drag polars for different mission segments of the aircraft. (b) Parametric analysis of lift and drag data. CL corresponding to maximum CL/CD maximizes the endurance at constant altitude. CL corresponding to maximum CL0.5/CD maximizes the range at constant altitude. Parameter CL/CD3/2 maximizes the SAR of the configuration and was selected based on the recommendations made by ESDU 73019 as a measure of merit, defining a design region for the cruise CL of the aircraft.

3.3 Constraint Diagram The initial sizing of the aircraft was completed based on the performance requirements presented by MIL-STD and methods presented by Roskam29. The wing loading and thrust-to-weight ratios were obtained by solving performance boundary equations. Gathered from the US air base analysis presented in Â§2.2, the average runway considered was 8,000â&#x20AC;&#x2122;. Based on ESDU Aerodynamics 9402830, it was assumed in this analysis that a maximum lift coefficient of 1.8 is achievable by using plain trailing edge flaps with no leading edge high lift devices. Weight figures obtained from preliminary weight estimates were used in conjunction with lift and drag characteristics obtained from preliminary aerodynamic analysis. A matching plot was constructed by overlaying the performance boundary graphs to identify the acceptable design space for wing loading and thrust-to-weight ratio for Ghost. The result of this analysis is presented in Figure 5.

Figure 5. Preliminary Aircraft Sizing. Design space is indicated by the white area. Design point is T/W = 0.26,W/S = 76

As can be seen in Figure 5, the thrust-to-weight ratio and wing loading of Ghost is limited by the critical performance requirements for stall with flaps and time to climb, found to be 87 knots and 23 min respectively. From the design point above and the initial weight estimates, Ghost was initially sized for 70,000 lbf of static thrust and a wing area of 3,500 ft2.

4.0 Stealth Considerations in Configuration Design “A stealth aircraft has to be stealthy in six disciplines: radar, infrared, visual, acoustic, smoke, and contrail. If you don’t do that, you flunk the course.” – Ben Rich, Team Lead for the F-11731 The RFP states that the proposed aircraft must utilize all-aspect broadband stealth features. Among the six disciplines of stealth, radar is the sensor that gives a very precise estimate of the target’s position and can track the changes in the target’s position as well as determine its speed and course, both of which are essential to achieving interception. 32 The particular importance of the radar signature is that it is by far the most prominent signature and it is the one that provides an observer with the greatest amount of useful information at the greatest distance. Without controlling the radar signature, it is impossible to achieve stealth.33 Thus minimizing the radar signature of the aircraft became the most significant design constraint when developing Ghost’s configuration. The strength of a radar signature is determined by the Radar Cross Section (RCS) of the aircraft. RCS is determined by first measuring, or calculating, the amount of radar energy reflected from a target toward an observer. Then, the designer calculates the size of a reflective sphere (the optical equivalent would be a spherical mirror) that would return the same amount of energy. The projected area of the sphere is the RCS. An airframe is a very complex shape and its RCS varies greatly with the angle of observation. Also, due to complex scattering and diffraction phenomena, the RCS varies with the wavelength of the radar.34 Several methods exist in order to minimize RCS for a given configuration. Suggestions from Roskam35 are shown in Figure 6.

Figure 6. Suggested methods for RCS improvements by Roskam, considering fuselage, inlet, exhaust nozzle, & wing

Engines in external pods or hung on pylons reflect significant radar energy back to the source. Other common design features that are equally poor in developing a low RCS design are vertical stabilizers, external stores, and an exposed engine face. Conventional bomber configurations such as the B-52 perform poorly in reducing radar signatures, having an RCS of 1,000 m2. 36 However, a flying wing configuration meets all of the basic requirements of a low observable because it is free of fins, vertical body sides, square body cross sections, and the engines are buried within the wings. Flying wings present additional aerodynamic benefit over conventional airplanes. The fuselage and tail of conventional configurations add weight and drag without producing lift. Additionally, drag is caused by aerodynamic interferences that result from the junctions of the fuselage to the wing and tail surfaces, all of which are eliminated with a flying wing configuration. Furthermore, the mass of the aircraft is spread evenly across the wingspan so bending loads are much smaller which result in a lighter and more efficient structure. According to Jack Northrop, the flying wing produces less drag than the conventional aircraft of the same weight and can cruise faster on less power.37 However, the flying wing presents challenges in stability and control which can be addressed with an effective computer monitored control system. From the above analysis, SCAD chose a flying wing configuration. There exists a decision to design the aircraft based on subsonic, transonic, or supersonic flight speeds. Having a stealth aircraft that flies subsonically increases its ability to benefit from stealth-increasing characteristics. However, flying slowly decreases survivability due to the increased time required to fly into a hostile environment as well as its inability to outfly even the most basic defense systems or aircraft. A supersonic aircraft has the optimal advantage in reducing the amount of time required to fly to a target as well as being able to outfly many enemy defenses. However, this ability comes at a high price. Flying supersonically creates exceptionally high drag, as shock waves and other aerodynamic phenomena occur, leading to substantial fuel burn and costly refueling. Additionally, supersonic speeds involve unwanted aerodynamic heating, usually destroying stealth materials of low heat conductivity, as well as the need for afterburners or high exhausts, all of which generate significant thermal signatures leading to decreased stealthiness. From these considerations, SCAD chose to design an airplane flying at transonic speeds. At this flight regime, increased stealth and survivability are able to be maintained with costs higher (yet acceptable) than flying subsonically, but not as high as supersonically. Stealth materials coated on the airplaneâ&#x20AC;&#x2122;s surfaces generally decrease aerodynamic smoothness which degrades aerodynamic performance. While at transonic

speeds, such degradations are not nearly as significant as at supersonic speeds. §5.1 elaborates further on the configuration selection and justification

5.0 Configuration Description 5.1 Configuration Selection Since the RFP does not include any requirements regarding the configuration, and the ones regarding the performance are relatively “soft” requirements, the design space was very wide, with several configurations potentially fulfilling the RFP. This made it necessary to evaluate all the possible configurations to select the most appropriate one before starting the development. Since the RFP does not provide hard requirements regarding flying speeds, three options were considered: A supersonic cruise configuration, a supersonic dash-capable one, and a fully transonic one. As previously stated, the supersonic cruise configuration presented some advantages, including shorter times to complete the mission and better survivability due to the shorter time spent in the range of enemy air defenses. However, it has been shown that the speed and altitude at which really high survivability is achieved are around Mach 3 and 70,000’ respectively38, which would lead to a very costly bomber. The disadvantages of this configuration, which also include very high fuel consumption and adverse effects on the skin materials due to aerodynamic heating, resulted in the fully supersonic configuration being discarded. Figure 7 shows some of the supersonic concepts proposed during the early design stages.

Figure 7 Proposed supersonic cruise configurations. The lower range and endurance resulted in these configurations being discarded

A supersonic dash-capable configuration was also evaluated. This configuration would perform its mission by flying transonically throughout most of the mission, and then sprinting supersonically into and out of the weapon delivery area. Several studies have considered the supersonic dash capability as a feature that might be included in the next generation bomber 39 given the positive effects this has in survivability and response times. However, fixed-sweep aircraft designed for a mainly transonic mission with supersonic dash capabilities accrue weight and range 21

penalties

optimal

transonic

aerodynamic designs are not suitable for supersonic sprints. A variablesweep airplane was considered to solve this issue and provide a feasible supersonic dash-capable configuration. However,

although

feasible,

the

increased complexity, weight, and cost

Figure 8 Variable-sweep supersonic dash-capable considered, with unswept (left) and swept (right) wings.

configuration

of a variable-sweep aircraft40 resulted in the discarding of this configuration. Figure 8 shows the variable-sweep concept proposed during the early design phases. A transonic configuration was then selected for Ghost given its advantages in fuel efficiency (which results in longer range and endurance), the relatively simpler aerodynamic design and optimization, and the fact that it can use several legacy technologies, especially from the B-2 program, which drive the acquisition cost down as asked by the RFP. Once it was determined that Ghost was going to be a purely transonic aircraft, several possible configurations were proposed, including a joined wing configuration, an unconventional forward-empennage configuration, and a flying wing. Figure 9 shows some of the proposed transonic concepts. The flying wing configuration was chosen given its aerodynamic benefits and low observability. The following subsections describe the final configuration of Ghost in greater detail.

Figure 9 Purely-transonic concepts proposed during the first stages of the project. Clockwise from the top right: A joinedwing configuration; an unconventional empennage-first configuration; a low AR tailless configuration; and the flying wing concept which evolved to become Ghost.

5.2 Wing A “flying wing” configuration was chosen for Ghost due to its ability to provide a naturally low-RCS and high L/D aerodynamic properties. In general, flying wings have a lower RCS than conventional aircraft as they eliminate the fuselage and empennage, which are some of the main contributors to an aircraft’s RCS41. The wing planform for Ghost has an equivalent area of 3,565 ft2 and a 185’ span, resulting in an aspect ratio of 9.6. Such a high span was chosen to improve aerodynamic benefits as well as to allow Ghost to take advantage of the pre-existing hangars that were built for the B-52 program. Stealth required smooth wing surfaces, which influenced a wing designed to take advantage of natural laminar flow (NLF). To promote NLF, Ghost has a relatively low equivalent quarter chord sweep of 20.6° with the leading edge swept back at 22.6°. Custom NLF airfoils were selected to allow for laminar flow on approximately 40% of the upper and lower surfaces of the wing. A taper ratio of 0.45 was selected to improve the Oswald’s Efficiency factor of the wing at cruise. Figure 10 shows the wing planform for Ghost.

Figure 10 Wing planform and main dimensions. The dashed blue lines represent the equivalent planform as calculated following Roskam’s methodology.

The flying-wing configuration allowed for omission of slats, which further promoted NLF across the surface of the wing42. Additionally, the high-lift flying wing configuration allowed Ghost to take advantage of simple, plain flaps that span 40% of the total wing while minimizing breaks in the wing that could result in enemy radar detection. The wing also accommodates ailerons that serve as elevons and airbrake/rudders between the 60- 85% and the 85-95% spanwise locations on the wing, respectively. The flying wing nature of Ghost makes an advanced control scheme necessary, on which spoilers, differential air brakes and ailerons are used in conjunction to provide the required control in all axes, as will be further discussed later in this document. The wing structure is supported by 3 spars located at 20%, 50% and 75% of the chord. The ribs are placed perpendicular to the spars and have 24â&#x20AC;? of spacing between them, which is typical for this type of aircraft43. The only non-lifting portion of the aircraft exists at the root where the payload and cockpit module are located. Fuel is housed inside the wings and in sections of the non-lifting portion of the wing. Additionally, payload may be replaced with fuel modules to optimize the range or endurance for a given mission. The total estimated fuel volume is 2,872 ft 3, which is equivalent to roughly 21,485 U.S. gallons of fuel. Figure 11 shows the wing structure and the location of the control surfaces.

Figure 11 Structure of the wing and location of the control surfaces. Note the diagonal leading edge of the ribs which reduce the RCS contribution of Ghostâ&#x20AC;&#x2122;s leading edge.

5.3 Body 5.3.1 Payload Bays Ghost has two types of payload bays: the main weapons bays which carry 30,000 lb of ordnance to be delivered as part of the bomberâ&#x20AC;&#x2122;s mission and smaller self-defense payload bays that hold air-to-air weapons to be used in defense situations against airborne targets. The main payload bays were sized to accommodate all of the weapons designed to be delivered from bombers currently in use and under development by the U.S. Air Force. A survey of the types of ordnance that the payload bays should be compatible with dictated the baysâ&#x20AC;&#x2122; final dimensions, shown on Figure 12. The payload bays are compatible with the Common Strategic Rotary Launcher (CSRL) used for both conventional and nuclear weapons, and the Conventional Rotary Launcher (CRL) to be used with conventional weapons, which enable a faster delivery of different types of payload and reduce the need for several unique launchers fitted to each aircraft and carrying only one or two types of

Figure 12 Weapons Bay dimensions and cutaway showing a conventional rotary launcher carrying eight AGM-158 JASSMs

weapons44. The use of rotary launchers makes it necessary to have a semi-circular cross section shape that minimizes the amount of space used by the weapons bays. The main payload bays have movable bulkheads which split the available space into four different compartments that can be used to carry different types of payload, two rotary launchers per payload bay, or additional fuel modules. Ghost has two self-defense bays located on each side of the main payload bays. These were designed to hold a wide variety of air-to-air weapons to be used if the bomber comes under attack by hostile aircraft. These weapons include short- and medium-range missiles such as the AIM-9 Sidewinder and the AIM-120 AMRAAM, which enable for beyond-visual range defenses. Each missiles bay can carry two missiles, one directed towards the front and the other Figure 13 Self-defense missile bay dimensions. Shown carrying two AIM-9X Sidewinder Missiles.

towards the back of the aircraft, which are deployed using the LAU-141/A hydraulic trapeze launcher, which “is required for lock-on before launch missiles”45 and also has a deflector surface which protects the bay from the motor plume. Figures 13 and 14 show the dimensions of the missile bays and the location of the payload bays in the aircraft, respectively.

Figure 14 Location of the weapon bays in the aircraft. The doors have been rendered in a transparent material. The main payload bays are shown each carrying eight cruise missiles in a rotary launcher. The self-defense bays are shown carrying two AIM-9X sidewinder missiles each.

5.3.2 Cockpit Module The cockpit module of ghost was designed to accommodate a crew of a pilot and a co-pilot on long-endurance missions that have been frequently flown in similar aircraft in recent years 46. For this purpose, the module includes dedicated sleeping, toilet, and food storing/heating areas that enable a crew of two to perform extra-long endurance missions. Two pilots sit on Martin Baker Mk. 16 high-speed ejection seats, the same type used in the F-35 family of aircraft. These seats enable for ejection at the whole range of speeds at which Ghost operates, increasing the survivability of the crew in any situation. Compared to earlier ejection seats, the Mk. 16 also extends “the limits of escape system technology while simultaneously improving aircrew efficiency, reliability and ease of maintenance coupled with lower life cycle costs”47. Figure 15 shows the ejection seat. The cockpit module was designed to be removable and sharing the cross section shape and dimensions with the main payload bay, enabling the use of common structural members and

Figure 15 Martin Baker Mk.16-type ejection seat. The seat allows for ejection at both low and high speeds.

modular fuel tanks/accessories which can be accommodated in the space regularly occupied by the cockpit module when the aircraft is in the unmanned configuration. Ghost also features a 360 degree spherical situational awareness system similar to Northrop Grumman’s Distributed Aperture System (DAS) and Raytheon’s Advanced Distributed Aperture System (ADAS), which dramatically increases the situational awareness of the pilots in both defense and attack situations, by using a set of 6 sensors that enable the pilots to have a spherical view of their surroundings, as well as provide early warning of incoming threats (both weapons and aircraft), provide weapon support, and aid in day and night navigation 48. Chapter 8 of this document describes the system in further detail. The cockpit features two full-panel-width panoramic cockpit displays which can be used to display all the relevant mechanical, flight, and mission information simultaneously, and which also display the information acquired from the situational awareness sensors, enabling the pilots to see any angle outside the airplane displayed in the main screens. Figure 16 shows the cockpit module.

Figure 16 Cockpit module of Ghost. On the left is the sleeping area for extra-long missions. On the center, the cockpit, showing two 6’2” tall male pilots for reference. On the right, the toilet and the cook storing/heating area.

5.3. Power Plant Ghost will use engines that implement features of previous civilian and military families of engines. Of these types of engines, the Pratt and Whitney PW9000 has been the most publicized, combining highly efficient commercial engine cores from the PW1000G with the low-spool and stealth features from military engines such as the F13549. This combination of high-efficiency cores and military features will result in a fuel consumption reduction of about 20% compared to current military turbofan engines50, which has a significant impact on the range and endurance of the aircraft. Figure 17 shows the core of the engines to be used in Ghost.

Figure 17 Cutaway of the core of the engine to be used in Ghost, based on a typical core of a commercial turbofan engine, as the one that will be used in future military aircraft such as the PW9000

To increase the stealthiness of Ghost, engine cowlings were designed in order to minimize the RCS and infrared (IR) signature of the engines. The cowlings were designed to follow the overall shape of the body, so that the RCS of the body is not increased by the presence of the engines. The intakes were also designed to minimize the radar scattering from the fans, by concealing most of the face of the engines behind part of the cowlings. Finally, in order to minimize the IR signature of the exhaust gases, nozzles were designed which spread the hot gases across a wide opening in the back of the aircraft, allowing them to mix with cold atmospheric air and reducing the temperature and IR signature typically associated with the plume of hot gases from the engine. Figure 18 shows the location of the engines in the body, the cowlings and the inlets and nozzles of Ghost. Chapter 7 describes the power plant in further detail.

Figure 18 Location of the engines in the body of Ghost. The cores have been highlighted blue and the RCSreducing surfaces have been rendered in a transparent material to enable a better appreciation of the location.

6.0 Aerodynamics 6.1 Airfoil Selection The method for selection of airfoil profiles was dictated by three main elements. First, in order to maximize the delay to transition to turbulent flow on the upper surface, a favorable “rooftop” shape pressure coefficient distribution51 was sought. Delaying the transition to turbulence results in significant reductions in friction drag allowing better aerodynamic characteristics than an earlier separated airflow. Second, the airfoil geometry must be of sufficient thickness to house the wing structure and fuel volume. The limits for thickness-to-chord ratio were set to 10% for root and 8% for the outboard wing airfoil based on drag divergence Mach number considerations to be shown in §6.3. Third, selected airfoils needed to have high L/D ratios to provide the best or near best flight performance of the airplane, especially during cruise. In order to obtain a reasonable baseline airfoil and considering operations within the transonic regime, a study of 25 transonic airfoil geometries, available on the University of Illinois Urbana- Champaign’s web portal, was conducted. The airfoils were analyzed using the DesignFoil software on the merit of the maximum extent of laminar flow and maximum L/D. From the initial 25 airfoils studied, nine airfoils were selected for the design. Using the nine final airfoils, 16 combinations of upper and lower surface curves were analyzed in order to select the best performing airfoils. The combination of the NASA Langley’s NLF-415 was selected as upper profile, and the Wortmann FX-73170a as the lower profile at both the wing root and tip. Small twist adjustments were performed on the quarter span and tip airfoils to increase their section cruise L/D. CFD analysis using Star CCM+ was performed to verify the location of transition to turbulence as well as provide a visual representation of the effectiveness of the chosen airfoil. The analysis was performed at cruise conditions with an altitude of 45,000’ and a Mach number of 0.85, including a 2° wing incidence. The mesh was generated using a surface remesher and advanced layer (volume) models. An SST K-Omega turbulence model was used in the analysis. To perform the 2D analysis, a 3D model was used with free stream and symmetrical planes. Symmetrical planes ensure that the 3D model acts as a 2D infinite wing. Figure 19 and Figure 20 present a summary of the results of the transonic CFD analysis performed on the selected airfoil at the root and tip thicknesses.

Figure 19 Transonic CFD analyses were performed on the root airfoil profile with thickness-to-chord ratio of 10% to determine the location of the transition to turbulence. The analyses are simulating the stream wise flow speed of 0.85 Mach at 2° incidence with ISA atmospheric conditions at 45,000’. The chord length selected for the analysis corresponds to the final wing planform geometry. Pressure gradient contours indicate the existence of normal shocks and turbulence kinetic energy contours show transition locations.

Figure 20 Transonic CFD analyses were performed on the tip airfoil profile with thickness-to-chord ratio of 8% to determine the location of the transition to turbulence. The analyses are simulating the stream wise flow speed of 0.85 Mach at 2° incidence with ISA atmospheric conditions at 45,000’. The chord length selected for the analysis corresponds to the final wing planform geometry. Pressure gradient contours indicate the existence of normal shocks and turbulence kinetic energy contours show transition locations.

6.2 Airplane Drag Estimation The total airplane drag can be written as (2)

, where,

is the total airplane drag coefficient, and is called the free stream dynamic pressure with as the air density and steady state airspeed

(3)

is the wing planform or reference area. It is useful to break down the total drag of an airplane into that caused by its components, normally as: (4)

where

is the wing drag coefficient is the fuselage drag coefficient is the empennage drag coefficient is the nacelle/pylon drag coefficient is the leading/trailing edge slat/flap coefficient is the landing gear drag coefficient is the canopy/windshield drag coefficient is the store(s) drag coefficient is the trim drag coefficient is the interference drag coefficient is the miscellaneous drag coefficient typically caused by speed brakes, struts, inlet

drag, antennas, gaps, and the like. Since the configuration chosen for Ghost is that of a flying wing with no empennage, a small â&#x20AC;&#x2DC;fuselage likeâ&#x20AC;&#x2122; body, no nacelles, no leading edge devices, retractable landing gear, no canopy/windshield, and no stores, significant drag reductions can be made where many of the drag contributions become null or decreasingly small. The transonic wing drag coefficient can be found from (5)

where

is the wing zero-lift drag coefficient and

wing drag coefficient due to lift.

In the transonic speed range, the wing zero-lift drag coefficient is found from (6) where

is the drag coefficient due to friction and

is the wing wave drag

coefficient heavily influenced by thickness-to-chord ratio and wing sweep. The wing drag coefficient due to lift can be found from, (7)

where

is the wing lift coefficient in which for a flying wing, is just the

of the aircraft

is the Oswald efficiency factor is the aspect ratio of the wing wing twist angle is the induced drag factor due to linear twist is the zero lift drag factor due to linear twist. The design methodology used in the software Advanced Aircraft Analysis (AAA), based on Airplane Design I-VIII, Airplane Flight Dynamics and Automatic Flight Controls, Parts I and II, by Dr. Jan Roskam, and Airplane Aerodynamics and Performance, by Dr. C.T. Lan and Dr. Jan Roskam, provides rapid and systematic methods for estimating lift and drag in any flow regime. As a result, Ghostâ&#x20AC;&#x2122;s lift and drag characteristics were analyzed from the equations above using the AAA software. A summary of aerodynamic performance is presented later in this chapter.

6.3 Wave Drag Estimation Operating at high transonic speeds presents challenges to minimizing the onset of increased drag due to the presence of shock waves. Although typically associated with supersonic flow, shock waves can form at transonic speeds where local airflow accelerates to sonic speed. By radiating considerable amounts of energy, shock waves present significant increases in drag, once thought so powerful that airplanes prior to the 1940s could not be able to travel faster than the speed of sound, leading to the concept of the sound barrier. Due to the phenomenon of drag diverging to significant magnitudes, efforts have been made to reduce this effect on Ghost. The wave drag for an airplane is heavily influenced by the wave drag contributions of the wing. The wing wave drag coefficient follows from

̅ ( )

(

where

)

(8)

is the aspect ratio of the wing is the steady state flight Mach number is the drag divergence Mach number ̅ ( ) is the wing thickness ratio at the span wise station of the wing geometric chord and is the wing quarter chord sweep angle. The drag divergence Mach number can be found from the Korn equation extended to

account for sweep52, ̅ ( )

where

(9)

is the airfoil technology factor, set at 0.95 for a supercritical airfoil and

is the wing lift

coefficient. Using the above equations in conjunction with AAA, a drag rise analysis was performed for Ghost. Since the drag rise Mach number is heavily influenced by sweep and airfoil thickness, Ghost’s sweep and airfoil thickness were iterated to match an 0.85. The quarter chord sweep of the wing converged

0.07

on 20.9° and the airfoil root and tip

0.06

as 10% and 8%

slightly higher than

0.05

was found to be 0.86.

Figure 21 shows the drag rise as a function of Mach for Ghost. The

0.04

respectively. The resulting

0.03

is also considered, by the Boeing

0.02

Company, as the Mach number at which the rate of

0.01

change of total drag of the aircraft exceeds 0.1.53

∂CD /∂M = 0.1 Mach .86

0.6

0.65

0.7

0.75

0.8

0.85

0.9

0.95

Mach

Figure 21 Result of drag divergence analysis on Ghost indicating a MDD of 0.86

6.4 High Lift Systems Due to the low thickness of Ghost’s wing as well as considerations to sustain lowobservability, it was necessary to keep the high lift system fairly simple, but also provide enough additional lift for high takeoff and landing performance. To maintain maximum laminar flow on the wing surfaces no moving part on the leading edge was incorporated. It was determined that a plain trailing edge flap would be sufficient to generate a CLmax of 1.8, as was assumed in §3.3, given that the flaps span 40% of the total wing. Using the Torenbeek method for sizing flaps54, a parametric

study was performed to determine the required flap chord to wing chord ratio that will generate sufficient CLmax at takeoff. Figure 22 shows the results of this analysis for flaps having a streamwise extent between 15% and 35% of the wing chord. From this, the flaps were sized for 20% of the wing chord from the trailing edge. Efforts were made to define the geometry of the flap segment to ensure attachment of fast moving air to the upper surface with the flaps deployed. A low speed, transient CFD analysis was used to verify the attachment of flow at landing conditions with a flap deflection of 20°, the result of which can be seen in Figure 23.

Figure 22 Aircraft maximum lift coefficient vs. flap deflection for different flap chord to wing chord ratios. The takeoff and landing position of 20º at 20% wing chord is indicated.

Figure 23 CFD results for verification of flow attachment for 20° deflected simple, plain flap performed using ANSYS CFX transient CFD model.

6.5 Detailed Drag Polars To obtain a more accurate estimate of the lift and drag forces acting on the aircraft, a more detailed analysis of the aerodynamics of the aircraft was performed using the methods presented by Roskam55. The methodology used to determine cruise drag polars accounts for compressibility effects by taking advantage of the corrections presented in ESDU Transonic Aerodynamic Data Items*. The low speed drag polar methodology is adopted from Torenbeek56. Figure 24 presents the results of detailed drag analysis using 5th order drag polar equations, which will be used later in Ch. 12 to verify the satisfaction of performance requirements.

Figure 24 Drag polars at key mission segments. Cruise points depict optimal flight performance. Takeoff/Landing points indicate takeoff and landing at CLmax 1.8

The following data items have been used: 6407, 71019, 79004, and 83017

6.6 3D CFD Presented below are 3D CFD simulations of Ghost at cruise conditions. For numerical calculation simplicity, the 3D CAD model was sliced longitudinally along the center line and a symmetry plane was added in place of one half of the model. CFD analysis shows favorable pressure gradients along the surfaces of Ghost suggesting tailored aerodynamic surfaces extending the length of laminar flow. Although the RFP doesnâ&#x20AC;&#x2122;t expressly stress the aerodynamic performance of the bomber, as is the case with many military aircraft, so long as it is capable of completing a specified mission, strong considerations were made to keep aerodynamic performance relatively high. Where tradeoffs between aerodynamic performance and. low-observability existed (in the sense of surface contouring), low-observability took precedence overall, yet aerodynamic performance wasnâ&#x20AC;&#x2122;t reduced dramatically.

Figure 25 Results of 3D CFD analysis. Results indicated favorable flow conditions

7.0 Propulsion 7.1 Engine Technology Tradeoffs 7.1.1 Supersonic configuration – the F135 During the initial phases of the design, a supersonic bomber was considered and it was thought that a high performance military engine would be required to propel the aircraft. Therefore the first aircraft engine ever considered was the F-135 power plant from Pratt and Whitney. The F35 Lightning II is a fifth generation joint strike fighter that comes in three variants: F-35A (CTOL), F-35C (Carrier), and F-35B (STOVL). Each configuration uses either a F135-PW-100, F135-PW400, or F135-PW-600 engine depending on the mission requirements. The F-35A conventional takeoff and landing engine was the engine under consideration for the supersonic bomber. Parts of the F135 are derived from the F119 engine that powers the F-22 Raptor stealth fighter. While many of the military engine specifications are classified, extensive research was conducted to develop a component by component analysis of the power plant. The following table illustrates some of the specifications. (the ≈ sign signifies estimated values through a statistical analysis of similar engines) Table 5 Specifications of the F-135 engine

Bypass Ratio Inlet diameter Overall Pressure Ratio Mass Flow rate of air

0.57 46 Inches (1.1684 meters) 28 ≈90.72-139.6 kg/s

A counter rotating twin spool compressor section contained a 3 stage low pressure compressor fan and a 6 stage axial flow high pressure compressor (both derived from the F119). The compressor was followed by a short annular floatwall combustor with estimated values in the table below. Table 6 Combustor estimated values

Fuel to air ratio Combustor Inlet Air Pressure Combustor Inlet Air Temperature Turbine Inlet Temperature(T04)

≈0.1964 ≈4,150 kPa (600 lb/sq in) ≈649°C (1,200°F) ≈2800-4000 °F(1537-2200 °C)

The high pressure turbine was a single stage while the low pressure turbine was a double stage. It generated more shaft power than the F119 engine was cooled with double the airflow. Table 7 High & Low Pressure Turbine Specifications

High Pressure Turbine Rotation Speed

≈15000 rpm

Work

≈47,725 kW (64,000 shp)

Inlet Temperature

≈1,649°C (3,000°F)

Cooling air from HPC

≈538°C (1,000°F)

Low Pressure Turbine Inlet air

≈1,093°C (2,000°F)

Generally, the engine provided a decent 28,000 lbf of dry cruise thrust with 43,000 lbfs of wet thrust.

But in the end a supersonic configuration was dismissed, in which a straight F135

engine would not be useful. From a propulsion standpoint this makes sense because the F135 was not designed for supercruise conditions and would dramatically increase the cost of the aircraft. 7.1.2 Transonic configuration The next step was to analyze a transonic aircraft capable of speeds near Mach 0.8-0.9. To minimize cost, commercial off the shelf engines were considered. Using a database of existing engines (even some engines yet to be released) the engine that would be best suited for the purposes of a transonic configuration was able to be determined. The following table is a summary of the results. Key SFC Dry vs Thrust SFC Cruise vs Thrust SFC Wet vs Thrust BPR vs Thrust BPR vs SFC dry Historic engine

Table 8 Engines considered in early stage analysis

ENGINE

Thrust

(dry) lbs

(wet) lbs

(cruise)

SFC

Dry

(dry)

(wet)

(cruise)

Weight BPR

lb/lb/hr lb/lb/hr lb/lb/hr (lb)

RB.211-524H

60600

11,813

0.324

0.570

9,671

4.10

RB.211-524H-T

60600

11,813

0.324

0.570

9,470

4.10

RB.211-535E4-37

40100

8,700

0.324

0.598

7,264

4.30

GE90-85B

84700

17,500

0.324

0.520

15,596

8.40

PW4090

91,790

15,585

6.30

PW4098

98000

16,500

5.80

F118-GE-100

19,000

F101-GE-102

0.335 14,000

0.358

0.581

0.67

3200

17,000

30,780

0.562

2.46

4400

22,000

31,000

0.7

1.8

5200

31,000

55,000

0.72

1.7

7500

JTF17A-21

38300

61,000

0.750

1.78

GE4/J5P

51500

68,600

1.040

1.86

GEnx-1B70

72,300

Trent 1000

75,000

GEnx-1B54

57,400

56,300

12,822

GEnx-1B58

61,000

56,300

12,822

GEnx-1B64

67,500

61,500

12,822

GEnx-1B67

69,400

61,500

12,822

(Turbofan) YJ93-GE-3 Kuznetsov NK-32 (Turbofan)

66,500 0.564

1.4

11,300 12,822

9.6

5,765

11.00

Initially, the only requirements that were analyzed were the SFC, dry thrust, and weight. Looking at SFC versus static thrust provided an interesting scatter plot that would reveal engines that stood out in terms of fuel consumption and power. From this analysis the engines in bright green were added to the consideration pool for their high SFC values at static conditions. This scatter plot is illustrated below. A similar analysis was performed for engines with cruise SFC values. However, due to limited information from the database, not all the engine selections were displayed.

Nevertheless, the numbers highlighted in dark green correspond to those that display good SFC values at cruise. 0.9

SFC (cruise) lb/lb/hr

SFC (dry) lb/lb/hr

1.200 1.000 0.800 0.600 0.400

0.358 0.235 0.324 0.335

0.200 0.000 0

50000

100000

150000

Static Thrust (lb)

0.8 0.7 0.6 0.520

0.5 0.4 0.3 0.2 0.1 0 0

20000

40000

60000

80000

Static Thrust (lb)

Figure 26 Scatter plot of engine SFCs versus Static Thrust

In addition to these analyses, the Bypass ratio (BPR) of the engines seemed to be an important factor to consider. Since commercial engines have larger BPRs, they require large mass flow rates to operate at maximum performance. It was initially considered to take a commercial engine and alter the BPR, but the more the engine was altered, the less accurate the numerical predictions would be since the engine was never designed for the new specifications. After much analysis, it seemed like a combination of two engines would best fit Ghost: one designed for military applications and one designed for fuel burn reducing commercial applications. Upon review of recent literature, Pratt and Whitney has started working on adapting its smallest version of the PW1000G for military applications. According to Pratt & Whitney, this new engine would be a combination of the F-135-style low spool with the PW1000G core, rebranded as the PW9000. This development is the best avenue for Ghost and has been selected as the engine for further consideration.

7.2 Engine Characteristics/Optimization Finding specifications for the PW9000 was a difficult task as many parameters are speculated. Table 9 shows specifications of one variant of the PW9000, of which many are estimated and will most likely change as the engine becomes more developed.

Table 9 One Variant of the PW9000 Estimated Specifications

Thrust (Static) (lbs)

20,000

SFC (Takeoff) (lb/lb/hr)

0.350

Thrust (Cruise)

10,500

SFC (Cruise)

.53

Total Mass Airflow (Cruise) (slug/sec) 18.7 Total Mass Airflow (Static) (slug/sec)

49.2

OPR (static)

TIT (F)

3000

Original BPR

To achieve such performance an engine mathematical model has been built to validate the feasibility of the estimated specifications or modify them for our specific configuration. Using textbook propulsion equations, an analysis process was carried through for the PW9000. These equations assume that the fan pressure ratio (FPR) is optimal for the selected engine. It became evident that a BPR under 6 would require 2 fan stages to maintain a high FPR. This would mean that lowering the BPR too much would require a more in depth re-design of the engine. Another fan stage would accrue increased cost and weight, not to mention a re-balance of the turbine stages.

blades are excellent reflective surfaces contributing to high RCS. The BPR was adjusted by

adjusting

the difference

between the bypassed air and air through the core. Figure 27 shows the results of the varied BPR with constant mass flow.

SFC Thrust

1 0.8

40000 30000

0.6

20000

0.4

10000

0.2 0

Thrust (lbs)

chances of radar detection, as large fan

SFC (lbm/lbf/hr)

The diameter of the outer fan needed to be changed to 5 feet so that it could easily fit into a flying 1.2 50000 wing configuration as well as minimize the

BPR

Figure 27 BPR trade study at cruise conditions

As is evident, lowering the BPR will increase the thrust but also increase the SFC. Increasing the BPR beyond 6 would make the engine too large for low-observability considerations. Iterating through different engine parameters and aerodynamic performances, the following design was determined.

Table 10 PW9000 Specifications for Ghost

Number of Engines Cruise Mach Static Thrust Available Total (lb) Static Thrust per engine (lb) Static SFC (lb/lb-hr) Cruise Thrust Available total (lb) Cruise Thrust Available per engine (lb) Cruise SFC (lb/lb-hr)

4 0.85 72,523.5 18,130.9 0.37 15,443.9 3,860.0 0.55

OPR (static) Turbine inlet temperature (째F) BPR Fan Diameter (ft) Core Diameter (ft) Inlet Area (ft2) Total Cruise Mass Flow (slugs/s) Core Cruise Mass Flow (slugs/s) Total Static Mass Flow Rate (slugs/s) Core Static Mass Flow (slugs/s)

31.2 3,000 6.0 5.0 1.890 19.635 7.469 1.067 14.938 2.134

With the adjustments made, an SFC of .55 was achieved. Since the total thrust required at cruise is less than 14,000 lbs, the BPR and other parameters were adjusted accordingly to achieve this thrust. In fact, the original BPR of 6 was able to be maintained and the predicted SFC is .55 which is completely acceptable and may even be lower in the coming years with the rapid improvements in engine technology. The final engine weight will be near 8,400 lbs and 4 engines will be necessary in order to maintain the required thrust and still operate if one engine inoperative. A validation was performed using GasTurb, where a complete engine was modeled. Figure 28 shows the engine performance map of SFC and thrust per engine with varying altitude and Mach number. GasTurb suggests an SFC of just under 0.6 lb/(lb-hr), which is close to the value used for sizing in Ch. 3. However, taking into consideration uncertainties in assumed engine values and further developments in improving the engine, SCAD considers realistic SFC values of the engine at cruise anywhere from 0.55-0.6 lb/(lb-hr). SCAD realizes that the results of this Chapter are highly influenced by estimated assumptions of engine parameters and any of the parameters are capable of uncertainty especially when more updated engine data becomes available.

Figure 28 Engine performance map of SFC and thrust per engine with varying altitude and Mach number

8.0 Systems Architecture & Integration The avionics system architecture of Ghost is based on the results of the Joint Advanced Strike Technology (JAST) program.57 The JAST architecture was developed for Engineering and Manufacturing Development of next generation strike weapons systems for the Navy, Marine Corps, Air Force and allied nations, and has since been incorporated into the F-35 fighter platform. The architecture was chosen because of its many advantages over its predecessor architecture, the Joint Integrated Avionics Working Group (JIAWG) architecture. The JIAWG was a body charged with developing an avionics architecture based upon the Pave Pillar principles of a modular integrated architecture. The resulting Advanced Avionics Architecture was applied to the US Air Force Advanced tactical fighter/F-22 Raptor. The goal of the JIAWG avionics architecture was to equip a highly capable radar, electronic warfare (EW), and Communication, Navigation, and Identification (CNI) suite that would enable the aircraft to survive and execute its mission in a high-threat environment using stealth techniques.58 The resulting architecture was complex, leading to numerous project issues including non-standard buses, insufficient bandwidth, and excessive apertures. The JAST avionics architecture is mainly a result of the lessons learned from the JIAWG architecture. The two main features contrasting the two architectures, as described by Ian Moir in Military Avionics Systems, are: 



The centralization of the avionics computing function into multiprocessor signal and data processing resources in integrated avionics racks with extensive use of high-bandwidth Fiber-optic buses for interconnection; The rationalization of radio frequency (RF) systems into a common integrated sensor system utilizing shared apertures and frequency conversion modules.

Ghost’s avionics architecture, based on the JAST avionics architecture is depicted in Figure 29 and comprises the following major modular subsystems interconnected by fiber channel (FC):      

Central integrated computing resource comprising three separate Integrated Common Processors; AESA radar; Integrated CNI/EW and Electro-Optical (EO) systems; Display suite; Vehicle Management System; Weapons.

Figure 29 JAST (F-35) avionics system top-level architecture.59

These systems, although different in size, weight, power, and cooling requirements, are designed to function on four modular avionics racks. Each of the avionics racks is designed to accommodate standard Line Replaceable Units (LRUs). The LRUâ&#x20AC;&#x2122;s system enclosure formats, environmental parameters, module maximum weights and extraction forces, and mechanical rigidity are defined by MIL-STD-1788. This design allows for greater maintainability, ease of maintenance, and future block upgrades. In addition, space is allotted for future LRU needs. Additional avionics considerations are made to allow for nuclear capability on Ghost. Source Region Nuclear Magnetic Pulses from low-altitude to surface nuclear explosions produce an environment characterized by a combination of electromagnetic and ionizing radiation.60 In addition, high-altitude nuclear detonations and electromagnetic bombs can generate an electromagnetic pulse (EMP) that has the potential to damage or destroy electronic devices over widespread areas. Radar and EW equipment, satellite, ultra-high frequency (UHF), very high frequency (VHF), high frequency (HF), and low band communications equipment are all potentially vulnerable to the EMP effect.61 As a solution, a thin metallic shield was installed around the avionics boxes for protection.

8.1 AESA Radar The Active Electronically Scanned Array (AESA) radar selected for Ghost is based on the upgraded AN/APQ-181 AESA that is equipped on the B-2 Stealth Bomber. The AN/APQ-181 is a multimode radar system operating in the Ku-band (12.5 to 18 GHz), featuring 21 separate modes for terrain-following and terrain-avoidance, navigation system updates, target search, location, identification and acquisition and weapon delivery.62 The reliability and capability of the radar are improved by a completely redundant modular system which employs two electronically scanned antennas, sophisticated software modes and advanced Low Probability of Intercept (LPI) techniques that match the aircraft's overall stealth qualities. These techniques make the radar the stealthiest AESA developed.

Although very little details are known about the capabilities of this radar, it is reported that the upgrades for the AN/APQ-181 are mainly to correct a costly frequency range conflict under the Radar Modernization Program (RMP).63 The current hardware includes five LRUs: the AESA and its associated power supply, signal processor, data processor, and receiver/exciter.64 The signal processor operates in conjunction with the integrated antenna suite and the MIDS JTRS terminal. The processor determines which antenna to use and the minimum power required to accomplish a given task, a stealth-promoting feature. A B-2 RMP document states, “The RMP does not add additional capabilities to the B-2 radar beyond those in the legacy system.” 65 Thus, the antennas are assumed to be not as capable as newer AESA radars found on the F-22 and Joint Strike Fighter (JSF). Consequently the AESA radar integrated into Ghost would be a combination of the stealth capabilities of the APG-181 and the targeting, tracking, communication, and other more advanced capabilities as found on newer AESAs. Many of these current AESA radars were examined to determine the optimal example from which to base Ghost’s AESA design. A summary of this study is found in Table 11 on the following page. The advanced AN/APG-77 AESA radar antenna, successfully integrated onto the F-22, was selected because of its superior range and capability. The 1500 transmit/receive (TR) modules comprising AESA radar antenna are reported to have a detection range of 125 nm against a 1m2 cruise missile target. The multifunctional AESA radar is also capable of performing communications and jamming functions. Tests on the APG-77 have proven that images can be transmitted through the radar at a data rate of 274 Mbps. Lab transmission rates of 548 Mbps, and receive data rates of up to 1 Gigabit per second (Gbps) have also been reported.66 As a comparison, Link 16 transfers data up to only 238 kbs. Controlled by the integrated EW system, the powerful array is also able to generate narrow jamming beams over a certain frequency. Table 11 US fighter aircraft fitted or retrofitted with AESA radars

Platform F-22 Raptor F-35 (JSF) F-18E/F Upgrade F-16E/F (Block 60) F-15C B-2 Spirit

Radar

Number of TR modules

Range (nm)

AN/APG-77 AN/APG-81 AN/APG-79 AN/APG-80 AN/APG-63(V)2 AN/APG-181(V)2

1500 1100 1000 1500 1200 Unknown

125 95 80 70 90 Unknown

Status In Service Entering Service In Service In Service In Service In Development

8.2 Integrated CNI/EW and EO Systems Ghost seamlessly integrates the CNI, EW, and EO systems, which results in an architecture that reduces complexity, weight, and costs through fewer apertures, and ensures greater lethality and survivability. 8.2.1 Communication/Navigation/Identification The CNI subsystem successfully integrates the following elements:     

Aircraft communications; Data links; Navigation; Radar altimeter; Identification and interrogation. A key component allowing the integration of the aircraft communication and data links

systems is the Multifunctional Information Distribution System Joint Tactical Radio System (MIDS JTRS). The Rockwell Collins MIDS JTRS terminal accomplishes this system’s multifunctional capability. JTRS is a mid-1990s effort of the Joint Program Executive Office to replace 25 to 30 military radios with only a few software programmable radios. 67 The system is described as the nextgeneration voice-and-data radio used by the U.S. military in future field operations and the ‘backbone’ of the Future Combat System (FCS) program, intended to link the 18 manned and unmanned systems that would constitute FCS.

The radio system is designed to operate in the

frequencies ranges of 2 MHz to over 2.5 GHz. MIDS is a secure, scalable, modular, wireless, and jam-resistant digital information system currently providing Tactical Air Navigation (TACAN), Link-16, and J-Voice to airborne, ground, and maritime joint and coalition war-fighting platforms. MIDS operates in conjunction with the JTRS enterprise to provide real-time and low-cost information and situational awareness via digital and voice communications. The Rockwell Collins MIDS JTRS terminal “provides a single chassis, multiple channel radio that significantly reduces the number of different and unique radios needed on the battlefield.” 69 It is proposed that by 2025 MIDS JTRS will support many other secure JTRS waveforms, such as the Single Channel Ground and Airborne Radio System (SINCGARS), HAVEQUICK II, the Enhanced Position Location Reporting System (EPLRS), Satellite Communications (SATCOM), the Soldier

Radio Waveform (SRW), and the Multifunction Advanced Data Link (MADL) †. Table 12 outlines some of these waveforms. Table 12 Waveform increments of the MIDS JTRS terminal, implemented through software

Waveform Link 16 TACAN SINCGARS HAVE QUICK EPLRS SATCOM SRW MADL

Frequencies (MHz) 960 – 1215 960 – 1215 30 – 88 225 – 400 420 – 450 UHF 1.8 – 2.5 GHz N/A

Example System

Operators

MIDS L-3 AN/ARN-154(V) RT-1523 VHF Radio AN/ARC-164 UHF Airborne Radio AN/TSQ-158(V)4 Global Hawk UHF SATCOM JTRS HMS AN/PRC-155 F-35

DoD Aircraft and Ships Civil and Military Aircraft U.S. and Allied Military Forces U.S. and Allied Military Forces Army U.S. Military Forces Army Air Force & Navy

High bandwidth, secure, and stealthy voice, video, and chat communications are handled via two multiband SATCOM antennas. The experimental antennas, developed by a combined team from the Electronic Systems Center, the Space and Missile Systems Center, MIT Lincoln Laboratory and MITRE Corp., have recently been proven for use on wide-body aircraft, such as Ghost.70 The redundant system is able to communicate through the Wideband Global SATCOM (WGS) and MILSTAR constellations, as well as future Advanced EHF satellites. Other advantages of the multiband antennas include small size and weight, easy installation, consistent coverage in all directions and the ability to mount to the aircraft skin. The MIDS JTRS terminal, EHF SATCOM subsystem, Identification Friend or Foe (IFF) subsystem, Air Traffic Control (ATC) Mode S, electronic intelligence (ELINT) payload, and potential subsystems not currently equipped on the base bomber configuration, receive and process the communications data captured by an integrated antenna suite. The following figure and accompanying table show the antennas required to accomplish the CNI functions of Ghost.

The MIDS JTRS terminal does not currently support the multifunction advanced data link (MADL) waveform. However, advocates are seeking to implement this secure data-linking technology for fifth generation fighters, such as the JSF, and retrograde the system on other stealth platforms, such as the B-2 Spirit and F-22. Thus, the reasonable assumption is made that by 2025 MADL will be integrated into the MIDS JTRS architecture for the next-generation stealth bomber. †

(5) (2) (4) (2)

(7)

(3)

(1)

(2)

(7) (4) (1)

(6)

(3)

(8)

(5)

(2) (6) Figure 30 RF apertures based on the JSF/JAST architecture71 Table 13 Integrated antenna suite apertures by frequency band

Function

Frequency Band

Number of Antennas

Type

Location

Radio, SINCGARS

VHF

MTL

TOP/BOT

Radio, TACAN

UHF

MTL

TOP/BOT

ATC Mode S/IFF

L-

MASA

TOP/BOT

GPS

L-

MASA

TOP

SA, Data link

S-

MASA

PORT WING – FWD STBD WING – FWD

Radar, SA, targeting

X-

AESA

FWD

SATCOM

Ka-, EHF

Slot

TOP

Moir & Seabridge adequately describe the antenna arrays and interfacing architecture that are integrated in Ghost in Military Avionics Systems: “The primary arrays may typically comprise a large active array: multi-arm spiral arrays (MASAs), slot arrays and multi-turn loops (MTLs). These arrays are connected via an RF interconnect to a collection of receive frequency converters that convert the signal to intermediate frequency (IF). The IF receive signals are fed through an IF interconnect to the receiver modules. After detection, the baseband in-phase (I) and quadrature (Q) components are fed through the fiber-optic interconnect to the integrated core processing.”

The two main types of aircraft navigation include radio navigation and satellite-based navigation. Traditionally, VHF and UHF radio frequencies have been used to navigate routes through non-ranging beacons, VHF omni-ranging/distance measuring equipment (VOR/DME), TACAN, and long range navigation (LORAN) beacons. Modern aircraft are guided by the combination of the Global Positioning System (GPS), the more accurate differential GPS (DGPS) technique, and an inertial navigation system (INS). In 2002, the Department of Defense and the Department of Transportation published a Federal Radio Navigation Plan (FRP) as an official source of radio-navigation policy and planning for the Federal Government.72 The comprehensive FRP outlines the phasing out of widely used legacy navigation systems, such as VHF Omnidirectional Range (VOR), DME, VOR/DME, and TACAN. The phase-down of the VOR/DME and TACAN network is expected to begin in 2010 and these systems will continue to serve as navigational aids until complete transition to satellitebased navigation. By 2025 it is anticipated that these systems will be completely phased out by differential GPS systems. GPS inaccuracies and selective availability issues may be solved using the DGPS technique. Differential techniques involve the transmission of a corrected message derived from users located on the ground. The correction information is sent to the user who can apply the corrections and reduce the satellite ranging error.73 Two systems in the U.S. that derive these corrections are the local-area augmentation system (LAAS) and the wide-area augmentation system (WAAS). The basic accuracy of GPS without selective availability is about ±100 m as opposed to ±8 m when the full system is available. The Northrop Grumman LN-251 is a tightly coupled, integrated digital INS/GPS system that provides superior performance for navigation, geo-location of sensor targeting, and the ability to transfer align remote sensors. As Northrop Grumman states, “This results in unequaled navigation and Synthetic Aperture Radar (SAR) stabilization performance as well as the most accurate target location.”74 The system has been proven on unmanned applications, such as the Predator UAV, and has been selected for Ghost due to its lightweight, low cost, aerial refueling capability, and high performance class framework. The accuracy of the system is up to 0.8nm and 2.0nm/hr. With the rise of GPS jamming and spoofing equipment there is a natural concern of loss of accurate aircraft positioning, velocity, and targeting information. However, integrated GPS/inertial avionics having significant anti-jam capability could greatly reduce the area affected by a GPS

jammer or by unintentional interference. Industry research is proceeding to develop this technology and other anti-jamming techniques. Northrop Grumman, for example, developed a jammingsuppression solution using different suppression methods on each GPS receiver in a vehicle.75 In addition, Raytheon’s Digital Anti-jam Receiver (DAR) provides “jamming resistance for all combat aviation missions.”76 These technologies are integrated into Ghost’s CNI system for optimal survivability. Safe approach and landing capabilities are accomplished using a BAE MLR-2050 Joint Precision Approach and Landing System (JPALS). The multi-mode receiver (MMR) system replaces traditional instrument and microwave landing systems (ILS/MLS), offering a mix of landing aides: ILS, MLS, VOR and GPS. The MMR open-system provides precision landing guidance in hostile operating scenarios.77 Identification of friendly or foe (IFF) aircraft is primarily handled by the IFF interrogator and transponder systems. A trade study was performed to compare the BAE AN/APX-118(V), the BAE AN/APX-113, and the Northrop Grumman AN/APX-121 IFF systems. The AN/APX121(V) system from Northrop Grumman offered a number of advantages, including advanced microwave and digital design features that fully support organic maintenance concepts. In addition, the transponder design incorporates all Code S and Mode 5 requirements and the desired 1553B interface.78 The AN/APX-113 was also a viable candidate for the IFF function. Some features of this system include complete Mark XII or Mark XIIA identification system (including crypto computers) in one unit; DoD AIMS-certified STANAG 4193-compliant; Includes Mode S, Level 3 (ELS and EHS); Multiple antenna configurations (electronic or mechanical scan); Ada software; and Dual-redundant MIL-STD-1553 bus interface.79 However, the AN/APX-118(V) is the only system that offers remote control (as on the RQ-5 Predator), which further allows Ghost to serve as an unmanned platform. Thus, the APX-118 was selected as Ghost’s IFF system. 8.2.2 Electronic Warfare and Defense The mission profile of Ghost requires the aircraft to penetrate heavily defended airspace and consequently must employ “a variety of self-protection features.”80 The EW subsystem cooperates with the CNI and EO subsystems to fulfill this requirement, providing electronic countermeasures (ECM), electronic counter-countermeasures (ECCM), electronic support measures (ESM), and signals intelligence (SIGINT).

The EW subsystem comprises three main sub-subsystems: a Raytheon AN/ALR-94 radar warning system, the AN/ALQ-214(V) Deception Countermeasures System from BAE Systems, and the BAE AN/ALE-47 countermeasures dispensing system (CDS). In addition, the aircraft will integrate an optional lightweight Northrop Grumman LR-100 RWR/ESM/ELINT receiver system, for greater warning and ELINT capability in an unmanned configuration.81 Together these systems provide optimal survivability and defense from enemy airborne and ground-based weapons, electronic warfare, and countermeasures systems, shown below in Figure 31. Countermeasure Dispensers

Radar Antenna

AN/ALR-94 RWR/LWR System AN/ALQ-214(V) Deception Countermeasures System AESA ELINT Sensors

Laser Warning Sensors

LR-100 RWR/ESM/ELINT Receiver System

Figure 31. Ghost supports an integrated defensive aid system, designed to offer complete 360 degree uninterrupted defense

An upgraded radar and laser warning (LWR) system based on the AN/ALR-94 is adapted to function on Ghost. The system comprises of a passive receiver system to detect radar and laser signals; composed of approximately 24 antennas smoothly blended into the wings and fuselage to provide complete 360-degree coverage. Alluding to the importance of the system, Tom Burbage, former F-22 program head at Lockheed Martin, describes the ALR-94 as "the most technically complex piece of equipment on the aircraft." The system supports all of Ghost’s ESM activities: threat warning, target acquisition, and homing. Targets can be detected, tracked, and identified by the warning system well in advance of enemy threats. With a range of more than 250 nmi, the system has twice the range of the AESA, allowing the aircraft to limit its own radar emissions, maximize stealth and elude potential targets. As a target approaches, the receiver system can cue the AESA radar to track the target with a narrow beam, which can be as focused down to 2° by 2° in azimuth and elevation. If a hostile aircraft is injudicious in its use of radar, the upgraded ALR-94 may provide nearly all the information necessary to launch an AIM-120 AMRAAM air-to-air missile (AAM) and guide it to impact, making it virtually an anti-radiation AAM.82

The data from the AESA, ALR-94 and the datalinks are correlated according to their azimuth, elevation and range. Data is combined into a track file, and the final target picture is obtained by choosing the read-out from the most accurate sensor. For example, the passive system may provide the best azimuth data, while the radar produces the most accurate range.83 The BAE AN/ALQ-214(V) Integrated Defensive Electronic Countermeasures (IDECM) Radio Frequency Countermeasures (RFCM) system is described as providing “next-generation protection from RF threats.”84 The system uses radar warning information from the ALR-94 to drive transmitters that then deceive enemy radars and missile systems. The ALQ-214 is also teamed with the proven ALE-47 countermeasures dispensing system to determine the correct defense response and to dispense decoys. The system architecture includes:        

Receiver (designated as Weapons Replaceable Assembly (WRA) - 1); Modulator (WRA-2); Processor (WRA-3); Low-band transmitter (WRA-4); High-band transmitter (WRA-5); Mounting rack; Three pre-amplifiers; BAE AN/ALE-55 fiber optic towed decoy (separate, but integrated). The ALE-55 is commanded by the ALQ-214 to provide three layers of defensive jamming

against a radar-based threat: preventing radars from tracking, breaking radar locks, and acting as a target for incoming missiles.85

Figure 32 The IDECM RFCM receives RF/EO/IR signals and responds with countermeasures using the components shown86

Other electronic countermeasures are performed using the highly capable AESA radar. Current technology suggests that the radar can be directed to actively jam enemy radar and use digital radio frequency memory (DRFM) to “provide false information back to enemy radars on the aircraft’s RCS, range, angle, and velocity.”87 DRFM is a developed electronic method for copying an incoming radar or RF signal and digitally modifying it before transmitting it back to the enemy radar. DRFM can increase aircraft survivability by “delaying, denying, and defeating threat air-to-air and surface-to-air missile systems operating in the RF spectrum.” 88 Using existing EW subsystems, the Ghost stealth bomber can also serve as a basic platform for gathering SIGINT. The myriad of antenna types can be used to provide wide area spherical coverage of ELINT and communications intelligence (COMINT) sources. The Northrop Grumman LR-100 can also be integrated as an additional combat-proven, affordable, and high-performance RWR/ESM/ELINT receiver system for intelligence, surveillance, and reconnaissance (ISR) missions. The incoming intelligence can be paired with the aircraft navigational data and interpreted by the crew, air/ground operators, or can be stored in on-board mission computers. ELINT is received and processed according to the block diagram in Figure 33.

Figure 33 Typical ELINT block diagram89

8.2.3 Electro-Optical The EO subsystem includes one optional and two major sub-subsystems that are primarily responsible for the targeting, SA, and ISR functions of the aircraft. They include: an EO distributed

aperture system (DAS) provided by Northrop Grumman (AN/AAQ-37), allowing 360Â° day/night coverage; Electro-optic targeting system (EOTS) from Lockheed Martin (AN/AAQ-34), providing a multifunctional EO targeting system; Optional EISS developed by Raytheon, providing persistent C2ISR. 8.2.3.1 EO Targeting System The Ghost targeting system is based on an upgraded Global Positioning System (GPS) Aided Targeting System (GATS) that is employed on the B-2. GATS uses radar and GPS information to control the bomberâ&#x20AC;&#x2122;s weapons, as shown in Figure 34. In addition, this advanced, low observable, light-weight, and low cost system will have improved capabilities with the addition of the AN/AAQ-40 Electro-Optical Targeting System (EOTS) sensor, which is found on the JSF.

Figure 34 GATS Mission Profile.90

The multifunction EOTS targeting systems exploits the synergetic architecture of the combined GPS navigation, AESA radar, and DAS aperture data. The excellent range and range rate capabilities of the AESA's SAR capabilities, accurate position and velocity information provided by GPS, and the visual acuity of the DAS will provide weapons with highly accurate target location data relative to the current bomber position. The range of the system is unknown, but is believed to be 40-50 nm based on the capability of its predecessor, the Sniper XR/Pantera.91 The system also processes information from the AESA radar for a fire-control function.

The EOTS infrared sensor provides forward-looking IR (FLIR) and infrared search and track (IRST) for precision air-to-air and air-to-surface tracking. The sensor also provides highresolution imagery, tracking, automatic targeting, laser designation, range-finding, and laser spot tracking functionality. The compact and modular sensor is extruded through stealthy retractable window located on Ghost’s fuselage during operation and allows for ease of maintenance and upgradability. 8.2.3.2 EO DAS The advanced Northrop Grumman AN/AAQ-37 DAS designed for the JSF provides a highly capable video imaginary system using six advanced infrared digital high definition broad view sensors, positioned around the aircraft’s airframe to enable complete 360-degree EO coverage, shown in Figure 35. This system is designed to provide the pilots with targeting, weaponry, aircraft performance, and threat information, enhancing pilot's situational awareness as well as a complete and clear view of the surrounding environment throughout the mission. As a summary, the DAS provides92:     

Missile detection and tracking Launch point detection Situational awareness IRST & cueing Weapons support Day/night navigation

Figure 35. The 6 IR sensors positioned near the center plane of Ghost allow for a complete spherical coverage.

DAS is fully integrated into the aircraft with the AESA, CNI, and EW systems to immediately detect, track, and respond to all the air and surface hostile threats. Cooperating with the

radar warning systems, any moving object can be detected and identified. The system is also capable of cueing the integrated weapons targeting system (ALR-94) against a hostile target and has additional fire-control capability. This enables the pilot to simply but accurately direct the weapons towards it and fire, without even adjusting the position of the aircraft. This minimizes aircraft maneuvering and time spent in the danger areas, which is particularly critical for a large, non-agile bomber such as Ghost.93 Although the DAS sensors are currently only offered as IR sensors 94, the system integrated into Ghost’s EO subsystem (2025 time frame) will operate in the visible and ultraviolet (UV) portion of the electromagnetic spectrum as well. This will provide day/night vision as well as protection from future EW and UV laser guided weapons, further enhancing survivability in all different phases of flight. While the range capability of the system is not known, it is assumed to be much less than the 250 nm range of the ALR-94. DAS utilizes a terrain database and GPS receiver data to interface with the pilots by presenting information on a cockpit display. The pilot is thus provided with a clear, electronic picture of the environment around the aircraft including approach and landing patterns, runway environment, obstacles, and air traffic. 95 The system also serves as a traffic collision and avoidance system. The DAS aircraft detection and tracking system assists in simultaneously tracking and identifying multiple threats in every direction around the aircraft. 96 Further enhancing combat capability, Ghost is fitted with two helmet-mounted display systems (HMDS), projecting augmented reality directly to the pilots' helmet visors. DAS provides the information for the system to create real-time images for targeting, situational awareness, and visualization. The helmets’ visors display a complete panoramic view of the aircraft surroundings, including directly behind and below the aircraft’s plane, making the aircraft and the pilot practically invisible to the pilot's eyes.97 Both pilots are equipped with a HMDS helmet and can perform operations independent of each other. 8.2.3.3 EISS and ISR Ghost has the option to carry an integrated sensor payload, adapted from Raytheon’s EISS. EISS is a dedicated ISR suite that combines an EO/IR digital camera, SAR antenna, and a ground moving target indicator. These sensors work together using a common signal processor, providing Ghost with additional and enhanced imaging, wide area coverage, radar detection, and night vision

capabilities. The system, fitted in the Global Hawk UAS, is capable of precisely locating stationary or moving targets regardless of their location, time of the day, and weather condition. This system allows the controlling of the bomber in UAS mode by transmitting imagery and flight information from altitudes as high as 60,000 feet to a remote ground station via SATCOM. The EISS system provides the ground segment with continuous and persistent ISR, allowing them to react quickly and precisely.98

8.3 Interfacing A major challenge with the systems integration on Ghost is the interfacing. The standard interface for most modern avionics systems is the MIL-STD-1553 architecture, which defines the mechanical, electrical, and functional characteristics of a serial data bus. The latest revision, MILSTD-1553B offers a 1 Mbps serial communication bus.99 Current Commercial Off-The-Shelf (COTS) avionics are now offering a modern replacement to the aged military standard. Improved options include the ARINC 664, the IEEE 1394, and the Fiber Channel 1553 (FC-1553) interface standards. ARINC 664, or Avionics Full-Duplex Switched Ethernet (AFDX) is a deterministic protocol for real time application on Ethernet media. “AFDX is intended for aircraft flight critical interfaces, including Engines, Flight Controls, navigation systems.”100 The data bus is used on most higher-end commercial and transport aircraft and is not adopted by current military aircraft. The IEEE 1394 firewire interface architecture is a widely used data bus and scaleable in its original form. The interface has displayed potential for processing the high bandwidth required by Ghost’s avionics. Later versions developed under the IEEE 1394c or 1394d standard are able to transfer data up to 800 Mbps in a network form. This standard has been adopted for interconnecting portions of the instrumentation data system on the F-35.101 Despite the standard’s advantages, it is unable to tolerate failures by the nodes or the transmission media due to its daisychain architecture. IEEE 1394 is therefore not an attractive option for avionics applications. In aerospace applications, the FC is an optical high-throughput connection oriented network technology, presently offering data rates up to 1 Gbps. Future versions of up to 10 Gbps are under development.102 Another huge benefit of FC is its resistance to electromagnetic interference (EMI) from other components, bundled wires, and nuclear explosions. The roles of fiber-optic interfaces are to:

   

Handle incoming preprocessed sensor data; Handle video data destined for displays; Feed necessary data for the weapons systems; Interconnect the major avionics systems to the integrated cabinets. A standard utilizing FC is FC-AE-1553, modeled after the extensively integrated MIL-STD-

1553. Allowing the MIL-STD-1553 protocol to be mapped on to the high bandwidth FC network creates a low-overhead highly deterministic protocol with a high bandwidth capability. The features developed under the FC-AE-1553 standard offer an enormous increase in capability, while maintaining those parts that do not require a bandwidth increase intact. Ghost will implement a versatile FC standard to satisfy its COTS high-speed and EMI resistant interface requirements. FC may be implemented using StarFabric, which has been selected for applications on the JSF.103 A summary of the available interfacing systems are shown in Table 14. Table 14. Interfacing standards used on current avionics systems.

Rate (Mbps) Max Payload (kB) Max Data Transfer (Mbps) Medium Aircraft Usage

1553 1 NA NA Copper Common

ARINC 664 100 1.472 1.518 Copper/FC Commercial

FC-1553 2125** 2.121 4,300 FC JSF

IEEE 1394* 800 8.192 75 Copper JSF

*For FireWire S800T (IEEE 1394c-2006); **Under development

8.4 Avionics Cooling & Environmental Control System (ECS) Ghost contains dozens of advanced, high performing, and critical electronics systems, located primarily in four separate avionics modules. The close loop liquid avionics cooling system provides a high heat exchange capacity with a controlled low operating temperature for optimal electronic systems performance. The cooling system itself is powered by the electricity produced by the engines, instead of the alternative method of using bleed air. Heat pipes attached to the cold plates in each avionics module serve as the evaporator. The pipes are easy to maintain and replace. The system can also be easily upgraded to a higher cooling capacity to support additional electronics that can be expected in future block upgrades. Polyaphaolefins function as the cooling liquid due to its durability. The pipes are also more unlikely to rust with this cooling fluid than using water. The typical heat capacity of polyaphaolefins is approximately 2.1 kW per Kg.104

Cooling of the electronics systems is accomplished in a two loop transfer system. First, the cooling liquid transfers heat from electronics to a heat exchanger near the avionics racks in the first close loop system. second

Then, the

loop

system

transfers heat from the local heat exchanger to the fuel tank, which serves as a heat sink.

In both

loops, the cooling fluid remains in a liquid state, which minimizes the pressure change in the heat pipe and increases its life span. A sample

Figure 36 An avionics rack with cooling system.

of an avionics rack attached to a cooling system is shown in Figure 36. Minimizing vapor inside the heat pipe can also increase the cooling system’s effective thermal capacity and decrease orientation effects that are caused by the difference between liquid density and vapor density. The combined volume of all heat exchanger units is approximately 0.8 cubic meters. This provides an upper heat rejection value of about 120 kW. For such heat rejection, the electronic compressors connected to the system require about 70 kW to pump the cooling fluid through both systems.105 8.4.1 Cockpit Environmental Control System The bomber design contains a modular two-person cockpit. Due to the small size of the cockpit, a bleed air driven environmental control system would be suitable without lowering engine efficiency by a significant amount. Ghost utilizes a modern version of the ECS that was first developed for the B-2 bomber to control the pressure, temperature, humidity and airflow in the cockpit. At the center of the system is a Foil Bearing Air Cycle Machine developed by Hamilton Standard. The B-2 air cycle machine (ACM), improved from the B-1B ACM, is a high-speed foil air bearing ACM that has been proven successful. The 6.48 dm3 B-2 ACM has a proven durability. After tests of 1,600 hrs of endurance operation and 7,500 start/stop cycles, the machine remains in “like-new” condition.106 The whole ECS is installed on the top of the cockpit module, including its own small ram air intake and bleed air intake connections to the engine.

8.5 Cockpit Design The Ghost's cockpit is equipped with two full-panel-width panoramic cockpit display (PCD) units, providing a broad and improved view of outside the aircraft for each pilot. Information from the aircraft's avionics systems is provided to the pilots in an ergonomic cockpit configuration. This advanced cockpit layout is combination of touch screen LCD flat panels and flight display arrays and is designed versatile, reprogrammable, and upgradeable. PCD and HMD can both display flight information and imagery depending on the mission profile and environment.107 Ghost is provided with a cockpit speech-recognition system, developed by researchers at the Air Force Research Laboratory (AFRL) for the F-35 fighter aircraft. This first-time system is capable of recognizing the pilot's spoken commands to operate different aircraft subsystems, improving the pilot's ability to control the aircraft by eliminating the need to use his/her hands or glance at instruments. This system is thus designed to increase safety and efficiency while keeping the pilot focused on analyzing the combat environment.108 A much more advanced version of the proven system will link the Ghostâ&#x20AC;&#x2122;s integrated processor to the pilot. An adapted Martin-Baker US16E ejection seat is selected to satisfy Ghost's escape system requirements, including safe terrain clearance limits, physiological loading limits, pilot boarding mass and accommodation.109 The ejection seat, selected for F-35, has a highly modularized design and provides ease of seat removal with the canopy in-situ, which complements Ghostâ&#x20AC;&#x2122;s modular cockpit design. The lightweight seat is also selected for its support of the HMD and a 30gx crash and egress capability. Since ejection is a last option for the pilot, every part of this system, such as initiation, escape path clearance, parachute descent, and final functions perfectly provide the pilot with the assurance of reaching the ground uninjured. Another system adapted from the JSF is the oxygen system developed by Honeywell. Improving performance characteristic flaws of the F-22 oxygen system, Honeywell designed this life support system to perform even during high attitude maneuvers. 110 Mission flexibility, low life-cycle cost, no scheduled maintenance, and improved safety 111 make this system a reliable choice for Ghost.

8.6 Unmanned Configuration 8.6.1 Remote and Autonomous Operations Ghost is equipped with sufficient avionics systems and subsystems to allow for a complete C4ISR infrastructure enabling remote operations. The communications systems integrated with the navigation, identification, EW, and EO sensors permit ground stations to operate the unmanned configuration from virtually anywhere in the world. The digital sensor data received by Ghost can be transmitted at higher than 50 Mbps to a ground station in real time, either directly or through a communications satellite link.112‡ Considerations are made for communications link loss, operations in U.S. airspace, and cockpit replacement modules. The communications, navigation, and identification systems play the most significant role in enabling Ghost’s unmanned configuration. These systems, with the integrated sensor suite, are driven by autonomous software packages inherited from proven platforms such as the Global Hawk, Predator, and X-47B unmanned systems. The legacy systems particularly add reliability, maintainability, and safety, while reducing costs. Additional trade studies were performed to determine the optimal systems architecture for unmanned capability. The IFF system, for example, was selected because it was proven on the Predator UAS and offered an optional remote control unit for use on non-bused platforms. The Northrop Grumman LN-251 digital INS/GPS System, flown on many UAS platforms, was selected for its light weight, low cost, and automated aerial refueling capability. The optional sensor suite (EISS), integrated into the Global Hawk, allows for remote persistent ISR capabilities. While these systems may not be the most capable in their class, they all can be successfully integrated into the stealth platform to accomplish the unmanned mission. The table below briefly outlines these systems.

‡

Based on transfer rates provided by the Global Hawk UAS.

Table 15 Ghost systems for independent operations in an unmanned configuration

Systems SATCOM IFF

Type

Description

Communication

Ka- and EHF-band SATCOM for video and remote data transfers to ground segment.

Identification

INS/GPS

Navigation

Remote control capable IFF Transponder. The LN-251 provides superior performance for navigation, geolocation of sensor targeting, and the ability to transfer align remote sensors (aerial refueling). Provides all conditions, day/night, SAR, and EO/IR high-resolution video and imagery sensors; ISR & ELINT missions.

EISS

DAS

Provides the ground pilots with missile warning, navigation support and night operations.

EOTS

Multi-functional system for precision air-to-air and air-to-surface targeting.

RWR/LWR

Provides the ground segment with SA of air defense weapon systems using radar & laser technology.

AESA

Radar

Will allow joint forces to detect and track targets; Communications and SAR imaging capabilities.

In the event of partial or complete loss of C4ISR networks, Ghost will remain fully capable and operate independently in its unmanned configuration using the systems previously described, coupled with autonomous software instructions. A loss of link event will trigger pre-programmed flight patterns that are autonomously followed. Using pre-programmed air speed and waypoints, along with fuel and range information, the on-board IPUs determine the optimal flight pattern to follow. Typically, the unmanned bomber would enter a circular holding pattern in hopes that the connection would be reestablished. If the aircraft is in hostile airspace at the time of link loss, the IPUs would either guide the bomber on its current course or to the nearest safe zone, depending on the current mission. If no link is reestablished, the bomber will be directed to return to base with sufficient fuel remaining. Some autonomous maneuvering would also be possible during a link loss. An incoming threat, for example, would be avoided with the assistance of the autonomous defense countermeasures systems and flight control system (IPUs). One scenario might be to deploy the towed decoy (ALE-55), followed by chaffs (ALE-47), and then bank or maneuver away from the incoming threat, as required. Section 8 of FAA Guidance 08-01 establishes the communications requirements for the operation of UAS inside the US National Airspace System.113 The FAA requires an approved sense

and avoid function, which is provided by current sensor systems and software similar to Northrop Grumman’s Global Hawk sense and avoid system. 114 The software governs the rules of engagement in the event of a possible collision. Ghost is also equipped with a flight termination system as required by the FAA. Ghost’s modular design allows for the cockpit to be completely removed for remotely controlled unmanned operations. Other modules, useful for the UAS configuration, may be integrated in place of the cockpit. Options include:  

 

A fuel module, adding 6,700 lb of fuel (shown in Figure 37.) Modules containing additional avionics, such as more powerful radar for Airborne Warning and Control Systems, communications for redundancy and mission assurance, power supplies, and processing power. Future block upgrades. Empty Space for reduced weight (short-range or non-critical missions).

All necessary connections are integrated into Ghost’s fuselage to permit successful integration of these modules. For example, extended fuel, power, and communications lines are in place around the cockpit module location to connect to the respective systems. The ground control segment for Ghost’s unmanned operations includes a mission control element (MCE) and a launch and recovery element (LRE), a logical solution adopted from the Global Hawk architecture. 115 The MCE consists of a stationary control station located at a secure US Air Force Base, such as Beale AFB (Global Hawk) or

Figure 37. The fuel module holds 3,700 lbs of fuel

Whiteman AFB (B-2). The base will serve as the main launch and recovery base for Ghost. Five or more workstations operate in conjunction to provide continuous C4ISR operations for the unmanned bomber. They include: mission planning, sensor data and processing, targeting and weapons, air vehicle command and control operator, and communications. The MCE can be deployed with the supported command's primary exploitation site. The LRE is responsible for all launch and recovery operations and “includes a mission planning function as well as air vehicle command and control.” 116 The transportable station provides precision differential global positioning system corrections for navigational accuracy during takeoff and landings. The station may be separated geographically from the MCE to provide operational

support, as demonstrated in Figure 38. Both ground segments communicate with Ghost through external antennas for line-of-sight and satellite communications with the air vehicles.

Figure 38 A ground station concept used to perform remote C4ISR operations; similar to Ghost’s design. 117

8.6.2 Future C4ISR Capabilities The communications and defensive capabilities introduced in the previous sections provide the opportunity for Ghost to take on an advanced role in battle beyond its primary mission as a strategic bomber. C4ISR emphasizes the collection and dissemination of relevant data collected by numerous platforms to maximize combat and cost effectiveness. 118 The advanced and upgradeable communications systems, the potential for a wide variety of payload configurations, and the impressive ability for loiter facilitate the opportunity to act as a battleground “gateway” for numerous manned or unmanned, stealth or conventional aircraft. This capability has been desired by the U.S. military on a broader scale and was even utilized by the USAF and US Navy during a demonstration that allowed an F-22 to conduct surveillance and use the collected ISR to re-route two Tomahawak missiles that were in-flight after being fired by a submarine.119 On the command and control side, the wide variety of communications systems available to Ghost through the MIDS JTRS would allow Ghost to use LPI/LPD communication with other stealth aircraft, such as the F35 equipped with MADL, and disseminate the combined battlefield information to the entire fleet through the high-bandwidth LPI/LPD EHF satcom link. Thus, Ghost is capable of performing the role of a stealth airborne control node through which battle commanders can conduct an extensive stealth military campaign.

8.7 Power Generation The expected power consumption and requisite power generation required for Ghost could not be analyzed based on the installed systems due to their classified or proprietary nature. Therefore, the power requirement projections by the Power Division of the Air Force Research Laboratory of an airborne system with the same classification as Ghost for the 2015+ timeframe were used to determine power generation requirements. 120 Ghost was designed to be capable of generating 1,100 Kilovolt-Ampere (KVA) via one 225 KVA alternating current (AC) generator and one 50 kilowatt (KW) direct current (DC) generator per engine. The AC generators should be capable of an overload capacity of 8% to 15% for extended periods of time. These generators will provide power for the power consumers such as the actuators and ECS (when the cockpit module is installed). Furthermore, the AC generators should be capable of generating the reactive power required for the system should the Static VAR Compensator unit fail for any reason. The DC generators will provide power for the DC network as well as the field current required for synchronous generators that will work on the same shaft. The DC generators will feed the avionics, communication systems, radar system, and the lighting. The use of both AC and DC networks will allow Ghost to carry fewer voltage correction instruments and minimize the necessity of power factor correction devices. The protection strategies will be expected to be simpler and the system will be expected to have improved reliability over other possible systems.

8.8 Nuclear Capability The use of Fiber-Optic data transfer, hardened electronics, nuclear fire controls, and compatibility with the common strategic rotary launcher allows Ghost the ability to carry and drop nuclear ordnance. Any failure to meet USAF requirements could be expected to be corrected in future block upgrades.

9.0 Stealth 9.1 Radar Evasion To successfully defeat an air defense system, Ghost was designed to be effective at countering the wide variety of radar systems that would be expected to exist in a highly-defended battle arena, a summary of which is shown in Table 16. The type of radar system and its likely location in space relative to Ghost was analyzed and RCS-reducing design features and materials were strategically placed to improve the probability of mission success without sacrificing performance. The effect of Ghost’s design features on its RCS was analyzed via MATLAB software121 over a wide range of frequencies and compared to the B-2, as shown in Figure 39-Figure 46. Table 16. Radar bands used to track and engage aircraft by radar systems.

Band

Wavelength

Frequency

Useful Range

Platform

Surveillance VHF

1 – 10 m

50 – 330 MHz

Very Long

Surface

UHF

0.3 – 1 m

300 – 1,000 MHz

Very Long

Surface/AEW&C

15 – 30 cm

1 – 2 GHz

Long

Surface/AEW&C

7.5 – 15 cm

2 – 4 GHz

Moderate

Surface/AEW&C

4 – 8 GHz

Moderate

SAM

Tracking C

3.75 cm – 7.5 cm

Tracking/Engagement X

2.5 – 3.75 cm

8 – 12 GHz

Short

SAM/Airborne Fighters/AAM

1.67 – 2.5 cm

12 – 18 GHz

Short

SAM/Airborne Fighters/AAM

0.75 – 1.11 cm

27 – 40 GHz

Short

SAM/Miscellaneous Seekers

In order for a design feature to be effective against radar, the feature must be physically larger than the wavelength of the threatening radar system.122 Ghost was designed to have slim front, side and rear profiles in addition to a constantly-changing curve radius on the underbelly because these surfaces would be the most “visible” to long range, long wavelength surface- and airbornebased early warning systems (EWS).123 These EWS are typically used for acquiring basic information about speed, heading, and location of its target and then alerting aircraft that would be used to intercept. To determine the effect that the design shaping of Ghost had on its ability to evade radar, a comparison of the RCS signatures of the B-2 and Ghost was performed via MATLAB software 124 at four frequencies that provide representative samples of the spectrum shown in Table 16: 300

MHz, 1.5 GHz, 8 GHZ, and 28 GHz. The results of the longest range EWS are shown in Figure 39Figure 40 on the following page. Note: The RCS of the B-2 was used as a benchmark against which Ghost was compared. The reflectivity of each aircraft is comparative and the quantitative value (measured in dBm2) would be orders of magnitude lower if RAM were taken into account.

Top

Right Profile

Front

Left Profile

Bottom

Figure 39. B-2 RCS signature at 300 MHz, used by â&#x20AC;&#x153;very long rangeâ&#x20AC;? early warning systems. Color spectrum units: dBm2.

Top

Right Profile

Left Profile Front

Bottom

Figure 40. Ghost RCS profile at 300 MHz, used by very long range early warning systems. Color spectrum units: dBm2.

Ghost has a clear advantage over the B-2 with regards to the VHF band, which are used by the “very long range” EWS. This advantage continues at the 1.5 GHz frequency radar systems, which operate in the UHF-band used by “long range” EWS. The results of the 1.5 GHz analysis are shown below in Figure 41-Figure 42.

Top

Right Profile

Front

Left Profile

Bottom

Figure 41. B-2 RCS profile at 1.5 GHz, used by long range early warning systems. Color spectrum units: dBm2.

Top

Right Profile

Left Profile Front

Bottom

Figure 42. Ghost RCS profile at 1.5 GHz, used by long range early warning systems. Color spectrum units: dBm2.

The shorter wavelength radars that are harder to defeat typically have shorter useful ranges because of the relationship demonstrated by the Planck-Einstein equation, 71

(10)

where E is the energy, h is the Planck constant, and λ is the wavelength of the emitted electromagnetic radiation (EMR). As seen in (10), the power (or energy required per second) goes up as the wavelength of the EMR goes down. Thus, the shorter wavelength radars used for tracking and engagement generally have short ranges. While the RCS of Ghost will be significantly reduced against surface-based SAM platforms due to the aircraft’s constantly-changing curvature, enemy aircraft present a greater challenge. When a radar system is at a similar (or higher) altitude than Ghost, the engine inlets can potentially contribute significantly to the RCS. For instance, modern fighter aircraft radar systems are capable of counting the compressor blades on an engine and using that information to identify the aircraft type at a distance of up to or greater than 100 mi.125 To counter this ability, Ghost has sunken engines that are fed by RAM-lined high radius of curvature S-ducts, which are covered by an extensive fine mesh that will block all but the shortest of radar wavelengths. Any EMR that is not reflected away by the mesh will be absorbed by the RAM-lining on the inside of the S-ducts. Finally, the sunken engines reduce the total amount of engine face surface area, which minimizes the time airborne radar would have to view any exposed surface. A comparison between the B-2 and Ghost for 8 GHz, which lies at the fringe of the C- and X-bands used by short range tracking and engagement systems, was performed. The results of the analysis are shown in Figure 43-Figure 44. Top

Right Profile

Front

Left Profile

Bottom

Figure 43. B-2 RCS signature at 8 GHz, used by tracking and engagement systems. Color spectrum units: dBm2.

Top

Right Profile

Left Profile Front

Bottom

Figure 44. Ghost RCS signature at 8 GHz, used by tracking and engagement systems. Color spectrum units: dBm2.

The analysis shows that there is less discrepancy in the relative RCS size between the two aircraft. The front and side RCS profiles of Ghost are noticeably lower than the B-2. However, the top and bottom RCS profiles show a decreased advantage even though the B-2 has greater reflectivity overall in several small areas denoted by the red spots. A final K a-band 28 GHz analysis was performed to represent the higher end of the frequency spectrum, which is also used by a variety of short range tracking and engagement systems that include missile-mounted seekers. The results of the analysis are shown below and on the following page in Figure 45-Figure 46. Top

Right Profile

Front

Left Profile

Bottom Figure 45. B-2 RCS profile at 28 GHz, used by tracking, engagement, and seeker systems. Color spectrum units: dBm2.

Top

Right Profile

Left Profile Front

Bottom

Figure 46. Ghost RCS profile at 28 GHz, used by tracking, engagement, and seeker systems. Color spectrum units: dBm2.

Ghost loses some of its RCS advantage over the B-2 for the 28 GHz Ka-band. Fortunately, at this frequency and higher, the power requirements of enemy radar systems make their effective range significantly smaller than for the previous bands. Furthermore, the peak RCS of Ghost is still significantly smaller than the peak RCS of the B-2, which will reduce the likeliness of a radar system ever becoming aware of Ghost’s presence. A significant contributor to Ghost’s reduced RCS that was not able to be quantified in the above analysis is its lack of cockpit windshields and the vastly reduced transparent surface area that results. Typically the transparent windshield of a stealth aircraft is coated with metal oxides and treated to prevent radar from getting in and EMR produced by cockpit electronics from getting out.126 Ghost, however, utilizes powerful computers to stitch together the live feed of an array of cameras that require a fraction of transparent surface area of a windshield, which was discussed in §8.2.3.2. The result of this novel approach is that the crew is provided with unmatched visibility while the cost of producing the unique and expensive windshields is reduced and overall stealth is increased. Ghost also utilizes RAM embedded in its skin along with radar absorbing structure (RAS) beneath the skin that absorb or dramatically reduce the intensity of the incident and reflected radar waves. The skin is supported by a composite honeycomb structure, which has a core filled with layers of RAM that target specific wavelengths across the spectrum, an example of which is shown in Figure 47.

Figure 47. A patent by General Dynamics demonstrating radar absorption through layered RAM. 127

As a result, incoming radar EMR is absorbed on the way to the structure and any reflected wave is absorbed on the way out of the aircraft. 128 Therefore, any EMR that is reflected directly back to the source will have dramatically reduced intensity. To improve the effectiveness of the leading edge RAM, wedge-shaped RAS was introduced behind the skin of the leading and trailing edges. The result, shown below in Figure 48, is similar to that of the honeycomb structures. An incident radar wave loses energy as it is reflected numerous times between the walls of the RAM-filled wedge. Similar methods have proven successful on such aircraft as the prototypical A-12 and the current B-2.129 Incident Radar Wave

RAM-Filled Structure Spar/ Structure

Leading (or Trailing) Reflected Radar Edge Skin Wave Figure 48. Wedge-shaped RAS at the leading edge of the wing reduces radar energy through reflections. 130

9.2 Infrared Signature Ghost was designed to have a reduced IR signature through several methods. Ghost utilizes four high bypass ratio (BPR) engines with exhaust mixers that combine the hot exhaust of the combustor with the cold bypass air. The higher bypass ratio results in more cold air per unit of hot air, thus reducing the overall temperature of the exhaust. Furthermore, the exhausts are wide, flat, and extend out along the surface of the body, which induces vortices that encourage further mixing with the cold boundary layer.131 The overall result is a cooler exhaust that dissipates quickly into the atmosphere.

9.3 Visual, Smoke, Contrails, and Acoustic A by-product of designing Ghost for a low RCS is that the visual cues are also greatly reduced. The Northrop YB-49, one of Jack Northropâ&#x20AC;&#x2122;s original flying wings, demonstrated that it would have been practically invisible were it not for the black smoke of the exhaust when filmed flying head-on at a camera. An example of a tell-tale visual cue is shown in Figure 49. Fortunately, advances in combustion efficiency have essentially eliminated visible exhaust smoke from modern aircraft.

Figure 49 YB-49 and its highly visible black smoke exhaust. Source: Edwards.af.mil

However, the cruising altitude of 45,000â&#x20AC;&#x2122; leads to another problem for stealth aircraft: contrail formation. Contrails form when hot and humid exhaust mixes with cold ambient air that results in water saturation. The water saturation produces cloud droplets that freeze to form ice particles, which can be seen from miles away.132 Contrail formation, however, is a result of relative humidity and the altitude of their formation can change often. Thus, Ghost will predict contrail formation and adjust its flight path accordingly by using onboard sensors to test barometric pressure, temperature, and relative humidity with an algorithm based on the Appleman chart shown in Figure 50. Furthermore, the OphirÂŽ light detection and ranging Pilot Alert System can detect contrail formation in real-time and provide an alert if warranted so that the pilot, flight computer, or operator can react as needed.133 The acoustic signature of Ghost is minimized through three

Figure 50. An Appleman chart showing probability of contrail formation as a function of temperature, altitude, and relative humidity.

methods: engine placement, the use of sound deadening material, and a high cruise altitude. The four engines of Ghost are sunk into the body with the inlets and outlets placed behind the leading edges and in front of the trailing edges of the aircraft, respectively. As a result, any noise generated by the engines is directed upward and away from any potential surface-based listening devices. Sound deadening material was added to the inlet walls, which reduced the acoustic signature of

Ghost with negligible weight penalty.134 Finally, the high cruise altitude leads to a naturally quiet configuration.

10.0 Structure 10.1 Materials Selection SCAD determined that the optimal structural materials for Ghost would be a mix of aluminum and composites that include carbon fiber reinforced plastic (CFRP), glass/epoxy composites with multi-walled carbon nanotubes (MWNT), and ferrite epoxies. The three main factors in determining the materials were weight, manufacturing methods, and radar absorption. Strategic placement of lighter composite materials was used to reduce weight and take advantage of the ability to tailor the material for its ability to absorb specific radar wavelengths. Weight reduction improves the fuel economy performance by reducing overall mass and induced drag of the aircraft by reducing the required lift to maintain steady flight. Manufacturing methods was also considered because choosing the appropriate material type and form for a desired application on the aircraft plays a crucial role in determining the initial purchase price and the future maintenance costs for Ghost.135 The use of aluminum as the primary load bearing structures influenced the reduction in the overall cost of manufacturing because aluminum is high-strength, easy to form, and relatively cheap to produce when compared to other advanced materials such as composites. 136 The final determining factor, radar absorption, influenced the selection of composite materials for structural elements near the surface of Ghost. Composite materials were selected for non-primary structural elements because composites have excellent stiffness and strength properties while also providing the ability to control the content of the dielectric loss materials that are dispersed in the matrix of the composites.137 Use of composite radar absorbing materials in structural elements provides the advantage of radar absorption while also contributing to structural integrity, unlike conventional RAM which absorb radar, but are not structurally supportive. All of the aluminum structure sits at the core of the aircraft beneath layers of structural and non-structural radar-absorbing materials. 7075 Aluminum was selected for the critical structures such as the wing spars and payload bay support structures due to its strength properties, relative low cost and ease of manufacture. An all-composite design was considered but due to the size of Ghost and its lack of a continuous constant section fuselage, the complexity and cost in manufacture would be too high to meet the RFPâ&#x20AC;&#x2122;s requirements. 5454 Aluminum was selected for the high load, high cycle landing gear struts due to its durability and the critical nature of the landing gear subsystem. The composite materials 77

CFRP and glass/epoxy with MWNT were chosen for the supporting structures that include the ribs, longerons, and skin. These composite materials were selected due to their light weight, radar absorption, strength (particularly in a honeycomb or sandwich application), and ability to be mixed with other RAM such as ferrite epoxy to further improve radar absorption. CFRP honeycomb panels were used for the control surfaces such as the flaps and ailerons. For integration, the monolithic carbon composite sandwich and honeycomb skins were mechanically attached to the aluminum primary substructures and adhesively-bound to the composite support structures depending on the location on the airframe.

10.2 Component Description and Analysis 10.2.1 Wing Structure and Analysis The wing structure, shown in Figure 51, consists of three spars placed at 20%, 50% and 75% of the chord that are manufactured from 7075 Aluminum and a series of composite ribs that are spaced 24” apart on average, as discussed in §5.2. Aluminum was chosen for the spars because it is relatively inexpensive to acquire and manufacture for long and simple support structures, such as spars. Furthermore, radar reflection is not as great a concern because the conductive structure is deep within the radar-absorbing outer skin and body of Ghost. CFRP was chosen for the ribs

Figure 51. The wing structure showing the leading edge in the foreground and the trailing edge in the background.

because the relatively small size would not require additional large and expensive autoclave infrastructure. More importantly, CFRP is lightweight and can be tailored for a specific rib’s location along the wing and its expected loads. The leading edge is a RAS that is made of forward- and aft-facing composite wedges that are filled with layers of varying concentration of ferrite epoxy, or RAM. These wedges are designed to

absorb or dramatically reduce the intensity across the full spectrum of radar wavelengths that Ghost would be expected to encounter, as discussed in ยง9.1. The leading edge structure and ribs are adhesively bonded to an outer CFRP skin that is glass/epoxy composite with a MWNT honeycomb sandwich. The carbon composite honeycomb sandwich utilizes its empty space with layers of RAM in a similar method to that of the leading edge wedges. The skin outer CFRP layer consists of two single-piece skin panels on the upper and lower wing surfaces, which minimizes the likeliness of imperfections that can increase RCS. A smooth surface would have been made significantly more difficult with numerous skin panels. 10.2.2 Fuselage Primary and Support Structures The fuselage structure is manufactured with 7075 Aluminum and consists of a single primary section supported by reinforced forward and aft wing spars that split into upper and lower support structures. The fuselage structure is also anchored to the reinforced landing gear well structure and a strengthened keel beam that runs down the centerline from just aft of the primary payload bays to just aft of the crew module, shown in Figure 52. The support structures for the payload bays, missile bays, and engines are made of 7075 Aluminum and are mechanically bonded to CFRP longerons. An exploded view of the support structures are shown in Figure 53.

Figure 52. A view of the main structural elements of Ghost.

Figure 53. The support structure of the fuselage, payload bays, missile bays, and engines.

10.2.3 Landing Gear Well, Payload Bay, and Missile Bay Structures The landing gear well, shown in Figure 54, is manufactured with 5454 Aluminum and located between the two aft reinforced spars. The two primary payload bays are constructed with 7075 Aluminum and are mechanically attached to CFRP longerons. The payload bays are rectangular with domed tops that allow for optimum installation

the

rotary

munitions

launchers. The payload bays are fitted with

Figure 54. The landing gear and well structure.

numerous hardpoints attached to the frame to allow for a variety of internal configurations. Reinforced aluminum moveable bulkheads allow for the installation up to two rotary launchers per payload bay, depending on the size of the ordnance for a given mission. Stations that allow the attachment of an additional fuel line, fiber optic input, and power source are located every 51â&#x20AC;? along the payload bays to accommodate the installation of fuel or avionics modules in place of ordnance. The two AAM bays are constructed with the same 7075 Aluminum as the payload bays. The frame is mechanically attached to CFRP longerons Figure 55. The weapons bays structures.

and ribs that make up the support structure within

the fuselage area. Figure 55 shows the primary and support structures of the payload and missile bays.

10.2.4 Cockpit and Fuel Module Structure The cockpit module is made from 7075 Aluminum and is mechanically attached to a CFRP support frame. The fuel module, built to the same cross-sectional dimensions as the cockpit module and payload bays, is manufactured with CFRP and can be mounted to the same hardpoints that are found in the forward cockpit module bay and primary payload bays, should the mission require it. The cockpit module structure is shown in Figure 57 and a fuel module is shown in Figure 56.

Figure 56. Fuel module structure.

Figure 57. Cockpit module main and support structures.

11.0 Stability & Control MIL-F-8785138 requires that every aircraft should have a neutral point located behind the most aft center of gravity in order to maintain static longitudinal stability in all flight conditions. The location of the aircraft’s static margin was determined using the method presented by Roskam139. Ghost has a static margin of -12.37% at cruise conditions suggesting that the airplane is unstable. This makes sense for nearly every military aircraft. An unstable aircraft can be alleviated with the assistance of a fly-by-wire that replaces conventional manual flight controls with an electronic interface. This system allows automatic signals sent by the aircraft’s computers to perform functions without the pilots’ inputs that help stabilize the aircraft. 140 Table 17 shows major stability derivatives calculated as well as the static margin and the x locations in terms of wing mean geometric chord of the CG and aero-center. Table 17 Stability parameters

Segment

Takeoff

Cruise

Landing

[rad-1]

0.623

0.965

0.626

̇ [rad

11.301

23.153

11.723

[rad-1]

0.00426

0.00420

0.00418

[rad-1]

-0.094

-0.066

-0.069

.3543

.3600

.3543

0.2175

0.2632

.2173

-13.68%

-12.37%

-13.69

-1]

12.0 Weight Justification & Analysis 12.1 Detailed Weight Analysis A detailed weight analysis (Class II141) collaborates the methods established by the United States Air Force, General Dynamics, and Torenbeek142 to accurately project the weight of the aircraft by verified methods based on geometry of the aircraft.143 However, the versatility and utility of these methods are not without faults. Specifically, these methods are overly general, and are best applied to standard aircraft configurations. The methods are less accurate when applied to Ghost, which has unconventional characteristics, such as a flying wing configuration, radar-absorbent materials, EMP, and nuclear radiation shielding. Due to this deficiency, SCAD later pursued a Class III part-by-part weight estimation that broke down the design of Ghost into an appropriate custom weight estimation. Table 18 presents the results of the Class II weight estimation. Table 18. Summary of Class II weight estimation.

Weight Component

USAF Method (lbs.)

GD Method (lbs.)

Torenbeek Method (lbs.)

Average Values (lbs.)

Wing Fuselage Nose Landing Gear Main Landing Gear Structure subtotal Engines Fuel System Propulsion System Power Plant subtotal Air Induction System Flight Control System Hydraulic and Pneumatic System Instruments/Avionics/Electronics Electrical System Air Cond./Press./Icing System Oxygen System Auxiliary Power Unit Furnishings Operational Items Armament Weapon Provisions Other Items Fixed Equipment subtotal Empty Weight Maximum Takeoff Weight

------------------------------------------------------------------------------------------------------------------7,096 5,200 ------12,296 -------------

15,789 11,859 922 5,641 34,211 ------3,753 2,376 6,130 699 297 ------3,186 1,897 610 11 ------408 ------------------------7,108 -------------

22,413 ------1,348 8,244 32,005 41,000 4,146 677 45,823 349 ------1,537 3,447 ------------45 1,537 ------410 ------------2,562 9,887 -------------

23,310 22,232 1,297 7,936 54,775 29,034 3,275 1,266 33,574 434 245 1,266 2,996 1,563 503 25 1,266 336 338 5,841 5,200 2,110 22,124 110,473 254,579

12.2 Class III Weight Estimation The SCAD component-by-component weight analysis was done following the Class II weight analysis to ensure the integrity of the estimated weight of Ghost. The geometryâ&#x20AC;&#x2122;s weight was analyzed part-by-part considering the materials selected based on cost and structural needs. These methods recognize properties of advanced materials that otherwise are neglected in standard weight analysis. For instance, CFRP offers twice the strength at half the weight of 7075 T6 Aluminum. Furthermore, part-by-part analysis is not based on statistical data typically incorporated in empirical weight methods based off statistical data of aircraft over the last 40 years. Hence, the unique design aspects of Ghost including the radar absorbent material, unique design structures, and modern materials used must be accounted for individually. The foldout at the end of the chapter presents the results of the Class III part-by-part weight estimations in illustrated, exploded weight groups.

12.3 Center of Gravity Analysis The center of gravity location (CG) was estimated based on the results of calculated values of weight and the locations of individual components. The defined location of the empty weight components are shown in Table 19, and are also shown in the side profile for the aircraft in Figure 58. Table 19. Detailed CG location and moments of inertia of Ghost.

Component

Weight (lbs)

XCG (ft)

ZCG (ft)

|Lxx| (lb-ft)

|Lzz| (lb-ft)

Wing Fuselage Nose Landing Gear Main Landing Gear Engines Fuel System Air Induction System Propulsion System Flight Control System Hydraulic and Pneumatic System Instruments/Avionics/Electronics Electrical System Air Cond./Press./Icing System Oxygen System Auxiliary Power Unit Furnishings Operational Items Armament Weapon Provisions Other Items

23,310 22,232 1,297 7,936 29,034 3,275 434 1,266 245 1,266 2,996 1,563 503 25 1,266 336 338 5,841 5,200 2,110

26.66 24.01 11.41 34.11 28.47 27.50 32.28 29.39 20.51 22.81 9.83 21.16 21.69 20.43 24.72 5.35 7.05 25.46 15.91 23.69

0.11 1.23 -4.78 -4.06 5.01 2.29 4.10 4.30 -2.24 -0.67 0.76 0.33 1.65 2.19 4.12 0.93 -0.20 1.23 -0.28 3.00

621,445 533,798 14,802 270,690 826,587 90,052 14,019 37,199 5,025 28,884 29,447 33,075 10,901 519 31,303 1,798 2,381 148,719 82,732 49,995

2,564 27,346 6,201 32,219 145,458 7,499 1,781 5,443 549 848 2,277 516 829 56 5,217 312 68 7,185 1,456 6,331

The defined locations of empty weight and max takeoff weight (MTOW) of Ghost are presented in

Table 20. Table 21 and Table 22 show a detailed summary of

takeoff weight figures and moments of inertia, respectively.

Figure 58 CG locations, side profile

Table 20 Center of Gravity

Table 21 Class III Takeoff Weight

Empty Weight

MTOW

Wfix

21,303.3 lb

XCG

25.65 ft.

26.48 ft.

Wstructure

61,252.8 lb

YCG

0 ft.

WPP

38,854.3 lb

ZCG

1.55 ft.

1.86 ft.

WPL

30,000 lb

121,410.4 lb

WTO

265,515.6 lb

Table 22 Moment of Inertia

7,373,068 slugs-ft2 464,825

slugs-ft2

6,053,951 slugs-ft2 3,235,013 slugs-ft2

13.0 Performance 13.1 Takeoff Performance The required takeoff field length for Ghost is determined by applying relations presented by ESDU Data Item 85029144 and considering the ground effect on generated lift and drag.145 It is assumed that the aircraft uses the previously sized flaps during takeoff without assistance from leading edge high lift devices, making the maximum lift coefficient of 1.8 attainable. The rolling (unbraked) coefficient of friction for a dry, hard surface runway was assumed to be 0.025, according to suggestions by MIL–C–005011B (USAF)146. The takeoff trajectory was computed for normal takeoff and can be seen in Figure 59. Assumptions regarding takeoff performance computations and the results of this analysis are presented in Table 23 and 24.

Figure 59 Takeoff trajectory of Ghost with a takeoff distance of near 8,000’, having a ground run of 5,716’. Table 23 Takeoff Condition

1.8 0.089 ⁄ |

14.83 0.95

Table 24 Takeoff Performance

112 kts 127 kts 7,950’ 5,716’

13.2 Climb Performance Analyses were performed to determine the operational ceiling Ghost is capable of achieving. By military standards, the operational ceiling is defined as the altitude at which the rate of climb is equal to 100 ft/min at maximum power. Using the engine performance map developed for the power plant of Ghost, it was estimated that the ceiling rate of climb would occur at 50,000’, on par with the B-2 bomber147. Figure 60 presents the climb performance for Ghost.

Figure 60 ROC vs. velocity at various altitudes. Operational ceiling occurs at 50,000’ corresponding to an ROC of 100 ft/min

13.3 Max Speed An analysis was performed on the required and available power at cruise for Ghost. From this analysis it was determined that the maximum possible cruise speed at 45,000’ is 596 kts, corresponding to a Mach number of 1.02. At this velocity, the required power to overcome drag equals the maximum thrust of the engine. However, this velocity is only for absolute emergencies and will cause the engine to become un-airworthy afterwards. Thus a maximum operating speed has been defined as 530 kts corresponding to a Mach number of 0.91.

13.4 Payload-Range A payload-range chart was constructed for Ghost and is presented in Figure 61. Assumptions made for this analysis are presented in Table 25. It was determined that despite the airplane being sized for 8,000 nm, Ghost is capable of an extra 500 nm in the set-up of max payload with fuel volume to make max takeoff gross weight. Table 25 Assumptions for Payload-Range Diagram

15,443.9 lb 2° Mach Altitude

0.85 0.37 45,000’

TSFC

0.55 lb/lb-hr

Figure 61 Payload-Range Diagram

13.5 Mission Performance 13.5.1 Intercontinental Refueling To emphasize the key performance advantages Ghost has over its contemporary counterparts, a hypothetical intercontinental bombing mission based on an historical bombing campaign by the B-2 during the Kosovo conflict in 1999 was analyzed. A summary of the mission is provided in Table 26. Table 26. Key parameters for an intercontinental bombing mission planned for Ghost.

Aircraft

Start Location

End Location

Distance

Whiteman Air Base, MO

Varadin Bridge, Serbia

5,800 nm

First Leg: Transit to Target Ghost

Second Leg: Transit to Refuel Ghost

Varadin Bridge, Serbia

KC-135 Stratotanker

RAF Mildenhall, UK

Refuel Over the Mediterranean Sea Refuel Over the Mediterranean

600 nm 660 nm

Third Leg: Transit to Home Ghost KC-135 Tanker Aircraft

Refuel Over the Mediterranean Sea Refuel Over the Mediterranean Sea Total Distance

Whiteman Air Base, MO

4,700 nm

RAF Mildenhall, UK

660 nm

Fuel Used

Travelled

(or Transferred)

Ghost

11,100 nm

121,000 lb

KC-135 Stratotanker

1,320 nm

(10,300 lb)

In this mission, Ghost flies from the Whiteman, MO, the home of the B-2, to take out a vital bridge in Serbia. After a 60-minute loiter and bombing run, Ghost can safely meet a KC-135 aerial refueling tanker that is based out of RAF Mildenhall in England at a location off the coast of Italy over the Mediterranean Sea. At a rate of 6,000 lb/min,148 it takes less than two minutes for Ghost to accept the 10,300 lb of fuel required to return to Whiteman with 10% of maximum fuel remaining in reserves. Ghost was able to accomplish a similar mission to the B-2 with a single aerial refueling, when most intercontinental missions require aerial refueling en route and on the return leg. Ghostâ&#x20AC;&#x2122;s capabilities reduces the amount of required logistical support and planning time to allow faster mission turnaround or even allow the coordination of aerial refueling to be performed while the

mission is already underway. The mission profile is shown below in Figure 62 and a detailed breakdown of each mission segment is shown in Table 27 on the following page.

Figure 62. Intercontinental bombing mission profile with aerial refueling. Table 27. Detailed breakdown of the mission segments for an intercontinental bombing mission for Ghost.

Mission Segment

Altitude (ft.)

Mach

Distance

Time

(nm.)

(min.)

Î&#x201D;WF used (lb)

0a- Warm up

2,750

0b- Taxi Out

2,700

1- Takeoff

0-150

0.12

1,350

2- Climb

150-45,000

0.66

150

5,000

3- Cruise

45,000

0.85

5,080

615

59,000

4- Loiter

45,000

0.80

470

6,500

45,000

0.80

110

6- Cruise

45,000

0.85

598

4,000

7- Descent to Refuel

45,000-20,000

0.2

820

8- Refuel

20,000

0.45

(10,300)

9- Climb to Cruise

20,000-45,000

0.66

2,000

10- Cruise

45,000

0.85

4,700

570

34,300

11- Descent

45,000-200

0.2

1,360

12- Land/Taxi

200-0

1,080

5- Payload Expenditure

13.5.2 Unmanned Extended Loiter with Aerial Refueling The extended range of Ghost also results in an extensive amount of loiter-over-target time for missions that take place closer to an available base. A hypothetical mission profile to demonstrate the performance characteristics of Ghost in an unmanned configuration was evaluated based on the recent conflict in Libya. A summary of this mission is provided in Table 28. Table 28. Key parameters of an extended loiter mission in the unmanned configuration with a single aerial refuel.

Aircraft

Start Location

End Location

Distance/ Loiter Time

Tripoli, Libya

1,435 nm

11.7 hrs

First Leg: Transit to Target Ghost

RAF Fairford, UK

Second Leg: Loiter Ghost

Tripoli, Libya

Third Leg: Transit to Refuel Ghost

Tripoli, Libya

KC-135 Stratotanker

RAF Mildenhall, UK

Refuel Over the Mediterranean Sea Refuel Over the Mediterranean Sea

765 nm 660 nm

Third Leg: Transit to Target Ghost KC-135 Stratotanker

Refuel Over the Mediterranean Sea Refuel Over the Mediterranean Sea

Tripoli, Libya

765 nm

RAF Mildenhall, UK

660 nm

12 hrs

RAF Fairford, UK

1,435 nm

Fourth Leg: Loiter Ghost

Tripoli, Libya

Fifth Leg: Transit to Home Base Ghost

Tripoli, Libya

Total Loiter Time

23.5 hrs

In this mission, Ghost operates in its unmanned configuration out of the RAF Fairford, UK forward air base, which was chosen due to its ability to handle B-2 operations. The mission is to provide ISR and tactical bombing support in the light-to-moderately defended airspace over Tripoli, Libya. Loaded with 30,000 lbs in precision ordnance, Ghost flies the near-1,500 nm to the airspace over Tripoli, Libya for a 60-minute loiter before dropping half of its ordinance on newly discovered mobile SAM sites. Ghost then continues to loiter for another 10.5 hrs before a planned rendezvous 765 nm away near the coast of Italy with a KC-135 Stratotanker out of RAF Mildenhall. A transfer of 100,000 lbs allows Ghost to return to the airspace above Tripoli, Libya for an additional 12 hrs

before dropping its remaining 15,000 lbs of ordinance and returning to base at RAF Fairford. The details of the mission profile, including total mission time and distance are shown below in Figure 63

Figure 63 Unmanned extended loiter with aerial refueling mission profile

At maximum payload, Ghost is capable of nearly 24 hrs of loiter time above a potential target with a single aerial refuel. Furthermore, given the unmanned configuration, Ghost could conceivably remain airborne as long as tankers were available to refuel. A view of the aerial refueling system is shown below in and a detailed breakdown of each mission segment is shown on the following page in Table 29.

Figure 64. The aerial refueling receptacle and system.

Table 29 Detailed breakdown of the mission segments for an unmanned extended loiter with aerial refueling mission

Mission Segment

Altitude (ft.)

Mach

Distance

Time

Î&#x201D; WF

(nm.)

(min.)

(lb)

used

0a- Warm up

2,750

0b- Taxi Out

2,700

1- Takeoff

0-150

0.12

1,350

2- Climb

150-45,000

0.66

150

5,000

3- Cruise

45,000

0.85

1,435

172

18,220

4- Loiter

45,000

0.80

468

7,910

5- Payload Expenditure

45,000

0.80

110

6- Loiter

45,000

0.80

4,945

634

63,717

7- Cruise

45,000

0.85

765

5,027

8- Descent to Refuel

45,000-20,000

0.2

820

9- Refuel

20,000

0.45

101

(100,000)

10- Climb to Cruise

20,000-45,000

0.66

2,610

11- Cruise

45,000

0.85

765

6,785

12- Loiter

45,000

0.80

5,600

718

77,000

13- Payload Expenditure

45,000

0.80

110

14- Cruise

45,000

0.85

1,436

173

10,150

15- Descent

45,000-200

0.2

1,361

16- Land/Taxi

200-0

1,078

13.6 Landing Trajectories The method presented by ESDU Data Item 84040 149 was used to estimate the landing distance for the aircraft computed assuming a landing weight of 165,743 lbs. This weight consisted of the empty weight (121,410 lbs.), plus trapped fuel, 10% fuel reserve, crew weight, and full payload for the aircraft (44,333 lbs.). The ground effects are taken into account in this analysis, for which the results are presented in detail in Table 30. Figure 65 presents the results of the simulation of the landing trajectory of the aircraft.

Table 30 Landing Performance

112 kts 127 kts 7,950â&#x20AC;&#x2122; 5,716â&#x20AC;&#x2122;

Figure 65 Landing trajectory of Ghost

14.0 Cost 14.1 Unit Price per Airplane Given the emphasis by the RFP placed on the competitiveness of unit costs of the airplane, attention was paid to the financial drivers in various stages of the design. A special emphasis was placed on accurately representing the contributions to cost from stealth materials as well as those from the chosen aircraft systems. Roskamâ&#x20AC;&#x2122;s Cost Item method150 was used to estimate the Research, Development, Test, and Evaluation (R.D.T.E.) cost and acquisition cost. R.D.T.E. includes the costs of engineering and design, development and support, prototypes and testing operations, and project profit and financing. It was assumed that the research and technology development of the

project will yield a 10% return over a period of three years, while the financing cost will be 10% of the total research and development cost of the project. Acquisition cost includes the costs associated with engineering and design for the manufacturing phase, production program, and test operations, as well as 10% finance fees and a 12% depreciation of invested capital. Sensitivity analysis was performed to assess the effect of variation of the difficulty factors defined by Roskam on the final flyaway cost to estimate an uncertainty of the cost figures. The analysis was repeated for two production runs of 50 and 100 aircraft, the results of which can be seen in Table 31. Table 31 R&D, acquisition and unit cost breakdown for Ghost, assuming production runs of 50 and 100 aircraft

50 Production Run Cost (106 $)-2020 U.S. Dollar Research & Development Phase:

Cost Item

Engineering & Design Development, Support & Testing Test Aircraft

100 Production Run Cost (106)-2020 U.S. Dollar

205.0

205

70.1

1,947.3

Test Operations

76.5

Finance Cost

287.4

R&D subtotal

2,586.3

Profit

287.4

Total

2,873.7

Engineering & Design

80.1

114.4

Production Program

8,094.0

15,701.7

Test Operations

585.3

1,170.6

Finance Cost

973.3

1,887.4

Manufacturing Sub- Total

9732.7

18874.1

Profit

973.3

1,887.4

Total

10,706

20,761.5

Worst Case Scenario

372.8

303.8

Best Case Scenario

178.5

150.1

Best Guess

271.6

236.4

Uncertainty

Âą24.9

Âą22.5

Acquisition Phase:

Unit Price per Plane:

14.2 Operating Cost Breakdown Inferred from the RFP, the operation and maintenance costs of Ghost were computed to assess its viability against current in-service aircraft. Roskam’s method151 was used to perform DOC estimation with a 50/50 blend of JP-8 jet fuel and Syntroleum’s FT synthetic fuel. The most common type of jet fuel for military airframes has been Jet Propellant 8 (JP-8), however recent developments and considerations towards the use of alternative fuels have begun to spark within Pentagon discussions. The Pentagon hopes to reduce its use of crude oil from foreign producers and obtain about half of its aviation fuel from alternative sources by 2016. 152 The Air Force, the U.S. military’s largest user of fuel, has explored alternative fuel with a program that certified the B-52H to use a 50/50 blend of JP-8 and FT fuel. The Air Force has used the test protocols developed from the B-52H experiment to certify the B-1B to use the fuel as well as the rest of the fleet.153,154 The Commercial Aviation Alternative Fuels Initiative suggests that a synthetic blend is cost comparable to straight JP-8.155 The cost of jet fuel was obtained by consulting the fuel cost projections obtained from the U.S. Energy Information Administration interactive web portal.156 This portal presents projections for the cost of energy and main forms of fossil fuels assuming different economic scenarios, modeling the observed trends in energy supply and demand cycles. Reviewing these projections, it was determined that in 2020, an average JP-8 FT synthetic blend fuel cost of 4.00 $/gal will represent the middle ground between the worst and best economic scenarios.157 Table 32 provides the breakdown of the direct operating cost for Ghost. Table 32 Direct Operating Cost for Ghost

Cost Item

Ghost

Annual Utilization (nm)

11,800

Crew ($/nm)

0.67

Fuel & Oil ($/nm)

11.40

Insurance

104.92

Maintenance

23.31

Depreciation

1,245.50

Registration

5.29

Financing

104.71

Total DOC ($/nm)

1,495.80

14.0 Software Used Description 14.1 Advanced Aircraft Analysis (AAA) Advanced Aircraft Analysis (AAA) is the industry standard aircraft design, stability, and control analysis software. AAA is installed in over 55 countries and is used by major aeronautical engineering universities, aircraft manufacturers, and military organizations worldwide. Advanced Aircraft Analysis provides a powerful framework to support the iterative and nonunique process of aircraft preliminary design. The AAA program allows students and preliminary design engineers to take an aircraft configuration from early weight sizing through open loop and closed loop dynamic stability and sensitivity analysis, while working within regulatory and cost constraints. The design methodology used in Advanced Aircraft Analysis is based on Airplane Design IVIII, Airplane Flight Dynamics and Automatic Flight Controls, Parts I and II, by Dr. Jan Roskam, and Airplane Aerodynamics and Performance, by Dr. C.T. Lan and Dr. Jan Roskam. AAA incorporates the methods, statistical databases, formulas and relevant illustrations and drawings from these references.

14.2 Star CCM+ v7 STAR-CCM+ provides the world's most comprehensive engineering simulation inside a single integrated package. Much more than just a CFD solver, STAR-CCM+ is an entire engineering process for solving problems involving flow (of fluids or solids), heat transfer and stress.

14.3 GasTurb 11 Gasturb is a gas turbine performance simulation program for Microsoft Windows written and distributed by former MTU Aero Engines employee Joachim Kurzke. Based around a comprehensive set of pre-defined engine configurations, the program performs both design point and off-design performance modeling, parametric studies, cycle optimization and Monte Carlo simulations. The program is widely used both in the power generation and propulsion industries and in teaching institutions.

14.4 Physical Optics Radar Cross Section Prediction and Analysis Application (POFACETS) POFACETS is a graphical user interface (GUI) radar cross section (RCS) prediction code based on the physical optics (PO) approximation and implemented in MATLAB. It is accurate when 96

the target is large in terms of wavelength. Scattering objects are approximated by arrays of triangles (facets) and superposition is used to compute the total RCS of the model object. Multiple reflections are not included. The GUI consists of three modules: (1) Design Model, (2) Calculate Monostatic RCS, and (3) Calculate Bistatic RCS. Design Model provides a convenient way of modeling a complex object or loading an editing a previously designed model. The geometry of the model is defined using two sets of data. The first set defines the x, y, z coordinates of the vertices. The second set of data defines the component triangular facets of the object, their nodes and illumination and resistivity characteristics Calculate Monostatic RCS computes the total radar cross section of the target using a monostatic radar (co-located transmitter and receiver). The scattered field of each triangle is computed as if it was isolated and other triangles were not present. Multiple reflections, edge diffraction and surface waves are not included. Shadowing is approximately included by considering a facet to be completely illuminated or completely shadowed by the incident wave. Options for defining the roughness of the surface are available. Calculate Bistatic RCS computes the total radar cross section of the target using a bistatic radar (transmitter and receiver at different locations). The incidence direction is fixed and the observation direction changes.

14.5 DesignFOIL DesignFOIL is a Windows-based airfoil software tool. It helps to create, modify, and aerodynamically analyze airfoil shapes. It also performs basic wing layout, CAD export, and creates CFD preparation files. Although built for professionals, the user-friendly interface is used by many hobbyists as well.

14.6 Ansys CFX ANSYS CFX software is a high-performance, general purpose fluid dynamics program that has been applied to solve wide-ranging fluid flow problems for over 20 years. At the heart of ANSYS CFX is its advanced solver technology, the key to achieving reliable and accurate solutions quickly and robustly. The modern, highly parallelized solver is the foundation for an abundant choice of physical models to capture virtually any type of phenomena related to fluid flow. The solver and its many physical models are wrapped in a modern, intuitive, and flexible GUI and user environment, with extensive capabilities for customization and automation using session files, scripting and a powerful expression language.

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