Military Aeronautics

Military Aeronautics

By J.R. Wilson

Although the Wright brothers earned the United States credit for the first powered, manned heavier-than-air flight in 1903, when the U.S. entered World War I a decade later, it was far behind the European nations in the development of military aviation. It was a report to that effect that led President Woodrow Wilson to order creation of the nation’s first civilian government facility dedicated to aviation research and development (R&D) – the Langley Memorial Aeronautical Laboratory – under the new National Advisory Committee for Aeronautics (NACA).

The lab – renamed Langley Research Center with NASA’s formation in 1958, replacing the NACA – was, from the beginning, designed to explore airframe and propulsion engine design and performance to help the United States aviation industry, including its fledgling entry into military aircraft development. From 1917 into the 21st century, just about every U.S. military aircraft went through Langley at some point, either in initial design or to resolve problems encountered in flight-testing and operations.

“The NACA basically was formed and the military bought the land the lab was placed on. No other location at the time had the wind tunnels and other research capability located at Langley, which attracted the military,” Joseph Chambers, a retired Langley aeronautics research manager and author of a book on Langley’s contributions to U.S. military aircraft of the 1990s, said.

“In its early decades, Langley had a great deal of interaction with the military, especially the Navy, with the NACA headquarters located in the same building and floor as the Navy Department in Washington. That led to a very tight relationship, both with the Navy at Langley and Langley researchers going to Navy facilities. In the 1930s, the Army established a liaison office at Langley so they could be closer.”

“The nation had invested in unique facilities at Langley and people with expertise operating those. And they gained experience and grew in place while military facilities had constant turnover as military leaders and personnel moved on, taking their knowledge with them,” he said.

In pursuit of its goal to “solve the fundamental problems of flight,” state-of-the-art wind tunnels and supporting infrastructure were built to find unique solutions to the rapidly evolving realm of aviation. Those included wing shapes still used in airplane designs today; better propellers; engine cowlings; all-metal airplanes; new kinds of rotorcraft and helicopters; supersonic, transonic and hypersonic flight – all part of the legacy of Langley’s historic aeronautical advances in its first half-century.

In later decades, Langley researchers achieved breakthroughs in wind shear and lightning protection, digital control systems, glass cockpits, new kinds of composite materials, supercritical wings, and hybrid wing bodies. Much of its success was due to a long line of unique wind tunnels that have made Langley a world leader in aeronautical design analysis since the 1920s.

A P-51 Mustang in the Full Scale Tunnel at what was then called Langley Memorial Aeronautical Laboratory. The P-51’s laminar flow wings, which gave it such superlative performance, were a product of Langley research.

NASA Photo

In the years leading up to World War II, the NACA followed a fundamental research mission that included experiments with a wide range of unusual concepts, from airplanes with 12 propellers on each wing to a saucer-like “flying flapjack.” The day World War II began, its mission changed dramatically to support specific military interests. It became 911 calls rather than fundamental research, which was resumed after the war.

The list of Langley’s contributions since its inception is long and helped take the United States to a dominant position in military aviation by the end of World War II. Some of the highlights, starting in the 1920s, include: The development of airfoils “That was the first application of compressed air to wind tunnel testing, with more accurate results than any other wind tunnels. Langley began a progression of research tactics, doing a complete matrix of testing in those facilities, making adjustments to airfoil shapes, that were employed to design World War II military aircraft,” Chambers said. Laminar flow airfoil “They developed a unique laminar flow airfoil designed to have minimum drag at optimum conditions. The first operational application of that was the [World War II] P-51 Mustang, which gave it higher speed capability than other aircraft in combat.” Engine cowlings “The Navy preferred radial flow rather than liquid-cooled [engines], which led to very large engines. Langley developed a way to enclose radial engines with cowlings that minimized air resistance with continued cooling. That shaped all future propeller-driven aircraft development and was the recipient of Langley’s first Collier Trophy.” Most efficient engine shape and location “This led to DC-3s and all subsequent aircraft having their engines in the same vertical location as the wing, as opposed to underslung or above the wing.” Aircraft spinning “An area where contributions continue to this day for the military is spinning, which is a very complex thing to analyze from an aerodynamic perspective. Langley developed a free-flying technique in a wind tunnel, beginning in 1935, with the first of two spin tunnels that have been continuously operational since then. Every U.S. military aircraft in production was tested in that wind tunnel. When aircraft go into the fleet and some configuration change happens, the military typically returns to the Langley spin tunnel to see what those changes will mean.” Vertical takeoff and landing “In the 1950s, as we returned to more fundamental efforts, Langley had time to explore some revolutionary concepts, especially vertical takeoff and landing.

A Curtiss AT-5A advanced trainer variant of the P-1 Hawk pursuit plane with an NACA cowling installed. The cowling minimized drag but retained cooling for radial engines, and improved the performance of both military and civilian aircraft.

NASA Photo

By the 1950s and 1960s, designs for supersonic military aircraft incorporated wings that were swept back or could vary their sweep, as shown in this multiple exposure photograph. Langley researchers conducted tests in multiple wind tunnels on variable sweep models like one for a Navy combat air patrol mission.

NASA Photos

Helicopters became a major research area at Langley. Langley also developed the concept of individual flying platforms in the 1950s.” Variable wing sweep “In the 1960s, variable wing sweep came out of Langley, which has been applied to numerous military aircraft. At the end of World War II, as we overran German scientific facilities, we found they were about to go to flight with an aircraft that had wings that could be repositioned on the ground before flying. That was brought back to the U.S. and Bell Aircraft built the X-5 [in 1951] as the first continuous variable sweep aircraft. Unfortunately, that changes the inherent stability of the aircraft dramatically, to totally non-maneuverable with the wings swept aft. To maintain adequate levels of maneuverability, the wings had to be moved forward, which required massive equipment inside the aircraft. The Air Force was not impressed and the effort was cancelled.” Nevertheless, the NACA and its successor, NASA, were research organizations allowed to continue work on technology that was not immediately applicable because other breakthrough technologies were needed. In the case of variable sweep, Langley engineers came up with the idea of creating a double pivot configuration that eliminated the stability issue. It was adopted by the Air Force for the F-111 and the B-1 bomber and the F-14 for the Navy. Externally blown flap It allowed lower-speed handling and reduced landing and takeoff space. Langley researchers came up with the idea of rotating engine cells nose-down so the exhaust would blow over the trailing edge of the wing, thus augmenting lift. Model tests at Langley demonstrated the capability in the 1950s using turbojet engines, which had high heat exhaust and high velocity, which was not acceptable for the trailing edge. But Langley continued to work on it despite industry disinterest. The development of turbofan engines had lower airflow and heat and the concept was successfully applied to the Air Force C-17 in the late 1970s.”

Langley played an important role in the development of vertical flight. The Ling-Temco- Vought XC-142A was a tilt-wing prototype used in vertical takeoff and landing (VTOL) studies. Langley was extensively involved in wind-tunnel testing of XC-142A models, and in the flight evaluations of the actual airplane.

NASA Photo

Another aviation breakthrough in which Langley played a key role was enabling aircraft to fly faster than the speed of sound. Following World War II, Langley conducted unique wind tunnel research on transonic designs, aerodynamics and propulsion that helped lead to Air Force Capt. Chuck Yeager’s historic October 1947 supersonic flight in the rocket-engine-powered Bell X-1. That first breaking of the sound barrier by a manned aircraft paved the way for later generations of supersonic military aircraft.

NASA Langley researchers used the High Angle-of-Attack (Alpha) Research Vehicle (HARV) to test new technologies, including thrust vectoring, from 1987- 1996. The modified F-18 Hornet is now in NASA Langley’s official visitor center, the Virginia Air & Space Center, in downtown Hampton, Virginia.

NASA Photo

Environmental concerns and economic constraints limited commercial application of supersonic flight to only one aircraft – the Aérospatiale/BAC Concorde, a British-French supersonic passenger jet that operated from 1969 until 2003. It had a maximum speed of Mach 2.04 – restricted to over-ocean use only – and carried up to 128 passengers.

Langley, meanwhile, pushed the aerial speed limit even further with wind tunnel and flight tests that led to the X-15, which flew from 1958 to 1968 and set the winged manned aircraft speed record of Mach 6.7 (about 4,500 mph). The center continued to research propulsion, thermal and structural integration issues on a number of largely military hypersonics programs through the end of the century, including the National Aerospace Plane (NASP); Hyper-X, which included the Air Force X-43; the Air Force X-51 Waverider and the Hypersonic International Flight Research Experimentation (HIFiRE) Program, which explored fundamental technologies supporting practical hypersonic flight.

“We flew the X-43 in 2004, then the agency [NASA] decided to stop building hypersonic X-planes, so we turned a lot of that research over to the DOD. Langley was involved later with helping the Air Force resolve problems they had with the follow-on X-51,” noted Walt Engelund, Director of Space Technology & Exploration at Langley.

In 1994, testing in the 20- Foot Spin Tunnel at Langley helped determine spin-recovery parachute requirements for the F-22 fighter jet.

NASA Photo

The ability of a research organization to persist in developing a concept, even without much interest from industry or government, became a hallmark of Langley’s aeronautical programs, in large part because NASA does not design aircraft, but rather produces information that can be used by aircraft designers.

For example, in 1954, Langley engineer Richard Whitcomb was awarded the Collier Trophy for developing the transonic area rule to minimize drag, pushing aircraft more easily through the speed of sound by minimizing the platform’s total cross-section.

“The idea is to remove some of the area from the fuselage while adding area from the wing to smooth the shape. The F-102, in the design stage, had wind tunnel results at Langley showing the aircraft could not go through Mach 1. The Air Force told General Dynamics [the contractor] to apply Whitcomb’s area rule and wind tunnel tests showed it could then exceed the speed of sound while climbing,” Chambers said.

Other areas in which Langley played a major role include the development of thrust vectoring, used on the F-22; the design for supersonic cruising without afterburners; advanced composites, which led to tremendous weight savings on large aircraft such as the C-17; the use of grooved runways to improve drainage and reduce landing gear problems, which led to today’s grooved highways and automotive anti-hydroplaning efforts; and hybrid or blendedwing aircraft resembling a manta ray to reduce noise, conserve fuel and potentially reduce operating costs. Joint research with DOD and industry also led to encouraging results for alternate aircraft fuels.

“In the 1960s to ’80s, Langley was involved very closely to what the Navy and Air Force were doing in aircraft development. NASA participated in the response stages of design, reviewing proposals for some aircraft and even proposing tests, such as during the selection process that led to the F-15, long before the aircraft configuration was finalized, then continuing that support once the final design entered the fleet,” Chambers said.

“When the Air Force decided to go with the F-15, the Secretary of Defense contacted NASA Headquarters and asked for an in-house design team to incorporate the latest technology into some candidate designs to send to industry. Industry teams were briefed and that resulted in six different designs, such as two-dimensional inlets, variable sweep wings, etc. So NASA’s vision of what might be possible had big payoffs on future military aircraft designs.” While many of Langley’s contributions are well known, others were classified.

“From 1970 through the turn of the century, Langley facilities and expertise were part of many classified programs; some of those tests are still classified,” Chambers recalled. “Langley staff went out to development sites as independent assessors and our facilities were treated for classified testing. Industry would come in, run their tests, then take the data home with them.”

“Generally, Langley had continued military aircraft research, both fundamental configuration studies and intense peer-to-peer interest, until the mid-90s. At the end of the 1990s, we looked at emerging technologies and how those might benefit new aircraft designs. That included unmanned combat vehicles in the early 1990s and what benefits they might bring by removing the human pilot, looking at structures, weight, etc.,” he said.

Targeted military research still goes on frequently at Langley. NASA Langley has improved military helicopter crashworthiness starting in the 1970s with a number of tests, including the qualification of wire strike protection systems for military helicopters such as the AH-1 Cobra. Military rotorcraft crash tests have continued into the 21st century on helicopters like former U.S. Marine Corps CH-46 Sea Knights tested with Army crash test dummies in 2013 and 2014.

In recent years, the U.S. military and military aircraft manufacturers have also used NASA Langley wind tunnels to advance rotorcraft performance and test innovative hybrid wing/blended wing body aircraft concepts for possible use as future military cargo planes.

“The ability to forecast what changes will do is very important. The military wants answers today for its current aircraft. A research organization is looking at future aircraft. In terms of the 100-year history of Langley’s work on military aircraft, the vast majority was during the first 85 years, with the 1970s the most active.”