Flight performance and planning for ppng member

Page 1

FLIGHT PERFORMANCE AND PLANNING I

PPL FP & P


LECTURE ONE: VIRTUALLY ALL YOU NEED TO KNOW 1.

Mass and Balance

2.

Take off Performance

3.

Landing Performance

4.

En-route Performance – Climbs, Cruise, Descents

PPL FP & P


MASS AND BALANCE MASS is measured in kilogrammes (kg) and is a reflection of how much matter something contains An object’s mass does not change wherever it is

WEIGHT is a force measured in Newtons (N) An object’s weight is its mass multiplied by gravity On earth, 1 kg creates a force of 10 N

Astronaut weight on earth = 120 kg x 10 = 1200 N

Astronaut weight on moon = 120 kg x 1.6 = 200 N PPL FP & P

In aviation we refer to MASS and not weight


MASS AND BALANCE: BASIC EMPTY MASS

Airframe Engine Fixed Equipment

Unusable Fuel Full Oil

Items necessary for flight

Used for Loading Calculations

PPL FP & P


MASS AND BALANCE: EMPTY MASS

Airframe Engine Fixed Equipment

Unusable Fuel Undrainable Oil

Items necessary for flight

Specified in Flight Manual after weighing

PPL FP & P


MASS AND BALANCE: GROSS MASS

Basic Empty Mass Pilot

Payload (Passengers + Cargo) Ballast Fuel

+

+

+

+

PPL FP & P


MASS AND BALANCE: ZERO FUEL MASS

Basic Empty Mass Pilot

Payload (Passengers + Cargo) Ballast No Usable Fuel

+

+

+

Structural Limitation PPL FP & P


MASS AND BALANCE: RAMP, TAKE-OFF, LANDING MAXIMUM RAMP WEIGHT Maximum permitted mass prior to taxi May be maximum take-off weight + taxi fuel (3kg for C172)

MAXIMUM TAKE OFF MASS (MTOM) Maximum allowable gross mass permitted for take-off

MAXIMUM LANDING MASS (MLM) Maximum allowable gross mass permitted for landing Same as MTOM for most light aircraft If not may require fuel burn / dump prior to land PPL FP & P


MASS AND BALANCE: RAMP, TAKE-OFF, LANDING

MTOM and MLM may have another value which concerns performance

May be used when: short runway high obstacle on approach / climb out unfavourable wind unfavourable slope high temperature high pressure altitude

PPL FP & P


MASS AND BALANCE: WHY? Aircraft mass is balanced by lift Lift is a function of airspeed and air density Airspeed is limited by power available from engine / propeller

Air density is out of pilot control

Flying an overweight plane is a very bad idea because:

PPL FP & P


MASS AND BALANCE: WHY? Higher Stalling Speed Higher Take-off Speed Required Longer Take-off Run Worse Climb Performance Lower Service Ceiling Higher Fuel Consumption Lower Endurance Shorter Range Less manoeuvrability

Higher Landing Speed Greater Braking Requirements Longer Landing Distance

PPL FP & P


PRACTICE QUESTION!

“Which of the following statements about an overweight aircraft are true?: (a) Higher stalling speed (b) longer take off run required (c) improved performance (d) poor handling”

(a), (b) and (d)

PPL FP & P


WEIGHTS: CONVERTING UNITS It is VITAL that you use the correct units when calculating mass and balance

LITRES

POUNDS

1.58 6.0

3.8 7.2

US GAL

4.5

2.2 0.72 2.72

1.2 KG

3.27

IMP GAL

(Weights based on AVGAS (SG 0.72))

PPL FP & P


FUEL WEIGHT 1 litre of water weighs 1 kg 1 imperial gallon of water weighs 10 lb

Avgas is lighter than water and has a specific gravity of 0.72

1 imperial gallon of Avgas weighs 7.2 lb 1 US gallon of Avgas weighs 6 lb

PPL FP & P


PRACTICE QUESTION!

“What is the weight of 120 litres of AVGAS (SG 0.72)?”

120 litres x 0.72 = 86.4 kg

PPL FP & P


FORCES, MOMENTS & DATUMS: DEFINITIONS A MOMENT is the tendency of a force to twist or rotate an object The MOMENT ARM is the distance from the point of rotation to the action of the force Moment = Force x Distance

BALANCE occurs when the moments are equal

The DATUM can be selected anywhere and is the point from which the MOMENT ARMS are measured PPL FP & P


FORCES, MOMENTS & DATUMS: DEFINITIONS A balanced example – no resultant turning moment Datum

6 kg

3 kg

1m

2m

Weight x Distance = Moment 6

x

1

=

Weight x Distance = Moment

6 Moments are equal so no turning forces and are in balance

3

x

2

=

6

PPL FP & P


FORCES, MOMENTS & DATUMS: DEFINITIONS Choice of Datum does not change the result – same example, different datum Datum

6 kg

3 kg

2m 1m Weight x Distance = Moment 6

x

1

=

Weight x Distance = Moment

6 Moments are equal so no turning forces and are in balance

3

x

2

=

6

PPL FP & P


FORCES, MOMENTS & DATUMS: DEFINITIONS Moments are either clockwise or anticlockwise

Units used for moments may be pounds/inches or kilograms/millimetres

Anticlockwise rotation

PPL FP & P


WHY IS BALANCE IMPORTANT TO AIRCRAFT LOADING? Loading of an aircraft determines where its centre of gravity will be If an aircraft is loaded incorrectly the worst-case scenario on the ground is:

!

Airborne there might be other issues PPL FP & P


CENTRE OF GRAVITY Straight and Level Flight Lift equals weight and thrust equals drag

Four forces lead to two couples which are not always in balance The tail plane is used to provide forces to balance this Lift

Drag Thrust

Weight

Centre of Gravity (CG)

The tail plane rotates the aircraft around its centre of gravity PPL FP & P


CENTRE OF GRAVITY Any movement of the centre of pressure (for lift) or the centre of gravity (for weight) will require a balancing force from the tail plane

If the CG is too far forward the moment arm to the tail plane is long

Centre of Gravity (CG)

The aircraft is very stable in pitch

Forward CG position is limited to avoid a nose-heavy aircraft which would be difficult to pitch up (especially for take-off and landing when speed is slower)

PPL FP & P


CENTRE OF GRAVITY

Centre of Gravity (CG) If the CG is too far forward the moment arm to the tail plane is short The aircraft is less stable in pitch Rear CG position is limited so the aircraft’s natural ability to retain a steady pitch is maintained and so elevator “feel” is normal PPL FP & P


CENTRE OF GRAVITY The CG of an aircraft changes in flight normally due to fuel usage

It is safer to establish the aircraft’s loading at both take-off mass and as zerofuel mass to ensure the limits are not exceeded during flight

Take-off mass

Zero-fuel mass

PPL FP & P


CENTRE OF GRAVITY Usually fuel tanks are located near the CG so that the weight reduction does not change the CG position greatly

Every aircraft has a Centre of Gravity Envelope which must be adhered to

PPL FP & P


CENTRE OF GRAVITY

280

11200

5

320

0

0

1448

-

147

6174

1595

52235

52235 ÷ 1595 = 32.7” AFT OF DATUM

PPL FP & P


CENTRE OF GRAVITY

Our weight = 1595 lbs

Within Limits

Our Centre of Gravity 32.74� aft

Within limits

Or we can enter the information on the graph for our aircraft

PPL FP & P


CENTRE OF GRAVITY

x

1595 lb x

Zero fuel weight

32.7” Zero fuel CG location

PPL FP & P


PRACTICE QUESTION!

“Aircraft has a take off weight of 1600 lbs and a centre of gravity of 36.4” aft of the datum. If it uses 100 lbs of fuel (32” aft of datum), where will the centre of gravity be for landing?”

1600 lbs x 36.4” = 58240 (moment) 100 lbs x 32” = 3200 (moment) New moment = 58240 – 3200 = 55040 New weight = 1600 lbs – 100 lbs = 1500 lbs New Centre of Gravity = 55040 (moment) ÷1500 lbs = 36.69” aft

PPL FP & P


TAKE-OFF PERFORMANCE : DEFINITIONS TORA, TODA, Clearway

Clearway

Take-off run available (TORA)

Take-off distance available (TODA)

1st significant obstruction

PPL FP & P


TAKE-OFF PERFORMANCE : DEFINITIONS Take-off run available (TORA)

No stopway available

Accelerate-Stop Distance Available (ASDA) Take-off run available (TORA)

Stopway

Accelerate-Stop Distance Available (ASDA)

1st significant obstruction

PPL FP & P


TAKE-OFF PERFORMANCE : DEFINITIONS Measured Take-off distance is the measured distance it takes for an aircraft to accelerate on a dry paved surface and to get airborne and climb to a screen height of 50 feet Assumes: All engines operating at maximum power

Speed not less than Take-off Safety Speed (TOSS) / V2

TOSS is at least 20% margin over the stall (1.2V S)

PPL FP & P


PRACTICE QUESTION!

“The length of a take-off run available plus a clearway is also known as the?”

Take off Distance Available (TODA)

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING FLAP SETTING

Flap REDUCES ground roll Flap REDUCES rate/angle of climb by reducing the lift/drag ratio Clean takeoff (no flap)

Earlier Lift-off point

Original Lift-off point

50ft

Take-off (with flap)

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING WEIGHT

Increased weight INCREASES ground roll (longer to get to 1.2V S) Increased weight DEGRADES climb performance

Original Lift-off point

Heavier Lift-off point

50ft

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING DENSITY ALTITUDE

Increased density altitude INCREASES take-off roll Increased density altitude DECREASES climb performance

Original Lift-off point

Increased density altitude Lift-off point

Density altitude increases due to lower air pressure or higher air temperatures which both reduce engine power effectiveness

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING HUMIDITY

Increased humidity INCREASES take-off roll Increased humidity DECREASES climb performance

Original Lift-off point

Increased humidity Lift-off point

Increase humidity decreases aerodynamic and engine performance by effectively lowering air density (less air molecules to do the work)

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING WIND

Still Wind

Head Wind

Tail Wind

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING WINDSHEAR

Nil wind gradient

Windshear is wind that differs in strength and direction from one place to another Usually wind increases with height – assisting climb gradient If wind decreases with height it will degrade climb gradient PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING RUNWAY SURFACE

Paved level surface

Wet long grass

Mud / Sand Surface may retard acceleration and lengthen ground run

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING RUNWAY SLOPE

Paved level surface

Upslope

Slope assists or retards acceleration to VTOSS

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING RUNWAY SLOPE So you know slope affects take-off performance but how do you know what the slope of a runway is?

The UK AIP has all the runway statistics: Wycombe 17 elevation 516 feet, 35 elevation 482 ft, length of runway 695 m

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING RUNWAY SLOPE Over 695 m our runway gains / loses 34 feet in height (34 feet รท 695m) x 100 = 4.8% slope

Not as bad as this! PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING CROSSWINDS All aircraft have a crosswind limitation

Crosswinds weathercock the aircraft into wind and the rudder is used to oppose this

Crosswinds try to lift the into-wind wing and aileron is used to oppose this

When calculating crosswind make sure to use common units (degrees magnetic normally) PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS AFFECTING CROSSWINDS

No crosswind

30° off – crosswind ½ wind strength 45° off – crosswind

60° off – crosswind

wind strength

wind strength

Complete Crosswind

Example: On runway 24, wind 300/20 crosswind component is 18 kts

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS So now you know what affects take-off performance, how do you apply this? If you know the basic take-off distance for your aircraft you can then apply some factors to get a more accurate figure. Only use these factors if you do not have the aircraft actual figures

These are all included in the CAA Safety Sense Leaflet “Aeroplane Performance” which you can download from the CAA website

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS CONDITION

INCREASE IN TOD TO 50FT

FACTOR

10% increase in weight

20%

1.2

1000ft increase in elevation

10%

1.1

10° increase in temperature

10%

1.1

Dry Grass (up to 20cm on firm soil)

20%

1.2

Wet grass (up to 20cm on firm soil)

30%

1.3

Tailwind of 10% of lift-off speed

20%

1.2

Soft Ground / Snow

25%+

1.25+

Factors are multiplied…

PPL FP & P


TAKE-OFF PERFORMANCE : FACTORS Example: Original take-off distance 600 metres Taking off on Wet grass, aircraft is 10% heavier and temperature is 10째 warmer

600 m x 1.3 (grass) x 1.1 (weight) x 1.1 (temperature) = 943.8 metres

PPL FP & P


TAKE-OFF PERFORMANCE : SAFETY FACTORS There is then an additional “Safety Factor” which you can apply (it must be applied for public transport flights)

For take-off this factor is 1.33

In our example this means the total take-off distance required to clear a 50 ft obstacle would be 1255 metres (double the original distance)

PPL FP & P


TAKE-OFF PERFORMANCE : EXAMPLE 1 – TABLED DATA

Conditions

Any changes that are required

PPL FP & P


TAKE-OFF PERFORMANCE : EXAMPLE 1 – TABLED DATA

Example – 500 ft airfield at 15°C

We need to interpolate to find the information we need

Never extrapolate outside a performance table

PPL FP & P


TAKE-OFF PERFORMANCE : EXAMPLE 1 – TABLED DATA

725

1340

760 1407.5 795

1475

Grab your calculators and see what you get You may also want to apply a PSF to these figures

PPL FP & P


TAKE-OFF PERFORMANCE : EXAMPLE 1 – TABLED DATA So can we take off at our airfield? The AIP gives distances available:

Runway 06

Our example:

TORA of 735m TODA of 735m

TORR of 760 ft TODR of 1407 ft

We can take off!

Our example (metric): TORR of 232m TODR of 429m PPL FP & P


TAKE-OFF PERFORMANCE : EXAMPLE 2 – GRAPHICAL DATA Some aircraft have graphs instead of tables

PPL FP & P


TAKE-OFF PERFORMANCE Why Bother?

Belgium 2008 Too much cargo, 5 crew, runway too short Luckily no casualties

France 2010 2 people on board, alpine airfield 2 killed

PPL FP & P


PRACTICE QUESTION!

“What type of runway is performance data based upon?”

Hard, dry, level surface

PPL FP & P


PRACTICE QUESTION!

“What is the Public Transport Safety Factor to be applied for take-off?”

1.33

PPL FP & P


TAKE-OFF PERFORMANCE: PRESSURE ALTITUDE Performance data is often tabulated against Pressure Altitude (PA) This refers to the aerodrome elevation based on a standard pressure setting of 1013mb It is assumed that pressure drops by 1mb every 28 feet of altitude gain

If the aircraft is operating at a “higher� pressure altitude there is less oxygen for the engine to burn and less air for the propeller to turn etc etc

You need to know how to work out a pressure altitude:

PPL FP & P


TAKE-OFF PERFORMANCE: PRESSURE ALTITUDE Example – the pressure at and airfield (QFE) is 1009 mb If you set your altimeter to 1013mb at this airfield, what would it read?

1013mb – 1009mb = 4mb difference 4mb x 28 feet = 112 feet The Pressure Altitude is 112 feet

The “original” elevation of the airfield is irrelevant If you get a question about this on an exam paper you can use 30 feet per mb

PPL FP & P


PRACTICE QUESTION!

“An airfield has an elevation of 520 feet above mean sea level. The QFE is 982mb, what is the approximate pressure altitude?”

1013mb – 982mb = 31mb 31mb x 28 feet = 868 feet Pressure Altitude – 868 feet

PPL FP & P


LANDING PERFORMANCE : DEFINITIONS

Maximum braking applied

Aircraft speed 1.3 x VS Full flap, no power

50 ft

Landing distance available (LDA) PPL FP & P


LANDING PERFORMANCE : DEFINITIONS Measured Landing distance is the measured distance from a point 50 feet above the runway to the point at which the aircraft reaches a full stop

Assumes no power, full flap approach with a speed of 1.3 x stalling speed at a simulated 50 ft marker point

Allows a 30% margin above the stall for safety

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING WEIGHT

Increased weight INCREASES stall speed Increased stall speed INCREASES approach speed

Increased approach speed INCREASES ground roll Increased weight INCREASES kinetic energy so brakes have to absorb more energy increasing ground run

50ft

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING DENSITY ALTITUDE

Increased density altitude INCREASES true airspeed (IAS remains same) Touchdown speed is higher and so brakes have more kinetic energy to overcome

Higher Density Altitude, longer landing run

50ft

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING WIND

Same IAS, different groundspeeds

Still Wind

Head Wind

! Tail Wind

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING RUNWAY SLOPE

Paved level surface

Upslope

Slope assists or retards deceleration

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING FLAP SETTING

Flap REDUCES stall speed and therefore approach speed Lower approach speed reduces landing roll

Lower approach speed

Less deceleration required

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING RUNWAY SURFACE

Paved level surface

! Wet long grass

Surface may retard deceleration and lengthen ground run

PPL FP & P


PRACTICE QUESTION!

“If the stalling speed of an aircraft in the landing configuration is 50 kts, what will be the minimum approach speed?”

50 kts x 1.3 = 65 kts

PPL FP & P


PRACTICE QUESTION!

“If the aircraft is approaching an airfield with a tailwind, will the groundspeed be higher or lower than the True Airspeed?”

Higher

PPL FP & P


LANDING PERFORMANCE : FACTORS AFFECTING AQUAPLANING On a wet runway, the tyre may lose all contact with the surface The tyre “floats” above the surface and so brakes become ineffective

It happens to cars as well as aircraft!

Usually occurs at the speed of: 9 x  tyre pressure PPL FP & P


LANDING PERFORMANCE : FACTORS So now you know what affects landing performance, how do you apply this? If you know the basic landing distance for your aircraft you can then apply some factors to get a more accurate figure. Only use these factors if you do not have the aircraft actual figures

These are all included in the CAA Safety Sense Leaflet “Aeroplane Performance” which you can download from the CAA website

PPL FP & P


LANDING PERFORMANCE : FACTORS CONDITION

INCREASE IN LD FROM 50FT

FACTOR

10% increase in weight

10%

1.1

1000ft increase in elevation

5%

1.05

10° increase in temperature

5%

1.05

Dry Grass (up to 20cm on firm soil)

15%

1.15

Wet grass (up to 20cm on firm soil)

35%

1.35

Tailwind of 10% of lift-off speed

20%

1.2

Soft Ground / Snow

25%+

1.25+

Factors are multiplied…

PPL FP & P


LANDING PERFORMANCE : FACTORS Example: Original landing distance 600 metres Landing on Wet grass, aircraft is 10% heavier and temperature is 10째 warmer

600 m x 1.35 (grass) x 1.1 (weight) x 1.05 (temperature) = 935.55 metres

PPL FP & P


LANDING PERFORMANCE : SAFETY FACTORS There is then an additional “Safety Factor” which you can apply (it must be applied for public transport flights)

For landing this factor is 1.43

In our example this means the total landing distance required from 50 feet would be 1377.8 metres (more than double the original distance)

NB. The factor is higher for landing because of the variation at the “start point” of measuring the distance

PPL FP & P


LANDING PERFORMANCE : EXAMPLE 1 – TABLED DATA

Conditions

Any changes that are required

PPL FP & P


LANDING PERFORMANCE : EXAMPLE 1 – TABLED DATA

Example: Airfield at 1400 feet pressure altitude, temperature 22°C We need to interpolate to find the information we need

Never extrapolate outside a performance table

PPL FP & P


LANDING PERFORMANCE : EXAMPLE 1 – TABLED DATA

504 511

523

1246 1258

1276

Grab your calculators and see what you get You may also want to apply a PSF to these figures

PPL FP & P


LANDING PERFORMANCE : EXAMPLE 1 – TABLED DATA So can we land at our airfield? The AIP gives distances available:

Runway 06

Our example:

Our example (metric):

LDA of 735m

LDR of 1258 ft

LDR of 384m

We can take off!

PPL FP & P


LANDING PERFORMANCE : EXAMPLE 2 – GRAPHICAL DATA Again, some aircraft have graphs instead of tables

PPL FP & P


PRACTICE QUESTION!

“Will a snow-covered runway increase or decrease a landing distance, and by how much?”

Increase by 25% or more (Factor of 1.25 or more)

PPL FP & P


LANDING PERFORMANCE Why bother?

Honduras A320 over-ran runway on landing

Rochester

Cessna over-ran runway and skidded into hedge (pictured “parked up” after accident)

PPL FP & P


EN-ROUTE PERFORMANCE: BASICS Total Drag

Parasite Drag Drag

Increases with airspeed – more air molecules striking aircraft and being slowed down by it Induced Drag

Airspeed

Decreases with airspeed because the wing is not working as hard to produce lift PPL FP & P


EN-ROUTE PERFORMANCE: BASICS TOTAL DRAG has two maximums – one at low speed and one at high speed Drag

For straight and level flight the aircraft must produce enough THRUST to balance the DRAG

Airspeed

The POWER REQUIRED is high at low speed and also at high speed

PPL FP & P


EN-ROUTE PERFORMANCE The POWER REQUIRED curve shows the extra need for thrust at the two points of maximum drag

The POWER AVAILABLE curve shows the amount of excess power available (for acceleration or climb if required)

Slow flight

Fast flight

PPL FP & P


EN-ROUTE PERFORMANCE: CLIMBING Best ANGLE OF CLIMB = Best altitude gain for shortest distance

Occurs usually 5-10kts below best rate of climb speed Also known as VX

Best RATE OF CLIMB = Best altitude gain for shortest time Occurs where excess power is at its maximum

Also known as VY

PPL FP & P


EN-ROUTE PERFORMANCE

Climb Performance Information can be found in the aircraft Pilot Operating Handbook / Manual

PPL FP & P


ENDURANCE & RANGE: DEFINTITIONS ENDURANCE refers to the amount of TIME that an aircraft can fly

RANGE refers to the maximum DISTANCE that an aircraft can fly

Range and Endurance are important but much more so in highperformance aircraft where power setting, cruise altitudes and cruise speeds have a more significant effect

PPL FP & P


EN-ROUTE: THE CLIMB If being very accurate for time and fuel calculations!

For example, for this aircraft for a climb to 3000 feet it will take 3 minutes, 0.4 gallons of fuel and 3nm at a 65 kt climb

PPL FP & P


ENDURANCE SPEED Endurance Speed occurs where aircraft is airborne for longest time Need to minimise fuel burnt

Occurs at minimum power required point of the POWER REQUIRED graph

Minimum power required Best endurance speed

PPL FP & P


ENDURANCE SPEED

Detailed information about endurance speed is in the aircraft Pilot Operating Handbook / Manual

PPL FP & P


RANGE SPEED Range Speed occurs where aircraft can travel furthest distance Rate of distance coverage = speed Rate of fuel burn = power

Occurs where power – airspeed ratio is least More power required Best range speed

At any other point on the curve, the power/speed ratio is higher PPL FP & P


RANGE SPEED

Detailed information about range speed is in the aircraft Pilot Operating Handbook / Manual

PPL FP & P


SUMMARY OF RANGE / ENDURANCE

Best ENDURANCE speed Best RANGE speed

?????

PPL FP & P


EN-ROUTE: THE CRUISE All aircraft have a Cruise Performance table in the Pilot Operating Handbook / Manual

Different temperatures against different pressure altitudes

The C152 POH shows percentage of BHP, true airspeed and US gallons per hour

PPL FP & P


PRACTICE QUESTION!

“Flying at the minimum drag speed will allow the aircraft to achieve maximum .....?”

????

PPL FP & P


GLIDING In a glide an aircraft produces no thrust

Lift

Drag

Relative Airflow

Weight

Glidepath angle

A component of weight balances the drag PPL FP & P


GLIDING The greater the drag, the steeper the glide angle The shallowest glide is obtained when the drag is least – the best lift/drag ratio

LOW L/D RATIO High Drag Steep Angle Glide Distance Poor ie. L/D 3:1

HIGH L/D RATIO

Low Drag Shallow Angle Glide Distance Good PPL FP & P ie. L/D 6:1


GLIDING Gliders are designed to: Fly at a high L/D ratio Glide for the maximum distance Usually flown at best angle of attack (about 4째) L/D ratio = 43:1

English Electric Lightning L/D ratio = 14:1

PPL FP & P


GLIDING : FACTORS AFFECTING WIND Same pitch attitude, different flight paths

Still Wind Glide distance is the same relative to the airmass but different over the ground Head Wind

Tail Wind

PPL FP & P


GLIDING : FACTORS AFFECTING AIRSPEED

Best L/D ratio speed gives furthest glide

Too fast = Smaller angle of attack = L/D reduces and so Aircraft “dives” towards ground

Too slow = Larger angle of attack = L/D reduces and so aircraft “falls” toward ground

If gliding at recommended speed and are undershooting DO NOT slow down! PPL FP & P


GLIDING : FACTORS AFFECTING FLAP SETTING Generally – flaps lower the L/D ratio and reduce gliding distance

L

L D

D

W Clean Glide (no flap) L/D ratio highest

W

Glide with full flap L/D ratio lowest PPL FP & P


GLIDING : FACTORS AFFECTING WEIGHT Lighter aircraft has a slower speed for any given angle of attack

L/D ratio usually at 4째 angle of attack

Airspeed to maintain this angle will be lower but glide angle the same

Rate of descent will be reduced

PPL FP & P


GLIDING : FACTORS AFFECTING The best speed for gliding for your aircraft will be found in the Pilot Operating Handbook / Manual

Usually based on max weight – if big variation allowed, different speeds will be shown

PPL FP & P


PRACTICE QUESTION!

“To obtain maximum glide range, a heavy aircraft will need to do what to equal that of a light aircraft?”

Fly at a faster speed (to maintain the best angle of attack for gliding)

PPL FP & P


ADVERSE EFFECTS ON PERFORMANCE

FLAP Initial settings increase lift-production Later settings increase drag production Alter stall speed - alter best approach speed More power required to overcome extra drag

PPL FP & P


ADVERSE EFFECTS ON PERFORMANCE

ICE Adds weight to aircraft Decreases wings’ lift-producing capability Drag increased On propeller reduces thrust-producing capability May reduce engine thrust-producing capability

AIRFRAME CONDITION Dirty wing decreases wings’ liftproducing capability

PPL FP & P


ADVERSE EFFECTS ON PERFORMANCE: CARB ICE CARBURETTOR ICE can form in temperatures up to +30ËšC

As air passes through the VENTURI, it is forced to speed up and this causes the temperature to decrease If the air is moist then ICE will form and may block airflow into the engine This causes ENGINE ROUGH RUNNING and even ENGINE STOPPAGE

PPL FP & P


ADVERSE EFFECTS ON PERFORMANCE: CARB ICE This is more likely at LOW POWER SETTINGS where the gap between the THROTTLE BUTTERFLY and the outer wall of the carburettor is smaller

Carburettor icing is ALWAYS likely when the temperature is below +30ËšC and the aircraft is within 200nm of any sea surface

This must be probably on about 99% of days in the UK! PPL FP & P


ADVERSE EFFECTS ON PERFORMANCE: CARB ICE

PPL FP & P


PRACTICE QUESTION!

“When is carburettor ice most likely to occur?”

At low power settings (when the throttle butterfly is partially closed) with a temperature below 30°C

PPL FP & P


Syllabus complete Any Questions?

PPL FP & P


Turn static files into dynamic content formats.

Create a flipbook
Issuu converts static files into: digital portfolios, online yearbooks, online catalogs, digital photo albums and more. Sign up and create your flipbook.