Module 9

Aircraft Performance

Module 9

Where are we? 1 : Introduction to aircraft performance, atmosphere 2 : Aerodynamics, air data measurements 3 : Weights / CG, engine performance, level flight 4 : Turning flight, flight envelope 5 : Climb and descent performance 6 : Cruise and endurance 7 : Payload-range, cost index 8 : Take-off performance 9 : Take-off performance 10 : Enroute and landing performance 11 : Wet and contaminated runways 12 : Impact of performance requirements on aircraft design

Take-off performance (2 of 2)

2

Take-off Performance (Part 2)

Take-off performance (2 of 2)

3

Forces acting on the aircraft

L

T D θ horizontal

Ff = μ(W-L)

W

Wθ

Take-off performance (2 of 2)

4

Forces acting on the aircraft (cont’d) Friction force = Ff = µ (W-L) 

Two cases : brakes off and brakes on •

Brakes off (acceleration segment) •

FR = µ

R

(W-L)

-

µ -

R

= aircraft rolling friction coefficient

Typically, µ

R

= 0.02 on a hard runway surface

-

Brakes on (braking segment) •

FB = µ

B

(W-L)

-

µ -

B

= aircraft braking friction coefficient

Typically, µ

B

= 0.4 - 0.5 on a hard runway surface

-

Take-off performance (2 of 2)

5

Forces acting on the aircraft (cont’d) Lift and Drag 

CD and CL are defined for the aircraft in taxi attitude (α = 0 ) •

Ground effect must considered •

increase in CL and reduction in CD relative to free-air data -

Effect of Ground Lift Dumpers (GLD) deployment must be considered during a rejected take-off •

CL is reduced and CD is increased when GLD are deployed -

These effects improve stopping performance

-

Take-off performance (2 of 2)

6

Forces acting on the aircraft (cont’d) 

Wθ

• • •



Weight component along the runway longitudinal axis Θ is typically varying from -2 % (downhill) to + 2 % (uphill) Special certification requirements apply when |θ| > 2 %

Thrust

• •

Take-off thrust rating Reduced take-off thrust or a derate may be used to preserve engine life if the take-off is not performance limited

Take-off performance (2 of 2)

7

Calculation of distances (α = 0)

Take-off performance (2 of 2)

8

Calculation of distances (α = 0) (Cont’d) 

Take-off speeds (V1, VR, VLOF , V2, …) must first be converted from airspeeds to ground speeds

•

•



VG = V - Vwind

headwinds are positive for field performance analysis (!)

FAR / JAR 25 require that take-off and landing performance be based on factored wind speeds

•

•

50 % of the reported headwind and on 150 % of the reported tailwind

Example: for a reported headwind of 10 kts, calculations are based on a headwind 5 kts)

Take-off performance (2 of 2)

9

Calculation of distances (α = 0) (Cont’d)

Take-off performance (2 of 2)

10

Calculation of distances (α = 0) (Cont’d)

Take-off performance (2 of 2)

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Calculation of distances (α = 0) (cont’d)

Take-off performance (2 of 2)

12

Calculation of distances (α = 0) (cont’d)

Take-off performance (2 of 2)

13

Calculation of distances (VR to 35 ft)

Take-off performance (2 of 2)

14

Calculation of distances (VR to 35 ft) (Cont’d)

OEI

AEO tance s i d r fo used ) t o n ( lation u c l a c

Take-off performance (2 of - θ2)

15

Calculation of distances (VR to 35 ft) (Cont’d)

OEI

AEO

Take-off performance (2 of 2) - θ

16

T.O. – Take-off parameter

Take-off performance (2 of 2)

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T.O. – Take-off parameter (cont’d)

Take-off performance (2 of 2)

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T.O. – Performance-limited take-off weight

Take-off performance (2 of 2)

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T.O. – Brake energy considerations 



A very large amount of energy may be absorbed by the brakes during a rejected take-off

The energy absorbed by each braked wheel during a stop (BRKE) is calculated by integration of the braking force FB over distance increments ∆ s

∆

BRKE = FB ∆ s / nbrakes

Where : BRKE = brake energy absorbed per braked wheel (ft-lb) nbrakes = number of braked wheels



If a simplified methodology is used (calculation of average acceleration at VRMS ), BRKE is evaluated with the same equation but FB is evaluated at VRMS

Take-off performance (2 of 2)

20

T.O. – Brake energy considerations (Cont’d)

Take-off performance (2 of 2)

21

T.O. – Brake energy considerations (cont’d)

Take-off performance (2 of 2)

22

T.O. – Tire speed limits

Take-off performance (2 of 2)

23

T.O. – Take-off WAT limits

Take-off performance (2 of 2)

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T.O. – Take-off WAT limits (cont’d)

Requirement 25.121 ( a ) 25.121 ( b ) 25.121 ( c )

Name

Flap/Slat Ldg gear

First segment climb Take-off Second segment climbTake-off Final segment climb Retracted

down up up

Thrust

Speed Min. grad. Req'd

TO, OEI VLOFOEI TO, OEI V2 MCT, OEI VFTO

Take-off performance (2 of 2)

0% 2.40% 1.20%

25

T.O. – Take-off WAT limits (cont’d)

Take-off performance (2 of 2)

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T.O. – Take-off WAT limits (cont’d)

Take-off performance (2 of 2)

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T.O. – Obstacle clearance

Take-off performance (2 of 2)

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T.O. – Obstacle clearance (cont’d)

Take-off performance (2 of 2)

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T.O. – Obstacle clearance (cont’d)

Take-off performance (2 of 2)

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T.O. – Obstacle clearance (cont’d)

Take-off performance (2 of 2)

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T.O. – Improved climb

Take-off performance (2 of 2)

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T.O. – Improved climb (cont’d)

Take-off performance (2 of 2)

33

T.O. – Runway weight chart

Take-off performance (2 of 2)

34

T.O. – Runway weight chart (Cont’d)

Take-off performance (2 of 2)

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