Module 8

Aircraft Performance

Module 8

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 (1 of 2)

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Take-off Performance Introduction AEO Take-off distance and take-off run OEI Take-off distance and take-off run Accelerate-stop distance Speed versus distance Minimum runway length required  Distance versus V1      

 Balanced field length  Field length limited take-off weight  Take-off speeds  Speed and time increments from VR to 35 ft  Calculation of take-off speeds  Typical take-off performance data Take-off performance (1 of 2)

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Introduction  Take-off performance analysis is the most complex aspect of aircraft performance • Many certification requirements and many definitions must be considered when establishing take-off speeds and distances • Many operational requirements must be considered when establishing take-off weight limits • Two cases must be considered - Normal all-engine operation (AEO condition) - Engine failure at the most critical time during the take-off (OEI condition)

• Take-off may be continued OR discontinued following an engine failure

Take-off performance (1 of 2)

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Introduction (Cont’d)  The focus of this module is • Definition of take-off distances and take-off speeds • Calculation of take-off speeds • Operation on dry runways - Different requirements apply to wet and contaminated runways - Wet and contaminated runways will be discussed later

 Next module will cover • Calculation of take-off distances • Take-off climb gradient requirements • Obstacle clearance

Take-off performance (1 of 2)

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Introduction (Cont’d)  Take-off profile

Take-off performance (1 of 2)

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Introduction (Cont’d)  Take-off performance data is certified • FAR / JAR 25 requirements define how take-off performance data must be calculated for large transport category aircraft • Data is produced by aircraft manufacturers and approved by certification agencies and included in the Airplane Flight Manual (AFM)

 FAR/JAR 25 requirements define various distances that must be considered when determining the maximum permissible take-off weight from a given runway • • • •

All-Engine-Operating (AEO) take-off distance and take-off run One-engine-inoperative (OEI) take-off distance and take-off run AEO accelerate-stop distance OEI accelerate-stop distance

Take-off performance (1 of 2)

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AEO take-off distance and take-off run  AEO take-off distance (TOD AEO) and take-off run (TOR AEO) • TOD AEO extends from brake release to the point where the aircraft reaches the screen height (35 ft above the runway) • TOR AEO extends from brake release to the point halfway between lift-off and the point where the aircraft reaches 35 ft

Take-off performance (1 of 2)

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AEO take-off distance and take-off run (cont’d)

 Rotation at VR • VR is the airspeed at which the pilot pulls the stick aft so as to generate a pitch rate of approximately 3 degrees / sec. • VR is determined before take-off and the same VR speed will be used whether an engine fails or not during take-off

 Lift-off at VLOF AEO • VLOF AEO is the airspeed at which the main gear tires leave the ground during an AEO take-off Take-off performance (1 of 2)

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AEO take-off distance and take-off run (cont’d)

 V2 is the take-off safety speed • target climb speed in the take-off configuration if an engine fails during take-off (OEI take-off climb speed) • During an AEO take-off, the aircraft will reach a speed not less than V2 at 35 ft and will continue to accelerate to a fixed steady state climb speed (V2 + 10 kts is typical)

Take-off performance (1 of 2)

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AEO take-off distance and take-off run (cont’d)

 FAR / JAR 25 requirements specify that TOD AEO and TOR AEO be multiplied by a factor of 1.15 before being used to establish fieldlength limited take-off weights • Factored all-engine takeoff distance (FTOD AEO) FTOD AEO = 1.15 * TOD AEO • Factored all-engine takeoff run (FTOR AEO) FTOR AEO = 1.15 * TOR AEO

Take-off performance (1 of 2)

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OEI take-off distance and take-off run  OEI take-off distance (TOD OEI) and take-off run (TOR OEI) • TOD OEI extends from brake release to the point where the aircraft is 35 ft above the runway • TOR OEI extends from brake release to the point half way between lift-off and the point where the aircraft reaches 35 ft

Take-off performance (1 of 2)

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OEI take-off distance and take-off run (cont’d)

 FAR / JAR 25 requires no factorization of TOD OEI and TOR OEI  VEF : engine failure speed •

Speed at which the critical engine fails.

 V1 : Take-off decision speed • Speed at which the engine failure is recognized by the pilot and the decision to continue or discontinue the take-off is made. Take-off performance (1 of 2)

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OEI take-off distance and take-off run (cont’d)

 The time delay between VEF and V1 is called the engine failure recognition time (∆tREC) • Determined during flight tests • A time delay equal to the greater of the demonstrated value or 1.0 second is used for calculation of AFM take-off data

 Same value of VR is used for AEO and OEI conditions Take-off performance (1 of 2)

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OEI take-off distance and take-off run (cont’d)

 VLOF OEI is lower than VLOF AEO • Same VR is used for AEO and OEI take-off • •

Acceleration is lower with OEI due to lower thrust Time from VR to VLOF is similar for AEO and OEI take-offs

 Climb speed V2 must be reached at or before 35 ft • An airspeed equal to V2 must be maintained during the climb beyond the 35 ft point Take-off performance (1 of 2)

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Accelerate-stop distance  Accelerate-stop is a scenario where the aircraft is accelerated from V = 0 to a speed V1 at which the pilots decides to abort the take-off (throttle chop to idle) and bring the aircraft to a full stop on the runway using all available deceleration devices  Available deceleration devices include • • • •

Brakes (maximum anti-skid braking) Ground lift dumpers (ground spoilers) Airbrakes (if any) Thrust reversers

 FAR / JAR 25 does not allow performance credit for use of thrust reversers when calculating dry runway take-off performance

Take-off performance (1 of 2)

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Accelerate-stop distance (Cont’d)  The accelerate-stop scenario is also sometimes referred to as the rejected take-off (RTO)  FAR / JAR 25 requires that two accelerate-stop cases be considered : • AEO accelerate-stop distance (ASD AEO) • OEI accelerate-stop distance (ASD OEI)

 Demonstrated ASD versus AFM ASD • Demonstrated accelerate-stop performance is obtained during certification flight tests • AFM ASD is obtained by adding conservatism to demonstrated ASD Take-off performance (1 of 2)

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Accelerate-stop distance (cont’d) 

Demonstrated accelerate-stop distance

 VFB is the speed at which the aircraft is in the full braking configuration (all deceleration devices are fully activated) Take-off performance (1 of 2)

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Accelerate-stop distance (cont’d) 

During accelerate-stop tests, the time delay between V1 and VFB is determined •



An average of all available test points is used for AFM calculations

AFM accelerate-stop distance (ASD AFM) is obtained by adding a distance margin equivalent to 2 seconds at constant V1 speed to the demonstrated accelerate-stop distance (ASD DEM) •

ASD AFM = ASD DEM + (2 * V1G)

•

V1G = ground speed at V1

•

ASD AFM is based on the most limiting of ASD AEO and ASD OEI Take-off performance (1 of 2)

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Accelerate-stop distance (cont’d) 



Comparison of ASD AEO and ASD OEI for a given V1 speed •

Distance from brake release ( V = 0 ) to V1 is slightly shorter for the AEO condition

•

Distance from V1 to full stop is longer for the AEO condition because the residual thrust from all engines after decision to abort (may take more than 5 seconds for the engines to spool down from take-off thrust to idle thrust following throttle chop)

Item 2 above normally results in a greater increase in ASD than the reduction obtained from item 1 and, as a consequence: •

ASD AEO tends to be greater than ASD OEI when operating on a dry runway

Take-off performance (1 of 2)

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Speed versus distance

Take-off performance (1 of 2)

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Minimum runway length required The runway length available for take-off must not be less than the greater of the following distances: FTOD AEO TOD OEI ASD AEO

Note: Based on a simple scenario with no stopway, no clearway and no runway alignment distance

ASD OEI

It is possible to minimize the runway length required by selecting an optimumV1 speed Take-off performance (1 of 2)

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Distance versus V1 DISTANCE

Fixed values of weight, altitude, temperature and flap setting ASD (AEO) ASD (OEI)

Minimum Distance (BFL)

FTOD (AEO) TOD (OEI)

Optimum V1 V1 = V1B

Take-off performance (1 of 2)

V1

Balanced Field Length (BFL) 

V1 is a speed that is determined by the pilot before take-off



ASD increases as V1 is increased



TOD OEI reduces as V1 is increased



Minimum runway length required when V1 = V1B (balanced V1) •

When V1 = V1B, ASD = TOD OEI = BFL

Take-off performance (1 of 2)

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Balanced Field Length (cont’d)



V1 is the “go or no-go” decision speed •

If engine failure (EF) is recognized before V1, take-off must be rejected or TOD OEI may exceed runway length available

•

If EF is recognized after V1, take-off must be continued or ASD may exceed runway length available

•

If EF is recognized at V1, take-off can either be rejected or continued while meeting the runway length requirements Take-off performance (1 of 2)

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Field length limited take-off weight 

The field length limited take-off weight is the maximum weight at which it is possible to meet the applicable operational requirements (e.g. FAR 121 or JAR OPS-1)



Operational requirements make references to stopway, clearway and runway alignment distance



Clearways and stopways allow higher take-off weights for a given runway length



A clearway is an area beyond the runway, not less than 500 ft wide, centrally located about the extended centerline of the runway and under the control of the airport authorities. It is permitted to overfly the clearway before reaching the 35 foot point but the takeoff run must not exceed the end of the runway.

Take-off performance (1 of 2)

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Field length limited take-off weight (Cont’d) 

A stopway is an area beyond the runway, no less wide than the width of the runway and centrally located about the extended center line of the runway. A stopway must be able to support the airplane during a rejected take-off without causing structural damage to the airplane. Stopways must be designated by the airport authorities for use in decelerating the airplane during the rejected take-off. It is permitted to use the stopway during an accelerate-stop.



JAR OPS-1 requires that runway alignment distance (RAD) be considered when determining field length limited weights •

RAD is the portion of runway length used in order to position the aircraft for take-off Effective runway length = runway length – RAD

•

RAD is essentially a function of aircraft length, minimum turning radius and location of the taxi way relative to the runway

Take-off performance (1 of 2)

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Field length limited take-off weight (cont’d) 

Airport data is sometimes based on following definitions: TORA = Take-Off Run Available = runway length TODA = Take-Off Distance Available = runway length + clearway length ASDA = Accel.-Stop Dist. Available = runway length + stopway length



General scenario for determination of field length limited take-off weight (with stopway, clearway and RAD) FTOD AEO + RAD

≤

TODA

TOD OEI

+ RAD

≤

TODA

FTOR AEO + RAD

≤

TORA

TOR OEI

+ RAD

≤

TORA

ASD AEO + RAD

≤

ASDA

ASD OEI

≤

ASDA

+ RAD

Take-off performance (1 of 2)

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Take-off speeds 

Before take-off, V1, VR and V2 speeds must be determined by the pilot • • •



Indicated Airspeeds (not ground speeds) Sometimes referred to as “V speeds” Values can be “bugged” on the pilot airspeed indicator

V1 must respect the following limits •

V1 must not be less than V1MCG

•

V1 must not be greater than VR

•

V1 must not be greater than V1MBE

Take-off performance (1 of 2)

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Take-off speeds (Cont’d) 

V1MCG is the minimum V1 speed based on VMCG considerations •

V1MCG is the speed reached one second after an engine failure at VMCG

•

VMCG is the minimum control speed on the ground, i.e. the minimum speed at which an engine failure would result in a lateral deviation of not more than 30 ft from the runway center line in the case where the take-off is continued . Aircraft may not be controllable if an engine fails and the pilot decides to continue the take-off at a speed < V1MCG

•



V1MBE is the maximum V1 speed based on maximum brake energy considerations •

A take-off rejected at V1MBE will cause the wheel brakes to absorb the Maximum allowable Brake Energy Take-off performance (1 of 2)

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Take-off speeds (cont’d) 

VR must respect the following limits •

VR must not be less than V1MCG

•

VR must not be less than 1.05*VMCA

•

VR must be selected such that the aircraft will reach a speed of V2 at or before the 35 ft point when the recommended take-off technique is used

•

VR is such that when the aircraft is rotated at the maximum practicable rate at VR, the lift-off speed is not less than 1.05 VMU1 in the OEI condition 1.10 VMU2 in the AEO condition

Take-off performance (1 of 2)

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Take-off speeds (cont’d) 

VMCA is the minimum control speed in the air •

VMCA is the minimum speed at which it is possible to fly the aircraft with one engine inoperative and the other engine(s) at maximum take-off thrust



VMU1 is the minimum unstick speed with OEI, i.e. the minimum speed at which the aircraft can lift-off from the ground and climb safely with OEI



VMU2 is the minimum unstick speed with AEO, i.e. the minimum speed at which the aircraft can lift-off from the ground and climb safely with AEO

Take-off performance (1 of 2)

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Take-off speeds (cont’d) 



V2 must respect the following limits •

V2 must not be less than 1.13 VSR (for two-engine aircraft)

•

V2 must not be less than 1.1*VMCA

•

At V2 , a maneuvering margin equivalent to not less than a 30 degree bank turn must be available prior to stall warning

•

At V2 + 10 kts, a maneuvering margin equivalent to not less than a 40 degree bank must be available prior to stall warning

The diagram on the next slide shows the various limits that must be considered for V1, VR and V2 •

Double arrows represent take-off speed increments as obtained from take-off performance tests Take-off performance (1 of 2)

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Take-off speeds (cont’d)

Take-off performance (1 of 2)

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Speed and time increments from VR to 35 ft 

Speed and time increments between rotation, lift-off and 35 ft are measured during take-off performance tests and form the basis for calculation of: •

VR and V2

•

OEI and AEO T.O. distance from rotation to 35 ft



Speed increments are ground speed increments



Speed and time increments are normally plotted as a function of reference climb / acceleration parameter such as gradient at 35 ft Gradient at 35 ft = (T-D)/W – θ based on a speed of V2 and gear up Gradient covers range of OEI and AEO operating conditions Separate plots for (1) rotation to lift and (2) lift-off to 35 ft θ = runway slope (tangent of the angle between the runway and the horizon) – slope is positive uphill and negative downhill

Take-off performance (1 of 2)

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Speed and time increments from VR to 35 ft (Cont’d) 

From VR to VLOF ΔV is a ground speed increment GRAD35 = (T-D)/W – θ based on a speed of V2 and gear up

OEI

AEO with e c n ia ompl ements) c r o f ir ( requ u m V

Take-off performance (1 of - θ2)

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Speed and time increments from VR to 35 ft (Cont’d) 

From VLOF to 35 ft ΔV is a ground speed increment GRAD35 = (T-D)/W – θ based on a speed of V2 and gear up

OEI

AEO

Take-off performance (1 of 2) - θ

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Calculation of take-off speeds 



Take-off speeds VR and V2 are calculated using: • •

Take-off speed increments Flowchart shown previously

•

Assume V2 = V2min

•

V LOF OEI = V2min – ΔV

•

V R = VLOF OEI – ΔV

•

V LOF AEO = VR + ΔV

•

V 35 AEO = VLOF AEO + ΔV

(LOF-35 ft)OEI

(ROT-LOF)OEI

(ROT-LOF)AEO

(LOF-35 ft)AEO

The speeds calculated in each step must be compared with the applicable limits (e.g. V R must not be less than 1.05 Vmca). An iterative procedure must be applied if limits are encountered. Take-off performance (1 of 2)

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Typical take-off performance data 

The next two slides present typical take-off performance data



First slide is a typical take-off distance versus weight chart that is used for marketing purposes



Second slide presents tabulated Vspeeds and distances taken from a Quick Reference Handbook (QRH)



Even if the terminology “take-off distance” is used, the distances shown are the most limiting of :



-

FTOD AEO

-

TOD OEI

-

ASD AEO

-

ASD OEI

Typically, the distance shown is the BFL

Take-off performance (1 of 2)

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Typical take-off performance data

Take-off performance (1 of 2)

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Typical take-off performance data

Take-off performance (1 of 2)

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