1. jar 25 speeds

1. SPEEDS1. SPEEDS

Performance JAR 25Performance JAR 25

SPEEDSSPEEDS

JAR 25 aeroplanes

Factors affecting takeoff

Speeds

• Vs : stall speed

• Vmcg : minimum control speed on the ground

• Vmca : minimum control speed airborne

• Vef : critical engine failure speed

• Vmu : minimum unstick speed

• Vlof : lift off speed

• Vmaxtire : maximum tire speed

• Vmbe : maximum brake energy absorption speed

Operative speeds: V1 – Vr – V2

JAR 25 AEROPLANESJAR 25 AEROPLANES

Performance Class A aeroplanes (certified under FAR/JAR 25):

• All multi-engine turbojet powered aeroplanes.

• Multi-engine turboprops with a seating configuration of more than 9 seats, or a MTOW > 5700 Kg.

FACTORS AFFECTING TAKEOFFFACTORS AFFECTING TAKEOFF

Factors affecting takeoff performance are those affecting one or more of the forces involved in this phase of flight :

Lift

Weight

Drag Thrust

Fr


Those factors are:

Flap setting

Runway slope

Wind

Density altitude

Aircraft systems

Runway contamination


Acceleration distance with flaps 0º

Acceleration distance with flaps 15º

CL effect

CD effect

FLAP SETTING


RUNWAY SLOPE AND WIND

Runway slope and wind affect takeoff distances and speeds. Therefore, the pilot sometimes has to calculate what is known as “corrected runway length”, and then use that value in other graphs.


DENSITY ALTITUDE

Density altitude has a considerable influence on takeoff distances and speeds, since TAS values and engines performance depend on it.

DA effects will be discussed later on.

AIRCRAFT SYSTEMS

Engine bleed may reduce thrust available in about 10%. This will clearly affect takeoff performance. Other circumstances such as anti-skid inoperative may affect also.


RUNWAY CONTAMINATION

A contaminated runway can dramatically affect takeoff performances. Specific calculations of speeds and distances have to be done before taking off from a contaminated runway.

Under certain circumstances operation of the aircraft may be forbidden.

SPEEDSSPEEDS

JAR 25 aeroplanes


Speeds










SPEEDSSPEEDS

STALL SPEED (Vs)

Defined as minimum steady flight speed at which the aircraft is controllable, with null thrust and the centre of gravity at the forward limit, or the 94% of the Vs1g determined in the same conditions, whichever is greater.

ONE-G STALL SPEED (Vs1g)

Minimum calibrated airspeed at which the aeroplane can develop a lift force (normal to the flight path) equal to its weight, whilst at an angle of attack non greater than that at which the stall is identified.

Vs1g is always greater than Vs (about a 6%).

SPEEDSSPEEDS

MINIMUM CONTROL SPEED ON THE GROUND (Vmcg)

After an engine failure, Vmcg is the minimum speed during takeoff at which it is possible to maintain directional control with only the use of primary aerodynamic controls, to enable the takeoff to be safely continued, assuming:

• Takeoff configuration

• Critical engine failure

• Remaining engines at takeoff thrust

• MTOW and CG at the most unfavourable position (aft limit)

The maximum demonstrated separation from the runway centreline will be no more than 30 ft, and the rudder forces may not exceed 150 lb.

SPEEDSSPEEDS

Max 30 ft

Engine failure

MINIMUM CONTROL SPEED ON THE GROUND (Vmcg)

SPEEDSSPEEDS

MINIMUM CONTROL SPEED AIRBORNE (Vmca)

Minimum flight speed at which the aeroplane can be directionally controlled with engine failure, without loss of altitude, assuming:

• Critical engine inoperative

• Remaining engines at takeoff thrust

• MTOW and CG at the most unfavourable position (aft limit)

• Takeoff configuration and trim setting

• Landing gear up

• Maximum bank angle 5º towards the operative engine

• No ground effect

• Maximum force on rudder pedals is also 150 lbs (20 lbs for continuous use)

SPEEDSSPEEDS

ENGINE FAILURE SPEED (Vef)

Vef is the calibrated airspeed at which the critical engine is assumed to

fail. Vef must be selected by the applicant, but may not be less than

Vmcg.”

All takeoff performance figures after critical engine failure are calculated from this speed.

SPEEDSSPEEDS

MINIMUM UNSTICK SPEED (Vmu)

Vmu is the minimum speed at which the aircraft can safely lift-off and continue the takeoff without undue hazard.

Ground effect is not considered.

SPEEDSSPEEDS

Minimum unstick takeoff test

SPEEDSSPEEDS

LIFT-OFF SPEED (Vlof)

Vlof is the calibrated airspeed at which the aeroplane becomes airborne,

if rotated at VR.

It depends on the MTOW, flap setting and angle of attack.

Vlof and Vmu do not appear in the flight manuals

1.05 Vmu < Vlof (1 ENG OUT)

1.10 Vmu < Vlof (all engines)

SPEEDSSPEEDS

MAXIMUM TIRE SPEED (Vmaxtire)

Vmaxtire is the maximum speed that the tires can support.

The tire manufacturer specifies the maximum ground speed that can be reached, in order to limit the centrifugal forces and the heat elevation that may damage the tire structure.

For almost all Airbus aircraft models, Vmaxtire is equal to 195 knots (Ground Speed).

Take into account that Vmaxtire may limit takeoff weight.

SPEEDSSPEEDS

SPEEDSSPEEDS

MAXIMUM BRAKE ENERGY SPEED (Vmbe)

Vmbe is the maximum speed on the ground from which a stop can be accomplished within the energy capabilities of the brakes.

JAR/FAR 25.109(h): A flight test demonstration of the maximum brake kinetic energy accelerate-stop distance must be conducted with no more than 10% of the allowable brake wear range remaining on each of the aeroplane wheel brakes.

Vmbe depends on ATOW, DA, wind, runway slope, and the brakes temperature at the beginning of the takeoff run.

SPEEDSSPEEDS

JAR 25 aeroplanes


Speeds










SPEEDSSPEEDS

OPERATIVE SPEEDS

V1: Decision speed

VR: Rotation speed

V2: Takeoff safety speed

SPEEDSSPEEDS

DECISION SPEED (V1)

The decision speed V1 is the calibrated airspeed on the ground at which, as a result of engine failure or other reasons, the pilot is assumed to have made a decision to continue or discontinue the takeoff.

V1 is the speed at which, if a failure is recognised, the distance to bring the aeroplane to a full stop without the aid of the reverse thrust will not exceed the accelerate-stop distance available (ASDA); or, if takeoff is continued, the distance to a height of 35 ft will not exceed the usable takeoff distance (TODA).

V1

Abort takeoff Continue takeoff

SPEEDSSPEEDS

35 ft

Stop

V1Vef

V1Vef

Recognition time = 1s

Recognition time = 1s

SPEEDSSPEEDS

B737 PFD

SPEEDSSPEEDS

V1 CONSIDERATIONS

• V1 lower limit is Vmcg (+ speed gain in recognition time).

• V1 higher limit is Vmbe.

• V1 =< VR

These factors will increase V1:

More weight

Higher DA

Positive runway slope

Headwind

Engine anti-ice

Lower flap settings

SPEEDSSPEEDS

ROTATION SPEED (VR)

The rotation speed VR is the speed at which rotation must be initiated in

order to attain V2 not later than at 35 ft with one engine inoperative.

The assumed rate of rotation is 3º per second.

Remember also that rotating too late or too early will increase the takeoff run.

SPEEDSSPEEDS

TAKEOFF CLIMB SPEED (V2)

The takeoff climb speed V2 is the speed that will allow the initial climb

to be continued with a safe margin to stall and to Vmca with the critical engine failed.

Remember that it must be reached not later than at 35 ft.

V2 >= 1.1 Vmca

V2 >= 1.2 Vs

V2 >= 1.3 Vs1

SPEEDSSPEEDS

1. jar 25 speeds

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