getting to grips with aircraft performance 如何掌握飞机性能 1(32)

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The pressure altitude at the aerodrome;

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The ambient temperature at the aerodrome;

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The runway slope in the direction of take-off;

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The runway surface condition and the type of runway surface“

5.1. Wind
The wind component along the runway axis is an important influencing factor for takeoff. It affects the takeoff ground speed and, therefore, the takeoff distances, which are reduced in case of headwind and increased in case of tailwind.

The MTOW calculated prior to takeoff, must be determined considering 50% of the actual headwind component, or 150% of the actual tailwind component. This condition forms part of the Airbus performance software, so that an operator just has to consider the actual wind component for the MTOW determination.

“JAR/FAR 25.237
(a) A 90° cross component of wind velocity, demonstrated to be safe for take-off and landing, must be established for dry runways and must be at least 20 knots or 0.2 VS01, whichever is greater, except that it need not exceed 25 knots.”
The crosswind component does not affect takeoff performance. Nevertheless, it is necessary to demonstrate the safety of takeoff and landing procedures up to 25 knots of crosswind. The maximum demonstrated value must be published in the Aircraft Flight Manual.
5.2. Pressure Altitude
Pressure altitude influences airframe and engine performance. When the pressure altitude increases, the corresponding static pressure Ps and air density ρ decrease.
5.2.1. Effect on Aerodynamics
The force balance in level flight can be illustrated as follows:
Weight = m g = Lift = 1 ρ  S TAS2 CL
2
1 VS0 is the reference stall speed in clean configuration.

As a conclusion, when the pressure altitude increases for a given weight, the true air speed (TAS) must be increased to compensate for the air density reduction. Therefore, the takeoff distance is increased.
5.2.2. Effect on Engines
When the pressure altitude increases, the available takeoff thrust is reduced. Therefore, takeoff distances are longer and takeoff climb gradients are reduced.
5.2.3. Summary
When the pressure altitude . .. Takeoff distances . . Takeoff climb gradients .
.. MTOW .
5.3. Temperature
5.3.1. Effect on Aerodynamics
When the Outside Air Temperature (OAT) increases, the air density ρ decreases.  As mentioned above, the true air speed (TAS) must be increased to compensate for the air density reduction. As a result, the takeoff distance is increased.
5.3.2. Effect on Engines
The Takeoff thrust (TOGA) remains constant, equal to the Flat Rated Thrust, until the OAT reaches the Flat Rating Temperature (Tref). Above this temperature, the takeoff thrust starts decreasing (Figure C25) .
　
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