getting to grips with aircraft performance 如何掌握飞机性能 2(36)

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Indicated altitude 16,600 feet 10,900 feet

.. altitude  600 feet 400 feet
When temperature is ISA - 20:
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True altitude  16,000 feet 10,500 feet

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Indicated altitude 17,300 feet 11,350 feet

.. altitude  1,300 feet 850 feet
Conclusion:
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When the temperature moves away from the standard, altimetric errorincreases.

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The altimetric error induced by temperature is proportional to altitude.

2. APPENDIX 2 : TAKEOFF OPTIMIZATION PRINCIPLE
This section is specifically designed to explain the takeoff optimization principle. The optimization objective is to obtain the highest possible performance-limited takeoff weight, while fulfilling all airworthiness requirements.
For that purpose, it is necessary to determine what parameters influence takeoff performance and offer a freedom of choice. For instance, the Outside Air Temperature is a parameter which influences takeoff performance, but which cannot be chosen. This is a sustained parameter.
The following table gives an exhaustive list of parameters which influence takeoff performance. The left column shows sustained parameters, while the right one indicates parameters for which a choice is possible (free parameters).

Table J3: Influent Takeoff Parameters
2.1. Takeoff Configuration
Takeoff can be accomplished with one of the following three possible takeoff configurations: Conf 1+F, Conf 2 or Conf 3, on fly-by-wire aircraft.
Each configuration is associated with a set of certified performance and it is, therefore, always possible to determine a Maximum TakeOff Weight (MTOW) for each takeoff configuration. As a result, the optimum configuration is the one that provides the highest MTOW.
As a general rule, Conf 1+F gives better performance on long runways (better climb gradients), whereas Conf 3 gives better performance on short runways (shorter takeoff distances). Sometimes, other parameters, such as obstacles, can interfere. In this case, a compromise between climb and runway performance is requested, making Conf 2 the optimum configuration for takeoff.

2.2. Air Conditioning
Air conditioning, when switched on during takeoff, decreases the available power and thus degrades the takeoff performance. It is then advisable to switch it off during takeoff, but this is not always possible as some constraints exist (high air temperature in the cabin or/and company policy), unless APU bleed is used.
2.3. Takeoff Speed Optimization
Takeoff speeds represent the most important source of optimization and MTOW gain. The following section shows how this optimization is achieved thanks to speed ratios (V1/VR and V2/VS).
2.3.1. Speed Ratios: V1/VR and V2/VS
2.3.1.1. V1/VR Range
The decision speed V1 must always be less than the rotation speed VR. But, as VR depends on weight, the maximum V1 value is not fixed, whereas the maximum V1/VR ratio is equal to one (regulatory value).
　
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