getting to grips with aircraft performance 如何掌握飞机性能 1(26)

3.2.5. Influence of V1 on the Runway-Limited Takeoff Weight
Considering the runway requirements (TOR≤TORA, TOD≤TODA, and ASD≤ASDA), a Maximum Takeoff Weight (MTOW) can be obtained for each runway limitation. As an example, when for a given takeoff weight the TOD is equal to the TODA, this takeoff weight is maximum regarding the Takeoff Distance limitation.
As previously seen, for a given takeoff weight, any increase of V1 leads to shortening the TODN-1 and TORN-1, and increasing the ASD, but has no influence on TODN and TORN.
Therefore, for a given runway (i.e. given TORA, TODA and ASDA), any increase in V1 leads to an increase in the MTOWTOD(N-1) and MTOWTOR(N-1), and to a reduction in MTOWASD, but has no influence on MTOWTOD(N) and MTOWTOR(N).
The following graph (Figure C15) provides the runway-limited accelerate-go/stop takeoff weights as a function of V1. This graph clearly shows that a maximum takeoff weight is achieved in a particular range of V1.

4. CLIMB AND OBSTACLE LIMITATIONS
4.1. Takeoff Flight Path
4.1.1. Definitions

“JAR/FAR 25.111
(a) The takeoff path extends from a standing start to a point at which the aeroplane is at a height:
.
Of 1500 ft above the takeoff surface, or

.
At which the transition from the takeoff to the en-route configuration1 is

completed and the final takeoff speed2 is reached, whichever point is higher”.
“JAR/FAR 25.115 (a) The takeoff flight path begins 35 ft above the takeoff surface at the end of the takeoff distance.”
The takeoff path and takeoff flight path regulatory definitions assume that the aircraft is accelerated on the ground to VEF, at which point the critical engine is made inoperative and remains inoperative for the rest of the takeoff. Moreover, the V2 speed must be reached before the aircraft is 35 feet above the takeoff surface, and the aircraft must continue at a speed not less than V2, until it is 400 feet above the takeoff surface.
4.1.2. Takeoff Segments and Climb Requirements

The takeoff flight path can be divided into several segments. Each segment is characteristic of a distinct change in configuration, thrust, and speed. Moreover, the configuration, weight, and thrust of the aircraft must correspond to the most critical condition prevailing in the segment. Finally, the flight path must be based on the aircraft’s performance without ground effect. As a general rule, the aircraft is considered to be out of the ground effect, when it reaches a height equal to its wing span.
1 En route configuration: Clean configuration, Maximum Continuous Thrust (MCT) setting. 2 Final takeoff speed: Speed greater than 1.25 Vs, chosen equal to Green Dot speed (best climb gradient speed)

After an engine failure at VEF, whatever the operational conditions, the aircraft must fulfill minimum climb gradients, as required by JAR/FAR 25.121.
　
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