getting to grips with aircraft performance 如何掌握飞机性能 1(27)

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The following Table (C4) summarizes the different requirements and aircraft status during the four takeoff segments : Minimum required climb gradient one-engine inoperative, flaps / slats configuration, engine rating, speed reference, landing gear configuration…

FIRST SEGMENT  SECOND SEGMENT  THIRD SEGMENT  FINAL SEGMENT 
Minimum 
climb gradient Twin  0.0%  2.4%  - 1.2% 
(N-1) engines Quad  0.5%  3.0%  - 1.7% 
Start when  VLOF reached  Gear fully retracted  Acceleration height reached (min 400 feet)  En route configuration Achieved 
Slats / Flaps Configuration Engine rating Speed reference Landing gear Weight reference  Takeoff TOGA/FLEX VLOF Retraction Weight at the start of the gear retraction  Takeoff TOGA/FLEX V2 Retracted Weight when the gear is fully retracted  Slats / Flaps retraction TOGA/FLEX Acceleration from V2 to Green Dot Retracted Weight at the start of the acceleration segment  Clean MCT Green Dot Retracted Weight at the end of the acceleration segment 
Ground effect  Without  Without  Without  Without 

Table C4: Takeoff Segment Characteristics
4.1.3. Minimum and Maximum Acceleration Heights
4.1.3.1. Minimum Acceleration Height

“JAR/FAR 25.111 (c)(2) The aeroplane must reach V2 before it is 35 ft above the takeoff surface and must continue at a speed not less than V2 until it is 400 ft above the takeoff surface”
“JAR/FAR 25.111
(c)(3) At each point along the takeoff flight path, starting at the point at which the aeroplane reaches 400 ft above the takeoff surface, the available gradient of climb may not be less than:
.
1.2% for a two-engined airplane

.
1.7% for a four-engined airplane”

So, below 400 feet, the speed must be maintained constant to a minimum of V2. Above 400 feet, the aircraft must fulfill a minimum climb gradient, which can be transformed into an acceleration capability in level flight. Therefore, the regulatory minimum acceleration height is fixed to 400 feet above the takeoff surface.
Nevertheless, during the acceleration segment, obstacle clearance must be ensured at any moment. Therefore, the operational minimum acceleration height is equal to or greater than 400 feet (Figure C16).
4.1.3.2. Maximum Acceleration Height
The Maximum Takeoff Thrust (TOGA) is certified for use for a maximum of 10 minutes, in case of an engine failure at takeoff, and for a maximum of 5 minutes with all engines operating.
The Maximum Continuous Thrust (MCT), which is not time-limited, can only be selected once the enroute configuration is achieved (i.e. when the aircraft is in clean configuration at green dot speed).
As a result, the enroute configuration (end of the third segment) must be achieved within a maximum of 10 minutes after takeoff, thus enabling the determination of a maximum acceleration height (Figure C16).
　
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