Civil Aircraft Design: Takeoff

The contribution of the last three terms (-D/ T – лW/ T + /лL/ T) in Equa­tion 11.4 is minimal and can be omitted at this stage for the sizing calculation. In addition, for the one-engine inoperative condition after the decision speed (V1; see Section 13.4), the acceleration slows down, making the TOFL longer than the all – engines-operative case. Therefore, in the sizing computations to produce the spec­ified TOFL, further simplification is possible by applying a semi-empirical correc­tion factor primarily to compensate for loss of an engine. The correction factors are as follows (see [4]); all sizing calculations are performed at the MTOW and with Tsls:

For two engines, use a factor of 0.5 (loss of thrust by a half). Then, Equation 11.6 in the FPS system reduces to:

(W/S) = (TOFL x (T/ W) x CLstau)/3.15 (11.7a)

For the SI system:

(W/S) = 4.173 x TOFL x (T/ W) x CLstaii (11.7b)

For three engines, use a factor of 0.66 (loss of thrust by a third). Then, Equation 11.6 in the FPS system reduces to:

(W/S) = (TOFL x (T/ W) x CLstaii)/28.5 (11.8a)

For the SI system:

(W/S) = 5.5 x TOFL x (T/ W) x CLstaii (11.8b)

For four engines, use a factor of 0.75 (loss of thrust by a fourth). Then, Equation 11.6 in the FPS system reduces to:

(W/S) = (TOFL x (T/ W) x CLstaii)/25.1 (11.9a)

For the SI system:

(W/S) = 6.25 x TOFL x (T/W) x CLstaii (11.9b)

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