Discussion of the Takeoff Analysis

Increasing the flap setting improves the BFL capability at the expense of a loss in climb gradient. The next section verifies the gradient requirements. With one engine inoperative, the loss of thrust percentage for a two-engine aircraft is the highest (i.e., 50%). With one engine failed, the aircraft acceleration suffers severely and the ground run from V1 to liftoff is high.

Table 13.16 summarizes the takeoff performance and associated speed schedules for the two flap settings and provides an example of the procedure. The ratio of speed schedules can be varied for pilot ease, as long as it satisfies FAR requirements.

At a lower flap setting of 8 deg, the decision speed V1 is close to the rotation speed V1 = 0.93VR. The situation improves with a higher flap setting of 20 deg when V1 = 0.9VR.

Higher flap settings provide more time between the decision speed V1 and the rotation speed VR. However, it is not problematic if V1 is close to VR. If one engine fails close to the decision speed, then the rotation speed VR is reached very quickly; that is, even if a pilot’s reaction is slow, the aircraft will still take off if there is sufficient runway length available (the BFL can be considerably lower than the available airfield length). Also, Vmu is close to VR; hence, tail dragging is not likely. If an engine fails early enough, then a pilot has sufficient time to recognize the failure and abort the takeoff.

With more than two engines, the decision speed V1 is farther from the rotation speed VR. A pilot must remain alert as the aircraft speed approaches the decision speed V1 and must react quickly if an engine fails.

Figure 13.11. Balanced field length