Section 11.3.1 derives the associated governing equations to compute the TOFL. Equations 11.2 and 11.4 give:

0

where average acceleration:

a¯ = [(T − D) − µ(W − L)]g/ W

= g(T/ W)[1 − D/ T − µW/ T + µL/ T] = g[(T/ W − µ) − (L/ W)(D/L − µ)]

Values of the parameters are at 0.7 of the velocity of the segment.

Equation 13.1 now can be written separately for each segment and then equated for the BFL. The average acceleration a¯ is of the following segment:

The average acceleration is at 0.7 of the velocity interval and can be written in coefficient form as follows (in SI units, g is omitted):

The value of the friction coefficient µ on the hard runway surface is taken as µ = 0.03 and at braking as µB = 0.3 to 0.5 (for a Bizjet, it is 0.4). Thrust-loading (T/W) is obtained from the sizing exercise.

Let Vave be the average velocity between the initial velocity Vi and the final velocity Vf. Then, the ground distance covered:

The aircraft speed gain continues during the rotational (VR) and flares out to V2. BLF is established at V2 with one engine inoperative. Therefore, only a proper choice of the decision speed V1 gives the BFL. A number of iterations may be required to arrive at the proper V1, as shown in the coursework example in Section 13.5.

13.4.2 Landing Performance

Computation of the LFL uses similar equations as for computing the TOFL; the difference is that a landing encounters deceleration (i.e., negative acceleration). Values of the friction coefficient, µ, vary when the main wheels followed by the nose wheel touch down. The brakes are applied after the nose wheel touches down (typically 2 s after touchdown). Considerable heat is generated at full braking and may pose a fire hazard. If the brake parachutes are deployed, the drag of the parachute is accounted for in the deceleration. With a thrust reverser, the negative thrust must be considered a decelerating force. With full flaps extended and spoilers activated, aircraft drag is substantially higher than at takeoff.