Compute the acceleration on the aircraft during the takeoff

Compute the acceleration on the aircraft during the takeoff roll (ft/s2).

Givens:
Gross Weight = 350,000 pounds
Average Drag = 15,000 pounds
Average Thrust = 90,000 pounds
Assume No lift on wings until Rotation
Runway Surface, Dry concrete, Use Table 1.2
Note: Use \"g\" = 32.2 ft/s2

Solution

F=m*a

We need to compute,a. Therefore, a =F/m

We need to find, F and m with the help of above data. Let us compute m first,

W=m.g

m=W/g = 350,000/32.2 = 10869.56 slugs

The force will be given as, F = T - D- f

Here, T is thrust, D is drag and f is frictional force. T and D are known. f has to be calculated.

Use equation 1.11 shown in the snapshot,

f= u * N   = 0.02 * 350000 = 7000 pounds

Therefore, F = (90000- 15000- 7000)/10869.56 = 68000/10869.56

= 6.26 ft/s2

Therefore, the first option is correct.