Question

Find liftoff distance for an aircraft which has weight of 20kN and thrust of 8kN. Consider thrust is much larger than drag and friction parameters. Consider maximum lift coefficient of 1.1, reference area of 12m^2 and sea-level density.

(a) 454m

(b) 1000m

(c) 12m

(d) 12.12m

I got this question during an interview.

I would like to ask this question from Flight Mechanics in portion Performance and Flight Mechanics of Aircraft Design

Answer 1

Correct answer is (a) 454m

To elaborate: Given, Weight W = 20KN, Density d = 1.225 kg/m^3, maximum lift coefficient CL = 1.1, reference area S = 12 m^2, Thrust T = 8KN

Liftoff distance = 1.44*W^2/ (g*d*S*CL*T) = 1.44*(20000^2) / (9.81*1.225*1.1*12*8000) = 453.89 = 454m.