Question

Compute the landing ground roll for the CJ-1, assuming the following landing configuration: • CLmax = 2.4 • Using 100% flap deflection and spoilers at touch-down: • Lift coefficient = 0.4 • Drag coefficient =0.20 • Runway braking friction coefficient = 0.30

CJ-1: Wingspan = 53.3ft, wing are = 138ft^2, Normal gross weight = 19815lb, Fuel capacity: 119 gal of kerosen, power plant: two turbofan engines of 3650lb thrust each at sea level, specific fuel consumption = 0.6lb of fuel/(lb Thrust)(h), parasite drag coefficeint CD,0 = 0.02, Oswald efficiency factor e = 0.81

Answer 1

consider the free body diagram, The forces that are acting on the plane are aerodynamic lift and drag (L and D), the thrust force (T), normal force from ground (R) and friction force (R).
summing up the forces in vertical direction,
L + R - W = 0
R = W - L

summing up the forces in horizontal direction,
T - D - R = ma
T - D - (W - L) = ma
rewriting the above equation by substituting m= W/g and a = dV/dt

Assumptions
;
Final velocity is zero;
T = 0, during landing

V_TD = 269.236 ft/sec

Assume L/D = 8

Landing ground roll is given by

landing ground roll = S = 5489.68 feet