Question

5. Consider an airplane with wingspan 40 ft, wing area 250 ft2 , and weight 12,000 lb. Assume that the Oswald efficiency factor is 0.9. The airplane is flying at a velocity of 250 mph at a standard altitude of 5000 ft. Calculate the airplane drag due to lift.

Answer 1

Given,

b = 40 ft = 12.192 m

S = 250 ft² = 23.2258 m²

W = 12000 lb = 53378.66 N

e = 0.9

V = 250 mph = 111.76 m/s

h = 5000 ft = 1524 m

The density ratio of air at height of 1524 m is 0.8617, while its density at sea level is 1.225 kg/m³

Therefore density of air at 1524 m is

= 1.225 * 0.8617 = 1.055 kg/m³

We know induced drag is given by

                                                            ......(i)

AR = aspect ratio =

From (i)

Now,

Drag induced due to lift is given by

This is drag induced only due to lift.

Actual drag will be more if zero-lift drag is taken into consideration.