Question

A flying wing has a planform area of 3700 ft², a root chord at the airplane centerline of 34 ft, an overall taper ratio of 0.275, and a span of 170 ft. The average weighted airfoil thickness ratio is 10.2% and the wing has 36 degrees of sweepback at the 25% chordline. The air- plane is cruising at a pressure altitude of 17,000 ft on a standard day with a wing loading of 40 lb/ft². The cruise Mach number is 0.30. Determine the following:

(a) skin-friction drag coefficient (assume a spray-painted surface)

(b) pressure drag coefficient

(c) induced drag coefficient

(d) total drag coefficient

(e) total drag in pounds

Remember that a wing has both upper and lower surfaces exposed to the flow. Use the appropriate skin friction coefficient equation (Chp 4) that would include transition from laminar to turbulent; assume Re,trans = 500,000. If the surface is fully-rough, then consult 5.20 on pg 266. Form drag is based on the fineness ratio charts. The Oswald efficiency factor is high for wings—assume e = 0.95.

Answer 1

(A).Skin-friction drag coefficient

F=C_fxAxV²/2

F=0.0596x760x3700

F=269952pounds

Skin-friction drag coefficient(spray-painted surface) F=269952

(b) pressure drag coefficient.

C_{d p}=L/1/2V²S

C_{d p}=17000/1/2x0.95x40²x500000

C_{d p}=4.47x10^-5

pressure drag coefficient C_{d p}=4.47x10^-5

(c) induced drag coefficient.

C_di=C_L² /1/2xV²xb²

C_di=(0.30)²/0.5x0.95x40²xx170²

C_di=6.51x10^-9

induced drag coefficient C_di=6.51x10^-9

(d) total drag coefficient.

C_dt=pressure drag coefficient C_{d p}X induced drag coefficient C_di

C_dt=4.47x10^-5X6.51x10^-9

C_dt=29.099X10^-14

total drag coefficient C_dt=29.099X10^-14

(e) total drag in pounds

D_t=269952pounds