Sky writing

An airplane flying horizontally at a constant speed of 130 km/hr is towing a thin, plastic, advertising sign that has a length of 30 m and a height of 2 m.
a) Determine the drag force on the sign.
b) Determine the location of transition to turbulence on the sign. Then, estimate the wall shear stress, the disturbance thickness, the displacement thickness and the momentum thickness of the boundary layers at the downstream end of the sign.
c) If the specific consumption of the airplane fuel is 0.8×10-6 kg/J, the specific gravity of the fuel is 0.97, the price of the fuel is 0.95 $/litre and the efficiency of the engine is 0.73, calculate the cost per hour for towing the sign, in addition to the cost of flying the airplane itself.