As shown in V9.25 and Fig. P9.105, a spoiler (i.e., an upside-down airfoil) is mounted above the

Question:

As shown in V9.25 and Fig. P9.105, a spoiler (i.e., an upside-down airfoil) is mounted above the rear wheels of a race car to produce negative lift (i.e., downforce), thereby improving tractive force. The spoiler's airfoil is angled \(10^{\circ}\) with the race track and has lift and drag coefficient characteristics of Fig. 9.39. The race car is traveling at \(200 \mathrm{mph}\) in air at \(90^{\circ} \mathrm{F}\) and 14.72 psia.

(a) If the coefficient of friction between the wheels and pavement is 0.6, by how much would use of the spoiler increase the maximum tractive force that would be generated between the wheels and the track? Assume the airspeed past the spoiler equals the car speed and that the airfoil acts directly over the drive wheels.

(b) How much drag is added to the car with the use of the spoiler's airfoil?

Figure P9.105