Question

As shown in the Video and in the figure below, a spoiler is used on race cars to produce a negative lift, thereby giving a better tractive force. The lift coefficient for the airfoil shown is CL -1.1, and the coefficient of friction between the wheels and the pavement is 0.60. At a speed of 200 mph, by how much would use of the spoiler increase the maximum tractive force that could be generated between the wheels and ground? Assume the air speed past the spoiler equals the car speed and that the airfoil acts directly over the drive wheels b spoiler length 3.9ft Spoiler 1.3ft 200mph lb

Answer 1

Solution: Convert speed from mph to ft/s: v = 200 mph 1466 = 200 mp 1 mph = 293.334 ft/s = 200 mph 1.46667 ft/s Refer to table,"Properties of air" to obtain the density of air: p=0.0023769 slug/ft Calculate the lift force exerted on the car: F, = C2P Av2 ==(1.1)(0.0023769)(1.3x3.9)(293.334)? = 570.3039 lb UN, = F Calculate the maximum tractive force: F = uN = uF; = (0.6) (570.3039) F = 342.182 lb