Here's the author's disclaimer about the wind tunnel data, from Construction of Test Apparatus - Wind Tunnel (p.8):
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Upon calculating Reynold's number with respect to the length of the model truck, the flow was found to be laminar. In the real world, flow over a vehicle traveling at highwa speeds (around 55 mph) is turbulent. Therefore, turbulent flow was desired. However, after many failed attempts to change the cross-sectional area of the wind tunnel inlet, roughing up the surface of the model... and even attempting to speed up the single-speed motor, and consulting Dr. Said Dini of the Mechanical Engineering Department, it was concluded that this could not be done with this particular wind tunnel. Therefore, all drag coefficient results are for laminar flow.
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