Drag Force Exerted on an 18-Wheeler
without Air Deflector

Drag Force Exerted on an 18-Wheeler
with Air Deflector

The drag force is given by

     D = C_D ρAV²/2

where the density of air (ρ) is 0.00238 slugs/ft³ from the tables in the Appendix. It is assumed that the average speed of the 18-wheeler is 65 mph, and its frontal area is 100 ft².

The drag exerted on the 18-wheeler without the air deflector is calculated to be

     D = (0.95)(0.00238)(100)(65*5,280/3,600)²/2
         = 1,027 lb_f

The drag exerted on the 18-wheeler with the air deflector is calculated to be

     D = (0.75)(0.00238)(100)(65*5,280/3,600)²/2
         = 811 lb_f

By installing the air deflector, there is a 21% reduction in drag. Hence, the company will save money on fuel consumption cost.