TRADE OF VEHICLE BODY REPAIR - eCollege

Module 3– Unit 4
Aerodynamic drag increases with speed; thus if the speed of a
vehicle is doubled, the corresponding engine power must be
increased by eight times. Engineers express the magnitude of
aerodynamic drag using the drag coefficient Cd. The coefficient
expresses the aerodynamic efficiency of the vehicle: the smaller the
value of the coefficient, the smaller the aerodynamic drag.
Figure 15 illustrates the improvements in aerodynamic drag
coefficient achieved by alterations to the shape of vehicles. Over the
years, the value Cd has been reduced roughly as follows:
1910 0.95 1960 0.40
1920 0.82 1970 0.36
1930 0.56 1980 0.30
1940 0.45 1990 0.22
1950 0.42 1993 0.20 (probable)
Figure 15: Theoretical Drag Curves
Theoretical drag curves for four types of vehicle, all reduced for
comparison purposes to a …… section of 2m². Since air resistance
increases in proportion to the square of the speed, a truck with Cd
1.0 requires 35 bhp at 100km/h, whereas a coupé with Cd 0.2
requires only 7bhp.
Vehicle Body Repairs - Phase 2 31