Drag Coefficient, C D
DA =
Drag force
Density of Air, ρ
Eqn. 4-2 Air pressure
Frontal area of vehicle Density of Vehicle Drag air velocity coefficient Eqn. 4-4
From: /ev/handbook/aerodynamics.html
Figure 4.20
2
Drag Power
Drag force, lbf
Example Problem #1
Velocity, ft/sec
n
PD = D A ⋅V 1hp ft PD = (lbf ) ⋅ ft ⋅ lbf sec 550 sec2
Road Loads Chapter 4 – Road Loads
n n n n
Aerodynamic drag (in –X direction) Aerodynamic lift (in –Z direction) Tire rolling resistance Road gradient (hills)
Drag Coefficient, C D
Typical Drag Coefficients
Drag Coefficients Cd for a range of Vehicles Average 1975 U.S. Estate Wagon 0.60 Average 1979 U.S. Car 0.48 GM 1-Ton full size van 0.47 Average 1987 U.S. Car 0.37 Average 1992 U.S. Car 0.33 Chrysler T-115 1990 Minivan 0.32 1986 Subaru XT Coupe 0.31 Best 1993 U.S. Sedan 0.29 General Motors Electric Impact 0.19 GM Sunraycer Solar Car 0.13
D ⋅V = A hp 550
Estimate the drag force and the drag power required on a GM Electric Impact vehicle at
¡
60 mph (97 kph)
What is the “equation” when DA in lbf, V in mph and PD in hp? What is the “equation” when DA in N, V in kph and PD in kW?
2 2
36.0 ft
2 2
3.25 m 2 2.97 m 2.30 m 2 2.01 m 2 1.80 m 1.71 m 2 1.64 m
2 2
35.0 ft 2 32.0 ft 24.7 ft 2 21.6 ft 2 19.4 ft 18.4 ft 2 17.6 ft
2 2
Track
From: /ev/handbook/aerodynamics.html
3
Other Aerodynamic Effects
4
1
Area of Vehicle, A
For passenger cars, A ~ 0.9 * Height * Track Height
(Bosch Automotive Handbook, p. 338)
Typical Frontal Areas
Vehicle GM 1-Ton full size van Ford Minivan Chrysler Minivan Typical U.S. Sedan 5 passenger Volvo ECC 1991 Honda Civic DX GM Experimental Ultralite Renault VESTA II Frontal Area 3.35 m
Example Problem #2
n
Aerodynamic Lift and Drag
Estimate the drag force and the drag power required on my ’96 Ranger at
¡ ¡ ¡
30 mph (48 kph) 60 mph (97 kph) 75 mph (120 kph)
1 ρV 2CD A 2
519 o F Pr ρ = 0 .00236 o 29 .92 inHg 460 F + Tr
lbf ⋅ sec2 ft 4
Air temperature
ρ = 1 .202
kg m3
(Bosch Automotive Handbook, p. 339)