Aerodynamic Drag Force and Power

The reason a vehicle needs so much more power at highway speed. rho is the mass air density (weight density / g), V the speed, Cd the shape drag coefficient (a modern car ~0.30, a pickup ~0.45, a semi ~0.6-0.8, a motorcycle+rider ~0.6, a flat plate ~1.28, a sphere ~0.47), A the frontal area; the power to overcome it is P = F V. A car at 70 mph, 24 ft^2 frontal, Cd 0.30 in standard air sees 90 lbf of drag and needs 16.8 hp (12.6 kW) just for the air - speed up to 80 and it jumps to 25 hp, the cube-law (80/70)^3 = 1.49 penalty that makes high-speed cruising thirsty. Aero drag only; rolling resistance, driveline loss, grade, and headwind are separate parts of the road load. A planning estimate; the manufacturer road-load data governs.

F = 1/2 rho V^2 Cd A; rho = (weight density)/g (g = 32.174 ft/s^2); V in ft/s (mph x 1.46667); P = F V; hp = F V / 550.

The aerodynamic drag equation F = 1/2 rho V^2 Cd A and the drag power P = F V (standard fluid mechanics; SAE road-load), by name.

The drag equation and drag power are standard fluid-mechanics results; the drag coefficient, frontal area, speed, and air density are the user's inputs.

Estimate. AHJ and licensed professional govern.

Field names used by the API: speed_mph, frontal_area_ft2, drag_coefficient, air_density_lb_ft3, drag_force_lbf, drag_power_hp

• Drag equation F = 1/2 rho V^2 Cd A, bluff body in steady incompressible airfluid mechanics
• Drag power P = F V; grows with the cube of speedSAE road-load
• Scope aero drag only; rolling resistance, driveline, grade, headwind are separatescope of this tile