How much horsepower?

[MolaKule]

This is a question as to how much engine or electric motor Horsepower it takes to overcome aerodynamic drag on a vehicle.

F (in Newtons) = 1/2 x rho x CdragA x V^2.

rho is air density = 1.2 kg/m^3,

CdragA = 0.58 m^2 for our example Prius,

Vehicle speed V is 70 mph.

Power (in Watts) = F x V.

How much mechanical Horsepower is needed to overcome the aerodynamic drag at 70 mph?

 

[Cujet]

I come up with just over 14HP to overcome aero drag. Rolling resistance, drive train alternator/AC (heat/elec pwr/AC, etc) take their toll too.

Guess, maybe 3HP for accessories
Guess rolling resistance could be 10HP
Drivetrain losses exist too and I guess the prius might have less than 10% losses

So overall, guessing just under 30HP

The prius engine is 41% Thermally efficient at its best. Maybe 40% is more likely at 70. Meaning a BSFC of 235g/kWh (40%) by memory. (about what my Lister Diesels can achieve) and a MPG of 50 at 70MPH. Prob not too far off.

 

[MolaKule]

Horsepower needed to overcome aerodynamic drag is the only answer needed.

 

[Cujet]

Horsepower needed to overcome aerodynamic drag is the only answer needed.

14

 

[Rand]

edit:
10881watts or 14.59hp