The brake power (B.P.) of the engine is given by (where W = Brake load or dead load in newtons, l = Length of arm in metres, N = Speed of engine in r.p.m., S - Spring balance reading in newtons, D = Dia. of brake drum in metres, and d = Dia. of rope in metres)
The air standard efficiency ofan I.C. engine is given by (where r = Compression ratio, and Y = Ratio of specific heats)
The mechanical efficiency (Î·_{m}) of the engine is given by
If V_{1} is the jet velocity and V_{0} is the vehicle velocity, then the propulsive efficiency of a rocket is given by
If V_{1} is the jet velocity and V_{0} is the vehicle velocity, then propulsive efficiency of a turbo-jet engine is