[size=4]

Maximum Speed

[/size]

Power = Force * Velocity

Drag ~ constant * Velocity^2

Force = mass * acceleration

At maximum speed there is acceleration so sum of forces = 0

Total Force = 0

(Power / Velocity) - (Constant * Velocity^2) = 0

Power / Velocity = Constant * Velocity^2

Power = Constant * Velocity^3

The constant value, k varies from aircraft to aircraft and is a measure of how aerodynamic the airframe is.

Lets take an example.

Supermarine Spitfire Mk IA

Power = 1030hp

Maximum Speed = 571 kph

1030 ^1/3 (cube root) / 571 = 0.01768

Now to find out how fast it goes if we have 1185hp(Mk VC)

(1185 ^ 1/3) / 0.01768 = 598kph

The actual figure for Spitfire Mk VC is 602kph, only slightly different from predicted result.

Spitfire Mk XIV

Power = 2050hp

maximum theoretical speed = 718kph

Actual maximum speed = 721kph.

Its a quick and easy way of calculating maximum speed for different powerplants.