Jet Propulsion/Performance

Aircraft Performance

Range

The Breguet Range Equation gives the range achieved by a vehicle. For a constant L/D ratio of the aircraft

$Range=u{I}_{sp}\left(\frac{L}{D}\right)\ln \left(\frac{W_{initial}}{W_{final}}\right)$

where

R = distance flown (m)

u = velocity (m/s)

I_sp = specific impulse (s)

L/D = lift-to-drag ratio (dimensionless)

W_initial = gross aircraft weight at the start of cruise (kg)

W_final = gross weight at the end of cruise (kg)

Example

For an aircraft with 50% fuel, velocity of 600 m/s, an L/d of 10 and engines with a specific impulse of 3000 the range is:

$R=(600m/s)(3000s)(10)\ln (2)=12,477km$

Engine Performance

Engine Performance describes th most important attributes of the engine for the aircraft. These are primarily the thrust available to propel the aircraft, and efficency of fuel consumption.

Available thrust is usually quoted in kN or lbs, fuel efficiency is usually quoted as a specific fuel consumption

$sfc=\frac{fuelflow}{thrust}$

sfc can only be directly compared at a specific flight condition, usually a nominal cruise condition.