Jet Engine Simulator

Tools · Propulsion

Jet thrust calculator

Enter the airflow, the flight speed and the exhaust velocity to get the thrust, then add the fuel flow for the specific fuel consumption (TSFC) and the propulsive efficiency.

Go to the calculatorSee thrust on a running engine

Calculator

kg/s
Air entering the engine each second
m/s
0 on a test stand; 250 m/s ≈ 486 knots
m/s
Speed of the jet leaving the nozzle
kg/s
Optional: for TSFC
kPa
Equal to ambient for a fully expanded nozzle
kPa
Sea level: 101.325 kPa
m²
Only matters when Pe ≠ Pa
Thrust30.45 kN6,845 lbf · 3,105 kgf
Fuel consumption (TSFC)24.6 mg/N·s0.870 lb/lbf·h
Momentum thrust30.45 kN
Pressure thrust0.00 kN
Specific thrust, F/ṁ609 N·s/kg
Fuel–air ratio0.0150
Propulsive efficiencyneeds a flight speed above 0
Thrust power, F × V00 when standing still

The thrust equation

F = (ṁ + ṁf) · Ve − ṁ · V0 + (Pe − Pa) · AeThe first part is momentum thrust: the engine pushes air and fuel out faster than the air came in. The term ṁ·V0 is ram drag, the momentum the air already had. The last part is pressure thrust, which appears when the nozzle cannot expand the gas all the way down to ambient pressure, as in a choked convergent nozzle.

On a test stand (V0 = 0) there is no ram drag, so the same engine always shows more thrust on the stand than in flight. With the default numbers, 50 kg/s of air leaving at 600 m/s gives 30.45 kN. Fly the same engine at 250 m/s with the same exhaust speed and the thrust falls to 17.95 kN.

Specific fuel consumption (TSFC)

TSFC = ṁf / FFuel burned per second for each newton of thrust. Lower is better. 1 lb/(lbf·h) = 28.33 mg/(N·s).

Turbojets typically burn somewhere around 0.8 to 1.0 lb/(lbf·h) without afterburner, and high-bypass turbofans far less. In the game's standard dyno test (at 70 % power) the Training turbojet burns 25.0 mg/(N·s), about 0.88 lb/(lbf·h), and the Airliner turbofan 11.2 mg/(N·s), about 0.39 lb/(lbf·h). The default inputs here, 0.75 kg/s of fuel for 30.45 kN, work out to 24.6 mg/(N·s).

Propulsive efficiency

ηp = 2 · V0 / (V0 + Ve)The share of the jet's energy that actually pushes the aircraft. The rest is left behind as a fast-moving wake.

At 250 m/s with a 600 m/s jet, ηp is 58.8 %. Bring the jet speed closer to the flight speed (by moving more air more slowly) and ηp rises. That is the whole idea behind turbofans and turboprops.

Assumptions and limits

This is the one-dimensional momentum balance for a single jet with uniform exit conditions. For a turbofan, work out each stream (core and bypass) separately and add the thrusts. Real nozzles lose a little velocity to friction and divergence, and installed thrust is lower again because of inlet and nacelle drag.