HISTORICAL DRAWING · 1939 (filed 1937)

Turbojet flow path

What momentum thrust follows from assumed inlet and exit conditions?

F. Whittle, US 2,168,726 "Propulsion of Aircraft and Gas Turbines", sheet 1 (turbojet cross-section). Used in place of GB 347,206 (see below)
F. Whittle, US 2,168,726 "Propulsion of Aircraft and Gas Turbines", sheet 1 (turbojet cross-section). Used in place of GB 347,206 (see below). View the original source and attribution ↗

A contemporary sketch model

Every number below is a modern illustrative assumption. The historical drawing supplies a question; the source model is an exercise in reasoning about it.

airflow = 10 kg/s "Illustrative inlet air mass flow"
fuelFlow = 0.2 kg/s "Illustrative fuel mass flow"
flightSpeed = 100 m/s
exitSpeed = 450 m/s in 350..550 "Assumed exhaust speed"
pressureThrust = 0 N "Assumed pressure-matched exhaust"
thrust := (airflow+fuelFlow)*exitSpeed-airflow*flightSpeed+pressureThrust [N]
check thrustBudget: thrust >= 3500 N
sweep Exhaust: exitSpeed = 350, 450, 550 m/s

Model limits

An algebraic momentum balance; no compressor/turbine matching, combustion, thermal cycle or CFD.

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