EMD4543 Aircraft Propulsion

Thrust and Other Performance Parameter

The RB211-535E4, a typical high bypass-ratio

turbofan (Hill and Peterson, 1992).

𝐾. 𝐸.=

𝜂𝑝=

𝜂𝐸𝑛𝑒𝑟𝑔𝑦=

The Overall Engine Efficiency is given by:

𝜂𝑝 𝜂θ𝜂𝑂𝑣𝑒𝑟𝑎𝑙𝑙= =

Implications of propulsive efficiency for engine design

If we consider our expressions for thrust and propulsive efficiency together,

we see that

and

Also note that for

where is the inlet area of an engine, shown in.

The balance between propulsive efficiency and specific thrust (thrust per unit

mass flow) is shown in graph below:

Propulsive efficiency and specific thrust as a function of exhaust velocity

Implications of propulsive efficiency for engine design :

• Fighter (Supersonic) Aircraft:

Smaller inlet areas and higher thrust per unit mass flow

• Transport (Subsonic) Aircraft

Higher efficiency and fly at lower speeds usually employ engines with relatively larger inlet areas and lower thrust per unit mass flow

Propulsive efficiency comparison for

various gas turbine engine

configurations (Rolls-Royce, 1992)

The F-22 Raptor (Copyright 1999 by

Lockheed Martin).

The small inlet of one of the F-22 Raptor's two engines is

visible just below the cockpit indicating Design Point condition

at Supersonic Cruise

END