It is defined such that it is related to the effective exhaust velocity by:
2.
Actual and effective exhaust velocity are the same in rocket engines not utilizing air.
3.
The effective exhaust velocity in units of m / s is also in reasonably common usage.
4.
However, the effective exhaust velocity allows for various losses, and notably, is reduced when operated within an atmosphere.
5.
For air-breathing engines the effective exhaust velocity is not physically meaningful, although it can be used for comparison purposes nevertheless.
6.
For air-breathing jet engines, particularly turbofans, the actual exhaust velocity and the effective exhaust velocity are different by orders of magnitude.
7.
This allows a better match between the airspeed and the exhaust speed, which saves energy / propellant and enormously increases the effective exhaust velocity while reducing the actual exhaust velocity.
8.
In practice the effective exhaust velocities of rockets varies but can be extremely high, ~ 4500 m / s, about 15 times the sea level speed of sound in air.
9.
The Tsiolkovsky rocket equation shows that for a rocket with a given empty mass and a given amount of fuel, the total change in velocity it can accomplish is proportional to the effective exhaust velocity.
10.
The values expressed in N�s / kg are not uncommonly seen and are numerically equal to the effective exhaust velocity in m / s ( from Newton's second law and the definition of the newton ).
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