In a turboshaft engine, the nozzle exhaust air velocity is the speed at which the exhaust gases exit the engine nozzle. Turboshaft engines are commonly used in helicopters and some fixed-wing aircraft. The nozzle in a turboshaft engine is designed to accelerate and direct the exhaust gases to generate thrust or provide mechanical power to drive a rotor.
The relationship between the nozzle inlet and exit air velocities can be expressed using the continuity equation, derived from the conservation of mass.
The continuity equation is based on the principle of mass conservation, and Bernoulli’s equation expresses the conservation of energy.
The continuity equation is given by:
where:
-  and  are the cross-sectional areas at the nozzle entrance and exit, respectively,
-  and  are the velocities at the nozzle entrance and exit, respectively.
which gives
where,
- A1Â is the Area of Nozzle Inlet in m2
- A2Â is the Area of Nozzle Exhaust in m2
- V1Â is the Inlet air Velocity in m/s
- V2Â is the Exhaust Air Velocity in m/s