The design of the inlet for a ramjet engine is a critical aspect of optimizing its performance. Ramjets operate at supersonic speeds and rely on efficient air intake to achieve combustion. The inlet is designed to slow down and compress the incoming supersonic airflow, preparing it for combustion within the engine.
The cross-sectional area of the nozzle inlet is an important parameter, and it is typically designed to accommodate the incoming airflow and create the conditions necessary for efficient combustion. The relationship between the cross-sectional areas and velocities at the inlet and exit for a ramjet engine can be described by the continuity equation:
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