Where are bellmouth inlet ducts typically found?

Bellmouth inlet ducts are primarily used in helicopter engines due to their specific design benefits suited for rotary-wing aircraft. These ducts facilitate a smooth airflow entering the engine, which is crucial for engine performance and efficiency in helicopters that often operate in varying altitudes and speeds. Their design helps to reduce turbulence and maintain a consistent air pressure as air enters the engine, which is essential for the unique operational characteristics of helicopters.

While commercial jet engines, small propeller aircraft, and military fighter jets also have inlets, the usage of bellmouth inlet ducts is less common in those applications. Instead, other types of inlet designs may be employed that are better suited to their operational requirements. The characteristics of helicopters, including their need for efficient power generation at different operational altitudes and speeds, make bellmouth inlet ducts a favorable choice for their engine designs.