Numerical and experimental study on inflow rates for ground testing of fire extinguishing agent concentration in helicopter engine nacelles

The fire extinguishing agent concentration test in civil helicopter engine nacelles is a critical airworthiness verification test. Such testing has long relied on flight tests, which face challenges including high risks, high flight test costs, substantial modifications, and prolonged cycles. Addressing the development of a domestic helicopter model, this study pioneered a ground simulation test in China. By comparing and calibrating the input airflow values for ground simulation against flight test data, the test conditions for agent concentration were established, ultimately demonstrating airworthiness compliance through ground-based testing. The ground simulation accurately replicated the in-flight airflow and temperature environment of the helicopter. It determined the pitot tube measurement method and airflow calculation approach, providing precise input conditions for the ground test. Based on flight test data, the simulation identified the maximum critical operating conditions encountered during flight tests, thereby defining the input airflow parameters for evaluating the fire extinguishing agent distribution in ground-based testing.