ANALYTICAL PREDICTION AND FLIGHT TEST EVALUATION OF BELL ACAP HELICOPTER CABIN NOISE

The application of Statistical Energy Analysis (SEA) approach to Bell ACAP (Advanced Composite Airframe Program) helicopter for cabin noise modeling and prediction is discussed. The SEA model of the composite airframe is based on the following major structural sections of the helicopter; roof, bulkheads and frames, side panels, internal acoustic spaces, floor, and external acoustic spaces. Each of these sections is substructured into smaller parts, and the degree of resolution required is defined by its proximity to the transmission gearbox attachment points. The substructures are further subdivided into subsystems which represent mode group types, such as bending or in-plane modes. Ground and flight tests conducted to obtain acoustic and vibration data for validating the SEA prediction model are described. Good agreement between the predicted and flight test data showed that the SEA technique can be used to model and predict cabin noise of an all composite airframe. The flight test noise data showed that the ACAP helicopter cabin noise is dominated by the main transmission gear box. There was no local amplification of noise observed in the ACAP cockpit.