Acoustic testing techniques for replicating in-flight dynamic loads

Modern weapon systems used on combat aircrafts have complex electronic assemblies that are required to operate in challenging dynamic environments throughout their life cycle. Among the various sources of excitation, aerodynamic noise is considered most significant. The paper presents vibroacoustic measurements from captive flight, and attempts to replicate them in acoustic laboratory testing. The question of interest is which testing method, in terms of configuration and control scheme, is the most adequate to accurately simulate the vibratory response of inner assemblies to flight loads. The paper examines acoustic test methods in a reverberant chamber. The tested article is a subsystem of a weapon system that includes electrical assemblies, integrated inside a structural shell. Two test configurations are compared-'enclosed', in which the subsystem is tested inside its structural shell, and 'exposed', in which the subsystem is directly exposed to acoustic excitation. Acceleration measurements show that when excited by in-flight acoustic levels, the acceleration responses of the exposed subsystem, are significantly lower than those measured in flight. For the enclosed configuration, although the acoustic levels inside the envelope are attenuated by the structure, the resulting accelerations are significantly higher and closer to those from flight.