Learjet 25D Jet-Noise Flyover Measurements: Uncertainty Analysis

Acoustic data acquired in a well-instrumented flight test, utilizing a Learjet 25D aircraft, and a ground-based scale-model test facility are further analyzed. The aircraft's CJ610-8A engines produce a noise signature that is dominated by jet noise, making it an ideal candidate for studies concerning the airport-noise impact during takeoff operations of future supersonic business jets. The flyover acoustics, aircraft position, engine conditions, atmospheric data, and wind limits were recorded. In this paper, computed one-third-octave source spectra from the flight- and scale-model-test data are compared. Flyover effective perceived noise levels were computed for a representative future takeoff trajectory, with estimated uncertainties, using the flight and scale-model data. The scale-model based effective perceived noise levels fall within the uncertainty of the corresponding flight values. The difference between the flight and scale-model levels decreases as the jet-nozzle pressure ratio increases, i.e, as the propulsion noise becomes increasingly dominated by the jet-noise component. The purpose of the work is to ultimately enable improvements to system studies of future commercial supersonic aircraft by reducing the uncertainties in noise prediction models. In particular, the near term aim is to establish and reduce the uncertainty in the rig-to-flight transformation, which is a crucial part in jet-noise prediction methodology.