The noise generated by supersonic-tip-speed propellers is a possible cabin environment problem for future airplanes powered by these propellers. Models of these types of propellers were previously tested for acoustics in the Lewis 8-by-6-foot wind tunnel. One of these propeller models, SR-3, has now been tested in flight on the Dryden JetStar airplane and preliminary noise data have been obtained. Preliminary comparisons of the maximum blade passing tone variation with helical tip Mach number taken in flight with those taken in the tunnel showed good agreement when corrected to the same test conditions. This indicated that the wind tunnel is a viable location for measuring the noise of these propeller models. Comparisons of the directivities at 0.6 and 0.7 axial Mach number showed reasonable agreement. At 0.7 and 0.8 axial Mach number the tunnel directivity fell off quicker towards the front than did the airplane data. A possible explanation for this is boundary layer refraction which could be different in the wind tunnel than in flight. This may indicate that some corrections should be applied to both the airplane and wind tunnel data at the forward angles. At the peak noise angle the boundary layer refraction does not appear to be significant and no correction appears necessary.

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High-speed turboprops offer an attractive candidate for future aircraft because of their high propulsive efficiency. However, one of the possible problems associated with these propellers is a high level at cruise that might create a cabin environment problem for future aircraft powered by these propellers. Models of these propellers have been tested for acoustics in the Lewis 8-by-6-ft wind tunnel and on the Dryden JetStar airplane. This paper shows comparisons between the airplane and wind tunnel data for the SR-6 propeller. The comparison of the maximum blade passing tone variation with helical tip Mach number taken in flight with that taken in the tunnel showed good agreement when corrected to the same test conditions. Directivity comparisons also showed fairly good agreement. These good comparisons indicate that the wind tunnel is a viable location for measuring the blade passage tone of these propellers.

AhstrnctFlyover measurements of the.airframe noise of AeroCommander , JetStar, CV-990, and R-747 aircraft are presented. Data a r e shown for both cruise and landing configurations. Correlations between airframe noise and aircraft parameters a r c developed and presented, The landing approach nirframe noise for the test aircraft was approximatcly 10 EPNdB below present FAA certification requirements.