No abstract

Noise certification under FAR 36, Appendix F, requires the measurement of maximum A-weighted sound level during flyovers at maximum continuous power, 1000 ft above ground, at a sealevel airport. In order to investigate the effect of altitude and horsepower on sound-level measurements, tests on a Cessna 172 and Beech 33 were made at three airports having elevations of 42, 2350, and 6750 ft. Engine power was varied from approximately 50% of raged maximum continuous to the maximum available at the test altitude. The results for these two representative general aviation aircraft show that above approximately 65% power A-weighted sound level is essentially constant and independent of altitude, depending primarily on propeller tip helical Mach number. Noise certification of propeller-driven small aircraft can thus be reliably performed at a wide range of test sites irrespective of site elevation. [Work supported by FAA.]

A noise and performance comparison of these STOL airplane configurations is summarized. Aircraft were sized for a 2000-ft takeoff field length, 150 passengers, and a STOL range of 500 miles. A discussion of thrust augmentation ratios, airplane “thumb-print” sizing, thrust requirements, thrust lapse rates, static test configurations, 500-ft SL noise comparisons, and noise “footprints” is presented for each concept. Each concept originally showed approximately equal noise levels on a static test stand but more intensive test work shows that the augmentor holds superior potential for low noise.

No abstract

The business jet fleet registered in the United States as of July 1975 consisted of approximately 1500 aircraft, of which only 10 percent were powered by new, medium bypass ratio turbofan engines, and 75 percent by turbojet engines. A review of the noise reduction potential for existing aircraft has been completed on a model-by-model basis. An optimal combination of flight operational procedures and noise suppression techniques for existing engines has been derived for each aircraft model to minimize noise levels at FAR 36 certification measurement locations, consistent with existing noise control technology and operating economics. The alternative of new engine installations has also been evaluated. Comparisons between noise levels for modified and unmodified aircraft are presented.