TF-34 turbofan quiet engine study

A study of high bypass turbofan engines in heavily sound-suppressed nacelles based on the TF-34 engine. The four-engine noise objective was 95 PNdb at four locations typical of takeoff and landing. Three engines were studied; these had fan pressure ratios, bypass ratios, and fan tip speeds respectively of 1.48/6.5/404 m/sec (1327 ft/sec), 1.25/13/305 (1000), 1.25/13/366(1200). The bypass 13 engines had a variable pitch fan, direct- and gear-driven. Noise suppressive treatment was identified which met 95 PNdb objective except for sideline liftoff at 6.5 bypass, full power, which was 2 PNdb noisier; at 90% power, 95 PNdb was achieved.