A flight test program utilizing a JT15D-1 turbofan engine has been conducted with the objectives of studying flight effects on fan noise and evaluating the simulation effectiveness of both a wind tunnel and a static test configuration that incorporated an inlet control device (ICD). In conjunction with synchronized laser-radar tracking and meteorological profile information, data obtained from a linear array of ground microphones was narrowband-analyzed and ensemble-averaged to yield highly accurate far-field flight acoustic results. Utilizing appropriate corrections, flight. wind tunnel, and static acoustic data were normalized to a static-equivalent, 100-foot radius, lossless reference condition. Data comparisons showed that both the static test with ICD and wind tunnel were generally very effective in simulating flight blade-passage-frequency (BPF) noise levels. However, differences were observed in broadband noise levels and in the details of the multiple-pure-tone harmonics.
The Army is considering the use of multiengine heavy-lift helicopters in its future aviation program. The engine load-sharing characteristics of the CH-54A Skycrane helicopter were investigated to determine if unequal load sharing would be a significant problem. Torque-split samples were selected from 67 hours of flight-load data. The parameters measured and recorded on oscillograph records were airspeed, altitude, engine gas producer rpm, engine torque, main rotor rpm, vertical acceleration at aircraft center of gravity, and outside air temperature. The gross weight at takeoff and landing and the barometric pressure were measured and recorded as supplemental data. The data were presented in a series of frequency-of-occurrence graphs; variation in torque splits was indicated with the other measured parameters. The analysis of the data indicates that the engine load splitting is significant at takeoff and landing and should be investigated further. u.
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