Measured noise of model fan-under-wing and fan-on-flap jet flap configurations
National Aeronautics and Space Administration, 1972 - Transportation - 55 pages
Noise measurements were made on two jet flap systems proposed for STOL aircraft. In one case a 14.0-cm- (5.5-in.-) diameter fan was mounted under the wing such that the exhaust impinged on downwardly deflected flap segments. In the other case, the fan was located on the upper surface of the flap such that fan and flap moved as a unit, with no exhaust impingement. Results for takeoff and approach fan speeds and flap deflections were used to estimate STOL airplane perceived noise levels. Internally generated noise directivity corresponded with fan axis orientation for the fan-on-flap, but no consistent redirection of internal noise was observed with changes in flap angle for the fan-under-wing. With the fan-on-flap arrangement, the wing shielded some fan inlet noise from the ground. Since no impingement of the exhaust on solid surfaces occurred, the external noise was jet noise alone. In contrast, for the fan-under-wing, the jet/flap interaction noise dominated the external noise except at angles near the jet axis even with no flap deflection. If internal noise is reduced by fan design and acoustic treatment, the jet/flap interaction noise will dominate.
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100-percent speed 4.57-meter radius 76 percent 76-percent speed aft angles angle in flyover angle in sideline angle of attack Angle relative approach conditions blade passage frequency BLOWN FLAP combination tones decibel deflected flap Estimated perceived noise exhaust jet exhaust velocities external interaction noise fan and flap fan axis Fan speed fan-on-flap arrangement fan-on-flap configuration fan-under-wing arrangement Figure 15 figure 17 figure 20 final jet direction flap angle flap deflection flap surfaces flyover plane frequency scaling function of angle internal noise internally generated noise jet flap noise jet flap systems jet noise jet/flap interaction noise level of external level of jet meters 500 ft Microphone angles noise data noise directivity Noise measurements noise on 4.57-meter overall sound pressure Perceived noise estimates perceived noise levels PNdB radius in flyover shielded shown in figure sideline plane Simulated takeoff sound pressure level STOL takeoff and approach thrust turbine noise wing undersurface