White Paper: Test & Measurement

Tiltrotor Acoustic Data Acquisition through 130B40

SPONSORED BY:

The fluctuating pressures that act on the surfaces of flight vehicles due to propulsion systems and movable surface flows tend to induce oscillatory motions of the fuselage surfaces. These vibrations produce acoustic noise inside the aircraft. Too high a noise level can have adverse effects on the crew and passengers. For such vehicles to be working successfully and commercially viable, the interior noise levels must be acceptable to civil passengers.

Structural-acoustic measurements were taken aboard an existing tiltrotor aircraft to better investigate the physical mechanisms that originate the interior noise in the tiltrotor. The transmission mechanism through the fuselage is responsible for the vibration and noise level, which can be measured inside, and for identifying potential solutions for their mitigation.

The in-flight measurements have been first carried out on a flying Leonardo Helicopter tiltrotor, undergoing certification for use in the civil sphere. All photos showing the tiltrotor are property of Leonardo Helicopters and provided as a courtesy.

The sources that induce pressure loads on the external fuselage of the tiltrotor are essential of two types: a rotor noise due to the presence of the large rotors located at the wingtips and the boundary layer noise. Propeller engines generate a noise field that is highly tonal in frequency content and highly directional in spatial distribution. In high-speed flight, boundary layer noise can be a significant part of the noise perceived in the cabin. The obtained results are interesting and promising: these measurement procedures could also be addressed to more traditional airplanes and, possibly, to ground vehicles for characterizing, from this point of view, different transport systems.

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