Flowfield and acoustic measurements from a model tiltrotor in hover

Rotor inflow aerodynamics and noise measurements were made on three configu rations of an 8% scale model of the XV-15 tiltrotor in hover: 1) single Iso lated rotor, 2) two rotors with no fuselage, and 3) complete tiltrotor airc raft. For the tiltrotor aircraft configuration and for the configuration of two rotors without the fuselage, the mean inflow velocity was higher at ps i = 270 deg compared with the rest of the rotor disk, leading to reduced bl ade angle of attack and blade loading in this region. This azimuthally vary ing blade loading caused an impulsive noise that radiated preferentially be hind the model. For the complete tiltrotor configuration, the turbulence in gested by the rotors was intermittent and depended on the instantaneous pos ition of the fountain now, which shifted from side to side across the longi tudinal plane of the model. The fountain turbulence had a higher velocity s cale, smaller length scale, and was closer to isotropic than the ingested a mbient turbulence. The tiltrotor configuration radiated less harmonic noise , but more broadband noise than the configuration with two rotors and no fu selage. Diagonal fences on the wings of the tiltrotor reduced the inflow tu rbulence intensity in the fountain region by a factor of about 3, and reduc ed the noise by 4.1 dBA behind the model. Scaling relations were derived to extrapolate the model measurements to the full-scale XV-15.