Wind tunnel experiments were conducted to quantify the interactional aerodynamic effects between an articulated rotor and a ~eometricslly idealized, but realistic, helicopter fuselage shape. Tests were conducted on the isolated . fuselage, isolated rotor, and on the rotor and fuselage combination. Independent strain-gauge halanee loads were acquired for the rotor and the fuselage, along with steady and unsteady pressure measurements on the fuselage. These data were obtained for various combinations of advance ratio, shaft till, and rotor thrust. The results show that the rotor wake produces fairly large effects on the mean fuselage loads and pressure distributions. These loads were very sensitive to the flight condition, but quickly decreased with increasing advance ratio. An idealized wake skew angle was found to be an effective parameter governing the magnitude of these mean interaclional loads. Unsteady pressure fluctuations due to blade passage and close wake interactions were clearly the most dominant form of loading on the fuselage. The magnitude of the unsteady loads was found to be primarily a function of rotor thrust and, except in regions of close or direct wake impingement on the fuselage, were relatively independent of advance ratio. The results also show that when operating at low advance ratio, the presence of the fuselage produces both a moderate increase in rotor thrust and a decrease in power relative to the isolated rotor performance.
NotationA = Rotor disk area, .rrR2, ft2 b = Number of blades c = lade chord,$ CL, = Fuselage lift coefficient in wind-axis, L/I(q,SI) CM, = Fuselage moment coefficient in wind-axis, M,l(q,S,L) C, = Time averaged pressurc coefficient, ( pp,)lq, C; = Time averaged pressure coefficient, 100(pp,)l (LoQ2R2) ~z ,~-~~ , C; = Unsteady pressure coefficient, 100(pUp,)l (I oQ2R2) C, = &tor thrust coefficient, TI(pn2R4) Dl, = Rotor hub effective diameter, ft D = Fuselage maximum diameter, ft L = Fuselage length, ft Lf = Fuselage lift in wind-axis, Ibf Mf = Fuselage moment in wind-axis, ft.lb p = Time averaged static pressure, lbflft2 p" = Unsteady component of unsteady pressure, lbflft2 -Presenled at the 45th Annual Forum of the American Helicopter Society, Boston, Mass. May 22-24, 1989. 4-= Free stream dynamic pressure, + p E , lbflft2 Q = Rotor torque, ft.lb R = Rotor radius, ft Sf = Maximum fuselage cross-sectional area, ft2 T = Rotor thrust, lbf V, = Tunnel free-stream velocity, ftls XI, = Distance of hub aft of fuselage nose, ft X, = Distance aft of fuselage nose, ft a, = Shaft tilt angle (positive aft), deg = Collective pitch angle, deg p = Air density, slugslfi3 u = Rotor solidity, bclnR JI = Blade azimuth angle, deg A = Rotor inflow ratio computed by momentum theory p = Advance ratio, V,IQR x = Wake skew angle, tan-'(plh), deg = Rotor rotational frequency, radls
