William H. Rae

Bio: William H. Rae is an academic researcher from University of Washington. The author has an hindex of 1, co-authored 1 publications receiving 24 citations.

Limits on minimum speed V/STOL wind-tunnel tests.

Abstract: body of revolution, far from the axis," Proc. Roy. Soc. (London) A201, 89-109 (March 1950). 8 Hubbard, H. H., Maglieri, D. J., Huckel, V., and Hilton, D. A. (with appendix by H. W. Carlson), "Ground measurements of sonic-boom pressures for the altitude range of 10,000 to 75,000 feet," NASA TR R-198 (1964). (Supersedes NASA TM X-633.) 9 Walkden, F., "The shock pattern of a wing-body combination, far from the flight path," Aeronaut. Quart. IX, Pt. 2, 164194 (May 1958). 10 Whitham, G. B.; "The flow pattern of a supersonic projectile," Commun. Pure Appl. Math. V, 301-348 (August 1952). 11 Middle ton, W. D. and Carlson, H. W., "A numerical method for calculating near-field sonic-boom pressure signatures," NASA TND-3082(1965). 12 Carlson, H. W., Mack, R, J., and Morris, O. A., "Sonicboom pressure-field estimation techniques," J. Acoust. Soc. Am. (submitted for publication). 13 McLean, F. E. and Shrout, B. L., "Design methods for minimization of sonic-boom pressure-field disturbances," J. Acoust. Soc. Am. (submitted for publication).

Rotor Aerodynamics in Ground Effect at Low Advance Ratios.

Abstract: : The results of an experimental study of the aerodynamic characteristics of a helicopter rotor operating in ground effect at low advance ratios are presented. Flow visualization studies were conducted along with measurement of the forces and moments acting on the rotor as a function of advance ratio, height above ground and collective pitch. Steady state experiments as well as non-steady experiments involving translational acceleration were conducted. Three distinct flow regimes were noted from the flow visualization studies. At the low end of the advance ratio range a recirculating flow was present, at intermediate advance ratios a horseshoe shaped vorted formed under the rotor, and at the high end of the advance ratio range studied, the rotor wake flows entirely downstream. At test conditions were the recirculating flow or ground vortex is present there are marked departures from classical ground effect theory. Translational acceleration was found to have a significant effect on the rotor forces and moments indicating that some appreciable time is required for the establishment of the ground effect flow field when a recirculating flow or ground vortex exists in the steady state. The results indicate that magnitude of the ground effects experienced by a helicopter are sensitive to the flight path of the helicopter. (Author)

An Experimental Evaluation of Wind Tunnel Wall Correction Methods for Helicopter Performance.

Abstract: : Accurate measurements of rotorcraft performance as measured in a wind tunnel are strongly influenced by the test section configuration, whether it be closed or open jet. The influence of wind tunnel walls on the induced velocity of lifting bodies has been studied by many researchers over the years. Methods have been developed to adjust the angle-of-attack and dynamic pressure for fixed wing aircraft in a wind tunnel to approximate free flight conditions. These methods have largely been adopted by the rotorcraft community with very little testing to verify the applicability of these methods to helicopter rotors and flight test measurements. Recent tests conducted by the Deutsche Forschungsanstalt fur Luft- und Raumfahrt e.V. (DLR) in the Duits-Nederlandse Wind Tunnel (DNW) have provided data suitable for the evaluation of these methods. A 40% scale model Bo105 rotor was tested in five different wind tunnel test sections: 1) 6x6m closed, 2) 8x6m closed, 3) 8x6m open slots, 4) 9.5x9.5m closed, and 5) the 8x6m open jet. These data along with full-scale data from a NASA Ames 40- by 80-Foot Wind Tunnel test and a DLR flight test program provide a means to evaluate wind tunnel wall correction methods specifically for helicopter rotors. Good correlation of rotor power over a range of advance ratios for these three data sets has been shown using wall correction methods after accounting for trim deficiencies between the data sets.

Theoretical study of the effect of ground proximity on the induced efficiency of helicopter rotors

Abstract: A study of rotors in forward flight within ground effect showed that the ground-induced interference is an upwash and a decrease in forward velocity. The interference velocities are large, oppose the normal flow through the rotor, and have large effects on the induced efficiency. Hovering with small ground clearances may result in significant blade stall. As speed is increased from hover in ground effect, power initially increases rather than decreases. At very low heights above the ground, the power requirements become nonlinear with speed as a result of the streamwise interference. The streamwise interference becomes greater as the wake approaches the ground and eventually distorts the wake to form the ground vortex which contributes to certain observed directional stability problems.

Wind Tunnel Wall Effects at Extreme Force Coefficients

Abstract: Wind tunnel wall constraints effects at extreme force coefficients during V/STOL testing shown different from effects in conventional aircraft testing