HUB AND PYLON FAIRING INTEGRATION FOR HELICOPTER DRAG REDUCTION

The results of testing hub and pylon fairings mounted on a one-fifth scale helicopter with the goal of reducing parasite drag are presented. The baseline model was the Bell Model 222 flight-test aircraft with rotating 680 bearingless hub and blade cuffs. The fairings were designed by NASA Ames and Bell Helicopter Textron under a joint program. The test was conducted in the NASA Ames Research Center 7- by 10-Foot Wind Tunnel. Lift, drag, and pitching moment, as well as side force and yawing moment, were measured. The primary objective of the test was to validate the drag reduction capability of integrated hub and pylon configurations in the aerodynamic environment produced by a rotating hub in forward flight. In addition to the baseline helicopter without fairings, three hub fairings and three pylon fairings were tested in various combinations. The three hub fairings tested reflect two different conceptual design approaches to implementing an integrated fairing configuration on an actual aircraft. The design philosophy is discussed in detail and comparisons are made between the wind tunnel models and potential full-scale prototypes. The data show that model drag can be reduced by as much as 20.8% by combining a small hub fairing with circular arc upper and flat lower surfaces and a non-tapered 34% thick pylon fairing. Aerodynamic effects caused by the fairings, which may have a significant impact on static longitudinal and directional stability, were observed. The model drag reduction is scaled based on Model 222 full-scale flight test data and used to estimate improvements in top speed and range. The results support previous research which showed that the greatest reduction in model drag is achieved if the hub and pylon fairings are integrated with minimum gap between the two.