S-97 RAIDER® Wake-Empennage Interaction Fight Data and Correlation

A combination of experimental and analytical methods has been applied to study the aerodynamic interaction of the S97 RAIDER® coaxial main rotor and its wake on an empennage. The primary goal was to characterize the periodic aerodynamic forcing from the rotor on the horizontal stabilizer over a wide range of flight conditions, and use those data to develop and validate computational fluid dynamics (CFD) methods that can then be applied to optimize future designs. The flight test aircraft was instrumented with 29 unsteady pressure sensors and flown for speed sweeps from 20 to 180 kts as well as a range of maneuvers. The data were processed to provide both unsteady and time-averaged aerodynamic forces and moments. Two CFD codes were then applied: HELIOS/RCAS using discrete main rotor and propulsor blades and STARCCM+ using a recently developed unsteady virtual blade model. Both codes captured the trends of the flight test data and agreed that the vibratory aerodynamic forcing on the empennage was not particularly large. The flight data were also compared with previously acquired powered wind tunnel model data, and showed good agreement. Finally, the Sikorsky GenHel flight dynamics model was applied to level flight and maneuver conditions, and the match was also acceptable. This study has that current state-of-the-art methodology, carefully applied, can capture complex aerodynamic interactions with sufficient accuracy for aircraft design, and that this implementation of X2 Technology(TM) does not result in unacceptable rotor on empennage interactions.