Rotor Wake/Fixed Wing Interactions with Flap Deflection”, American Helicopter Society 55th Annual Forum

The basic features in the interaction of a rotor wake with a wing in low-speed forward flight are studied using low-speed wind tunnel experiments. The configuration captures several of the aerodynamic interactions in the tiltrotor transition phase, and during wake/empennage interactions. Previous work showed that the pressure field on the wing surface below the rotor is dominated by n-per-rev "blade passage", while the velocity field is dominated by once-per-rev repetition of the vortex geometry, due to vortex interactions. The effect of deflecting trailing edge flaps is studied here. Large area SCV is used to enable velocity field acquisition at various sections and test conditions. Flap deflection modifies the spanwise flow on the wing surface, and causes an apparent lateral shift in the wake interaction. This shift influences the effectiveness of inboard vs. outboard flaps, and opens possibilities for augmenting rolling moments. The paper describes both a unique capability for scanning several cross-sections of a periodic velocity field during such interaction conditions, and the correlation of data from velocity, pressure and force measurements to synthesize the nature of the complex flowfield with its multiple periodicities