Experimental/Numerical Evaluation Of Integral Trailing Edge Flaps For Helicopter Rotor Applications

Two-dimensional wind tunnel tests were conducted in the NASA Langley 0.3-m Transonic Cryogenic Tunnel (TCT) to identify a suitable trailing edge flap geometry for helicopter rotor aerodynamic/dynamic applications. Two pressure-instrumented models of the Boeing HH-06 (9.5% thick), HH-10 (12% thick) airfoils having 25% chord integral trailing edge flaps were tested. Airfoil and flap "inserts" were used interchangeably to yield flap "overhang" nose balance values of 35%, 40%, and 45%. Specific objectives of the tests were: a) to investigate the effects of flap overhang nose balance on the aerodynamic characteristics of the airfoil/flap and, b) to establish a comprehensive aerodynamic database for lifting-line simulations of flapped rotors. To limit the number of test configurations, pre-test analyses were conducted to evaluate the aerodynamic characteristics of a number of candidate flap geometries. The analyses were performed using a modified version of the NASA Ames ARC2D thin-layer Navier-Stokes flow solver. Results from the wind tunnel tests/analyses affirmed the important effect of the flap percentage overhang on the hinge moments - hence on the required flap actuation loads. At transonic speeds, prediction of a secondary supersonic flow pocket on the shoulder of the flap was corroborated using the measured pressure data.