Rotor Stall Alleviation with Active Gurney Flap

This paper focuses on stall alleviation of a UH-60A Black Hawk helicopter using an Active Gurney Flap on the lower surface of the blades situated between 70-80% span, 10% upstream from the trailing-edge and actuated at 1/rev frequency to a maximum deployment height of 2% chord. The unsteady aerodynamics of the upstream Gurney Flap are represented in the model, as are rotor wake effects and blade elastic deformations. At high gross-weight and altitude Gurney Flap deployment on the retreating side reduces the rotor disk angles of attack in that region, allows unloading of very heavily loaded portions of the disk for the baseline aircraft, and reduces power requirements by over 11% at the point the baseline aircraft stalls. Gurney Flap actuation also increases the maximum gross weight capability of the aircraft (by almost 1,000 lbs), the maximum altitude capability (by 1,400 ft) and the maximum speed capability (by 28 kts). The 1/rev Gurney Flap actuation (deployed on the retreating side to alleviate retreating blade stall) was also observed to reduce 4/rev hub vibratory loads at the stall boundary. At 90 kts, 8,000 ft, the 4/rev hub vertical force reduced by 24%, the vibratory in-plane forces reduced by 68%, and the vibratory in-plane moments reduced by 44%. Gurney Flap actuation on a torsionally stiffer rotor appeared to produce comparable reductions in power for the flight condition examined.