Evaluation of Model Helicopter Main Rotor Blade with Slotted Airfoils at the Tip

Data for rotors using unconventional airfoils are of interest to permit an evaluation of this technology’s capability to meet the U.S. Army’s need for increased helicopter mission effectiveness and improved safety and survivability. Thus, an experimental investigation was conducted in the NASA Langley Transonic Dynamics Tunnel to evaluate the effect of using slotted airfoils in the rotor blade tip region (85%-100% radius) on rotor aerodynamic performance and loads. Four rotor configurations were tested in forward flight at advance ratios from 0.15 to 0.45 and in hover inground effect. The hover tip Mach number was 0.627, which is representative of a design point of 4000-ft geometric altitude and a temperature of 95° F. The baseline rotor configuration had a conventional single-element airfoil in the tip region. A second rotor configuration had a forward-slotted airfoil with a −6° slat, a third configuration had a forward-slotted airfoil with a −10° slat, and a fourth configuration had an aft-slotted airfoil with a 3° flap (trailing edge down). The results of this investigation indicate that the −6° slat configuration offers some performance and loads benefits over the other three configurations at the higher rotor lift coefficients at each advance ratio.