Analysis and design of a flap-equipped low-twist rotor for hover

This study evaluates the potential benefits that fixed but deployable trailing-edge flaps may have on a low-twist hovering rotor using a blade-element method combined with two-dimensional and three-dimensional computational fluid dynamics. Low blade twist is beneficial in terms of forward-flight performance, which, combined with a deployable flap, could also offer good hover performance, resulting in an overall better design in comparison with a plain twisted blade. To evaluate this concept, a parametric study of flap configurations was conducted using a simple blade-element method based on computational-fluid-dynamics-generated two-dimensional aerodynamics. This simple model indicated that up to 6 deg of blade twist could be recovered at high rotor thrust by using an optimized flap configuration. Performance improvements were also obtained for outboard slotted-flap configurations. The optimum slotted-flap designs were also evaluated using three-dimensional computational fluid dynamics, which confirmed that an inboard flap combined with a low-twist (-7deg) rotor blade matched the performance of a plain blade with -13deg of twist. A blended-flap configuration was also applied and evaluated. This simpler design demonstrated the equivalent performance of a clean rotor with 10 deg of blade twist, providing further evidence of the potential of the fixed inboard flap concept.