Helicopter blade with a tip having a selected combination of sweep, taper and anhedral to improve hover efficiency

Claim 1

A helicopter blade having high blade twist, a leading edge, a trailing edge, a root, a tip, a chord dimension extending between said edges, and being fabricated so that aerodynamic blade loading during rotor hover operation will induce slight torsional deflection of the blade to a preferred pitch position and thereby improve rotor performance and reduce the total power required to drive the rotor and including: a root section adapted to be connected to a helicopter rotor hub for rotation therewith about an axis of rotation, a central portion of selected aerodynamic shape connected to and extending outwardly from the blade root portion, a tip portion connected to and extending outwardly from the blade central portion to establish a blade radius between the axis of rotation and the blade tip, said blade tip portion being selectively shaped to improve helicopter hover performance by diminishing the intensity of the tip vortex generated during hover operation and directing the tip vortex away from the following blade to minimize interference therewith, said tip portion extending for approximately 7% of blade radius, said tip portion being swept rearwardly to reduce the velocity of the air in the direction of the tip local chord to thereby reduce blade tip loading and the strength of the tip trailing edge vortex generated in hover, said tip portion also being tapered so that the chord dimension at its outboard end is approximately 1/2 the chord dimension at its inboard end to reduce tip portion area and to thereby further reduce blade tip loading and the strength of the tip trailing edge vortex generated in hover, and said tip portion also being deflected downwardly throughout the outer 4% of blade radius so as to direct the shed trailing edge tip vortex away from the following blade in hover.