Rotary airfoil and design method therefor

Abstract

The rotary airfoil 100 defines a cross section and a span, wherein the cross section is a function of the point along the span (e.g., spanwise point) and defines an upper surface and a lower surface at each spanwise point. The rotary airfoil 100 also defines, at a cross section, a lift coefficient (CL) that is a function of the angle of attack at which the airfoil is rotated through the air. The system can optionally include: a rotor hub to mount the rotary airfoil, a tilt mechanism to pivot the rotary airfoil between a forward configuration and a hover configuration, and a pitching mechanism to change the angle of attack of the rotary airfoil 100.

1 . An airfoil blade, the blade comprising:
 a first airfoil cross section, the first airfoil cross section defining:
 a chord line defining a chord length L; 
 a leading edge, comprising a leading edge radius between 0.002 L and 0.05 L; 
 a trailing edge, comprising a trailing edge thickness between zero and 0.03 L; 
 a maximum thickness between 0.07 L and 0.2 L and located between 0.2 L and 0.6 L along the chord line; and 
 a maximum camber between zero and 0.2 L and located between 0.2 L and 0.7 L along the chord line. 
   
     
     
         2 . The airfoil blade of  claim 1 , wherein:
 the leading edge radius is approximately 0.006 L;   the trailing edge thickness is approximately 0.005 L;   the maximum thickness is approximately 0.12 L at the position of approximately 0.4 L along the chord line; and   the maximum camber is approximately 0.024 L at the position of approximately 0.44 L along the chord line.   
     
     
         3 . The airfoil blade of  claim 2 , the first airfoil cross section as described in Table 1. 
     
     
         4 . The airfoil blade of  claim 1 , the first airfoil cross section as described in Table 2. 
     
     
         5 . The airfoil blade of  claim 1 , wherein the airfoil blade defines a blade length between 1 m and 4 m. 
     
     
         6 . The airfoil blade of  claim 5 , wherein the blade is tapered along the blade length. 
     
     
         7 . The airfoil blade of  claim 1 , wherein the airfoil blade defines a twisting angle along the blade length, the twisting angle between 20 degrees and 50 degrees. 
     
     
         8 . The airfoil blade of  claim 1 , further comprising an anhedral blade tip. 
     
     
         9 . The airfoil blade of  claim 1 , wherein the chord length L is between 0.02 m and 1 m. 
     
     
         10 . The airfoil bade of  claim 1 , wherein a rotor comprises the airfoil blade, wherein the rotor generates less than 80 dBA at a measurement distance of 100 meters when operating in a Reynold's number range between 50 k and 1,000 k. 
     
     
         11 . A rotor for a tilt-rotor aircraft, the rotor defining a disc plane, the rotor comprising:
 a plurality of airfoil blades, each of the plurality of airfoil blades defines a lift coefficient curve at a Reynold's number range between 50 k-10,000 k comprising:
 a first angle of attack (AoA) range; 
 a second AoA range, wherein a lower bound of the second AoA range is greater an upper bound of the first AoA range, the second AoA range spanning a width of greater than 5 degrees angle of attack; 
 a semi-critical AoA between the lower bound of the second AoA range and the upper bound of the first AoA range; and 
 a maximum coefficient of lift (CL) at a critical AoA greater than an upper bound of the second AoA range; and 
   a rotor tilt mechanism, the rotor tilt mechanism configured to transform the rotor between:
 a forward configuration, wherein each of the plurality of airfoil blades operates in the first AoA range and the disc plane is parallel to a pitch-yaw plane of the tilt-rotor aircraft; and 
 a hover configuration, wherein each of the plurality airfoil blades operates in the second AoA range and the disc plane intersects the pitch-yaw plane. 
   
     
     
         12 . The rotor of  claim 11 , further comprising a blade pitching mechanism, wherein in the forward configuration the blade pitching mechanism orients each of the plurality of airfoil blades at a forward AoA within the first AoA range, wherein in the hover configuration the blade pitching mechanism orients each of the plurality of airfoil blades at a hover AoA within the second AoA range. 
     
     
         13 . The rotor of  claim 11 , wherein each airfoil further comprises a bump on the upper surface of the airfoil blade, wherein a separation point of each airfoil is located on a trailing portion of the respective bump. 
     
     
         14 . The rotor of  claim 11 , wherein the CL versus AoA curve in the first AoA range defines a first slope (M), wherein the CL versus AoA curve in the second AoA range defines a second slope, wherein the second slope is between zero and 0.95M. 
     
     
         15 . The rotor of  claim 14 , wherein an absolute value of a rate of change of the second slope is less than 0.05M per degree. 
     
     
         16 . The rotor of  claim 14 , wherein the CL versus AoA curve comprises a third AoA range between the first AoA range and the second AoA range, wherein the lift coefficient curve defines a third slope in the third AoA range, wherein the third AoA slope is less than half the second slope. 
     
     
         17 . The rotor of  claim 11 , wherein the lift coefficient curve defines a first slope between 0.1 per degree and 0.13 per degree in the first AoA range, wherein the life coefficient curve defines a second slope less than 0.1 per degree in the second AoA range. 
     
     
         18 . The rotor of  claim 11 , wherein the hover configuration operates below 80 dBA measured from 100 meters. 
     
     
         19 . The rotor of  claim 11 , further comprising a hub, each of the plurality of blades radiating from the hub in the disc plane, wherein an electric motor is integrated into the hub. 
     
     
         20 . The rotor of  claim 11 , the aircraft comprising a second rotor adjacent to the rotor, wherein the second rotor is offset from the disc plane.