Method For Controlling Vertical Take-Off And Landing Aircraft Using Different Propeller Blade Angle Of Attack Ranges For Different Flight Modes

Abstract

A method for the control of a vertical take-off and landing (VTOL) aircraft which reduces the acoustic profile of the rotary airfoil in hover for VTOL applications. The rotary airfoil incurs an efficiency penalty in order to improve the acoustic performance during hover. The aircraft operates the rotary airfoils of the propeller during hover in the hover angle of attack range, and the aircraft operates the rotary airfoils during forward flight in the forward angle of attack range.

1 . A method of thrust control of a vertical takeoff and landing aircraft, the method comprising:
 tilting a propeller having a plurality of blades with variable pitch, the propeller being configured to tilt to a vertical orientation for hover flight mode and a horizontal orientation for forward flight mode;   rotating the propeller to generate thrust; and   controlling the variable pitch propeller to operate within different pitch regimes in the hover and forward flight modes, the pitch regime for the forward flight mode corresponding to a first angle of attack range and the pitch regime for the hover flight mode corresponding to a second angle of attack range.   
     
     
         2 . The method of  claim 1 , wherein the angle of attack range for forward flight mode is less than the angle of attack range for hover flight mode. 
     
     
         3 . The method of  claim 1 , wherein each of the plurality of blades is characterized by a lift coefficient curve having a shallower curve for a second angle of attack range than the lift coefficient curve for a first angle of attack range, and wherein the pitch regime for the hover flight mode corresponding to the second angle of attack range and the pitch regime for the forward flight mode corresponding to the first angle of attack range. 
     
     
         4 . The method of  claim 1  wherein the first angle of attack range and the second angle of attack range do not overlap. 
     
     
         5 . The method of  claim 2  wherein the first angle of attack range and the second angle of attack range do not overlap. 
     
     
         6 . The method of  claim 3  wherein the first angle of attack range and the second angle of attack range do not overlap. 
     
     
         7 . The method of  claim 6  wherein the first angle of attack range has a minimum of −5 degrees and a maximum of 5 degrees, and wherein the second angle of attack range has a minimum of 8 degrees and a maximum of 10 degrees. 
     
     
         8 . The method of  claim 1  wherein the blades comprise a raised feature on an upper side of the airfoil, the raised feature comprising a convex portion of the upper side and a concave portion of the upper side trailing the convex portion. 
     
     
         9 . The method of  claim 3  wherein the blades comprise a raised feature on an upper side of the airfoil, the raised feature comprising a convex portion of the upper side and a concave portion of the upper side trailing the convex portion. 
     
     
         10 . The method of  claim 8  wherein the slope of the lift coefficient curve of the blades in the first A0A range is in the range of 0.25 to 0.75 times the slope of the lift coefficient curve of the blades in the second AoA range. 
     
     
         11 . The method of  claim 8  wherein the slope of the lift coefficient curve of the blades in the first A0A range is in the range of 0.25 to 0.50 times the slope of the lift coefficient curve of the blades in the second AoA range.