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.

What is claimed is: 
     
         1 . An apparatus of a vertical takeoff and landing aircraft, the apparatus comprising:
 a flight control system configured to command and control a tiltable rotor assembly by performing one of more actions, the actions 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 . 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.   
     
     
         3 . The method of  claim 2 , wherein the angle of attack range for forward flight mode is less than the angle of attack range for hover flight mode. 
     
     
         4 . The method of  claim 2 , 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 corresponds to the second angle of attack range and the pitch regime for the forward flight mode corresponds to the first angle of attack range. 
     
     
         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 4 , wherein the first angle of attack range and the second angle of attack range do not overlap. 
     
     
         8 . The method of  claim 4 , wherein the first angle of attack range and the second angle of attack range partially overlap. 
     
     
         9 . The method of  claim 7 , 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. 
     
     
         10 . The method of  claim 2 , wherein the first angle of attack range corresponds to a first region of a lift coefficient curve characterized by the blades and the second angle of attack range corresponds to a second region of the lift coefficient curve, wherein the first region has a slope 0.25 to 0.75 times a slope of the second region. 
     
     
         11 . The method of  claim 2 , wherein the first angle of attack range corresponds to a first region of a lift coefficient curve characterized by the blades and the second angle of attack range corresponds to a second region of the lift coefficient curve, wherein the first region has a slope 0.25 to 0.50 a slope of the second region.