Abstract:
A rotor aircraft has an engine, a propeller, wings, and a rotor. An electric motor is coupled to the rotor drive shaft for applying torque to the rotor drive shaft. The electric motor is sized to supply all of the torque to pre-rotate the rotor to a selected speed prior to liftoff of the aircraft. The wings are capable of providing substantially all of the lift required during forward flight at a cruise speed. The rotor being is capable of being trimmed to provide substantially zero lift and auto-rotate at cruise speed. Sensors sense flight conditions of the aircraft and provide signals to a controller that selectively causes the electric motor to cease applying torque to the rotor drive shaft during autorotation at cruise speed. The controller also causes the electric motor to apply torque to the rotor drive shaft if the sensors indicate additional rotor speed is needed.

Description:
CROSS REFERENCE TO RELATED APPLICATION 
       [0001]    This application is a continuation-in-part of Ser. No. 13/305,441, filed Nov. 28, 2011. 
     
    
     FIELD OF THE INVENTION 
       [0002]    This invention relates in general to an aircraft having a rotor for providing lift for take off and landing, and wings for providing lift at cruise flight speeds, the aircraft having an electric motor for selective rotation of the rotor. 
       BACKGROUND 
       [0003]    A type of slowed rotor aircraft, sometimes called a gyroplane, is illustrated in U.S. Pat. No. 5,727,754. The aircraft has a rotor similar to a helicopter blade rotor. The aircraft has a propeller that provides forward thrust, and wings for providing substantially all of the lift in cruise flight. The rotor blades have weighted tips to create inertia. The aircraft in the &#39;754 patent will perform a jump takeoff by rotating the rotor at a speed higher than that needed for steady state flight while the collective pitch is at zero and the landing gear brakes on. The propeller is also rotated prior to takeoff. The collective pitch of the rotor and propeller are then increased to a takeoff level and the brakes released, which causes the aircraft to lift. A clutch disengages the engine from the rotor at the moment of takeoff, but the inertia of the rotor continues spinning the rotor after liftoff. 
         [0004]    As the aircraft accelerates forward and the rotor rpm decays, the rotor is tilted back relative to the airstream, causing the rotor to auto-rotate. The auto-rotation of the rotor occurs due to the airstream passing through the rotor blades. As the aircraft gains forward speed, the wings will begin providing a greater portion of the lift required to maintain the aircraft in flight. As the aircraft forward flight speed increases further, the wings will provide substantially all of the lift, at which point the rotor collective pitch will have been reduced to at or near zero. The rotor rpm will be maintained at a slow rate by tilting the rotor relative to the fuselage. 
       SUMMARY 
       [0005]    The rotor aircraft described herein has an engine and a propeller driven by the engine to provide forward thrust to the aircraft. Wings provide lift while in forward flight. A rotor having a rotor drive shaft is mounted for selectively providing lift. An electric motor selectively applies torque to the rotor drive shaft. At least one rudder is positioned within a prop blast region of the propeller. The rudder is sized to counter torque applied by the electric motor to the rotor drive shaft while the aircraft is airborne. 
         [0006]    The electric motor may comprise the sole source for applying torque to the rotor drive shaft. Alternately, a clutch may be connected between the engine and the rotor drive shaft for selectively engaging and disengaging the engine from the rotor drive shaft. The clutch is located such that the electric motor is able to supply torque to the rotor drive shaft while the clutch is disengaged. 
         [0007]    The electric motor may be sized to supply all of the torque to pre-rotate the rotor to a selected liftoff rotational speed prior to liftoff of the aircraft. If so, a clutch between the engine and the rotor drive shaft may not be needed. Alternately, the electric motor may be sized to pre-rotate the rotor prior to lift off to a selected fraction of a pre-rotation liftoff speed while the clutch is disengaged. When reaching the selected fraction, the clutch may be engaged to enable the engine to apply torque to the rotor drive shaft to reach the pre-rotation liftoff speed. 
         [0008]    The aircraft has sensors for sensing flight conditions of the aircraft. A controller controls the electric motor while the aircraft is airborne in response to input from the sensors. The wings are capable of providing substantially all of the lift required during forward flight at a cruise speed. The rotor is capable of being positioned to provide substantially zero lift and auto-rotate due to air flowing through the rotor at the cruise speed. The controller may cause the electric motor to cease applying torque to the rotor drive shaft during autorotation at cruise speed. The controller may cause the electric motor to apply torque to the rotor drive shaft during flight if the sensors indicate additional rotor speed is needed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a top view of a slowed rotor winged aircraft in accordance with this disclosure. 
           [0010]      FIG. 2  is a schematic illustrating the principal drive components for the propeller and the rotor of the aircraft of  FIG. 1  and employing an electric motor to apply torque to the rotor drive shaft. 
           [0011]      FIG. 3  is a schematic similar to  FIG. 2 , but illustrating an alternate embodiment wherein the engine is also coupled to the rotor drive shaft to apply torque to the rotor drive shaft. 
       
    
    
     DETAILED DESCRIPTION 
       [0012]    Referring to  FIG. 1 , aircraft  11  has a fuselage  13 . A pair of high aspect ratio wings  15  extends outward from fuselage  13 . The length of each wing  15  over the chord between the leading edge and trailing edge is quite high so as to provide efficient flight at high altitudes. Wings  15  preferably have ailerons  17  that extend from the tip to more than half the distance to fuselage  13 . Each aileron  17  has a width that is about one-third the chord length of wing  15  and is moveable from a level position to a full ninety degrees relative to the fixed portion of each wing  15 . 
         [0013]    Aircraft  11  also has a pair of vertical stabilizers  19 , each of which has a moveable rudder  21 . Each vertical stabilizer  19  is mounted on a separate boom or tail portion  23  extending aft of fuselage  13 . An elevator  24  extends between vertical stabilizers  19 . 
         [0014]    A rotor mast  25  extends upward from fuselage  13  and supports a rotor  27 , which comprises at least two blades. Preferably, rotor mast  25  may be tilted in forward and rearward directions relative to fuselage  13 . The blades of rotor  27  are weighted at their tips by weights for increasing stiffness at high rotational speeds and for creating inertia. Each blade of rotor  27  may have a shell that encloses a longitudinal twistable carbon fiber spar (not shown). The spar is continuous through the shell and attaches to the shell at approximately 40 percent of its radius. Other rotor constructions are possible. Each blade of rotor  27  is pivotal to various collective pitches about a centerline extending from rotor mast  25 . 
         [0015]    A forward thrust device, which in this example is a single propeller  29 , is mounted on a rear portion of fuselage  13  and faces rearward. Rudders  21  are positioned aft of propeller  29  in a region that receives a discharge or prop blast from propeller  29 . Even when aircraft  11  is not moving forward, part of the airstream from propeller  29  flows past each rudder  21 . Propeller  29  may have a continuous carbon fiber spar (not shown) that runs from blade tip to blade tip. The carbon fiber spar is twistable inside a shell of propeller  29  to vary the collective pitch. Other devices and arrangements to provide forward thrust to aircraft  11  are possible. 
         [0016]      FIG. 2  schematically illustrates a power source  31  within fuselage  13  that drives propellers  29 . Power source  31  may include a variety of engines, including gas turbine engines. The terms “power source” and “engine” may be used interchangeably herein. Power source  31  has an output drive shaft  33  that may lead directly to propeller  29 , particularly if power source  31  is a gasoline powered internal combustion engine. If power source  31  is a gas turbine engine, a gear arrangement between output drive shaft  33  and propeller  29  would normally be required because of the much higher rotational speed of a gas turbine engine than propeller  29 . 
         [0017]    A rotor drive shaft  35  extends upward from fuselage  13  within rotor mast  25  ( FIG. 1 ) to rotor  27 . An electric motor  37  is coupled to rotor drive shaft  35  for applying torque to rotor drive shaft  35 . Electric motor  37  may be a variety of types, and preferably is a variable speed type. Electric motor  37  may be connected directly to rotor drive shaft  35  or connected by a mechanism employed to release engagement of electric motor  37  when it is not being powered to rotate rotor  27 . If necessary, electric motor  37  can be operated as a generator, retarding the rotational speed of rotor  27 . 
         [0018]    In the embodiment of  FIG. 2 , there is no connection between engine output shaft  33  and rotor drive shaft  35 , thus all torque applied to rotor drive shaft  35  must come from electric motor  37 . In the embodiment of  FIG. 2 , electric motor  37  has enough capacity to pre-rotate rotor  27  to a selected liftoff rotational speed while aircraft  11  is still on ground. That pre-rotational liftoff speed may be in a range from 300 to 400 rpm. A battery  39  supplies power to electric motor  37 . Battery  37  may be charged by engine  31  or some other method. 
         [0019]    A controller  41  controls electric motor  37 , such as by controlling the power provided from battery  39 . A number of flight condition sensors  43  are linked to controller  41 . These sensors  43  may include ones that sense the following: airspeed; angle of attack of wings  15 ; torque applied to rotor drive shaft  35 ; lift provided by rotor  27 ; and rotational speed of rotor drive shaft  35 . Other conditions may also be sensed. Controller  41  includes a processor that computes a desired rotational speed or torque to be applied to rotor drive shaft  35  by electric motor  37  depending upon the flight conditions sensed. 
         [0020]    In operation of the embodiment of  FIG. 2 , for take-off and while still on the ground, electric motor  35  will apply torque to rotate rotor  37  up to a selected liftoff rotational speed while the collective pitch is at or near zero. Meanwhile, engine  31  will rotate propeller  29  while the propeller collective pitch remains near zero. The pilot applies the brakes. When rotor  27  reaches the full liftoff speed, either the pilot or controller  41  increases the collective pitches on rotor  37  and propeller  29  and releases the brakes. Aircraft  11  will accelerate forward and become airborne. The weighted tips of rotor  27  provide considerable momentum to continue rotating rotor  27 . Controller  41  could be programmed to cease powering electrical motor  37  at liftoff. However, preferably electrical motor  37  continues to apply torque to rotor  27  after liftoff, although the rotational speed of rotor  27  will decay. As aircraft  11  gains speed, the pilot or controller  41  will begin tilting rotor mast  25  aft, which causes an airstream to flow from the lower side through rotor  27 . Rotor  27  will begin auto-rotating in response to the airstream. Wings  15  increasingly provide lift for aircraft  11  as the forward speed increases. Controller  41  gradually reduces the collective pitch of rotor  27  and also gradually reduces the torque applied to rotor  27  by electric motor  37 . 
         [0021]    While torque is being applied to rotor drive shaft  35  by electric motor  37  a counter torque is generated against fuselage  13 . There is no tail rotor in the embodiment shown. The pilot will orient rudders  21  to prevent fuselage  13  from spinning in an opposite direction to rotor  27 . While still at slow forward speed, the prop blast over rudders  21  resists this counter torque. 
         [0022]    At a steady state cruising speed, the collective pitch of rotor  27  will be at or near zero and the tilt of rotor mast  25  placed so that rotor  27  will be auto-rotating at a slowed speed, such as 100 to 200 rpm. Controller  41  may control electric motor  37  so that it will not be supplying any torque to rotor drive shaft  35 . Under these conditions, rotor  27  supplies very little of the lift for aircraft  11 . 
         [0023]    Occasions may arise during flight that require rotor  27  to rapidly increase its speed, without significantly increasing its collective pitch. For example, turbulence encountered during cruise flight may result in a loss in some of the lift provided by wings  15 . Increasing the collective pitch and tilt of rotor  27  would increase the speed of rotor  27 , however, these steps could result in excessive flapping of the blades of rotor  27 . Instead, when sensing a need for more lift to be provided by rotor  27 , controller  41  will cause electric motor  37  to begin applying torque to rotor drive shaft  35 , rapidly increasing the rotational speed of rotor  27 . Controller  41  may decrease and completely cut off the torque supplied by electric motor  27  once the conditions merit. A similar need for a rapid increase in the rotational speed of rotor  27  would occur in the event engine  31  fails. 
         [0024]    During a short landing, as the forward airspeed of aircraft  11  declines, wings  15  will supply less lift. Rotor  27  may be tilted and the collective pitch increased to provide more of the lift. If desired, controller  41  may cause electric motor  41  to apply torque to rotor shaft  35  during landing to augment the rotational speed caused by auto-rotation and control the rotor speed. 
         [0025]    In the embodiment of  FIG. 3 , the same numerals are used for common components. In this embodiment, a gear box  45  is connected between the output shaft  47  of engine  31  and propeller  29 . A clutch  49  connects between electric motor  37  and gear box  45 . When clutch  49  is engaged, engine  31  will supply torque to rotor shaft  35 . When clutch  49  is disengaged, controller  41  may cause electric motor  37  to supply torque to rotor drive shaft  35 . The arrangement of  FIG. 3  is particularly useful when engine  31  is a gas turbine engine. A gas turbine engine typically cannot supply torque until the rpm of the engine is at least 50% of its operating rpm. 
         [0026]    In the  FIG. 3  embodiment, for a short take-off, electric motor  37  will be sized so that it can pre-rotate rotor  37  without assistance up to a selected fraction of its liftoff rpm. For example, electric motor  37  may have the capacity to rotate rotor  37  to up about 150-200 rpm, if the selected pre-rotation lift off speed is 300-400 rpm. Once electric motor  37  reaches the fractional speed, clutch  49  is engaged so that engine  31  will spin rotor  27  on up to the selected pre-rotational lift off speed. Electric motor  37  could remain engaged after clutch  49  engages engine  31 . 
         [0027]    Once the pilot initiates liftoff, clutch  49  disengages engine  31  and the rotational speed of rotor  27  begins declining. Controller  41  may continue to cause electric motor  37  to apply torque until steady state forward flight conditions occur. Controller  41  may control the torque input of electric motor  37  to rotor shaft  35  in the same manner as in the embodiment of  FIG. 2 . 
         [0028]    The first embodiment eliminates a need for a clutch between the engine and the propeller. If the engine is an internal combustion type, a gear box may be eliminated. In the second embodiment, the electric motor pre-rotates the rotor to a selected fraction of the liftoff rotational speed, at which time the engine will be engaged to complete the pre-rotation. In both embodiments, the electrical motor can be used during flight for increasing the speed of rotation rapidly if needed. 
         [0029]    While the disclosure has been shown in only two of its forms, it should be apparent to those skilled in the art that it is not so limited but is susceptible to various changes without departing from the scope of the invention.