Abstract:
A fixed wing rotorcraft uses differential thrust between wing mounted propellers to provide counter torque when the rotor is being powered by a power source. The rotorcraft is comprised of a fuselage to which fixed wings are attached. A rotor is attached on an upper side of the fuselage and provides lift at low speeds while the wings provide a majority of the lift at high speeds. When at high speeds the rotor may be slowed to reduce advancing tip speed and retreating blade stall. Forward thrust and counter torque is provided by propellers mounted on either side of the fuselage or even on the wings.

Description:
[0001]    This application claims the benefit of U.S. Provisional application Ser. No. 60/206,021, filed May 22, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of Invention  
           [0003]    This invention relates in general to a gyro-type aircraft, and more specifically to gyro-type aircraft that have the ability to hover.  
           [0004]    2. Description of the Related Art  
           [0005]    Air transport of cargo is typically handled by either large airplanes or large helicopters. Large airplanes have an advantage of being much faster than helicopters, but the disadvantage of requiring long runways. Large helicopters have the advantage of vertical take off and landing but are not as fast as airplanes. Another advantage of helicopters is the ability to hover, or maintain a relatively static position over a location on the surface below. This feature is useful in many situations including rescue operations over water and unstable surfaces.  
           [0006]    One vehicle that can achieve relatively high speeds and achieve vertical take off and landings is the gyroplane, as described in U.S. Pat. No. 5,727,754. The gyroplane uses pre-rotation of a weighted rotor to achieve vertical take off without the need for a tail rotor. The rotor is not powered once the gyroplane leaves the ground. The craft flies in a manner similar to auto-gyros, except that at high speeds the rotor may be unloaded as the wings begin to create sufficient lift. This allows the rotor to slow and reduces advancing tip speed, which is the major limiting factor in highspeed rotor craft. In it&#39;s current state of development the pre-rotation method of vertical take off posses some technical problems for lifting large payloads. Also, the gyroplane cannot hover.  
           [0007]    It would be advantageous to have a cargo craft capable of traveling at higher speeds than a helicopter, but also able to achieve vertical take off and landing and hovering. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0008]    [0008]FIG. 1 is a top view of an aircraft constructed in accordance with this invention.  
         [0009]    [0009]FIG. 2 is a front elevational view of the aircraft of FIG. 1.  
         [0010]    [0010]FIG. 3 is a side elevational view of the aircraft of FIG. 1.  
         [0011]    [0011]FIG. 4 is a sectional view of the propeller of the aircraft in FIG. 1 in normal forward flight mode.  
         [0012]    [0012]FIG. 5 is a sectional view of the propeller of the aircraft in FIG. 1 in reverse flow mode. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT  
       [0013]    Referring to FIG. 1, aircraft  11  has an elongated fuselage  13 . A pair of high aspect ratio wings  15  extend 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 90 degrees relative to the fixed portion of each wing  15 .  
         [0014]    Aircraft  11  also has a pair of vertical stabilizers  19 , each of which has a moveable rudder  21  (FIG. 3). Each vertical stabilizer  19  is mounted at the aft end of fuselage  13  on a horizontal airfoil and structural member that is referred to herein as a stabilator  23 . Stabilator  23  is also pivotal from a level position in a plane parallel with wings  15  to a 90 degree downward position relative to the level position. Vertical stabilizers  19 , being attached to horizontal stabilator  23 , rotate downward in unison with stabilator  23 .  
         [0015]    A rotor  25  extends upward from fuselage  13  and supports at least one pair of blades  27  and preferably two pairs as shown in FIG. 1. Rotor  25  is tiltable in forward and rearward directions relative to fuselage  13 . Blades  27  are weighted at their ends by heavy weights  26  for increasing stiffness at high rotational speeds and creating inertia. Blades  27  may be constructed generally as shown in U.S. Pat. No. 6,024,325, issued Feb. 15, 2000, all of which material is hereby incorporated by reference. Each blade  27  comprises a shell or body that encloses a longitudinal twistable carbon spar (not shown). The spar is continuous through the body and attaches to the body at approximately 40 percent of its radius. Each blade  27  is pivotal to various pitches about a centerline extending from rotor  25 .  
         [0016]    A pair of propellers  28  are mounted to fuselage  13  by a horizontal strut  29 . One propeller  28  is located on each side of fuselage  13 . In the preferred embodiment, propellers  28  are pusher type, facing aft. Each propeller  28  may be constructed generally as shown in U.S. Pat. No. 6,155,784 issued Dec. 5, 2000, all of which material is hereby incorporated by reference. Each propeller  28  has a continuous carbon spar (not shown) that runs from blade tip to blade tip. Each carbon spar is twistable inside a blade body  30  (FIGS. 4 and 5), so that the blade pitch can vary.  
         [0017]    Referring to FIGS. 4 and 5, each propeller  28  has a convex, curved, low pressure side  28   a , and a high pressure side  28   b , which in the preferred embodiment is flat. Each blade of propeller  28  has a leading edge  28   c  and a trailing edge  28   d . During a normal forward flight mode, as shown in FIG. 4, leading edge  28   c  is forward of trailing edge  28   d . Rotation of propeller  28  while at this pitch causes air flow to the right, as shown in the drawing. Since it is arranged as a pusher propeller, the flight direction would be to the left for normal flight. When the pitch is changed to reverse flow, as shown in FIG. 5, leading edge  28   c  is now tilted aft of trailing edge  28   d . This results in airflow to the left.  
         [0018]    Since propeller  28  is a pusher type, aircraft  11  would not normally be flying in a forward direction while propeller  28  is pitched as shown in FIG. 5. Rather, the reversibility of the pitch enables propellers  28  to be utilized to counter rotational torque produced by rotor blades  27  when they are driven during flight. Propellers  28  always rotate counter to each other, as shown in FIG. 2. However, when rotational torque of rotor  25  is to be countered, one propeller  28  is pitched for reverse thrust, as shown in FIG. 5, while the other is pitched for forward thrust, as shown in FIG. 4. The degree of pitch differs, and the difference between the two pitches will provide a counter torque that is controlled to equal rotational torque produced by rotor  25 .  
         [0019]    [0019]FIG. 1 illustrates schematically a power source  31  that preferably comprises multiple gas turbine engines located within fuselage  13  and connected by drive shafts (not shown) to propellers  28  and rotor  25 . Power source  31  includes a two-speed gear box or automatic transmission is incorporated in the drive train leading to propellers  28 . One gear ratio results in propellers  28  rotating at a low speed relative to engine rpm for high altitude cruising flight and other instances that will be explained below. Another gear ratio rotates propellers  28  at a higher speed relative to the engine speed for takeoff and lower velocity flight.  
         [0020]    Power source  31  also includes a clutch in the drive train leading to rotor  25 . The clutch is of an overrunning type that will allow rotor  25  to spin at higher revolutions than the drive shaft driven by the engines, but when the rotor speed drops to a certain level, it begins again to be driven by the engine. The clutch also can be actuated to completely disengage rotor  25  from being driven by power source  31 . The various modes will be described below in the operational description.  
         [0021]    Referring to FIG. 3, aircraft  11  has a nose gear  33  and a set of main landing gear  35 . Preferably, landing gears  33 ,  35  are of a type that will absorb high impact loads that may occur during hard landings, such as described in U.S. Pat. No. 5,944,283, issued Aug. 31, 1999, all of which material is hereby incorporated by reference. The landing gears  33 ,  35  are retractable. Main landing gear  35  retracts into a fairing  37  located partially above wings  15 .  
         [0022]    Aircraft  11  has a controller  39  that controls propellers  28 . Controller  39  includes a computer that continuously monitors horsepower, engine rpm, true air speed, temperature and thrust, and controls the rpm of propellers  28  by varying the pitch to maintain the best engine/propeller efficiency from static conditions to maximum cruise for any given altitude. Controller  39  also controls the two-speed propeller transmission of power source  31 . It changes the drive ratio automatically when the rpm of propellers  28  needs to be slowed to maintain the best efficiency. This ratio change also allows engine  31  to continue to run at high rpms so more horsepower and better efficiencies are obtained at the higher cruise altitudes and speeds.  
         [0023]    Aircraft  11  can perform inertia assisted jump takeoff as well as a conventional hover takeoff. Furthermore, it can perform a longer runway takeoff, if desired. The inertia boosted takeoffs are particularly appropriate when the density altitude is high and aircraft  11  is at a gross weight. For an inertia assisted takeoff, the pilot increases the speed of the gas turbine engines to an rpm that is faster than its normal cruise speed. To avoid the propellers  28  from overspeeding while this occurs, controller  39  shifts the transmission to cause propellers  28  to rotate at the low speed ratio relative to the speed of the engine. Rotor  25  is driven by engines  31  to a high rotational speed, which may be between 125 and 130 rpm for a large diameter rotor. Both propellers  28  will be at the same pitch so that thrust tends to push the aircraft  11  forward. The pilot can keep the forward movement from occurring by keeping the brakes on while rotor  25  reaches the maximum speed. Torque due to rotor  25  being driven does not need to be countered because the landing gear  33 ,  35  is still supporting aircraft  11  on the ground. To reduce downwash on the airfoils due to the spinning blades  27 , ailerons  17  and stabilator  23  will be pivoted 90 degrees downward  
         [0024]    After rotor  25  reaches its maximum overspeed, the pilot reduces the rpm speed of the engines to a normal rpm. At the same time, the automatic transmission for propellers  28  changes the speed of the propellers  28  to the high speed ratio to provide optimum rpm for static thrust. Because of weights  26 , rotor blades  27  continue to spin at a high speed, faster than the speed of the drive shaft driven by the engine. The override clutch, which is part of power source  31 , enables rotor blades  27  to spin at a higher speed than the engine rpm.  
         [0025]    The pilot then changes the pitch on rotor blades  27 , referred to as collective, and releases the brakes. Aircraft  11  will begin to move forward and lift simultaneously due to the combined effects of the static thrust from propellers  28  and the rotor  25 . At this point rotor  25  will still be rotating faster than the engine drive because of inertia. Since it is not being driven by the drive shaft, rotor  25  will produce no torque on fuselage  13  at this point. Acceleration up to about 50 mph preferably occurs in less than 5 seconds. By this time, rotor  25  rpm will have slowed to its hover speed, preferably around 96 rpm and the override clutch automatically engages rotor  25 , enabling the power source  31  to again drive rotor  25 . A portion of the horsepower of power source  31  will be driving rotor  25  while another portion continues to drive the twin propellers  28 . Because of the forward speed, no counter to rotational torque of rotor  25  is required at this point.  
         [0026]    The pilot begins to reduce rotor collective pitch as forward speed increases. This allows aircraft  11  to accelerate to a more efficient condition for climb and keeps rotor blades  27  flapping within desired limits. This action also reduces the horsepower and torque going to rotor  25 . At a certain point, such as around 100 mph, the collective pitch on rotor  25  has been reduced and the pilot has tilted rotor  25  backward to a point where the rotor  25  is in full auto-rotation. During auto-rotation, rotor  25  is being driven by the air flowing through blades  27  due to forward movement of aircraft  11  and no longer requires power source  31  to drive rotor  25 . Preferably, the clutch now completely disengages rotor  25  from power source  31 . The two propellers  28  cause aircraft  11  to continue to accelerate. As aircraft  11  accelerates, the pilot continues to reduce collective rotor pitch because the wings  15  will be producing more lift. The pilot will preferably maintain a shallow climb so that aircraft  11  will continue to accelerate to a better climb speed. This requires the pilot to tilt rotor  25  forward to maintain lift equilibrium. This reduces the air flowing up through the blades  27  of rotor  25 , lets the rotor speed slow down, and further reduces rotor lift, transferring additional weight to wings  15 .  
         [0027]    At around 150 mph, the collective pitch of rotor blades  27  will be at minimum. Ailerons  17  and stabilator  23  are back to their normal positions for forward flight. At around 200 mph, the high aspect ratio wings  15  now support more than 75 percent of the weight of aircraft  11 . The rotor  25  speed is even slower, around 40 rpm, and produces less than 25 percent of the lift. This reduces the drag on rotor blades  27 .  
         [0028]    At around 250 mph, the automatic transmission of engine power source  31  changes to the low speed ratio to reduce the speed of propellers  28  relative to the engine speed. Reducing the tip speed of propellers  28  keeps the efficiency of propellers  28  at peak levels. At the same time, it allows the engine from power source  31  to continue turning at a high rpm, which allows the gas turbine engines to produce their maximum horsepower at higher altitudes. The result is that aircraft speed and flight efficiency are significantly improved. At 400 mph, the engine speed, range and flight efficiency increase dramatically once reaching a high enough altitude, such as 30,000 feet. The high aspect ratio of wings  15  allows aircraft  11  to fly very efficiently. Rotor blades  27  slow to a minimum speed of about 25 rpm, further reducing the drag on rotor blades  27 .  
         [0029]    Landing is preferably at a very steep angle and occurs in reverse order to the takeoff described above. While landing, rotor  25  is tilted aft and the collective pitch of rotor blades  27  is increased as necessary to control the rotor rpm. Air flow through rotor blades  27  will cause rotor blades  27  to speed up in rpm. The collective pitch is increased to slow the sink rate and provide for a soft landing. The clutch of power source  31  will be engaged to drive rotor  25  if it drops below the engine rpm speed. Ailerons  17  and stabilator  23  are pivoted downward. The lift produced by rotor  25  during the landing acts as a brake to slow aircraft  11  speed.  
         [0030]    For a hover type takeoff, rotor  25  will be driven at all times and will not be operated in the overspeed mode. The high speed gear ratio for propellers  28  is utilized from the beginning. Controller  39  shifts the pitch of one propeller  28  for forward thrust and the other propeller  28  for rearward thrust so as to counter torque produced by rotor  25 . The net thrust produced by propellers  28  is adjusted to equal the torque produced by rotor  25 . The pilot increases the collective pitch on rotor blades  27 , which causes the aircraft  11  to lift vertically. Propellers  28  continue to produce thrust in opposite directions, producing a torque that equals the torque on rotor  25 . The torque and thrust will continuously be monitored and the pitches on propellers  28  varied to balance the counter torque to that of the torque produced by rotor blades  27 . The pilot can continue to hover. Rudder  21  can be manipulated to provided fine yaw control if needed.  
         [0031]    When the pilot wishes to accelerate forward, he pushes a thumb slide switch mounted on the control stick that instructs controller  39  to now provide forward thrust. The more the thumb slide witch is moved forward the more of the aircraft&#39;s excess horse power is directed toward forward thrust. The controller  39  will change the pitches so that both propellers  28  now provide more net forward thrust. At some point the torque going through the rotor drive shaft will be reduced such that both propellers can produce forward thrust. The forward motion of aircraft  11  enables the pilot to reduce collective pitch on rotor blades  27  and repeat the steps explained above in connection with the rotor inertia assisted takeoff.  
         [0032]    The invention has significant advantages. The aircraft can take-off and land vertically and on short runways, yet still be capable of high speed flight. The aircraft can hover, as well and carry a substantial cargo.  
         [0033]    Although the invention has been described in some of its forms, it is not thus limited but is susceptible to various changes and modification without departing from the spirit of the invention. For example, although providing a differential in the thrust of the dual propellers counters the torque provided to the rotor by the power source in the preferred embodiment, other means for countering torque are available to use with this gyro-plane type vehicle. Intermeshing rotors that rotate in opposite directions which could be adapted to be used in this invention. Also, dual rotors separated, as in the CH-47 Chinook produced in the 1960&#39;s, can also be adapted to the gyro-plane model to provide torque countering. In both vehicles the two rotors, or sets of rotors, spin in opposite directions, thereby countering the torque being provided by power source. To incorporate these other torque countering means into this invention, wings and either propellers or tubojet power sources would be added. The wings would take up the load at higher speeds and the propellers or turbojet engines would provide forward thrust at higher speeds, thus allowing the rotors to unload as described above. Also, although the preferred embodiment has two separate wings, a single wing incorporated with the fuselage would also be feasible.