Abstract:
A yaw control system and a method of controlling yaw for an aircraft are provided. The yaw control system includes a first wing set and a second wing set which are rotatable in opposite directions. Each of the wing sets includes at least two wings each including a pivotable flap forming a trailing edge of its respective wing. A flap control assembly controls the pivotable flaps of the first wing set and of the second wing set such that when the pivotable flaps of the first wing set are pivoted in a first direction by a first set angle, the pivotable flaps of the second wing set are simultaneously pivoted by a second set angle in an opposite direction, thereby providing yaw control for the aircraft.

Description:
FIELD OF THE INVENTION 
       [0001]    The present teachings relate to a yaw control system and a method of controlling yaw. In particular, the present teachings relate to a yaw control system for aircraft having counter-rotating wing sets that eliminates the need for a tail boom by shifting a part of the total lift from one wing set to the other wing set to control yaw. 
       BACKGROUND OF THE INVENTION 
       [0002]    Designs for vertical take-off and landing (VTOL) aircraft have existed for hundreds of years. As VTOL aircraft, helicopters have been effective but they are neither simple nor inexpensive to manufacture. 
         [0003]    Many known single rotor helicopters incorporate mechanically complicated structures, such as swash plates, to control pitch and roll, as well as a tail rotor to control yaw. Known dual wing (dual rotor), counter-rotating, concentric-axis helicopters rely on a tail boom rudder or tail rotor to control yaw and incorporate swash plate configurations to control pitch and roll. 
         [0004]    As a result, current helicopters are complex machines that are expensive to buy and maintain. 
         [0005]    Accordingly, there exists a need for a system and method that achieves yaw control in an aircraft in a simple and inexpensive manner. 
       SUMMARY OF THE INVENTION 
       [0006]    The present teachings disclose a system and method of controlling yaw for aircraft. 
         [0007]    In particular, a yaw control system of the present teachings includes a first wing set rotatable in a first direction and a second wing set rotatable in a second direction. The first wing set includes at least two wings each including a pivotable flap forming a trailing edge of its respective wing. The second wing set also includes at least two wings each including a pivotable flap forming a trailing edge of its respective wing. A flap control assembly controls the pivotable flaps of the first wing set and of the second wing set such that when the pivotable flaps of the first wing set are pivoted in a first direction by a first set angle, the pivotable flaps of the second wing set are simultaneously pivoted by a second set angle in an opposite direction. 
         [0008]    According to a further embodiment of the present teachings, a coaxial rotor system is provided. The coaxial rotor system includes a first rotor rotatable about an axis and having at least two wings each having a movable flap defining a wing trailing edge, and a second rotor rotatable about the axis and having at least two wings each having a movable flap defining a wing trailing edge. A flap control assembly is arranged to move the flaps of the first rotor in a first direction by a first set distance while simultaneously moving the flaps of the second rotor in an opposite direction by a second set distance such that a net lift produced by the first rotor and the second rotor remain substantially constant while one of the rotors experiences an increased drag while the other rotor experiences a decreased drag thereby creating a yaw altering torque. 
         [0009]    According to a yet further embodiment of the present teachings, a method of controlling yaw in an aircraft is provided. The method includes providing a coaxial axis, dual rotor blade system whereby each rotor includes at least two wings each having an airfoil curvature that is capable of being modified. The method further includes creating a first yaw altering torque by increasing the curvature of the airfoils of the wings of the first rotor while simultaneously decreasing the curvature of the airfoils of the wings of the second rotor such that an increase of lift generated by the first rotor is substantially equal to the decrease in lift generated by the second rotor. 
         [0010]    Additional features and advantages of various embodiments will be set forth, in part, in the description that follows, and, in part, will be apparent from the description, or may be learned by practice of various embodiments. The objectives and other advantages of various embodiments will be realized and attained by means of the elements and combinations particularly pointed out in the description herein. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0011]      FIG. 1  is a side view of the yaw control system of the present teachings incorporated in an ultralight helicopter; 
           [0012]      FIG. 2  is a front end view of the ultralight helicopter shown in  FIG. 1 ; 
           [0013]      FIG. 3  is a top view of the ultralight helicopter shown in  FIG. 1 ; 
           [0014]      FIG. 4  is a close-up perspective view of the yaw control system shown in  FIG. 1  according to various embodiments; 
           [0015]      FIG. 5  is an enlarged, perspective view of region  5  of  FIG. 1  and shows portions of the yaw control system according to various embodiments; 
           [0016]      FIG. 6  is a side view of a trailing edge of a wing showing portions of the yaw control system according to various embodiments; 
           [0017]      FIG. 7  is a top view of the wing of  FIG. 6  showing portions of the yaw control system according to various embodiments; 
           [0018]      FIG. 8  is a side end view of the wing of  FIG. 6  showing portions of the yaw control system according to various embodiments; 
           [0019]      FIG. 9  is a schematic drawing of the yaw control system of the present teachings in a position that produces a right-hand yaw; and 
           [0020]      FIG. 10  is a schematic drawing of the yaw control system of the present teachings in a position that produces a left-hand yaw. 
       
    
    
       [0021]    It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are intended to provide an explanation of various embodiments of the present teachings. 
       DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0022]      FIG. 1  shows an ultralight helicopter  100  incorporating the yaw control system  20  of the present teachings. While an ultralight helicopter  100  is described and shown throughout the present application, the yaw control system  20  of the present teachings can be incorporated in other types of aircraft, such as, for example, a backpack flyer for combat or rescue, a heavy-lift flyer for construction or cargo transport, a multi-passenger transporter allowing flexible deployment locations, and the like. 
         [0023]    Referring to  FIGS. 1 and 2 , a seat  24  for a pilot can be attached to an airframe  26  of the aircraft  100 . A wing mast  34  or other type of support structure forming a portion of the airframe  26  can be arranged to pivotally support a powertrain and transmission for a wing set assembly  150  of the aircraft  100 . For example, the powertrain and transmission can include a transmission  28  and one or more engines  30 ,  32 . The one or more engines  30 ,  32  can be supplied with fuel by way of one or more fuel lines  58  and fuel tanks  59 . As will be discussed in more detail below, the one or more engines  30 ,  32  and the transmission  28  can be arranged to power a wing set assembly including a counter-rotating dual wing set  150 . The dual wing set  150  can include a bottom wing set  70  and a top wing set  72 . A pilot-actuated control handle assembly  48  can be provided to provide operator control over at least the one or more engines  30 ,  32 , the dual wing set  150 , and the pitch and roll of the aircraft  100 . 
         [0024]    Referring to  FIG. 4 , the wing mast  34  of the airframe  26  can pivotally support the transmission  28  through center of gravity alignment arms  38 ,  40  and a wing control gimbals  36 . The wing control gimbals  36  can be arranged in operative connection with the transmission  28  by way of support brackets  42 ,  44 . A transmission base plate  46  can be arranged on an underside of a housing of the transmission  28 . One or more engines  30 ,  32  can be supported by the transmission base plate  46 . A pair of concentric axis, counter-rotating drive shafts  52 ,  54  can rotatably extend from the housing of the transmission  28  and can be arranged in driving connection with the bottom wing set  70  and the top wing set  72 , respectively. The drive shafts  52 ,  54  can be rotatably supported by one or more drive shaft bearings  56  arranged on either side of the housing of the transmission  28 . As shown in  FIG. 1 , each of the bottom wing set  70  and the top wing set  72  can be secured to a respective drive shaft  52 ,  54  via a connection hub  74  or other connection mechanism. 
         [0025]    As shown in  FIGS. 1 ,  2 ,  4 , the pilot-actuated control handle assembly  48  can include one or more control bars  60 ,  62 . Each of the one or more control bars  60 ,  62  can include a user-manipulatable handle portion, such as handle portions  68 ,  78 , respectively. For example, control bar  60  can support a handgrip-style engine speed control handle  68  at its lower end. The engine speed control handle  68  can include a throttle control that is in operative connection with a fuel control mechanism, such as, for example, one or more carburetors of the engines  30 ,  32 . 
         [0026]    Further, yaw control bar  62  can support a handgrip-style yaw control handle  78  at its lower end. As will be more fully discussed below, manipulation of the yaw control handle  78  can be arranged to control the yaw control system  20  of the present teachings. For example, manipulation of the yaw control handle  78  can result in one or more control signals being communicated to the dual wing set  150 . Such signals can be communicated to the dual wing set  150  wirelessly by way of a radio transmitter  64  mounted on the aircraft  100 , as shown in  FIG. 1 . 
         [0027]    Referring to  FIG. 4 , the one or more control bars  60 ,  62  can be operatively connected to a pivotably arranged portion of the aircraft  100 , such as, for example, the housing of the transmission  28 . Preferably, the control bars  60 ,  62  can be connected to the transmission base plate  46 . During flight, a pilot can adjust the pitch of the wing sets  70 ,  72  by pulling or pushing the control bars  60 ,  62  toward and away from his body. Such a motion will result in the wing sets  70 ,  72  being pivoted with respect to the airframe  26  through a pitch pivot axis  110 . The pitch pivot axis  110  can extend in a lateral direction with respect to the longitudinal axis of the aircraft  100 . In this manner, the wing sets  70 ,  72  can be pitched to the front or back of the aircraft  100 . 
         [0028]    Similarly, a pilot can adjust the roll angle of the wing sets  70 ,  72  by moving the control bars  60 ,  62  in a direction to the left or right of his body. Such a motion will result in the wing sets  70 ,  72  being rolled with respect to the airframe  26  through a roll pivot axis  112 . The roll pivot axis  112  can extend in a direction which coincides with the longitudinal axis of the aircraft  100 . 
         [0029]    The yaw control system  20  of the present teachings will now be described with reference to  FIGS. 3 ,  5 - 8 . Referring initially to  FIGS. 3 and 7 , each wing set  70 ,  72  can include a pair of wings  120 . The wings  120  of a respective wing set can extend radially outwardly in diametrically opposite directions by way of wing spars  122 . The wings  120  and/or the wing spars  122  can be arranged to provide the wing sets  70 ,  72  with a fixed angle of attack. 
         [0030]    One or more wings  120  can include a pivotable flap, referred hereinafter to as a yawleron  82 . As shown in  FIGS. 5 and 8 , the yawlerons  82  can be pivotally attached to a wing  120  by way of one or more hinges  80  such that the yawlerons  82  form a trailing edge of the wing  120 . The hinges  80  allow the yawlerons  82  to pivot about a pivot axis  124  above and below a plane of a chord of a wing  120 . Each yawleron  82  can define the trailing edge of a respective wing  120 . According to an embodiment, a yawleron  82  can define about 50% or more of the trailing edge of a wing  120 , and preferably can define about 90% or more of the trailing edge of a wing  120 , and most preferably can define substantially the entire trailing edge of a wing  120 . 
         [0031]    A control system for controlling the pivotal motion of the yawlerons  82  will be described with reference to  FIG. 5 . Each hinged yawleron  82  can be operatively connected to one or more motors  84  which can be powered to control pivotal movement of the yawleron  82 . For example, the motor  84  can be a servo motor that is mounted on a wing  120 . The servo motor  84  can be connected to the yawleron  82  by an actuator linking rod  88 . One end of the linking rod  88  can be connected with the yawleron  82  by way of a bracket arm  86  and the other end of the linking rod  88  can connect to a drive wheel and pin assembly  90 . Accordingly, a control signal directing a rotation of the servo motor  84  in one direction will pivotally raise the yawleron  82  about hinge pivot axis  124  and a control signal directing a rotation of the servo motor  84  in the other direction will pivotally lower the yawleron  82  about hinge pivot axis  124 . 
         [0032]    As shown in  FIGS. 6 and 7 , one or more receivers  66  can be provided to receive control signals from the pilot to control the operation of one or more servo motors  84 . Receivers  66  can be provided in various locations on the aircraft  100 , and preferably on or in the vicinity of the wings  120 . The receivers  66  can be wireless receivers which receive wireless signals from one or more radio transmitters  64  situated on the aircraft  100 . As shown in  FIG. 1 , a radio transmitter  64  can be mounted on the housing of the transmission  28  but could be located anywhere on the aircraft  100  so as to be in radio contact with the one or more of the radio receivers  66 . The radio transmitter  64  can broadcast electromagnetic energy whose frequency can resonate with one or more of the radio receivers  66  arranged with the wings  120 . During operation, a radio receiver  66  arranged in a wing  120  receives control signals from the radio transmitter  64  and sends a corresponding control signal to a servo motor  84  which is energized to raise or lower a yawleron  82 . 
         [0033]    One or more power packs  92  can be provided to deliver electrical power to the servo motor  84  and the radio receiver  66 . The one or more power packs  92  can be provided in various locations on the aircraft  100 , and preferably on or in the vicinity of a wing  120 . 
         [0034]    According to various embodiments, other control mechanisms can be implemented to achieve pivotal motion of the yawlerons  82 . For example, mechanical, pneumatic, electric, radio, or other control links to a pilot can be calibrated as required to optimize the pivotal motion of the yawlerons  82 . 
         [0035]    During operation of the yaw control system  20  of the present teachings, a pilot manipulates a controller, such as, for example, the yaw control handle  78 , which results in a coordinated movement of the yawlerons  82  to achieve yaw adjustment of the aircraft  100 . More specifically, in each of the bottom wing set  70  and the top wing set  72 , the yawlerons  82  of each wing  120  are arranged to pivot in tandem. In other words, both of the yawlerons  82  of the top wing set  72  are coordinated to pivot upwardly and downwardly in concert with respect to a neutral position. Similarly, both of the yawlerons  82  of the bottom wing set  70  are also coordinated to pivot upwardly and downwardly in concert with respect to a neutral position. The coordinated pivoting movement of the yawlerons  82  in each of the wing sets  70 ,  72 , can be arranged such that the pivot angles of each yawleron  82  is substantially identical during the full range of pivotal motion of the yawlerons  82 . 
         [0036]    Simultaneously, the yawlerons  82  of the bottom wing set  70  and the yawlerons of the top wing set  72  are also coordinated to move in concert with each other as follows. As the yawlerons  82  of the bottom wing set  70  are pivoted downwardly from the neutral position, the yawlerons  82  of the top wing set  72  are pivoted upwardly from the neutral position. The opposite is also true for the coordinated movement between the wingsets  70 ,  72 . That is, as the yawlerons  82  of the bottom wing set  70  are pivoted upwardly from the neutral position, the yawlerons  82  of the top wing set  72  are pivoted downwardly from the neutral position. 
         [0037]    At any time during the operation of the yaw control system  20  of the present teachings, the wing set  70 ,  72  whose yawlerons  82  are in a downwardly pivoted position with respect to a neutral position generates more lift than when its yawlerons  82  are in the neutral position. The wing set  70 ,  72  whose yawlerons  82  are in the upwardly pivoted position with respect to a neutral position generates less lift than when its yawlerons  82  are in the neutral position. In the yaw control system  20  of the present teachings, the ratio of the amount of downward pivot of the yawlerons  82  of one of the wingsets  70 ,  72  to the amount of upward pivot of the yawlerons  82  of the other wingsets  70 ,  72  can be strictly coordinated so that an increase in lift of one wing set  70 ,  72  is equal to the decrease in lift of the other wing set  70 ,  72 . Accordingly, a total lift produced by both wing sets  70 ,  72  at any time during flight is substantially equal to the total lift of both wing sets  70 ,  72  when their yawlerons  82  are in the neutral position. 
         [0038]    Accordingly, in effect some part of the lift is shifted from one wing set  70 ,  72  to the other wing set  70 ,  72  during operation of the yaw control system  20  of the present teachings. The wing set  70 ,  72  producing the increased lift experiences a concomitant increase in drag, while the other wing set  70 ,  72  experiences a decreased drag. These corresponding increases and decreases in drag can be used to control the yawing of the aircraft  100 , as explained further below. 
         [0039]    As has been discussed above, the wing sets  70 ,  72  are rotated by at least one or more engines  30 ,  32  that are connected to the airframe  26 . When the yawlerons  82  are in a neutral position, the engines  30 ,  32  experience no net torque. When one of the wing sets  70 ,  72  is subjected to increased drag, it offers increased resistance to rotation. The other wing set  70 ,  72  experiences less drag and offers less resistance to being rotated. Increased resistance from one wing set  70 ,  72  coupled with less resistance from the other wing set  70 ,  72  results in a net torque in one direction on the one or more engines  30 ,  32  which is transmitted to the airframe  26 . This torque manifests itself as yaw by the airframe  26  in the same direction of rotation as the net torque on the one or more engines  30 ,  32 . When the lift is shifted to the opposite wing set  70 ,  72 , the torque is generated in the opposite direction whereby the airframe  26  yaws in the opposite direction. 
         [0040]    As the lift is shifted between the wingsets  70 ,  72 , the total lift on the aircraft  100  is unchanged. Accordingly, in level flight the altitude of the aircraft  100  remains unchanged. Similarly, a rate of descent or a rate of ascent will be unchanged as the aircraft  100  yaws in either direction. In a hover mode, the aircraft  100  will remain at a constant altitude as the aircraft  100  yaws in either direction. 
         [0041]    Accordingly, in the yaw control system  20  of the present teachings, the yawlerons  82  of the top and bottom wing sets  70 ,  72  are arranged to move simultaneously in opposite directions in strictly defined increments so that the combined lift of the wing sets  70 ,  72  remains constant while producing yaw in a direction desired by the pilot of the aircraft  100 . 
         [0042]    According to various embodiments, the yawlerons  82  of the top wing set  72  and the yawlerons  82  of the bottom wing set  70  do not necessarily move or pivot by the same amount of rotation. Instead, they can be arranged to move independently to different angles in order to optimally achieve the most efficient shift of lift from one wing set to the other wing set. That is, the yawleron ‘up’ angle of one wing set does not necessarily correspond to the optimum ‘down’ angle of the other wing set. Such an arrangement can be due to the characteristics of the specific airfoil design that is chosen for the wings. 
         [0043]    A brief description of pilot controlled operation of yaw control system  20  of the present teachings will now be provided with additional reference to  FIGS. 9 and 10 . 
         [0044]    As a pilot rotates the yaw control handle  62  in a clockwise direction, for example, signals can be sent from the radio transmitter  64  to one or more radio receivers  66  arranged on the wings  120 . Radio receivers  66  arranged on the wings  120  of the top wing set  72  can receive signals directing corresponding servo motors  84  to rotate and to reciprocate linking rods  88 , thereby pivoting bracket arms  86  attached to corresponding yawlerons  82 . As shown in  FIG. 9 , this pivoting action rotates the yawlerons  82  of the top wing set  72  in concert downwardly about their hinge axes  124 . As a result, the curvature of the airfoils of the wings  120  of the top wing set  72  are effectively increased, producing increased lift which is accompanied by an increased drag on the top wing set  72 . 
         [0045]    Simultaneously, radio receivers  66  arranged on the wings  120  of the bottom wing set  70  each direct corresponding servo motors  84  to rotate and reciprocate linking rods  88 , thereby pivoting bracket arms  86  attached to corresponding yawlerons  82 . As shown in  FIG. 9 , this pivoting action rotates the yawlerons  82  of the bottom wing set  70  in concert upwardly about their hinge axes  124 . As a result, the curvature of the airfoils of the wings  120  of the bottom wing set  70  are effectively decreased, resulting in decreased lift which is accompanied by a decreased drag on the bottom wing set  70 . 
         [0046]    In this condition, the sum of the torque vectors on the wing drive shafts  52 ,  54  is not equal to zero. For example, the wing drive shaft  54  for the top wing set  72  is producing more torque in a counter-clockwise direction than the wing drive shaft  52  is producing in a clockwise direction. The airframe  26  is not anchored to any massive body and is therefore free to rotate about an axis substantially coaxial with the axis of the wing drive shafts  52 ,  54 . Because the torque on the wing drive shafts  52 ,  54  is generated by the one or more engines  30 ,  32  which are attached to the airframe  26 , an equal but opposite torque vector acts on the airframe  26  through the corresponding engine which turns the airframe  26  in a clockwise direction, and the aircraft  100  yaws to the right. 
         [0047]    According to various embodiments, the radio transmitter  64  and the one or more receivers  66  can be arranged to respond proportionally to the amount of rotation of the yaw control handle  62 . For example, turning the yaw control handle  62  one-third of its maximum rotation will produce one-third of a maximum movement of the yawlerons  82  in the desired directions. Therefore, the yaw control handle  62  of the yaw control system  20  of the present teachings can be arranged to control rate of yaw and yaw direction. 
         [0048]    At this point, if for example, the airframe  26  is facing 90 degrees to the right from the direction the pilot desires, the pilot can rotate the yaw control handle  62  in a counter-clockwise direction. This action sets the yawlerons  82  into a configuration opposite to previously described, see  FIG. 10 , and the airframe  26  yaws left. When the airframe  26  is facing in the desired direction, the pilot returns the yaw control handle  62  to its neutral position, and yawing of the aircraft  100  is halted. 
         [0049]    Those skilled in the art can appreciate from the foregoing description that the present teachings can be implemented in a variety of forms. Therefore, while these teachings have been described in connection with particular embodiments and examples thereof, the true scope of the present teachings should not be so limited. Various changes and modifications may be made without departing from the scope of the teachings herein.