THRUST VECTORING IN AERIAL VEHICLES
The present invention relates to the use of thrust vectoring in aerial vehicles, and in particular to the use of thrust vectoring in micro aerial vehicles .
Micro aerial vehicles are used in a number of applications such as defence observations and environmental inspections. It is generally known to control the pitch and stability of an aircraft using control surfaces on an aerofoil. In particular, in micro aerial vehicles, it is common for the trailing edge of an aerofoil to include a reflex to improve the longitudinal stability. However, this reflex decreases the overall lift of the aerofoil. A further problem encountered with such vehicles is a reduction in efficiency resulting from the use of a rudder to control direction of flight and lateral stability. In particular, at high angles of attack, a large amount of flow is separated at the wing region in micro aerial vehicles during flight. Since the rudder is generally located directly above the wing, this separation of flow has a direct effect on the efficiency of the rudder in controlling the direction of flight and maintaining lateral stability. Micro aerial vehicles, and in particular those with fixed wings, can travel at relatively high speeds and it is therefore a problem to maintain directional control and stability whilst also increasing the overall aerodynamic efficiency. Furthermore, aerodynamic efficiency is important in micro aerial vehicles because it can significantly affect their range. Since the use of moving control surfaces tends to reduce the aerodynamic efficiency, it is desirable to reduce their use.
Accordingly, the present invention provides an aerial vehicle comprising an aerofoil or wing, a propeller, which may be generally forward facing, a drive motor arranged to drive the propeller about a drive axis to generate thrust, and mounting means on which the propeller is mounted
so that the drive axis can be moved, or have its orientation varied, relative to the aerofoil thereby to vary the direction of the thrust, the vehicle further comprising thrust control means arranged to control pivoting or movement of the propeller so as to control the direction of the thrust, thereby to control the direction of travel of the vehicle.
The thrust control means may be arranged to move the propeller to change the direction of the thrust at least partially in a lateral direction thereby to control yaw of the vehicle. The thrust control means may be arranged to vary a lateral component of the thrust thereby to control yaw of the vehicle.
The propeller may be arranged to pivot about a substantially vertical pivoting axis to control the yaw of the vehicle.
The thrust control means may be arranged to move the propeller to change the direction of thrust at least partially in a vertical direction thereby to control pitch of the vehicle. The thrust control means may be arranged to vary a vertical component of the thrust thereby to control pitch of the vehicle. The propeller may be arranged to pivot about a horizontal pivoting axis to control the pitch of the vehicle.
The motor may be arranged to pivot with the propeller. The propeller and motor may together form a pivoting assembly which has a centre of gravity, and the mounting means may be arranged such that the centre of gravity moves at least partially in a lateral direction as the drive axis moves. The centre of gravity may be arranged to move partially in the same lateral direction as the direction in which the propeller is turned.
The propeller may be centrally mounted on the vehicle, in particular it may be mounted centrally in the lateral direction of the vehicle.
The aerial vehicle may further comprise a receiver arranged to receive a signal from a transmitter to control the thrust control means.
The aerial vehicle may further comprise biasing means arranged to bias the propeller towards a reference position in which the aerial vehicle is stable. Preferably, the biasing means biases the propeller towards a position in which the vehicle is in straight-ahead flight.
The aerial vehicle may further comprise control means arranged to vary the speed of rotation of the drive motor. In addition to controlling the forward thrust, variations in the speed of rotation of the drive motor may be arranged to control the pitch of the aerial vehicle.
Preferred embodiments of the invention will now be described with reference to the accompanying drawings in which:
Figure 1 is a schematic representation of a micro aerial vehicle according to an embodiment of the present invention;
Figure 2 is a schematic plan view of the vector control means and propeller of the micro aerial vehicle of Figure 1 ;
Figure 3 illustrates the side thrust generated by deflection of the propeller of Figures 1 and 2;
Figure 4 is a schematic representation of the pitch control of a micro aerial vehicle according to a second embodiment of the invention; and
Figure 5 is a further schematic representation of the micro aerial vehicle of Figure 4.
Referring to Figure 1, a micro aerial vehicle 1 according to one embodiment of the invention comprises a fixed wing 2 mounted on a body 3, and a propeller 4 powered by a drive motor 6. The motor 6 is mounted on the front end of the body 3 on a pivoting mounting so that it can rotate about a vertical axis, thereby varying the direction of thrust provided by the propeller 4 as will be described in more detail below. A thrust vector control system 8 is arranged to control the thrust vectoring, i.e. the direction of thrust, of the propeller. The propeller 4 is located at the front end of the body 3 and faces in a forward direction with respect to the intended direction of flight of the vehicle. The propeller is positioned centrally in the transverse direction of the wing 2 and body 3 for stability and balance. The fixed wing comprises an aerofoil 2 with a large surface area and no moving control surfaces to maximise the lift of the aerofoil and the aerodynamic efficiency of the micro aerial vehicle 1.
The propeller 4 comprises two propeller blades 10 extending from a spindle 12. It will be appreciated that any suitable number of blades may be used. The spindle 12 is rotated about its drive axis and powered by the drive motor 6 to rotate the propeller 4 and provide thrust in a forward direction. In addition to the thrust generated by the propeller 4, the speed of rotation of the propeller also controls the pitch of the micro aerial vehicle 1. Indeed, the pitching moment and thrust generated by the propeller 4 are directly proportional to the speed of rotation of the propeller 4. Control of the forward thrust and pitching moment provided by the forward facing propeller 4 provides both good longitudinal stability and good longitudinal manoeuvrability of the vehicle.
The thrust vector control system 8 controls the yaw of the micro aerial vehicle 1. Referring to Figure 2, the vector control system 8 comprises two spaced apart actuation rods 14, 16 each driven from a rear end by an electric actuator 18, 20 respectively. The electric actuators are mounted
on either side of the body 3 underneath the fixed wing 2, but may be in any other suitable location. The actuation rods 14, 16 are connected at their front ends to respective points 22, 24 on a cross beam 25 on the propeller drive motor 6. The propeller 4 is supported on the drive motor 6 and the drive motor is mounted on a pivoting mounting 5 such that the drive motor 6 and propeller 4 are arranged to pivot about a vertical pivot axis 32 which is perpendicular to, and intersects, the axis of rotation 30 of the propeller. Points 22 and 24 are located offset to the left and right respectively of the vertical pivoting axis 32 of the motor 6 and propeller 4. Actuation of rod 14 in a forward direction therefore pushes on the cross beam 25 at point 22, to the left of the pivot axis 32, causing the drive motor 6 to pivot and turn the propeller 4 to point to the right. Similarly, actuation of rod 16 in a forward direction pushes on the cross beam 25 at point 24, to the right of the pivot axis 32, and causes the propeller 4 to pivot and turn the propeller 4 to point to the left.
Referring to Figure 3 , it can be seen that rotation of the drive motor 6 and propeller 4 through an angle, for example of 5°, about the vertical axis 32 from its reference 'straight ahead' direction in line with the longitudinal axis of the vehicle, causes the propeller 4 to produce both forward thrust shown by thrust vector component 26 and a side thrust shown by thrust vector component 28, giving a resultant thrust vector in the direction in which the propeller is pointing. The distance of extension or retraction of rods 14 and 16 controls the angle of rotation of the drive motor 6 and, combined with the rotational speed provided by the drive motor 6, controls the lateral component of the thrust from the propeller. Specifically the magnitude and direction (left or right) of the lateral component of thrust is varied and controlled, and the proportion of the total thrust of the propeller which is in the lateral direction is controlled. In this way, the thrust vectoring provided by control of the direction in which the propeller is facing, and hence the direction of the thrust which
it produces relative to the body and wing of the vehicle, controls the yaw of the micro aerial vehicle 1.
Referring to Figure 2, the centre of gravity 34 of the pivoting assembly which comprises the motor 6 and propeller 4, is forward of the vertical axis 32. Therefore rotation of the pivoting assembly including the drive motor 6 about the pivot axis 32 moves the position of the centre of gravity 34 of the assembly laterally with respect to the main body 3 of the aerial vehicle 1. The redistribution of weight causes the aerial vehicle 1 to roll, which adds to the effect of the side thrust to control the direction of flight. For example, forward actuation of rod 16 will cause the drive motor to pivot to the left about pivot axis 32 on the pivoting mounting 5, moving the position of the centre of gravity 34 of the pivoting assembly to the left of its central starting reference point on the central plane of the vehicle. This movement tends to cause the aerial vehicle 1 to roll to the left, adding to the direction change caused by the side thrust generated by the propeller 4.
The micro aerial vehicle 1 is controlled remotely and the vehicle therefore includes a receiver (not shown) , such as a radio frequency receiver, in communication with a remote transmitter. The speed of rotation of the drive motor 6, and hence the propeller 4, and the direction of the propeller are therefore controlled remotely by an operator using the transmitter to control the forward thrust and pitch of the vehicle 1 , as well as yaw. For example, the remote transmitter may be part of a control unit comprising a joystick control, and the electric actuators 18, 20 may control lateral deflection of the motor and propeller in response to movement of the joystick.
The actuators 18, 20 are arranged to allow free movement of the rods 14, 16 when they are not applying force to them, and the propeller 4 is biased
to return to a central reference position for example using a spring mechanism. This means that, when no steering input is being applied, the vehicle will stabilize in straight-ahead flight.
In an alternative embodiment, the vectoring control system only comprises one bi-directional electric actuator 18 and one actuation rod 14 connected to the drive motor 6 at a position offset to one side of the pivot axis 32. Forward movement of the actuation rod from its starting position will cause the drive motor 6 to pivot about the pivot axis 32 in one direction, and rearward motion of the actuation rod 14 from its starting position will cause the drive motor 6 to rotate in an opposite direction about the vertical axis 32. In another alternative embodiment, the vectoring control system comprises two actuation rods 14, 16 connected to the drive motor at positions offset to either side of the pivot axis and controlled by a single electric actuator 18
The thrust vectoring described above can greatly improve the efficiency of the micro aerial vehicle over the traditional rudder controlled systems. For example, in known systems, if the forward thrust and pitching is controlled by the speed of the drive motor 6 and yaw is controlled by a rudder then this rudder is the only control surface and lateral stability and manoeuvrability is poor. If the vehicle starts to roll it can only be stabilised through large deflection of the rudder, resulting in high energy consumption by the rudder power source. Thrust vectoring in accordance with embodiments of the invention as described above eliminates or reduces the need for the rudder control surface so that all movement of the vehicle can be controlled by thrust vectoring. Tests and computer simulations have shown that the side force created by the thrust is much greater than side force created by a control surface such as a rudder and a vehicle controlled by the thrust vectoring system is therefore more manoeuvrable and laterally stable. Similarly, for the same degree of
manoeuvrability the thrust vectoring system is much more efficient than the rudder controlled system.
In a further embodiment of the invention, as shown in Figure 4, the drive motor 6 is mounted beneath a support 46 and the drive motor 6 and propeller 4 are arranged to pivot about a horizontal lateral pivot axis 38 through the support 46. This allows control of the pitch of the aerial vehicle. Rotating the drive motor 6 and propeller 4 to point upwards generates both forward thrust and upward thrust, causing the vehicle to rise. Rotation of the drive motor 6 and propeller 4 to point downwards generates forward thrust and downward thrust causing the vehicle to descend. Movement of the drive motor 6 and propeller about the pivot axis 38 is controlled by an actuation rod 40, which driven by an electric motor 44. The actuation rod is connected to the drive motor at a position above the support 46 such that forward motion or extension of the actuation rod 40 causes the drive motor 6 and propeller to pivot about pivot axis 38 and point downwards, generating downward thrust. Similarly, referring to Figure 5, backward movement or retraction of the actuation rod 40 causes the drive motor 6 and propeller 4 to rotate about the horizontal axis and point upwards, generating upward thrust. In this way the direction (up or down) and magnitude of the vertical component of the thrust from the propeller can be controlled, which in turn enables the proportion of the propeller thrust that is in the vertical direction to be controlled.
This rotation of the motor and propeller can be used in addition to controlling the pitch by the speed of rotation of the motor to further improve the control, manoeuvrability and stability of the vehicle in the longitudinal direction, i.e. in pitch.
Rotation of the drive motor 6 and propeller 4 to control pitch may also be used in combination with the yaw control described above to provide full directional control of the aerial vehicle using thrust vectoring.
It will be appreciated that there are many variations of the embodiment described above. For example, a micro aerial vehicle as described above may typically have a wingspan of less than 50cm. However, the vehicle may be a larger aerial vehicle arranged to be controlled by an on-board pilot or alternatively may be a smaller aerial vehicle or 'fly' . The larger aerial vehicles may be mounted on wheels to enable them to take off and land on a surface. The smaller micro aerial vehicles may be manufactured without wheels to reduce the weight of the vehicle and drag. These may be launched by hand.
The aerial vehicle may comprise more than one forward facing propeller in an arrangement to best suit the size and design of the vehicle. For example, a propeller could be mounted on the leading edge of each of two wings. One or both of the propellers may be controlled by a thrust vectoring system as described above to provide maximum directional control and lateral stability.