Patent Description:
Substantial prior art exists for multi-rotor helicopter designs. <CIT>, <CIT>, <CIT>, <CIT>, <CIT>, and <CIT>, are just a few of the numerous U. patents that disclose variations on the multi-rotor theme. Multi-rotor airborne craft designs have proliferated, largely because of the simplicity and utility provided by the multiple, identical fan and motor units. With a single motor speed input to these units, they control lift or altitude, craft attitude in pitch, roll and yaw and thrust or forward flight speed. For example, for attitude control, the simple axial fan, quadrotor format, generates roll by increasing the speed of the two rotors on one side of the craft and decreasing it on the other, generates pitch by increasing the speed of the two rotors a the front and decreasing it on the two rotors at the back and generates yaw by increasing the speed of two diagonally opposite rotors while decreasing the speed of the other two. This yaw torque is a result of diagonally opposite fans rotating in the same direction and the fans on the opposite diagonal rotating in the opposite direction. Any difference between the speed of these two pars then generates a resultant yaw torque on the craft. It should be noted that altitude is maintained during each of these manoeuvres because speed is increased on two fans while decreasing it on another two. It should also be noted that since half the compliment of fans rotates in one direction and the other half rotates in the opposite direction, gyroscopic forces and spool up torques are cancelled.

The cross-flow fan (CFF), tangential fan, or transverse fan, partially embedded within an airfoil and with suitable exit ducting to produce distributed propulsion and potentially the attendant propulsive efficiency, has been disclosed in numerous technical journals including (DANG). Due to the 2D nature of the flow the fan readily integrates into an airfoil for use in both thrust production and vectoring and boundary layer control. In addition to increased propulsive efficiency, embedded crossflow fan propulsion provides reduced noise and increased safety, since the propulsor is now buried within the structure of the aircraft (e.g. no exposed propellers).

In addition, multiple cross-flow fan propelled aircraft designs have been disclosed in <CIT>, <CIT>, <CIT>, <CIT>, and <CIT> and <CIT>. These designs do not disclose a compact quadrotor cross-flow fan layout and generally maintain a substantially vertical craft attitude in take-off and landing which is not accepted for passenger use but may be acceptable for drone applications. To counter this problem alternative VTOL solutions have therefore been proposed using multiple axial fans in <CIT>. This allows substantially horizontal craft attitude during take-off and landing but adds considerable weight and complexity to the craft for use during only a very short period of its operational mission. ITRM20100476A1 discloses a compact quadrotor cross-flow fan layout.

However while there are apparent advantages in multirotor craft, particularly those with embedded CFFs, a significant attitude control challenge is created when a multirotor layout deploys CFFs instead of axial fans. The mission in most applications of an VTOL craft consumes most energy during horizontal forward flight which requires the forward flight geometry to be prioritised by design and optimised over the needs of attitude control in hovering flight for example. This means that multiple crossflow fans are best deployed with all fans rotating in the one direction so that each fan helps provide efficient distributed propulsion in the one forward direction. This in turn means that diagonal rotors cannot rotate in the opposite direction to those on the other diagonal. Thus the conventional method used for yaw control as noted above in craft with multiple axial fans is no longer feasible. In addition, the gyroscopic forces generated by the rotor when the craft is rolling or yawing and the rotor spool up reaction torques are no longer cancelled.

A novel crossflow fan lift, propulsion and control element (LPCE) solution is proposed in <CIT>) and the said element is incorporated herein by reference. A number of novel multi-rotor crossflow fan eVTOL craft are proposed in Provisional Patent <CIT> (Schlunke) and the said craft are incorporated herein by reference.

The Prior art does not disclose multiple compact crossflow fan LPCEs, disposed around a craft in a compact quad format to provide the control authority and simplicity benefits of a quadrotor, efficient distributed propulsion in forward flight and sufficient vertical thrust for VTOL operation. Neither does the prior art disclose a solution to the challenge of controlling yaw when a multiple crossflow fan LPCEs are deployed with all fans rotating in the one direction so that each LPCE provides distributed propulsion in the one forward direction. The mission in most applications of an eVTOL craft consumes most energy during horizontal forward flight which requires the forward flight geometry to be prioritised by design and optimised over the needs of attitude control in hovering flight for example.

It is therefore an object of this invention to provide a system for yaw control that overcomes at least some of the problems as described herein.

The object of the invention is achieved by means of the patent claims.

In one embodiment, there is provided a VTOL airborne craft as per claim <NUM>.

There is also provided a VTOL airborne craft as per claim <NUM>.

The LPCEs can comprise helically bladed rotors to produce said lateral thrust component directed away from the central fore and aft vertical plane of the craft and as distant as possible from the central lateral vertical plane of the craft.

The system may further comprise yaw vanes and ducts that produce said lateral thrust component directed away from the central fore and aft vertical plane of the craft and as distant as possible from the central lateral vertical plane of the craft.

The yaw vanes may be positioned so as to engage with the exit thrust of the rotors during VTOL operation only, advantageously provide minimal drag in forward horizontal flight and also advantageously provide feet for landing and protecting the flaps of the LPCE.

The system for controlling yaw may comprise means for speeding up the FRH and RLH rotors and slowing down the FLH and RRH rotors, thereby producing a clockwise torque when viewed from above about the said crafts vertical axis and maintaining a constant downward thrust.

The system may comprise means for speeding up the FLH and RRH rotors and slowing down the FRH and RLH rotors, thereby producing an anticlockwise torque when viewed from above about the said crafts vertical axis and maintaining a constant downward thrust.

The described system may enable the use of conventional quadrotor software in a crossflow fan eVTOL airborne craft.

The present invention will be more fully understood and appreciated by reading the following Detailed Description in conjunction with the accompanying drawings, in which:.

Referring now to the drawings, there is seen in <FIG> the front view of an eVTOL airborne craft comprising multiple short span, crossflow fan Lift Propulsion and Control Elements (LPCEs) <NUM>, disposed around a central longitudinal fuselage <NUM> in a compact quadrotor format to create a craft with a footprint substantially similar to a car and capable of both efficient distributed propulsion in forward or rearward flight and sufficient vertical thrust for VTOL operation. Each LPCE <NUM> being comprised of an airfoil <NUM>, a flexlip <NUM> attached to and forming part of airfoil <NUM>, a crossflow fan rotor <NUM>, a flap <NUM> rotatable and mounted about the axis of rotor <NUM> and an exit duct <NUM> from the crossflow fan rotor <NUM>.

Referring now to <FIG> there is seen the rear view of the eVTOL airborne craft of <FIG> comprising multiple short span, crossflow fan Lift Propulsion and Control Elements (LPCEs) <NUM>, disposed around a central longitudinal fuselage <NUM> in a compact quadrotor format to create a craft with a footprint substantially similar to a car and capable of both efficient distributed propulsion in forward flight and sufficient vertical thrust for VTOL operation. Each LPCE <NUM> being comprised of an airfoil <NUM>, a flexlip <NUM> attached to and forming part of airfoil <NUM>, a crossflow fan rotor <NUM>, a flap <NUM> rotatable and mounted about the axis of rotor <NUM> and an exit duct <NUM> from the crossflow fan rotor <NUM>.

Referring now to <FIG> there is seen the front view of an eVTOL airborne craft comprising multiple short span, crossflow fan Lift Propulsion and Control Elements (LPCEs) <NUM>, disposed around a central fuselage <NUM> in a compact quadrotor format to create a craft with a footprint substantially similar to a car and capable of both efficient distributed propulsion in forward flight and sufficient vertical thrust for VTOL operation. Each LPCE <NUM> being comprised of an airfoil <NUM>, a flexlip <NUM> attached to and forming part of airfoil <NUM>, a crossflow fan rotor <NUM>, a flap <NUM> rotatable and mounted about the axis of rotor <NUM> and an exit duct <NUM> from the crossflow fan rotor <NUM>.

In this example, the central fuselage <NUM> is proportioned to receive two occupants seated in tandem, and comprises- two substantially similar Lift Propulsion and Control Elements (LPCEs) <NUM> mounted to the starboard side of said fuselage, one in a forward position, and one in an aft position, two substantially similar LPCEs <NUM> mounted to the port side of said fuselage, one in a forward position, one in an aft position, and two wingtip fences <NUM>, terminating the outer extremity of the two LPCEs on either side of the craft and extending chord wise from forward of the leading edge of the forward mounted LPCE to aft of the trailing edge of the flap on the aft LPCE.

In this embodiment of the invention, the orientation of the LPCEs is longitudinal relative to the footprint of a car and the seating position is lateral, allowing longer span LPCEs to be implemented while still preserving a similar footprint to a car.

Referring now to <FIG> there is seen an example of an LPCE with an airfoil <NUM>, a flexlip <NUM> attached to and forming part of airfoil <NUM>, a crossflow fan rotor <NUM>, a flap <NUM> rotatable and mounted about the axis of rotor <NUM> and an exit duct <NUM> from the crossflow fan rotor <NUM> and formed by the lower face <NUM> of flap <NUM> and the upper face <NUM> of flexlip <NUM>. With the flexlip <NUM> and flap <NUM> configured in this position and with a suitable fan speed, a longitudinal jet of air from duct <NUM> is ejected along the length of the lift, propulsion and control element to produce forward or rearward thrust and achieve distributed propulsion, and desirably the forward (or rearward) flight propulsive efficiency benefits. Synergistically, the edge <NUM> of face <NUM> restricts the inlet area to the crossflow fan to provide an optimal flow rate through the fan for best propulsive efficiency.

Referring now to <FIG> there is seen an LPCE with an airfoil <NUM>, a flexlip <NUM> attached to and forming part of airfoil <NUM>, a crossflow fan rotor <NUM>, a flap <NUM> rotatable and mounted about the axis of rotor <NUM> and an exit duct <NUM> from the crossflow fan rotor <NUM> and formed by the lower face <NUM> of flap <NUM> and the upper face <NUM> of flexlip <NUM>. With the flexlip <NUM> and flap <NUM> configured in this position, ie. with the flexlip and flap rotated with respect to <FIG>, and with a suitable fan speed, a longitudinal jet of air from duct <NUM> is ejected along the length of the lift, propulsion and control element to achieve a substantially vertical jet thereby producing upward thrust or vertical lift for VTOL operation. Synergistically, the edge <NUM> of face <NUM> moves to create a much larger inlet area to the crossflow fan thereby providing an optimal flow rate through the fan for vertical thrust.

Referring now to <FIG>, there is seen a diagrammatic section of an LPCE, for example the one illustrated in <FIG> and <FIG>, with an airfoil <NUM> with an upper surface radius <NUM> and an angle of attack <NUM> to the airstream direction <NUM> and a crossflow fan assembly consisting of a rotor <NUM>, a rear wall <NUM> and a vortex wall <NUM>, a rear flexlip <NUM> which flexes through an angle <NUM> and has an upper face <NUM>, a flap <NUM> that rotates about the rotor axis <NUM>, can rotate through an angle <NUM> and has a lower face <NUM>, an exit duct <NUM> formed by face16 and face <NUM>. Desirably, the angle of attack <NUM> is set achieve a maximum lift to drag ratio in conjunction with the angle of the exit duct jet. Desirably the area ratio of the fan inlet area to fan exit area is optimised by the movement of flap <NUM> for both high propulsive efficiency in the upper position and high vertical thrust in the lower position. This LPCE can potentially be deployed for attitude control functions, including yaw in addition to providing sufficient lift for VTOL and efficient propulsion in forward flight.

Yaw could be controlled during VTOL operation in a craft as described in <FIG> by vectoring the thrust away from the vertical and toward a more horizontal direction on one or both of the LPCEs on the Right Hand side of the craft to achieve an anticlockwise yaw torque, viewing the craft from above. Similarly, by vectoring the thrust away from the vertical and toward a more horizontal direction on one or both of the LPCEs on the Left Hand side of the craft, a clockwise yaw torque is achieved viewing the craft from above. Desirably the rotor speed would be increased to compensate for any loss of lift in the vertical direction and thereby avoid roll. However, all fans rotate anticlockwise so the gyroscopic forces from the rotors during anticlockwise yaw induces roll left so little compensation is necessary. There will be some pitch upward as the rotors spool up to compensate for lost lift but this is easily compensated by preferentially speeding the rotor of the rear LPCE.

Referring now to <FIG>, there is seen a diagram of the craft of <FIG> from above with four LPCEs, <NUM> disposed about the fuselage. A clockwise yaw torque <NUM> is indicated as viewed from above and the lateral thrust <NUM> and <NUM> from each of the LPCEs required to induce the torque <NUM> is shown. A vane and/or a helical rotor at each LPCE can produce a lateral component of thrust in the directions indicated, particularly during VTOL operation. There is seen a larger thrust component <NUM> from the Front Left Hand <NUM> and Rear Right Hand <NUM> LPCEs. This can be achieved by increasing the speed of the rotor of diagonally opposite LPCEs. Any increased lift as a result can be compensated by a reduction in the speed of the Front Right Hand <NUM> and Rear Left Hand LPCEs which delivers reduced thrust <NUM> increasing the force difference and hence the desired yaw torque. In this way conventional attitude control software from the ubiquitous axial fan quadrotors can be utilised because the speed difference between diagonally opposite pairs of fans is also used in these devices for yaw control.

Referring now to <FIG> a rotor is illustrated as might be deployed in one of the LPCEs disclosed above, said rotor having an axis <NUM>, and helically disposed blades <NUM>. This rotor, when rotated in direction <NUM> about axis <NUM> inside the housing of an LPCE will generate a thrust <NUM> that is primarily radial from the rotor. However, the helix angle of the blades will generate a lateral component of thrust <NUM> as shown which can then be used for yaw stability as described herein. Desirably the helical blades can also lower noise levels from the LPCE and strengthen the rotor.

Claim 1:
A vertical take-off and landing (VTOL) airborne craft comprising a system for controlling yaw during vertical take-off and landing (VTOL) operation of said airborne craft, wherein the airborne craft further comprises:
four crossflow fan lift, propulsion and control elements (LPCEs), each comprising a rotor and at least one airfoil with a flexlip and a flap, wherein the flexlip and the flap form vectoring means, wherein the LPCEs are disposed around a central longitudinal fuselage of the airborne craft in a compact quadrotor format, and wherein the rotors in the crossflow fan lift, propulsion and control elements (LPCEs) rotate in one common direction, wherein the system comprises:
the flexlip and the flap vector thrust from the four of the LPCEs of the airborne craft from a substantially vertical direction as it will be arranged for VTOL operation to a more horizontal forward or rearward direction, generating a forward or rearward thrust component perpendicular to the LPCE rotor axis, and
means for adjusting the rotor speed to compensate for the loss of vertical lift, where the forward thrust component from a front and/or rear Right Hand LPCE or rearward thrust component from a front and/or rear Left Hand LPCE produces a clockwise torque when viewed from above about the central vertical axis of the airborne craft and the rearward thrust component from a front and/or rear Right Hand LPCE or forward thrust component from a front and/or rear Left Hand LPCE produces an anticlockwise torque when viewed from above about the central vertical axis of the airborne craft.