FIELD OF THE INVENTION

The present invention relates to airborne craft and, more specifically to a multirotor, distributed propulsion vertical take-off and landing (VTOL) craft, manned or unmanned.

BACKGROUND OF THE INVENTION

Electrical Vertical Take-Off and Landing (eVTOL) airborne craft have recently emerged as potential solutions for urban traffic congestion and the attendant fuel consumption and emissions problems.

This solution has been studied extensively by Moore et al while at both NASA and Uber and a number of high potential technical options have been identified for promising near term research and development (https://www.uber.com/us/en/elevate/). These include the use of distributed propulsion to achieve improved propulsive efficiency leading to reduced energy consumption in horizontal and forward flight, the dominant component of typical mission energy requirements. Reduced battery size and/or increased range and/or increased payload and/or improved hover reserve are all desirable results of the improved forward flight propulsive efficiency. eVTOL was a further technology proposed by Moore et al and has continued to grow in popularity as the weight and cost of batteries , electric motors and motor controllers continues to fall under pressure from the growing global penetration of electric vehicles.

Distributed propulsion was first researched extensively during the investigation of Jet Flaps in the early 1960’s by Williams et al (J. Williams, S. F.-J. Butler and M. N. Wood The Aerodynamics of Jet Flaps R & M. No. 3304) on the Hunting H.126 which was shared with NACA in the U.S. This technology has surfaced more recently in projects by Maxwell and NASA where multiple axial electric propulsion fans are distributed along a conventional airfoil, a form of distributed propulsion that has been deployed even more recently by Lillium, Airbus and others.

Efficient crossflow fans were developed and documented by Hancock et al (Hancock JP. Test of a high efficiency transverse fan. AIAA-80-1243) and their deployment in aircraft propulsion and flow control has been extensively investigated and documented by Dang, Bushnell (Thong Q.Dang, PeterR. Bushnell, Aerodynamics of cross-flow fans and their application to aircraft propulsion, Progress in Aerospace Sciences 45(2009)1-29) and flow control and Kummer et al. Through the period around 2019-2020, major eVTOL contenders for the urban airborne mobility market encountered the challenge of carrying sufficient energy reserve to fly on from a compromised landing site to an alternate uncompromised site or to hover for up to 45 minutes. The mass of additional battery required is challenging for an eVTOL craft because the energy required to generate lift during hover is generally at least 5 times greater than that required for forward flight. This hover reserve dictated a larger more expensive craft, carrying more passengers and the dedicated landing infrastructure became correspondingly more sophisticated and expensive.

Substantial prior art exists for multi-rotor helicopter designs. U.S. Pat. No. 2,529,033 (Linville), issued Nov. 7, 1950, U.S. Pat. No. 2,540,404 (John), issued Feb. 6, 1951, U.S. Pat. No. 2,623,711 (Pullen), issued Dec. 30, 1952, U.S. Pat. No. 2,646,130 (Udelman), issued Jul. 21, 1953, U.S. Patent Publication No. 2014/0032034 (Raptopoulos), published Jan. 30, 2014, and U.S. Design Pat. No. D71O, 452 (Barajas), issued Aug. 5, 2014, are just a few of the numerous U.S. 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 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 but each pair rotates in opposite directions. It can be noted that altitude is maintained during each of these manoeuvres because speed is increased on two fans while decreasing it on another two.

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 U.S. Pat. No. 6,016,992 (Kolacny), issued Jan. 25, 2000, U.S. Pat. No. 6,527,229 (Peebles), issued Mar. 4, 2003, U.S. Pat. No. 7,641,144 (Kummer), issued Jan. 5, 2010, U.S. Pat. No. 8,579,573 35 (Kolacny), issued Nov. 12, 2013, and U.S. Patent Publication Nos. 2012/0111994 (Kummer), published May 10, 2012 and 2014/0048657 (Lin), published Feb. 20, 2014. Some attempts have been made to vary the geometry of the fan exit region in multiple cross-flow fan propelled aircraft designs. These geometry changes vector the exit flow through relatively small angles for flight at high angles of attack and/or pitch control during forward flight. However VTOL capability using the same airfoil fan and exit ducting has not been achieved at passenger sensitive craft pitch angles due to the difficulty of creating an aerodynamically efficient and capable geometry for both VTOL and forward flight operation. Alternative VTOL solutions have therefore been proposed using multiple axial fans in U.S. Pat. No. 9,783,291 B2 (Kummer), issued Oct. 10, 2017.

A novel crossflow fan lift, propulsion and control element (LPCE) solution is proposed in Australian provisional Patent 2021902564 (Schlunke) and the said element is incorporated herein by reference.

SUMMARY OF THE INVENTION

It then becomes clear that, despite many advantages, 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, sufficient vertical thrust for VTOL operation and an acceptably horizontal attitude during take-off and landing for human occupant comfort. Neither does the prior art disclose a compact crossflow fan LPCE using an airfoil with the very low aspect ratio near unity that is needed to achieve a craft footprint similar to that of an automobile. As a result, prior art vehicles intended for urban operation cannot achieve the automotive footprint desired to give access to car parks, roadways and driveways for landings and takeoff and emergency diversions from an intended landing site. Prior art eVTOL vehicles therefore require much larger formats to carry both their payload and the necessary battery reserve to facilitate flight to alternative landing sites in an emergency. Prior art vehicles and their landing site infrastructure are therefore expensive and are a challenging economic solution to urban congestion.

The object of the invention is to provide an airborne craft that overcomes at least some of the above mentioned problems.

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

In one embodiment, there is provided an airborne craft comprising multiple crossflow fan LPCEs (Lift, propulsion and control element), arranged around a central fuselage in such a way that the LPCEs provide both distributed propulsion in forward flight and sufficient vertical thrust for vertical take-off and landing (VTOL) where the arrangement of LPCEs is configured to ensure that the fuselage remains substantially horizontal in vertical, horizontal and transitional flight.

The multiple short span, crossflow fan LPCEs, can be of the type described in detail in Australian provisional Patent 2021902564 (Schlunke).

In some embodiments, the central fuselage is longitudinal, and the airborne craft comprises four short span crossflow fan LPCEs arranged around the central fuselage in a compact quadrotor format with a footprint substantially similar to a car.

The capable of both efficient distributed propulsion in forward flight and sufficient vertical thrust for VTOL operation.

The rotor speed of the fans in said multiple LPCEs can be configured to be varied to provide attitude control authority and control system simplicity.

In one embodiment there is provided an airborne craft comprising a central fuselage proportioned to receive two occupants seated in tandem, two substantially similar Lift Propulsion and Control Elements (LPCEs) mounted to the starboard side of said fuselage, one in a forward position, one in an aft position, two further substantially similar LPCEs mounted to the port side of said fuselage, one in a forward position, one in an aft position, and two wingtip fences, terminating the outer extremity of the two LPCEs on either side of the craft and extending chordwise 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 further embodiments of the present invention a. The two forward LPCEs as described above can be attached to the fuselage to deliver an optimal angle of attack between the LPCEs and the incoming air in forward flight, desirably in the range from 5 to 25 degrees. The angle between the forward LPCEs and the floor of the fuselage can be zero so that the floor of the craft is also at the desired angle of attack (AO A). b. The two forward LPCEs as described above can be blended into an appropriately shaped nose section of the fuselage to form a continuous wing leading edge across the front of the craft. c. The front pair of LPCEs can be attached to the fuselage to have the same angle to the fuselage as the rear pair of LPCEs d. The front pair of LPCEs can be attached to the fuselage to have a different angle to the fuselage as the rear pair of LPCEs, said angle providing an increased angle of attack for the rear LPCEs, said increased angle being desirably between 1 and 25 degrees e. The front pair of LPCEs can be attached to the fuselage to have a different height from the fuselage floor as the rear pair of LPCEs, such height being in the range from 0 to 2.0m f. At least one of the thickness and the chord of the airfoil profile of the rear LPCEs airfoils, can be different to the respective thickness and/or chord of the LPCEs in the front. g. The diameter of the rear LPCEs rotors can be different to those of the front. h. More than 1 pair of rear LPCEs can be provided, said additional pairs being positioned above and forward or aft of first pair of rear LPCs to provide further lift, said additional pairs having the same or different spans as said first pair

An embodiment of the present invention may include any combination of the aspects described.

It is also an aspect of the present invention that the Lift, Propulsion and Control Elements (LPCEs) can incorporate an airfoil whose span will be in the range from 0.7 to 1.2m and whose aspect ratio will be in the range from 0.5 to 2. This is well outside the range used by conventional fixed wing aircraft. The very short span generates very high lift because of the combination of a very thick airfoil, a crossflow fan which avoids separation on the upper face of the airfoil by ingesting the boundary layer and an outboard wingtip fence that negates tip vortex losses.

It is also an aspect of the present invention that wingtip fences can extend radially outward from the outboard profile of each LPCE a distance of between 1% and 15% of the chord of the said airfoil within the LPCE. This avoids the loss of lift normally associated with very low aspect ratio wing elements.

It is also an aspect of the present invention that said wingtip fences can extend from the forward LPCE to the rear LPCE and are structurally connected to each to provide additional craft stiffness and crash safety.

In one aspect, the airborne craft comprises four LPCEs each comprising a thick airfoil, embedded cross-flow fan and exit duct element that produces distributed flow to achieve high propulsive efficiency in forward flight and wherein said exit duct can be reconfigured to produce a vertical jet for vertical take-off and landing (VTOL).

In a further aspect there is provided an airborne craft with at least 3 LPCEs that can be configured in the crafts airframe in multiple locations, where each LPCE comprises a. an airfoil extending from a leading edge to a trailing edge and b. a cross-flow fan rotor at least partially embedded in and substantially the same length as said airfoil and mounted adjacent to the trailing edge of said airfoil c. an exit duct for said fan with two faces comprising i. The lower face of a flap connected to said airfoil and rotatable about said rotor axis, said flap also having an upper face whose inner edge controls the inlet flow area to said rotor. ii. The upper face of a lip that moves in concert with said flap lower face and substantially parallel with it to direct the airflow from said fan so that substantially uniform distributed thrust is developed along the length of said element.

In a further aspect, the exit duct is provided as described wherein the flap and lip are mechanically connected and actuated to produce thrust that can be vectored from a substantially horizontal direction to a substantially vertical direction.

BRIEF DESCRIPTION OF THE DRAWINGS

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

FIG. l is a diagram of the front view of a preferred embodiment of a craft according to the present invention.

FIG. 2 is a diagram of the rear view of a preferred embodiment of a craft according to the present invention.

FIG. 3 is a diagram of the front view of a further preferred embodiment of a craft according to the present invention.

FIG: 4 is a diagram of a lift, propulsion and control element (LPCE) showing the exit duct geometry of the flap and flexlip when configured for forward flight.

FIG: 5 is a diagram of an LPCE showing the exit duct geometry of the flap and flexlip when configured for VTOL operation.

FIG: 6 is a diagram of the cross section of an LPCE according to the present invention showing the airfoil, embedded crossflow fan and exit duct geometry and the range of movement of the flap and flexlip.

Fig 7 is a diagram of the cross section of a forward LPCE and an aft LPCE according to the present invention in a configuration relative to each other that is preferred for forward flight FIG. 8 is a diagram illustrating the flow around and through the wing and crossflow fan element when configured for horizontal forward flight

FIG. 9 is a diagram illustrating the flow around and through the wing and crossflow fan element when configured for VTOL.

DETAILED DESCRIPTION

Referring now to the drawings, there is seen in fig 1 the front view of an eVTOL airborne craft comprising multiple short span, crossflow fan Lift Propulsion and Control Elements (LPCEs) 10, disposed around a central longitudinal fuselage 40 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 10 being comprised of an airfoil 20, a flexlip 24 attached to and forming part of airfoil 20, a crossflow fan rotor 14, a flap 26 rotatable and mounted about the axis of rotor 14 and an exit duct 15 from the crossflow fan rotor 14.

Referring now to fig 2 there is seen the rear view of the eVTOL airborne craft of fig 1 comprising multiple short span, crossflow fan Lift Propulsion and Control Elements (LPCEs) 10, disposed around a central longitudinal fuselage 40 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 10 being comprised of an airfoil 20, a flexlip 24 attached to and forming part of airfoil 20, a crossflow fan rotor 14, a flap 26 rotatable and mounted about the axis of rotor 14 and an exit duct 15 from the crossflow fan rotor 14.

Referring now to fig 3 there is seen the front view of an eVTOL airborne craft comprising multiple short span, crossflow fan Lift Propulsion and Control Elements (LPCEs) 10, disposed around a central fuselage 40 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 10 being comprised of an airfoil 20, a flexlip 24 attached to and forming part of airfoil 20, a crossflow fan rotor 14, a flap 26 rotatable and mounted about the axis of rotor 14 and an exit duct 15 from the crossflow fan rotor 14.

In this example, the central fuselage 40 is proportioned to receive two occupants seated in tandem, and comprises- two substantially similar Lift Propulsion and Control Elements (LPCEs) 10 mounted to the starboard side of said fuselage, one in a forward position, and one in an aft position, two substantially similar LPCEs 10 mounted to the port side of said fuselage, one in a forward position, one in an aft position, and two wingtip fences 41, 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 4 there is seen an LPCE with an airfoil 20, a flexlip 24 attached to and forming part of airfoil 20, a crossflow fan rotor 14, a flap 26 rotatable and mounted about the axis of rotor 14 and an exit duct 15 from the crossflow fan rotor 14 and formed by the lower face 17 of flap 26 and the upper face 16 of flexlip 24. With the flexlip 24 and flap 26 configured in this position and with a suitable fan speed, a longitudinal jet of air from duct 15 is ejected along the length of the lift, propulsion and control element to achieve distributed propulsion, and desirably the forward flight propulsive efficiency benefits. Synergistically, the edge 18 of face 19 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 5 there is seen an LPCE with an airfoil 20, a flexlip 24 attached to and forming part of airfoil 20, a crossflow fan rotor 14, a flap 26 rotatable and mounted about the axis of rotor 14 and an exit duct 15 from the crossflow fan rotor 14 and formed by the lower face 17 of flap 26 and the upper face 16 of flexlip 24. With the flexlip 24 and flap 26 configured in this position, ie. with the flexlip and flap rotated with respect to figure 4, and with a suitable fan speed, a longitudinal jet of air from duct 15 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 18 of face 19 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 6, there is seen a diagrammatic section of an LPCE, for example the one illustrated in figures 4 and 4, with an airfoil 20 with an upper surface radius 21 and an angle of attack 22 to the airstream direction 23 and a crossflow fan assembly consisting of a rotor 14, a rear wall 11 and a vortex wall 12, a rear flexlip24 which flexes through an angle25 and has an upper face 16, a flap 26 that rotates about the rotor axis 27, can rotate through an angle 28 and has a lower face 17, an exit duct 15 formed by face 16 and face 17. Desirably, the angle of attack 22 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 optimized by the movement of flap 26 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 1 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 7, there is seen a diagrammatic section of two LPCEs arranged in accordance with this invention so that Fig 6 is a diagrammatic section view through the centre of either of the port or starboard side pair of LPCEs of the craft seen in fig 1. The Orientation of the LPCEs relative to each other is seen as they are mounted to the fuselage 40 in fig 1 and fig 2 and relative to the direction of the approaching air stream 54. It is an aspect of this invention that the forward LPCEs will have an angle of attack 55 to the airstream 54 and that the angle of attack of the aft LPCs 56 can be different and preferably greater by between 2 and 12 degrees. In fig 7, there is also seen a height distance 53. It is an aspect of this invention that said distance can be either positive or negative, positioning the aft LPCE above or below the forward LPCE. Desirably, distance 53 will be in the range from -2 chord lengths C to +2chord lengths, the chord length being shown in fig5. In fig 6, there is also seen a longitudinal distance 52. Desirably this distance is selected to achieve a craft length which is substantially similar to that of cars, desirably in the range from 3m to 5m. Desirably this distance would be in the range from 3 chord lengths C to 5 chord lengths C.

Despite relatively low fan efficiency, the present invention is competitive with conventional propulsion technologies. The raised inlet formed by flap 26 eliminates the fan size restriction created if the fan is fully embedded within the airfoil 20. Also, cross-flow fan performance is quite insensitive to even large amounts of wake ingestion, making it ideal for this type of configuration. The fan of the present invention is capable of drawing in the boundary layer, regardless of its thickness. Referring to the thick airfoil 20 seen in FIG 3, 4 and 5, even for a low angle of attack 22, the wake can be quite large, producing large pressure drag. This renders very thick wing sections impractical for most aircraft applications as the drag penalty outweighs any benefits gained in lift or interior volume. Without the suction effect of a rear-mounted crossflow fan rotor 14, the flow separates even at only a small angle of attack. The embedded cross-flow fan near the trailing edge eliminate flow separation by drawing the flow back toward the surface and into the fan ducting, yielding very high lift coefficients. This is turn results in low in-flight aircraft stall speed without the use of additional high lift devices, such as slotted flaps and leading edge slats but more importantly, facilitates short span high lift wings that can be readily configured into lifting elements described herein for compact airborne craft.

In forward flight, the distributed propulsion generated by the long span wise jet of air from duct 15 gives rise to the phenomenon known as distributed propulsion which can be used to achieve a very high propulsive efficiency in forward flight. This, together with the lower drag resulting from the absence of engine nacelle, pylon, and interference drag offsets any low fan efficiency.

By vectoring the thrust using co-ordinated control of the flap 26 and flexlip 24, consequentially opening the inlet to the crossflow fan and increasing fan speed, additional lifting force sufficient to achieve VTOL is possible. This configuration is illustrated in Fig.6 and Fig.7 and in Fig.9 where the wide range of authority of the flexlip and flap are evident.