Aircraft structure

Abstract

A tandem wing aircraft (10) comprises a fuselage (20) having a nose (30) and a tail portion (45). A first wing structure (40) extends away from a right side of the fuselage (20) including a first forward wing (50) and a first rearward wing (60). A second wing structure (70) extends away from a left side of the fuselage (20) including a second forward wing (80) and a second rearward wing (90). A plurality of electric motors (100) having rotors (110) mounted on each of the first and second wing structures (40, 70). The tail portion (45) of the fuselage (20) terminates at a longitudinally extending edge, the edge being defined by the junction of an upper surface (130) and a lower surface (160), the edge extending generally perpendicular to a direction of forward flight. The first rearward wing (60) and second rearward wing (90) are connected to define a continuous span which passes above the upper surface (130), the continuous span being supported by a support structure (300) which extends upwardly away from the fuselage (20).

Description

Aircraft structure Field of the invention

[0001] The present invention relates to an aircraft structure. In particular, the present invention relates to an aircraft structure for a VTOL aircraft, and more particularly an electric eVTOL aircraft. However, it will be appreciated that the present invention may have application with other aircraft. Background of the invention

[0002] VTOL aircraft are capable of take-off and landing vertically, or at some inclination which is close to vertical. This style of aircraft includes helicopters and certain fixed wing aircraft. Advantageously, VTOL aircraft permit take-off and landing in limited spaces, which negates the need for a long runway, and permits take-off and landing in small spaces and such as landing pads on buildings and other structures, or unprepared surfaces, such as fields and car parks.

[0003] There are several inherent problems associated with VTOL aircraft, and particularly electrically powered VTOL aircraft. One issue concerns the limited range of flight. Due to the large amounts of energy required for the take-off and landing stages of flight, the energy remaining for the forward flight is significantly reduced.

[0004] Another problem relates to aerodynamic drag. Aerodynamic drag refers to the forces that oppose the relative forward motion of an aircraft. Drag opposes the forward motion of the aircraft and must be overcome by thrust. By reducing the amount of aerodynamic drag, the amount of thrust required for a given payload can be reduced. As such, improving the aircraft design to reduce the drag forces may have a positive impact on the aircraft payload and / or maximum range. This is particularly relevant for electric powered VTOL aircraft, as the reduction in drag forces can have a material impact on the required battery size for a given flight range.

[0005] Another issue that requires consideration for VTOL aircraft is the “stall speed”, which is the minimum steady flight speed at which the aircraft is controllable. A conventional aircraft flying at its stall speed cannot climb, and an aircraft flying below its stall speed cannot stop descending. Any attempt to do so by increasing angle of attack, without first increasing air speed, will result in a stall. Stall speed is particularly importantfor thrust vectoring VTOL aircraft (such as tilt wing, tilt rotor or tilt jet aircraft), noting that they must transition from vertical to forward flight modes, in which there is initially little or no forward flight speed, and as such the aircraft in practice will be flying below its stall speed at certain stages of flight. This constraint must be addressed in order to control the flight. Stall speed is important for VTOL aircraft as flight below the stall speed requires more power than flight above stall as the wings produce enough lift and the rotors are only required to produce forward thrust.

[0006] A further challenge with VTOL aircraft, and other small aircraft generally, concerns fuselage access, and particularly the loading and unloading of cargo and patients in the context of medical and military applications. This is affected by the limited available space for making large openings in the fuselage walls, because the attachment points for the wings and the underlying structure for mounting the wings to the fuselage limit the remaining space for creating the entry and exit points for the fuselage. Unlike large commercial and military aircraft, VTOL aircraft designs normally apply to smaller aircraft, typically having small entry points, requiring the passengers and crew to be able bodied and furthermore requiring the passengers and crew to enter and exit past the wings and rotors.

[0007] A proposed aircraft known as the Parsifal project is the subject of US patent publication US 2006 / 0144991. That publication is based on the “Prandlt plane” concept from the 1920s, utilising a swept wing concept, in which on each side of the aircraft there is one wing which loops and closes back on itself in a closed-wing design with no wingtips. This design is intended to reduce the amount of drag acting on the aircraft. It also has a fuselage tail shape that is wider horizontally than vertically in order to improve longitudinal static stability. It also has a control surface along the trailing edge of this horizontal section of fuselage to enable trimming in flight. However, the aircraft which is the subject of that patent publication is a large passenger carrying aircraft with no ability to use the rear fuselage for cabin access. It is also a conventional aircraft, having one or two jet engines located on each side of the fuselage and not developed for VTOL flight.

[0008] Any reference herein to known prior art does not, unless the contrary indication appears, constitute an admission that such prior art is commonly known by those skilled in the art to which the invention relates, at the priority date of this application.Summary of the invention

[0009] The present invention provides a tandem wing aircraft comprising: a fuselage having a nose and a tail portion; a first wing structure extending away from a right side of the fuselage including a first forward wing and a first rearward wing; and a second wing structure extending away from a left side of the fuselage including a second forward wing and a second rearward wing; a plurality of electric motors having rotors mounted on each of the first and second wing structures; wherein the tail portion of the fuselage terminates at a longitudinally extending edge, the edge being defined by the junction of an upper surface and a lower surface, the edge extending generally perpendicular to a direction of forward flight; further wherein the first rearward wing and second rearward wing are connected to define a continuous span which passes above the upper surface, the continuous span being supported by a support structure which extends upwardly away from the fuselage to define a clearance between the continuous span and the fuselage.

[0010] The tandem wing aircraft further preferably comprises a cargo door located in the tail portion, the cargo door having: an upper door defined by the upper surface and having an upper door proximal end pivotally secured to the fuselage and an upper door distal end; and a lower door assembly defined by the lower surface and having a lower door proximal end pivotally secured to the fuselage and a lower door distal end, wherein the upper door distal end and the lower door assembly distal end are configured to be moved into proximity with each other when the rear cargo door is closed.

[0011] The support structure preferably includes a first spar and a second spar, the first and second spars being located on laterally opposing sides of the upper door.

[0012] Preferably at each of the two laterally opposing sides of the fuselage, a rear afterbody portion of the fuselage terminates at an acute point.

[0013] Preferably the two opposing acute points and the upper and lower doors together define a closure when the rear cargo door is closed.

[0014] The support structure preferably extends upwardly away from the rear afterbody portion.

[0015] There are preferably two electric motors having rotors mounted on each of the first forward wing, the first rearward wing, the second forward wing and the second rearward wing.

[0016] External surfaces of the upper door and the lower door are preferably curved.

[0017] The upper door can preferably be selectively rotated to an open or partially open position to increase the aerodynamic drag acting on the fuselage.

[0018] The vertical take-off and landing (VTOL) aircraft further preferably comprises cross bracing in the form of two or four tie bars arranged in a cross-formation and extending between two lateral sides of the aircraft across the width of the fuselage and located on a plane which extends through or near where the upper door proximal end is pivotally secured to the fuselage.

[0019] The lower door assembly further preferably comprises two half panels which close along a longitudinally extending, sagittal plane of the aircraft.

[0020] The vertical take-off and landing (VTOL) further preferably comprises a bulkhead frame brace defined by an inwardly extending structure with fillet curved or chamfered corners, defining a generally rectangular opening, the bulkhead frame brace extending between two lateral sides of the aircraft across the width of the fuselage and located on a plane which extends through or near where the upper door proximal end is pivotally secured to the fuselage.

[0021] The vertical take-off and landing (VTOL) aircraft further preferably comprises four tie bars each extending between the wall and floor or wall and ceiling of the fuselage, the tie bars defining a generally rectangular opening with chamfered corners, the tie bars being located on a plane which extends through or near where the upper door proximal end is pivotally secured to the fuselage.

[0022] The upper door is preferably defined by two separate panels.

[0023] The two separate panels are preferably in a permanently fixed orientation relative to each other.

[0024] The two separate panels are preferably in a contiguous co-planar arrangement when the upper door is closed, and they translate to an acute angularly offset arrangement when the upper door moves to an open configuration. Brief description of the drawings

[0025] Figure 1 is a rear perspective view of a vertical take-off and landing (VTOL) aircraft according to the invention with a rear cargo door depicted in a closed position;

[0026] Figure 2 depicts the vertical take-off and landing (VTOL) aircraft of Figure 1 with the rear cargo door depicted in an open position;

[0027] Figure 3 is a side schematic view of the fuselage of the VTOL aircraft of figure 1;

[0028] Figure 4 is a schematic rear perspective view of the aircraft of figure 1 with the rear cargo door open;

[0029] Figure 5 is a rear perspective view of a vertical take-off and landing (VTOL) aircraft according to a second embodiment of the invention;

[0030] Figure 6 is a rear perspective view of a vertical take-off and landing (VTOL) aircraft according to a third embodiment of the invention;

[0031] Figure 7 is a rear perspective view of a vertical take-off and landing (VTOL) aircraft according to a fourth embodiment of the invention;

[0032] Figure 8 is a rear perspective view of a vertical take-off and landing (VTOL) aircraft according to a fifth embodiment of the invention; and

[0033] Figure 9 is a rear perspective view of a vertical take-off and landing (VTOL) aircraft according to a sixth embodiment of the invention. Detailed description of preferred embodiments

[0034] The aircraft 10 of the invention is a tandem wing aircraft 10, which is configured for either vertical take-off and landing (VTOL) or alternatively conventional take-off and landing (CTOL). The components of aircraft 10 may be structured and / or operate similarly to the components described in Applicant’s own publications: International Application No. PCT / AU2018 / 050962, filed on 6 September 2018, International Application No. PCT / AU2018 / 050963, filed on 6 September 2018, International Application No. PCT / AU2020 / 050261, filed on 19 March 2020, and International Application No. PCT / AU2021 / 051078, filed on 17 September 2021, which are incorporated by reference herein in their entirety.

[0035] Whilst the tandem wing aircraft 10 is described and depicted in the context of a vertical take-off and landing (VTOL) aircraft 10, it will be appreciated that theaircraft 10 may alternatively be embodied as a conventional take-off and landing (CTOL).

[0036] The aircraft has a fuselage 20. The front of the fuselage 20 defines a fuselage nose 30, and the rear, downstream end of the fuselage 20 defines a tail portion 45.

[0037] The aircraft 10 is herein described and depicted as a box-wing aircraft. However, it will be appreciated that the aircraft may alternatively be embodied as a non- box-wing tandem aircraft 10.

[0038] The depicted aircraft 10 has a first box wing structure 40 extending away from the right side of the fuselage 20 including a first forward wing 50 and a connected first rearward wing 60. The aircraft 10 includes a second box wing structure 70 extending away from the left side of the fuselage 20 including a second forward wing 80 and a connected second rearward wing 90.

[0039] The wings 50, 60, 80, 90 have a high aspect ratio, which is beneficial with respect to increased lift. The wing aspect ratio is preferably the square of the span divided by the wing area and applies independently to each of the respective wings.

[0040] The wings on each side of the fuselage 20 are connected by a connecting portion 75 which may be used to store batteries and or a fuel supply (such as hydrogen) and / or other electrical componentry or luggage and cargo.

[0041] Whilst the aircraft 10 is described in the context of a box-wing aircraft, it will be appreciated that other aircraft layouts may be envisaged including a strut-wing design. Alternatively, the front and rear wings may be completely independent and not connected to each other.

[0042] The aircraft 10 includes a plurality of electric motors 100 having rotors 110 mounted on each of the first and second box wing structures 40, 70. In the embodiment depicted in the drawings, there are two electric motors 100 having rotors 110 mounted on each of the first forward wing 50, the first rearward wing 60, the second forward wing 80 and the second rearward wing 90, resulting in eight rotors 110 in total. Furthermore, the rotors 110 are depicted as quad blade rotors. However, it will be appreciated that other rotor designs may alternatively be deployed. Furthermore, in an alternative arrangement (not shown) one or more than two electric motors 100 having rotors 110 may be mounted on each of the first forward wing 50, the first rearward wing 60, the second forward wing 80 and the second rearward wing 90.

[0043] Some or all of the rotors 110 are tiltable between take-off and landing configuration (having a generally vertical axis of rotation) and forward flight configuration (having a generally horizontal axis of rotation). The rotors 110 and motors 100 may tilt together. Alternatively, the rotors 110 may be coupled to the motors 100 for independent angular movement between horizontal and vertical positions.

[0044] With reference to figures 1 and 2, the tail portion 45 of the fuselage 20 terminates at a longitudinally extending edge 48, the edge 48 being defined by the junction of an upper surface 130 and a lower surface 160. The edge 48 extending generally perpendicular to a direction of forward flight, and the edge 48 being horizontal when the aircraft is stationary.

[0045] In the embodiment depicted, a cargo door 120 is located in the tail portion 45. The cargo door includes an upper door defined by the upper surface 130 and a lower door assembly defined by the lower surface 160. However, in an alternative arrangement, the upper and lower surfaces 130, 160 may be fixed (non-moveable) fairings.

[0046] The upper door 130 has an upper door proximal end 140 pivotally secured to the fuselage 20 and an upper door distal free end 150. The axis of rotation of the upper door 130, about the upper door proximal end 140 extends generally horizontally.

[0047] The cargo door lower door 160 has a lower door proximal end 170 which is pivotally secured to the fuselage 20 and a lower door distal end 180. The axis of rotation of the lower door 160, about the lower door proximal end 170 extends generally horizontally.

[0048] As depicted in figure 1, the upper door distal end 150 and the lower door distal end 180 are configured to be moved by rotation into proximity with each other when the rear cargo door 120 is closed.

[0049] As shown in Figure 4, each of the lower door 160 and the upper door 130 is connected to one or more hydraulic or pneumatic cylinder 200, 210. The cylinders 200, 210 may provide dampening and / or actuation of the upper and lower doors 130, 160.

[0050] The lower door 160 and the upper door 130 may be configured to open together. Alternatively, the lower door 160 and the upper door 130 may be separately actuated.

[0051] With reference to figure 1, the first rearward wing 60 and the second rearward wing 90 are connected to define a continuous wing-span which passes above the upper door 130, and above a rear afterbody portion 330 of the aircraft 10. The continuous span is supported by a support structure 300 which extends upwardly away from the fuselage 20.

[0052] As depicted in the drawings, the support structure 300 includes a first spar 310 and a second spar 320 which are located on laterally opposing sides of the upper door 130. The spars 310, 320 are arranged in a V-tail configuration, and they are arranged at an inclination relative to vertical, meaning that the spars 310, 320 are closer to each other at the fuselage and further apart from each other at the point of securement to the continuous rear wing-span.

[0053] On each of the two laterally opposing sides of the fuselage 20, at a rearwardly extending location, behind the cabin, a rear afterbody portion 330 of the fuselage terminates at an acute point 340, which are defined by the termination of the two lateral side walls of the fuselage 20. As depicted in figure 3, the points 340 enable the fuselage 20 to have lateral profile which is predominantly aerofoil shaped, terminating at an acute edge, defined by the upper door distal end 150 and the lower door distal end 180.

[0054] The two opposing acute points 340 and the upper and lower door 130, 160 together define a closure when the rear cargo door 120 is closed.

[0055] The fuselage tail shape profile which tapers to a point generates low drag. Furthermore, the fuselage tail shape interacting with the continuous rear wing-span generates a high-pressure zone.

[0056] With reference to figure 3, the motion of sustained and accelerated fluid around the front wings 50, 80 and rear wings 60, 90 generate areas of lower and higher pressure, acting on the upper and lower portions of the wings, respectively. This effect, further coupled with the geometry of fuselage 20 and relative position of front wings 50, 80 and rear wings 60, 90 to the fuselage 20, generates pulling and pushing forces exerted on the fuselage 20. These forces increase in magnitude with the increase of the angle-of-attack, and thus contribute towards a drag reduction effect imposed on the body of the fuselage 20. The net forces exerted on the fuselage 20 can fully overcome the parasitic drag generated by the body of the fuselage 20, especially at large angles-of-attack. This can result in a net propulsive action in the reference frame of the fuselage 20.

[0057] A well-designed fuselage 20 structure for a box-wing VTOL 10 provides a direct load path from the front wings 50, 80 to the rear wing 60, 90, and good torsional stiffness for acceptable flutter resistance and motor 100 failures. To achieve this the rear door 120 can have a latch and / or lock mechanism to transmit torsional loads, the rear door frame can be stiffened to provide torsional stiffness, or a cross frame or cargo net that provides a shear load path across the rear opening.

[0058] The front and rear wings 50, 60, 80, 90 have moveable trailing control surfaces. In addition, the rear wingspan (between the two spars) may have a trailing edge surface that can be moveable and used for flight control or trimming surface.

[0059] In one embodiment, the upper door and the lower door external surfaces are curved to define a portion of an aerofoil in profile, having improved aerodynamic properties for generating lift and reducing drag.

[0060] The upper door 130 and / or the lower door 160 can be selectively rotated to an open or partially open position to increase the aerodynamic drag acting on the fuselage. This may be used as an emergency braking feature to slow the aircraft in an emergency by generating increased drag beyond the drag forces generated by the trailing control surfaces on the wings 50, 60, 80, 90. Opening the upper door 130 and / or the lower door 160 creates a recirculating low-pressure region behind the aircraft, further dragging it down.

[0061] In one example, the upper door 130 may open from about 30 degrees below horizontal to about 30 degrees above horizontal.

[0062] As shown in figure 2, the spars 310, 320 provide several advantages. By lifting the rear wings 60, 90, the additional intermediate section of wing that is created increases the amount of lift that can be generated, without altering the length of the rear wings 60, 90 from tip to tip. Furthermore, the additional height of the rear wings 60, 90 relative to the fuselage 20 enables the upper door 130 to open to a greater angle, and hence height, improving cabin access for loading goods and passengers.

[0063] The location of the rear wings 60, 90, and the lift generated in the centre section 95 of the rear wing, can impart a positive pressure on the rear fuselage 20, which has the impact of reducing drag.

[0064] In the embodiment depicted in figure 4, the lower door 160 includes a central set of stairs and lateral racking to hold cargo such as luggage or medical equipment.

[0065] The rear cargo door 120 may be the only access point to the cabin. Alternatively, an additional front or side access door may be provided.

[0066] Advantageously, the large rear cargo door 120 enables immobile persons to be loaded easily and quickly for example on a stretcher in a medical or military application. Furthermore, the rear approach and exit significantly reduces the likelihood of a person coming dangerously close to a propellor when it is rotating.

[0067] Advantageously, the combination of the rear door fuselage, rear wing above afterbody with V-tail configuration, and fuselage and wing combinations reduces drag.

[0068] Advantageously, a key performance benefit of the (VTOL) aircraft 10 is that it provides low drag and minimised stall speed.

[0069] Furthermore, the aircraft 10 provides increased range and cruising speed.

[0070] The rear cargo door 120 may be opened during flight (figure 2). This enables the aircraft 10 to be used for example for parachuting, for the deployment of cargo in flight, and for hovering winch rescues.

[0071] The structural design that allows that would be a flight envelope (i.e. a speed range) that allows the aircraft 10 to fly with the 120 door open, and a door structure that can then be closed and secured such that it provides increased rigidity in high speed flight. In one embodiment, the rear cargo door 120 may be electrically controlled by a flight computer that directs the upper door 130 and lower door 160 to move to the closed and locked configuration (figure 1) as the aircraft speed approaches the limit of the predetermined flight envelope. Similarly, the door 120 may be openable mechanically or electrically when the speed has dropped below the upper limit of the predetermined (permissible open door) flight envelope, as the aircraft 10 slows.

[0072] The large rear cargo door 120 facilitates efficient patient or cargo loading and may be configured to provide a ramp or steps, with a ramp enabling disabled access, for example wheel-chairs.

[0073] As depicted in figure 3, the front wings 50, 80 are mounted near or slightly above the bottom of the fuselage 20. In contrast, the rear wings 60, 90 are mounted above the fuselage 20. This creates a considerable vertical separation between thefront wings 50, 80 and the rear wings 60, 90, such that air down-stream of the front wings 50, 80 does not directly interact with the rear wings 60, 90. The spars 310, 320 assist to increase the vertical separation. The vertical separation of the front wings 50, 80 and rear wings 60, 90 causes less mutual influence between the front wings 50, 80 and rear wings 60, 90. This results in lower induced drag and higher aerodynamic efficiency of the aircraft 10.

[0074] The lower door 160 may include one or more rollers to enable containers, stretches, pallets and other cargo and personnel to be loaded and unloaded into and from the cargo door 120.

[0075] Figure 5 depicts a second embodiment of the aircraft 10. In the second embodiment, cross bracing in the form of four tie bars 400 in a cross-formation extends between the two lateral sides of the aircraft 10, across the width of the fuselage 20 and located on a plane which extends through or near where the upper door proximal end 140 is pivotally secured to the fuselage 20 and the lower door proximal end 170 is pivotally secured to the fuselage 20.

[0076] The tie bars 400 provide improved structural rigidity and torsional stiffness. The arrangement of tie bars 400 may be permanently secured to the fuselage 20, or alternatively the tie bars 400 may be selectively removable. For example, the tie bars 400 may be secured to hooks or other mounting points on the internal wall of the fuselage 20 and removable when the aircraft 10 is stationary.

[0077] Although the tie bars 400 are depicted as being connected in the centre of the cross, it will be appreciated that an alternative arrangement may be provided with two crossing tie bars 400 which are not centrally connected to each other.

[0078] The struts 400 may be mounted to a door frame structure which can be pivoted between open and closed positions, to provide improved fuselage access when the aircraft 10 is stationary.

[0079] The cross bracing may be openable in flight at low speeds to enable for example, cargo drop in flight, rescue winching and parachuting / skydiving like activities. In one arrangement, the tie bars 400 may be locked / unopenable when the flight speed exceeds or approaches a predetermined threshold. Alternatively, an alarm or other warning light or sound may be activated automatically if the tie bars 400 are not in a closed position, across the fuselage 20, when the flight speed approaches thepredetermined threshold. Furthermore, the motors may be restricted from exceeding the predetermined threshold until the tie bars 400 are secured in position.

[0080] Figure 6 depicts a third embodiment of the aircraft 10. In the third embodiment, the lower door assembly 160 is defined by two half panels 410, 420 which separate along a longitudinally extending, sagittal plane of the aircraft 10. This arrangement enables the two panels 410, 420 to be opened in a “bomb bay” formation, which enable the aircraft 10 to be used to deploy products such as cargo, munitions, military equipment, humanitarian aid and other products during flight.

[0081] The two half panels 410, 420 are depicted with two locks or latches 430. It will be appreciated that other latching arrangements such as a single lock may be possible. The two half panels 410, 420 may be actuated with hydraulic or pneumatic struts.

[0082] Figure 7 depicts a fourth embodiment of the aircraft 10. In the fourth embodiment, a bulkhead frame brace 500 is located around the internal wall of the fuselage 20 on a plane which extends through or near where the upper door proximal end 140 is pivotally secured to the fuselage 20 and the lower door proximal end 170 is pivotally secured to the fuselage 20.

[0083] The bulkhead frame brace 500 is defined by an inwardly extending structure with fillet curved or chamfered corners, defining a generally rectangular opening. In the same way as the earlier described embodiments, the arrangement of figure 7 provides improved structural rigidity and torsional stiffness. Furthermore, this embodiment minimally inhibits access to and from the fuselage 20. The structure of the bulkhead frame brace 500 may be defined by a metallic frame which is attached to the fuselage, and overlaid with a polymer covering, such as a reinforced polymer, fibreglass, carbon fibre or another suitable engineering material. Alternatively, the bulkhead frame brace 500 may be formed entirely from a reinforced polymer. The lower door is actuated with hydraulic or pneumatic struts 520.

[0084] The fifth embodiment depicted in figure 8 is a lightweight variation of the fourth embodiment, which uses a corner tie bar 510 at each of the four corners on the plane which extends through or near where the upper door proximal end 140 is pivotally secured to the fuselage 20 and the lower door proximal end 170 is pivotally secured to the fuselage 20. This embodiment minimally affects the fuselage weight and alsominimally inhibits access to the fuselage 20. The lower door is actuated with hydraulic or pneumatic struts 520.

[0085] In the sixth embodiment of Figure 9, the upper door proximal end 140 is pivotally secured to the fuselage 20 and the lower door proximal end 170 is pivotally secured to the fuselage 20. The upper door 130 is provided in a split, two-panel configuration. The two panels 132, 134 may be in a permanently fixed orientation relative to each other. Alternatively, the two panels may be in a contiguous co-planar arrangement when the upper door 130 is closed, and they translate to an acute angularly offset arrangement (depicted) when the upper door 130 is in the open configuration. In the embodiment of Figure 9, the lower door 160 is able to rotate to a generally vertical position when fully open, which may assist with cargo drops, skydiving etc, and this also provides improved access for loading / unloading, by enabling a truck such as a fork truck, or another vehicle to closely approach the fuselage 20.

[0086] Advantageously, the wide rear cargo door enables improved cargo and passenger loading whilst providing low drag conditions in forward flight.

[0087] Advantageously, the shape of the rear after body facilitates the integration of a wide rear door assembly without incurring a drag penalty.

[0088] Wherever it is used, the word “comprising” is to be understood in its “open” sense, that is, in the sense of “including”, and thus not limited to its “closed” sense, that is the sense of “consisting only of”. A corresponding meaning is to be attributed to the corresponding words “comprise”, “comprised” and “comprises” where they appear.

Claims

Claims:

1. A tandem wing aircraft comprising: a fuselage having a nose and a tail portion; a first wing structure extending away from a right side of the fuselage including a first forward wing and a first rearward wing; and a second wing structure extending away from a left side of the fuselage including a second forward wing and a second rearward wing; a plurality of electric motors having rotors mounted on each of the first and second wing structures; wherein the tail portion of the fuselage terminates at a longitudinally extending edge, the edge being defined by the junction of an upper surface and a lower surface, the edge extending generally perpendicular to a direction of forward flight; further wherein the first rearward wing and second rearward wing are connected to define a continuous span which passes above the upper surface, the continuous span being supported by a support structure which extends upwardly away from the fuselage to define a clearance between the continuous span and the fuselage.

2. The tandem wing aircraft of claim 1, further comprising a cargo door located in the tail portion, the cargo door having: an upper door defined by the upper surface and having an upper door proximal end pivotally secured to the fuselage and an upper door distal end; and a lower door assembly defined by the lower surface and having a lower door proximal end pivotally secured to the fuselage and a lower door distal end, wherein the upper door distal end and the lower door assembly distal end are configured to be moved into proximity with each other when the rear cargo door is closed.

3. The tandem wing aircraft of claim 1 or 2, wherein the support structure includes a first spar and a second spar, the first and second spars being located on laterally opposing sides of the upper door.

4. The tandem wing aircraft of any one of the preceding claims, wherein on each of the two laterally opposing sides of the fuselage, a rear afterbody portion of the fuselage terminates at an acute point.

5. The tandem wing aircraft of claim 4, wherein the two opposing acute points and the upper and lower doors together define a closure when the rear cargo door is closed.

6. The tandem wing aircraft of claim 5, wherein the support structure extends upwardly away from the rear afterbody portion.

7. The tandem wing aircraft of any one of the preceding claims, wherein there are two electric motors having rotors mounted on each of the first forward wing, the first rearward wing, the second forward wing and the second rearward wing.

8. The tandem wing aircraft of any one of the preceding claims, wherein external surfaces of the upper door and the lower door are curved.

9. The tandem wing aircraft of any one of the preceding claims wherein the upper door can be selectively rotated to an open or partially open position to increase the aerodynamic drag acting on the fuselage.

10. The tandem wing aircraft of any one of the preceding claims further comprising cross bracing in the form of two or four tie bars arranged in a cross-formation and extending between two lateral sides of the aircraft across the width of the fuselage and located on a plane which extends through or near where the upper door proximal end is pivotally secured to the fuselage.

11. The tandem wing aircraft of any one of claims 1 to 9, wherein the lower door assembly further comprises two half panels which close along a longitudinally extending, sagittal plane of the aircraft.

12. The tandem wing aircraft of any one of claims 1 to 8, further comprising a bulkhead frame brace defined by an inwardly extending structure with fillet curved or chamfered corners, defining a generally rectangular opening, the bulkhead frame brace extending between two lateral sides of the aircraft across the width of the fuselage and located on a plane which extends through or near where the upper door proximal end is pivotally secured to the fuselage.

13. The tandem wing aircraft of any one of claims 1 to 9, further comprising four tie bars each extending between the wall and floor or wall and ceiling of the fuselage, the tie bars defining a generally rectangular opening with chamfered corners, the tie bars being located on a plane which extends through or near where the upper door proximal end is pivotally secured to the fuselage.

14. The tandem wing aircraft of any one of claims 1 to 9, wherein the upper door is defined by two separate panels.

15. The tandem wing aircraft of claim 14, wherein the two separate panels are in a permanently fixed orientation relative to each other.

16. The tandem wing aircraft of claim 14 wherein the two separate panels are in a contiguous co-planar arrangement when the upper door is closed, and they translate to an acute angularly offset arrangement when the upper door moves to an open configuration.

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