Aviation structure

Abstract

The aircraft includes a fuselage (24), first and second forward wings (20, 22) attached to and / or extending from opposite sides of the fuselage (24), first and second aft wings (30, 32) and a continuous aft wing span (34) defining a fixed center connection (36), a first wing connection member (42) extending between the first forward wing (20) and the first aft wing (30), and a second wing connection member (44) extending between the second forward wing (22) and the second aft wing (32). 2), wherein an aft wing span (34) is supported by a centrally located V-tail joint defined by first and second angled arms (100, 110), and first and second electric motors each having a rotor mounted on each wing (20, 22, 30, 32), each rotor pivoting between a first configuration for vertical flight and a second configuration for forward flight.

Description

[Technical Field]

[0001] This disclosure relates to aircraft structures. In particular, the present disclosure relates to an improved structure for box-wing aircraft, and more particularly for vertical take-off and landing (VTOL) box-wing aircraft. However, it should be understood that the improved structure disclosed herein may be applied to other aircraft types. [Background technology]

[0002] Aeroelasticity is concerned with the interaction between inertial, elastic, and aerodynamic forces acting on an elastic body exposed to a fluid flow. One particular aspect of aeroelasticity is called "flutter." Flutter is concerned with unrestrained vibrations that can result in the destruction of an aircraft. Flutter must be considered when designing aircraft structures.

[0003] Flutter relates to the dynamic instability of an elastic structure in a fluid flow, caused by the feedback between the deflection of the object and the forces exerted by the fluid flow. In a linear system, the "flutter point" is the point at which the structure experiences simple harmonic motion - zero net damping - and further reduction in net damping will lead to self-excited oscillation and eventual failure.

[0004] Structures exposed to aerodynamic forces, including wings and aerofoils, must be carefully designed within known parameters to avoid flutter. Changing the mass distribution of an aircraft or the stiffness of one component can induce flutter in seemingly unrelated aerodynamic components. Flutter can develop uncontrollably and cause severe damage or destruction of the aircraft.

[0005] Changes in mass distribution and local structural stiffness can be used to change the flight speed of the aircraft as it reaches the flutter point. In fact, the aircraft must be designed in such a way that it does not operate at or near the flutter point.

[0006] However, designing an aircraft to avoid catastrophic failure due to flutter can be difficult because small changes to one parameter can have a significant effect on how the aircraft structure reacts at different flight speeds and conditions.

[0007] One way to reduce the risk of flutter point failure is to limit the maximum flight speed to a level significantly below the speed at which the flutter point is encountered, however, this may be impractical and, in fact, may adversely affect the commercial viability of a given aircraft design due to an undesirable maximum speed limitation.

[0008] Another means of reducing the risk of operating an aircraft at or near flutter speed is to increase the stiffness of the fuselage and especially the wings. While such an increase in stiffness may increase the maximum operating speed at which an aircraft can safely operate without reaching the flutter point, the drawback is that increased stiffness generally comes with an increase in weight. This has the disadvantage of reducing the maximum payload the aircraft can carry, which unfortunately reduces the number of people or cargo weight that can be transported. Again, this reduction in payload is undesirable and may adversely affect the overall commercial viability of a proposed aircraft design.

[0009] A box-wing or closed-wing aircraft is a specific type of aircraft in which there are two wings, typically on either side of the aircraft, connected to each other and having struts / braces or winglets at or near each wingtip, such that the forward and aft (or upper and lower) wings on each side of the aircraft are mechanically connected to each other (in addition to their connection to the fuselage).

[0010] A box wing structure can provide additional wing stiffness, which is beneficial against flutter. However, there are certain problems and challenges associated with box wing aircraft.

[0011] When a box-wing aircraft has a rotor attached to each wing, a problem arises in that the airflow through the rotor attached to the forward wing can adversely affect the rotor attached to the aft wing due to the forward rotor's wake effectively passing through the aft rotor. Thus, the vertical overlap between the swept areas of the forward and aft wing rotors can be noisy and aerodynamically inefficient.

[0012] In some box-wing aircraft, the rear wing is attached directly to the aircraft fuselage. This configuration improves the rear wing's stiffness, which is favorable for increasing the flutter point. However, this attachment configuration often reduces the vertical spacing between the forward and rear wings, which can result in the aforementioned undesirable overlap between the forward and rear wing rotor swept areas. Furthermore, the attachment configuration of the rear wing to the fuselage results in an aerodynamically inefficient central portion of the total rear wing span due to the reduced wing length available for generating lift.

[0013] To address the above drawbacks, it is known to fasten the rear wing to the fuselage with a vertical "T" connection, which physically separates the rear wing vertically from the fuselage. This helps to make the rear wing taller, thus increasing the vertical spacing between the forward and rear wings. This also increases the aerodynamic length of the wing available for generating lift. However, a T-connection is not optimal for flutter because the stiffness of the rear wing attachment is reduced in this configuration. Therefore, the aforementioned flutter problem, which can undesirably reduce the maximum speed at which an aircraft can operate below the flutter point, can become an issue with this configuration.

[0014] WO 2019 / 211875 discloses a hybrid vertical take-off and landing aircraft that has separate rotors for different flight conditions, such as take-off and forward flight, such that ten of the rotors are fixed for vertical take-off and landing and two of the rotors are tilted for cruise / forward flight.

[0015] WO 2019 / 211875 discloses a V-tail attachment configuration for the aft wingspan, which is attached to the rear of the fuselage with two angularly offset arms. One drawback of using that system is that the aft wing span is not continuous but is shortened due to the V-tail connection to the fuselage, which is undesirable as there is no central section of the aft wingspan and the aft wingspan is made up of two separate wings, reducing the wing length available for generating lift. Summary of the Invention [Problem to be solved by the invention]

[0016] It is an object of the present invention to substantially overcome or at least ameliorate one or more of the above disadvantages, or to provide a useful alternative. [Means for solving the problem]

[0017] The present invention provides The torso and first and second forward wings attached to and / or extending from opposite sides of the fuselage; a continuous aft wing span defining first and second aft wings and a central fixed connection; a first wing connecting member extending between the first forward wing and the first aft wing; a second wing connecting member extending between the second forward wing and the second aft wing; an aircraft structure comprising: The aft wing span is supported by a centrally located V-tail joint defined by first and second angled arms; First and second electric motors, each having a rotor mounted on each wing, each rotor pivoting between a first configuration for vertical flight and a second configuration for forward flight.

[0018] Each of the first and second angled arms preferably has a proximal end secured to the fuselage and a distal end secured to the aft wingspan.

[0019] Each of the first and second angled arms preferably has a proximal end fixed to a common aft wing support, which in turn is fixed to the fuselage, and a distal end fixed to the aft wing span.

[0020] The wingspan ratio is

number

[0021] The first and second angled arms are preferably mounted to the aft bulkhead of the fuselage, and a tail cone is mounted to the aft bulkhead, the tail cone covering at least a lowermost portion of each arm.

[0022] Each arm preferably has a proximal mounting portion located within the tail cone and a distal exposed portion extending above the tail cone.

[0023] The distal exposure preferably has an aerodynamic fairing on the leading edge.

[0024] An aerodynamic shield is preferably located at the intersection where the distal exposed portion of each arm extends upwardly beyond the fuselage.

[0025] Preferred embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a front perspective view of an aircraft according to the present invention; [Figure 2] FIG. 2 is a front view of the aircraft of FIG. 1. [Figure 3] FIG. 1 is a perspective partial detail view showing the intersection of the V-tail assembly with the fuselage. [Figure 4] 1 is a schematic exploded view of major aerodynamic components of an aircraft according to one embodiment; [Figure 5]FIG. 10 is a rear view of a V-tail according to a further embodiment. [Figure 6] FIG. 6 is a rear perspective view of the V-tail of FIG. 5. [Figure 7] The V-tail of Figures 5 and 6 is shown with the tail cone attached. [Figure 8] A cross-sectional view of the tail. DETAILED DESCRIPTION OF THE INVENTION

[0027] A vertical take-off and landing (VTOL) box-wing aircraft 10 is disclosed, although it should be understood that the present invention may be applied to conventional box-wing aircraft or other types of aircraft configurations.

[0028] In a preferred embodiment, as shown in the drawings, the aircraft 10 has two pairs of wings: forward wings 20, 22 and aft wings 30, 32. Each of the forward wings 20, 22 is attached to opposite regions on the sides of the fuselage 24 or extends through the fuselage 24 to define a single forward wingspan. The aft wings 30, 32 define a continuously extending wingspan 34 that is attached to the fuselage 24 by two arms as described below.

[0029] In the embodiment shown in the drawings, the aircraft 10 is shown as a single-seat or double-seat aircraft 10. However, larger multi-seat embodiments are also envisioned. The aircraft 10 may be controlled from within by a pilot or may be remotely controlled.

[0030] In the embodiment shown in the drawings, the distal portions of the forward wings 20, 22 and aft wings 30, 32 are connected by a wing connecting member or web 42 so that the two pairs of wings 20, 22, 30, 32 define a box-wing or closed-wing configuration.

[0031] The wing connecting member 42 can be used to store batteries, fuel tanks, hydrogen tanks, or even cargo bays. By placing mass such as batteries on the wing connecting member 42, mass placement can be optimized, improving flutter stability and increasing flutter speed.

[0032] The fuel / energy / cargo stored in the connecting member 42 provides the following advantages: Configuration changes with minimal complications to other aircraft structures, Improvements in battery technology or simple implementation of other energy sources, including hydrogen, Other operational benefits include battery hot swapping, Improved safety due to separation from the wing and the crew compartment, Improved damage tolerance due to greater separation between redundant battery compartments (on the wingtips).

[0033] Furthermore, locating the batteries in the wingtip connecting members 42 allows the wing to be optimized for aerodynamic efficiency as opposed to volumetric efficiency (if the batteries are housed within the wing).

[0034] In another embodiment (not shown), the forward wings 20, 22 and aft wings 30, 32 may be strut-braced wings connected by tie bars or struts. Strut-braced wings are generally lighter than traditional cantilever wings.

[0035] Although the aircraft 10 described herein is a box-wing or strut-braced aircraft 10, those skilled in the art will appreciate that the aircraft 10 may also be a conventional cantilever aircraft in which the forward wings 20, 22 and aft wings 30, 32 are separate and not interconnected.

[0036] Referring to the drawings, the forward and aft wings 20, 22 are vertically separated such that the forward and aft wings 20, 22 are positioned vertically below the aft wings 30, 32. The vertical separation is at least equal to, and preferably greater than, one rotor diameter so that the diameters swept by the forward and aft rotors do not vertically overlap. In one embodiment, the aft wings are separated by more than one rotor radius to ensure spacing from the connecting member 42. In embodiments where noise reduction is an explicit goal, the vertical separation is such that the rotors 70 mounted on the aft wings 30, 32 do not pass through the wake of the rotors 70 mounted on the forward wings 20, 22. This means that the vertical separation of the wings is equal to at least one rotor diameter.

[0037] Preferably, there are two rotors 70 on each wing, resulting in four rotors located along the total forward wingspan and four rotors 70 located along the total aft wingspan. Each rotor 70 rotates between a generally vertical axis takeoff / landing configuration and a generally horizontal axis forward flight configuration.

[0038] Each of the forward and aft wings 20, 22 and 30, 32 has a fixed leading edge 25, 35. The leading edges 25, 35 have a curved profile in the shape of an aerofoil section. The leading edges 25, 35 do not rotate or otherwise move relative to the fuselage 24.

[0039] The aft wings 30, 32 are defined by a continuous wingspan that extends continuously above the fuselage.

[0040] The (VTOL) box-wing aircraft 10 utilizes a box-wing design to reduce the effects of wingtip vortices. Additionally:

[0041] It uses rotors 70 mounted at (or near) the wing tips to actively suppress tip vortex generation and improve upon the natural aerodynamic effectiveness of the box wing.

[0042] It uses the vertical aerodynamic cross section of the rear of the box wing to enhance directional stability.

[0043] Aft of each fixed leading edge 25, 35, the forward wings 20, 22 and / or aft wings 30, 32 have a pivotally mounted aileron or control surface 50. Each control surface 50 pivots between a generally vertical configuration for takeoff and landing and a generally horizontal configuration for forward flight (as shown in Figures 1 and 2).

[0044] In a preferred embodiment, the control surface 50 is a single surface that extends continuously along the entire length (or at least a majority of the entire length) of the forward wings 20, 22. Alternatively, each wing 20, 22, 30, 32 may have one or more independently pivotable control surfaces 50 such that the control surfaces 50 can pivot about the leading edges 25, 35 independently of the other control surfaces 50. For example, the aft wing span 34 has two control surfaces 50.

[0045] In a preferred embodiment, each rear wing 30, 32 has a single control surface 50, and the central region between the two wings 30, 32 above the fuselage is fixed.

[0046] Vertical take-off and landing (VTOL) aircraft 10 includes multiple electric motors 60. Each motor 60 has a propeller or rotor 70. A body portion 62 of each motor 60 is mounted adjacent to the upper or lower surface (as shown) of a movable control surface 50, generally forward of the fixed leading edges 25, 35. Control surfaces 50 can rotate in a range of approximately 80 to 100 degrees, preferably approximately 90 degrees, for both horizontal and vertical flight modes.

[0047] The motor 60 may be mounted sufficiently forward of the fixed leading edges 25, 35 so that the rotor blades can be folded aft and remain clear of the wing structure. However, the preferred embodiment uses non-folding rotors 70 with a variable pitch mechanism. Fixed pitch blades may also be used.

[0048] There are two possible mounting configurations for the motors 60 and control surfaces 50: a) each motor 60 may be pivotally connected to one of the fixed leading edges 25, 35, with the control surface 50 fixed to the body portion 62 of the motor 60; or b) The control surface 50 may be pivotally connected to one of the fixed leading edges 25, 35, the control surface being fixed to the body portion 62 of the motor 60.

[0049] The electric motors 60, together with the control surfaces 50, each rotate about the leading edges 25, 35 between a first position in which the rotors of each motor 60 have a generally vertical axis of rotation and a second position in which the rotors of each motor 60 have a generally horizontal axis of rotation.

[0050] All rotors 70 are movable, not fixed, meaning they can move between a generally vertical axis of rotation for takeoff and landing and a generally horizontal axis of rotation for forward flight, and therefore no fixed rotors are redundant during the cruise mode of operation.

[0051] Thus, the (VTOL) box-wing aircraft 10 does not have external features not used in cruise flight that create unnecessary drag, such as redundant rotors, and therefore operates in its most aerodynamic configuration in forward flight.

[0052] The rotors 70 on each blade surface are non-planar relative to one another so that the rotational axes of the motors are angularly offset. In this way, the rotational axes of adjacent motors are not parallel so that different thrust can be used by tilting the blades.

[0053] This reduces the net torque required by the tilt wing actuator. It also assists the wing tilt by generating a moment on the tilt wing mechanism, providing an additional layer of redundancy to the tilt wing operation.

[0054] The (VTOL) box-wing aircraft 10 uses and maximizes the blow-lift phenomenon, thereby: The thrust from the rotor increases the lift coefficient from the wing, The split tilt wing configuration maximizes the wing's lift coefficient at high angles of attack.

[0055] The (VTOL) box-wing aircraft 10 operates triple redundantly throughout vertical and forward flight. Typically, it uses eight rotors for thrust and flight control, allowing it to operate even if multiple rotors fail in forward flight.

[0056] The aircraft 10 has a V-tail configuration for mounting the aft wingspan 34. Specifically, the central fixed member 36 of the aft wingspan 34 is attached to the fuselage 24 with two spaced arms 100, 110 that are angled relative to one another. The V-tail configuration improves the aeroelastic performance of the aircraft 10 by increasing stiffness and thereby raising the flutter point, allowing the aircraft 10 to operate safely at higher flight speeds. Each of the two arms 100, 110 provides a degree of diagonal support in addition to vertically supporting the aft wingspan 34 above the fuselage 24.

[0057] The aircraft 10 utilizes a V-tail section attached to a continuous full-span aft wing structure. The V-tail design (with a continuous full-span wing structure) improves aeroelastic behavior and allows the aircraft 10 to operate at higher cruise speeds.

[0058] The arms 100, 110 are preferably angularly separated from one another at an angle of between about 19 degrees and about 26 degrees.

[0059] The optimal geometry allows for an inherent increase in the stiffness of the joint between the arms 100, 110 and the aft wingspan 34, ultimately delaying the onset of flutter in box-wing aircraft. The use of a geometry that delays the onset of flutter to higher speeds allows for both lighter aircraft and higher cruise speeds.

[0060] Possible modifications or improvements may include further geometric sensitivity analyses that may affect the stiffness of a box-wing aircraft in relation to its flutter speed. One such analysis may include an analysis of height-to-span ratio or wing sweep angle. Similar geometric analyses may be applied to other configurations of the aircraft.

[0061] Another possible development of the present invention, along with a set of flowcharts containing the methodology, may include this type of analysis in the future design process of a box-wing aircraft.

[0062] As shown in Figure 1, the aft span 34 includes a centrally located fixed member 36 located between the two aft wings 30, 32. The fixed member 36 has the cross-sectional profile of the aerofoil, but the trailing end region of the aerofoil is not movable.

[0063] The aft wingspan 34 of the aircraft 10 is attached to the tips of the V-tail arms 100, 110 below the fixed member 36.

[0064] Each of the arms 100, 110 may be independently fastened, glued, or welded to the aft bulkhead of the fuselage 24, or may be secured by a combination of one or more fastening techniques. Alternatively, the arms 100, 110 may be secured to another portion of the fuselage 24.

[0065] In an alternative embodiment, the two arms 100, 110 are integrally formed or secured together to define a single aft wing support 120, defined by a wishbone or Y-shaped piece, and have a single attachment point (or group of attachment points) for securing the aft wing support 120 to the fuselage 24.

[0066] The tail cone 140 is secured to the rear of the fuselage 24 such that the arms 100 , 110 extend from the top of the fuselage 24 to the interface between the tail cone 140 and the fuselage 24 .

[0067] The arms 100, 110 may be secured to the fixed member 36 based on a set of possible span ratios (ratio of the distance between the distal ends of each arm 100, 110 of the V-tail to the length of the aft span 34) that allow for greater aeroelastic stiffness.

[0068] Aircraft 10 may be used in any box-wing aircraft, including conventional and vertical takeoff and landing configurations. It is configured in a box-wing configuration with a V-tail tail that allows the aft wingspan 34 of the aircraft to be taller than the fuselage 23.

[0069] Using the additional stiffness that the V-tail configuration adds to the aft wingspan 34, a sensitivity analysis was performed by applicant to determine the geometric effect of the V-tail angle on the system stiffness and therefore flutter speed. A fixed connection was assumed between the aft wingspan 34 and the V-tail arms 100, 110. Various V-tail span ratios were analyzed, showing an optimum range of 0.088 to 0.105, which provided the highest flutter speed. For V-tail span ratios above 0.105, flutter speed decreased significantly. The following figure shows the full results of the analysis. [Table 1]

[0070] The reason for these large reductions is due to changes in the dominant flutter modes, which are due to changes in geometry that slightly alter the shape, frequency, and damping of the fundamental eigenmode of the structure.

[0071] The aircraft 10 utilizes a V-tail geometry to improve the aeroelastic performance of the aircraft.

[0072] In the embodiment of Figure 4, the V-tail arms 100, 110 may be joined at their lower proximal ends, or alternatively, the arms 100, 110 may be formed separately but placed abutting or nearly abutting at their proximal ends.

[0073] In an alternative embodiment shown in Figures 5-7, arms 100, 110 together provide a Y-tail support, with arms 100, 110 each defined by a proximal mounting portion 115 and a distal exposed portion 125. Mounting portion 115 is configured to be attached to the aft bulkhead of fuselage 24. The two mounting portions 115 extend generally parallel to one another and are positioned abutting one another. In this manner, the two mounting portions 115 can be secured to one another in addition to being secured to the aft bulkhead for additional rigidity.

[0074] The distal exposed portion 125 of each arm 100, 110 extends above the tail cone 140 and is exposed to the airflow during flight. The distal exposed portion 125 has an aerodynamic fairing 150 at its leading edge, as shown in Figure 3. The top of the distal exposed portion 125 is attached to the aft wing span 34.

[0075] 3, an aerodynamic shield 160 is located at the intersection where the distal exposed portion 125 of each arm 100, 110 extends beyond the fuselage 24. The shield 160 may be fastened, glued, or a combination of fastening and gluing, or otherwise secured to the fuselage 24.

[0076] The distal exposed portion 125 of each arm 100, 110 may be tapered, with its thickness (measured in the direction of forward flight) narrowest near its interface with the aft wingspan 34, as shown in Figure 3. Alternatively, the distal exposed portion 125 of each arm 100, 110 may be non-tapered and have a generally uniform thickness.

[0077] The cross section of the right arm 100 rotates slightly clockwise as viewed from above as you move from the tip towards the fuselage 24. In other words, the profile aligns with the flow at the junction to the wing, and the trailing edge rotates inward towards the fuselage 24. Similarly, the cross section of the left arm 110 rotates slightly counterclockwise as viewed from above as you move from the tip towards the fuselage 24.

[0078] Advantageously, the arms 100, 110 of the aircraft 10 ensure that the angle of the V-tail provides an effective amount of stiffness against flutter instability.

[0079] Although the present invention has been described with reference to specific examples, those skilled in the art will appreciate that the present invention can be embodied in many other forms.

Claims

1. The torso and first and second forward wings attached to and / or extending from opposite sides of the fuselage; a continuous aft wing span defining first and second aft wings and a central fixed connection; a first wing connecting member extending between the first forward wing and the first aft wing; a second wing connecting member extending between the second forward wing and the second aft wing; An aircraft structure comprising: the aft span is supported by a centrally located V-tail joint defined by first and second angularly angled arms; each of the first and second angled arms having a proximal end fixed to the fuselage and a distal end fixed to the central fixed connection of the aft wingspan; The wingspan ratio is [Equation 1] and is defined as the ratio of first and second electric motors, each having a rotor mounted on each wing, each rotor pivoting between a first configuration for vertical flight and a second configuration for forward flight; aircraft structure.

2. 2. The aircraft structure of claim 1, wherein each of the first and second angularly inclined arms has a proximal end fixed to a common aft wing support, the aft wing support being fixed to the fuselage, and a distal end fixed to the aft wing span.

3. An aircraft according to any one of claims 1 to 2, wherein the first and second angularly inclined arms are angularly offset relative to one another by approximately 19 to 26 degrees.

4. An aircraft structure according to any one of claims 1 to 3, wherein each wing has a fixed leading edge and a pivoting trailing edge control surface.

5. 5. An aircraft structure according to claim 1, wherein the first and second angled arms are attached to an aft bulkhead of the fuselage, and a tail cone is attached to the aft bulkhead, the tail cone covering at least a lowermost portion of each arm.

6. The aircraft structure of claim 5 , wherein each arm has a proximal mounting portion located within the tail cone and a distal exposed portion extending above the tail cone.

7. The aircraft structure of claim 6 , wherein the distal exposure has an aerodynamic fairing at a leading edge.

8. 8. The aircraft structure of claim 7, wherein an aerodynamic shield is located at the intersection where the distal exposed portion of each arm extends upwardly beyond the fuselage.

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