Vertical take-off and landing aircraft

Abstract

A vertically takeoff and landing aircraft (1) comprises: a fuselage (2); at least one propulsion system (5); at least four lift propellers (10); and at least two fixed wing planes (20, 30, 40), the fixed wing plane (30, 40) located behind the foremost lift propeller (10) being located above the lift propellers (10). The lift propellers (10) are distributed on both sides of the fixed wing plane (30) and on both sides of the fuselage (2) such that the lift propellers (10) are spaced in the longitudinal direction by at least the size of the chord length (Cl, C2) of the fixed wing plane between the lift propellers (10) and in the transverse direction by at least the width (L1, L2) of the fuselage (2) between the lift propellers (10). At least one of the fixed wing planes (30) has a variable span, and the aircraft (1) comprises a control system for changing the span in flight.

Description

Technical Field

[0001] The present invention relates to vertical take-off and landing (VTOL) aircraft, i.e., "VTOL" aircraft. More specifically, the present invention relates to VTOL aircraft with variable wingspans. Background Art

[0002] In the past, various VTOL aircraft configurations have been studied, usually with the aim of avoiding a degradation of the inherent aerodynamic performance of the aircraft. In fact, such devices generally have the following characteristics: in addition to a fixed-wing plane for rising during forward flight, they also have a plurality of propellers that ensure the lift of the device during take-off and vertical landing. At the same time, if the propellers are designed to be pivotable, they can provide a propulsion function, or the propulsion function can be provided by other devices such as fans, turbojet engines, or any other device capable of generating thrust.

[0003] The simultaneous use of a fixed-wing plane and propellers on the same VTOL aircraft necessarily results in an aerodynamic interaction phenomenon between the wakes of these components (propeller / fixed-wing plane wakes, propeller / propeller wakes, fixed-wing plane / fixed-wing plane wakes). These interactions generally affect the aerodynamic performance of the aircraft, thus affecting its flight quality and mission performance.

[0004] This phenomenon is exacerbated when the aircraft is equipped with electric motor-driven propellers. In fact, compared with other types of electric motors or engines, in order to obtain the same take-off power, it is necessary to increase the number of electric motors, thus increasing the number of propellers for rising. In addition, flight safety requirements usually lead to an increase in the number of propellers to compensate for the failure of electric motors. The increase in the number of propellers exacerbates the interaction phenomenon and its impact on the performance of the aircraft. In addition, so many propellers require modifications to the fixed-wing plane for take-off and landing, and ultimately result in relatively large dimensions for the length and width of the aircraft. This lack of compactness means that the aircraft cannot take off or land in restricted areas such as forests (clearings, wooded areas) or urban areas.

[0005] Finally, weight limitation of VTOL aircraft is a matter of continuous concern.

[0006] Therefore, there is a need for a new type of VTOL aircraft that is more compact, relatively lighter, and has reduced aerodynamic interactions. Summary of the Invention

[0007] The vertical take-off and landing aircraft according to the present invention includes a fuselage, at least one propulsion system, four lift propellers, and at least two fixed-wing planes. The fixed-wing planes include a main wing plane and a rear wing plane located at the rear of the aircraft. Both the main wing plane and the rear wing plane are located behind the foremost lift propeller and above the lift propellers. The main wing plane has a variable wingspan and includes a pair of wing portions, each of which can be folded along the transverse axis of the aircraft, such that the movable end portion of the wing portion is positioned along and above the fixed portion of the wing portion when folded. The aircraft includes a control system for changing the wingspan of the main wing plane during flight by deploying each wing portion laterally. The four lift propellers are distributed on both sides of the main plane and both sides of the fuselage such that:

[0008] Two lift propellers located on the same side of the fuselage are connected to the fixed portion of the wing portion located on that side of the fuselage and are longitudinally spaced apart by at least the length of the chord between the two lift propellers on that side of the fuselage of the fixed-wing plane, and two lift propellers located on the same side of the main plane are laterally spaced apart by at least the width between the two lift propellers on that side of the fuselage of the main plane.

[0009] This aircraft has a structure for reducing the influence of the aerodynamic interaction between the lift propellers and the fixed-wing plane. In fact, the relative positions of the fixed-wing plane and the lift propellers are defined such that the wake of all the propellers has a negligible aerodynamic effect on the fixed-wing plane located downstream of these propellers. Also, folding the movable end portion of each wing portion above the fixed portion of the wing portion reduces the influence of the aerodynamic interaction with the propellers during folding.

[0010] In addition, the variable wingspan of the main plane reduces the overall lateral dimension of the wing portion plane, thus making the aircraft more compact during the vertical take-off and landing phases.

[0011] Finally, the fixed portion of each wing portion has the function of supporting the mechanical stress associated with the folded wing portion, but also has the function of bearing the mechanical stress associated with the two lift propellers connected to the wing portion. Therefore, the fixed portion can be designed to provide the mechanical strength required for this dual function. In comparison, other parts of the aircraft that eliminate these mechanical stresses can be designed more freely. In particular, the overall size and mass of the fuselage can be restricted while retaining the accessible space inside the fuselage. Ultimately, concentrating the mechanical stresses in the fixed portion of the wing portion results in a more compact and optimized mass structure compared to distributing these stresses between different parts of the aircraft.

[0012] In addition, the positioning of the lift propeller relative to the fixed-wing plane reduces the impact of the propeller wake on the wings of the fixed-wing plane, particularly the main wing plane, in terms of aerodynamic loads. Thus, the propeller does not add additional mechanical stress to the fixed portions of the wings of the main wing plane.

[0013] In some embodiments, the control system is configured to increase the wingspan when transitioning from low-speed flight to cruise flight and to decrease the wingspan when transitioning from cruise flight to low-speed flight. Thus, the wingspan in cruise flight is greater than the wingspan in low-speed flight. In particular, the wingspan is maximum in cruise flight and minimum in low-speed flight.

[0014] A fixed wing refers to all non-rotating lift surfaces of an aircraft. The wings are so-called "fixed" wings, as opposed to so-called "rotor" wings. Certain portions of the fixed wings may still be movable, thereby changing the wingspan. The fixed-wing plane can be a paired-wing type (the paired wings can be joined above or at the bottom of the fuselage, or can extend on both sides of the fuselage), a tail-wing type, or a canard-wing type of lift surface.

[0015] In this specification, the longitudinal direction and the lateral direction are parallel to the longitudinal axis and the lateral axis of the aircraft, respectively. The axes of the aircraft are imaginary lines that pass through the aircraft as follows:

[0016] - The longitudinal axis or roll axis extends from the nose (front end) to the tail (rear end) of the aircraft, passing through the fuselage and through the center of gravity of the device;

[0017] - The lateral axis or pitch axis extends from one end of the main fixed-wing plane to the other end of the plane, thereby passing through the center of gravity of the device;

[0018] - The vertical axis or yaw axis passes vertically through the center of gravity of the device and is perpendicular to the other two axes.

[0019] The front and rear, as well as the upstream and downstream, are defined relative to the direction of forward movement of the aircraft.

[0020] As described above, the lift propellers are longitudinally spaced by at least the magnitude of the chord length of the fixed-wing plane between the lift propellers, and the lift propellers are laterally spaced by the width of the fuselage between the lift propellers. The chord length is an imaginary line between the leading edge and the trailing edge of the plane of the wing section. The chord length of the fixed-wing plane between the propellers is the chord length in a vertical plane containing the axis of rotation of the propellers around the plane of the wing section. The width of the fuselage between the propellers is the maximum lateral dimension of the fuselage, which is measured in a vertical plane containing the axis of rotation of the propellers around the fuselage. In some embodiments, the lift propellers are longitudinally spaced by a distance that is between 1.3 times and 3 times the magnitude of the chord length, and / or the lift propellers are laterally spaced by a distance that is between 1.3 times and 3 times the width of the fuselage. The separation distance between the two propellers is the distance between the closest ends of the blades of the propellers.

[0021] This separation between the lift propellers greatly reduces the mixing of the propeller wakes below the aircraft, especially during low-speed flight. During transition flight (from low-speed flight to cruise flight), the aerodynamic loads on the lift propellers are reduced due to the increased contribution of the fixed-wing plane to lift, and thus the interaction between the propeller / propeller wakes is greatly reduced. During cruise flight, since the lift propellers can be stopped, this interaction can be eliminated. In particular, in some embodiments, the control system of the aircraft is configured to rotate the lift propellers during low-speed flight and stop the lift propellers during cruise flight.

[0022] Regarding the effect of the wake of the fixed-wing plane on the lift propellers, it is almost non-existent during low-speed flight because the fixed-wing plane has a small or no wake. The first effect is felt when the aircraft accelerates, i.e., at the start of the transition phase from low-speed flight to cruise flight. During this transition phase, due to the low lift of the fixed-wing plane, the interaction between the fixed-wing plane / propeller wakes is relatively weak. Finally, during cruise flight, this interaction does not exist because the propellers are stopped and only the fixed-wing plane carries the weight of the aircraft.

[0023] Low-speed flight refers to hovering (stationary, speed zero or close to zero) or low-speed flight, i.e., flying at a speed below 56 km / h (30 knots). Cruise flight refers to flying at a speed higher than the following speed (the so-called minimum cruise speed, denoted as Vc min): the speed at which the lift generated by the fixed wing completely cancels out the weight of the aircraft.

[0024] The transition phase corresponds to changing from low-speed flight to cruise flight and from cruise flight to low-speed flight.

[0025] In some embodiments, the wingspan of at least one fixed wing plane in a fixed wing plane can be changed between a maximum wingspan and a minimum wingspan, the minimum wingspan being less than or equal to 50% of the maximum wingspan, and more particularly, the minimum wingspan being less than or equal to 40% of the maximum wingspan. A minimum wingspan equal to 50% of the maximum wingspan corresponds to a minimum wingspan that is half of the maximum wingspan.

[0026] During low-speed flight, the wingspan can be reduced to a minimum. The aircraft then becomes more compact and has better wind resistance.

[0027] The main plane includes a pair of wings and has a variable wingspan. Each wing is foldable, and the control system is configured to laterally deploy each wing along a lateral direction. Thus, the wingspan is changed laterally, that is, the wingspan is changed along the lateral axis of the aircraft. This particularly avoids having to pivot the wings in a horizontal plane and having the wings pass over the lift propellers, which would otherwise create adverse aerodynamic interactions.

[0028] Each wing has a movable part and a fixed part. The fixed part is the proximal or central part of the wing that is connected to the fuselage. The movable part is the end or distal part of the wing, that is, the part that is farthest from the fuselage.

[0029] The wing is foldable such that the movable end part of the wing is positioned on the fixed part when folded (i.e., on top of the fixed part). Thus, the wing folds upward, which limits the aerodynamic interaction with the propellers compared to folding laterally or downward. In addition, compared to folding downward, when the control system operates to change the wingspan on the ground, folding upward allows the wing to avoid contacting the ground.

[0030] In some embodiments, the lift propeller includes two blades, and the control system is configured to stop the lift propeller in a stop position such that the blades are parallel to the longitudinal axis of the aircraft. When the propeller blades are positioned in this way, the direction of the propeller blades is the same as the direction of the fuselage, which reduces the aerodynamic drag of the aircraft during cruise flight.

[0031] In some embodiments, the lift propeller is a contra-rotating propeller. This type of propeller can particularly reduce the diameter of the propeller rotor, thereby improving the compactness of the aircraft.

[0032] In some embodiments, some lift propellers can be converted into propulsion propellers. This makes it possible to limit the number of propellers on board the aircraft. In particular, the propellers can have a lift function during one flight phase, such as low-speed flight, and a propulsion function during another flight phase, such as cruise flight. Due to the reduction in the number of propellers, this dual use of the lift propellers makes the aircraft more compact and lighter.

[0033] After reading the following detailed description, the above and other features and advantages will become apparent. The detailed description refers to the accompanying drawings. Description of the Drawings

[0034] The drawings are schematic and not necessarily to scale; the drawings are primarily intended to illustrate the principles of the present invention. In these figures, from one figure to another, the same elements (or parts of elements) are denoted by the same reference numerals.

[0035] Figure 1 This figure shows an example of a VTOL aircraft as seen from the side.

[0036] Figure 2 This figure shows an example of the Figure 1 VTOL aircraft in

[0037] Figure 3 as seen from above, with the main fixed-wing plane of the VTOL aircraft deployed. Figure 2 This figure is similar to the view in Detailed Description of the Embodiments

[0038] The following will describe in detail the specific embodiments of the provided aircraft with reference to the examples shown in the drawings. These embodiments illustrate the features and advantages of the present invention. However, it should be noted that the present invention is not limited to these embodiments or the examples shown.

[0039] Generally speaking, the provided VTOL aircraft includes a fuselage, at least one propulsion system, at least four lift propellers, and at least two fixed-wing planes. The aircraft can be a manned aircraft; alternatively, the aircraft can be an unmanned aircraft, such as a drone.

[0040] In the example in the figure, the VTOL aircraft 1 includes a fuselage 2, a propulsion system 5, four lift propellers 10, and three fixed-wing planes 20, 30, 40. The foremost first fixed-wing plane 20 of the aircraft 1 is a canard wing. The second fixed-wing plane 30 in the middle part of the aircraft 1 is the main wing plane. The second fixed-wing plane 30 is of the wing pair 32 type. In the example, the second fixed-wing plane 30 is composed of a right wing part and a left wing part joined together above the fuselage 2. The third fixed-wing plane 40 at the rear of the aircraft 1 is called the rear wing plane, and the third fixed-wing plane 40 is of the tail wing type.

[0041] ​​​Four lift propellers 10 are distributed on both sides of the fixed-wing plane 30 and on both sides of the fuselage 2. In other words, two lift propellers 10 are located on the right side of the fuselage on both sides of the right wing portion 32 (i.e., in front of and behind the right wing portion 32), and two lift propellers 10 are located on the left side of the fuselage on both sides of the left wing portion 32 (i.e., in front of and behind the left wing portion 32).

[0042] The left lift propellers 10 (i.e., the left front and left rear lift propellers 10) are longitudinally spaced apart by at least the size of the chord length C1 of the fixed-wing plane 30 located between the left lift propellers 10. The right lift propellers 10 (i.e., the right front and right rear lift propellers 10) are longitudinally spaced apart by at least the size of the chord length C2 of the fixed-wing plane 30 located between the right lift propellers.

[0043] The axis of rotation of the propellers 10 is vertical. In the example, each lift propeller 10 is a dual contra-rotating propeller.

[0044] Along the longitudinal direction, the propellers 10 are arranged in two rows: the front row and the rear row. The rear wing plane 40 is located behind the rear row. The lift propellers 10 in the front row (i.e., the right front and left front lift propellers) are laterally spaced apart by at least the width Ll of the fuselage 2 located between the lift propellers 10 in the front row. The lift propellers 10 in the rear row (i.e., the right rear and left rear lift propellers) are laterally spaced apart by at least the width L2 of the fuselage 2 located between the lift propellers 10 in the rear row.

[0045] The longitudinal axis X of the aircraft 1 is shown by a dashed line in Figure 1 and Figure 2 The lateral axis Y shown in Figure 2 is perpendicular to the longitudinal axis X and extends from one end of the main fixed-wing plane 30 to the other end, thus passing through the center of gravity G of the aircraft. Figure 1 The vertical axis Z shown in

[0046] is perpendicular to the axes X and Y and passes through the center of gravity G. The terms "lower", "upper", "top", "bottom", "above" and "below" refer to the height difference on the vertical axis. Figure 1 The fixed-wing planes located behind the foremost propellers 10, i.e., the wing planes 30 and 40, are located behind the front row of propellers 10 and above the group of lift propellers 10, as shown in Figure 1 This means that the lower surfaces (the parts below the wings) of the fixed-wing planes 30, 40 are all at a height higher than the highest rotation plane of the propellers 10. In the example of

[0047] The fixed-wing plane 30 has a variable wingspan, and the aircraft 1 includes a control system, which is a set of on-board devices and mechanical, hydraulic, and / or electrical connectors. The control system is used to change the wingspan of the wing plane 30 during flight. In the case of a VTOL UAV, the control system can be automatically controlled and / or remotely controlled. In the case of a manned VTOL aircraft, the control system can be automatically controlled and / or manually controlled from the cockpit. The control system is generally adapted to be controlled according to the flight rules of the aircraft so that the wingspan is adapted to the flight phase. In some embodiments, the control system is configured to increase the wingspan when changing from low-speed flight to cruise flight and decrease the wingspan when changing from cruise flight to low-speed flight. Thus, the aircraft can take off and land from a restricted area with a reduced wingspan through the wing 32.

[0048] Each wing 32 is foldable to position the movable end portion 33 of the wing along and above the fixed portion 31 of the wing. Any folding at an intermediate position (e.g., at a right angle) should be avoided to avoid generating wind loads.

[0049] In the example of the figure, the movable end portion 33 of each wing 32 can be folded along the folding line 34.

[0050] In Figure 2 , the movable portion 33 is laterally deployed, and the wingspan of the wing 32 is the largest. In Figure 3 , the movable portion 33 is folded towards the back, and the wingspan of the wing 32 is the smallest. Each movable portion 33 is folded towards the back from above and is positioned along and above the fixed portion 31.

[0051] In the example of the drawings, the propulsion system 5 of the aircraft is a propulsion propeller mounted at the front end of the aircraft 1. Other propulsion systems 5 can be considered, such as fans, turbojet engines, jet engines, or an array of "small" propellers for distributed propulsion. These propulsion systems can be positioned above the lift propellers. In some embodiments, these propulsion systems are positioned on the highest fixed surface to reduce interaction with the lift propellers; alternatively, these propulsion systems are mounted to the wing 32 by means of offset axes.

[0052] In some embodiments, each lift propeller 10 includes two blades 12 (and thus four blades 12 in the case of a twin-propeller), and the control system is configured to: in cruise flight, stop the lift propeller 10 at a stop position such that the blades 12 are parallel to the longitudinal axis X of the aircraft to reduce the drag of the blades 12. For the same reason, in some embodiments, the blades 12 can be decoupled from the rotor to place one blade of the blades 12 above the other blade to reduce the aerodynamic impact during cruise flight.

[0053] Examples of optimized operation of the provided VTOL aircraft in different flight phases are described below.

[0054] (1) Low-speed flight (including landing and takeoff):

[0055] The VTOL aircraft 1 maneuvers in this flight phase to orient itself by means of the lift propellers 10 having a vertical axis. Thus, the VTOL aircraft 1 can travel at speeds up to 56 km / h (30 knots) with the wings 32 folded. Thus, due to the reduced wingspan of the foldable wings 32, the aircraft exhibits increased wind resistance. The system of foldable wings 32 during low-speed flight ensures a minimum overall size during takeoff and landing. For the same mass, during takeoff and landing, the size of most existing VTOL devices is at least twice that of the VTOL aircraft 1.

[0056] (2) Transition phase:

[0057] After the wings 32 are deployed, the transition from low-speed flight to cruise flight is achieved by means of the propulsion system 5. During the transition, the lift propellers 10 having a vertical axis remain in a horizontal travel plane. This separation of the lift members and the propulsion members during the transition reduces the high-power maneuvering requirements of the lift propellers 10. The positioning of the lift propellers 10 allows for minimizing the aerodynamic interaction with the fixed surface. Most of the slipstream of the propellers 10 is cleared from the wings 32. In addition, since the propellers 10 are positioned below the plane of the wings 32, the impact is further reduced.

[0058] (3) Cruise flight:

[0059] In this flight phase, the propellers 10 are stopped and the blades 12 are positioned along the fuselage 2 to reduce the drag of the blades 12. There is no interaction between the rotating surface and the fixed surface.

[0060] The embodiments described in this specification are for illustrative purposes only and not for limiting purposes. Those skilled in the art can easily modify these embodiments or conceive of other embodiments while remaining within the scope of the present invention.

[0061] In particular, if some of the features of the previously described embodiments are sufficient by themselves to provide one of the advantages of the present invention, a person skilled in the art will be able to easily conceive of alternatives that include only these features of the previously described embodiments. In addition, the different features of these embodiments can be used separately or in combination with each other. When the different features of these embodiments are combined, these features can be combined in the manner described above or in a different manner, and the present invention is not limited to the specific combinations described in this specification. In particular, unless otherwise specified, the features described in connection with one embodiment can be applied in a similar manner to another embodiment.

Claims

1. A vertical take-off and landing aircraft, the aircraft comprising: a fuselage (2); at least one propulsion system (5); four lift propellers (10); at least two fixed-wing planes (20, 30, 40), the fixed-wing planes including a main wing plane (30) and a rear wing plane (40) located at the rear of the aircraft; wherein, both the main wing plane (30) and the rear wing plane (40) are located behind the foremost lift propeller (10) and above the lift propellers (10); the main wing plane (30) has a variable wingspan and includes paired wing portions (32), each wing portion (32) being capable of folding along the transverse axis of the aircraft such that the movable end portion (33) of the wing portion is positioned along the fixed portion (31) of the wing portion and is positioned above the fixed portion (31) of the wing portion when folded; the aircraft includes a control system configured to change the wingspan of the main wing plane (30) during flight by causing each wing portion (32) to unfold laterally; the four lift propellers (10) are distributed on both sides of the main wing plane (30) and on both sides of the fuselage (2), two of the lift propellers (10) located on the same side of the fuselage (2) are connected to the fixed portion (31) of the wing portion (32) located on that side of the fuselage (2), and the two lift propellers (10) located on the same side of the fuselage (2) are longitudinally spaced by at least the size of the chord length (Cl, C2) of the main wing plane (30) between the two lift propellers (10) located on that side of the fuselage (2); and two of the lift propellers (10) located on the same side of the main wing plane (30) are laterally spaced by at least the width (L1, L2) of the fuselage (2) between the two lift propellers (10) located on that side of the main wing plane (30).

2. The aircraft according to claim 1, wherein, the control system is configured to rotate the lift propellers (10) during low-speed flight and stop the lift propellers (10) during cruise flight.

3. The aircraft according to any one of the preceding claims, wherein, the control system is configured to increase the wingspan when changing from low-speed flight to cruise flight and decrease the wingspan when changing from cruise flight to low-speed flight.

4. The aircraft according to any one of the preceding claims, wherein, the wingspan is capable of changing between a maximum wingspan and a minimum wingspan, the minimum wingspan being less than or equal to 50% of the maximum wingspan, and more particularly, the minimum wingspan being less than or equal to 40% of the maximum wingspan.

5. The aircraft according to any one of the preceding claims, wherein, two of the lift propellers (10) located on the same side of the fuselage (2) are longitudinally spaced by a distance: the distance is between 1.3 times and 3 times the size of the chord length (Cl, C2).

6. The aircraft according to any one of the preceding claims, wherein, two of the lift propellers (10) located on the same side of the main wing plane (30) are laterally spaced by the following distance: the distance is between 1.3 times and 3 times the width (L1, L2) of the fuselage.

7. The aircraft according to any one of the preceding claims, wherein, the two lift propellers (10) include two blades (12), and the control system is configured to stop the lift propellers (10) at a stop position such that the blades (12) are parallel to the longitudinal axis of the aircraft.

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