A vertical take-off and landing small unmanned aerial vehicle

Abstract

The application relates to a vertical take-off and landing small unmanned aerial vehicle, and the core is that one high-strength carbon fiber pipe is arranged on each side of the fuselage as a tilting shaft, so that the unmanned aerial vehicle simultaneously has the dual functions of a central main wing main load-bearing beam and a rotating shaft. The tilting shaft penetrates through internal wing ribs and is supported in combination with a coaxial bearing, the whole rotating system of an outer wing, a rudder surface and a rotor power system is driven by a driving mechanism to realize flexible switching between vertical take-off and landing and flat flight modes. The integrated design of the "beam-shaft combination" realizes the shortest transmission path, greatly improves the load ratio, and releases the internal space of the wing for load arrangement.

Description

Technical Field

[0001] This invention relates to a small vertical take-off and landing unmanned aerial vehicle (UAV), belonging to the field of aircraft structure technology. Background Technology

[0002] With the rapid development of drone technology, electric vertical takeoff and landing (VTOL) aircraft, which can combine the flexibility of VTOL with the long endurance of fixed-wing aircraft, have become the core carrier of the low-altitude economy. In particular, small drones with a total weight of around 2 kg are widely used in precision inspection and urban logistics due to their small size and rapid deployment. However, for such small models, how to achieve reliable mode transitions (tilts) within a very small space and weight budget while ensuring structural strength remains a major challenge in the industry.

[0003] The applicant's research revealed that while various technologies have been attempted for tilting mechanisms in vertical takeoff and landing (VTOL) aircraft, significant shortcomings remain when considering the application scenarios of small flying wing configurations weighing around 2 kg. 1) Chinese Patent CN118323437A discloses a multi-link transmission mechanism consisting of upper / lower movable arms and supporting curved arms. This mechanism is extremely complex, with numerous parts and a large number of rotating pairs. For a small UAV weighing around 2kg, this design would result in significant structural weight and space occupation. Furthermore, its tilting power mechanism is independent of the wing's main load-bearing structure (main beam), leading to redundant force transmission paths and inefficient load transfer, greatly reducing the range of the small aircraft.

[0004] 2) Chinese patents with authorization announcement numbers CN222905886U and CN223059281U both disclose a motor-driven tilting mechanism installed at the end of an independent power arm, mainly targeting aircraft with independent long arm structures (such as compound wing or multi-rotor modified aircraft). The core of its structure lies in connecting the motor spindle to the drive rocker arm to bear the rotor thrust. This configuration relies on an external nacelle or long arm to support the tilting seat. If applied to small flying wing aircraft that aim for a high lift-to-drag ratio, the additional drag generated by the power arm will offset the aerodynamic advantages of the flying wing layout.

[0005] 3) US Patent No. US20090266941A1 discloses a beam-shaft assembly structure for connecting the inner wing and the tilting nacelle. However, its initial design purpose was to solve the heavy-load support problem of large tiltrotor aircraft (such as those with ton-level payloads). It integrates an extremely complex bevel gearbox and transverse drive shaft to handle the power transmission of high-power engines. However, for a 2kg-class pure electric small UAV, the required manufacturing precision and assembly complexity exceed the cost and mass production feasibility of small UAVs.

[0006] In summary, existing technologies often suffer from problems such as excessive structural weight, circuitous force transmission paths, and low space utilization, making them unsuitable for the flying wing layout of 2kg-class all-electric small drones. Furthermore, the payload ratio of conventional 1-3kg small drones is typically 10%-15%, which is still insufficient for 2kg small drones that place extreme emphasis on payload ratio. Summary of the Invention

[0007] The technical problem to be solved by the present invention is to provide a small unmanned aerial vehicle with a simplified structure, lighter weight and significantly improved payload ratio, thereby reducing costs and improving space utilization.

[0008] To address the aforementioned technical problems, this invention proposes a small vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV), comprising: The central main wing adopts a blended wing-body design with the fuselage to form the main fuselage. The two sides of the central main wing are symmetrically provided with outer wings, and the outer wings are provided with control surfaces and rotor drive devices. The control surfaces and the rotor drive devices work together to adjust the flight attitude of the UAV. Two tilting shafts are respectively located on both sides of the fuselage; the tilting shafts extend along the wingspan direction and pass through the wing ribs inside the central main wing as the main load-bearing beam of the central main wing, and the outer ends of the tilting shafts are fixedly connected to the outer wing through load-bearing connectors. A tilt drive mechanism is installed inside the central main wing to drive the tilt shaft to rotate around its axis, thereby causing the outer wing, the control surface and the rotor drive device to rotate as a whole, thus realizing flight mode switching.

[0009] Preferably, the tilting shaft is inserted into at least two coaxially arranged bearings; each bearing is installed in a corresponding bearing housing, and the bearing housing is located between two adjacent ribs of the central main wing and is fixedly connected to both adjacent ribs.

[0010] Compared with the prior art, the present invention has the following significant advantages: 1) This invention achieves a high degree of integration of load-bearing and motion functions by simultaneously using the tilt axis as the load-bearing beam of the wing. The beam-axis integrated design eliminates the traditional independent tilt mechanism seat and its connecting parts, significantly reducing the number of parts and structural weight. This is crucial for small 2kg-class UAVs, significantly improving their payload ratio and flight time. The applicant's tests show that the UAV with the above improvements can achieve a payload ratio of approximately 35%.

[0011] 2) This invention directly applies the aerodynamic load on the outer wing to the tilt axis center, which serves as the main beam, through the load-bearing connector and coaxial bearing. This achieves the design of the shortest force transmission path, avoids the stress concentration problem caused by the load transmission having to go through multiple turns in the traditional tilt mechanism, and ensures the reliability of the structure during mode transitions and high-speed flight.

[0012] 3) Because the present invention adopts a coaxial integrated design inside the wing, the tilt axis and the load-bearing beam of the wing are combined into one, eliminating redundant support structures on or inside the wing surface, freeing up the originally small space inside the flying wing layout, especially the space at the thickest part of the wing, which facilitates the placement of batteries, electronic speed controllers, flight control systems and other mission payloads.

[0013] 4) This invention eliminates the need for a separate tilting nacelle, allowing the rotor drive unit to be directly integrated into the outer wing section. In level flight mode, the outer wing and the central main wing together form a complete, streamlined wing lifting surface, eliminating the additional interference drag caused by the nacelle and improving the cruise lift-to-drag ratio.

[0014] 5) The applicant demonstrated through fluid-structure interaction simulation that, at the moment of most intense mode switching and greatest stress (such as at an airspeed of 15 m / s), the deformation of the tilt axis is minimal, the bearing operates stably, and it will not jam due to the deformation of the wing under stress, thus improving flight safety. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the structure of an embodiment of the present invention.

[0016] Figure 2 yes Figure 1 A partial schematic diagram of the tilt drive mechanism and tilt shaft.

[0017] Figure 3 and Figure 4 This is a schematic diagram of the tilt shaft installation structure.

[0018] Figure 5 This is a schematic diagram of the drone's state during level flight.

[0019] Figure 6 This is a schematic diagram of the drone's vertical takeoff and landing.

[0020] Reference numerals: 1. Central main wing; 2. Outer wing; 3. Rotor drive; 4. Control surface; 5. Tilting shaft; 6. Wing rib; 7. Tilting drive mechanism; 7-1. Tilting control servo; 7-2. Transmission gear set; 8. Bearing; 9. Bearing housing; 10. Winglet. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. All simulation and experimental conclusions involved in this invention are based on a 2kg-class small flying-wing UAV platform.

[0022] This embodiment discloses a vertical takeoff and landing (VTOL) unmanned aerial vehicle (UAV) with an external wing tilt-rotor configuration. The UAV adopts a blended wing-body configuration, lacking a traditional tail and independent fuselage. The entire aircraft serves as a unified lifting surface to bear aerodynamic loads, offering advantages such as streamlined shape, high lift-to-drag ratio, and low cruise drag. By introducing an external wing dynamic tilt-rotor structure, the flying wing configuration maintains excellent aerodynamic performance while possessing VTOL capabilities, expanding the application scenarios of the aircraft.

[0023] The core of the vertical takeoff and landing (VTOL) small UAV in this embodiment lies in functional integration, aiming to solve the problems of limited space, redundant structure, and heavy weight associated with traditional flying wing layouts. For example... Figure 1 ( Figure 1 (without propeller installed) Figure 5 and Figure 6 As shown, the UAV includes a central main wing 1, which is integrated with the fuselage using a blended wing-body design to form the main fuselage section. In 2kg-class applications, the overall wingspan is typically designed to be around 750.0mm. The absence of a traditional tail and the independent fuselage design allow the entire aircraft to function as a unified lifting surface. Aerodynamic simulations show that under level flight conditions, the lift distribution between the inner and outer wings is uniform, effectively improving the cruise lift-to-drag ratio and delaying wingtip stall. Symmetrical outer wings are located on both sides of the central main wing, and these outer wings are equipped with control surfaces and rotor drive devices; the control surfaces and rotor drive devices work together to adjust the UAV's flight attitude.

[0024] like Figures 2 to 4 As shown, the key innovation of this embodiment lies in the addition of a tilting shaft 5 extending along the wingspan on each side of the fuselage. This shaft is not only a rotation axis but also the main load-bearing beam of the central main wing 1. The tilting shaft 5 passes through the wing ribs inside the central main wing, and its outer end is fixedly connected to the outer wing via a load-bearing connector. The tilting shaft 5 is preferably made of plain-weave carbon fiber tubing with a Young's modulus of 135 GPa. This embodiment adopts an integrated design of "main beam-tilting mechanism," eliminating the independent mechanical seat, achieving extreme lightweighting, and significantly improving the payload ratio of the 2kg-class model. The applicant conducted tests, and the fuselage weight (including the power system, etc.) was 1.3kg, the payload was 0.7kg, and the takeoff weight could reach 2kg, with a payload ratio of 35%, far exceeding the payload ratio of existing small and medium-sized UAVs (such as the payload ratio of only 10-15% in the prior art as described in the background section).

[0025] This embodiment also includes a tilt drive mechanism installed inside the central main wing, used to drive the tilt shaft to rotate around its axis, thereby rotating the outer wing, the control surfaces, and the rotor drive device as a whole, realizing flight mode switching, including vertical takeoff and landing mode, level flight mode, and the dynamic process of switching between the two typical operating conditions of vertical takeoff and landing and level flight. In this embodiment, the tilt drive mechanism uses a tilt control servo 7-1 to drive the tilt shaft 5 through a transmission gear set 7-2 to achieve angle conversion from 0° to 90°. In this embodiment, the tilting of the outer wing is completed synchronously by the tilt drive mechanisms on both sides, ensuring the consistency and stability of the tilting process. The control surfaces 4 set on the trailing edge of the outer wing, in conjunction with the power differential, realize the attitude and direction control of the aircraft in vertical takeoff and landing mode and level flight mode.

[0026] Of course, the tilt drive mechanism 7 can also employ other conventional techniques such as worm gear transmission. For example, the servo motor 7-1 drives the worm, which in turn drives the worm wheel fixed on the tilt shaft 5. Utilizing the self-locking characteristics of the worm gear, the wing attitude can be maintained in cruise mode without continuous power supply to the servo motor. This not only improves system stability but also significantly reduces power consumption for 2kg-class UAVs during long-endurance missions.

[0027] The central main wing 1 has a cavity inside to house the batteries, electronic speed controllers, and flight control system. Thanks to the coaxial integrated design, the space previously occupied by independent tilt mounts within the wing is freed up, significantly optimizing the center of gravity distribution.

[0028] In this embodiment, the aerodynamic load of the outer wing 2 is borne by the heat-shrink film skin and the linden wood ribs 6, and acts directly on the center of the tilt axis 5 through the coaxial bearing 8. This shortest force transmission path design avoids the accumulation of stress on redundant connecting parts and ensures the continuity of load transmission.

[0029] Preferably, the tilting shaft is housed within at least two coaxially arranged bearings; each bearing is installed in a corresponding bearing housing, the bearing housing being located between two adjacent ribs of the central main wing and fixedly connected to both adjacent ribs. In this embodiment, the tilting shaft 5 is housed within at least two coaxially arranged bearings 8, and the bearing housing 9 is fixedly connected between adjacent ribs 6. The bearings 8 achieve separation of load-bearing and rotational functions, ensuring that the main beam can withstand bending moments and shear forces while allowing the outer wing 2 to rotate smoothly, avoiding the risk of motion jamming and improving the reliability and service life of the mechanism. For small flying wing models in the 2kg class, self-lubricating composite material bushings can also be used to replace the bearings 8. Self-lubricating bushings can further reduce structural mass. They have good damping characteristics, can absorb high-frequency vibrations generated by the rotor, and protect the tilting shaft 5, which serves as the main beam, from fatigue damage.

[0030] The applicant conducted a simulation analysis using unidirectional fluid-structure interaction (Fluent & Mechanical) at an extreme switching airspeed of 15 m / s. Under this condition, the outer wing 2 experiences peak load, with simulation showing a pressure drag of 19.172 N. With an added simulated torque of 2.0 N·m, the maximum equivalent stress on the tilt shaft 5 in vertical takeoff mode is 87.678 MPa, far below the allowable value for T300 carbon fiber. In vertical takeoff and landing mode, the wingtip displacement is 60.399 mm, and in level flight mode, it is only 20.081 mm, both meeting the industrial stiffness requirement of "displacement not exceeding 10% of half the wingspan (i.e., 75 mm)". This embodiment can also be improved in the following way: the outer wing 2 is provided with a winglet 10 at its end, which also serves as a landing gear support point. Through the above-mentioned functional integration design, the UAV suppresses wingtip vortices and reduces induced drag during level flight; in vertical take-off and landing mode, the outer wing 2 tilts downward to allow the winglet to support the ground, thereby further reducing the system mass of the 2kg-class UAV.

[0031] In this embodiment, the UAV connects the central main wing to the two outer wings via a tilt-drive mechanism. The outer wings are equipped with rotor drive devices and control surfaces. During vertical takeoff and landing, the tilt-drive mechanism drives the outer wings to rotate around the connecting axis to a state approximately perpendicular to the central main wing. The propellers on the outer wings exert vertical thrust upwards, directly providing lift for the entire aircraft, thereby achieving vertical takeoff and landing. During cruise, the outer wings rotate back to a position level with the central main wing, forming a complete flying wing configuration together with the central main wing. The power system provides horizontal thrust, and the aircraft relies on the aerodynamic lift of the wings to achieve efficient level flight.

[0032] The takeoff process of the drone in this embodiment is as follows: Before takeoff, the outer wings are rotated downwards by 90 degrees, with the four ends of the winglets acting as landing gear to support the fuselage. In this position, the propeller disks mounted on the outer wings are parallel to the ground, the thrust line is perpendicular to the ground, and the thrust direction is vertically upwards. The motors on the fuselage drive the propellers to rotate, pushing the air downwards and generating upward thrust. At this moment, the thrust of the propellers is the lift of the drone, pulling it to take off.

[0033] In vertical takeoff and landing mode, the control surfaces arranged on the trailing edge of the outer wing work in coordination with the differential speed of the left and right motors to achieve pitch, roll and yaw attitude control, thereby controlling the attitude and direction of motion of the UAV and ensuring flight stability during the vertical takeoff and landing phase.

[0034] Once the drone climbs above 20 meters and its horizontal airspeed exceeds 8 m / s, it enters a mode switching window. After the operator manually triggers the tilt program, the servo motors located inside the fuselage rotate to a preset angle, driving the outer wings on both sides to rotate synchronously upwards around the tilt axis via a gear transmission mechanism. As the outer wings rotate from a 90-degree vertical position to a 0-degree horizontal position, as the tilt angle decreases, the direction of the propeller thrust gradually changes from vertically upwards to horizontally forwards. The drone's horizontal speed increases, the lift provided by the propeller decreases, and the aerodynamic lift generated by the wings increases. Ultimately, the lift is entirely generated by the complete horizontal wings.

[0035] When the outer wings rotate to a 0-degree position completely aligned with the main wing, the mode transition phase ends, and the tilting mechanism stops. At this point, the UAV configuration transforms into a conventional flying wing layout, with the outer wings on both sides and the central main wing forming a complete lifting surface, and the propeller thrust axis turning horizontal. During level flight cruise, the UAV relies on the aerodynamic lift generated by the pressure difference between the upper and lower surfaces of the wings to support its flight weight, and the power system only needs to provide horizontal thrust to overcome drag. The trailing edge control surfaces of the outer wings continue to be responsible for flight attitude control, ensuring stability during cruise.

[0036] The applicant manufactured a 2kg-class prototype and completed the full-process test flight of vertical take-off and landing and level flight cruise. The actual test results showed that the prototype had minimal structural deformation, and the outer wing 2 did not exhibit significant elastic torsion or vibration under high thrust switching conditions. This verified the reliability of the beam-shaft integrated composite mechanism during mode switching and proved the high feasibility of this structural scheme in the engineering application of 2kg-class flying wing UAVs. The above description is merely a preferred embodiment of the present invention. Any modifications, equivalent substitutions, or improvements made by those skilled in the art within the spirit and scope of the present invention should be included within the protection scope of the present invention.

Claims

1. A small vertical takeoff and landing unmanned aerial vehicle (UAV), characterized in that, include: The central main wing adopts a blended wing-body design with the fuselage to form the main fuselage. The two sides of the central main wing are symmetrically provided with outer wings, and the outer wings are provided with control surfaces and rotor drive devices. The control surfaces and the rotor drive devices work together to adjust the flight attitude of the UAV. Two tilting shafts are respectively located on both sides of the fuselage; the tilting shafts extend along the wingspan direction and pass through the wing ribs inside the central main wing as the main load-bearing beam of the central main wing, and the outer ends of the tilting shafts are fixedly connected to the outer wing through load-bearing connectors. A tilt drive mechanism is installed inside the central main wing to drive the tilt shaft to rotate around its axis, thereby causing the outer wing, the control surface and the rotor drive device to rotate as a whole, thus realizing flight mode switching.

2. The small vertical take-off and landing UAV according to claim 1, characterized in that: The tilting shaft is inserted into at least two coaxially arranged bearings; each bearing is installed in a corresponding bearing housing, and the bearing housing is located between two adjacent ribs of the central main wing and is fixedly connected to both adjacent ribs.

3. The small vertical takeoff and landing unmanned aerial vehicle according to claim 1, characterized in that: The tilt drive mechanism includes a tilt control servo and a transmission gear set. The tilt control servo is fixed to the rib of the central main wing, and the tilt control servo outputs power to the tilt shaft through the transmission gear set.

4. The small vertical takeoff and landing unmanned aerial vehicle according to any one of claims 1-3, characterized in that: The control surfaces are located on the trailing edge of the outer wing.

5. The small vertical takeoff and landing unmanned aerial vehicle according to any one of claims 1-3, characterized in that: The tilt axis is a high-strength carbon fiber tube, and the tilt axis maintains the structural integrity inside the central main wing.

6. The small vertical takeoff and landing unmanned aerial vehicle according to any one of claims 1-3, characterized in that: The central wing has a cavity inside for housing the battery, ESC, and flight control system.

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