An eVTOL aircraft and its foldable lift propellers and flight control method

Abstract

The application discloses an eVTOL aircraft, a foldable lift propeller and a flight control method, and belongs to the technical field of electric aircrafts, and is used for solving the problems of large dead weight and large parasitic resistance of a lift propeller in a cruising stage of an existing hybrid wing configuration and the problem of lack of reliable locking means of an existing folding propeller. The aircraft comprises a fuselage, canard wings, wings and tail wings which are arranged along the longitudinal direction of the fuselage in sequence, and constitutes a three-wing surface aerodynamic layout; one tiltable power nacelle is arranged at each end of the wing, a tilting rotor is arranged in each tiltable power nacelle, the tiltable power nacelle is driven by a tilting actuator, and can be deflected between a vertical state with upward thrust and a horizontal state with forward thrust. Through the above arrangement, the front projection area of the lift propeller in the cruising stage is the smallest after being folded and locked, the dead weight and the parasitic resistance can be eliminated, and the hovering efficiency and the cruising resistance are cooperatively optimized.

Description

Technical Field

[0001] This invention relates to the field of electric aircraft technology, specifically to an eVTOL aircraft and its foldable lift propeller and flight control method. Background Technology

[0002] The current mainstream configurations of electric vertical takeoff and landing (eVTOL) aircraft can be broadly categorized into three types: multirotor, compound wing, and tiltrotor. Multirotor configurations rely on the rotors to continuously provide lift during the cruise phase, resulting in high disk loading, low aerodynamic efficiency, and limitations on range and cruise speed. Compound wing configurations have an independent lift propeller in addition to the thrust system; the two systems operate independently. After the lift propeller stops rotating during the cruise phase, it only generates drag and does not provide lift, resulting in significant dead weight and parasitic drag. Increasing the wing area to reduce wing loading further exacerbates the accumulation of weight and drag. Full tiltrotor configurations require all rotors to simultaneously handle both hovering and forward flight conditions. The propeller design point must compromise between these two significantly different operating states. During the cruise phase, all rotors are under low load, deviating from the optimal operating point. The tilting of all nacelles also introduces problems such as mechanical complexity and a high risk of single-point failure.

[0003] Chinese patent application CN117048822A discloses a compound tiltrotor aircraft, which adopts a configuration combining fixed wings and tiltrotors. Tiltable rotor nacelles are installed at both ends of the wings, allowing for switching between vertical takeoff and landing (VTOL) and forward flight modes through nacelle tilting. Fixed lift propellers are mounted on the fuselage or wings to supplement hover lift. However, in this design, the fixed lift propellers cannot be folded or retracted after stopping during cruise, and lack a reliable mechanical locking mechanism. The blades are in a free state in the cruise airflow, easily generating aerodynamic hinge torque that drives blade deflection and oscillation, creating additional drag. The stopped lift propeller acts as dead weight suspended on the wing surface, increasing structural weight and parasitic drag. Furthermore, this design does not disclose active measures to suppress the weight gain effect of the rotor downwash on the wing surface during VTOL, nor does it address a control strategy for optimizing the distribution of cruise lift across multiple wing surfaces, making it difficult to achieve synergistic optimization of hovering efficiency and cruise aerodynamic efficiency. Therefore, we propose an eVTOL aircraft, its foldable lift propeller, and flight control method to solve the above problems. Summary of the Invention

[0004] (a) Technical problems to be solved To address the shortcomings of existing technologies, this invention provides an eVTOL aircraft and its foldable lift propeller and flight control method. It has the advantages of having the smallest frontal projection area after the lift propeller is folded and locked during the cruise phase, eliminating dead weight and parasitic drag, and achieving synergistic optimization of hovering efficiency and cruise drag. It solves the problem that the lift propeller of existing compound-wing eVTOL aircraft only generates drag and does not provide lift after stopping during the cruise phase, resulting in high dead weight and high parasitic drag.

[0005] (II) Technical Solution To achieve the goal of minimizing the frontal projected area of ​​the lift propeller after folding and locking during the cruise phase, eliminating dead weight and parasitic drag, and synergistically optimizing hovering efficiency and cruise drag, this invention provides the following technical solution: An eVTOL aircraft and its foldable lift propeller and flight control method are disclosed. The electric vertical takeoff and landing aircraft includes: a fuselage; a canard, a wing, and a tail, arranged longitudinally along the fuselage to form a three-surface aerodynamic layout; two tiltable power nacelles, respectively located at the ends of the wing, each nacelle containing a tilt rotor, the tiltable power nacelles being driven by tilt actuators and capable of deflecting between a thrust-up vertical state and a thrust-forward horizontal state; at least two fixed power nacelles, respectively located at the ends of the canard and the tail, each fixed power nacelle containing a foldable lift propeller; wherein each... The foldable lift propeller includes a lower blade assembly, an upper blade assembly, a folding drive mechanism, and a locking mechanism. The lower blade assembly is fixedly connected to the propeller shaft via a lower hub. The upper blade assembly is mounted on the upper hub, which is fitted onto the propeller shaft and can rotate relative to it. The folding drive mechanism drives the upper hub to rotate relative to the lower hub between an unfolded position and a folded position. In the unfolded position, the upper blade assembly and the lower blade assembly are evenly distributed and staggered circumferentially. In the folded position, the upper blade assembly and the lower blade assembly overlap in the same feathering direction. The locking mechanism locks the upper hub in the folded position. With the above configuration, the tiltrotors at both ends of the wings are dedicated to cruise thrust and can be optimally designed for cruise conditions; the foldable lift propellers at the canard and tail fins unfold to provide lift for a multi-bladed configuration during hovering and stop and fold and lock into a double-layered feathering configuration during cruise, with the blade chord direction basically consistent with the airflow direction and the frontal projection area minimized, thereby eliminating dead weight and parasitic drag and achieving simultaneous optimization of hovering efficiency and cruise drag.

[0006] Furthermore, the locking mechanism is a pin-type locking mechanism, including a locking pin and a driving component for moving the locking pin. The lower rotor hub or fixed base is provided with a locking hole. When the upper rotor hub rotates to the folded position, the locking pin inserts into the locking hole, achieving circumferential locking between the upper and lower rotor hubs. The pin-type locking mechanism has a simple structure and rapid response. The locking pin can automatically insert into the locking hole under the drive of a spring or electromagnet, reliably withstanding the aerodynamic hinge torque and inertial torque generated by the cruising airflow on the rotor blades, preventing the rotor blades from oscillating and fluttering in the airflow.

[0007] Preferably, the locking mechanism is a toothed engagement locking mechanism, wherein the mating end faces of the upper and lower propeller hubs are respectively provided with locking teeth. When the upper propeller hub rotates to the folded position, the locking teeth on the end faces of the upper and lower propeller hubs engage axially, bearing the pneumatic hinge torque and inertial torque. The toothed engagement locking mechanism utilizes the end face teeth... Axial meshing transmits and bears the working load, with strong load-bearing capacity, and is suitable for working conditions with large pneumatic loads; pin locking and toothed meshing locking can be used in combination, with the toothed type bearing the working load and the pin type providing position retention, further improving locking reliability.

[0008] Specifically, the outer end of the tiltable power nacelle is provided with a nacelle outer end winglet, which increases the effective aspect ratio of the wing when the tiltable power nacelle is in a horizontal state. During cruise flight, the nacelle outer end winglet acts as a wingtip winglet, which can effectively increase the effective wing area and aspect ratio, reduce induced drag, improve the cruise lift-to-drag ratio, and improve the overall cruise aerodynamic performance of the aircraft.

[0009] Furthermore, the outer end of the wing is equipped with a flaperon driven by an electric servo, and the trailing edge of the tail is equipped with an elevator driven by an electric servo. During vertical takeoff and landing (VTOL), the flaperon and elevator deflect downwards to their maximum angle to reduce the weight gain effect of the rotor downwash on the wing surface. By actively deflecting the control surfaces to their maximum angle during VTOL, the wing surface becomes more parallel to the rotor downwash direction, significantly reducing the aerodynamic downforce generated by the downwash on the wing surface, thereby reducing induced power loss during hovering and improving hovering efficiency.

[0010] In some embodiments, the tilt rotor is a variable-pitch propeller, whose pitch is adjusted according to operating conditions via a pitch-adjusting mechanism. During the cruise phase, the combination of pitch and rotational speed is selected based on flight speed and altitude. The variable-pitch propeller can always operate at its optimal efficiency under different flight speeds and altitudes, reducing cruise power requirements and increasing overall flight time and range.

[0011] As a preferred embodiment, the lower part of the fuselage is equipped with a tricycle landing gear, and the lower part of the fuselage tail is equipped with a ventral fin. The tricycle landing gear has ground traction capability, while having a small structural weight and low aerodynamic drag; the ventral fin, located under the tail of the fuselage, can enhance directional stability and improve low-speed flight handling quality.

[0012] The present invention also provides a foldable lift propeller, comprising: a propeller shaft; a lower propeller hub fixedly connected to the propeller shaft, wherein at least two lower propeller blades are disposed on the lower propeller hub, and the lower propeller blades are evenly distributed circumferentially; an upper propeller hub sleeved on the propeller shaft and rotatable relative to the propeller shaft, wherein at least two upper propeller blades are disposed on the upper propeller hub, and the upper propeller blades are evenly distributed circumferentially; a folding drive mechanism for driving the upper propeller hub to rotate relative to the lower propeller hub between an unfolded position and a folded position; in the unfolded position, the upper propeller blades and the lower propeller blades are evenly distributed circumferentially offset to form a multi-blade unfolded configuration; in the folded position, the upper propeller blades and the lower propeller blades overlap in the same longitudinal direction to form a double-layer overlapping configuration; and a locking mechanism for locking the upper propeller hub relative to the lower propeller hub in the folded position, so that the chord direction of the lower propeller blades in the double-layer overlapping configuration is consistent with the airflow direction. This foldable lift propeller switches between unfolded and folded states by rotating the upper and lower hubs relative to each other. When folded, the upper and lower blades completely overlap in the feathering direction, resulting in the smallest frontal projection area compared to existing overall folding or single-layer feathering solutions. The locking mechanism mechanically locks the folded state, preventing the blades from wobbling in the cruise airflow and completely eliminating flutter and additional drag.

[0013] Furthermore, the folding drive mechanism is either an electric actuator located within the propeller hub or a combination of a torsion spring and a motor. The electric actuator enables precise angle control and has a fast response speed; the combination of the torsion spring and motor, with the assistance of spring energy storage, can reduce the peak power requirement of the drive motor. Both forms can reliably drive the upper propeller hub to rotate between the unfolded and folded positions.

[0014] This invention also provides a flight control method for an electric vertical takeoff and landing (EVTOL) aircraft, applied to the aforementioned EVTOL aircraft, comprising the following steps: Vertical takeoff and landing step: controlling the tilt rotor to be in a vertical state, controlling the foldable lift propeller to be in the deployed position, with six sets of rotor and propeller systems working simultaneously to provide lift for the entire aircraft, using the differential thrust of each power unit to achieve pitch, roll and yaw attitude control, while controlling the flaps and ailerons of the wing and the elevator rudder of the tail to deflect downward to the maximum deflection angle to reduce the weight gain effect of the rotor downwash; Transition step: controlling the tilt rotor to gradually tilt forward, while providing lift and thrust components; As flight speed increases, the lift borne by the three surfaces gradually increases, and the rotational speed of the foldable lift propeller gradually decreases until it stops. Then, the folding drive mechanism drives the upper hub to the folded position and locks it in place by the locking mechanism. The control weight allocation is scheduled according to flight speed, and the control efficiency transitions continuously from differential thrust to the control surfaces. Cruise steps: the tilt rotor is controlled to provide thrust in a horizontal state, and the foldable lift propeller remains folded and locked. The three surfaces share the lift, and the load distribution is optimized to minimize trim drag. The tilt rotor selects the most efficient combination of pitch and rotational speed based on flight speed and altitude. This flight control method achieves coordinated operation of the power system and control surfaces in each flight phase through a phased control strategy. During the transition phase, the control weight allocation is continuously scheduled according to speed to ensure uninterrupted control efficiency. Simultaneously, the timing of the lift propeller's stopping, folding, and locking is precisely matched with the increase in lift borne by the wing surfaces, achieving a smooth transition.

[0015] (III) Beneficial Effects Compared with the prior art, the present invention provides an eVTOL aircraft and its foldable lift propeller and flight control method, which has the following advantages: 1. By designing the foldable lift propeller as a double-layer folding structure with upper and lower hubs rotating relative to each other and equipped with a mechanical locking mechanism, the upper and lower blades of the lift propeller completely overlap in the feathering direction after folding during the cruise phase. The chord direction of the blades is basically consistent with the airflow direction, minimizing the frontal projected area. This completely eliminates the dead weight and parasitic drag generated after the lift propeller stops rotating in the compound airfoil configuration. At the same time, the locking mechanism prevents the blades from swinging in the airflow, eliminating flutter and additional drag, overcoming the shortcomings of existing folding propeller designs, such as large projected area after folding and lack of reliable locking means.

[0016] 2. By adopting a division of labor in which only two tiltable power nacelles at the wingtips bear the cruise thrust, and fixed power nacelles at the canard and tail fin tips carry foldable lift propellers to bear the hovering lift, the tilt rotor can be optimally designed specifically for cruise conditions, always operating at its high-efficiency point. This overcomes the shortcomings of fully tiltable propellers, such as the compromise in design point and deviation from the optimal operating point during cruise. At the same time, only two nacelles need to tilt, which greatly reduces the complexity of the mechanism and the risk of single-point failure.

[0017] 3. By actively deflecting the flaps and ailerons at the outer end of the wing and the elevator rudder at the trailing edge of the tail to the maximum deflection angle during the vertical takeoff and landing phase, the wing surface and the direction of the rotor downwash airflow tend to be parallel, which significantly reduces the aerodynamic downforce generated by the downwash airflow on the wing surface, reduces the induced power loss during the hovering phase, improves the overall hovering efficiency, and solves the technical problem of the weight-increasing effect of the rotor downwash airflow on the wing surface and control surfaces in the existing scheme. Attached Figure Description

[0018] Figure 1 This is a three-dimensional schematic diagram of the overall structure of the electric vertical takeoff and landing aircraft provided in the embodiment of the present invention in the vertical takeoff and landing state.

[0019] Figure 2 This diagram shows a three-dimensional view of the overall structure of the electric vertical takeoff and landing aircraft provided in the embodiment of the present invention during cruise.

[0020] Explanation of reference numerals in the attached diagram: 1. Tilting rotor; 2. Tilting power nacelle; 3. Nacelle outer winglet; 4. Foldable lift propeller; 5. Fixed power nacelle; 6. Canard; 7. Fuselage; 8. Nose landing gear; 9. Main landing gear; 10. Wing; 11. Ventral fin; 12. V-tail; 13. Elevator; 14. Flaps and ailerons. Detailed Implementation

[0021] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] See Figure 1 and Figure 2This application provides an electric vertical takeoff and landing (EVTOL) aircraft, which adopts a three-surface aerodynamic layout of canard 6, wing 10, and V-tail 12. The canard 6 is located at the front of the fuselage 7, the wing 10 is located in the middle of the fuselage 7, and the V-tail 12 is located at the rear of the fuselage 7, with the three wing surfaces arranged longitudinally along the fuselage 7. Each end of the wing 10 has a tiltable power nacelle 2, and each tiltable power nacelle 2 is equipped with a tilt rotor 1. The tiltable power nacelle 2 is driven by a tilt actuator and can continuously deflect between a vertical state with upward thrust and a horizontal state with forward thrust. Each end of the canard 6 and the V-tail 12 has a fixed power nacelle 5, and each fixed power nacelle 5 is equipped with a foldable lift propeller 4. The entire aircraft has a total of six rotor and propeller systems. The lower part of fuselage 7 is equipped with a tricycle landing gear, including the nose landing gear 8 and the main landing gear 9, which provides ground traction while maintaining a low structural weight and aerodynamic drag. A ventral fin 11 is located under the tail of fuselage 7 to enhance directional stability and improve low-speed flight handling.

[0023] The tiltable power nacelle 2 is provided with an outer winglet 3 at its outer end. The outer winglet 3 is fixedly connected to the tiltable power nacelle 2 and tilts together with the tiltable power nacelle 2. When the tiltable power nacelle 2 is in a horizontal state, the outer winglet 3 is equivalent to a wingtip winglet, which can effectively increase the effective area and aspect ratio of the wing 10, reduce induced drag, and improve the cruise lift-to-drag ratio.

[0024] The outer edge of the wing 10 is equipped with a flaperon 14 driven by an electric servo, and the trailing edge of the V-tail 12 is equipped with an elevator 13 driven by an electric servo. During vertical takeoff and landing, both the flaperon 14 and the elevator 13 are driven by their respective electric servos, deflecting downwards to their maximum deflection angle, making the wing surface nearly parallel to the direction of the rotor downwash airflow. This significantly reduces the aerodynamic downforce generated by the downwash on the wing surface, thereby reducing induced power loss during hovering and improving hovering efficiency. During cruise flight, the flaperon 14 performs lift enhancement and lateral roll control, while the elevator 13 performs pitch and yaw control.

[0025] Each foldable lift propeller 4 includes a propeller shaft, a lower propeller hub, an upper propeller hub, a lower blade assembly, an upper blade assembly, a folding drive mechanism, and a locking mechanism. The lower propeller hub is fixedly connected to the propeller shaft, which can be achieved through integrated machining or key connection. The lower propeller hub has two lower blades, evenly distributed at 180 degrees circumferentially. The upper propeller hub is fitted onto the outside of the propeller shaft and rotates relative to it via bearings, allowing it to rotate freely. The upper propeller hub has two upper blades, also evenly distributed at 180 degrees circumferentially. The folding drive mechanism is located inside the propeller hub and drives the upper propeller hub to rotate relative to the lower propeller hub between the unfolded and folded positions.

[0026] In the deployed position, the folding drive mechanism rotates the upper rotor hub, causing the upper and lower blades to be evenly staggered circumferentially. Specifically, the two upper blades and the two lower blades are each 90 degrees apart circumferentially, forming a four-bladed multi-blade configuration. This configuration increases the rotor disk solidity, reduces the rotor disk load, and improves hovering aerodynamic efficiency. Simultaneously, the four blades share the aerodynamic load, significantly reducing the out-of-plane bending moment borne by a single blade and decreasing the fatigue load on the canard 6 and V-tail 12 structures.

[0027] In the folded position, the folding drive mechanism drives the upper rotor hub to continue rotating, causing the upper and lower blades to overlap in the same feathering direction, forming a double-layered stacked configuration with two blades on each side. In this configuration, the blade chord direction is basically consistent with the local airflow direction, minimizing the frontal projected area and eliminating the chattering and additional drag caused by blade wobbling with the airflow. The locking mechanism locks the upper rotor hub relative to the lower rotor hub in the folded position, ensuring the double-layered stacked configuration remains stable in the cruise airflow and reliably withstands aerodynamic hinge torque and inertial torque.

[0028] In one embodiment, the locking mechanism is a pin-type locking mechanism. The pin-type locking mechanism includes a locking pin and a driving component that drives the locking pin; the driving component can be a spring or an electromagnet. A locking hole is provided on the lower rotor hub or mounting base, the position of which matches the corresponding position of the locking pin when the upper rotor hub is in the folded position. When the upper rotor hub rotates to the folded position, the spring-driven locking pin automatically inserts into the locking hole under the guidance of the inclined surface, achieving circumferential locking between the upper and lower rotor hubs. When unlocking is required, the unlocking electromagnet is energized, retracting the locking pin, and the folding drive mechanism then drives the upper rotor hub to the unfolded position. The pin-type locking mechanism has a simple structure, rapid response, and can reliably withstand the aerodynamic hinge torque and inertial torque generated by the cruising airflow on the rotor blades, preventing the rotor blades from oscillating in the airflow.

[0029] In another embodiment, the locking mechanism is a toothed engagement locking mechanism. Locking teeth are respectively provided on the mating end faces of the upper and lower rotor hubs, and the tooth profiles of the two sets of locking teeth mesh with each other. When the upper rotor hub rotates to the folded position, the locking teeth on the end face of the upper rotor hub and the locking teeth on the end face of the lower rotor hub are axially aligned and meshed, transmitting and bearing the working load through the axial meshing of the end face teeth. The toothed engagement locking mechanism has a strong load-bearing capacity and is suitable for operating conditions with large aerodynamic loads. Pin-type locking and toothed engagement locking can also be used in combination. When used in combination, the toothed mechanism bears the working load, while the pin provides position retention, further improving locking reliability.

[0030] In one embodiment, the folding drive mechanism is an electric actuator located within the propeller hub, enabling precise angle control and rapid response. In another embodiment, the folding drive mechanism is a combination of a torsion spring and a motor, with the torsion spring storing energy to assist the motor drive, thus reducing the peak power requirement of the drive motor. Both forms can reliably drive the upper propeller hub to rotate between the unfolded and folded positions.

[0031] In one embodiment, the tiltrotor 1 is a five-bladed variable-pitch propeller, with the pitch adjusted according to operating conditions via a pitch-adjusting mechanism. During the cruise phase, the tiltrotor 1 selects the most efficient combination of pitch and rotational speed based on flight speed and altitude, ensuring the rotor always operates at a high-efficiency point, reducing cruise power requirements, and increasing overall flight time and range.

[0032] The following describes the phased working process of the entire machine.

[0033] During the vertical takeoff and landing phase, see Figure 1 The tiltable power nacelle 2 is driven to a vertical position by a tilt actuator, and the tilt rotor 1 provides lift upwards along its axis. The foldable lift propeller 4 is driven to its deployed position by a folding drive mechanism, with four blades evenly distributed circumferentially in a multi-bladed deployment configuration. The six rotor and propeller systems work simultaneously to provide lift for the entire aircraft. Attitude control is primarily achieved through differential thrust from the six power units: pitch control is achieved through thrust differential between the forward canard power unit and the rear V-tail power unit; roll control is achieved through thrust differential between the left and right power units; and yaw control is achieved through anti-torque differential between the rotors. The control surfaces provide minor auxiliary attitude control during this phase. Simultaneously, the flaps 14 and elevator 13 deflect downwards to their maximum angle, reducing the aerodynamic downforce generated by the rotor downwash on the wing surface and minimizing hover induced power loss.

[0034] During the transition phase of flight, the tilt actuator drives the tiltable power nacelle 2 to gradually tilt forward, while the tilt rotor 1 simultaneously provides both lift and thrust components. As flight speed increases, the aerodynamic lift borne by the canard 6, wing 10, and V-tail 12 gradually increases, while the lift required by the foldable lift propeller 4 gradually decreases, and its rotational speed gradually decreases until it stops. After the foldable lift propeller 4 stops, the folding drive mechanism drives the upper rotor hub to the folded position, with the upper and lower blades overlapping in the feathering direction. Subsequently, the locking mechanism locks the upper rotor hub in the folded position. Simultaneously, the flight control system continuously adjusts the control allocation weights according to flight speed, smoothly transitioning the control effectiveness from differential thrust to the control surfaces, ensuring the continuity of control effectiveness during the transition phase and avoiding control interruptions.

[0035] During the cruise phase, see Figure 2The tilt actuator drives the tiltable powered nacelle 2 to a horizontal position, and the tilt rotor 1 provides thrust to the entire aircraft by moving its axis forward. The foldable lift propeller 4 remains folded and locked, with the upper and lower blades overlapping in the feathering direction. The blade chord direction is basically consistent with the airflow direction, minimizing the frontal projected area and generating no additional drag. Lift is shared by three wing surfaces: the canard 6, the wing 10, and the V-tail 12. The load distribution of the three wing surfaces is optimized according to the goal of minimizing trim drag or maximizing the lift-to-drag ratio. Compared with a single-wing surface configuration, it can obtain the required lift with a smaller total wing surface area, reducing the weight of the wing structure and achieving zero lift drag. The outer winglets 3 of the nacelle are in a horizontal position along with the tiltable powered nacelle 2, increasing the effective aspect ratio of the wing 10 and further reducing induced drag. The tilt rotor 1 selects the most efficient combination of pitch and rotational speed based on the flight speed and altitude.

[0036] In terms of safety redundancy, if any one of the six power units fails, the flight control system will reconfigure the control allocation of the remaining power units and control surfaces to maintain attitude control capabilities and complete the mission or achieve a safe landing. The tilt actuator has a mechanical self-locking function; if the tilt mechanism fails, the power nacelle 2 can be tilted and locked at the current angle, and the flight control system can reconfigure control using the remaining controllable power and control surfaces. If the folding locking mechanism of the foldable lift propeller 4 fails during the cruise phase, the flight control system will brake the propeller and maintain it at a predetermined low-drag feathering position to reduce the impact on cruise performance.

[0037] Regarding layout and power variations, while maintaining the core concept of dual tilt rotors at the wingtips and multiple sets of foldable locking lift propellers, the number of foldable lift propellers 4 can be two to eight sets, arranged at the ends of the canards 6, V-tails 12, or other positions on the wing surface; the tail fin can be replaced with a combination of a conventional horizontal tail and a vertical tail; the number of blades on the tilt rotor 1 can be three to six, and the pitch mechanism can be replaced with a fixed-pitch plus variable-speed adjustment method; the power source can be pure electric, hybrid electric, or hydrogen fuel power; the tilt actuator can be electric, electromechanical, or hydraulic. All the above variations do not depart from the core technical concept of this application.

[0038] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An electric vertical takeoff and landing aircraft, characterized in that, include: body; The canard, wings and tail are arranged sequentially along the longitudinal direction of the fuselage to form a three-surface aerodynamic layout; Two tiltable power nacelles are respectively located at both ends of the wing. Each tiltable power nacelle is equipped with a tilt rotor. The tiltable power nacelle is driven by a tilt actuator and can deflect between a vertical state with upward thrust and a horizontal state with forward thrust. At least two fixed power nacelles are respectively located at the ends of the canard and the tail fin, and each fixed power nacelle is equipped with a foldable lift propeller; Each foldable lift propeller includes a lower blade assembly, an upper blade assembly, a folding drive mechanism, and a locking mechanism. The lower blade assembly is fixedly connected to the propeller shaft via a lower hub. The upper blade assembly is mounted on the upper hub, which is fitted onto the propeller shaft and can rotate relative to it. The folding drive mechanism drives the upper hub to rotate relative to the lower hub between an unfolded position and a folded position. In the unfolded position, the upper and lower blade assemblies are circumferentially staggered and evenly distributed. In the folded position, the upper and lower blade assemblies overlap in the same feathering direction. The locking mechanism locks the upper hub in the folded position.

2. The electric vertical takeoff and landing aircraft according to claim 1, characterized in that, The locking mechanism is a pin-type locking mechanism, including a locking pin and a driving component for driving the locking pin to move. The lower propeller hub or fixed seat is provided with a locking hole. When the upper propeller hub is rotated to the folded position, the locking pin is inserted into the locking hole to achieve circumferential locking between the upper propeller hub and the lower propeller hub.

3. The electric vertical takeoff and landing aircraft according to claim 1, characterized in that, The locking mechanism is a toothed meshing locking mechanism. The mating end faces of the upper propeller hub and the lower propeller hub are respectively provided with locking teeth. When the upper propeller hub is rotated to the folded position, the locking teeth on the end face of the upper propeller hub and the locking teeth on the end face of the lower propeller hub are axially meshed, bearing the pneumatic hinge torque and inertial torque.

4. The electric vertical takeoff and landing aircraft according to claim 1, characterized in that, The outer end of the tiltable power nacelle is provided with a nacelle outer end wing, which increases the effective aspect ratio of the wing when the tiltable power nacelle is in a horizontal state.

5. The electric vertical takeoff and landing aircraft according to claim 1, characterized in that, The outer end of the wing is provided with a flaperon driven by an electric servo, and the trailing edge of the V-tail is provided with an elevator driven by an electric servo. The flaperon and the elevator deflect downward to the maximum deflection angle during the vertical takeoff and landing phase to reduce the weight gain effect of the rotor downwash on the wing surface.

6. The electric vertical takeoff and landing aircraft according to claim 1, characterized in that, The tilt rotor is a variable-pitch propeller, which adjusts the pitch according to the operating conditions through a pitch-adjusting mechanism. During the cruise phase, the combination of pitch and rotation speed is selected based on the flight speed and altitude.

7. The electric vertical takeoff and landing aircraft according to claim 1, characterized in that, The lower part of the fuselage is equipped with a tricycle landing gear, and the lower part of the tail section of the fuselage is equipped with a ventral fin.

8. A foldable lift propeller, characterized in that, include: propeller shaft; The lower rotor hub is fixedly connected to the rotor shaft, and at least two lower rotor blades are provided on the lower rotor hub, with each lower rotor blade being evenly distributed circumferentially. An upper rotor hub is fitted onto the rotor shaft and can rotate relative to the rotor shaft. At least two upper rotor blades are provided on the upper rotor hub, and each upper rotor blade is evenly distributed circumferentially. A folding drive mechanism drives the upper rotor hub to rotate relative to the lower rotor hub between an unfolded position and a folded position; in the unfolded position, the upper and lower rotor blades are circumferentially staggered and evenly distributed, forming a multi-blade unfolded configuration; in the folded position, the upper and lower rotor blades overlap in the same longitudinal direction, forming a double-layered overlapping configuration; and A locking mechanism locks the upper blade hub relative to the lower blade hub at the folded position, so that the chord direction of the lower blade in the double-layered configuration is consistent with the airflow direction.

9. The foldable lift propeller according to claim 8, characterized in that, The folding drive mechanism is an electric actuator located inside the propeller hub, or a combination of a torsion spring and a motor.

10. A flight control method for an electric vertical takeoff and landing (EVTOL) aircraft, applied to the EVTOL aircraft according to any one of claims 1 to 7, characterized in that, Includes the following steps: Vertical takeoff and landing steps: Control the tilt rotor to be in a vertical state, control the foldable lift propeller to be in the deployed position, and the six sets of rotor and propeller systems work simultaneously to provide lift for the whole aircraft. The differential thrust of each power unit is used to achieve pitch, roll and yaw attitude control. At the same time, control the flaps and ailerons of the wing and the elevator rudder of the tail to deflect downward to the maximum deflection angle to reduce the weight gain effect of the rotor downwash. Transition steps: Control the tilt rotor to tilt forward gradually, providing both lift and thrust components; as the flight speed increases, the lift borne by the three surfaces gradually increases, and the rotational speed of the foldable lift propeller gradually decreases until it stops. Then, control the folding drive mechanism to drive the upper hub to the folding position and lock it by the locking mechanism; control the weight distribution according to the flight speed, and the control effectiveness continuously transitions from differential thrust to control surfaces. Cruise procedure: The tilt rotor is controlled to be in a horizontal state to provide thrust, and the foldable lift propeller is kept in a folded and locked state; the three surfaces share the lift, and the load distribution of the three surfaces is optimized according to the goal of minimizing trim drag; the tilt rotor selects the most efficient combination of pitch and rotation speed according to the flight speed and flight altitude.

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