Tail rotor tilt mechanism for an aircraft and multi-modal attitude control method

Abstract

The application relates to the technical field of aircraft attitude control, and discloses a tail rotor tilting mechanism of an aircraft and a multi-mode attitude control method. The mechanism comprises a tail rotor group arranged at the tail and a tilting driving device, and the tilting driving device drives the whole tail rotor group to tilt; the trailing edge of the tail hook is in an S curve shape and forms a bulge-shaped embracing space, the tilting driving device is embedded in or embraced outside the space, and a tail hook bearing structure is integrally formed with the installation space of the tilting driving device; a hollow part is arranged at the lower part of the vertical tail, and the hollow part is used for the rotation and tilting movement of the rotor disc. In the hovering mode, the gravity center is located between the wing tip propulsion rotor and the tail rotor group, and the two share the gravity of the whole machine; the control method is used for linkage control of the attack angle and the tilting angle according to three modes of cruising, hovering and sprinting, the tilting angle and the attack angle are reversely matched to maintain the thrust direction, and the pitch of the propulsion propeller and the gravity center position of the whole machine are linkage adjusted. The mechanism is simple and does not damage the aerodynamic shape, the same propulsion system is shared by the three modes, and the mode switching transition is stable.

Description

Technical Field

[0001] This invention relates to the field of aircraft tilting mechanisms and flight control technology, specifically to a tail rotor tilting mechanism for an aircraft, and a multimodal attitude control method based on the tilting mechanism. Background Technology

[0002] Tiltrotor aircraft achieve both vertical takeoff and landing and high-speed cruise by changing the direction of rotor thrust. Most existing tiltrotor aircraft adopt a single-disc tilting scheme, and the tilting mechanism is mostly located in the wing area. The mechanism is complex, large in size and weight, and often requires additional rectification structure, which can easily disrupt the aerodynamic shape of the airframe.

[0003] The layout of arranging the rotor assembly at the tail and tilting the entire rotor assembly is relatively rare in existing technology. This type of layout needs to solve the following problems simultaneously: First, the switching between multiple flight modes such as hovering, cruise, and sprint requires that the lift direction of the tail be adjustable; second, the tilting mechanism needs to be small in size and light in weight, and must not damage the aerodynamic surfaces of the airframe; third, there is an interference problem between the rotation and tilting motion space of the tail rotor and the vertical tail structure.

[0004] There is no existing integrated mechanism that embeds the tilting drive unit within the space encircled by the tail hook of the vertical tail, and drives the entire tail rotor assembly to tilt using the tilting drive unit. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a tail rotor tilting mechanism that enables the output force direction of the tail rotor to be adjustable in various flight modes such as hovering, cruise, and sprint. At the same time, the tilting mechanism is small in size and light in weight, does not damage the aerodynamic surface of the airframe, and solves the problem of interference between the rotation and tilting space of the tail rotor and the vertical tail structure; and to provide a multi-modal attitude control method that works in conjunction with the mechanism.

[0006] To solve the above-mentioned technical problems, the present invention adopts the following technical solution: a tail rotor tilting mechanism for an aircraft, the aircraft including a fuselage, wings disposed on the fuselage, and a vertical tail disposed at the tail of the fuselage, the tail rotor tilting mechanism including: a tail rotor assembly disposed at the tail of the aircraft, including at least one rotor mounted on the vertical tail; a tilting drive device including a tilting drive component, the tilting drive component being convexly connected to the tail rotor assembly, for driving the tail rotor assembly to tilt as a whole, thereby changing the tilt angle of the rotor disk relative to the fuselage.

[0007] Furthermore, the upper part of the vertical tail is provided with a tail hook, the trailing edge of the tail hook is in the shape of an S-curve, the S-curve shape forms a bulge at the trailing edge of the tail hook, the top of the trailing edge of the bulge is provided with a protruding connecting part, and the tail rotor assembly is installed on the protruding connecting part; the tilt drive is embedded in or wrapped around the protruding connecting part, the load-bearing structure of the tail hook is integrally formed with the installation space of the tilt drive device, and the installation space includes the bulge and the protruding connecting part.

[0008] Furthermore, the tail rotor assembly is a coaxial dual rotor assembly, including an upper rotor and a lower rotor coaxially arranged on the tail hook. The rotation axes of the upper rotor and the lower rotor coincide, and they are each driven by their respective motors.

[0009] Furthermore, the upper rotor and the lower rotor have unequal diameters, with the larger one having a diameter ranging from 20% to 200% of the aircraft's wingspan, and the smaller one having a diameter not exceeding 60% of the aircraft's wingspan. The proportion of the larger rotor's diameter depends on the functional requirements of the fixed wing's aspect ratio and the combined lift of the rotors; the proportion of the smaller rotor's diameter depends on the size of the vertical tail and the space available for the tailhook. The coaxial dual-rotor assembly may also omit one rotor, meaning the tail rotor assembly is a single rotor.

[0010] Furthermore, the upper rotor and the lower rotor each have two, three, four, or more blades, or they may be internal blades.

[0011] Furthermore, the tilting drive component is a sleeve-type servo or a plate-type servo; when a sleeve-type servo is used, the tail hook passes through the sleeve of the servo; when a plate-type servo is used, the plate-type servo is inserted into the tail hook and fixed with the servo shaft, or wraps around the tail hook and is fixed with the servo shaft; the servo drives the tail hook and the tail rotor assembly mounted on the tail hook to tilt around the servo shaft as a whole.

[0012] Furthermore, it also includes a connecting seat that extends through the trailing edge of the tail hook, connecting the servo to the tail rotor assembly and transmitting tilting drive force.

[0013] Furthermore, when the tail rotor assembly is a coaxial dual rotor assembly, a hollow section is provided in the lower rear part of the vertical tail, so that the upper part of the vertical tail forms a tail hook. The hollow section constitutes a channel for the rotor disk of the tail rotor assembly to rotate and move with the tail rotor assembly.

[0014] Furthermore, the lower part of the vertical tail or the lower part of the tailhook is provided with an auxiliary rudder to supplement the heading control of the aircraft.

[0015] Furthermore, the tilt drive unit drives the tilt angle of the tail rotor assembly to be continuously adjustable. The adjustment range of the tilt angle covers the forward tilt position, the neutral position and the backward tilt position, and is limited to satisfying the overall thrust balance in the hovering state and the minimum drag torque balance in the cruise and sprint states.

[0016] Furthermore, a propulsion motor and a propulsion propeller driven by the propulsion motor are provided at the wingtip or the inner side of the wingtip. The upward mounting angle of the axis of the propulsion motor relative to the longitudinal axis of the fuselage is 0°~60° and the outward mounting angle is 0°~40°.

[0017] Furthermore, the propulsion propeller is a variable-pitch propeller, and the pitch of the variable-pitch propeller is adjusted in conjunction with the flight mode of the aircraft: in hovering mode (including hovering forward state), the propulsion propeller shares the weight of the entire aircraft and the forward thrust, and the pitch is adjusted to a high pitch state; in cruise mode, the propulsion propeller only overcomes aerodynamic drag, and the pitch is adjusted to a low pitch state; in sprint mode, the pitch is gradually increased as the flight speed increases.

[0018] Furthermore, the wing has an installation angle of 0° to 15°, which makes the overall angle of attack of the aircraft in cruise mode zero or close to zero cruise trim angle of attack; the wing has a dihedral angle of -5° to 10°, and when the dihedral angle is negative, it is called an anhedral angle.

[0019] Furthermore, it also includes a center of gravity adjustment device, which includes a linear motor and a movable load located inside the fuselage. The movable load is a battery or other load that affects the position of the overall center of gravity. The linear motor drives the movable load to move along the longitudinal axis of the fuselage. The position of the movable load on the longitudinal axis of the fuselage corresponds to the flight mode of the aircraft, so that the position of the overall center of gravity is set according to the static stability margin target.

[0020] Furthermore, in hovering mode, the center of gravity of the entire aircraft is located between the propulsion propeller and the tail rotor assembly located at or inside the wingtip, and the propulsion propeller and the tail rotor assembly jointly bear the weight of the entire aircraft.

[0021] This invention also provides a multi-modal attitude control method for an aircraft, wherein the aircraft employs the aforementioned tail rotor tilting mechanism, comprising the following steps: Step 1: Obtaining a flight mode command, wherein the flight mode includes cruise mode, hovering mode, and sprint mode; Step 2: Responding to the flight mode command to hovering mode, there are two cases: one is switching from cruise mode to hovering mode, controlling the center of gravity of the entire aircraft to move backward between the propeller and the tail rotor assembly, the entire aircraft pitches up around the hovering center of gravity to the positive angle of attack and gradually increases it to exceed the stall angle of attack, while controlling the tilting drive to drive the tail rotor assembly to tilt forward, as the angle of attack of the entire aircraft increases, the propeller... The propeller's ground-to-ground angle and the tail rotor assembly's ground-to-ground angle gradually become equal in magnitude and opposite in direction, ultimately with the propeller and tail rotor assembly jointly providing the aircraft's lift; the second is the takeoff and hover mode, where the aircraft's center of gravity is controlled to shift rearward between the propeller and tail rotor assembly, the fuselage's aerodynamic angle of attack is greater than the stall angle of attack, and the aircraft's lift is jointly borne by the propeller and tail rotor assembly, achieving takeoff and hovering; Step 3: In response to the flight mode command being sprint mode, the aircraft is controlled to nose-down around the cruise center of gravity to a negative angle of attack, while simultaneously controlling the tilt drive to drive the tail rotor assembly to tilt backward, maintaining the rotor disk Parallel to the ground to reduce drag and maintain lift sharing and pitch control capabilities; Step 4: Responding to the flight mode command to cruise mode, there are two cases: one is switching from hover mode to cruise mode, controlling the overall center of gravity to move forward from between the propeller and the tail rotor assembly towards the cruise center of gravity. As the overall center of gravity moves forward, the overall angle of attack gradually decreases and approaches the stall angle of attack. At the same time, the thrust direction of the propeller gradually deviates towards parallel to the ground as the overall angle of attack decreases, and the flight speed continuously increases; when the overall angle of attack returns to within the stall angle of attack and the flight speed is greater than the minimum level flight speed, the overall lift is taken over by the wing and fuselage lifting bodies, and the tail... The rotor assembly switches to provide pitch control and dynamic pitch balance, and then continues to accelerate into cruise mode; during the above switching process, the propeller disk of the tail rotor assembly always remains parallel to the ground; the second is cruise hold, controlling the overall angle of attack to the cruise trim angle of attack, which is zero or close to zero, and controlling the tail rotor assembly to return to the neutral position, maintaining the propeller disk parallel to the ground; wherein, during the transition between cruise and sprint modes, and between hover mode and cruise mode, the tilt angle of the tail rotor assembly is linked to the overall angle of attack, and the tilt angle and the angle of attack are inversely proportional to each other, so as to maintain the thrust direction of the propeller disk perpendicular to the ground.

[0022] Furthermore, the aircraft is provided with a variable-pitch propeller at the wingtip or inside the wingtip, which serves as a propulsion propeller. The method further includes: adjusting the pitch of the variable-pitch propeller in conjunction with the flight mode, wherein when switching to hover mode, the pitch is increased because the variable-pitch propeller bears the weight of the entire aircraft; when switching to cruise mode, the pitch is decreased; and when switching to sprint mode, the pitch is gradually increased as the flight speed increases.

[0023] Furthermore, during the transition from hovering mode to cruise mode, the center of gravity of the entire aircraft gradually shifts forward, and the thrust of the propeller gradually deflects and increases in a direction parallel to the ground. In the initial stage of the transition, the lift of the entire aircraft is shared by the propeller and the tail rotor assembly. As the center of gravity shifts forward, the forward speed increases, and the angle of attack decreases, the wing and fuselage lifting bodies begin to generate lift, and the lift of the entire aircraft is then shared by the propeller, the wing, the fuselage lifting bodies, and the tail rotor assembly. When the angle of attack of the wing and fuselage lifting bodies is less than the stall angle of attack and the forward speed is greater than the minimum level flight speed, the lift of the entire aircraft is entirely borne by the wing and fuselage lifting bodies, and the tail rotor assembly switches to providing pitch control and dynamic pitch balancing.

[0024] Furthermore, the fuselage is equipped with a linear motor that drives a movable load to move along the longitudinal axis of the fuselage to adjust the overall center of gravity: when switching to hover mode, the linear motor drives the movable load to move backward, thus shifting the overall center of gravity backward; when switching to cruise mode or sprint mode, the linear motor drives the movable load to move forward, thus shifting the overall center of gravity forward; the position of the overall center of gravity in each flight mode is set according to the static stability margin target, and the movement of the movable load is coordinated with the reverse ratio control of the tilt angle and the angle of attack. During the mode switching transition, the tail rotor assembly increases the lift output to compensate for the decrease in lift at the front during the switching process.

[0025] Compared with existing technologies, the advantages of this invention are: a single tilting drive unit drives the entire tail rotor assembly to tilt, minimizing the number of mechanisms, resulting in small size and light weight; the S-shaped tail hook serves as both the rotation space and mounting position for the tilting mechanism, with the load-bearing shape and mechanism space integrally formed, without adding rectifiers or damaging aerodynamic surfaces; the hollowed-out lower rear part of the vertical tail provides a rotation and tilting movement channel for the rotor disk, solving the interference problem between the rotor disk and the vertical tail structure; in hovering mode, the center of gravity of the aircraft is located between the wingtip propeller and the tail rotor assembly, with both sharing the weight of the aircraft, eliminating the need for the tail rotor assembly to separately support the weight of the aircraft, resulting in higher power margin; the three flight modes share the same propulsion system, and mode switching only requires changing the combination of angle of attack and tilt angle, simplifying the control chain; variable pitch propulsion. The propeller pitch is adjusted in conjunction with the mode. During hovering (including hovering forward), a high pitch is used to bear the weight of the entire aircraft and forward thrust. During cruise, a low pitch is used to overcome aerodynamic drag. During sprint, the pitch is gradually increased with speed, balancing hovering output and cruise economy. The lift is smoothly transferred between multiple lift sources throughout the transition from hovering to cruise. At high speed, the lift is fully supported by the wing and fuselage lifting bodies, making full use of wing efficiency. The linear motor drives the movable load to actively adjust the center of gravity of the entire aircraft, which is linked with tilt and angle of attack control. During the transition, the tail rotor assembly increases the lift output to supplement the lift reduction of the front rotor. The transition attitude is stable and no additional trim control surfaces are required. Attached Figure Description

[0026] Figure 1 is a side view of the aircraft in cruise state according to an embodiment of the present invention.

[0027] Figure 2 is a top view of the aircraft in cruise mode according to an embodiment of the present invention.

[0028] Figure 3 is a partially enlarged view of the tail coaxial dual rotor tilting mechanism of an embodiment of the present invention.

[0029] Figure 4 is a cross-sectional schematic diagram of the tailhook-servo motor encircling structure according to an embodiment of the present invention.

[0030] Figure 5 is a schematic diagram of the hollowed-out part of the vertical tail and the propeller disk channel in an embodiment of the present invention.

[0031] Figure 6 is a schematic diagram of the cruise mode attitude according to an embodiment of the present invention.

[0032] Figure 7 is a schematic diagram of the hovering mode attitude of an embodiment of the present invention.

[0033] Figure 8 is a schematic diagram of the sprint mode posture according to an embodiment of the present invention.

[0034] Figure 9 is a flowchart of the multimodal attitude control method according to an embodiment of the present invention.

[0035] In this diagram, 100 represents the aircraft; 110 the fuselage; 120 the wing; 130 the propulsion motor; 131 the variable-pitch propeller; 140 the vertical tail; 141 the hollow section (propeller disk channel); 150 the tailhook; 151 the S-curve bulge; 152 the protruding connecting part at the trailing edge of the tailhook; 160 the center of gravity; 170 the auxiliary rudder; 180 the payload (battery, etc.); 190 the linear motor; 200 the coaxial twin rotor assembly; 210 the upper rotor; 211 the upper motor; 220 the lower rotor; 221 the lower motor; 300 the tilt drive; 310 the servo; 311 the servo shaft; and 320 the connecting base. Detailed Implementation

[0036] The present invention will be further described below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0037] Example 1 (Tail-mounted coaxial dual-rotor tilting mechanism): As shown in Figures 1 and 2, the aircraft 100 includes a fuselage 110, wings 120 disposed on the fuselage 110, and a tailhook 150 and a vertical stabilizer 140 disposed at the tail of the fuselage. In this example, the wings 120 are forward-swept wings with an installation angle of 8° (or 5°) and a dihedral angle of 4°.

[0038] As shown in Figures 1 and 3, a coaxial dual-rotor assembly 200 is disposed at the tail of the aircraft 100, including an upper rotor 210 and a lower rotor 220 coaxially arranged on the vertical stabilizer 140. In this embodiment, the upper rotor 210 is a large two-bladed rotor, and the lower rotor 220 is a small four-bladed rotor, with their rotation axes coinciding. The upper rotor 210 is driven by an upper motor 211, and the lower rotor 220 is driven by a lower motor 221. Both the upper and lower motors have a round-shouldered bottle-shaped shape. The rest are labeled as shown in the figures.

[0039] As shown in Figures 3, 4, and 5, the tilt drive device 300 includes a servo motor 310, and the relevant nesting relationship is shown in the figures of this embodiment.

[0040] As shown in Figure 4, the upper trailing edge connecting part of the tailhook 150 has an S-curve shape, namely an S-curve bulge 151; following this is the protruding connecting part 152 of the tailhook's trailing edge, where a connecting seat 320 is installed. The servo motor 310 is embedded from the region of 150 into the connecting seat 320 in the region of 152, and then inserted and connected by the servo motor shaft 311. In this embodiment, the servo motor shaft is located at the center of 152, and the servo motor 310 is installed inside it. Thus, the load-bearing structure of the tailhook 150 and the installation space of the tilt drive device 300 are integrally formed. This S-shaped envelope simultaneously constitutes the rotation space and installation position of the servo motor tilt mechanism, eliminating the need for additional rectifiers and not damaging the aerodynamic surface of the fuselage.

[0041] As shown in Figure 4, a hollow portion 141 is provided at the lower rear of the vertical tail 140, forming a channel for the rotor disk of the lower rotor 220 to rotate and move with the coaxial twin rotor assembly 200. In this embodiment, the hollow portion 141 is opened on one side of the trailing edge of the vertical tail to form a notch, serving as a channel for the rotor disk of the lower rotor 220; in this embodiment, except for the auxiliary rudder 170, the vertical tail 140 is a single watertight integral component after processing to ensure structural stability.

[0042] The lower part of the vertical tail 140 is provided with an auxiliary rudder 170, which has a quadrilateral planar shape and is arranged according to the side view of the vertical tail, and is used to supplement the heading control of the aircraft 100.

[0043] The wingtip of the wing 120 is equipped with a propulsion motor 130 and a variable-pitch propulsion propeller 131 driven by it. In this embodiment, the variable-pitch propeller 131 is a three-bladed variable-pitch propeller, one on each wingtip. In this embodiment, the axis of the propulsion motor 130 is tilted upwards by 20° and outwards by 15° relative to the longitudinal axis of the fuselage, and the axis of the propulsion motor passes through the wingtip chord. The front end face of the propulsion motor cylinder is flush with or slightly beyond the leading edge of the wingtip. The pitch of the variable-pitch propeller 131 is adjusted in conjunction with the flight mode: in hover mode (including hover forward state), the variable-pitch propeller 131 shares the weight of the entire aircraft and the forward thrust, and the pitch is adjusted to a high pitch state; in cruise mode, the variable-pitch propeller 131 only overcomes aerodynamic drag, and the pitch is adjusted to a low pitch state; in sprint mode, the pitch gradually increases with the increase of flight speed.

[0044] The fuselage 110 is equipped with a center of gravity adjustment device, including a linear motor 190 and a load (battery, etc.) 180. The linear motor 190 drives the load 180 to move along the longitudinal axis of the fuselage to adjust the overall center of gravity of the aircraft. The position of the overall center of gravity of the aircraft in each flight mode is set according to the static stability margin target, as detailed in the following modal embodiments.

[0045] As shown in Figure 6, in cruise mode, the overall angle of attack is controlled at 0°, and the servo motor 310 drives the coaxial twin rotor assembly 200 back to the neutral position (tilt angle δ_p = 90°, i.e., the rotor disk axis is consistent with the fuselage reference). The lift of the entire aircraft is borne by the wing 120. In this embodiment, the cruise center of gravity is located at the front. In cruise mode, the variable-pitch propeller 131 is in a low-pitch state, only overcoming aerodynamic drag, while the propulsion motor 130 remains in a fixed installation state with a pitch of 20° and a cant of 15°.

[0046] As shown in Figure 7, in response to the hover mode command, the aircraft adopts a tail-seat attitude, controlling the entire aircraft to pitch up around the hovering center of gravity to an angle of attack of approximately 40°. Simultaneously, the servo motor 310 drives the coaxial twin rotor assembly 200 to tilt forward by 10° around the servo motor axis 311 (the tilt angle δ_p changes from 90° to 80°), making the rotor disk of the coaxial twin rotor assembly 200 tend to have the same ground angle as the variable-pitch propeller 131, but in the opposite direction. The linear motor 190 drives the load 180 to move backward, so that the center of gravity 160 is located between the variable-pitch propeller 131 on both wingtips and the coaxial twin rotor assembly 200, with the variable-pitch propeller 131 and the coaxial twin rotor assembly 200 jointly bearing the weight of the entire aircraft. In hover mode (including hover forward mode), the variable pitch propeller 131 is adjusted to a high pitch state to share the weight of the whole machine and forward thrust; in this embodiment, the propeller motor axis tilt angle to the ground is 60° and the blade tilt angle to the ground is 30° in hover mode.

[0047] As shown in Figure 8, in response to the sprint mode command, the entire aircraft is controlled to tilt down around the cruise center of gravity to an angle of attack of -5°. Simultaneously, the servo motor 310 drives the coaxial twin rotor assembly 200 to tilt backward by 5° around the servo motor axis 311 (tilt angle δ_p changes from 90° to 95°), maintaining the direction of the rotor disk's thrust to the ground and the minimum windward area of ​​the rotor disk. In this embodiment, 59 m / s is the sprint mode: within this set speed range, the wing 120 and fuselage bear the lift, the coaxial twin rotor assembly 200 performs pitch balancing and pitch control; the propulsion motor 130 has a 20° installation angle relative to the fuselage, and the propulsion motor axis tilt angle to the ground automatically becomes 15° due to the change in the overall angle of attack. The pitch of the variable-pitch propeller 131 increases due to the increased drag caused by the increased speed.

[0048] As shown in Figure 9, the multimodal attitude control method includes the following steps: S1, obtaining flight mode commands, including cruise mode, hover mode, and sprint mode; S2, in response to the hover mode command, controlling the center of gravity of the entire aircraft to shift backward between the variable-pitch propeller 131 and the coaxial dual rotor assembly 200, the entire aircraft pitches up around the hovering center of gravity to a positive angle of attack (approximately 40° in this embodiment, which can be gradually increased to exceed the stall angle of attack as the hovering forward flight requirement increases), and simultaneously controlling the servo motor 310 to drive the coaxial dual rotor assembly 200 to tilt forward (10° in this embodiment). As the angle of attack of the entire aircraft increases, the rotor disks of the variable-pitch propeller 131 and the coaxial dual rotor assembly 200 tend to be 30° relative to the ground, and finally the variable-pitch propeller 131 and the coaxial dual rotor assembly 200... Together, they provide lift for the entire aircraft; S3, in response to the sprint mode command, control the entire aircraft to tilt down around the cruise center of gravity to a negative angle of attack (-5° in this embodiment), and simultaneously control the coaxial twin rotor assembly 200 to tilt back (5° in this embodiment) to maintain the rotor disk parallel to the ground; S4, in response to the cruise mode command, control the angle of attack of the entire aircraft to the cruise trim angle of attack (the optimal cruise trim angle of attack measured in this embodiment is about 5.9°, which is a small angle of attack close to zero), and control the coaxial twin rotor assembly 200 to return to the neutral position to maintain the rotor disk parallel to the ground.

[0049] In this mode, the rotation center of hovering and cruise (sprint) modes are their respective centers of gravity. In cruise and sprint modes, the tilt angle of the coaxial twin rotor assembly 200 is linked to the overall aircraft angle of attack, with the tilt angle and angle of attack in opposite directions to maintain the thrust direction of the rotor disk perpendicular to the ground. Simultaneously, the pitch of the variable-pitch propeller 131 is adjusted according to the mode: the pitch increases when switching to hovering mode, decreases when switching to cruise mode, and gradually increases with flight speed in sprint mode. All three modes share the same propulsion system; mode switching only changes the combination of angle of attack and tilt angle. During the mode switching transition, the linear motor 190 drives the load 180 to move along the fuselage longitudinal axis to adjust the overall aircraft center of gravity: when switching to hovering mode, the load 180 moves backward, and the overall aircraft center of gravity moves backward; when switching to cruise or sprint mode, the load 180 moves forward, and the overall aircraft center of gravity moves forward. During the transition from hovering mode to cruise mode, the initial lift is shared by the variable-pitch propeller 131 and the coaxial rotor assembly 200. As the center of gravity shifts forward, the forward speed increases, and the angle of attack decreases, the wing 120 and the fuselage lifting body begin to generate lift, and the overall lift is then shared by the variable-pitch propeller 131, the wing 120, the fuselage 110 lifting body, and the coaxial rotor assembly 200. When the angle of attack of the wing and fuselage lifting body is less than the stall angle of attack and the forward speed is greater than the minimum level flight speed, the entire lift is borne by the wing 120 and the fuselage 110 lifting body, and the coaxial rotor assembly 200 provides pitch control and dynamic pitch balancing. Simultaneously with the shift in the center of gravity, the coaxial rotor assembly 200 increases its output, allowing the coaxial rotor disk to supplement the gradually decreasing lift of the propeller during the transition.

[0050] According to CFD calculations, the aircraft 100 in this embodiment exhibits soft stall characteristics of a lifting body during cruise and mode transition: the lift changes smoothly with the increase of the angle of attack, there is no steep stall point, and the attitude control margin is sufficient during the mode switching transition.

[0051] It should be noted that the specific values ​​in the above embodiments are design values ​​within the scope of this embodiment and are not intended to limit the scope of protection of this invention. Alternative embodiments of this invention include: the aircraft is a tail-seat vertical takeoff and landing aircraft, or other aircraft that requires a rotor assembly at the tail and requires adjustable tail lift direction (including runway-mounted composite layout aircraft); the tail rotor assembly is replaced with a single rotor, in which case a tailhook is not required. The aircraft features a curved, bulging shape and a hollowed-out vertical tail section, allowing the rotor to be directly mounted on the vertical tail or tailhook. The tilt drive is embedded within or enclosed in the protruding connecting part at the trailing edge of the tailhook. The servo is a plate-type servo, either inserted into the tailhook and fixed with a servo shaft, or wrapped around the tailhook and fixed with a servo shaft. The auxiliary rudder is omitted; heading control is achieved through differential left and right propellers. The tilt function is omitted; the tail rotor assembly is fixedly mounted to the rear of the fuselage, or the tilt angle is locked at a neutral position for use as a fixed tail rotor while the tilt drive structure is retained. The coaxial twin rotors are redesigned with an upper rotor diameter smaller than the lower rotor diameter. The rotor blades can be two, three, four, multiple, or concealed. The movable load is a battery or other load affecting the overall center of gravity. The vertical tail does not have a hollowed-out section; the rotor disk channel is formed by the gap between the vertical tail and the fuselage. The wing installation angle is 5°, 8°, or 0°~15°. Other values ​​within; the entire aircraft is scaled up to the level of a logistics transport aircraft. Those skilled in the art can adaptively scale the rotor diameter and number of blades, and the servo specifications according to the overall aircraft scale, and adaptively adjust the ratio of tilt angle and angle of attack according to the principle that the thrust direction of the rotor disk is perpendicular to the ground in cruise and sprint modes.

[0052] The specific embodiments of the present invention have been described above with reference to the accompanying drawings. However, these descriptions should not be construed as limiting the scope of the present invention. The scope of protection of the present invention is defined by the appended claims. Any modifications based on the claims of the present invention are within the scope of protection of the present invention.

Claims

1. A tail rotor tilting mechanism for an aircraft, the aircraft comprising a fuselage, wings disposed on the fuselage, and a vertical tail disposed at the tail of the fuselage, characterized in that, include: A tail rotor assembly, located at the tail of the aircraft, includes at least one rotor mounted on the vertical tail; A tilt drive device includes a tilt drive component, which is connected to the tail rotor assembly for driving the tail rotor assembly to tilt as a whole, thereby changing the tilt angle of the rotor disk relative to the fuselage.

2. The tail rotor tilting mechanism according to claim 1, characterized in that, The upper part of the vertical tail is provided with a tail hook, the trailing edge of the tail hook is in the shape of an S-curve, the S-curve shape forms a bulge at the trailing edge of the tail hook, and the top of the trailing edge of the bulge is provided with a protruding connecting part, the tail rotor assembly is installed on the protruding connecting part; the tilt drive component is embedded in or wrapped around the protruding connecting part, the load-bearing structure of the tail hook is integrally formed with the installation space of the tilt drive device, and the installation space includes the bulge and the protruding connecting part.

3. The tail rotor tilting mechanism according to claim 2, characterized in that, The tail rotor assembly is a coaxial dual rotor assembly, including an upper rotor and a lower rotor coaxially arranged on the tail hook. The rotation axes of the upper rotor and the lower rotor coincide, and each is driven by its own motor.

4. The tail rotor tilting mechanism according to claim 3, characterized in that, The upper rotor and the lower rotor have different diameters, with the larger one having a diameter of 20% to 200% of the aircraft's wingspan, and the smaller one having a diameter of no more than 60% of the aircraft's wingspan.

5. The tail rotor tilting mechanism according to claim 2, characterized in that, The tilting drive is a sleeve-type servo or a plate-type servo; when a sleeve-type servo is used, the tail hook passes through the sleeve of the servo; when a plate-type servo is used, the plate-type servo is inserted into the tail hook and fixed with the servo shaft, or wraps around the tail hook and is fixed with the servo shaft; the servo drives the tail hook and the tail rotor assembly mounted on the tail hook to tilt around the servo shaft as a whole.

6. The tail rotor tilting mechanism according to claim 1, characterized in that, The lower rear part of the vertical tail has a hollow section, so that the upper part of the vertical tail is a tail hook. The hollow section forms a channel for the rotor disk of the tail rotor assembly to rotate and move with the tail rotor assembly.

7. The tail rotor tilting mechanism according to claim 6, characterized in that, The lower part of the vertical tail or the lower part of the tailhook is provided with an auxiliary rudder to supplement the heading control of the aircraft.

8. The tail rotor tilting mechanism according to claim 1, characterized in that, The tilt drive unit drives the tilt angle of the tail rotor assembly to be continuously adjustable. The adjustment range of the tilt angle covers the forward tilt position, the neutral position and the backward tilt position, and is limited to satisfying the overall thrust balance in the hovering state and the minimum drag torque balance in the cruise and sprint states.

9. The tail rotor tilting mechanism according to claim 1, characterized in that, The wingtip or inner side of the wingtip is equipped with a propulsion motor and a propulsion propeller driven by it. The upward mounting angle of the axis of the propulsion motor relative to the longitudinal axis of the fuselage is 0°~60° and the outward mounting angle is 0°~40°.

10. The tail rotor tilting mechanism according to claim 9, characterized in that, In hovering mode, the center of gravity of the aircraft is located between the propulsion propeller and the tail rotor assembly located at or inside the wingtip, and the propulsion propeller and the tail rotor assembly jointly bear the weight of the aircraft.

11. The tail rotor tilting mechanism according to claim 9, characterized in that, The propulsion propeller is a variable-pitch propeller, and the pitch of the variable-pitch propeller is adjusted in conjunction with the flight mode of the aircraft: in hover mode (including hover forward state), the propulsion propeller shares the weight of the whole aircraft and the forward thrust, and the pitch is adjusted to a high pitch state; in cruise mode, the propulsion propeller only overcomes aerodynamic drag, and the pitch is adjusted to a low pitch state; in sprint mode, the pitch is gradually increased as the flight speed increases.

12. The tail rotor tilting mechanism according to claim 1, characterized in that, It also includes a center of gravity adjustment device, which includes a linear motor and a movable load located in the fuselage. The movable load is a battery or other load that affects the position of the center of gravity of the whole aircraft. The linear motor drives the movable load to move along the longitudinal axis of the fuselage. The position of the movable load on the longitudinal axis of the fuselage corresponds to the flight mode of the aircraft, so that the position of the center of gravity of the whole aircraft is set according to the static stability margin target.

13. A multi-modal attitude control method for an aircraft, wherein the aircraft employs the tail rotor tilting mechanism as described in any one of claims 9 to 12, characterized in that, Includes the following steps: Step 1: Obtain flight mode instructions, including cruise mode, hover mode, and sprint mode; Step 2: In response to the flight mode command, hover mode is activated, which can be implemented in two ways: First, the cruise mode is switched to hover mode, and the aircraft's center of gravity is shifted rearward to between the propeller and the tail rotor assembly. The aircraft pitches up around the hovering center of gravity to a positive angle of attack and gradually increases it to exceed the stall angle of attack. At the same time, the tilt drive is controlled to tilt the tail rotor assembly forward. As the aircraft's angle of attack increases, the ground angle of the propeller and the ground angle of the tail rotor assembly gradually become equal in magnitude and opposite in direction. Ultimately, the propeller and the tail rotor assembly jointly provide the lift for the entire aircraft. Second, the takeoff hover mode is activated, and the aircraft's center of gravity is shifted rearward to between the propeller and the tail rotor assembly. The aerodynamic angle of attack of the fuselage is greater than the stall angle of attack. The lift for the entire aircraft is jointly provided by the propeller and the tail rotor assembly, achieving takeoff and hovering. Step 3: In response to the flight mode command being sprint mode, control the entire aircraft to pitch down around the cruise center of gravity to a negative angle of attack, and simultaneously control the tilt drive to drive the tail rotor assembly to tilt backward, maintaining the rotor disk parallel to the ground, so as to reduce drag and maintain lift sharing and pitch control capabilities. Step 4: In response to the flight mode command to cruise mode, there are two scenarios: First, switching from hover mode to cruise mode involves shifting the aircraft's center of gravity forward from between the propeller and the tail rotor assembly. As the center of gravity shifts forward, the aircraft's angle of attack gradually decreases and approaches the stall angle of attack. Simultaneously, the thrust direction of the propeller gradually deviates towards parallel to the ground as the angle of attack decreases, and the flight speed continuously increases. When the aircraft's angle of attack returns to within the stall angle of attack and the flight speed is greater than the minimum level flight speed, the lift is taken over by the wing and fuselage lifting bodies, and the tail rotor assembly switches to providing pitch control and dynamic pitch balancing. Subsequently, the aircraft continues to accelerate into cruise mode. During the above switching process, the rotor disk of the tail rotor assembly remains parallel to the ground. Second, cruise hold involves controlling the aircraft's angle of attack to the cruise trim angle of attack, which is zero or close to zero, and controlling the tail rotor assembly to return to the neutral position, maintaining the rotor disk parallel to the ground. In cruise and sprint modes, and during the transition between hover and cruise modes, the tilt angle of the tail rotor assembly is controlled in conjunction with the overall angle of attack. The tilt angle and the angle of attack are inversely proportional to each other to maintain the thrust direction of the rotor disk perpendicular to the ground.

14. The multimodal attitude control method according to claim 13, characterized in that, The aircraft is equipped with a variable-pitch propeller at the wingtip or inside the wingtip, which serves as a propulsion propeller. The method further includes: adjusting the pitch of the variable-pitch propeller in conjunction with the flight mode, wherein when switching to hover mode, the pitch is increased because the variable-pitch propeller bears the weight of the entire aircraft; when switching to cruise mode, the pitch is decreased; and when switching to sprint mode, the pitch is gradually increased as the flight speed increases.

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