A short takeoff / vertical landing (STOVL) aircraft with a hybrid propulsion system

Abstract

This invention discloses a short takeoff / vertical landing (STOVL) aircraft with a hybrid propulsion system. It employs a fuselage frame as the main load-bearing structure, combined with an aerodynamic layout of all-moving canards, main wings, mid-section wings, and twin vertical tails. The hybrid propulsion system comprises four sets of cross-rotating motor-propellers and thrust-direction-adjustable STOVL level flight engines. The engines operate throughout the entire flight, while the motor-propellers are only engaged during STOVL and mode switching. Through linear adjustment of motor power, coordinated changes in engine thrust direction and magnitude, and speed-dependent aerodynamic lift of the wings, seamless and smooth transitions are achieved between STOVL / hovering, mode switching, high-speed level flight, and payload modes. Compared to existing technologies, this design reduces structural dead weight and control complexity, extends endurance, and balances STOVL flexibility with high-speed cruise efficiency.

Description

Technical Field

[0001] This invention belongs to the field of aircraft design technology, specifically relating to a short takeoff / vertical landing (STOVL) aircraft with a composite propulsion system. Background Technology

[0002] Currently, low-altitude aircraft are mainly divided into two categories: multi-rotor UAVs and fixed-wing UAVs. Multi-rotor UAVs can achieve vertical take-off and landing and hovering, have low requirements for take-off and landing sites, and are adaptable to complex and restricted environments, but they have drawbacks such as low flight efficiency, short endurance and range, and inability to fly at high speeds. Fixed-wing UAVs have high cruise efficiency, long range, and excellent energy utilization, but they need to rely on runways or auxiliary take-off devices and have poor site adaptability.

[0003] To integrate the advantages of both types of aircraft, compound wing configurations have become the mainstream research and development direction for short takeoff / vertical landing (STOVL) fixed-wing aircraft. Existing compound wings mostly adopt a conventional layout, adding multiple propeller power units to the wings, arms, or fuselage to achieve vertical takeoff and landing (VTOL). They are equipped with independent level flight propulsion; in level flight, the fixed wing provides the main lift, and the level flight propulsion provides thrust; in VTOL, the multiple propellers provide lift. The power of the two power systems is linearly adjusted during mode switching, resulting in simple control logic. However, this type of solution suffers from the core problem of structural dead weight: the multiple propeller power units become dead weight in level flight mode, and the level flight propulsion unit becomes dead weight in VTOL mode, severely limiting the aircraft's range, payload, and flight performance. Summary of the Invention

[0004] Purpose of the invention: To address the aforementioned existing technologies, this invention proposes a short takeoff / vertical landing (STOVL) aircraft with a composite propulsion system, overcoming the shortcomings of existing composite wing aircraft such as heavy dead weight and limited performance, and achieving reduced dead weight, increased range, seamless mode switching, and optimized flight stability.

[0005] Technical solution: A short takeoff / vertical landing (STOVL) aircraft with a composite power system, comprising: a main wing, a fuselage frame, a mid-section wing, a vertical tail, canards, a vertical takeoff and landing level flight engine, and four sets of electric motors and propellers; The four sets of motor propellers are: front upper motor propeller, front lower motor propeller, rear upper motor propeller, and rear lower motor propeller. The fuselage frame is the main load-bearing structure of the aircraft, and canards, front upper motor propellers, front lower motor propellers, mid-section wings, rear upper motor propellers, and rear lower motor propellers are arranged sequentially from nose to tail; among them, the symmetrically arranged canards are all-moving canards; The vertical takeoff and landing level flight engines are symmetrically mounted on both sides of the mid-section wing, and the two vertical tails with control surfaces are symmetrically arranged on the main wingtips on both sides of the mid-section wing.

[0006] Furthermore, the vertical takeoff and landing level flight engine is a variable thrust engine, and the engine adopts a structure with adjustable horizontal air intake and exhaust direction.

[0007] Furthermore, the thrust direction adjustment range of the vertical takeoff and landing level flight engine is 0°~95°; in the vertical takeoff and landing state, the straight-line distance from the thrust application point of the vertical takeoff and landing level flight engine to the tail end accounts for 15%~25% of the total fuselage length.

[0008] Furthermore, the diameter of the two upper propellers is D1, and the diameter of the two lower propellers is D2, with D1 / D2 = 1.2~1.5; and the propeller diameter is not greater than the lateral width of the fuselage at the propeller location.

[0009] Furthermore, the chord sweep angle and average sweep angle of the main wing are both no greater than 15°, and the aspect ratio is no less than 6.

[0010] Furthermore, the control surfaces of the main wing are arranged within 70% to 85% of the span from the wing root to the wingtip of a single main wing, and the effective area is 8% to 12% of the overall effective aerodynamic area of ​​the main wing, with a maximum deflection angle not exceeding ±25°.

[0011] Furthermore, the center of gravity of the aircraft is located in the region between the leading edge of the mid-section wing and 1 / 3 of the chord length of the mid-section wing. The distance from the front upper / front lower motor propeller to the center of gravity is L1, and the distance from the rear upper / rear lower motor propeller to the center of gravity is L2, and L2≤L1≤2L2.

[0012] Furthermore, the four sets of motor propellers are arranged in a cross-rotation configuration, with the front upper motor propeller rotating in the same direction as the rear lower motor propeller, and the front lower motor propeller rotating in the same direction as the rear upper motor propeller, while the two sets rotate in opposite directions.

[0013] Furthermore, the vertical takeoff and landing (VTOL) engine operates continuously throughout the entire process of VTOL, mode switching, and high-speed level flight, while the four sets of motor propellers only operate during VTOL and mode switching, and cease operation during high-speed level flight. When the aircraft is in the loaded mode, the rear upper motor propeller and the rear lower motor propeller stop working, and only the front upper motor propeller and the front lower motor propeller provide vertical lift.

[0014] Furthermore, during the mode switching phase, the lift of the four sets of motor propeller systems decreases linearly, the thrust direction of the vertical take-off and landing level flight engine is gradually adjusted from vertical upward to horizontal, and the thrust magnitude increases synchronously and linearly. As the flight speed increases, the aerodynamic lift generated by the main wing, mid-section wing and canard gradually increases, and the engine thrust increase rate matches the wing aerodynamic lift growth rate. Pitch attitude control during the mode switching phase is coarsely adjusted by the thrust difference between the front and rear motor propellers and finely adjusted and balanced by the deflection of the all-moving canard. During the mode switching phase, the roll attitude control gradually transitions from being dominated by the thrust difference of the symmetrically arranged vertical takeoff and landing level flight engines to being dominated by the main wing control surfaces as the flight speed increases. During the mode switching phase, the yaw attitude control gradually transitions from being dominated by the speed difference of the four sets of cross-rotating motor propellers to being dominated by the twin vertical tail control surfaces as the flight speed increases.

[0015] Beneficial effects: (1) The vertical lift and forward propulsion are separated into a composite power system. The vertical take-off and landing engine works throughout the entire flight, while the four lightweight motor propellers only work during the vertical take-off and landing and mode switching phases. This eliminates the defects of traditional tilt mechanism and single power dead weight, reduces the structural dead weight and control complexity of the aircraft, extends the flight time, and balances the flexibility of vertical take-off and landing with the efficiency of high-speed cruise.

[0016] (2) During the mode switching stage, the lift of the motor propeller system decreases linearly, the thrust of the vertical take-off and landing engine gradually increases, and the lift generated by the wing gradually increases. The lift / thrust transition slope matches the aerodynamic lift growth rate, thus achieving seamless mode switching.

[0017] (3) Through the coordinated optimization design of the composite power plant and the wing surface aerodynamic layout, the interference between the power system and the wings and fuselage is reduced, and the aerodynamic efficiency is greatly improved; the symmetrical twin tail design improves the aircraft's ability to resist crosswinds at low altitudes and improves its directional static stability, effectively improving the flight quality during the mode switching phase and enhancing the ability to take off and land accurately in confined spaces. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the overall structure of the aircraft of the present invention; Figure 2 This is a front view of the aircraft of the present invention; Figure 3 This is a side view of the aircraft of the present invention; Figure 4 This is a top view of the aircraft of the present invention.

[0019] In the diagram: 1-Front upper motor propeller; 2-Main wing; 3-Fuselage frame; 4-Mid-section wing; 5-Rear upper motor propeller; 6-Vertical tail; 7-Canard; 8-Front lower motor propeller; 9-Vertical takeoff and landing level flight engine; 10-Rear lower motor propeller. Detailed Implementation

[0020] The invention will now be further explained with reference to the accompanying drawings.

[0021] like Figures 1 to 4As shown, a short takeoff / vertical landing (STOVL) aircraft with a composite power system has a core structure including a fuselage frame 3, canards 7, a vertical takeoff and landing (VTOL) engine 9, a main wing 2, a vertical tail 6, a mid-section wing 4, and four sets of motor propellers.

[0022] The fuselage frame 3 is the main load-bearing structure of the aircraft. From the nose to the tail, the canard 7, the front upper motor propeller 1, the front lower motor propeller 8, the mid-section wing 4, the rear upper motor propeller 5, and the rear lower motor propeller 10 are arranged in sequence. On both sides of the mid-section wing 4, two vertical take-off and landing level flight engines 9, the main wing 2, and the twin vertical tails 6 are arranged symmetrically.

[0023] The twin vertical tail 6 consists of two vertical tail fins, each with control surfaces, located at the tips of the main wing 2. The aerodynamic focus of the twin vertical tails is located behind the aircraft's center of gravity, ensuring directional and attitude stability.

[0024] The vertical takeoff and landing (VTOL) level flight engine 9 is a thrust-direction variable engine, meaning it uses a horizontal air intake and its exhaust direction is adjustable to achieve thrust direction adjustment. There is an even number of VTOL level flight engines 9, symmetrically mounted on both sides of the mid-section wing 4. The specific engine type of the VTOL level flight engine 9 can be turbine-powered or ducted-powered.

[0025] The canard 7 located at the front of the fuselage is a fully movable canard that can deflect synchronously, used for pitch attitude trim during mode switching and high-speed level flight.

[0026] The front upper motor propeller 1 and the front lower motor propeller 8 are positioned between the canard 7 and the mid-section wing 4, while the rear upper motor propeller 5 and the rear lower motor propeller 10 are positioned at the very end of the fuselage. All four sets of motor propellers are used to generate upward lift and for pitch attitude control during vertical takeoff and landing and mode switching. Whether all four motor propellers are operating or partially operating, they are configured in a cross-rotation configuration: when all are operating, the front upper and rear lower motors rotate in the same direction, and the front lower and rear upper motors rotate in the same direction, with the two sets of motors rotating in opposite directions; when partially operating, the operating motors maintain counter-rotation to counteract the torque, while the non-operating motors do not rotate.

[0027] The aircraft uses the total lift required for vertical takeoff and landing as the design input, and combines the rated thrust, efficiency and drive power distribution of a single motor propeller to determine the propeller diameter. At the same time, the propeller diameter is not greater than the lateral width of the fuselage at the propeller location. Under the premise of ensuring sufficient lift and aerodynamic efficiency, the aerodynamic interference between the propeller and the fuselage is minimized, thereby improving the lift efficiency and flight stability of the vertical takeoff and landing mode.

[0028] In addition, to accommodate both level flight and vertical takeoff and landing modes, the aircraft is subject to the following constraints: 1. In unloaded mode, the aircraft's center of gravity is located within the area between the leading edge (nose) of the mid-wing 4 and one-third of the mid-wing chord length, and the center of gravity position is fixed. When the aircraft is in loaded mode, the center of gravity shifts forward to in front of the center of gravity in unloaded mode, but does not exceed the range of the midpoint between the longitudinal lines connecting the front and rear motors. By limiting the forward shift range of the center of gravity, it is ensured that the aircraft can achieve pitch trim using only the front motor and canard 7 when in loaded mode.

[0029] 2. The distance from the front upper / front lower motor propeller to the center of gravity is denoted as L1, and the distance from the rear upper / rear lower motor propeller to the center of gravity is denoted as L2, satisfying L2≤L1≤2L2.

[0030] 3. To reduce the change in aerodynamic center of gravity of the main wing 2 due to the increase in the aircraft's level flight speed, the chord sweep angle and average sweep angle of the main wing 2 are not greater than 15°, and the aspect ratio is not less than 6, so as to reduce the aerodynamic center of gravity shift during high-speed level flight.

[0031] 4. To reduce the impact of ground effect during vertical takeoff and landing and lower the probability of foreign object entanglement, the diameter of the propellers on the upper side of both units is D1, and the diameter of the propellers on the lower side of both units is D2, with D1 / D2 = 1.2~1.5.

[0032] 5. The thrust direction adjustment range of engine 9 in vertical takeoff and landing level flight is 0°~95°; in vertical takeoff and landing state, the straight distance from the thrust application point of engine 9 to the tail end accounts for 15%~25% of the total fuselage length.

[0033] 6. The effective area of ​​the main wing control surface is 8% to 12% of the overall effective aerodynamic area of ​​the main wing 2; the maximum deflection angle of the main wing control surface does not exceed ±25°; the main wing control surface is arranged within the spanwise range of 70% to 85% from the root to the tip of the main wing on one side to ensure roll control efficiency.

[0034] The pitch, roll, and yaw attitude control methods for the aircraft with the above structure are as follows: (a) Attitude control methods for vertical takeoff and landing / hovering modes: Vertical takeoff and landing (VTOL) and hovering are achieved through four sets of electric motors and propellers and symmetrically arranged VTOL level flight engines 9. Specifically, the four sets of electric motors and propellers provide the main vertical lift, while the VTOL level flight engines 9 provide auxiliary lift and attitude control with upward vector thrust.

[0035] 1. The aircraft's pitch attitude control method is achieved through the thrust difference between the front and rear propeller sets. Specifically, if the thrust of the front propeller set is greater than that of the rear propeller set, the nose rises; if the thrust of the rear propeller set is greater than that of the front propeller set, the nose falls. The all-moving canard 7 maintains only the initial attitude and does not actively yaw, providing passive attitude stabilization.

[0036] 2. The aircraft's roll attitude control method is as follows: At zero forward speed, the main wing control surfaces have no aerodynamic control efficiency, and the roll attitude is adjusted by the thrust difference between the symmetrically arranged vertical takeoff and landing level flight engines 9. During this stage, the main wing control surfaces remain in a neutral position and do not participate in roll control.

[0037] 3. The control method for the aircraft's yaw attitude is as follows: net reverse torque is generated by adjusting the speed difference of the propellers of the four sets of cross-rotating motors to achieve yaw adjustment. At this time, the twin vertical tail control surfaces only provide passive heading stability.

[0038] For example, if the machine head needs to turn left, slightly increase the speed of the front upper and rear lower motors, and decrease the speed of the front lower and rear upper motors, thereby generating a net counter torque to the left. If the machine head needs to turn right, slightly increase the speed of the front lower and rear upper motors, and decrease the speed of the front upper and rear lower motors, thereby generating a net counter torque to the right.

[0039] (ii) Attitude control methods during the mode switching phase: The mode switching phase is a two-way transition process between vertical takeoff and landing / hovering mode and high-speed level flight mode. The core is to achieve a smooth connection between lift and thrust. The specific working method is as follows: through the coordinated work of four sets of motor propellers, symmetrically arranged vertical takeoff and landing level flight engines 9, and various wing surfaces, the switching of power mode and lift source is gradually completed.

[0040] From vertical takeoff and landing / hovering mode to high-speed level flight mode (positive transition): the power of the four sets of motor propellers decreases linearly, and the vertical lift they provide gradually decreases in sync; at the same time, the thrust direction of the vertical takeoff and landing level flight engine 9 is gradually adjusted from vertically upward to horizontally forward, and the thrust magnitude increases linearly in sync, gradually taking over the forward propulsion function of the aircraft; as the flight speed increases, the aerodynamic lift of the main wing, mid-section wing and canard gradually increases, gradually replacing the vertical lift provided by the motor propellers, and finally completing a seamless transition from vertical lift dominance to aerodynamic lift dominance, and from motor-assisted to engine-dominated propulsion.

[0041] Switching from high-speed level flight mode to vertical takeoff and landing / hovering mode (reverse transition): In contrast to the forward transition logic, the power of the four sets of motor propellers increases linearly, gradually restoring the vertical lift supply; the thrust direction of the vertical takeoff and landing level flight engine 9 is gradually adjusted from horizontal forward to vertical upward, and the thrust magnitude decreases linearly in sync; the aerodynamic lift of the main wing, mid-section wing and canard gradually weakens, and the vertical lift provided by the motor propellers gradually becomes dominant, finally completing a smooth switch from aerodynamic lift dominance to vertical lift dominance, and from engine propulsion to motor assistance, ensuring that the reverse transition is free of attitude fluctuations and power interruptions.

[0042] 1. The aircraft's pitch attitude control method is achieved through the thrust difference between the front and rear propeller motors, in conjunction with the deflection angle of the all-moving canard 7. Among them, the thrust difference is responsible for coarse pitch attitude adjustment, quickly adapting to the attitude requirements of engine thrust vector steering and wing lift increase; the all-moving canard is responsible for fine pitch attitude adjustment and trim, eliminating attitude oscillations and ensuring a smooth transition.

[0043] For example, during the transition from vertical takeoff and landing to level flight, the thrust of the rear motor propeller is increased while the thrust of the front motor propeller is decreased, pushing the tail of the aircraft upward and the nose downward. The canard 7 deflects downward in sync, further stabilizing the nose-down attitude and smoothly transitioning into the transition. This process, through the cooperation of thrust difference and canard 7, completes pitch control.

[0044] 2. The aircraft's roll attitude control method is as follows: it is achieved through the thrust difference between the symmetrically arranged vertical takeoff and landing level flight engines 9 and the coordinated deflection of the main wing control surfaces. As the flight speed increases, roll control gradually transitions from being dominated by the engine thrust difference to being dominated by the main wing control surfaces.

[0045] Specifically, in the low-speed phase (initial transition): the forward flight speed is low, the control surface aerodynamics are insufficient, the engine thrust is poor and the control surface provides slight assistance, and basic roll adjustment is completed; for example: increase the thrust of the right engine, decrease the thrust of the left engine, and tilt the fuselage to the right; at the same time, deflect the control surface of the left main wing and deflect the control surface of the right main wing downward, and enhance the roll to the right through aerodynamics.

[0046] Mid-speed range (mid-transition): Forward flight speed increases, aerodynamic efficiency of the main wing control surfaces improves, left and right control surfaces deflect in opposite directions, and roll torque is output in coordination with engine thrust difference.

[0047] High-speed phase (late transition period): The engine thrust difference gradually decreases to zero, and roll control is mainly completed by the main wing control surfaces, in preparation for high-speed level flight.

[0048] The motor propeller power decreases linearly, the thrust of the vertical takeoff and landing level flight engine 9 gradually shifts to the horizontal, the canard 7 adjusts the pitch attitude, and the main wing 2 control surfaces gradually take over the roll control.

[0049] 3. The control method for the yaw attitude of the aircraft is: the yaw control is completed by the speed difference of the propellers of the four sets of cross-rotating motors and the differential deflection of the twin vertical tail control surfaces.

[0050] Low speed range: The yaw torque is still mainly provided by the difference in motor speed, with minor assistance from the twin vertical tail control surfaces.

[0051] Mid-speed range: As forward speed increases, the aerodynamic efficiency of the twin vertical tails increases, and the left and right vertical tail control surfaces deflect differentially in opposite directions, generating aerodynamic yaw torque, which is superimposed on the motor torque.

[0052] Late transition phase: The motor yaw torque gradually decreases, while the control surface aerodynamic torque gradually increases, preparing for high-speed level flight pure control surface control.

[0053] (III) Attitude control methods in high-speed level flight mode: In high-speed level flight mode, the four sets of motor propellers stop working and no longer provide vertical lift; the vertical take-off and landing level flight engine 9 maintains horizontal forward thrust, providing continuous forward power for the aircraft; the main wing and the mid-section wing 4 generate the main aerodynamic lift under the action of flight speed, balancing the aircraft's gravity; the canard 7 is used to maintain flight attitude stability, so that the aircraft can maintain a stable high-speed level flight state.

[0054] 1. The aircraft pitch attitude control method is as follows: the motor and propeller are completely stopped, and the all-moving canard 7 actively deflects to achieve trim and attitude adjustment.

[0055] 2. The aircraft's roll attitude control method is: pure aerodynamic control is achieved by deflecting the main wing control surfaces.

[0056] 3. The control method for the yaw attitude of the aircraft is as follows: the motor and propeller stop working, and the yaw angle is adjusted and the heading is stabilized by differential deflection of the twin vertical tail control surfaces at the tip of the main wing 2.

[0057] (iv) Attitude control methods for mounted modes: After being loaded with a heavy load, the aircraft's center of gravity shifts forward to between the original center of gravity and the midpoint of the line connecting the front and rear motors. The lever arm between the rear dual motors and the center of gravity shortens drastically, resulting in a very small pitch control torque under the same thrust, significantly reducing control efficiency and making it unable to effectively participate in pitch trim and attitude adjustment. At the same time, the operation of the rear motors would cause energy waste and control interference, so the rear dual motors do not rotate. In this mode, only the propellers of the two front motors provide vertical lift; the symmetrically arranged vertical takeoff and landing level flight engines 9 provide corresponding thrust according to the flight conditions, and the main wing 2, mid-section wing 4, and canard 7 generate aerodynamic lift with flight speed, jointly balancing the weight of the aircraft and the load, achieving stable flight under load.

[0058] 1. The aircraft's pitch attitude control method is as follows: trim and adjustment are achieved by the thrust of the front upper / front lower motor propellers combined with the deflection of the all-moving canards. Specifically, the front upper / front lower motor propellers output controllable thrust to provide the basic pitch torque; the all-moving canards deflect synchronously to correct the pitch deviation caused by the forward shift of the center of gravity; the two work together to ensure pitch stability during high-speed level flight under heavy loads and avoid attitude loss of control.

[0059] 2. The aircraft's roll attitude control method is as follows: the shutdown of the rear motors does not affect roll control; it is still controlled by the thrust difference of the VTOL level flight engine 9 and the main wing control surfaces. Specifically, for low-speed loaded flight: roll is mainly controlled by the thrust difference between the left and right sides of the engines; for high-speed loaded flight: roll is mainly controlled by the differential deflection of the main wing control surfaces.

[0060] 3. The control method for the aircraft's yaw attitude is as follows: relying solely on the fine adjustment of the speed difference between the front upper and front lower counter-rotating motors to generate net counter-torque, and cooperating with the twin vertical tail control surfaces to complete the yaw adjustment. At this time, the rear motor does not participate.

[0061] Specifically, the front upper and front lower motors rotate in opposite directions, generating net counter-torque through a small speed difference to provide basic yaw moment; the twin vertical tail control surfaces deflect differentially according to the current flight speed, aerodynamically assisting in course correction to meet yaw control requirements under load. The rear motor is close to the center of gravity and has low yaw control efficiency, but it does not affect the heading control accuracy in the loaded mode after shutdown.

[0062] In this embodiment, the fuselage frame 3, main wing 2, mid-section wing 4 and twin vertical tails 6 are all made of carbon fiber and composite materials, and the overall structure is lightweight and has the strength to meet flight requirements. The aircraft has an overall length of 880mm, a wingspan of 1500mm, a chord sweep angle of 10° for the main wing 2, and an aspect ratio of 7. The diameters of the two upper propellers are D1=330.4mm and D2=254mm, with a ratio of D1 / D2=1.32. The distance from the front upper / front lower motor propeller to the center of gravity is L1=276mm, and the distance from the rear upper / rear lower motor propeller to the center of gravity is L2=266mm. The thrust application point of the VTOL engine 9 in vertical takeoff and landing mode is 20% of the fuselage length from the tail. The effective area of ​​the main wing control surfaces is 10% of the overall effective aerodynamic area of ​​the main wing 2. The maximum deflection angle of the main wing control surfaces is ±20°. The motor power is 600~800W. The engine thrust is 15N~25N. The takeoff weight is 5kg. The aircraft's center of gravity is located between the leading edge of the mid-section wing 4 and one-third of the chord length of the mid-section wing 4. To verify the improvements in structural dead weight, endurance, and flight stability of the short takeoff / vertical landing (STOVL) aircraft configuration with a composite propulsion system described in this embodiment, a conventional composite wing configuration of the same class was selected as a comparison object for comparative analysis and simulation verification under unified design specifications and mission profiles. The comparison configuration adopts a typical layout of "separation of multi-propeller vertical takeoff and landing system and independent level flight propulsion system," and its structural dimensions, maximum takeoff weight, and energy system parameters are consistent with those of this embodiment. Evaluation was conducted under standard atmospheric and windless conditions, following a unified mission profile of "vertical takeoff—30s hover—mode switching—level flight cruise—reverse transition—vertical landing." The results show that under the two typical operating conditions of vertical takeoff and landing and level flight, the structural dead weight ratio of the comparison configuration is 38.5% and 34.2%, respectively, while that of this embodiment is reduced to 29.8% and 26.7%, respectively. The average dead weight ratio decreased from 36.4% to 28.3%, an overall reduction of approximately 22%. This improvement mainly stems from the coordinated operation of the vertical takeoff and landing level flight engine with adjustable thrust direction and the electric motor propeller, enabling the power system to participate in effective work in multi-modal processes and avoiding the problem of the power system becoming redundant loads for each other in the traditional configuration.

[0063] Regarding endurance, by establishing a power demand model and combining it with a unified energy system for mission energy consumption calculation, the power consumption of the comparative configuration during hovering and cruise phases is 4.8 kW and 2.6 kW, respectively, while in this embodiment it is reduced to 4.2 kW and 2.1 kW, respectively. Under the same mission profile, the total energy consumption is reduced from 1.00 (normalized) to 0.73, a reduction of approximately 27%, corresponding to an increase in endurance from 60 min to 76 min, an improvement of approximately 26.7%. This improvement stems from the induced power reduction due to the reduction in structural dead weight, the energy optimization strategy of shutting down the motors and propellers during level flight and only keeping the high-efficiency propulsion system in operation, and the continuous linear distribution of power output during mode switching, which reduces energy loss.

[0064] Regarding flight stability, numerical simulations were used to calculate the directional static stability derivative. The results showed that the directional static stability derivative of the comparative configuration was 0.072, while that of this embodiment was increased to 0.095, an improvement of approximately 31.9%. This improvement is mainly attributed to the larger lever arm resulting from the twin vertical tails being positioned at the wingtips of the main engine, and the reduced aerodynamic interference due to the vertical tails being farther from the propeller wake region. Simultaneously, the symmetrical layout of the entire aircraft and reasonable center of gravity constraints improved lateral aerodynamic center stability. Semi-physical flight tests further demonstrated that during mode switching, the attitude fluctuation amplitude of this embodiment was reduced from ±7° to ±3°, and the directional stability establishment time was shortened by approximately 28%, verifying its stability advantages. Furthermore, in terms of control characteristics, this embodiment, through the coordinated design of the thrust vectoring engine, motor-propeller, and aerodynamic control surfaces, reduced the number of control input variables from 10 to 7, and transformed the segmented control method into a continuous linear control relationship, reducing the overall control complexity by approximately 32%.

[0065] In summary, under the same conditions, this embodiment achieves a structural dead weight reduction of approximately 22%, an endurance increase of approximately 26.7%, a control complexity reduction of over 30%, and a directional static stability improvement of over 30%, significantly enhancing the overall performance and engineering practicality of the aircraft.

[0066] Furthermore, based on this aircraft, by replacing some power components and adding some compartments, it is possible to switch between power sources such as jet engines, piston engines, and electric engines, thus enabling manned and unmanned configuration conversion.

[0067] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A short takeoff / vertical landing (STOVL) aircraft with a composite propulsion system, characterized in that, include: Includes main wing (2), fuselage frame (3), mid-section wing (4), vertical tail (6), canard (7), vertical takeoff and landing level flight engine (9), and four sets of electric motor propellers; The four sets of motor propellers are front upper motor propeller (1), front lower motor propeller (8), rear upper motor propeller (5), and rear lower motor propeller (10). The fuselage frame (3) is the main load-bearing structure of the aircraft. From the nose to the tail, the canard (7), the front upper motor propeller (1), the front lower motor propeller (8), the mid-section wing (4), the rear upper motor propeller (5), and the rear lower motor propeller (10) are arranged in sequence. Among them, the symmetrically arranged canard (7) is a fully movable canard. The vertical takeoff and landing level flight engine (9) is symmetrically mounted on both sides of the mid-section wing (4), and the two vertical tails (6) with control surfaces are symmetrically arranged on the tips of the main wing (2) on both sides of the mid-section wing (4).

2. The aircraft according to claim 1, characterized in that, The vertical takeoff and landing level flight engine (9) is a thrust direction variable engine, and the engine adopts a structure with adjustable horizontal air intake and exhaust direction.

3. The aircraft according to claim 2, characterized in that, The thrust direction adjustment range of the vertical takeoff and landing level flight engine (9) is 0°~95°; in the vertical takeoff and landing state, the straight distance from the thrust application point of the vertical takeoff and landing level flight engine (9) to the tail end accounts for 15%~25% of the total fuselage length.

4. The aircraft according to claim 1, characterized in that, The diameter of the two propellers on the upper side is D1, and the diameter of the two propellers on the lower side is D2, where D1 / D2 = 1.2~1.5; and the diameter of the propellers is not greater than the transverse width of the fuselage at the propeller location.

5. The aircraft according to claim 1, characterized in that, The chord sweep angle and average sweep angle of the main wing (2) are both no greater than 15°, and the aspect ratio is no less than 6.

6. The aircraft according to claim 1, characterized in that, The control surfaces of the main wing (2) are arranged in the span of 70% to 85% from the root to the tip of the main wing on one side, and the effective area is 8% to 12% of the overall effective aerodynamic area of ​​the main wing (2), with a maximum deflection angle not exceeding ±25°.

7. The aircraft according to claim 1, characterized in that, The center of gravity of the aircraft is located in the area between the leading edge of the mid-section wing (4) and 1 / 3 of the chord length of the mid-section wing (4). The distance from the front upper / front lower motor propeller to the center of gravity is L1, and the distance from the rear upper / rear lower motor propeller to the center of gravity is L2, and L2≤L1≤2L2.

8. The aircraft according to claim 1, characterized in that, The four sets of motor propellers are arranged in a cross-rotation configuration, in which the front upper motor propeller (1) and the rear lower motor propeller (10) rotate in the same direction, and the front lower motor propeller (8) and the rear upper motor propeller (5) rotate in the same direction, with the two sets rotating in opposite directions.

9. The aircraft according to claim 1, characterized in that, The vertical takeoff and landing level flight engine (9) works continuously throughout the entire phase of vertical takeoff and landing, mode switching and high-speed level flight, while the four sets of motor propellers only work in the vertical takeoff and landing mode and mode switching phases, and stop operating in the high-speed level flight mode. When the aircraft is in the loaded mode, the rear upper motor propeller (5) and the rear lower motor propeller (10) stop working, and only the front upper motor propeller (1) and the front lower motor propeller (8) provide vertical lift.

10. The aircraft according to claim 1, characterized in that, During the mode switching phase, the lift of the four sets of motor propeller systems decreases linearly, and the thrust direction of the vertical take-off and landing level flight engine (9) is gradually adjusted from vertical upward to horizontal, and the thrust magnitude increases synchronously and linearly. As the flight speed increases, the aerodynamic lift generated by the main wing, mid-section wing and canard gradually increases, and the engine thrust increase rate matches the wing aerodynamic lift growth rate. The pitch attitude control during the mode switching phase is coarsely adjusted by the thrust difference between the front and rear motor propellers, and finely adjusted and balanced by the deflection of the all-moving canard (7). During the mode switching phase, the roll attitude control gradually transitions from being dominated by the thrust difference of the symmetrically arranged vertical take-off and landing level flight engines (9) to being dominated by the control surfaces of the main wing (2) as the flight speed increases. During the mode switching phase, the yaw attitude control gradually transitions from being dominated by the speed difference of the four sets of cross-rotating motor propellers to being dominated by the double vertical tail (6) control surfaces as the flight speed increases.

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