High-altitude ultra-long-endurance high aspect ratio integrated unmanned flight platform driven by microwave energy

Abstract

The present invention proposes a microwave energy driven high altitude ultra-long flight time large aspect ratio integrated unmanned aerial platform, which adopts a large aspect ratio wing-body fusion layout; the rectifying receiving antenna as the source of the whole machine power device is integrated with the whole machine aerodynamic and structural design; the wing-body fusion part airfoil of the rectifying receiving antenna arrangement area adopts an airfoil with a flat lower surface and a lift-to-drag ratio that meets the requirements, and adopts a rear loading form; the unmanned aerial platform tail support is rear-mounted with an inverted V-tail to arrange the corresponding rudder surface, and the whole machine is balanced through the V-tail; the electric propeller is located above the rear of the fuselage symmetry plane as a power device. Under the premise of ensuring the energy receiving efficiency, the present invention uses an airborne integrated rectifying receiving antenna to receive radio frequency energy and convert it into direct current electricity, drives the unmanned platform to fly and perform tasks, eliminates the problems of aerodynamic structure and energy reception caused by the outdoor wire, improves the efficiency of the entire platform, and theoretically can truly achieve unlimited flight time.

Description

Technical Field

[0001] The present invention relates to the technical field of unmanned flight platforms, and particularly to an integrated unmanned flight platform with large aspect ratio and ultra-long endurance at high altitude driven by microwave energy. Background Art

[0002] In tasks such as continuous and uninterrupted monitoring and reconnaissance of a certain area, ground information monitoring and signal relaying during emergency rescue, high-altitude long-endurance unmanned flight platforms are the key implementation solutions.

[0003] Currently, the mainstream high-altitude long-endurance unmanned flight platforms all use solar energy as the main power source for the flight platform, including stratospheric solar airships and high-altitude long-endurance solar drones. Although theoretically having "unlimited endurance", due to the influence of weather, latitude, and day-night illumination, solar aircraft need to charge with solar energy during the day and reduce altitude at night to use batteries to maintain power flight and improve flight efficiency. The conversion efficiency of the battery panels receiving solar energy is at most no more than 30%. When the charging is affected too much, continuous flight cannot be maintained. In addition, since batteries are needed to maintain flight when sunlight is weak, the battery weight almost accounts for more than 40% of the total weight of the whole aircraft, seriously affecting the carrying capacity of other payloads. Therefore, the airframe structure weight of solar drones is very light. In order to lay as many battery panels as possible, their aspect ratio is usually very large, bringing serious aerodynamic elasticity problems and control problems. It can be said that although flight can be achieved using unlimited solar energy, poor payload capacity, high control difficulty, large influence of environmental factors, and low energy conversion efficiency are the key problems restricting the development of such aircraft.

[0004] To achieve ultra-long endurance and stable flight of unmanned aerial vehicles, using microwaves as the energy source for the power device of unmanned aerial vehicles has become a new energy supply method for unmanned platforms. There are relatively few current microwave energy-powered unmanned platforms. Except for some early airships and unmanned aerial vehicles, not many examples have been seen. For example, in 1980, Canada carried out a research named SHARP (Stationary High Altitude Relay Program). In this research, a 4.1 kg unmanned aerial vehicle was designed, and this unmanned aerial vehicle flew continuously for 20 minutes under the drive of a 10 kw ground transmitting antenna, verifying the feasibility of this energy drive method. However, the main problems existing in these platforms currently are: because the antenna for receiving microwave energy requires the receiving surface to be in a circular planar shape, the current platform solutions all directly install this receiving antenna on the body of the unmanned platform in the form of a component, and there is no integrated design between the antenna and the unmanned aerial vehicle. Although this method is simple, it brings various problems in terms of aerodynamics, structure, and energy reception, with extremely poor performance of the flight platform and low efficiency of the entire system.

[0005] Aerodynamic aspect: The receiving antenna is mostly hung under the belly of the unmanned platform in a hoisting manner, which causes great damage to the overall aerodynamic characteristics. This is mainly reflected in a sharp increase in resistance, and the handling and stability characteristics of the whole aircraft will also change significantly. For high-altitude long-endurance UAVs powered by electric energy to drive propellers, this is a great interference, seriously deteriorating the final platform performance.

[0006] Structural aspect: Due to the existence of the rectifying circuit board, the receiving antenna has a relatively large density, so the total weight is relatively large. Especially on large unmanned flight platforms with high energy requirements, the weight brought by the large-area rectifying structure antenna is very likely to offset the benefits of this power supply form. In addition, due to the large size of the antenna, the aeroelastic and vibration effects during flight are obvious.

[0007] Energy reception aspect: After the rectifying circuit is separately hoisted on the unmanned platform, it is loaded during flight, which is prone to structural deformation, resulting in displacement and phase deviation of the rectifying receiving unit, affecting the beam collection efficiency. Summary of the Invention

[0008] To solve the problems existing in the prior art and achieve stable endurance of a high-altitude solar unmanned flight platform operating at an altitude of 18 km, the present invention proposes a microwave energy-driven high-altitude ultra-long-endurance large aspect ratio integrated unmanned flight platform. On the premise of ensuring the energy reception efficiency, by radiating microwave energy on the ground, using an airborne integrated rectifying receiving antenna to receive radio frequency energy and convert it into direct current electrical energy, driving the unmanned platform to fly and perform tasks, eliminating the problems in terms of aerodynamic structure and energy reception brought by the exposed antenna, improving the efficiency of the entire platform, and theoretically being able to truly achieve infinite endurance flight.

[0009] The technical solution of the present invention is as follows:

[0010] The described microwave energy-driven high-altitude ultra-long-endurance large aspect ratio integrated unmanned flight platform adopts a large aspect ratio wing-body fusion layout, and winglets are added at the wingtips; the rectifying receiving antenna as the power device source of the whole aircraft is integrated with the aerodynamics and structure of the whole aircraft, ensuring the aerodynamic characteristics of the whole aircraft in terms of appearance; the integrated rectifying receiving antenna is located at the lower part of the fuselage, and the entire receiving area presents a planar shape to ensure the efficiency of the rectifying receiving unit; the airfoil of the wing-body fusion part in the area where the rectifying receiving antenna is arranged adopts an airfoil with a flat lower surface and a lift-to-drag ratio meeting the requirements, and a rear-loading form is adopted; the tail support of the unmanned flight platform is rear-mounted with an inverted V-tail to arrange the corresponding control surfaces, and the whole aircraft is trimmed through the V-tail; the electric propeller is used as the power device and is located above the rear of the fuselage symmetry plane.

[0011] Further, it adopts a large aspect ratio wing-body fusion layout, the total wingspan of the whole wing is 30 m, the aspect ratio is 20, and the wing area is 45 m 2 , and the area of the rectifying antenna is 15.918 m2 ; There is no torsion along the span of the whole aircraft;

[0012] The rectifying receiving antenna is located at the wing-body fusion part. The airfoil of the wing-body fusion section is a high-lift-drag ratio airfoil with a lift-drag ratio meeting the set requirements. The maximum relative thickness is 12.0044%, the position of the maximum thickness is at 30% of the chord length, the lower surface is adapted to the antenna requirements, and there is a straight section with a corresponding length;

[0013] The rectifying receiving antenna is in a circular plane with a diameter of 4.502 m. The center of the circle is 3.015 m away from the nose position. The integrated rectifying antenna is composed of a skin, upper and lower layers of foam, and rectifying antenna components encapsulated.

[0014] 3. The high-altitude ultra-long-endurance large aspect ratio integrated unmanned flight platform driven by microwave energy according to claim 1 or 2, characterized in that:

[0015] The length of the tail strut of the unmanned flight platform is 6 m. The tail strut is rear-mounted with an inverted V-tail to arrange corresponding control surfaces. The area of each V-tail is 1.8375 m 2 , 40% of the area of its trailing edge is the control surface, the span is 2.5 m, and the chord length is 0.3 m, which is used for longitudinal and lateral attitude control; The ailerons are located on the outer side of the wing, the span is 3.5 m, and the chord length is 0.15 m, and they participate in lateral attitude control together with the V-tail.

[0016] Furthermore, winglets are added at the wingtips, and the airfoil of the winglets is the NACA0012 airfoil.

[0017] Furthermore, a two-blade electric tail pusher is used as the power device. The blade uses the S1223 blade element airfoil, the twist angle from the blade root to the blade tip is 60 degrees, and the blade diameter is 2.5 m.

[0018] Furthermore, a nose-gear type is adopted. Among them, due to the influence of the antenna on the lower surface, the nose gear is retracted upward into the upper surface cabin of the fuselage, and the main gear is retracted forward into the landing gear cabin on the lower surface of the flight platform.

[0019] Beneficial effects

[0020] Existing microwave energy transmission unmanned flight platforms all adopt the method of installing microwave receiving antenna components behind the airframe platform to form a microwave-powered flight platform. Due to the low overall efficiency of converting from the ground transmitting end to direct current during ultra-long-distance transmission flight, the weight and resistance brought by installing the antenna greatly limit the applicability and expandability of this scheme.

[0021] Compared with existing platforms, the present invention comprehensively considers the receiving rectenna as a design constraint for the entire platform, forming a fusion integrated design scheme. The rectenna reception is integrally embedded in the airframe as part of the platform's outer shape, and is highly consistent with the outer surface of the airframe in terms of structural design. This design method can significantly improve the aerodynamic characteristics of the unmanned flight platform driven by microwave energy while ensuring the efficiency and electrical performance of the receiving rectenna, basically eliminating the resistance effect problem caused by adding the antenna, and at the same time achieving no significant increase in the structural weight of the entire platform, improving the efficiency of the entire aircraft. The design concept and platform outer shape scheme of the present invention can better meet the requirements of high-altitude (≥18 km) and long-endurance unmanned aerial vehicles.

[0022] Additional aspects and advantages of the present invention will be given in part in the following description, will become apparent in part from the following description, or will be learned through the practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The above and / or additional aspects and advantages of the present invention will become apparent and be readily understood from the description of the embodiments in conjunction with the following drawings, wherein:

[0024] Figure 1 : Global view of a high aspect ratio integrated unmanned flight platform;

[0025] Figure 2 : Three-view drawing of a high aspect ratio integrated unmanned flight platform;

[0026] Figure 3 : View of the receiving antenna position and antenna view of a high aspect ratio integrated unmanned flight platform;

[0027] Figure 4 : Schematic diagram of the structure of the integrated rectenna of a high aspect ratio integrated unmanned flight platform;

[0028] Wherein: reference numeral 1 is a winglet, reference numeral 2 is an outer wing section, reference numeral 3 is a nose landing gear, reference numeral 4 is an electric propeller propulsion system, reference numeral 5 is a tail boom, reference numeral 6 is an inverted V-tail, reference numeral 7 is an inner wing section (wing-body fusion section), reference numeral 8 is an aileron, reference numeral 9 is a V-tail rudder surface, reference numeral 10 is an integrated receiving rectenna, and reference numeral 11 is a fusion connection structure between the antenna and the platform;

[0029] Figure 5 : Airfoil shape diagram of the wing of the integrated rectenna receiving area;

[0030] Figure 6 : Aerodynamic characteristics at H = 18 km; (a) lift coefficient, (b) drag coefficient, (c) lift-drag ratio, (d) pitching moment coefficient;

[0031] Figure 7: Flow field at H = 18 km; (a) Angle of attack of 2 degrees, (b) Angle of attack of 3 degrees, (c) Angle of attack of 6 degrees, (d) Angle of attack of 10 degrees, (e) Angle of attack of 12 degrees;

[0032] Figure 8 : Reflection coefficient of the receiving antenna;

[0033] Figure 9 : Axial ratio of the receiving antenna;

[0034] Figure 10 : 3D radiation pattern of the receiving antenna;

[0035] Figure 11 : Radiation pattern of the receiving antenna in the XOZ plane;

[0036] Figure 12 : Radiation pattern of the receiving antenna in the YOZ plane. Specific implementation manner

[0037] In order to achieve high-altitude unmanned flight with extremely long endurance, the present invention proposes an integrated high-altitude long-endurance unmanned platform driven by microwave energy transmission, as Figure 1 shown. This platform adopts a layout of a large aspect ratio wing-body fusion, and winglets are added at the wingtips to further reduce the induced drag. As the power device source of the whole aircraft, the rectifying receiving antenna is integrally designed with the aerodynamics and structure of the whole aircraft, ensuring the aerodynamic characteristics of the whole aircraft in terms of appearance. And because the rectifying receiving antenna adopts a composite design form similar to the skin and foam of the airframe surface structure, the two can achieve a high degree of unity and integration in structure and have similar mechanical characteristics. Therefore, their load-bearing characteristics can be considered as a whole, effectively avoiding the drawback of poor structural weight characteristics after the installation of an external rectifying antenna.

[0038] During actual design and processing, the overall platform design of the rectifying antenna is considered from the perspective of overall integration, fully considering the transferability and relevance of various overall, aerodynamic, structural and other parameters. And when entering the detailed design stage, component design under the constraint of the integrated platform can be adopted to accelerate the iteration process. By decomposing the constraint conditions and design indicators through the integrated idea, interactive design is carried out on the platform and the antenna. Finally, modular R & D under integration is achieved. The rectifying antenna is combined with the platform in the form of an integrated module, that is, the antenna and the platform can be completely composed of a whole system through a simple connection relationship.

[0039] The integrated rectifying receiving antenna is located at the lower part of the fuselage, and the entire receiving area presents a planar shape to ensure the efficiency of the rectifying receiving unit. The airfoil of this part of the wing adopts a high-lift airfoil, and the appearance is as Figure 5As shown, although the lower surface is flat, after adopting the form of rear loading, the aerodynamic efficiency is still relatively high, effectively taking into account the requirements of the antenna form and lift characteristics. The rear-mounted inverted V-tail of the tail boom is mainly used to arrange the corresponding control surfaces, and the whole aircraft is trimmed through the V-tail. The electric propeller is located above the rear of the fuselage symmetry plane, reducing the shielding of the fuselage on the propeller airflow.

[0040] The overall characteristics of the integrated high-altitude long-endurance unmanned platform driven by microwave energy transmission proposed by the present invention are as follows:

[0041] 1) The total wingspan is 30 m, and the aspect ratio is 20. The set large aspect ratio can ensure the aerodynamic efficiency of low-speed high-altitude flight; of course, the aspect ratio can be further optimized and modified according to performance requirements. This parameter is related to the power supply of the integrated receiving antenna, so it is optimized and set according to the corresponding requirements.

[0042] 2) The wing area is 45 m 2 , and the area of the integrated antenna is 15.918 m 2 , and the area ratio is determined according to the energy demand;

[0043] 3) The airfoil of the wing-body fusion section is a high-lift-to-drag-ratio airfoil with a lift-to-drag ratio meeting the set requirements. The maximum relative thickness is 12.0044%, and the position of the maximum thickness is at 30% of the chord length. The lower surface is adapted to the requirements of the antenna, and there is a straight line segment of a corresponding length; the airfoil of the winglet is a conventional NACA0012 airfoil, mainly used to reduce the induced drag and improve the overall aerodynamic efficiency of the aircraft; the whole aircraft has no twist along the span direction. Of course, the selection of the airfoil can be further optimized and adapted according to performance requirements;

[0044] 4) The integrated integrated antenna is in a circular plane with a diameter of 4.502 m. The center of the circle is 3.015 m away from the nose position. The integrated integrated antenna is composed of a skin, upper and lower layers of foam, and integrated antenna components. The energy reception capacity is about 1 km / m 2 , and the required cruise power supply is 8 KW;

[0045] 5) The length of the tail boom is 6 m, and the area of each V-tail is 1.8375 m 2 , and 40% of the area of its trailing edge is the control surface. The span is 2.5 m and the chord length is 0.3 m, mainly used for longitudinal and lateral attitude control;

[0046] 6) The ailerons are located on the outer side of the wing, close to the winglets. Their span is 3.5 m and the chord length is 0.15 m, participating in lateral control together with the V-tail;

[0047] 7) The two-blade electric tail propeller is adopted as the power device. The blade uses the S1223 airfoil. The twist angle from the blade root to the blade tip is 60 degrees. The blade diameter is 2.5m. Of course, the blade can be further optimized and improved according to the requirements of the propulsion device.

[0048] 8) The nose-wheel landing gear is of the nose-gear type. The nose wheel retracts upward into the upper surface cabin of the fuselage due to the influence of the lower surface antenna, and the main landing gear retracts forward into the landing gear bay on the lower surface.

[0049] This unmanned flight platform is suitable for flying at an altitude of 18 km. The ground microwave energy transmitting end radiates microwave energy into the air. After the airborne integrated antenna receives the microwave energy, it is rectified and converted, converting the radio frequency energy into direct current to drive the unmanned platform to fly and supply power to the airborne equipment. Below, the numerical simulation method based on the Reynolds-averaged Navier-Stokes equation is used to simulate and analyze the aerodynamic characteristics of the whole aircraft, verifying the high-efficiency lift-to-drag ratio characteristics of this design scheme, and verifying the feasibility and efficiency of the energy transmission process through electromagnetic simulation.

[0050] 1) Aerodynamic simulation

[0051] The simulation object is the microwave-powered unmanned flight platform designed by the present invention. The platform wingspan is 30m, the reference area is 45m 2 , the area of the rectenna is 15.918m 2 , and the aspect ratio is 20. The calculation state is H = 18 km, and the Reynolds number is only 0.34×10e6, belonging to the low Reynolds number range. Therefore, separation bubbles may be generated at relatively small angles of attack, so the γ-Re θ transition model is used for simulation.

[0052] Figure 6 The aerodynamic characteristics at the cruise speeds of 10, 20, and 40 m / s calculated are shown. The designed airfoil has a rear loading, the overall camber is slightly larger, and the overall lift characteristics are relatively good. The lift-to-drag ratio characteristics are good. Under the constraint that the aspect ratio does not exceed 20, the maximum lift-to-drag ratio of the clean configuration exceeds 20. At the cruise altitude of H = 18 km, the maximum lift-to-drag ratio can reach more than 24. Generally speaking, the aerodynamic characteristics of the designed configuration are good. Due to the design of winglets at the wingtips and the relatively large aspect ratio, the lift-to-drag ratio characteristics of this configuration are relatively good.

[0053] The pitching moment coefficient characteristics are related to the position of the moment reference point, that is, the center of gravity position. The center of gravity position is determined according to each component and the corresponding loading. The initially selected center of gravity position is 2.5 m from the nose of the aircraft, and the corresponding position is close to the nose because the airfoil thickness of the cross-section here is relatively large, forming a relatively large loading space.

[0054] 2) Radio frequency energy conversion simulation

[0055] The receiving unit design uses an H4B dielectric plate with a thickness of 0.5 mm, a dielectric constant of 3.5, and a loss tangent tanσ = 0.003. The dimensions of the receiving antenna unit are D = 15.59 mm, a = 30 mm, w = 0.5 mm, s = 0.15 mm, l1 = 6.4 mm, l2 = 3.82 mm, l3 = 3.74 mm, l4 = 9.75 mm, l5 = 3.04 mm, and l6 = 3.44 mm.

[0056] Table 3-2 Antenna Parameters

[0057] D (mm) a (mm) w (mm) s (mm) <![CDATA[l1(mm)]]> 15.59 30 0.5 0.15 6.4 <![CDATA[l2(mm)]]> <![CDATA[l3(mm)]]> <![CDATA[l4(mm)]]> <![CDATA[l5(mm)]]> <![CDATA[l6(mm)]]> 3.82 3.74 9.75 3.04 3.44

[0058] Modeling is carried out through HFSS software, and an antenna structure with good performance is obtained through simulation optimization. The simulated reflection coefficient is as Figure 8 shown. The impedance bandwidth is 260 MHz, and the reflection coefficients at the fundamental frequency of 5.8 GHz, the second harmonic of 11.6 GHz, and the third harmonic of 17.4 GHz are -20.47 dB, -0.69 dB, and -1.80 dB respectively. It can better absorb the fundamental frequency energy of 5.8 GHz and can suppress the second and third harmonics generated by the rectifier circuit to a certain extent.

[0059] The simulated axial ratio curve of the antenna is as Figure 9 shown. The axial ratio bandwidth of the antenna is 50 MHz (5.77 GHz - 5.82 GHz), and the axial ratio at 5.8 GHz is 0.79, indicating that the axial ratio of the antenna is good.

[0060] The 3D pattern of the antenna is as Figure 10 shown, and the patterns in the XOZ plane and the YOZ plane are as Figure 11 and Figure 12 shown respectively. It can be seen from the figure that the maximum radiation direction is the Z direction, the gain is G = 6.45 dB, and it is right-handed circular polarization.

[0061] Through simulation analysis, it can be seen that the present invention can greatly improve the aerodynamic characteristics of the unmanned flight platform driven by microwave energy on the premise of ensuring the efficiency and electrical performance of the receiving rectenna, basically eliminating the resistance effect problem caused by installing the antenna, and at the same time achieving no significant increase in the structural weight of the whole platform, improving the efficiency of the whole aircraft. Moreover, electromagnetic simulation also verifies the feasibility and efficiency of the energy transmission process.

[0062] Although the embodiments of the present invention have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present invention without departing from the principle and purpose of the present invention.

Claims

1. A high-altitude ultra-long-endurance large aspect ratio integrated unmanned flight platform driven by microwave energy, characterized in that: Adopt a high aspect ratio wing-body fusion layout, with a full wingspan of 30 m, an aspect ratio of 20, and a wing area of 45 m 2 , and the area of the fairing antenna is 15.918 m 2 ; There is no torsion along the span of the whole aircraft; Winglets are added at the wingtips, and the airfoil of the winglets is the NACA0012 airfoil; The rectifying receiving antenna as the power plant source of the whole aircraft is integrated with the aerodynamics and structure of the whole aircraft, ensuring the aerodynamic characteristics of the whole aircraft in terms of appearance; the integrated rectifying receiving antenna is located at the wing-body fusion part under the fuselage, and the entire receiving area presents a planar shape to ensure the efficiency of the rectifying receiving unit; the airfoil of the wing-body fusion part in the layout area of the rectifying receiving antenna adopts a high lift-to-drag ratio airfoil with a flat lower surface and a lift-to-drag ratio meeting the requirements, the maximum relative thickness is 12.0044%, the maximum thickness position is at 30% of the chord length, and it adopts a rear-loaded form. The lower surface is adapted to the requirements of the antenna and has a straight line segment of corresponding length; the rectifying receiving antenna is in a circular plane with a diameter of 4.502 m, and the center of the circle is 3.015 m away from the nose position. The integrated rectifying antenna is composed of skin, upper and lower layers of foam, and rectifying antenna components encapsulated. At a cruising altitude of 18 km, the maximum lift-to-drag ratio reaches more than 24. The tail support of the unmanned flight platform is arranged with a rear-mounted inverted V-tail to arrange the corresponding control surfaces, and the whole aircraft is trimmed through the V-tail; the electric propeller is located above the rear of the fuselage symmetry plane as the power plant. The length of the tail strut of the unmanned flight platform is 6 m. The tail strut is rear-mounted with an inverted V-tail to arrange the corresponding control surfaces. The area of each V-tail is 1.8375 m 2 , and 40% of the area of its trailing edge is the control surface. The span is 2.5 m and the chord length is 0.3 m, which is used for longitudinal and lateral attitude control; the ailerons are located on the outer side of the wing, with a span of 3.5 m and a chord length of 0.15 m, and participate in lateral attitude control together with the V-tail; A two-blade electric pusher propeller is used as the power plant, the blade adopts the S1223 blade element airfoil, the twist angle from the blade root to the blade tip is 60 degrees, and the blade diameter is 2.5 m. A nose-wheel landing gear is adopted. Among them, due to the influence of the antenna on the lower surface, the nose landing gear adopts a retracting method of retracting upward into the upper surface cabin of the fuselage, and the main landing gear adopts a retracting method of retracting forward into the landing gear compartment on the lower surface of the flight platform.

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