High lift-drag ratio airfoil profile and ultra-redundant composite configuration unmanned aerial vehicle suitable for low altitude and low speed

Abstract

The invention belongs to the technical field of aircraft airfoil design, and particularly discloses a high-lift-drag-ratio airfoil and an unmanned aerial vehicle suitable for a low-altitude low-speed ultra-redundant composite configuration. The maximum thickness of the airfoil is 9% of the chord length c of the airfoil; the maximum thickness position of the airfoil is 22.8% of the chord length c of the airfoil; the maximum camber of the airfoil is 5.67% of the chord length c of the airfoil; the maximum camber position of the airfoil is 44.8% of the chord length c of the airfoil; and the thickness of the rear edge of the airfoil is 0.326% of the chord length c of the airfoil. The airfoil is specially designed for a low-altitude and low-speed composite configuration unmanned aerial vehicle, can simultaneously realize a high lift coefficient and an ultrahigh lift-drag ratio under the severe working conditions that the Reynolds number is 250,000 and the Mach number is 0.044, and has a smooth stall attack angle of about 13 degrees.

Description

Technical Field

[0001] This invention belongs to the field of aircraft airfoil design technology, specifically relating to a high lift-to-drag ratio airfoil and a super-redundant composite configuration UAV suitable for low-altitude, low-speed operation. Background Technology

[0002] The super-redundant composite configuration UAV is a new type of UAV that adds a pair of independently controllable wings to a multi-rotor aircraft platform. The purpose of this configuration is to use the wings to provide additional aerodynamic forces during cruise flight, thereby distributing the load of the multi-rotor, reducing flight energy consumption, and improving the UAV's endurance and flight speed.

[0003] However, the core technological challenge for this type of drone lies in: Extremely low speed and low Reynolds number conditions: When ultra-redundant composite configuration UAVs switch to fixed-wing mode for cruise, the speed is typically low (e.g., 15 m / s), and the corresponding Reynolds number (Re) is usually in the range of 250,000. ); High lift requirement: In order to effectively distribute the rotor load, the wing needs to provide the highest possible lift coefficient ( This is to ensure that the machine can still support most of its weight at low speeds; High efficiency requirement: In order to improve flight endurance, the airfoil must have an extremely high lift-to-drag ratio (L / D).

[0004] Existing low-speed UAV airfoils, such as the traditional NACA series airfoils, or some publicly available low-speed high lift-to-drag ratio airfoils (such as airfoils designed for 500,000 Reynolds numbers), typically have the following problems: at extremely low Reynolds numbers (250,000), laminar boundary layer separation is prone to occur, leading to a sharp drop in lift coefficient and a sharp increase in drag coefficient, resulting in poor lift-to-drag ratio performance and inability to meet the high efficiency requirement of L / D>100; or their design lift coefficient is too low, which cannot effectively meet the lift requirements of compound configuration UAVs under high loads. Summary of the Invention

[0005] Purpose of the Invention: The purpose of this invention is to address the shortcomings of existing technologies by providing a high lift-to-drag ratio airfoil and a low-altitude, low-speed, super-redundant composite configuration UAV suitable for low-altitude (H<1000m) and low-speed (Ma<0.05) flight. This invention achieves good lift-to-drag characteristics with a high lift coefficient, aiming to solve the following technical problems: Under the constraints of limited wingspan and installation space, by leveraging the excellent aerodynamic performance of the airfoil, the lift coefficient of the UAV during low-speed, low-altitude flight is significantly improved, allowing the UAV to distribute more rotor thrust to the horizontal flight direction, thereby increasing flight speed; simultaneously, the lift-to-drag ratio characteristics are improved, thereby reducing flight energy consumption and extending endurance, meeting the dual performance requirements of high lift and energy saving for composite configuration UAVs.

[0006] Technical solution: The high lift-to-drag ratio airfoil of the present invention, applicable to low-altitude, low-speed, super-redundant composite configuration UAV, has the following key geometric features: the maximum thickness of the airfoil is 9% of the airfoil chord length c; the location of the maximum thickness of the airfoil is 22.8% of the airfoil chord length c; the maximum camber of the airfoil is 5.67% of the airfoil chord length c; the location of the maximum camber of the airfoil is 44.8% of the airfoil chord length c; and the trailing edge thickness of the airfoil is 0.326% of the airfoil chord length c.

[0007] To further improve the above technical solution, the coordinates of the upper surface of the trailing edge of the airfoil... and lower surface coordinates The class function C(x) and the type function , definition: Among them, the class function In the formula: N1 and N2 define the categories of the geometric shapes they represent, N1=0.5 and N2=1.0; Let be the coordinates of the chord length. and These are the y-coordinates of the airfoil's trailing edge; The definition formula for the type function is as follows: , In the formula: and These are the upper surface coefficient and the lower surface coefficient, respectively. Let the Bernstein polynomial function be defined as follows: , In the formula, N is the order of the Bernstein polynomial function.

[0008] Furthermore, the upper surface coefficient The corresponding values ​​for i = 0 to 5 are: [0.1862701458, 0.2581436207, 0.2032954597, 0.3730005229, 0.1061849286, 0.2997725357]; The lower surface coefficient The corresponding values ​​for i = 0 to 5 are: [-0.115751595, 0.0240482316, -0.0188652560, 0.205723604, 0.0173757674, 0.126403021].

[0009] Furthermore, under flight conditions with a Reynolds number of 250,000 and a Mach number less than 0.05, the airfoil exhibits a lift coefficient of [missing information]. When the value is 1.3±0.5, its lift-to-drag ratio is greater than 100.

[0010] Furthermore, the airfoil has a stall angle of attack of 13° under the flight conditions.

[0011] Furthermore, under the designed lift coefficient, the flow transition position on the upper surface of the airfoil is at 50% chord length.

[0012] The present invention also provides a super-redundant composite configuration UAV suitable for low-altitude and low-speed operation, comprising an airframe, multiple rotors for vertical take-off and landing, and at least one wing for cruise flight, wherein the airfoil of the at least one wing adopts any of the high lift-to-drag ratio airfoils described above.

[0013] Beneficial effects: Compared with the prior art, the advantages of the present invention are as follows: The airfoil provided by the present invention, through a specific geometric combination of thin airfoil (about 9%c) and high camber (about 5.67%c), combined with the forward shift of the maximum thickness position, has excellent lift-drag characteristics under the condition of Reynolds number in the range of 250,000. With a design lift coefficient of around 1.3±0.5, the lift-drag ratio is greater than 100. Compared with airfoils with similar performance in the prior art at 250,000 Reynolds number, the lift-drag ratio performance of this airfoil is improved by more than 15%, which significantly reduces the energy consumption of UAVs during cruise and improves the endurance. This airfoil is suitable for flight conditions with Reynolds numbers in the range of 250,000 and Mach numbers less than 0.05. It can achieve a stall angle of attack of 13° and the stall process is smooth, ensuring the safety and control stability of the UAV during low-speed, high-angle-of-attack flight. The optimized pressure distribution on the upper surface of the airfoil ensures that, under the design lift coefficient, the upper surface of the leading edge has a suction peak with a Cp value of approximately -2.2, and the flow transition position of the laminar boundary layer is controlled at approximately 50% of the chord length, thereby maximizing the maintenance of the laminar region and effectively reducing frictional drag. This is a key technical guarantee for achieving an ultra-high lift-to-drag ratio.

[0014] The super-redundant composite configuration UAV equipped with this wing can make full use of the lift generated by the wing and distribute more of the rotor's thrust to the horizontal component, thereby effectively improving the overall flight speed and mission execution efficiency while maintaining low energy consumption. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the geometric profile of the airfoil of the present invention.

[0016] Figure 2 This is the airfoil surface pressure distribution under the maximum lift-to-drag ratio condition of the present invention.

[0017] Figure 3 This is the curve showing the change of the lift coefficient of the airfoil of this invention with the angle of attack.

[0018] Figure 4This is a comparison of the geometric shape of the present invention with that of the comparative airfoil 1.

[0019] Figure 5 This is a graph showing the lift coefficient of the airfoil of the present invention and the airfoil 1 as a function of angle of attack.

[0020] Figure 6 This is a curve showing the drag coefficient of the airfoil of the present invention and the comparative airfoil 1 as a function of angle of attack.

[0021] Figure 7 This is a graph showing the lift-to-drag ratio of the airfoil of the present invention and the comparative airfoil 1 as a function of angle of attack.

[0022] Figure 8 This is a comparison of the geometric shape of the present invention with that of the comparative airfoil 2.

[0023] Figure 9 This is a graph showing the lift coefficient of the airfoil of the present invention and the airfoil 2 as a function of angle of attack.

[0024] Figure 10 This is a curve showing the drag coefficient of the airfoil of the present invention and the airfoil 2 as a function of angle of attack.

[0025] Figure 11 This is a graph showing the lift-to-drag ratio of the airfoil of the present invention and the comparative airfoil 2 as a function of angle of attack.

[0026] Figure 12 This is a schematic diagram of a super-redundant composite configuration UAV using the airfoil of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings, but the scope of protection of the present invention is not limited to the embodiments described.

[0028] Example 1: The high lift-to-drag ratio airfoil (code name YJ-HY-01) provided by the present invention is suitable for low-altitude, low-speed, ultra-redundant composite configuration UAVs and is specifically designed for the airfoil profile of ultra-redundant composite configuration UAVs under low-speed cruise conditions.

[0029] like Figure 1 As shown, the target geometric parameters for this airfoil design are as follows: maximum relative thickness: 9.0%c; maximum relative thickness location: 22.8%c; maximum relative camber: 5.67%c; maximum relative camber location: 44.8%c; trailing edge thickness: 0.326%c, where c is the airfoil chord length. These parameters ensure the airfoil's thinness and high camber characteristics.

[0030] The geometry of this airfoil is defined by the CST (Class / Shape Function Transformation) method, which represents the airfoil as a product of a shape function and a class function, plus the trailing edge thickness of the airfoil. The expressions for the upper and lower surfaces of the airfoil are shown below: In the formula, Called a class function, Let be the coordinates of the chord length. Called a type function, and These are the y-coordinates of the airfoil's trailing edge. The definition is as follows: In the formula, N1 and N2 define the categories of the geometric shapes represented, with N1=0.5 and N2=1.0.

[0031] The definition formula for the type function S(x) is shown below: In the formula, Let the Bernstein polynomial function be defined as follows: In the formula, N is the order of the Bernstein polynomial function, and the airfoil in this invention... and (correspond to As shown in Table 1: Table 1. Coefficients of the expression for airfoil geometric coordinates The main design parameters of the YJ-HY-01 airfoil provided by this invention are: (1) flight speed 15m / s; (2) design Reynolds number in the range of 250,000; (3) high lift characteristics and large stall angle of attack; (4) excellent lift-drag characteristics, with a lift-drag ratio greater than 100 around the design lift coefficient of 1.3±0.5.

[0032] Figure 2 The pressure distribution pattern of the YJ-HY-01 airfoil under design conditions (maximum lift-to-drag ratio); Figure 3 The curve shows the lift coefficient of the airfoil of the present invention as a function of angle of attack under this operating condition, and it can be seen that its stall angle of attack is 13°.

[0033] The specific analysis of the airfoil pressure distribution is as follows: 1. Leading edge segment (X / C=0) The sharp drop in CP on the upper surface to around -2.2 indicates that the airflow on the upper surface of the leading edge is strongly accelerated, forming a low-pressure area, which is a typical leading-edge suction peak, which is conducive to improving the lift of the airfoil. The rapid rise of CP on the lower surface to 1 indicates that the airflow on the lower surface of the leading edge is blocked, the pressure increases sharply, forming a high-pressure area, which, together with the low pressure on the upper surface, forms the basis for lift.

[0034] 2. Leading edge segment ~ interruption (X / C=0.1~0.5) The slow rise of pressure gradient (CP) on the upper surface indicates stable airflow over the airfoil, a reasonable pressure gradient, and no severe separation. The lower surface CP remains in the 0.2-0.5 range, maintaining continuous positive pressure and providing thrust for lift. Transition occurs on the upper surface of the airfoil at approximately 0.5°C.

[0035] 3. The latter part (X / C = 0.5~1) The upper wing surface CP continued to rise gently, while the lower wing surface CP remained generally stable, indicating that the airflow was smooth before converging at the trailing edge, without large-area separation, and the wake vortex intensity was low.

[0036] Overall, the low pressure gradient (CP) region from the leading edge to the mid-section of the upper wing is extensive, forming a significant pressure difference with the continuous positive pressure on the lower wing surface. This effectively converts the pressure into lift, making it suitable for scenarios with high lift requirements. The upper wing surface exhibits a gentle pressure gradient without drastic fluctuations, indicating good boundary layer adhesion and low risk of airflow separation. The lower wing surface has stable pressure and smooth trailing-edge convergence, reducing pressure drag and induced drag. This pressure distribution corresponds to aerodynamic advantages of sufficient lift and low drag, making it suitable for long-endurance and energy-efficient flight. The gradual pressure recovery process on the upper wing surface without abrupt changes indicates a smooth transition from low-pressure acceleration to trailing-edge convergence, delaying the stall critical angle of attack and resulting in superior flight safety and controllability.

[0037] In summary, this airfoil can undergo a transition followed by separation at a flight speed of 15 m / s and 250,000 Reynolds, without laminar flow separation. Under its design conditions, it possesses the advantages of high lift and high lift-to-drag ratio, as well as smooth stall characteristics.

[0038] Example 2: To further verify the advantages of the airfoil of the present invention, this airfoil was implemented on a 15kg-class composite configuration UAV, such as... Figure 12 As shown, the device includes an airframe, multiple rotors for vertical takeoff and landing, and at least one wing for cruise flight. The wing profile adopts the airfoil (YJ-HY-01) provided in Example 1, with a wing chord length of 0.25m and a span of 0.75m. Using this airfoil, the UAV can provide the main lift with high efficiency (L / D>100) and high lift (lift coefficient of 1.3) when in low-speed cruise mode (Re=250,000). Through a large number of flight tests, the test results show that when the UAV flies at a speed of 10~20m / s, the composite configuration UAV with wings consumes 20% less energy than a regular 15kg multi-rotor UAV, greatly improving the UAV's endurance.

[0039] Example 3: To demonstrate the characteristics of the YJ-HY-01 airfoil provided by the present invention, the following example is used for comparison to verify the advantages of the YJ-HY-01 airfoil of the present invention. The aerodynamic performance analysis is performed using the airfoil aerodynamic analysis software XFOIL, and the calculated state parameters are: free transition, Mach number 0.044, Reynolds number 2.5×10⁵, and iteration steps 500.

[0040] Using the airfoil disclosed in patent application CN110498037B entitled "A high lift-to-drag ratio laminar flow airfoil suitable for low-altitude, low-speed UAVs" as the comparative airfoil 1, and comparing it with the airfoil YJ-HY-01 of the present invention, the differences in aerodynamic performance between the airfoil of the present invention (YJ-HY-01) and the comparative airfoil 1 are analyzed and compared.

[0041] Figure 4 This is a geometrical comparison between the airfoil of the present invention and airfoil 1 (comparison airfoil 1). The maximum relative thickness of YJ-HY-01 is 9%, while the maximum relative thickness of airfoil 1 is 10%. YJ-HY-01 is thinner than airfoil 1, which can reduce the structural weight of the wing in later stages. Figures 5-7 The lift characteristics, drag characteristics, and lift-drag characteristic curves of the airfoil of the present invention and the comparative airfoil 1 are compared respectively.

[0042] from Figures 5-7 As can be seen, the lift characteristics of the airfoil YJ-HY-01 of this invention are all better than those of the comparative airfoil 1, the stall characteristics are the same, and the lift-to-drag ratio under different lift conditions is mostly better than that of the comparative airfoil 1, and in some cases comparable to it. In the design state (lift coefficient is 1.3), the lift-to-drag ratio of the airfoil of this invention is as high as 103, while that of the comparative airfoil 1 is only 86 in this state, and its maximum lift-to-drag ratio is only 95.

[0043] Example 4: Using the typical low-speed UAV airfoil NACA4412 as the comparison airfoil 2, and comparing it with the airfoil YJ-HY-01 of the present invention, the differences in aerodynamic performance between the airfoil of the present invention (YJ-HY-01) and the comparison airfoil 2 are analyzed and compared.

[0044] Figure 8 This is a geometrical comparison between the airfoil of the present invention and airfoil 2 (comparison). Airfoil 2 has a maximum thickness of 12%, which leads to an increase in wing surface area and internal structural dimensions, thereby increasing the structural empty weight of the UAV. The maximum relative thickness of YJ-HY-01 is 9%, which can reduce the weight of the subsequent wing and thus improve the range. Figures 9-11 The lift characteristics, drag characteristics, and lift-drag characteristic curves of the airfoil of the present invention and the comparative airfoil 1 are compared respectively.

[0045] from Figures 9-11As can be seen, the lift characteristics of the airfoil YJ-HY-01 of this invention are all better than those of the comparative airfoil 2. The lift-to-drag ratio under different lift conditions is mostly better than that of the comparative airfoil 2, and in some cases comparable to it. In the design state (lift coefficient of 1.3), the lift-to-drag ratio of the airfoil of this invention is as high as 103, while that of the comparative airfoil 2 is only 84 in this state, and its maximum lift-to-drag ratio is only 85.

[0046] The above two representative examples demonstrate that the YJ-HY-01 airfoil of this invention can operate without separation at 250,000 Reynolds number, possesses high lift and high lift-to-drag ratio at the designed lift coefficient, and exhibits smooth stall characteristics, thus meeting the performance requirements of composite configuration UAVs.

[0047] As described above, although the invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the invention itself. Various changes in form and detail may be made without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. A high lift-to-drag ratio airfoil, characterized in that, The maximum thickness of the airfoil is 9% of the airfoil chord length c; the location of the maximum thickness of the airfoil is 22.8% of the airfoil chord length c; the maximum camber of the airfoil is 5.67% of the airfoil chord length c; the location of the maximum camber of the airfoil is 44.8% of the airfoil chord length c; and the trailing edge thickness of the airfoil is 0.326% of the airfoil chord length c.

2. The high lift-to-drag ratio airfoil according to claim 1, characterized in that, The upper surface coordinates of the trailing edge of the airfoil and lower surface coordinates The class function C(x) and the type function , definition: in, Let be the coordinates of the chord length. and These are the y-coordinates of the airfoil's trailing edge.

3. The high lift-to-drag ratio airfoil according to claim 2, characterized in that, The class function is defined as follows: , In the formula: N1 and N2 define the categories of the geometric shapes they represent, N1=0.5 and N2=1.0; The definition formula for the type function is as follows: ， In the formula: and These are the upper surface coefficient and the lower surface coefficient, respectively. Let the Bernstein polynomial function be defined as follows: ， In the formula, N is the order of the Bernstein polynomial function.

4. The high lift-to-drag ratio airfoil according to claim 3, characterized in that, The upper surface coefficient The corresponding values ​​for i = 0 to 5 are: [0.1862701458, 0.2581436207, 0.2032954597, 0.3730005229, 0.1061849286, 0.2997725357]; The lower surface coefficient The corresponding values ​​for i = 0 to 5 are: [-0.115751595, 0.0240482316, -0.0188652560, 0.205723604, 0.0173757674, 0.126403021].

5. The high lift-to-drag ratio airfoil according to claim 1, characterized in that, Under flight conditions with a Reynolds number of 250,000 and a Mach number less than 0.05, the airfoil exhibits a lift coefficient of [missing information]. When the value is 1.3±0.5, its lift-to-drag ratio is greater than 100.

6. The high lift-to-drag ratio airfoil according to claim 5, characterized in that, The airfoil has a stall angle of attack of 13° under the flight conditions.

7. The high lift-to-drag ratio airfoil according to claim 5, characterized in that, Under the designed lift coefficient, the flow transition point on the upper surface of the airfoil is at 50% chord length.

8. A low-altitude, low-speed, ultra-redundant composite configuration unmanned aerial vehicle (UAV), comprising a fuselage, multiple rotors for vertical takeoff and landing, and at least one wing for cruise flight, characterized in that, The airfoil of the at least one wing is a high lift-to-drag ratio airfoil according to any one of claims 1 to 7.

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