Flapping wing design method with low-power-consumption thrust increasing characteristic, flapping wing and long-endurance flapping wing aircraft

Abstract

The invention provides a flapping wing design method with low power consumption and thrust increasing characteristics, a flapping wing and a long-endurance flapping wing aircraft. When the ornithopter flies, the driving mechanism drives the flapping wings to perform single-degree-of-freedom flapping motion, the wing surfaces generate optimal passive deformation matched with the flight speed under the action of aerodynamic force, deformation and motion of wings in the flight process of birds in nature are simulated, and the design of bionic wings with high thrust, high lift and low power consumption is realized; the flapping wings have better thrust characteristics, the trimming frequency is reduced, so that power consumption is greatly reduced, the shape of a fuselage shell meets the aerodynamics requirement, the resistance effect caused by the fuselage is reduced, and the fuselage has the advantages of being light in weight, good in impact resistance effect and the like due to the section shape, the material and the structural form of the fuselage. And the requirements of typical flight states such as cruise flight and belly landing are met.

Description

Technical Field

[0001] The present invention relates to the technical field of bionic flapping-wing aircraft, in particular to a flapping wing with low power consumption and power-increasing characteristics and a long-endurance flapping-wing aircraft. Background Art

[0002] The bird-like flapping-wing aircraft is a micro-aircraft that draws on the flying method and principle of birds. Due to its light weight and small size, it is easy to carry, has low cost of use, and has certain bionics. Its high concealment characteristics can be used in military fields such as reconnaissance and surveillance, as well as in civilian fields such as scientific investigation and environmental monitoring. It has broad application prospects.

[0003] Around this topic, many research institutions have developed a number of flapping-wing aircraft, among which the more successful ones include the SmartBird bionic seagull flapping-wing aircraft of Germany's Festo, the BatBot bat-like flapping-wing aircraft of California Institute of Technology, and the "Delfly" of Delft University in the Netherlands. However, these flapping-wing aircraft are still some distance away from the aircraft platforms of practical drone systems, especially in terms of short flight endurance. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention proposes a flapping wing design method with low power consumption and increased power consumption, a flapping wing and a long-endurance flapping wing aircraft.

[0005] The present invention provides a flapping wing design method with low power consumption and increased power characteristics, comprising the following steps:

[0006] Step 1: Design the flapping wing with the thrust optimization as the design goal;

[0007] Step 2: Use the CFD method to calculate the flow field of the flapping wing designed in step 1, determine the optimal torsion angle at different span positions of the flapping wing, and interpolate the optimal deformation form of the flapping wing based on the optimal torsion angle at different span positions of the flapping wing;

[0008] Step 3: Conduct a wind tunnel test on the motion process of the flapping wing obtained in step 1, and obtain the measured deformation form of the flapping wing based on high-speed camera technology;

[0009] Step 4: Compare the deformation results of the measured flapping wing deformation form with the optimal deformation form obtained in step 2. If the measured flapping wing deformation form reaches the optimal deformation form, the flapping wing is obtained. Otherwise, return to step 1 and redesign the flapping wing.

[0010] Furthermore, in step 1, the designed flapping wing is divided into an inner arm wing and an outer hand wing, and the maximum chord length of the hand wing part is greater than the maximum chord length of the arm wing part, the hand wing area ratio is greater than the arm wing area ratio, the arm wing section airfoil selects a thick and curved airfoil, and the hand wing section airfoil selects a thin and flat airfoil.

[0011] The present invention also proposes a flapping wing, which is obtained based on the above method.

[0012] Furthermore, the flapping wing has a wingspan of 0.68 m, a maximum chord length of the hand wing of 0.13 m, and a maximum chord length of the arm wing of 0.10 m, wherein the hand wing area accounts for 0.65, and the arm wing area accounts for 0.35. Other structural parameters are shown in the following table:

[0013]

[0014] The present invention also provides a long-endurance flapping-wing aircraft, wherein the flapping wings adopt the flapping wings obtained above.

[0015] Furthermore, the long-endurance flapping-wing aircraft also includes a composite fuselage shell, a composite equipment mounting frame, a drive mechanism, and a tail wing.

[0016] Furthermore, the tail wing adopts an inverted V-shaped tail wing.

[0017] Beneficial Effects

[0018] When the flapping-wing aircraft proposed by the present invention flies, the driving mechanism drives the flapping wing to perform a single-degree-of-freedom flapping motion, and the wing surface produces the best passive deformation matching the flight speed under the action of aerodynamic force, imitating the deformation and movement of the wings of birds in nature during flight, and realizing a bionic wing design with high thrust, high lift and low power consumption; the flapping wing has better thrust characteristics, reduces the trim frequency, and thus greatly reduces power consumption, the shape of the fuselage shell meets the aerodynamic requirements, reduces the drag effect brought by the fuselage, and the cross-sectional shape, material and structural form of the fuselage make the fuselage have the characteristics of light weight and good impact resistance, meeting the requirements of typical flight states such as cruise flight and belly landing, because the middle section of the fuselage is an equal straight section and the cross-sectional shape is a rounded rectangle, it is convenient to install various required loads, and its internal skeleton and appearance material have the ability to effectively protect the safety of internal subsystem equipment when an accident occurs during flight. During flight, an inverted V-shaped tail wing layout is used to control the roll of the aircraft, lift control and provide partial lift; thereby realizing the long-endurance flight of the bird-like flapping-wing aircraft.

[0019] Additional aspects and advantages of the present invention will be given in part in the following description and in part will be obvious from the following description, or will be learned through practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The above and / or additional aspects and advantages of the present invention will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0021] Figure 1 : Schematic diagram of flapping wing;

[0022] Figure 2 : Relationship between thrust coefficient and pitch angle;

[0023] Figure 3 : spanwise position motion parameters and geometric parameters;

[0024] Figure 4 : The optimal torsional deformation angle corresponding to different spanwise positions;

[0025] Figure 5 : Flowchart of the embodiment method;

[0026] Figure 6 : Schematic diagram of flapping-wing aircraft;

[0027] Among them: 1. Composite nose; 2. Magnetic compass; 3. Drive mechanism; 4. Second bulkhead; 5. Flight control module; 6. Flapping wing; 7. Composite fuselage; 8. Tail; 9. Digital transmission antenna; 10. Control surface; 11. Servo pull rod; 12. Image transmission antenna. DETAILED DESCRIPTION

[0028] Embodiments of the present invention are described in detail below. The embodiments are exemplary and intended to be used to explain the present invention, but should not be construed as limiting the present invention.

[0029] This embodiment first proposes a flapping wing design method with low power consumption and increased power characteristics.

[0030] By observing flying creatures at close range, we can find that their wings will undergo a large torsional motion, especially when ascending or hovering, which requires a large thrust. Through quasi-steady and unsteady analysis, the mechanical energy generated by the flapping motion of the flapping wings is converted into thrust through the chord-wise torsion process. Therefore, for bird-like flapping wing aircraft, suitable torsional motion will bring better aerodynamic performance, and torsional motion can be achieved through active torsional technology or passive torsion. However, after carefully adjusting the torsional motion based on the analytical method, it was found that the power consumption of active torsion is unaffordable, resulting in an improvement in overall efficiency that is usually not obvious. For this reason, passive torsion is used in this embodiment.

[0031] The flapping wing is divided into two single wings on the left and right, adopting a single-section wing layout, symmetrically installed on both sides of the fuselage, and is made of a frame and a skin bonded together, and is divided into two parts: the hand wing (outer side) and the arm wing (inner side). Figure 1As shown, the maximum chord length of the hand-wing part is greater than the maximum chord length of the arm-wing part. According to the mechanism of lift thrust generated by bird wings, the thrust is mainly generated by the hand-wing part, and the lift is mainly generated by the arm-wing part and the hand-wing part. Therefore, in this embodiment, the design is imitated according to the characteristics of bird wings. The arm-wing section airfoil of the flapping wing selects a thick and curved airfoil, and the hand-wing section airfoil selects a thin and flat airfoil, which is in line with the low-energy consumption design principle of the aircraft. In addition, the design of increasing the chord length and area of ​​the hand-wing part can also help increase the thrust.

[0032] As mentioned above, the main form of motion of a flapping wing is flapping motion, and the mechanical energy generated by it is converted into thrust through the chord-wise torsion process, while the torsion motion is generated by the passive deformation of the flapping wing during the flapping process. From a two-dimensional perspective, the flapping motion and passive torsion motion of the flapping wing are manifested as the heaving and floating motion of the airfoil at different spanwise positions, and the torsion motion is manifested as the passive pitching motion of the airfoil at different spanwise positions.

[0033] Therefore, in this embodiment, the flapping wing heave, float and pitch motions under different states are analyzed, and the motion function is as follows:

[0034] h=h0cos(2πft)

[0035] θ=θ0cos(2πft+ψ)

[0036] Among them, h0 is the heave amplitude, θ0 is the pitch amplitude, ψ is the heave and pitch phase difference, and the best propulsion efficiency is obtained when ψ is 90°. Through CFD analysis, it can be found that under the same motion state, as the pitch angle increases, the thrust coefficient increases first and then decreases, such as Figure 2 As shown. During the movement of the flapping wing, the wing part produces a large passive deformation under the action of aerodynamic force. The passive deformation is closely related to the thrust, and the passive deformation does not increase the extra power consumption. Therefore, under a given motion state, there is an optimal pitch angle to maximize the thrust, that is, there is an optimal torsion angle at different spanwise positions of the flapping wing. The flapping wing has different spanwise positions as shown in Figure 3 Then, for a certain flapping wing, the optimal torsion angle of each section of the flapping wing can be determined based on the CFD calculation results, such as Figure 4 As shown, the horizontal axis is the Strouhal number St, and the vertical axis is the optimal torsional deformation angle corresponding to the St value. The Strouhal number is:

[0037]

[0038] Where f is the flapping frequency, t is the characteristic length, and U is the incoming flow velocity.

[0039] Based on the above analysis, the flapping wing design method with low power consumption and increased power consumption proposed in this embodiment includes the following steps:

[0040] Step 1: Taking the thrust optimization as the design goal, a flapping wing is designed by a conventional method; the flapping wing is divided into an inner arm wing and an outer hand wing, and the maximum chord length of the hand wing part is greater than the maximum chord length of the arm wing part, the hand wing area ratio is greater than the arm wing area ratio, the arm wing section airfoil is selected to be thick and curved, and the hand wing section airfoil is selected to be thin and flat;

[0041] Step 2: Use the CFD method to calculate the flow field of the flapping wing designed in step 1, determine the optimal torsion angle at different span positions of the flapping wing, and interpolate the optimal deformation form of the flapping wing based on the optimal torsion angle at different span positions of the flapping wing;

[0042] Step 3: Conduct a wind tunnel test on the motion process of the flapping wing obtained in step 1, and obtain the measured deformation form of the flapping wing based on high-speed imaging technology (DIC);

[0043] Step 4: Compare the deformation results of the measured flapping wing deformation form with the optimal deformation form obtained in step 2. If the measured flapping wing deformation form reaches the optimal deformation form, the flapping wing is obtained. Otherwise, return to step 1 and redesign the flapping wing.

[0044] In this embodiment, the flapping wing has a wingspan of 0.68 m, a maximum chord length of the hand wing of 0.13 m, and a maximum chord length of the arm wing of 0.10 m, wherein the hand wing area accounts for 0.65, and the arm wing area accounts for 0.35. Other structural parameters are shown in the following table:

[0045]

[0046] The flapping wing obtained in this way can generate greater thrust at the same flapping frequency. When the total drag of the aircraft remains unchanged, the increase in thrust helps to reduce the flapping frequency in the trimmed state. Since the power consumption of a flapping wing is generally proportional to the cube of the flapping frequency, reducing the trimmed flapping frequency can significantly reduce power consumption.

[0047] Based on the flapping wings obtained above, this embodiment also proposes a long-endurance flapping-wing aircraft, such as Figure 6 As shown, it has the advantages of light weight and long battery life.

[0048] The long-endurance flapping-wing aircraft comprises a composite fuselage shell, a composite equipment mounting frame, the flapping wings with low-power consumption and power-increasing characteristics, a low-power consumption bionic drive mechanism, and a tail wing.

[0049] The lightweight composite fuselage shell is divided into the nose and the body. The material is resin-based carbon fiber composite material. The front end of the nose is in the form of a bird head. The middle section of the nose continues to expand backward. The surface of the expansion section is a quadratic surface, which is connected to the body through a slot. The body is divided into a front straight section and a rear contraction section. The cross-section of the straight section is a rounded rectangle. The contraction section starts from the middle of the fuselage, and the two sides gradually contract toward the longitudinal symmetry plane of the body. The lower surface of the contraction section gradually contracts upward. The entire body is closed at the tail. The curved surfaces on the left and right and lower surfaces of the contraction section are quadratic surfaces. The rocker arm of the flapping wing drive mechanism is extended through an opening at the upper part of the connection between the nose and the body to avoid motion interference.

[0050] The composite equipment installation frame inside the fuselage is divided into two parts: the nose frame and the body frame. It is designed in the form of a space truss. The material is a resin-based carbon fiber composite material. It is used to install equipment such as flapping wing drive mechanisms, flight control systems, and power energy modules, and serves as a fixing and connecting component between the nose shell and the body shell. The specific form is: the nose frame is composed of a first bulkhead fixedly connected to the nose shell and a nose part equipment installation frame. The first bulkhead is fixed to the nose shell by bonding, and is connected to the body frame in a detachable form with buckles and screws, which is convenient for installation and maintenance. The nose part equipment installation frame is mainly used to install GPS and airspeed meters. The nose part equipment installation frame is fixedly connected to the body frame by screws; the body frame is bonded to the body shell through a second bulkhead located at the front end of the body frame, and the rear end of the body frame is contacted and fixed with the body shell. The body frame also serves as a mounting frame for the flapping wing drive mechanism, power energy module and flight control system.

[0051] The driving mechanism is fixed on the second bulkhead at the front end of the body frame, and includes a driving motor, a reduction gear set, a pair of left and right connecting rods and left and right rocker arms. The left and right rocker arms and the left and right connecting rods are simultaneously connected to the pins of the final gear of the gear set to form a planar four-bar structure. The driving motor converts the rotational motion of the motor into the up and down reciprocating motion of the rocker arm through the two-stage reduction gear set. The specific form is: the output shaft of the driving motor is connected to the primary driving gear, the primary driving gear is further meshed with the primary driven gear, the primary driven gear is connected to the same transmission shaft with the secondary driving gear, the secondary driving gear is further meshed with the secondary driven gear, a hole is turned in the middle position of the secondary driven gear, and the pin is used to connect the left and right connecting rods. The other end of the left and right connecting rods is hinged with one end of the corresponding rocker arm to form a four-bar linkage mechanism, so as to realize the conversion of the rotational motion of the driving motor into the up and down reciprocating motion of the rocker arm. The other end of the rocker arm has a blind hole for connecting the flapping wing to realize the reciprocating flapping of the flapping wing. In order to support the long-term reliable operation of the driving mechanism, the rocker crank shaft bushing and the rocker crank shaft in the driving mechanism are manufactured by using wear-resistant bearing steel materials. Use copper sleeves to replace the vulnerable bearings on the low-speed shaft and connecting rod in the drive mechanism. Heat treat the low-speed shaft to improve its hardness and wear resistance. Install washers between the rocker arm and the drive mechanism frame to reduce the rocker arm's shaking. Slot the frame on the connecting rod's movement path to reduce the friction between the connecting rod and the frame due to shaking. Fill the mounting holes of the low-speed shaft and high-speed shaft of the drive mechanism with grease to reduce friction. Open heat dissipation holes on the frame to assist the drive motor in dissipating heat to improve the drive motor's efficiency.

[0052] like Figure 1 As shown, the framework of the flapping wing is composed of a main beam located at the leading edge, an auxiliary beam located behind the main beam, and a number of wing ribs glued to the main beam and the auxiliary beam. The materials are all resin-based carbon fiber composite materials, and a polyurethane film is pasted on the framework as the wing skin. The main beam of the flapping wing is fixed by inserting the root into the blind hole on the rocker arm of the driving mechanism. It can rotate around the blind hole in a small range. This constraint can effectively avoid the phenomenon of connection falling off during the flapping process. The root of the auxiliary beam is hinged with the locking device on the fuselage. The flapping wing locking device is glued and fixed to the fuselage shell, and is used for connecting the flapping wing auxiliary beam. It is an integral structure formed by bending elastic metal wire, including a locking buckle and a limiting rod. The limiting rod passes through the connection hole at the root of the flapping wing auxiliary beam, and then buckles into the locking buckle fixed to the fuselage to achieve the connection and fixation of the flapping wing auxiliary beam. The locking device used to connect the flapping wing auxiliary beam is an integral structure. The locking buckle and the limit rod are extended through two holes in the fuselage, and the remaining steel wire structure is bonded and fixed to the inside of the fuselage shell. In this way, even if the locking buckle is loosened due to external force during flight, the normal connection between the auxiliary beam and the limit rod can still be guaranteed, thereby improving the reliability of the flapping wing aircraft.

[0053] The tail is an inverted V-shaped tail with a root chord length of C r=0.09m, span b1 =0.28m, chord length c t1 =0.05m, the reverse angle Γ1 = 20°, including a servo, a servo mounting frame, a tail connecting piece and a rudder surface. The servo is installed in the servo mounting frame and fixed to the tail of the fuselage shell by bonding. The V-tail connecting piece is used to connect the fuselage and the tail wing. The rotation of the servo drives the connecting rod to control the rudder surface to achieve different angles, thereby realizing the attitude control of the flapping-wing aircraft. Since the inverted V-tail has fewer fuselage and tail connecting components, the inverted V-shaped tail wing produces less interference resistance; while the left and right rudder surfaces differentially provide a rolling control torque, a favorable yaw control torque will be generated to improve the lateral heading maneuverability; and the inverted V-shaped tail wing provides a larger dynamic derivative, which improves the damping characteristics of the entire aircraft, thereby obtaining a stronger anti-interference ability and a better transient response, ensuring that the aircraft has good control and stability characteristics, and achieving stable flight and control.

[0054] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention without departing from the principles and intent of the present invention.

Claims

1. A flapping wing design method with low power consumption and increased power characteristics, characterized in that: The following steps are involved: Step 1: Design the flapping wing with the thrust optimization as the design goal; Step 2: Use the CFD method to calculate the flow field of the flapping wing designed in step 1, determine the optimal torsion angle at different span positions of the flapping wing, and interpolate the optimal deformation form of the flapping wing based on the optimal torsion angle at different span positions of the flapping wing; Step 3: Conduct a wind tunnel test on the motion process of the flapping wing obtained in step 1, and obtain the measured deformation form of the flapping wing based on high-speed camera technology; Step 4: Compare the deformation results of the measured flapping wing deformation form with the optimal deformation form obtained in step 2. If the measured flapping wing deformation form reaches the optimal deformation form, the flapping wing is obtained. Otherwise, return to step 1 and redesign the flapping wing.

2. A flapping wing design method with low power consumption and increased power according to claim 1, characterized in that: In step 1, the designed flapping wing is divided into an inner arm wing and an outer hand wing, and the maximum chord length of the hand wing part is greater than the maximum chord length of the arm wing part, the hand wing area ratio is greater than the arm wing area ratio, the arm wing section airfoil selects a thick and curved airfoil, and the hand wing section airfoil selects a thin and flat airfoil.

3. A flapping wing with low power consumption and increased power characteristics, characterized in that: The method according to claim 1 or 2 is used to design the product.

4. The flapping wing with low power consumption and increased power according to claim 1, characterized in that: The flapping wing has a wingspan of 0.68 m, a maximum chord length of the hand wing of 0.13 m, and a maximum chord length of the arm wing of 0.10 m, wherein the hand wing area accounts for 0.65, and the arm wing area accounts for 0.

35. Other structural parameters are shown in the following table:

5. A long-endurance flapping-wing aircraft, characterized in that: The flapping wing adopts the flapping wing described in claim 3 or 4.

6. A long-endurance flapping-wing aircraft according to claim 5, characterized in that: It also includes a composite fuselage shell, a composite equipment mounting frame, a drive mechanism and a tail.

7. A long-endurance flapping-wing aircraft according to claim 6, characterized in that: The tail wing adopts an inverted V-shaped tail wing.

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