Distributed power combined dovetail unmanned aerial vehicle and landing control enhancement method thereof

Abstract

This invention discloses a distributed propulsion combined with a dovetail-shaped unmanned aerial vehicle (UAV) and its landing control enhancement method, belonging to the field of UAVs. The UAV includes a fuselage, multiple pairs of propellers mounted along the spanwise direction at the front of the fuselage, and multiple pairs of dovetails mounted along the spanwise direction at the rear of the fuselage. The propellers and dovetails are used in pairs and are symmetrically distributed about the UAV's plane of symmetry. The main aerodynamic surface of each dovetail is parallel to the UAV's plane of symmetry, and its root is hinged to the rear of the UAV fuselage. The landing control enhancement method, when the UAV begins its descent and landing, pre-determines the preset angle of the dovetails to enhance landing control. This invention solves the problem of poor stability and maneuverability during low-speed, high-angle-of-attack landing flights in existing technologies.

Description

Technical Field

[0001] This invention belongs to the field of unmanned aerial vehicles (UAVs), specifically relating to a distributed dynamic UAV with a swallowtail design and a landing control enhancement method thereof. Background Technology

[0002] Low-speed, high-aspect-ratio, long-endurance unmanned aerial vehicles (UAVs), especially ultra-long-endurance solar-powered UAVs, are easily affected by wind during flight due to their low wing loading, leading to decreased flight stability and control precision. Particularly during landing, to reduce touchdown speed and improve flight safety, UAVs often fly at low speeds and high angles of attack, resulting in weaker trajectory and attitude stability compared to the cruise phase. However, to land safely at the designated location on the runway, these UAVs require faster response times and higher trajectory control precision. Therefore, safe landing of these UAVs in complex environments presents significant challenges.

[0003] The existing automatic landing control methods for UAVs have made a lot of work on the landing flight control algorithm, but still have the following two major defects: (1) They do not take into account the flight dynamics characteristics of actual low-speed, high angle of attack landing flight, and do not evaluate the impact of reduced flight stability and maneuverability on the control effect, which may ultimately lead to the inability to meet the requirements of speed and accuracy of landing trajectory control; (2) In order to enhance maneuverability, if the control surfaces are simply increased or added on the original basis, the structural weight of the entire aircraft will be increased, thereby affecting the long-endurance performance of the UAV. Summary of the Invention

[0004] The technical problem to be solved:

[0005] To overcome the shortcomings of existing technologies, this invention provides a distributed propulsion and swallowtail-based unmanned aerial vehicle (UAV) and its landing control enhancement method. This UAV discretizes and distributes its propeller and vertical tail symmetrically relative to the UAV's symmetrical plane. When the UAV begins its descent and landing, a preset angle of attack of the swallowtail is initially determined, thereby enhancing landing control. This invention solves the problem of poor stability and maneuverability during low-speed, high-angle-of-attack landing flights in existing technologies.

[0006] The technical solution of the present invention is: a distributed power combined with a dovetail unmanned aerial vehicle, comprising a fuselage, multiple pairs of propellers mounted along the spanwise direction at the front end of the fuselage, and multiple pairs of dovetails mounted along the spanwise direction at the rear end of the fuselage, wherein the propellers and dovetails are used in pairs and are symmetrically distributed about the drone.

[0007] The main aerodynamic surface of the dovetail is parallel to the plane of symmetry of the UAV, and its root is hinged to the rear end of the UAV fuselage.

[0008] A further technical solution of the present invention is that each pair of propellers is located on the spanwise outer side of its corresponding dovetail pair.

[0009] A further technical solution of the present invention is: the relative position R of the swallowtail in the spanwise direction of the UAV s,y The relative position R of the dovetail leading edge in the chord direction of the UAV is 0.1 to 1 times the spanwise length of the UAV. s,x Greater than or equal to 0.05 times the chord length of the drone.

[0010] A further technical solution of the present invention is: a plurality of connectors parallel to the plane of symmetry are installed along the span of the rear end of the fuselage, which are used to hinge each dovetail.

[0011] A further technical solution of the present invention is that the cross-section of the dovetail is airfoil-shaped.

[0012] A landing control enhancement method for a UAV with distributed dynamics and a swallowtail design, comprising the following steps:

[0013] Step 1: Obtain raw data for the swallowtail and the drone's propulsion system;

[0014] Step 2: Calculate the difference between the sideslip angle of the whole aircraft and the deflection angle of the dovetail control surface under the condition of lateral incoming flow for different dovetail angles, and obtain the local effective angle of attack of different dovetails, thereby calculating the aerodynamic force / moment of each dovetail.

[0015] Step 3: Decompose the aerodynamic force of the dovetail in the body coordinate system, obtain the moment of the dovetail relative to the moment reference point of the whole aircraft, then make it dimensionless, and differentiate it with respect to the sideslip angle of the whole aircraft to obtain the derivative of the heading static stability.

[0016] Step 4: Change the angle of the lateral incoming flow, repeat steps 2-3, and calculate the curves of the yaw moment coefficient and the derivative of the heading static stability as a function of the sideslip angle;

[0017] Step 5: Change the angle of the dovetail and repeat steps 2-3 to calculate the curves of the yaw moment coefficient and the derivative of the directional static stability as a function of the sideslip angle and the angle of the dovetail. Also, calculate the curves of the lift and drag coefficients of the entire aircraft as a function of the angle of the dovetail.

[0018] Step 6: Calculate the curves of the throttle and propeller speed of the power system as a function of the dovetail angle, based on different flight conditions;

[0019] Step 7: Under different propeller reference speeds, calculate the velocity increment of the distributed propellers at different positions when the UAV has a yaw rate, thereby calculating the additional directional damping derivative brought by the distributed propellers. Combined with Step 6, obtain the curve of the additional directional damping derivative of the UAV as a function of the dovetail angle.

[0020] Step 8: Based on Step 5, calculate the curves of damping and longitudinal trajectory stability of the UAV's long-period mode as a function of the dovetail angle;

[0021] Step 9: Based on the results of steps 5-8, select the swallowtail angle required to restore the stability and maneuverability of the UAV to the cruise state. When the UAV is about to switch from level flight to landing glide state, initially determine the preset swallowtail angle to this angle, thereby achieving the purpose of enhancing landing control.

[0022] A further technical solution of the present invention is: in step 1, the original data of the dovetail and the UAV power system include the lift, drag, and torque aerodynamic characteristics of the dovetail, its characteristics at large angles of attack / sideslip angles, the relationship curve of the propeller thrust coefficient with the advance ratio, and the relationship curve of the propeller speed with the power.

[0023] A further technical solution of the present invention is that when the angle of the swallowtail is preset to the range of 30-45 degrees, the heading static stability of the UAV is enhanced.

[0024] A further technical solution of the present invention is that when the dovetail angle increases from 0 degrees to 45 degrees, the long-period modal damping ratio increases from -0.02 to 0.05.

[0025] A further technical solution of the present invention is that the relative distance between the propellers is greater than 0.31 times the spanwise length, which can enhance the directional damping. The relative distance is the relative distance between the propellers and the plane of symmetry of the UAV.

[0026] Beneficial effects

[0027] The beneficial effects of the present invention are as follows: by using the technology created by the present invention, the directional flight stability and maneuverability of the UAV during the landing process can be enhanced, the directional damping characteristics of the UAV can be enhanced, and the long-period modal damping characteristics and longitudinal trajectory stability of the UAV can be enhanced.

[0028] From the perspective of flight dynamics design, this invention enhances the directional and longitudinal stability and maneuverability of UAVs in a minimalist manner without introducing a flight control system and with almost no weight loss. It is particularly beneficial for enhancing the landing performance of low-speed, high-aspect-ratio, long-endurance UAVs.

[0029] The more swallowtail and propellers the UAV has, the greater the spanwise distance relative to the center of gravity, and the more significant the effect of enhancing the UAV's heading and longitudinal stability, especially when encountering crosswinds during landing. Attached Figure Description

[0030] Figure 1 A schematic diagram of the drone's external shape (top view);

[0031] Figure 2A schematic diagram (top view) of yaw control for a swallowtail deflection in the same direction;

[0032] Figure 3 A schematic diagram of stabilization control for differential deflection of the swallowtail (top view);

[0033] Figure 4 Three-dimensional aerodynamic characteristic curves of the swallowtail; (a) lift coefficient; (b) drag coefficient; (c) moment coefficient;

[0034] Figure 5 The curves showing the relationship between the yaw moment coefficient and sideslip angle for the entire aircraft under different dovetail angles;

[0035] Figure 6 The additional drag coefficient of the entire machine caused by different dovetail angles;

[0036] Figure 7 For different dovetail angles, the long-period modal damping ratios are given;

[0037] Figure 8 This is a curve showing the relationship between the propeller's thrust coefficient and the advance ratio.

[0038] Figure 9 The additional directional damping derivative introduced by the distributed propeller;

[0039] Figure 10 To improve the yaw control efficiency of distributed propellers at different throttle settings;

[0040] Figure 11 For a lateral landing without opening the swallowtail (wind speed 2m / s); (a) horizontal trajectory, (b) lateral position deviation, (c) deviation between target height and actual height;

[0041] Figure 12 The target landing was a lateral landing with the tail of the swallow open at 45 degrees (wind speed 7 m / s); (a) horizontal trajectory; (b) lateral position deviation; (c) deviation between target height and actual height.

[0042] Explanation of reference numerals in the attached diagram: 1 represents the wing of the UAV; 21, 22, 23, 24... represent distributed dovetails; 31, 32, 33, 34... represent the aerodynamic centers of the dovetails; 41, 42, 43, 44... represent the hinges connecting the dovetails to the fuselage, around which the dovetails can rotate; 51, 52, 53, 54... represent distributed propellers; 6 represents the center of gravity of the UAV. Detailed Implementation

[0043] The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the invention, and should not be construed as limiting the invention.

[0044] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," and "counterclockwise," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0045] Due to the limitations of existing technologies in meeting the requirements for speed and accuracy in landing trajectory control, and the fact that increasing the number of control surfaces would increase the overall structural weight of the UAV and thus affect its long-endurance performance, this invention provides a distributed propulsion combined with a dovetail UAV and its landing control enhancement method. The UAV includes a fuselage, multiple pairs of propellers mounted longitudinally at the front of the fuselage, and multiple pairs of dovetails mounted longitudinally at the rear of the fuselage. The number of propellers and dovetails corresponds one-to-one, and they are symmetrically distributed about the UAV's plane of symmetry. The main aerodynamic surface of each dovetail is parallel to the UAV's plane of symmetry, and its root is hinged to the rear of the UAV fuselage. The landing control enhancement method involves, upon initiating the descent and landing, symmetrically opening the dovetails to a designed angle as a baseline state. This angle is determined comprehensively based on the aerodynamic characteristics of the dovetails, the UAV's directional static stability, directional maneuverability, directional modal characteristics, long-period modal stability, and propeller thrust characteristics. The technology invented in this invention can enhance the directional flight stability and maneuverability of a UAV during landing, improve its directional damping characteristics, and enhance its long-period modal damping characteristics and longitudinal trajectory stability. The specific technical solution is as follows:

[0046] (1) Design of landing control enhancement device

[0047] ① Based on the overall characteristics of the UAV, the power system and vertical tail / rudder were designed. The propellers and vertical tail were discretized and distributed, resulting in one or more pairs of propellers and dovetails symmetrically distributed relative to the vertical plane of the UAV, such as... Figure 1 As shown, the propeller is located in the front half of the aircraft, and the dovetail is located in the rear half of the aircraft, with a certain distance from the wings. The main aerodynamic surface is parallel to the plane of symmetry of the UAV. Each set of propellers and dovetails can be controlled independently. The farther the propellers and dovetails are from the plane of symmetry, the more obvious the effect of enhancing stability and maneuverability.

[0048] ② The leading edge of the dovetail is connected to the fuselage via a hinge. During cruise flight, to reduce drag and increase flight time, the initial position of the dovetail is set so that the chord direction is parallel to the x-axis of the fuselage axis. During flight, it can be swung left and right in the same direction as needed to be used as a regular rudder. The differential motion of the distributed propellers on the left and right wings is used as a directional control enhancement device (e.g., Figure 2 (As shown). When enhanced flight stability and maneuverability are required, especially during the landing phase, the swallowtail can be differentially extended to a designated position as a reference state, thereby enhancing stability and maneuverability (e.g. Figure 3 (as shown);

[0049] (2) Design landing control enhancement methods

[0050] When beginning the descent and landing, the dovetail is symmetrically extended to a designed angle as the baseline state. This angle is determined comprehensively based on the aerodynamic characteristics of the dovetail, the UAV's directional static stability, directional maneuverability, directional modal characteristics, as well as the stability of long-period modes and the propeller thrust characteristics. The specific steps are as follows:

[0051] ① Obtain raw data on the dovetail and propulsion system: Obtain the lift, drag, and torque aerodynamic characteristics of the dovetail, especially its characteristics at high angles of attack / sideslip angles; Obtain the curves showing the relationship between the propeller thrust coefficient and the advance ratio, as well as the curves showing the relationship between the propeller speed and the power.

[0052] ② Spread the swallowtail at different angles;

[0053] ③ Under the condition of lateral airflow across the entire aircraft, the local effective angle of attack of different dovetails is obtained by calculating the difference between the sideslip angle of the entire aircraft and the deflection angle of the dovetail control surface. Thus, the aerodynamic force / moment of each dovetail is calculated. Special attention is paid to the problem of sudden change in yaw moment caused by vertical tail stall due to large crosswinds and large sideslip that are more likely to be encountered by low-speed, high-aspect-ratio, long-endurance UAVs during the landing phase.

[0054] ④ Decompose the aerodynamic force of the dovetail in the body coordinate system, obtain the moment of the dovetail relative to the moment reference point of the whole aircraft, then make it dimensionless, and differentiate it with respect to the sideslip angle of the whole aircraft to obtain the derivative of the heading static stability.

[0055] ⑤ Change the angle of the lateral incoming flow and repeat steps ③-④ to calculate the curves of the yaw moment coefficient and the derivative of the heading static stability as a function of the sideslip angle;

[0056] ⑥ Change the angle of the swallowtail and repeat steps ②-④ to calculate the curves of the yaw moment coefficient and the derivative of the heading static stability as a function of the sideslip angle and the angle of the swallowtail. Also, calculate the curves of the lift and drag coefficients of the entire aircraft as a function of the angle of the swallowtail.

[0057] ⑦ Based on different flight conditions (especially focusing on speed, climb / glide angle, etc.), calculate the curves of the power system throttle and propeller speed as a function of the dovetail angle;

[0058] ⑧ Under different propeller reference speeds, calculate the velocity increment of the distributed propellers at different positions when the UAV has a yaw angular velocity, thereby calculating the additional directional damping derivative brought by the distributed propellers. Combined with step ⑦, obtain the curve of the additional directional damping derivative of the UAV as a function of the dovetail angle.

[0059] ⑨ Based on step ⑥, the curves of damping and longitudinal trajectory stability of the UAV's long-period mode as a function of the dovetail angle are calculated;

[0060] ⑩ Based on steps ⑥-⑨, especially step ⑦, focus on the decrease in directional damping and longitudinal trajectory stability caused by the decrease in rotor speed when switching from the cruise level flight phase to the glide landing phase, before the dovetail is fully extended. Find the dovetail angle required to restore the stability and maneuverability of the UAV to the cruise state. When the UAV is about to switch from level flight to the landing glide landing state, initially determine the preset dovetail angle to this angle, thereby achieving the purpose of enhancing landing control.

[0061] In the case of landing in strong crosswinds, by combining the yaw moment coefficients of different swallowtail angles and different sideslip angles, and taking into account factors such as greater heading stability, the size of the sideslip angle that begins to appear nonlinearly, and step 10, the pre-set swallowtail angle is finally determined, thereby obtaining the landing under the condition of landing in strong crosswinds (1) attached figure.

[0062] The technical solution will be further explained below with reference to the accompanying drawings.

[0063] Reference Figure 1 The diagram shown is a top view of the UAV. 1 is the wing of the UAV; 21, 22, 23, 24... are distributed dovetails; 31, 32, 33, 34... are the aerodynamic centers of the dovetails; 41, 42, 43, 44... are the hinges connecting the dovetails to the fuselage, around which the dovetails can rotate; 51, 52, 53, 54... are distributed propellers; 6 is the center of gravity of the UAV, which is also the point of application of the torque of the entire aircraft.

[0064] Each of the distributed dovetails and propellers can be independently controlled. The two typical control modes of the dovetails are unidirectional deflection and differential deflection, as shown below: Figure 2 and Figure 3 As shown.

[0065] (1) Implementation method for increasing heading stability by the dovetail angle

[0066] exist Figure 3In this context, β is the sideslip angle, defined as the airflow angle from the body axis x. b The direction of the wind blowing from the right is positive; δ s The dovetail deflection angle is defined by referring to the definition of the rudder deflection angle, where the trailing edge of the dovetail swings to the left as positive.

[0067] As shown in the figure, under positive sideslip flight conditions, the airflow angle of the left swallowtail is smaller than that of the right swallowtail. These different airflow angles result in different aerodynamic characteristics, providing a basis for the flight dynamics stabilization design of the swallowtail.

[0068] Among them, the local effective angle of attack α of any one of the swallowtails s The calculation formula is:

[0069] α s =β-δ s (1)

[0070] The aerodynamic force generated by the swallowtail in the horizontal plane is decomposed into lift and drag, denoted as L and D respectively, where L is along the y-axis. a The negative direction, D along x a The negative direction. Their calculation formulas are:

[0071]

[0072] Where: Q is the dynamic pressure of the drone, S s This represents the area of ​​a single swallowtail. The lift coefficient C. L and drag coefficient C D It can be obtained by three-dimensional correction from the airfoil aerodynamic database of the swallowtail.

[0073] The aerodynamic forces of the swallowtail in the body coordinate system are decomposed as follows:

[0074]

[0075] Wherein: F x and F y Let x and y represent the aerodynamic forces of the swallowtail in the body coordinate system. b and y b Components on the axis.

[0076] Therefore, the yaw moment generated by the aerodynamic force of the swallowtail relative to the center of gravity of the entire aircraft can be obtained as follows:

[0077]

[0078] Where: R s,y and R s,x These represent the relative positions of the swallowtail in the spanwise and chordwise directions of the drone, respectively.

[0079] Substituting the equation into the equation and expanding it, we obtain the yaw moment about the aircraft's center of gravity generated by the lift and drag of the dovetail:

[0080] N = R s,y (Dcosβ-Lsinβ)-R s,x (Dsinβ+Lcosβ) (5)

[0081] The pitching moment of the swallowtail generates the yaw moment about the aircraft's center of gravity as follows:

[0082] N m =-C m QS s c s (6)

[0083] Where: c s Let C be the average aerodynamic chord length of a single dovetail joint. Pitch moment coefficient C m It can be obtained by three-dimensional correction from the airfoil aerodynamic database of the swallowtail.

[0084] Combining the formulas, the yaw moment coefficient of the i-th swallowtail relative to the whole aircraft is obtained as follows:

[0085]

[0086] Where S and b are the reference area and span of the entire aircraft, respectively.

[0087] Its dimensionless form is:

[0088]

[0089] in:

[0090]

[0091] To more intuitively understand the influence of the swallowtail on the directional stability of the UAV, the above equation is expanded with small perturbations. When the change in the airflow angle on the swallowtail is small, the first-order approximate calculation formulas for its lift, drag, and pitching moment are as follows:

[0092]

[0093] Where: C Lα C Dα and C mα Let be the derivatives of the swallowtail at the calculated effective angle of attack. Substituting this into the equation, we get:

[0094]

[0095] Therefore, the derivative of the overall yaw moment coefficient with respect to the sideslip angle (the derivative of the heading static stability) when the initial sideslip angle is 0 can be obtained as follows:

[0096]

[0097] The second to last term in the above formula This is the derivative of the directional static stability generated by the conventional vertical tail. Furthermore, note the C in the above equation. Lα C Dα and C mα This is related to the angle of the swallowtail. Therefore, by rationally designing the relative positions of the distributed swallowtails in the drone's spanwise direction... and And a positive swallowtail angle δ is preset. s , making If the value is positive, a larger directional static stability coefficient can be obtained than that of a conventional vertical tail.

[0098] Specifically, taking the swallowtail located at the rear right side of the aircraft as an example, its position is... When the effective angle of attack is greater than 0, the aerodynamic characteristics of the dovetail are C. Dα >0, C mα <0, C Lα <0 near the stall angle of attack, while >0 at other angles of attack (e.g.) Figure 4 As shown in the figure, according to the formula, when the sideslip angle is 0, the effective angle of attack > 0 corresponds to δ s <0, meaning the rear edge of the swallowtail on the right side swings to the right. At this point, according to the formula, besides... Item in C Lα >0 will weaken C nβ Besides, the other four items will enhance C. nβ Therefore, a larger directional static stability derivative can be obtained than that of a conventional vertical tail.

[0099] Similarly, for the dovetail located at the left rear of the aircraft, swinging its trailing edge to the left achieves the same directional static stability enhancement effect as swinging the trailing edge of the right rear dovetail to the right. In this case, the overall dovetail is flared outwards, as shown... Figure 3 As shown, the swallowtail angle mentioned later refers to the left swallowtail swinging to the left and the right swallowtail swinging to the right together to that angle.

[0100] According to the formula, the yaw moment coefficients corresponding to different opening angles and sideslip angles of each swallowtail are calculated, and the summation is used to obtain the yaw moment coefficients of the entire aircraft. Then, by differentiating with respect to the sideslip angle, a more accurate law of the influence of different swallowtail opening angles and different sideslip angle states on the heading static stability of the UAV can be obtained.

[0101] Example 1: Using a dovetail to increase heading stability

[0102] An existing small solar-powered drone is equipped with a pair of distributed dovetails. The aerodynamic characteristics of a single dovetail after three-dimensional correction are as follows:

[0103] Based on this, the pre-set dovetail angle δ sThe yaw moment coefficient curves for the entire aircraft at different sideslip angles of 0, 10, 20, 30, 40, 45, 50, and 60 degrees are calculated as follows: Figure 5 Down:

[0104] according to Figure 5 First, observe the small lateral angle state. When the swallowtail angle is 10 or 20 degrees, C nβ When the angle is less than 0 degrees; while when the swallowtail angle is 30 or 40 degrees, C nβ The case where the angle of the swallowtail is greater than 0 degrees; when the angle of the swallowtail is δ s At 45 degrees, the yaw moment coefficient at a sideslip angle β of 8 degrees is almost identical to that when the swallowtail is not spread; when the swallowtail angle is greater than 50 degrees, C nβ Furthermore, the angle is less than 0 degrees. Therefore, by presetting the angle of the swallowtail to the range of 30-45 degrees, the directional static stability of the UAV relative to the 0-degree angle will be enhanced.

[0105] Next, observe the state of the large lateral angle: For a swallowtail angle of 0 degrees, when the sideslip angle is greater than 11 degrees, the lift coefficient of the swallowtail begins to decrease sharply, thus causing C... n It also decreases sharply, and when the sideslip angle is in the range of 11-19 degrees, it is directionally statically unstable (C). nβ <0), when the sideslip angle is greater than 19 degrees, the lift coefficient begins to increase again, and the drag coefficient also becomes greater than the lift coefficient, becoming the dominant value. Furthermore, the drag coefficient exhibits a stronger linear characteristic, thus the UAV's heading becomes statically stable again. For the dovetail angle δ s When the angle is 45 degrees, after the sideslip angle exceeds 11 degrees, its C n Significantly greater than δ s The case at 0 degrees, especially at a sideslip angle of 22 degrees, shows a 7-fold increase, and maintains good linearity up to 27 degrees. While nonlinearity also appears beyond 27 degrees, its C... n Overall, it is still better than δ s At 0 degrees, it is about twice as large. Further calculations show that, assuming the solar-powered drone's flight speed is 10 m / s, and sideslip angles of 11 and 27 degrees correspond to crosswinds of 1.9 m / s and 4.5 m / s respectively, then, under the constraint that the drone's directional moment coefficient does not exhibit obvious nonlinear characteristics, opening the tail by 45 degrees can increase the drone's maximum tolerable crosswind by 2.4 times.

[0106] In other words, by presetting the angle of the distributed swallowtail to the range of 30-45 degrees, the stall characteristics of the swallowtail can be delayed, resulting in stronger directional static stability and crosswind resistance.

[0107] (2) Implementation of increasing the dovetail angle for long-period modal damping

[0108] According to flight dynamics, the damping ratio of an aircraft's long-period mode is approximately proportional to the drag coefficient of the reference state. Therefore, as the dovetail angle increases, the damping ratio of the UAV's long-period mode increases, thereby improving the UAV's trajectory stability.

[0109] The formula for calculating the increase in the drag coefficient of the entire aircraft after the swallowtail is opened is:

[0110]

[0111] Where: subscript i represents the i-th swallowtail; ΔC D,i S represents the increment of the drag coefficient of the i-th swallowtail. s,i Let S represent the area of ​​the i-th swallowtail, and let S represent the total wing area of ​​the aircraft.

[0112] Example 2: Using dovetail joints to increase long-period modal damping

[0113] according to Figure 4 The drag coefficient increment after the i-th dovetail opens can be calculated. Then, according to the formula, the overall drag coefficient increment for different dovetail opening angles can be calculated, such as... Figure 6 As shown:

[0114] Depend on Figure 6 It can be seen that when the dovetail angle is 45 degrees, the overall drag coefficient increases by approximately 0.07, nearly doubling compared to the 0-angle state. Further calculations reveal the relationship between the long-period modal damping ratio and the dovetail angle for this example UAV in cruise mode. Figure 7 As shown;

[0115] Depend on Figure 7 It can be seen that when the swallowtail angle increases from 0 to 45 degrees, the long-period mode damping ratio increases from -0.02 (divergent) to 0.05, which is greater than the first-level flight quality requirement, and significantly enhances the flight quality characteristics of the long-period mode.

[0116] (3) Implementation of Distributed Propellers to Increase Heading Damping and Heading Control Capability

[0117] After the distributed propellers deviate from the plane of symmetry of the UAV, when the UAV has a yaw angular velocity r, the forward velocity increment ΔV on the shaft of one of the propellers is approximately:

[0118] ΔV=-rR p (13)

[0119] Where: R p The distance from the propeller to the overall torque reference point (center of gravity) of the aircraft (e.g.) Figure 1 (As shown).

[0120] The propeller's advance ratio increment ΔJ is:

[0121]

[0122] In the formula: n is the rotational speed of the propeller, and D represents the diameter of the propeller disk.

[0123] At this point, the increase in propeller thrust ΔT caused by the yaw angular velocity is:

[0124]

[0125] Among them: For a typical propeller, near the cruise state there are

[0126] The additional yawing moment ΔN caused by the increase in propeller thrust is:

[0127] ΔN=-ΔTR p (16)

[0128] Dimensionlessizing it, we get:

[0129]

[0130] The additional yaw damping derivative is further obtained as follows:

[0131]

[0132] Therefore, it can be seen that, due to Therefore, ΔC nr <0, meaning that distributed propellers along the spanwise direction will increase the yaw damping of the UAV, and the distance R from the propeller to the plane of symmetry. p The larger the value, the more significant the increase in yaw damping.

[0133] Example 3: Using distributed propellers to increase directional damping

[0134] Taking a UAV consistent with Embodiment 1 as an example, the directional damping coefficient generated by the aerodynamic layout of this aircraft is approximately -0.004 when the dovetail angle is 0 degrees in cruise mode. This aircraft uses two distributed propellers symmetrically arranged on the left and right wings.

[0135] The curve showing the relationship between the thrust coefficient of a single propeller and the advance ratio is as follows: Figure 8 As shown.

[0136] The relative distance (y_rel = 2*R) from the distributed propeller to the UAV's plane of symmetry was calculated. p / b) When the change occurs, the increment of the directional damping derivative caused by the propeller is as follows: Figure 9As shown in the figure, when the relative distance between the distributed propellers is 0.31, the incremental increase in the derivative of the additional directional damping is already equal to that generated by the aerodynamic layout, achieving a significant enhancement in directional damping.

[0137] Similarly, when the distributed propellers on both wings are differentially controlled, a yaw moment that is significantly greater than that of the swallowtail deflection used as a rudder can be generated, thus achieving significant heading control capability.

[0138] (4) Implementation of Distributed Propellers and Swallowtails to Enhance Course Control During Landing

[0139] When using distributed propeller differential for yaw control, analogous to a rudder, its maneuverability can be... To describe, where δ d This represents the throttle difference between the left and right sides of the drone's plane of symmetry. The calculation formula is:

[0140]

[0141] Where: δ t This represents the total throttle level of the drone.

[0142] This demonstrates that the yaw control performance of distributed propellers is related to... It can be directly proportional. (From...) Figure 8 It can be seen that, The yaw control efficiency is lower at low throttle and highest at medium throttle. During cruise, the drone operates at a medium throttle, but during landing, the required power for descent is minimal, or even zero, resulting in a significant decrease in yaw control effectiveness. Therefore, employing a swallowtail-shaped landing glide approach increases drag, necessitating a larger trim throttle. This allows the yaw control efficiency during the landing glide phase to be restored to a level comparable to that during cruise, enhancing landing control capabilities.

[0143] Example 4: Using distributed propellers and dovetails to increase directional control capability during landing.

[0144] according to Figure 8 The yaw control performance curves of the distributed propeller at the same flight speed and different throttles, calculated using the formula, are as follows: Figure 10 As shown.

[0145] This demonstrates that, compared to the normal glide flight state with the tail not extended (throttle approximately 0.1), the yaw control efficiency in the cruise state (throttle approximately 0.4) is increased by about 5 times. Therefore, extending the tail during the landing glide phase to increase the drag of the UAV and restore the throttle to near the cruise state will further enhance the UAV's yaw control capability, thereby facilitating the implementation of control stabilization.

[0146] (5) Implementation of Distributed Propeller and Swallowtail Landing Control Enhancement

[0147] Example 5: Enhancing Landing Control with Distributed Propellers and Dovetails

[0148] When a drone lands in a crosswind, it may veer sideways due to wind interference, thus affecting landing safety. To ultimately verify the effectiveness of the landing control enhancement method using distributed propellers and a dovetail mechanism proposed in this patent, two landing control tests were conducted on the same high aspect ratio solar-powered drone.

[0149] During the first landing, the crosswind was approximately 2 m / s, and the tail of the aircraft did not extend. The landing trajectory and lateral position deviation at this time were as follows: Figure 11 As shown.

[0150] During the second landing, the crosswind was approximately 7 m / s, causing the swallowtail to spread at a 45-degree angle. The landing trajectory and lateral position deviation at this point were as follows: Figure 11 As shown.

[0151] Reference Figure 12 As shown in the figure, comparing the two landing results reveals that the second landing was at a higher altitude and with higher wind speeds, which was more unfavorable for flight. The figure also shows that the initial errors in altitude and lateral trajectory of the UAV after turning and aligning with the runway were larger than in the first landing. However, due to the 45-degree opening of the swallowtail, the UAV's subsequent lateral position deviation curve was smoother and converged faster. The tracking errors in lateral position and altitude converged to zero more quickly, demonstrating a significant landing control enhancement effect. This verifies the effectiveness of the UAV landing control enhancement method using distributed dynamics combined with the swallowtail proposed in this patent. (Control Enhancement)

[0152] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled 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 principles and spirit of the present invention.

Claims

1. A method for enhancing landing control of a UAV with distributed dynamics and a swallowtail design, characterized in that, The specific steps are as follows: Step 1: Obtain raw data for the swallowtail and the drone's propulsion system; Step 2: Calculate the difference between the sideslip angle of the whole aircraft and the deflection angle of the dovetail control surface under the condition of lateral incoming flow for different dovetail angles, and obtain the local effective angle of attack of different dovetails, thereby calculating the aerodynamic force / moment of each dovetail. Step 3: Decompose the aerodynamic force of the dovetail in the body coordinate system, obtain the moment of the dovetail relative to the moment reference point of the whole aircraft, then make it dimensionless, and differentiate it with respect to the sideslip angle of the whole aircraft to obtain the derivative of the heading static stability. Step 4: Change the angle of the lateral incoming flow, repeat steps 2-3, and calculate the curves of the yaw moment coefficient and the derivative of the heading static stability as a function of the sideslip angle; Step 5: Change the angle of the dovetail and repeat steps 2-3 to calculate the curves of the yaw moment coefficient and the derivative of the directional static stability as a function of the sideslip angle and the angle of the dovetail. Also, calculate the curves of the lift and drag coefficients of the entire aircraft as a function of the angle of the dovetail. Step 6: Calculate the curves of the throttle and propeller speed of the power system as a function of the dovetail angle, based on different flight conditions; Step 7: Under different propeller reference speeds, calculate the velocity increment of the distributed propellers at different positions when the UAV has a yaw rate, thereby calculating the additional directional damping derivative brought by the distributed propellers. Combined with Step 6, obtain the curve of the additional directional damping derivative of the UAV as a function of the dovetail angle. Step 8: Based on Step 5, calculate the curves of damping and longitudinal trajectory stability of the UAV's long-period mode as a function of the dovetail angle; Step 9: Based on the results of steps 5-8, select the swallowtail angle required to restore the stability and maneuverability of the UAV to the cruise state. When the UAV is about to switch from level flight to landing glide state, initially determine the preset swallowtail angle to this angle, thereby achieving the purpose of enhancing landing control. The distributed power combined with dovetail drone includes a fuselage, multiple pairs of propellers mounted along the span of the front of the fuselage, and multiple pairs of dovetails mounted along the span of the rear of the fuselage. The propellers and dovetails are used in pairs and are symmetrically distributed about the drone. The main aerodynamic surface of the dovetail is parallel to the plane of symmetry of the UAV, and its root is hinged to the rear end of the UAV fuselage.

2. The landing control enhancement method according to claim 1, characterized in that: Each pair of propellers is located outward in the spanwise direction of its corresponding dovetail pair.

3. The landing control enhancement method according to claim 1, characterized in that: The relative position of the swallowtail in the drone's span The relative position of the leading edge of the dovetail along the chord direction of the UAV is 0.1 to 1 times the spanwise length of the UAV. Greater than or equal to 0.05 times the chord length of the drone.

4. The landing control enhancement method according to claim 1, characterized in that: The rear end of the fuselage is equipped with multiple connectors parallel to the plane of symmetry, which are used to hinge each dovetail.

5. The landing control enhancement method according to claim 1, characterized in that: The cross-section of the swallowtail is airfoil-shaped.

6. The landing control enhancement method according to claim 1, characterized in that: In step 1, the raw data of the dovetail and UAV power system include the lift, drag, and torque aerodynamic characteristics of the dovetail, its characteristics at large angles of attack / sideslip angles, the propeller thrust coefficient as a function of the advance ratio, and the propeller speed as a function of power.

7. The landing control enhancement method according to claim 1, characterized in that: When the angle of the swallowtail is preset to the range of 30-45 degrees, the directional static stability of the UAV is enhanced.

8. The landing control enhancement method according to claim 1, characterized in that: When the dovetail angle increases from 0 degrees to 45 degrees, the long-period modal damping ratio increases from -0.02 to 0.

05.

9. The landing control enhancement method according to claim 1, characterized in that: The relative distance between the propellers is greater than 0.31 times the spanwise length, which can enhance directional damping. The relative distance is the distance between the propellers and the plane of symmetry of the UAV.

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