Method and device for increasing flutter critical speed of unmanned aerial vehicle with variable wingtip and high aspect ratio

Abstract

The invention provides a method and device for increasing the flutter critical speed of an unmanned aerial vehicle with variable wingtips and a large aspect ratio, and the method comprises the steps: carrying out the flutter analysis of the deflection process of a first-stage wingtip, and finding out the flutter critical speed after the deflection angle of the first-stage wingtip exceeds a deflection critical point (the deflection angle point corresponding to the peak value of the flutter critical speed); the flutter critical speed of the unmanned aerial vehicle can be improved by controlling the secondary wingtips to deflect and be parallel to the main wings. Based on the discovery, the deflection critical point of the first-stage wingtip is firstly obtained through flutter analysis, the deflection angle of the first-stage wingtip is judged in real time in the deflection process, the second-stage wingtip is controlled to deflect after the deflection angle of the first-stage wingtip exceeds the critical point, and the second-stage wingtip is kept parallel to the main wing until the first-stage wingtip reaches the target deflection angle; and the first-stage wingtip and the second-stage wingtip are locked without deflection. Through verification and analysis, the flutter critical speed improvement effect of the unmanned aerial vehicle is remarkable, the flutter critical speed is increased along with the increase of the deflection angle of the first-level wingtip, and safe flight of the unmanned aerial vehicle is ensured.

Description

Technical Field

[0001] The present invention belongs to the technical field of aeroelastic design of wingtip-variable unmanned aerial vehicles (UAVs), and in particular relates to a method and device for improving the flutter critical speed of a UAV with a large aspect ratio and variable wingtip. Background Art

[0002] Flutter is a self-excited, divergent vibration caused by the coupling of unsteady aerodynamic forces with the elastic structure of an aircraft. It can cause catastrophic damage to the aircraft structure and pose a serious threat to flight safety. High-aspect-ratio wings, due to their low structural stiffness and high flexibility, present particularly significant aeroelastic challenges. High-aspect-ratio wingtip-variable UAVs, based on variable wingtip technology, overcome the shortcomings of traditional fixed wingtips in off-design operating conditions. By varying the wingtip deflection angle according to different flight conditions, the wing achieves optimal aerodynamic performance across the entire flight envelope. However, at different wingtip deflection angles, the mass and stiffness distribution of the wing structure changes, and so does its aeroelastic properties. When the wingtip length of a high-aspect-ratio UAV is long, the critical flutter speed begins to decrease from its peak value after the wingtip deflection angle increases to a critical point. This decrease in critical flutter speed limits the safe flight range of the UAV at large wingtip deflection angles, thereby restricting the UAV's overall flight envelope.

[0003] Currently, methods for improving critical flutter speed include increasing wing stiffness and optimizing wing mass distribution. However, these methods have limited effectiveness in improving critical flutter speed. Increasing wing stiffness increases the weight of the wing structure, negatively impacting the overall performance of the drone, such as reducing its maneuverability. Wing mass distribution optimization methods are limited by the overall center of gravity of the drone, resulting in a narrow adjustable mass range and difficulty in achieving significant optimization, which also limits the improvement of critical flutter speed. Summary of the Invention

[0004] In order to improve the problem of the decrease in the critical flutter speed of a large aspect ratio UAV with variable wingtips after the wingtip deflection angle exceeds the critical point, the applicant of the present invention analyzed and studied the deflection process of the first-stage wingtip in the variable wingtip, and found through multiple deflection tests that after the first-stage wingtip deflection angle exceeds the critical point, when the second-stage wingtip is driven to deflect parallel to the main wing, the critical flutter speed of the UAV will not only not decrease, but will be significantly improved.

[0005] Based on the above findings, the technical solution provided by the present invention is:

[0006] A method for improving the flutter critical speed of a high-aspect-ratio UAV with variable wingtips, wherein the wingtips include a primary wingtip and a secondary wingtip that are rotatably connected; the improving method comprises the following steps:

[0007] Step 1: Under the conditions that the first-stage wingtip is deflected and the second-stage wingtip is not deflected, obtain the first-stage wingtip deflection angle corresponding to the peak value of the UAV flutter critical speed, and use this first-stage wingtip deflection angle as the first-stage wingtip deflection angle critical point;

[0008] Step 2: Wingtip deflection control:

[0009] Step 2.1: Initially, lock the primary and secondary wingtips so that they do not deflect and are parallel to the main wing.

[0010] Step 2.2: Unlock the primary wingtip, drive the primary wingtip to deflect and lift, and obtain the primary wingtip deflection angle in real time to determine whether the primary wingtip deflection angle exceeds the primary wingtip deflection angle critical point; if not, keep the secondary wingtip in a locked state; if so, unlock the secondary wingtip, and drive the secondary wingtip to deflect in a direction opposite to the rotation direction of the primary wingtip; continue to drive the primary and secondary wingtip deflection until the primary wingtip deflects to a preset target angle and the secondary wingtip is parallel to the main wing, and lock the primary and secondary wingtip at the same time to terminate the deflection movement of the two.

[0011] Furthermore, in step 1, the critical point of the first-level wingtip deflection angle is obtained by the following method:

[0012] Step 1.1: Obtain the deflectable angle range of the first-stage wingtip and divide it into multiple discrete deflection levels; the deflection intervals between adjacent deflection levels are configured to be equal intervals;

[0013] Step 1.2: Under the condition that the secondary wingtip does not deflect, use the flutter analysis method to calculate the UAV's critical flutter speed when the primary wingtip is deflected to different deflection levels; obtain the peak value of the UAV's critical flutter speed, and use the primary wingtip deflection angle corresponding to this peak value as the primary wingtip deflection angle critical point.

[0014] Furthermore, the deflection interval is no greater than 15°.

[0015] Furthermore, in step 2.2, after the primary wingtip deflection angle is greater than the primary wingtip deflection angle critical point, the primary wingtip deflection angle and the secondary wingtip deflection angle are obtained in real time, and the primary wingtip and the secondary wingtip are continuously driven to deflect until the secondary wingtip deflection angle is equal to the primary wingtip deflection angle, the secondary wingtip is parallel to the main wing, and the primary wingtip and the secondary wingtip are locked at the same time, and the primary wingtip and the secondary wingtip stop rotating.

[0016] The present invention also provides a device for increasing the critical flutter speed of a large aspect ratio UAV with variable wingtips. The UAV variable wingtips include a primary wingtip and a secondary wingtip. The two ends of the primary wingtip are connected to the end of the main wing and the end of the secondary wingtip through a primary wingtip hinge and a secondary wingtip hinge, respectively. The device for increasing the critical flutter speed of the UAV includes:

[0017] A data acquisition unit, used to detect the deflection angles of the first and second wingtips in real time;

[0018] The wingtip drive control unit is configured with a primary wingtip deflection angle critical point; and is used to: receive detection data from the data acquisition unit, and when the primary wingtip deflection angle is greater than the primary wingtip deflection angle critical point, control the unlocking of the secondary wingtip hinge and drive the secondary wingtip to rotate in the opposite direction until the secondary wingtip deflection angle data is consistent with the primary wingtip deflection angle data.

[0019] Furthermore, the data acquisition unit includes a primary angle sensor and a secondary angle sensor; the primary angle sensor is installed on the primary wingtip hinge to detect the rotation angle of the primary wingtip hinge; the secondary angle sensor is installed on the secondary wingtip hinge to detect the rotation angle of the secondary wingtip hinge.

[0020] Furthermore, the length of the secondary wingtip is determined according to the following method:

[0021] Step S1: Establish a simulation model of a UAV with variable wingtips, obtain the total length of the variable wingtips, and initialize the primary wingtip length and the secondary wingtip length;

[0022] Step S2: Setting the adjustment step size, adjusting the primary wingtip length and the secondary wingtip length by variable parameters, and performing flutter analysis on the UAV. When the primary wingtip is deflected to different deflection levels, the critical flutter speed of the UAV is obtained when the secondary wingtip is deflected to be parallel to the main wing.

[0023] Step S3: Compare the critical flutter speeds of the drone corresponding to secondary wingtips of different lengths, and take the secondary wingtip with the greatest improvement in the critical flutter speed of the drone as the optimal secondary wingtip.

[0024] Furthermore, the adjustment step length is no greater than 0.1 m.

[0025] The advantages of the present invention are:

[0026] 1. Without changing the original variable wingtip wing structure, the present invention's method drives the secondary wingtip to deflect in a direction opposite to the primary wingtip's deflection angle after the primary wingtip deflects to a point greater than a critical point, until the primary wingtip deflects to a target angle, maintaining the secondary wingtip parallel to the main wing. This significantly improves the critical flutter speed of a high-aspect-ratio drone with variable wingtips, ensuring drone flight safety. Taking the drone in the embodiment of the present invention as an example, the specific improvement effects are as follows:

[0027] (1) In Example 1, the critical point of the first-stage wingtip deflection angle is 60°. When the target deflection angle of the first-stage wingtip hinge is 75° and the secondary wingtip is parallel to the main wing, the critical flutter speed of the drone increases by 20.96%. When the target deflection angle of the first-stage wingtip hinge is 90° and the secondary wingtip is parallel to the main wing, the critical flutter speed of the drone increases by 55.96%.

[0028] (2) In Example 2, the critical point of the first-stage wingtip deflection angle is 45°. When the target deflection angle of the first-stage wingtip hinge is 60° and the secondary wingtip is parallel to the main wing, the critical flutter speed of the UAV is increased by 10.93%; when the target deflection angle of the first-stage wingtip hinge is 75° and the secondary wingtip is parallel to the main wing, the critical flutter speed of the UAV is increased by 47.83%; when the target deflection angle of the first-stage wingtip hinge is 90° and the secondary wingtip is parallel to the main wing, the critical flutter speed of the UAV is increased by 104.93%.

[0029] 2. Based on the different effects of improving the critical flutter speed of drones with different secondary wingtip lengths, the present invention also provides a method for determining the optimal length of the secondary wingtip. The secondary wingtip designed based on this method has the best effect of improving the critical flutter speed of the drone. BRIEF DESCRIPTION OF THE DRAWINGS

[0030] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0031] Figure 1 This is a flow chart of wingtip deflection control in a high aspect ratio UAV with variable wingtip;

[0032] Figure 2 A three-dimensional view of the UAV with variable wingtip and large aspect ratio;

[0033] Figure 3 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 0° and the second-stage wingtip not deflected;

[0034] Figure 4 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 15° and the second-stage wingtip not deflected;

[0035] Figure 5 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 30° and the second-stage wingtip not deflected;

[0036] Figure 6 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 45° and the second-stage wingtip not deflected;

[0037] Figure 7 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 60° and the second-stage wingtip not deflected;

[0038] Figure 8 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 75° and the second-stage wingtip not deflected;

[0039] Figure 9 This is a front view of the high aspect ratio drone with variable wingtips in Example 1 of the present application, with the first-stage wingtip deflection angle of 90° and the second-stage wingtip not deflected;

[0040] Figure 10 This is a front view of the high aspect ratio drone with variable wingtip in Example 1 of the present application, with a first-stage wingtip deflection angle of 75° and a second-stage wingtip deflection;

[0041] Figure 11 This is a front view of the high aspect ratio drone with variable wingtip in Example 1 of the present application, with a first-stage wingtip deflection angle of 90° and a second-stage wingtip deflection;

[0042] Figure 12 This is a comparison chart of the flutter critical speed before and after the secondary wingtip deflection of the high aspect ratio drone with variable wingtip in Example 1 of the present application at different secondary wingtip lengths;

[0043] Figure 13 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 0° and the second-stage wingtip not deflected;

[0044] Figure 14 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 15° and the second-stage wingtip not deflected;

[0045] Figure 15 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 30° and the second-stage wingtip not deflected;

[0046] Figure 16 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 45° and the second-stage wingtip not deflected;

[0047] Figure 17 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 60° and the second-stage wingtip not deflected;

[0048] Figure 18 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 75° and the second-stage wingtip not deflected;

[0049] Figure 19 This is a front view of the high aspect ratio drone with variable wingtips in Example 2 of the present application, with the first-stage wingtip deflection angle of 90° and the second-stage wingtip not deflected;

[0050] Figure 20 This is a front view of the high aspect ratio drone with variable wingtip in Example 2 of this application, with a first-stage wingtip deflection angle of 60° and a second-stage wingtip deflection;

[0051] Figure 21 This is a front view of the high aspect ratio drone with variable wingtip in Example 2 of this application, with a first-stage wingtip deflection angle of 75° and a second-stage wingtip deflection;

[0052] Figure 22 This is a front view of the high aspect ratio drone with variable wingtip in Example 2 of the present application, with a first-stage wingtip deflection angle of 90° and a second-stage wingtip deflection;

[0053] Figure 23 This is a comparison chart of the flutter critical speed before and after the deflection of the secondary wingtip of the variable-wingtip high aspect ratio drone in Example 2 of this application at different secondary wingtip lengths.

[0054] Description of reference numerals:

[0055] 100-UAV, 110-Fuselage, 120-Main wing, 121-First level wingtip, 122-Second level wingtip, 123-First level wingtip hinge,

[0056] 124-Secondary wingtip hinge. DETAILED DESCRIPTION

[0057] The following describes in detail embodiments of the present invention. The embodiments are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0058] To address the problem of a decrease in the critical flutter speed of a high-aspect-ratio wingtip variable-wingtip UAV after the wingtip deflection angle exceeds a critical point, an embodiment of the present invention provides a method for increasing the critical flutter speed of a high-aspect-ratio wingtip variable-wingtip UAV, comprising the following steps:

[0059] Step 1: Under the conditions of first-stage wingtip deflection and second-stage wingtip non-deflection, calculate the critical flutter speed of the UAV using flutter analysis, and obtain the first-stage wingtip deflection angle corresponding to the peak value of the UAV flutter critical speed, which is used as the critical point of the first-stage wingtip deflection angle. The specific process is as follows:

[0060] Step 1.1: Based on the deflection angle range of the first-stage wingtip of a high-aspect-ratio UAV with variable wingtip height, discretize the first-stage wingtip deflection angle into several deflection levels, with a deflection level of 6 or higher. The deflection intervals between adjacent deflection levels are equally spaced. The deflection intervals are set to no greater than 15°, and the smaller the deflection interval, the better, to ensure accurate determination of the critical point of the first-stage wingtip deflection angle.

[0061] Step 1.2: With the secondary wingtip undeflected, use flutter analysis to calculate the critical flutter speeds of the drone when the primary wingtip is deflected to different levels. Based on the trend of the critical flutter speed, determine the primary wingtip deflection angle at which the critical flutter speed reaches its peak. This primary wingtip deflection angle is the critical point at which the critical flutter speed begins to decrease.

[0062] Step 2: Design the wingtip drive control unit. The wingtip deflection control process is as follows: Figure 1 A primary angle sensor is provided at the primary wingtip hinge 123 , and a secondary angle sensor is provided at the secondary wingtip hinge 124 , which are respectively used to detect the deflection angle of the corresponding wingtip hinge and send the hinge deflection angle data to the wingtip drive control unit.

[0063] In the initial state, neither the primary nor the secondary wingtip hinge is deflected, and the hinge deflection angle detected by each angle sensor is 0°. When the primary angle sensor detects that the primary wingtip hinge's deflection angle is less than or equal to the primary wingtip deflection angle critical point, the wingtip drive control unit does not send a rotation command to the secondary wingtip hinge, and the secondary wingtip hinge does not rotate. At this time, the secondary wingtip hinge deflection angle detected by the secondary angle sensor is 0°.

[0064] When the primary angle sensor detects that the deflection angle of the primary wingtip hinge 123 is greater than the critical point of the primary wingtip deflection angle, the wingtip drive control unit receives the deflection angle of the primary wingtip hinge detected by the primary angle sensor and sends it to the secondary wingtip hinge, so that the secondary wingtip deflects in the direction opposite to the deflection direction of the primary wingtip hinge. During the deflection of the secondary wingtip, the secondary angle sensor detects the deflection angle of the secondary wingtip hinge in real time and sends it to the wingtip drive control unit. When the deflection angle of the secondary wingtip hinge is equal to the target deflection angle of the primary wingtip hinge, the secondary wingtip is parallel to the main wing, and the wingtip drive control unit stops sending rotation instructions to the primary wingtip hinge and the secondary wingtip hinge, locks the primary wingtip hinge and the secondary wingtip hinge, and the primary wingtip and the secondary wingtip stop rotating.

[0065] Based on the above method, the present invention also provides a device for increasing the critical flutter speed of a high-aspect-ratio UAV with variable wingtips. The UAV variable wingtips include a primary wingtip 121 and a secondary wingtip 122. The primary wingtip's ends are connected to the main wing and the secondary wingtip via a primary wingtip hinge 123 and a secondary wingtip hinge 124, respectively. The device includes a data acquisition unit comprising a primary angle sensor and a secondary angle sensor. The primary angle sensor is mounted on the primary wingtip hinge 123 and detects the rotation angle of the primary wingtip hinge. The secondary angle sensor is mounted on the secondary wingtip hinge 124 and detects the rotation angle of the secondary wingtip hinge. A wingtip drive control unit is configured with a primary wingtip deflection angle threshold. The control unit receives detection data from the data acquisition unit and, when the primary wingtip deflection angle exceeds the primary wingtip deflection angle threshold, controls the unlocking of the secondary wingtip hinge and drives the secondary wingtip to rotate in the opposite direction until the secondary wingtip deflection angle data matches the primary wingtip deflection angle data, at which point the secondary wingtip is parallel to the main wing.

[0066] In order to verify the effect of the method of the present invention on improving the flutter critical speed after the wingtip deflection angle of the wingtip variable high aspect ratio drone exceeds the critical point, Example 1 and Example 2 provide wingtip variable high aspect ratio drones with different wingtip total lengths for verification.

[0067] Example 1

[0068] Reference Figure 2 Embodiment 1 provides a high-aspect-ratio wingtip-variable drone 100, comprising a fuselage 110, a main wing 120, a primary wingtip 121, and a secondary wingtip 122. The drone has a total span of 2.4 meters, a main wing 120 span of 1.8 meters, and a total wingtip length of 0.3 meters. The length of the primary wingtip 121 is L1 meters, and the length of the secondary wingtip 122 is L2 meters. Table 1 lists some structural parameters of the high-aspect-ratio wingtip-variable drone in Embodiment 1.

[0069] Table 1

[0070] Main wing span length <![CDATA[Length L1 of the first wing tip]]> <![CDATA[Secondary wing tip length L2]]> 1.8m 0.2m 0.1m 1.8m 0.1m 0.2m

[0071] In the first embodiment, the wingtip drive control unit controls the deflection of the first-stage wingtip 121 through the first-stage wingtip hinge 123 at the connection between the main wing 120 and the first-stage wingtip 121, and the deflection angle range is 0°-90°. Based on the computational complexity, the first embodiment divides the deflection angle range into 6 deflection levels according to a deflection interval of 15°, namely 15°, 30°, 45°, 60°, 75°, and 90°. When the second-stage wingtip is not deflected, the critical flutter speed of the drone changes when the first-stage wingtip is driven to deflect to different deflection levels as follows:

[0072] Wingtip variable aspect ratio UAV in such Figure 3 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio wingtip drone is deflected at 0°, while the second-stage wingtip hinge 124 is not deflected. Flutter analysis shows that the critical flutter speed of the high-aspect-ratio wingtip drone is 31.36 m / s.

[0073] Wingtip variable aspect ratio UAV in such Figure 4 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip drone deflects by 15°, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip drone is 32.19 m / s.

[0074] Wingtip variable aspect ratio UAV in such Figure 5 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio wingtip drone deflects 30 degrees, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio wingtip drone is 34.37 m / s.

[0075] Wingtip variable aspect ratio UAV in such Figure 6 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip drone deflects at a 45° angle, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip drone is 38.21 m / s.

[0076] Wingtip variable aspect ratio UAV in such Figure 7 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip UAV deflects by 60°, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip UAV is 42.67 m / s.

[0077] Wingtip variable aspect ratio UAV in such Figure 8 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip drone deflects 75 degrees, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip drone is 36.43 m / s.

[0078] Wingtip variable aspect ratio UAV in such Figure 9 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip UAV is deflected by 90°, while the second-stage wingtip hinge 124 is not deflected. Flutter analysis shows that the critical flutter speed of the high-aspect-ratio variable-wingtip UAV is 31.67 m / s.

[0079] The above flutter analysis results show that when the secondary wingtip hinge 124 is not deflected and the primary wingtip deflection level does not exceed 60°, the drone's critical flutter speed increases with the increase in the deflection angle of the primary wingtip hinge 123. The critical flutter speed of the drone reaches its peak at a deflection angle of 60°. When the deflection angle of the primary wingtip hinge 123 exceeds 60°, the critical flutter speed of the drone begins to decrease. Therefore, in Example 1, the rotation angle of 60° of the primary wingtip hinge 123 of the drone is the critical point of the primary wingtip deflection angle.

[0080] When the first-stage wingtip deflection angle exceeds 60°, the wingtip drive control unit automatically controls the second-stage wingtip to start deflecting. In order to determine the effect of different lengths of second-stage wingtip deflection on the critical flutter speed of the drone. In Example 1, 0.1m is used as the length adjustment step to calculate the critical flutter speed of the wingtip-variable drone after the second-stage wingtip 122 deflection of different lengths. Specifically, a variable parameter adjustment analysis can be performed by establishing a wingtip-variable drone simulation model. The specific analysis process is as follows:

[0081] Reference Figure 10 The primary wingtip hinge 123 of the variable-wingtip high-aspect-ratio UAV is deflected to a 75° angle. The secondary wingtip hinge 124, in response to commands from the wingtip drive control unit, deflects until the secondary wingtip is parallel to the main wing 120. Once deflected, the secondary wingtip hinge is locked and prevents rotation. Flutter analysis shows that when the length of the secondary wingtip 122 is 0.1m, the critical flutter speed of the variable-wingtip high-aspect-ratio UAV is 44.07m / s; when the length is 0.2m, the critical flutter speed is 36.76m / s.

[0082] Reference Figure 11 The primary wingtip hinge 123 of the variable-wingtip high-aspect-ratio UAV is deflected to a 90° angle. The secondary wingtip hinge 124, in response to commands from the wingtip drive control unit, deflects until the secondary wingtip 122 is parallel to the main wing 120. Once deflected, the secondary wingtip hinge is locked and prevents rotation. Flutter analysis shows that when the length of the secondary wingtip 122 is 0.1m, the critical flutter speed of the variable-wingtip high-aspect-ratio UAV is 49.39m / s; when the length of the secondary wingtip 122 is 0.2m, the critical flutter speed is 38.86m / s.

[0083] Example 1: Comparison of the critical flutter speed of a high aspect ratio UAV with variable wingtip before and after deflection of the secondary wingtip of different lengths. Figure 12As shown in the figure, it can be seen that when the length L2 of the secondary wingtip 122 is 0.1m, the secondary wingtip deflection has the best improvement effect on the reduction of the flutter critical speed. In addition, when the length L2 of the secondary wingtip 122 is 0.1m, the flutter critical speed improvement effect of the UAV when the first-stage wingtip is at different deflection levels is as follows:

[0084] When the primary wingtip hinge 123 is deflected at a 75° angle, the secondary wingtip hinge 124 deflects until the secondary wingtip 122 is parallel to the main wing. This increases the critical flutter speed of the drone from 36.43 m / s (without secondary wingtip deflection) to 44.07 m / s, a 20.96% increase. When the primary wingtip hinge 123 is deflected at a 90° angle, the secondary wingtip hinge 124 deflects until the secondary wingtip 122 is parallel to the main wing. This increases the critical flutter speed from 31.67 m / s (without secondary wingtip deflection) to 49.39 m / s, a 55.96% increase.

[0085] Example 2

[0086] The difference between Example 2 and Example 1 lies in the total wingtip length. However, the total span of the high-aspect-ratio wingtip-variable UAV remains unchanged at 2.4m. In this embodiment, the main wing 120 has a span of 1.6m and a total wingtip length of 0.4m. The length of the primary wingtip 121 is set to L1m, and the length of the secondary wingtip 122 is set to L2m. Table 2 shows some structural parameters of the high-aspect-ratio wingtip-variable UAV in Example 2.

[0087] Table 2

[0088] Main wing span length <![CDATA[Length L1 of the first wing tip]]> <![CDATA[Secondary wing tip length L2]]> 1.6m 0.3m 0.1m 1.6m 0.2m 0.2m 1.6m 0.1m 0.3m

[0089] In Example 2, the wingtip drive control unit uses the primary wingtip hinge 123 at the connection between the main wing 120 and the left and right primary wingtips 121 to control the deflection of the primary wingtips 121, with a deflection angle range of 0°-90°. Based on computational complexity, Example 1 divides the deflection angle range into six deflection levels at 15° deflection intervals. The secondary wingtips are not deflected, and the critical flutter speed of the drone changes as the primary wingtips deflect to different deflection levels as shown below:

[0090] Wingtip variable aspect ratio UAV in such Figure 13 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio wingtip drone is deflected at 0°, while the second-stage wingtip hinge 124 is not deflected. Flutter analysis indicates that the critical flutter speed of the high-aspect-ratio wingtip drone is 31.10 m / s.

[0091] Wingtip variable aspect ratio UAV in such Figure 14During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip UAV deflects by 15°, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip UAV is 32.23 m / s.

[0092] Wingtip variable aspect ratio UAV in such Figure 15 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip drone deflects 30 degrees, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip drone is 35.33 m / s.

[0093] Wingtip variable aspect ratio UAV in such Figure 16 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio wingtip drone deflects at a 45° angle, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio wingtip drone is 41.55 m / s.

[0094] Wingtip variable aspect ratio UAV in such Figure 17 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip drone deflects 60 degrees, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio variable-wingtip drone is 35.13 m / s.

[0095] Wingtip variable aspect ratio UAV in such Figure 18 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio wingtip drone deflects 75 degrees, while the second-stage wingtip hinge 124 remains undeflected. Flutter analysis reveals that the critical flutter speed of the high-aspect-ratio wingtip drone is 28.79 m / s.

[0096] Wingtip variable aspect ratio UAV in such Figure 19 During flight, the first-stage wingtip hinge 123 of the high-aspect-ratio variable-wingtip UAV is deflected by 90°, while the second-stage wingtip hinge 124 is not deflected. Flutter analysis shows that the critical flutter speed of the high-aspect-ratio variable-wingtip UAV is 25.88 m / s.

[0097] The above flutter analysis results show that when the secondary wingtip hinge 124 is not deflected and the primary wingtip deflection level does not exceed 45°, the drone's critical flutter speed increases with the increase in the deflection angle of the primary wingtip hinge 123. The critical flutter speed of the drone reaches its peak at a deflection angle of 45°. When the deflection angle of the primary wingtip hinge 123 exceeds 45°, the critical flutter speed of the drone begins to decrease. Therefore, in Example 1, the 45° deflection angle of the primary wingtip hinge 123 of the drone is the critical point for the primary wingtip deflection angle.

[0098] When the primary wingtip deflection angle exceeds 45°, the wingtip drive control unit automatically controls the secondary wingtip to start deflecting. In order to determine the effect of secondary wingtip deflection of different lengths on the flutter critical speed of the drone. In Example 2, 0.1m is used as the length adjustment step to calculate the flutter critical speed of the wingtip-variable drone after the secondary wingtip 122 deflection of different lengths. The specific process is as follows:

[0099] Reference Figure 20 At this point, the primary wingtip hinge 123 of the variable-wingtip high-aspect-ratio UAV is deflected to a 60° angle. The secondary wingtip hinge 124, following instructions from the wingtip drive control unit, deflects until the secondary wingtip 122 is parallel to the main wing 120. Once deflected, the secondary wingtip hinge is locked and prevents rotation. Flutter analysis reveals that when the length of the secondary wingtip 122 is 0.1m, the critical flutter speed of the variable-wingtip high-aspect-ratio UAV is 46.21m / s; when the length is 0.2m, the critical flutter speed is 38.97m / s; and when the length is 0.3m, the critical flutter speed is 34.25m / s.

[0100] Reference Figure 21 At this point, the primary wingtip hinge 123 of the variable-wingtip high-aspect-ratio UAV is deflected to a 75° angle. The secondary wingtip hinge 124, following instructions from the wingtip drive control unit, deflects until the secondary wingtip 122 is parallel to the main wing 120. Once deflected into position, the secondary wingtip hinge is locked and prevents rotation. Flutter analysis reveals that when the secondary wingtip 122 length L2 = 0.1m, the critical flutter speed of the variable-wingtip high-aspect-ratio UAV is 43.24m / s; when the secondary wingtip 122 length L2 = 0.2m, the critical flutter speed is 42.55m / s; and when the secondary wingtip 122 length L2 = 0.3m, the critical flutter speed is 36.38m / s.

[0101] Reference Figure 22 At this point, the primary wingtip hinge 123 of the variable-wingtip high-aspect-ratio UAV is deflected to a 90° angle. The secondary wingtip hinge 124, following instructions from the wingtip drive control unit, deflects until the secondary wingtip 122 is parallel to the main wing 120. Once deflected, the secondary wingtip hinge is locked and prevents rotation. Flutter analysis reveals that when the secondary wingtip 122 length L2 = 0.1m, the critical flutter speed of the variable-wingtip high-aspect-ratio UAV is 37.79m / s; when the secondary wingtip 122 length L2 = 0.2m, the critical flutter speed is 53.04m / s; and when the secondary wingtip 122 length L2 = 0.3m, the critical flutter speed is 36.84m / s.

[0102] Example 2: Comparison of critical flutter speeds of a high aspect ratio UAV with variable wing tips before and after deflection of secondary wing tips of different lengths. Figure 23 As shown in the figure, it can be seen that when the length of the secondary wingtip 122 is L2 = 0.2m, the secondary wingtip deflection has the best effect on improving the flutter critical speed. In addition, when the length of the secondary wingtip 122 is L2 = 0.2m, the effect of improving the flutter critical speed of the drone at different levels of the first wingtip deflection is as follows:

[0103] When the deflection angle of the primary wingtip hinge 123 is 60°, the secondary wingtip hinge 124 deflects until the secondary wingtip 122 is parallel to the main wing. The critical flutter speed increases from 35.13 m / s when the secondary wingtip deflection is not implemented to 38.97 m / s, and the critical flutter speed increases by 10.93%.

[0104] When the deflection angle of the primary wingtip hinge 123 is 75°, the secondary wingtip hinge 124 deflects to make the secondary wingtip 122 parallel to the main wing, and the flutter critical speed increases from 28.79 m / s when the secondary wingtip deflection is not implemented to 42.55 m / s, and the flutter critical speed increases by 47.83%.

[0105] When the deflection angle of the primary wingtip hinge 123 is 90°, the secondary wingtip hinge 124 deflects to make the secondary wingtip 122 parallel to the main wing, and the flutter critical speed increases from 25.88 m / s when the secondary wingtip deflection is not implemented to 53.04 m / s, and the flutter critical speed increases by 104.93%.

[0106] The above description is only a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any technician familiar with this technical field can easily think of various equivalent modifications or replacements within the technical scope disclosed in the present invention, and these modifications or replacements should all be included in the scope of protection of the present invention.

Claims

1. A method for improving the critical flutter speed of a high aspect ratio UAV with variable wingtip, wherein: The wingtip includes a primary wingtip and a secondary wingtip that are rotatably connected; and the lifting method includes the following steps: Step 1: Under the conditions that the first-stage wingtip is deflected and the second-stage wingtip is not deflected, obtain the first-stage wingtip deflection angle corresponding to the peak value of the UAV flutter critical speed, and use this first-stage wingtip deflection angle as the first-stage wingtip deflection angle critical point; Step 2: Wingtip deflection control: Step 2.1: Initially, lock the primary and secondary wingtips so that they do not deflect and are parallel to the main wing. Step 2.2: Unlocking the primary wingtip, driving the primary wingtip to deflect and lift, and obtaining the primary wingtip deflection angle in real time to determine whether the primary wingtip deflection angle exceeds the primary wingtip deflection angle critical point; if not, keeping the secondary wingtip in a locked state; if so, unlocking the secondary wingtip and driving the secondary wingtip to deflect in a direction opposite to the primary wingtip deflection direction; The primary and secondary wingtips are continuously driven to deflect until the primary wingtip deflects to the preset target angle and the secondary wingtip is parallel to the main wing. At the same time, the primary and secondary wingtips are locked to terminate their deflection motion.

2. The lifting method according to claim 1, characterized in that: In step 1, the critical point of the first-stage wingtip deflection angle is obtained by the following method: Step 1.1: Obtain the deflectable angle range of the first-stage wingtip and divide it into multiple discrete deflection levels; the deflection intervals between adjacent deflection levels are configured to be equal intervals; Step 1.2: Under the condition that the secondary wingtip does not deflect, use the flutter analysis method to calculate the UAV's critical flutter speed when the primary wingtip is deflected to different deflection levels; obtain the peak value of the UAV's critical flutter speed, and use the primary wingtip deflection angle corresponding to this peak value as the primary wingtip deflection angle critical point.

3. The lifting method according to claim 2, characterized in that: The deflection interval is no greater than 15°.

4. The lifting method according to claim 3, characterized in that: In step 2.2, after the primary wingtip deflection angle is greater than the primary wingtip deflection angle critical point, the primary wingtip deflection angle and the secondary wingtip deflection angle are obtained in real time, and the primary wingtip and the secondary wingtip are continuously driven to deflect until the secondary wingtip deflection angle is equal to the primary wingtip deflection angle, the secondary wingtip is parallel to the main wing, and the primary wingtip and the secondary wingtip are locked at the same time, and the primary wingtip and the secondary wingtip stop rotating.

5. A control device for increasing the critical flutter speed of a high-aspect-ratio UAV with variable wingtips, wherein the variable wingtips of the UAV include a primary wingtip and a secondary wingtip, wherein the ends of the primary wingtip are connected to the end of the main wing and the end of the secondary wingtip via a primary wingtip hinge and a secondary wingtip hinge, respectively; characterized in that: The UAV flutter critical speed improvement control device includes: A data acquisition unit, used to detect the deflection angles of the first and second wingtips in real time; The wingtip drive control unit is configured with a first-level wingtip deflection angle critical point; and is used to: receive detection data from the data acquisition unit, and when the first-level wingtip deflection angle is greater than the first-level wingtip deflection angle critical point, control the unlocking of the second-level wingtip hinge and drive the second-level wingtip to rotate in the opposite direction until the second-level wingtip deflection angle data is consistent with the first-level wingtip deflection angle data.

6. The UAV flutter critical speed improvement control device according to claim 5, characterized in that: The data acquisition unit includes a primary angle sensor and a secondary angle sensor; The primary angle sensor is mounted on the primary wingtip hinge and is used to detect the rotation angle of the primary wingtip hinge; The secondary angle sensor is installed on the secondary wingtip hinge and is used to detect the rotation angle of the secondary wingtip hinge.

7. The UAV flutter critical speed improvement control device according to claim 5 or 6, characterized in that: The length of the secondary wingtip is determined according to the following method: Step S1: Establish a simulation model of a UAV with variable wingtips, obtain the total length of the variable wingtips, and initialize the primary wingtip length and the secondary wingtip length; Step S2: Setting the adjustment step size, adjusting the primary wingtip length and the secondary wingtip length by variable parameters, and performing flutter analysis on the UAV. When the primary wingtip is deflected to different deflection levels, the critical flutter speed of the UAV is obtained when the secondary wingtip is deflected to be parallel to the main wing. Step S3: Compare the critical flutter speeds of the drone corresponding to secondary wingtips of different lengths, and take the secondary wingtip with the greatest improvement in the critical flutter speed of the drone as the optimal secondary wingtip.

8. The UAV flutter critical speed improvement control device according to claim 7, characterized in that: The adjustment step length is no greater than 0.1 m.

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