A longitudinal controllable domain and stability analysis method for low-speed fixed-wing unmanned aerial vehicle

Abstract

The application discloses a kind of low-speed fixed-wing unmanned aerial vehicle longitudinal controllable field and stability analysis method, comprising: determining the desired working range of angle of attack and track inclination state;Angle of attack and track inclination expected value are substituted into trim calculation, and the trim elevator deflection, trim airspeed and trim thrust are obtained;With angle of attack as horizontal axis, track inclination as vertical axis, the trim elevator deflection, trim airspeed and trim thrust are expressed in the form of contour distribution, and the full-state trim contour distribution diagram is obtained;Introduce aircraft performance constraints and control constraints in the full-state trim contour distribution diagram, and obtain the controllable field;Select the desired working point in the controllable field, calculate the speed, angle of attack trend in the neighborhood of the working point, obtain the speed angle of attack phase diagram, and judge the stability of the working point through the speed angle of attack phase diagram.The application is applied to the technical field of unmanned aerial vehicle, has the advantages of low complexity of trim solution, strong result display intuitiveness and high application analysis efficiency.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of unmanned aerial vehicles, in particular to a longitudinal controllable domain and stability analysis method of a low-speed fixed-wing unmanned aerial vehicle. BACKGROUND

[0002] In the field of aircraft design and application, flight envelope represents flight performance to some extent, and in the process of unmanned aerial vehicle control system design, more attention is paid to balance state stability and controllability. Balance state calculation is usually called trimming, and the current trimming method is generally to determine the flight speed and flight path angle at the target working point, and further solve the corresponding trimming angle of attack, elevator deflection and thrust through iterative method. This method has the disadvantages of serious coupling and low solving efficiency, and the stability cannot be directly judged, which needs further help of small perturbation linearization or pole distribution method, increasing the calculation complexity.

[0003] In addition, in the process of autonomous landing of unmanned aerial vehicle, it is usually divided into stages such as unpowered glide, pull and taxi. The control targets include height, speed, sink rate and aircraft attitude. Among them, the sink rate is related to the speed, and will further affect the height change, and there is a coupling and constraint relationship among the three. In the design of conventional control method, the focus is on whether the target state is reachable and stable, and the state transition process and the balance constraint relationship between the target states are often ignored, and there is a lack of intuitive formula or chart for explicit analysis of the state transition process, which will affect the actual flight control effect.

[0004] In summary, the traditional unmanned aerial vehicle control characteristic, stability analysis and control method design process has certain defects in application, and it is difficult to meet the actual demand. SUMMARY

[0005] In view of the technical defects existing in the process of designing the existing unmanned aerial vehicle control method, the present application provides a longitudinal controllable domain and stability analysis method of a low-speed fixed-wing unmanned aerial vehicle, which has the advantages of low coupling degree, high efficiency and strong graphical intuition.

[0006] To achieve the above purpose, the present application provides a longitudinal controllable domain and stability analysis method of a low-speed fixed-wing unmanned aerial vehicle, comprising the following steps:

[0007] Step 1, determining the expected working range of the angle of attack and flight path angle state of the unmanned aerial vehicle;

[0008] Step 2, traversing the expected working range of the angle of attack and flight path angle state, substituting the expected value of the angle of attack and flight path angle into the trimming calculation to obtain the trimming elevator deflection, trimming speed and trimming thrust;

[0009] Step 3, with the angle of attack as the horizontal axis and the flight path angle as the vertical axis, the trim elevator deflection, the trim airspeed and the trim thrust are expressed in the form of contour distribution, and the full-state trim contour distribution map is obtained;

[0010] Step 4, the aircraft performance constraints and control constraints are introduced into the full-state trim contour distribution map, and the controllable domain of the unmanned aerial vehicle is obtained;

[0011] Step 5, the desired working point of the unmanned aerial vehicle is selected in the controllable domain, the speed and angle of attack change trend in the neighborhood of the desired working point is calculated, the speed and angle of attack phase diagram is obtained, and the stability of the desired working point is judged through the speed and angle of attack phase diagram, specifically: in the speed and angle of attack phase diagram, the angle of attack and speed change near a certain trim state are expressed in the form of trend line with arrows, and the stability of the trim state can be further determined according to the trend characteristics.

[0012] Compared with the prior art, the present application has the following beneficial technical effects:

[0013] 1. In the process of rapid calculation of trim states, the present application adjusts the calculation order of trim states, avoids the coupling problem of lift coefficient, drag coefficient and pitching moment coefficient caused by simultaneous changes of angle of attack and elevator deflection, greatly reduces the complexity of solving a single trim state, and improves the calculation efficiency of full-state trim;

[0014] 2. In the process of determining the controllable domain based on the full-state trim contour distribution map, the trim states and distribution in the flight envelope range are displayed in a visual form, the controllable domain distribution under the control condition constraints of the unmanned aerial vehicle is intuitively shown, the required working point and its transfer process state are selected in the controllable domain, the smooth transition of the control process can be realized, and the problems of poor tracking accuracy and difficulty in speed reduction caused by the fact that the instructions do not meet the balance constraints in the actual control process are avoided;

[0015] 3. In the process of stability analysis based on the angle of attack and speed phase diagram, the angle of attack and speed change near a certain trim state are expressed in the form of trend line with arrows, the stability of the trim state is intuitively reflected, and through stability analysis, the control law design of the working point can be adjusted accordingly, and finally stable control near the balance working point is realized. BRIEF DESCRIPTION OF DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the drawings needed to be used in the embodiments or prior art description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of the drawings shown.

[0017] Figure 1 The flow chart of the longitudinal controllable domain and stability analysis method of the low-speed fixed-wing unmanned aerial vehicle in the embodiment of the present application is shown in the figure.

[0018] Figure 2 The controllable domain contour distribution map obtained for the characteristics of the unmanned aerial vehicle in the embodiment of the present application is shown in the figure.

[0019] Figure 3 The angle of attack velocity phase diagram obtained for the points S1 and S2 in the embodiment of the present application is shown in the figure. Figure 2

[0020] The implementation, functional features and advantages of the present application will be further described with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0021] The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all the other embodiments obtained by those skilled in the art without creative efforts belong to the protection scope of the present application.

[0022] It should be noted that all the directionality indications (such as up, down, left, right, front, back, etc.) in the embodiments of the present application are only used to explain the relative position relationship, motion condition, etc. between the components in a certain specific posture (as shown in the drawings). If the specific posture changes, the directionality indications also change accordingly.

[0023] In addition, the technical solutions in the embodiments of the present application can be combined with each other, but it must be based on the fact that the technical solutions can be realized by those skilled in the art. When the combination of the technical solutions appears contradictory or unachievable, it should be considered that the combination of the technical solutions does not exist and is not within the protection scope of the present application.

[0024] The embodiment discloses a longitudinal controllable domain and stability analysis method of a low-speed fixed-wing unmanned aerial vehicle, referring to Figure 1 , and specifically comprising the following steps 1-5.

[0025] Step 1: determining the expected working range of the angle of attack and the track inclination state of the unmanned aerial vehicle according to the designed flight performance of the unmanned aerial vehicle;

[0026] Step 2: traversing the expected working range of the angle of attack and the track inclination state, and substituting the expected values of the angle of attack and the track inclination into the trimming calculation to obtain the trimming elevator deflection, the trimming airspeed and the trimming thrust, wherein the specific implementation of the trimming calculation is as follows:

[0027] ​Step 2.1, obtain the lift coefficient, drag coefficient and pitching moment coefficient of the UAV with respect to the angle of attack and elevator deflection;

[0028] Step 2.2, establish the force and moment balance equations of the aerodynamic force, gravity and engine thrust, which are:

[0029]

[0030] wherein Q is the dynamic pressure, the airspeed is implied in the dynamic pressure Q, S is the wing wetted area of the UAV, γ is the flight path angle, T is the thrust, C L (α, δ e ), C D (α, δ e ), C m (α, δ e ) are the lift coefficient, drag coefficient and pitching moment coefficient of the UAV determined in step 2.1, and C L (α, δ e ), C D (α, δ e ), C m (α, δ e ) are all related to the angle of attack α and the elevator deflection δ e of the UAV;

[0031] Step 2.3, limit the angle of attack and flight path angle of the trim state based on the expected working range of the angle of attack and flight path angle state of the UAV, and the elevator deflection corresponding to the current trim angle of attack can be calculated by applying the gradient descent method to the third equation of the balance equations in equation (1), and the iteration formula is:

[0032] δ e (k+1) = δ e (k) + μ(0 - C m (α trim , δ e (k))) (2)

[0033] wherein δ e (k+1) is the elevator deflection of the k+1th iteration, δ e (k) is the elevator deflection of the kth iteration, μ is the iteration coefficient for adjusting the iteration convergence characteristics, and α trim is the angle of attack of the trim state;

[0034] Step 2.4, substitute the angle of attack, flight path angle of the trim state and the elevator deflection obtained in step 2.3 into the second equation of the balance equations in equation (1) to obtain the trim airspeed, which is:

[0035]

[0036] wherein V a,trimθ trim θ is the trim angle of attack, ρ is the air density, m is the mass of the UAV, g is the gravity acceleration, C D,trim C is the trim drag coefficient, C L,trim C is the trim lift coefficient.

[0037] Step 2.5, the trim angle of attack, the path angle and the elevator deflection obtained in step 2.3, the trim airspeed obtained in step 2.4 are substituted into the first equation of the balance equation group, and the trim thrust is obtained:

[0038]

[0039] T trim is the trim thrust.

[0040] Step 3, with the trim elevator deflection, the trim airspeed and the trim thrust in the form of contour distribution, the full-state trim contour distribution map is obtained, specifically:

[0041] On the basis of step 2, the trim elevator deflection, the airspeed and the engine thrust corresponding to different trim angles of attack and path angles in the expected working range are calculated, and then the contour distribution of the trim airspeed, the engine thrust, the elevator deflection and the corresponding pitch angle is drawn with the angle of attack as the horizontal coordinate and the path angle as the vertical coordinate, that is, the full-state trim contour distribution map is obtained. In the full-state trim contour distribution map, the angle of attack, the path angle, the airspeed, the elevator deflection, the engine thrust and the pitch angle corresponding to a point are the same set of trim states.

[0042] Step 4, the controllable domain of the UAV is obtained by introducing the aircraft performance constraints and control constraints in the full-state trim contour distribution map, specifically:

[0043] In the full-state trim contour distribution map, the zero-thrust contour to the maximum-thrust contour region, the elevator deflection limit region and the airspeed non-negative region are determined, and the intersection of the three regions is the controllable domain of the UAV, and further, the smooth transition process of different states can be designed in the map.

[0044] Step 5, the expected working point of the UAV is selected in the controllable domain, the speed and angle of attack trend in the neighborhood of the expected working point is calculated, the speed and angle of attack phase diagram is obtained, and the stability of the expected working point is judged through the speed and angle of attack phase diagram, and the specific implementation process is:

[0045] Step 5.1, the expected working point of the UAV is selected in the full-state trim contour distribution map, and the thrust and pitch angle of the working point are limited;

[0046] Step 5.2, the dynamic differential equation of the angle of attack and the speed is established, which is:

[0047]

[0048] In the formula, V a Let α be the speed of the drone, α be the angle of attack of the drone, D be the drag, and θ be the speed of the drone. c T is the pitch angle corresponding to the desired operating point. c Let L be the thrust corresponding to the desired operating point and L be the lift. Substitute the thrust and pitch angle of the UAV at the desired operating point in step 5.1 into the dynamic differential equation, and iterate through and calculate the rate of change of airspeed and angle of attack in the neighborhood of the desired operating point of the UAV.

[0049] Step 5.3: Obtain the angular velocity phase diagram based on the airspeed and the rate of change in the neighborhood of the desired operating point of the UAV, and use the angular velocity phase diagram to determine the stability of the desired operating point of the UAV in Step 5.1.

[0050] Figure 2 This refers to the elevation distribution map, such as the full-state alignment, calculated based on the characteristics of a certain UAV. Figure 2 The thick solid line represents the thrust contour distribution, the vertical dashed line represents the velocity distribution, the vertical thin solid line represents the rudder deflection angle, and the diagonal dotted line represents the pitch angle. The rudder deflection is limited to ±30 degrees. Figure 2 The rudder deflection is within the limited range, therefore the area between the zero thrust line and the maximum thrust line is the controllable region. Figure 2 The distribution of medium-speed contour lines becomes sparser as the angle of attack increases. Within the Y-shaped region enclosed by the 11 m / s and 10 m / s speed lines, the speed changes very little while the angle of attack changes significantly. Therefore, the trim state in this region is more sensitive to speed changes.

[0051] Select Figure 2 Points S1 and S2 are the desired operating points, i.e., constrained thrust and pitch angle. The velocity and angle of attack trends in the surrounding region are calculated to obtain... Figure 3 The diagram shows the angular velocity phase diagram for states S1 and S2. Figure 3 The trend changes in the medium can be used to intuitively determine that the S1 working point is an unstable saddle point, and the S2 state is a stable focus.

[0052] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A method for analyzing longitudinal controllable domain and stability of low-speed fixed-wing unmanned aerial vehicle, characterized in that, Comprising the following steps: Step 1, determining the desired working range of the angle of attack and the path inclination state of the unmanned aerial vehicle; Step 2, traversing the desired working range of the angle of attack and the path inclination state, substituting the angle of attack and the path inclination expectation value into the trimming calculation to obtain the trimming elevator deflection, the trimming airspeed and the trimming thrust, specifically: Step 2.1, obtaining the lift coefficient, the drag coefficient and the pitching moment coefficient of the unmanned aerial vehicle varying with the angle of attack and the elevator deflection; Step 2.2, establishing the force and torque balance equation group of the aerodynamic force, the gravity and the engine thrust, which is: wherein, Q is the dynamic pressure, S is the unmanned aerial vehicle wing wetted area, Step 2.3, limiting the angle of attack and the path inclination of the trimming state, obtaining the current trimming angle of attack corresponding to the elevator deflection by applying the gradient descent method through the third formula of the balance equation group, which is: is the path inclination angle, T is the thrust, C L α , Step 2.4, substituting the angle of attack, the path inclination and the corresponding elevator deflection of the trimming state into the second formula of the balance equation group to obtain the trimming airspeed, which is: e is the lift coefficient of the unmanned aerial vehicle, C D α , Step 2.5, substituting the angle of attack, the path inclination and the corresponding elevator deflection, the trimming airspeed of the trimming state into the first formula of the balance equation group to obtain the trimming thrust, which is: e is the drag coefficient of the unmanned aerial vehicle, C m α , Step 3, taking the angle of attack as the horizontal axis and the path inclination as the vertical axis, representing the trimming elevator deflection, the trimming airspeed and the trimming thrust in the form of contour distribution to obtain the full-state trimming contour distribution map; e is the pitching moment coefficient of the unmanned aerial vehicle, C L α , Step 4, introducing the aircraft performance constraints and control constraints in the full-state trimming contour distribution map to obtain the controllable domain of the unmanned aerial vehicle; e , C D α , Step 5, selecting the desired working point of the unmanned aerial vehicle in the controllable domain, calculating the speed and angle of attack trend in the neighborhood of the desired working point to obtain the speed and angle of attack phase diagram, and judging the stability of the desired working point through the speed and angle of attack phase diagram. e , C m α , Step 4 specifically is: e are all related to the angle of attack α and the elevator deflection In the full-state trimming contour distribution map, the part where the zero-thrust contour intersects the maximum-thrust contour region, the elevator deflection limit region and the non-negative airspeed region is the controllable domain of the unmanned aerial vehicle. e of the unmanned aerial vehicle;​​​​​​ Step 5 specifically is: wherein Step 5.1, selecting the desired working point of the unmanned aerial vehicle in the full-state trimming contour distribution map and limiting the thrust and the pitch angle of the working point; e ( k +1) is the elevator deflection of the first k +1 iteration, Step 5.2, establishing the dynamics differential equation of the angle of attack and the speed, substituting the thrust and the pitch angle of the desired working point of the unmanned aerial vehicle in step 5.1 into the dynamics differential equation, and traversing to calculate the change rate in the neighborhood of the airspeed and the angle of attack at the desired working point of the unmanned aerial vehicle; e ( k ) is the elevator deflection of the first k iteration, Step 5.3, obtaining the angle of attack speed phase diagram according to the change rate in the neighborhood of the airspeed and the angle of attack at the desired working point of the unmanned aerial vehicle, and judging the stability of the desired working point of the unmanned aerial vehicle in step 5.1 through the angle of attack speed phase diagram. is an iteration coefficient for adjusting the iteration convergence characteristics, α trim is the angle of attack of the trimmed state; In step 5.2, the dynamics differential equation of the angle of attack and the speed is: wherein, V a,trim is the trim airspeed, Step 5.2, establishing the dynamics differential equation of the angle of attack and the speed, substituting the thrust and the pitch angle of the desired working point of the unmanned aerial vehicle in step 5.1 into the dynamics differential equation, and traversing to calculate the change rate in the neighborhood of the airspeed and the angle of attack at the desired working point of the unmanned aerial vehicle; trim is the trim pitch angle, ​ is the air density, m is the UAV mass, g is the gravitational acceleration, C D,trim is the trim drag coefficient, C L,trim is the trim lift coefficient; ​ In the formula, T trim is the trim force; ​ ​ ​ 2. The method of claim 1, wherein, ​ ​ 3. The method of claim 1, wherein, ​ ​ ​ ​ 4. The method of claim 3, wherein, ​ wherein, V a is the speed of the UAV, α is the angle of attack of the UAV, D is the drag force, ​ c is the pitch angle corresponding to the desired operating point, T c is the thrust corresponding to the desired operating point, L is the lift force.

Images