A method for constructing a three-dimensional tilt-rotor corridor for a quad-tilt-rotor UAV

Abstract

The present invention discloses a method for constructing a three-dimensional tilt corridor for a four-tilt-rotor UAV, which is used to solve the problem that a two-dimensional tilt corridor lacks dynamic features such as angle of attack and flight attitude, and is difficult to be directly used for tilt profile design. The present invention designs a three-dimensional tilt corridor solution equation based on a forward acceleration strategy for a four-tilt-rotor UAV, and takes the angle of attack, the nacelle inclination angle and the flight speed as unknown quantities, calculates all the flyable points that meet the conditions, and thus draws the nacelle inclination angle-flight speed-angle of attack three-dimensional tilt corridor envelope. On this basis, a comprehensive performance index function is designed to evaluate the safety of the flight state points in the tilt corridor, and different colors are used to illustrate it. The three-dimensional tilt corridor construction method proposed in the present invention can more specifically display the safe flight range of the four-tilt-rotor UAV, improve the efficiency and quality of transition flight, and provide a strong basis for the selection of tilt profiles in complex flight scenarios.

Description

Technical Field

[0001] The invention relates to the field of unmanned aerial vehicle flight technology, and mainly to a method for constructing a three-dimensional tilt-rotor corridor for a four-tilt-rotor unmanned aerial vehicle. Background Art

[0002] In recent years, the increasingly mature UAV technology has been widely used in battlefield environments, making UAVs gradually become one of the indispensable key equipment on the modern battlefield. However, the rotorcraft in the current traditional mainstream models is limited by the configuration, and has shortcomings such as slow flight speed, inability to achieve rapid maneuvers, short range, high noise, and small load capacity. Although fixed-wing aircraft make up for the above shortcomings, they are unable to take off and land vertically and hover, and are heavily dependent on terrain, which not only increases the cost of use, but also limits the application field and scope of fixed-wing aircraft. Tilt-rotor UAVs, as a new configuration aircraft that combines the characteristics of rotorcraft and fixed-wing aircraft, have gradually become a new research hotspot due to their advantages such as high speed, wide range, large payload, short-distance / vertical take-off and landing, and more and more aviation-developed countries are exploring them in depth.

[0003] Tilt-rotor UAVs are a new type of UAV with three flight modes, including helicopter mode, tilt-rotor transition mode and fixed-wing mode. Among them, the tilt-rotor transition mode, as a bridge connecting the helicopter mode and the fixed-wing mode, is the key to realizing the functions of high speed, wide range, large load, short-distance / vertical take-off and landing of quad-tilt-rotor UAVs. However, the continuous tilting of the nacelle of the UAV causes the aerodynamic shape to change continuously. In order to ensure the safety of transition flight, the lift and drag generated by the fixed wing and the rotor must overcome the gravity and resistance during the flight to keep the UAV in a dynamic balance. Limited by factors such as aerodynamic flight efficiency and engine power constraints, the engine nacelle can only tilt within a certain forward flight speed and angle of attack range, which is the traditional two-dimensional tilt corridor. However, the two-dimensional tilt corridor lacks key dynamic characteristics such as angle of attack and attitude during flight, and cannot be directly used in the tilt transition flight control design. Therefore, it is urgent to study a three-dimensional tilt-rotor corridor construction method suitable for quad-tilt-rotor UAVs to solve the problem of difficult design of tilt-rotor profiles and realize the safe flight of quad-tilt-rotor UAVs in complex flight scenarios. Summary of the invention

[0004] In order to solve the above technical problems, the present invention provides a method for constructing a three-dimensional tilt-rotor corridor for a four-tilt-rotor UAV. By establishing a three-dimensional tilt-rotor corridor solution equation and designing a comprehensive performance index function, a three-dimensional tilt-rotor corridor envelope of a nacelle inclination angle-flight speed-angle of attack with a state safety index is constructed, which provides an instruction basis for high-quality transition flight control and improves the safety of transition flight.

[0005] In order to achieve the above-mentioned purpose, the technical solution provided by the present invention is: a method for constructing a three-dimensional tilt corridor for a four-tilt-rotor UAV. The method takes into account that the traditional two-dimensional tilt corridor lacks key dynamic characteristics such as angle of attack and attitude during flight and cannot be directly used in the tilt transition flight control design. Therefore, the angle of attack is added as the third dimension of the transition corridor, and a nacelle inclination angle-flight speed-angle of attack three-dimensional tilt corridor envelope with a state safety index is designed in combination with a comprehensive performance index function to provide an instruction basis for high-quality transition flight control. It includes the following steps:

[0006] Step S1: According to the force analysis of the four-tilt-rotor UAV during flight, the solution equations of the three-dimensional tilt-rotor corridor including the forward inequality, the vertical force balance equation and the pitch moment balance equation are established:

[0007]

[0008] In the formula, s (·) = sin(·), s (·) =cos(·); T is the thrust and drag of the four rotors; L and D represent lift and drag, respectively; α is the fuselage angle of attack; γ∈[0°,90°] represents the tilt angle of the nacelle of the four-tilt rotor aircraft, γ=0° is the fixed-wing mode, γ=90° is the helicopter mode, and 0°<90° is the tilt transition mode; m is the mass of the drone; g is the acceleration of gravity; T f is the sum of the thrusts of the first two rotors; T b is the sum of the thrust of the last two rotors; M y is the pitch moment; l1 and l2 are the distances between the projections of the front two rotors and the rear two rotors on the symmetry plane of the aircraft and the center of gravity;

[0009] According to flight dynamics analysis, aerodynamic lift and drag are usually generated by the deflection of the UAV fuselage and the control surface, and their expressions can be written as:

[0010]

[0011] Where Q is the dynamic pressure; S ref is the reference area of ​​the drone; ρ is the air density; V is the true air speed in the body coordinate system; C x and C z are the aerodynamic drag coefficient and the aerodynamic lift coefficient respectively.

[0012] Pitch moment M y It is composed of the thrust torque generated by the rotor and the aerodynamic torque generated by the rudder, which can be expressed as:

[0013]

[0014] In the formula, K f is the rotor thrust coefficient; Ti_xu are the rotor thrust corrections; C my is the aerodynamic pitch moment coefficient; is the average aerodynamic chord length.

[0015] Step S2, taking the nacelle inclination angle as the traversal condition, using the optimoptions function in Matlab to select the Levenberg-Marquardt algorithm to find all feasible solutions that satisfy the solution equation of the above three-dimensional tilt corridor. Then, taking the flight speed as the X-axis variable, the nacelle inclination angle as the Y-axis variable, and the angle of attack as the Z-axis variable, the three-dimensional drawing function is used to outline the area composed of all flyable discrete data points, thereby constructing the envelope of the three-dimensional tilt corridor of nacelle inclination angle-flight speed-angle of attack.

[0016] Step S3: For the safety of transition flight, a comprehensive performance index function must be designed to evaluate the safety of the flight state points in the three-dimensional tilt-rotation corridor. Combined with the characteristics of the quad-tilt-rotor UAV, the comprehensive performance index function can be designed as:

[0017]

[0018] Where ω is the rotor speed; W ind1 and W ind2 They represent the weight coefficients of the angle of attack index and the rotor speed index respectively.

[0019] Beneficial effects:

[0020] The three-dimensional tilt corridor of nacelle tilt angle-flight speed-angle of attack designed in the present invention based on the forward acceleration strategy enriches the information elements of the traditional tilt corridor by using the comprehensive performance index function, clearly demonstrates the safe flight range of the tilt transition of the four-tilt-rotor UAV, provides an instruction basis for high-quality transition flight control, and improves the safety of transition flight. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 A flow chart for calculating the three-dimensional tilt corridor provided by the present invention;

[0022] Figure 2 A diagram of the quad-tilt-rotor unmanned aircraft provided by the present invention;

[0023] Figure 3 Force analysis diagram of the quad-tilt-rotor UAV provided by the present invention;

[0024] Figure 4 A schematic diagram showing the initial three-dimensional tilt corridor of the quad-tilt-rotor UAV provided by the present invention;

[0025] Figure 5A schematic diagram showing a three-dimensional tilt corridor of a quad-tilt-rotor UAV with a state safety indicator provided by the present invention;

[0026] In the figure: 1-4: first to fourth rotors; 5, 7, 9, 11: first to fourth ailerons; 6, 8, 10, 12: first to fourth elevators; 13: rudder; 14: tilt servo. DETAILED DESCRIPTION

[0027] The present invention will be further described below in conjunction with the accompanying drawings.

[0028] This embodiment provides a method for constructing a three-dimensional tilt corridor for a quad-tilt-rotor UAV. The relevant physical parameters of the quad-tilt-rotor UAV are: UAV mass m = 100 kg, wing reference area S ref =2.317m 2 , average aerodynamic span b = 0.55m, average aerodynamic chord length The distances between the projections of the front two rotor centers and the rear two rotor centers on the aircraft symmetry plane and the center of gravity in the X-axis direction are l1 = 0.4897m and l2 = 1.2143m respectively. The rotor thrust coefficient and torque coefficient are obtained through actual measurement, and the specific data are shown in Table 1:

[0029] Table 1 Rotor thrust coefficient and torque coefficient

[0030]

[0031] Table 1 gives the specific rotor thrust coefficient and torque coefficient and their respective corrections. Simply multiply the rotor speed by the relevant coefficient and subtract the correction. Figure 1 and Figure 3 As shown, the present invention establishes a three-dimensional tilt-rotor corridor solution equation based on the forward acceleration strategy according to the stress conditions of the four-tilt-rotor UAV, and uses the Levenberg-Marquardt algorithm to find all feasible solutions that satisfy the above three-dimensional tilt-rotor corridor solution equation, thereby constructing a "nacelle inclination angle-flight speed-angle of attack" three-dimensional tilt-rotor corridor. On this basis, a comprehensive performance index function is designed to evaluate the safety of flight state points within the three-dimensional tilt-rotor corridor flight, and different colors are used to illustrate. It includes the following steps:

[0032] Step S1: According to the force analysis of the four-tilt-rotor UAV during flight, a three-dimensional tilt-rotor corridor solution equation including a forward inequality, a vertical force balance equation, and a pitch moment balance equation is established:

[0033]

[0034] In the formula, s (·) = sin(·), c (·)=cos(·); T is the thrust and drag of the four rotors; L and D represent lift and drag, respectively; α is the fuselage angle of attack; γ∈[0°,90°] represents the inclination angle of the nacelle of the four-tilt rotor aircraft, γ=0° is the fixed-wing mode, γ=90° is the helicopter mode, and 0°<γ<90° is the tilt-rotor transition mode; m is the mass of the drone; g is the acceleration of gravity; T f is the sum of the thrusts of the first two rotors; T b is the sum of the thrust of the last two rotors; M y is the pitch moment; l1 and l2 are the distances between the projections of the front two rotors and the rear two rotors on the symmetry plane of the aircraft and the center of gravity;

[0035] According to flight dynamics analysis, aerodynamic lift and drag are usually generated by the deflection of the UAV fuselage and the control surface, and their expressions can be written as:

[0036]

[0037] Where Q is the dynamic pressure; S ref is the reference area of ​​the drone; ρ is the air density; V is the true air speed in the body coordinate system; C x and C z are the aerodynamic drag coefficient and the aerodynamic lift coefficient respectively.

[0038] Pitch moment M y It is composed of the thrust torque generated by the rotor and the aerodynamic torque generated by the rudder, which can be expressed as:

[0039]

[0040] In the formula, K f is the rotor thrust coefficient; T i_xu are the rotor thrust corrections; C my is the aerodynamic pitch moment coefficient; is the average aerodynamic chord length.

[0041] Step S2, taking the nacelle inclination angle as the traversal condition, using the optimoptions function in Matlab to select the Levenberg-Marquardt algorithm to find all feasible solutions that satisfy the above three-dimensional tilt corridor solution equation. Then, using the flight speed as the X-axis variable, the nacelle inclination angle as the Y-axis variable, and the angle of attack as the Z-axis variable, the three-dimensional drawing function is used to outline the area composed of all flyable discrete data points, thereby constructing the "nacelle inclination angle-flight speed-angle of attack" three-dimensional tilt corridor, such as Figure 4 shown.

[0042] Step S3: For the safety of transition flight, a comprehensive performance index function must be designed to evaluate the safety of the flight state points in the three-dimensional tilt-rotation corridor. Combined with the characteristics of the quad-tilt-rotor UAV, the comprehensive performance index function can be designed as:

[0043]

[0044] Where ω is the rotor speed; W ind1 and W ind2 They represent the weight coefficients of the angle of attack index and the rotor speed index respectively. Figure 5 A three-dimensional tilt corridor for a quad-tilt-rotor UAV with state safety indicators is presented.

[0045] The above is only a preferred embodiment of the present invention, and is not intended to limit the scope of implementation of the present invention. Several improvements and modifications may be made without departing from the principles of the present invention, and these improvements and modifications should also be regarded as the protection scope of the present invention.

Claims

1. A method for constructing a three-dimensional tilt corridor for a quad-tilt-rotor UAV, characterized in that: The method comprises: Step S1, according to the force analysis of the four-tilt-rotor UAV during flight, establish the solution equation of the three-dimensional tilt-rotor corridor including the forward inequality, the vertical force balance equation and the pitch moment balance equation; in step S1, the solution equation of the three-dimensional tilt-rotor corridor consists of the forward inequality, the vertical force balance equation and the pitch moment balance equation: In the formula, s (·) = sin(·), c (·) =cos(·)T is the sum of the thrusts of the four rotors; L and D represent lift and drag, respectively; α is the fuselage angle of attack; γ∈[0°,90°] represents the inclination angle of the nacelle of the four-tilt rotor aircraft, γ=0° is the fixed-wing mode, γ=90° is the helicopter mode, and 0°<γ<90° is the tilt-rotor transition mode; m is the mass of the drone; g is the acceleration of gravity; T f is the sum of the thrusts of the first two rotors; T b is the sum of the thrust of the last two rotors; M y is the pitch moment; l1 and l2 are the distances between the projections of the front two rotors and the rear two rotors on the symmetry plane of the aircraft and the center of gravity respectively; The expressions for the aerodynamic lift and drag are: Where Q is the dynamic pressure; S ref is the reference area of ​​the drone; ρ is the air density; V is the true air speed in the body coordinate system; C x and C z are the aerodynamic drag coefficient and aerodynamic lift coefficient respectively; Pitch moment M y It is composed of the thrust torque generated by the rotor and the aerodynamic torque generated by the control surface, which can be expressed as: In the formula, K f is the rotor thrust coefficient; T i_xu are the rotor thrust corrections; C my is the aerodynamic pitch moment coefficient; is the average aerodynamic chord length; ω is the rotor speed; Step S2, according to the solution equation of the three-dimensional tilt corridor, all flyable discrete data points that meet the constraint conditions are calculated by traversing the nacelle inclination angle, and the area formed by all flyable discrete data points is constructed by using the three-dimensional drawing function, so as to establish the envelope of the three-dimensional tilt corridor of nacelle inclination angle-flight speed-angle of attack; Step S3: Based on the solution equation of the three-dimensional tilt corridor, a comprehensive performance index function is designed to evaluate the safety of the flight state points in the three-dimensional tilt corridor, and the safety is indicated by using different colors.

2. The method for constructing a three-dimensional tilt corridor for a quad-tilt-rotor UAV according to claim 1, characterized in that: In step S2, taking the nacelle inclination angle as the traversal condition, all feasible solutions that satisfy the solution equation of the three-dimensional tilt corridor are obtained; then, taking the flight speed as the X-axis variable, the nacelle inclination angle as the Y-axis variable, and the angle of attack as the Z-axis variable, a three-dimensional drawing function is used to outline the area composed of all flyable discrete data points, thereby constructing the envelope of the nacelle inclination angle-flight speed-angle of attack three-dimensional tilt corridor.

3. The method for constructing a three-dimensional tilt corridor for a quad-tilt-rotor UAV according to claim 1, characterized in that: In step S3, according to the characteristics of the quad-tilt-rotor UAV, the comprehensive performance index function is designed as: Where ω is the rotor speed; W ind1 and W ind2 They represent the weight coefficients of the angle of attack index and the rotor speed index respectively.

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