A stall avoidance angle of attack limit design method

Abstract

The application relates to a stall-avoiding angle-of-attack limit design method, and belongs to the technical field of unmanned aerial vehicle control. The method comprises the following steps: acquiring aircraft parameters related to the angle of attack, acquiring the corresponding maximum pitching-down moment according to an angle-of-attack limiter starting threshold, and acquiring an actual crossing angle of attack according to the maximum pitching-down moment; designing an angle-of-attack integral formula according to a pitching axis mass moment of inertia, a wing area, an average aerodynamic chord length and a point dynamic pressure, and calculating an expected crossing angle of attack according to the angle-of-attack integral formula; comparing a difference value between the actual crossing angle of attack and the expected crossing angle of attack with a margin threshold, and judging whether the angle-of-attack limiter meets the requirements according to the comparison size. The application is based on the constraint relationship between the maximum pitching-down moment curve slope and the zero-crossing angle of attack, relies on the most original mechanical equation, designs the angle-of-attack limit design criterion, can be evaluated only by using a few simple parameters of the aircraft, is universal, and can be used for precise evaluation of a new round of aircraft layout in a short time under various states.

Description

Technical Field

[0001] The present invention belongs to the technical field of unmanned aerial vehicle control, and in particular relates to a method for designing an angle of attack limitation for avoiding stall of a tailless aircraft. Background Art

[0002] In order to take into account the requirements of stealth, high lift-to-drag ratio, supersonic high-maneuverability flight, etc., tailless aircraft adopts a wing-body fusion layout, cancels the vertical tail, and relaxes the static stability in both longitudinal and directional directions. Its longitudinal instability and maximum nose-down moment cannot be met in the entire range. It is difficult to meet the traditional maximum nose-down moment indicators in aerodynamics. There is an irrecoverable angle of attack zone for the longitudinal moment, resulting in a deep stall point for the aircraft. The control law needs to accurately limit the state of the aircraft.

[0003] The existing longitudinal evaluation indicators are unable to support the reasonable design of the angle of attack limit of the new layout, and the six-degree-of-freedom simulation can only cover a limited number of states. Summary of the Invention

[0004] The technical problems to be solved by the present invention are:

[0005] In order to avoid the deficiencies of the prior art, the present invention provides a method for designing an angle of attack limitation for a tailless aircraft to avoid stall.

[0006] In order to solve the above technical problems, the technical solution adopted by the present invention is:

[0007] A method for designing an angle of attack limitation for avoiding stall, characterized by comprising:

[0008] Acquiring aircraft parameters related to angle of attack, the aircraft parameters including: pitch axis mass moment of inertia, wing area, mean aerodynamic chord length, point dynamic pressure, and angle of attack limiter activation threshold;

[0009] The corresponding maximum nose-down moment is obtained according to the angle-of-attack limiter activation threshold, and the actual crossing angle of attack is obtained according to the maximum nose-down moment;

[0010] Design the angle of attack integral formula based on the pitch axis mass moment of inertia, wing area, mean aerodynamic chord length, and point dynamic pressure, and calculate the expected penetration angle of attack based on the angle of attack integral formula;

[0011] The difference between the actual crossing angle of attack and the expected crossing angle of attack is compared with the margin threshold, and the angle of attack limiter is judged to meet the requirements based on the comparison size.

[0012] A further technical solution of the present invention is as follows: obtaining the corresponding maximum nose-down moment according to the angle of attack limiter activation threshold is specifically: consulting the aircraft layout aerodynamic database and the maximum nose-down moment curve to obtain the maximum nose-down moment at the angle of attack limiter activation threshold.

[0013] A further technical solution of the present invention: the obtaining of the actual crossing angle of attack based on the maximum nose-down moment is specifically: obtaining the angle of attack when the maximum nose-down moment changes from negative to positive for the first time as the actual crossing angle of attack.

[0014] A further technical solution of the present invention is as follows: the calculation of the expected penetration angle of attack is specifically as follows:

[0015] cm n-1 =k(α n-1 -α0)+cm0

[0016]

[0017] α n =α n-1 +q n *Ts

[0018] Where k is the desired slope, α0 is the angle of attack limiter activation threshold, cm0 is the maximum nose-down moment at α0, cm n-1 is the pitch moment coefficient of the previous shot, α n-1 is the angle of attack of the previous shot, q n-1 is the pitch rate of the previous shot, α n is the current angle of attack, q n is the current pitch rate, QQ is the point pressure, S is the wing area, c is the average aerodynamic chord length, and Ts is the integration step size.

[0019] A further technical solution of the present invention is: the margin threshold is the difference between the upper limit of the angle of attack limiter and the actual crossing angle of attack.

[0020] A further technical solution of the present invention is as follows: judging whether the angle of attack limiter meets the requirements based on the comparison size is specifically: when the difference between the actual crossing angle of attack and the expected crossing angle of attack is greater than the margin threshold, the angle of attack limiter design meets the requirements.

[0021] A computer system, characterized in that it includes: one or more processors, and a computer-readable storage medium for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement any of the above methods.

[0022] A computer-readable storage medium is characterized by storing computer-executable instructions, which are used to implement any of the above methods when executed.

[0023] The beneficial effects of the present invention are:

[0024] This invention provides a stall-avoidance angle-of-attack (AoA) constraint design method for tailless aircraft. Based on the constraint relationship between the slope of the maximum nose-down moment curve and the zero-angle-of-attack (AoA) crossing, and relying on fundamental mechanical equations, the AoA constraint design criteria are designed. This method requires only a few simple aircraft parameters for evaluation, offering versatility and accurate assessment of a new aircraft configuration across multiple conditions within a short period of time. This invention has already been applied to the controllability assessment of new aircraft configurations and provides quantitative feedback on proposed iterations to the overall professional community. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] The accompanying drawings are only for the purpose of illustrating particular embodiments and are not to be considered limiting of the present invention. Like reference symbols denote like parts throughout the drawings.

[0026] Figure 1 Schematic diagram of angle of attack limiter design.

[0027] Figure 2 Design a flow chart for angle of attack limitation. DETAILED DESCRIPTION

[0028] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0029] The present invention provides a method for designing an angle of attack limiter for avoiding stall in a tailless aircraft. The method is based on the constraint relationship between the slope of the maximum nose-down moment curve and the zero angle of attack, and relies on the most primitive mechanical equations to design an angle of attack limiter design criterion. Only a few simple aircraft parameters are required for evaluation, and the method is universal and can provide a theoretical basis for the design of angle of attack limiters for tailless aircraft.

[0030] like Figure 2 As shown, the specific steps include:

[0031] Step 1: Obtain the pitch axis mass moment of inertia I of the layout aircraft y , wing area S, average aerodynamic chord length c, design point dynamic pressure QQ;

[0032] Step 2: Obtain the angle of attack limiter activation threshold α0, select the initial pitch rate q0, and the integration step size Ts;

[0033] Step 3: Check the aircraft aerodynamic database and the maximum nose-down moment curve to obtain the maximum nose-down moment cm0 at α0. The angle of attack when the maximum nose-down moment changes from negative to positive for the first time is taken as the crossing angle of attack α. L ;

[0034] Step 4: Assuming that the nose-down capability is fully utilized and the pitching moment curve is assumed to be a linear function, the longitudinal moment equation is:

[0035]

[0036] The pitch rate is:

[0037]

[0038] According to the angle of attack derivative formula:

[0039]

[0040] From this we can get the angle of attack formula:

[0041]

[0042] So we can get:

[0043] α=∫ t ∫ t kαdtdt

[0044]

[0045] Step 5: Iterate according to the following formula to adjust the expected slope k so that q n <0.001cm n-1 <0 and k<k max The situation exists when q n <0.001cm n-1 =0, record the current α n , and the expected angle of attack α is obtained D =α n ; where k max For the angle of attack range α0 to α L Maximum value of the slope of the maximum head-down moment;

[0046] cm n-1 =k(α n-1 -α0)+cm0

[0047]

[0048] α n =α n-1 +q n *Ts

[0049] Among them, cm n-1 is the pitch moment coefficient of the previous shot, α n-1 is the angle of attack of the previous shot, q n-1 is the pitch rate of the previous shot, α n is the current angle of attack, qn The pitch rate of the current shot.

[0050] Step 5: Compare α L With α D Size, if α L -α D ≥α TH , then the angle of attack limiter design meets the requirements, where α TH It is the difference between the upper limit of the angle of attack limiter and the actual crossing angle of attack.

[0051] Example 1:

[0052] For a certain type of tailless aircraft, the takeoff state point is selected as the evaluation point to evaluate the angle of attack limiter capability. The evaluation steps are as follows:

[0053] 1) Obtain the mass and inertia characteristics of the aircraft as shown in the following table

[0054]

[0055] 2) Set the evaluation point to Mach number 0.2 and the starting angle of attack of the angle of attack limiter to 8°.

[0056] 3) According to steps 1 to 6, the evaluation results can be obtained as follows

[0057]

[0058] 4) In the table above, the aircraft can suppress pitch when the actual angle of attack through zero is greater than the desired angle of attack through zero. The angle of attack margin represents the distance between the desired angle of attack and the actual angle of attack through zero. This theoretical calculation demonstrates the aircraft's maneuverability and interference rejection capabilities.

[0059] 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 designing angle of attack limitation to avoid stall, characterized in that: include: Acquiring aircraft parameters related to angle of attack, the aircraft parameters including: pitch axis mass moment of inertia, wing area, mean aerodynamic chord length, point dynamic pressure, and angle of attack limiter activation threshold; The corresponding maximum nose-down moment is obtained according to the angle-of-attack limiter activation threshold, and the actual crossing angle of attack is obtained according to the maximum nose-down moment; The angle of attack integral formula is designed based on the pitch axis mass moment of inertia, wing area, mean aerodynamic chord length, and point dynamic pressure. The expected penetration angle of attack is calculated based on the angle of attack integral formula. The calculation of the expected penetration angle of attack is specifically as follows: in, is the expected slope, The angle of attack limiter activation threshold, for The maximum bow moment at is the pitch moment coefficient of the previous beat, is the angle of attack of the previous shot, is the pitch rate of the previous beat, is the current angle of attack, is the current pitch rate, is the point dynamic pressure, is the wing area, is the mean aerodynamic chord length, is the integration step length; The difference between the actual crossing angle of attack and the expected crossing angle of attack is compared with the margin threshold, and the angle of attack limiter is judged to meet the requirements based on the comparison size.

2. The method for designing an angle of attack limitation for avoiding stall according to claim 1, characterized in that: The method of obtaining the corresponding maximum nose-down moment according to the angle of attack limiter activation threshold includes consulting an aircraft aerodynamic database and a maximum nose-down moment curve to obtain the maximum nose-down moment at the angle of attack limiter activation threshold.

3. The method for designing an angle of attack limitation for avoiding stall according to claim 2, characterized in that: The obtaining of the actual crossing angle of attack according to the maximum nose-down moment is specifically as follows: obtaining the angle of attack when the maximum nose-down moment changes from negative to positive for the first time as the actual crossing angle of attack.

4. The method for designing an angle of attack limitation for avoiding stall according to claim 1, characterized in that: The margin threshold is the difference between the upper limit of the angle of attack limiter and the actual crossing angle of attack.

5. The method for designing an angle of attack limitation to avoid stall according to claim 1, characterized in that: The method of judging whether the angle of attack limiter meets the requirements based on the comparison size is specifically: when the difference between the actual crossing angle of attack and the expected crossing angle of attack is greater than the margin threshold, the angle of attack limiter design meets the requirements.

6. A computer system, characterized in that include: One or more processors, a computer-readable storage medium for storing one or more programs, wherein when the one or more programs are executed by the one or more processors, the one or more processors implement any one of the methods described in claims 1-5.

7. A computer-readable storage medium, characterized in that Computer-executable instructions are stored, and when the instructions are executed, they are used to implement the method according to any one of claims 1 to 5.

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