Method for determining anti-tail-spin parachute parameters of airplane

Abstract

The invention belongs to the field of aircraft flight quality test flight, and particularly relates to a method for determining aircraft anti-tail spinning parachute parameters, which comprises the following steps: preliminarily obtaining an SCD rough value through an empirical formula, obtaining SCD2 through equivalent conversion of a dynamic similarity criterion, carrying out a vertical wind tunnel tail spinning test to obtain SCD1 ', and converting the SCD1 'into the size of an external field free flight model, then carrying out an outfield model free flying tail spin test until the umbrella resistance area SCD2'with the minimum size capable of changing the tail spin within the set number of turns is obtained; performing conversion through a conversion formula to obtain the reverse tail spinning parachute resistance area SCD real aircraft and the reverse tail spinning parachute cord length L parachute real aircraft of the real aircraft; and measuring the resistance coefficient CD of the anti-tail-spin umbrella through a wind tunnel force measurement test or numerical simulation calculation to obtain the geometric area S true machine of the anti-tail-spin umbrella. Reliable and feasible parameters of the anti-tail-spin umbrella are obtained through the steps, so that the parameters of the anti-tail-spin umbrella meet the requirement that tail spin is changed within two circles, and meanwhile it is guaranteed that the resistance area of the tail-spin umbrella is minimum.

Description

Technical Field

[0001] The present application belongs to the field of aircraft flight quality test flight, and in particular relates to a method for determining the parameters of an aircraft anti-spin parachute. Background Art

[0002] When an aircraft flies above the stall angle of attack, it often deviates, rotates, and gradually develops into a spin. A spin is one of the most dangerous uncontrolled movements of an aircraft. Historically, there have been countless flight accidents caused by spins. To this day, studying the spin characteristics of an aircraft is still an important part of aircraft design. For highly maneuverable aircraft such as fighter jets, it is particularly important to study the spin characteristics clearly. By studying the spin characteristics of an aircraft, developing an effective spin recovery method, or installing a suitable anti-spin parachute, risks can be resolved at critical moments and flight safety can be greatly enhanced.

[0003] Anti-spin parachutes are generally used during the tailspin test of an aircraft. As one of the high-risk test flight subjects, the tailspin characteristic test flight needs to be well protected. The purpose of using an anti-spin parachute is to ensure that if the aircraft fails to recover from the tailspin through the control surface after entering the tailspin, the anti-spin parachute can ensure that the aircraft recovers from the tailspin, thereby eliminating the test flight risk and ensuring safety.

[0004] The selection of anti-spin parachute parameters is very particular. If the aircraft is too large, it will be difficult to install it, and it will affect the aircraft's mass characteristics, and will also affect the aircraft's stability, mass characteristics, and aerodynamic characteristics. If the size is too small, it will not be able to effectively correct the spin, which will affect the safety of the test flight. Therefore, it is necessary to select the appropriate anti-spin parachute for aircraft of different types, weights, and sizes. Summary of the invention

[0005] The purpose of the present application is to provide a method for determining the parameters of an aircraft anti-spin parachute, so as to solve the problem that the existing anti-spin parachute parameter selection is relatively difficult.

[0006] The technical solution of the present application is: a method for determining the parameters of an aircraft anti-spin parachute, comprising: estimating the drag area S of the anti-spin parachute of a real aircraft by an empirical formula CD ;

[0007] The drag area S of the parachute estimated by the empirical formula CD As input, S is obtained after scaling by the dynamic similarity criterion. CD1 , with S CD1 As a benchmark, select several CD1 The drag area of ​​the anti-spin parachute within the range is determined, and the model free-fly spin recovery test is carried out in a vertical wind tunnel. The tests are carried out in order from small to large until the anti-spin parachute S with the minimum drag area that can recover the spin within the set number of turns is selected. CD1 ′;

[0008] S CD1 ′ is used as input, and S is equivalently converted according to the scale of the free-flight model in the external field through the dynamic similarity criterion. CD2 , with S CD2 Based on the above, carry out the outdoor model free flight tailspin test. If the tailspin can be recovered within the set number of circles, continue to reduce the size for testing. If it cannot be recovered, increase the size, and repeat the cycle until the minimum size parachute S that can meet the requirements of recovering the tailspin within the set number of circles in the outdoor free flight tailspin recovery test is obtained. CD2 ′;

[0009] The verified tail spin parachute size is converted into the anti-tail spin parachute drag area S of the real aircraft through the conversion formula CD真机 and the length of the anti-spin parachute line L 伞真机 ; Then, the drag coefficient CD of the anti-spin parachute is determined by wind tunnel force measurement test or numerical simulation calculation, and the geometric area S of the anti-spin parachute is obtained. 真机 .

[0010] Preferably, the drag area S of the real anti-spin parachute is CD The drag area / area of ​​the anti-spin parachute is preliminarily estimated by empirical formula combined with the aircraft size, moment of inertia, wing loading and atmospheric density for which the spin test is required.

[0011] Preferably, the empirical formula includes:

[0012]

[0013] Where S is the wing area, b is the wingspan, L P is the distance from the parachute hook to the center of gravity of the aircraft, I x ,I y are the moments of inertia around the roll axis and yaw axis of the fuselage respectively, P is the unit wing load, α is the angle of attack of the aircraft in the spin, ρ is the atmospheric density at the parachute opening altitude, and V is the true airspeed of the aircraft in the spin.

[0014] Preferably, the first setting ratio is 0.4 to 1.0 times.

[0015] Preferably, the number of turns is set to 2 turns.

[0016] Preferably, after scaling, S CD1 The corresponding scaling formula is:

[0017]

[0018] Where K is the ratio of the true chord length to the chord length of the vertical wind tunnel test model wing.

[0019] Preferably, in the field model free-fly spin test, S CD1′ is changed to a size suitable for outdoor free flight model test, and the change relationship is:

[0020] S CD2 =K1 2 ·S CD1 '

[0021] Among them, K1 is the ratio of the average aerodynamic chord length of the wing of the outdoor free flight test model and the vertical wind tunnel test model.

[0022] Preferably, while correcting the spin within the set number of turns, a group of fuselage lengths at the second set multiple is taken as the combination of parachute line length and parachute drag area for testing until the most suitable anti-spin parachute line length is obtained.

[0023] Preferably, the second setting ratio is 0.7 to 1.3 times.

[0024] Preferably, the conversion formula is:

[0025] S CD真机 =K2 2 ·S CD2 '

[0026] L 伞真机 =K2·L 模型

[0027] Among them, K2 is the ratio of the average aerodynamic chord length of the real aircraft and the outdoor free flight test model wing, L 模型 is the length of the anti-spin parachute rope in the model.

[0028] Preferably, the geometric area S 真机 The calculation formula is:

[0029]

[0030] The method for determining the parameters of the anti-spin parachute of an aircraft in the present application is to make a preliminary estimate through an empirical formula, refine the selection through a vertical wind tunnel spin recovery test, determine through an outdoor free flight spin recovery test, and finally convert to the size of the real aircraft, and refine the parameters of the anti-spin parachute step by step, and finally obtain reliable and feasible anti-spin parachute parameters, so that the parameters of the anti-spin parachute meet the requirements of recovering from a spin within 2 turns and ensure that the drag area of ​​the spin parachute is minimized. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] In order to more clearly illustrate the technical solution provided by the present application, the following is a brief introduction to the accompanying drawings. Obviously, the accompanying drawings described below are only some embodiments of the present application.

[0032] Figure 1 This is a schematic diagram of the overall process of this application. DETAILED DESCRIPTION

[0033] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0034] A method for determining the parameters of an aircraft anti-spin parachute. The parameters of an anti-spin parachute generally include three parameters: area, parachute rope length, and drag coefficient. Generally, the drag coefficient multiplied by the area can be expressed as the drag area, which is used to measure the drag effect that the anti-spin parachute can produce. The larger the drag area, the stronger the drag effect, and the more obvious the effect of correcting the spin.

[0035] like Figure 1 , including the following steps:

[0036] Step S100, estimating the drag area S of the real anti-spin parachute by using an empirical formula CD Generally speaking, in order to ensure the effectiveness of spin recovery, the parachute size estimated by empirical formula is too large.

[0037] Specifically: Based on the following empirical formulas, combined with the parameters such as the aircraft size, moment of inertia, wing loading, atmospheric density, etc. that require a spin test, a preliminary estimate of the drag area / area of ​​the anti-spin parachute is made.

[0038] The empirical formula specifically includes:

[0039]

[0040] Where S is the wing area, b is the wingspan, L P is the distance from the parachute hook to the center of gravity of the aircraft, I x ,I y are the moments of inertia around the roll axis and yaw axis of the fuselage (kg.m2), P is the unit wing load (kg / m2), α is the angle of attack of the aircraft in a spin (°), ρ is the atmospheric density at the parachute opening altitude, and V is the true airspeed of the aircraft in a spin (m / s).

[0041] Step S200, the drag area S of the umbrella is estimated by the empirical formula CD As input, S is obtained after scaling by the dynamic similarity criterion. CD1 , with S CD1 As a benchmark, select several CD1 The drag area of ​​the anti-spin parachute within the range is determined, and the model free-fly spin recovery test is carried out in a vertical wind tunnel. The tests are carried out in order from small to large until the anti-spin parachute S with the minimum drag area that can recover the spin within the set number of turns is selected. CD1 ′.

[0042] Preferably, the first setting ratio is 0.4 to 1.0 times.

[0043] Preferably, the number of turns is set to 2 turns.

[0044] Preferably, after scaling, S CD1 The corresponding scaling formula is:

[0045]

[0046] Where K is the ratio of the true chord length to the chord length of the vertical wind tunnel test model wing.

[0047] Due to the differences in altitude, air density, moment of inertia and Reynolds number faced by a real aircraft during flight, the results obtained through the vertical wind tunnel spin test cannot be directly converted to a real aircraft for application, and need to be further verified through field model free flight tests.

[0048] Step S300: CD1 ′ is used as input, and S is equivalently converted according to the scale of the free-flight model in the external field through the dynamic similarity criterion. CD2 , with S CD2 Based on the above, carry out the outdoor model free flight tailspin test. If the tailspin can be recovered within the set number of circles, continue to reduce the size for testing. If it cannot be recovered, increase the size, and repeat the cycle until the minimum size parachute S that can meet the requirements of recovering the tailspin within the set number of circles in the outdoor free flight tailspin recovery test is obtained. CD2 ′.

[0049] Preferably, in the field model free-fly spin test, S CD1 ′ is changed to a size suitable for outdoor free flight model test, and the change relationship is:

[0050] S CD2 =K1 2 ·S CD1 ' (5)

[0051] Among them, K1 is the ratio of the average aerodynamic chord length of the wing of the outdoor free flight test model and the vertical wind tunnel test model.

[0052] Preferably, while correcting the spin within the set number of turns, a group of fuselage lengths at the second set multiple is taken as the combination of parachute line length and parachute drag area for testing until the most suitable anti-spin parachute line length is obtained, so as to determine the most suitable anti-spin parachute line length.

[0053] Preferably, the second setting ratio is 0.7 to 1.3 times.

[0054] Step S400: convert the verified tail spin parachute size through a conversion formula to obtain the anti-tail spin parachute drag area S of the real aircraft CD真机 and the length of the anti-spin parachute line L 伞真机 ; Then, the drag coefficient CD of the anti-spin parachute is determined by wind tunnel force measurement test or numerical simulation calculation, and the geometric area S of the anti-spin parachute is obtained. 真机 .

[0055] Preferably, the conversion formula is:

[0056] S CD真机 =K2 2 ·S CD2 ' (6)

[0057] L 伞真机 =K2·L 模型 (7)

[0058] Among them, K2 is the ratio of the average aerodynamic chord length of the real aircraft and the outdoor free flight test model wing, L 模型 is the length of the anti-spin parachute rope in the model.

[0059] Preferably, the geometric area S 真机 The calculation formula is:

[0060]

[0061] So far, the parameters of the anti-spin parachute are: parachute rope length L 伞真机 、Umbrella drag area S CD真机 、Umbrella area S 真机 All have been confirmed.

[0062] In summary, the present application adopts a “four-step” design strategy, including preliminary estimation through empirical formulas, refined selection through vertical wind tunnel spin recovery tests, determination through outdoor free flight spin recovery tests, and final conversion to the size of the real aircraft. The parameters of the anti-spin parachute are refined step by step, and finally reliable and feasible anti-spin parachute parameters are obtained, so that the parameters of the anti-spin parachute can meet the requirements of recovering from a spin within 2 turns while ensuring that the drag area of ​​the spin parachute is minimized.

[0063] As a specific implementation method, a specific example is used to illustrate:

[0064] 1. Use the empirical formula to preliminarily calculate the drag area of ​​the anti-spin parachute as shown in the following table:

[0065] Table 1 Calculation results of the drag area of ​​the anti-spin parachute obtained by different empirical formulas

[0066]

[0067] 2. Compare the three calculated values ​​in Table 1, remove the points with large deviations, and average the remaining two calculated values ​​to obtain the preliminary anti-spin parachute drag area: 70.5m 2 ; Usually the result obtained by the empirical formula is relatively large, in order to ensure the effectiveness of the anti-spin parachute recovery;

[0068] 3. Based on the relationship between the vertical wind tunnel test model and the actual aircraft size, preliminarily calculate the area of ​​the anti-spin parachute in the vertical wind tunnel

[0069] 4. Carry out vertical wind tunnel tail spin test, and finally obtain the minimum anti-tail spin parachute size that can meet the requirements of tail spin recovery within 2 turns: S CD1 '=0.032m 2 ;

[0070] 5. S CD1 'Converted to the size matching the outdoor free flight test model: S CD2 =0.20m 2 ;

[0071] 6. According to the fuselage size of the outdoor free flight test model, the parachute rope lengths are selected as 2.0m, 2.5m and 3.0m respectively. CD2 +2.0m combination, and conduct outdoor free flight tailspin recovery test. Then change the parameter value and repeat the test. Finally, through test iteration, the minimum drag area and parachute rope length combination that can recover from tailspin within 2 turns is: 0.126m 2 +3m; converting this set of data to the real machine is: 39m 2 +52.8m.

[0072] 7. For the real aircraft, a hemispherical anti-spin parachute is planned for test flight. Its drag coefficient is measured to be 0.58, so the parachute geometric area should be designed to be: 67.2m 2 .

[0073] 8. According to the method of the present invention, the anti-spin parachute parameters are finally determined: parachute rope length L 伞真机 is 52.8m, and the drag area of ​​the parachute is S CD真机 39m 2 、Umbrella geometric area 67.2m 2 .

[0074] Finally, it should be noted that: the drawings of the embodiments disclosed in the present invention only involve structures related to the embodiments disclosed in the present invention, and other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other;

[0075] Finally: The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for determining the parameters of an aircraft anti-spin parachute, characterized in that: include: Estimate the drag area S of the real anti-spin parachute through empirical formula CD ; The drag area S of the parachute estimated by the empirical formula CD As input, S is obtained after scaling by the dynamic similarity criterion. CD1 , with S CD1 As a benchmark, select several CD1 The drag area of ​​the anti-spin parachute within the range is determined, and the model free-fly spin recovery test is carried out in a vertical wind tunnel. The tests are carried out in order from small to large until the anti-spin parachute S with the minimum drag area that can recover the spin within the set number of turns is selected. CD1 ′; S CD1 ′ is used as input, and S is equivalently converted according to the scale of the free-flight model in the external field through the dynamic similarity criterion. CD2 , with S CD2 Based on the above, carry out the outdoor model free flight tailspin test. If the tailspin can be recovered within the set number of circles, continue to reduce the size for testing. If it cannot be recovered, increase the size, and repeat the cycle until the minimum size parachute S that can meet the requirements of recovering the tailspin within the set number of circles in the outdoor free flight tailspin recovery test is obtained. CD2 ′; The verified tail spin parachute size is converted into the anti-tail spin parachute drag area S of the real aircraft through the conversion formula CD真机 and the length of the anti-spin parachute line L 伞真机 ; Then, the drag coefficient CD of the anti-spin parachute is determined by wind tunnel force measurement test or numerical simulation calculation, and the geometric area S of the anti-spin parachute is obtained. 真机 .

2. The method for determining the parameters of an aircraft anti-spin parachute as claimed in claim 1, characterized in that: The drag area S of the real anti-spin parachute CD The drag area / area of ​​the anti-spin parachute is preliminarily estimated by empirical formula combined with the aircraft size, moment of inertia, wing loading and atmospheric density on which the spin test is to be carried out.

3. The method for determining the parameters of an aircraft anti-spin parachute as claimed in claim 1, characterized in that: The empirical formula includes: Where S is the wing area, b is the wingspan, L P is the distance from the parachute hook to the center of gravity of the aircraft, I x ,I y are the moments of inertia around the roll axis and yaw axis of the aircraft respectively, P is the unit wing loading, α is the angle of attack of the aircraft in the spin, ρ is the atmospheric density at the parachute opening altitude, and V is the true airspeed of the aircraft in the spin.

4. The method for determining the parameters of an aircraft anti-spin parachute as claimed in claim 1, characterized in that: The first setting ratio is 0.4 to 1.0 times.

5. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: Set the number of laps to 2.

6. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: After scaling, we get S CD1 The corresponding scaling formula is: Where K is the ratio of the true chord length to the chord length of the vertical wind tunnel test model wing.

7. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: In the field model free-flight spin test, S CD1 ′ is changed to a size suitable for outdoor free flight model test, and the change relationship is: S CD2 =K1 2 ·S CD1 ' Among them, K1 is the ratio of the average aerodynamic chord length of the wing of the outdoor free flight test model and the vertical wind tunnel test model.

8. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: While correcting the spin within the set number of turns, take a group of fuselage lengths at the second set ratio as the combination of parachute line length and parachute drag area for testing until the most suitable anti-spin parachute line length is obtained.

9. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: The second setting ratio is 0.7 to 1.3 times.

10. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: The conversion formula is: S CD真机 =K2 2 ·S CD2 ' L 伞真机 =K2·L 模型 Among them, K2 is the ratio of the average aerodynamic chord length of the real aircraft and the outdoor free flight test model wing, L 模型 is the length of the anti-spin parachute rope in the model.

11. The method for determining the parameters of an aircraft anti-spin parachute according to claim 1, characterized in that: Geometric area S 真机 The calculation formula is:

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