A method of decoupling torsion from tension-compression strain in a helicopter rotor shaft

Abstract

The application provides a method for decoupling torsion from tension and compression strain of a helicopter rotor shaft, which comprises the following steps: firstly, sticking a strain gauge on one side of the helicopter rotor shaft along the direction of the rotor shaft and outside the rotor shaft, taking the center of the strain gauge as the center of a circle, and sticking a half circle of strain gauges outside the rotor shaft at every preset degree; secondly, sticking a strain gauge on the symmetric side of the helicopter rotor shaft along the direction of the rotor shaft and outside the rotor shaft, taking the center of the strain gauge as the center of a circle, and sticking a half circle of strain gauges outside the rotor shaft at every preset degree; thirdly, loading in the tension and compression direction of the rotor shaft and measuring the strain output of each strain gauge; fourthly, loading in the torsion direction of the rotor shaft and measuring the strain output of each strain gauge; fifthly, selecting two strain gauges to calculate the coupling factor of torsion to tension and compression strain, and selecting two strain gauges to complete the shaft force test of the rotor shaft. The application can decouple torsion from tension and compression strain of the helicopter rotor shaft, does not need to change the rear test equipment, and can accurately measure the tension of the helicopter rotor shaft in flight test.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of helicopter test flight test, and particularly relates to a method for eliminating the coupling of torsion to the tensile and compressive strain of a helicopter rotor shaft. BACKGROUND

[0002] The tensile force of a helicopter rotor shaft is a key parameter for analyzing the performance and quality of a helicopter test flight and determining the service life of the rotor shaft. A common test method for the tensile force of a rotor shaft measures the tensile force value by measuring the tensile and compressive strain of the shaft. The tensile and compressive strain of the rotor shaft is measured by pasting two groups of T-shaped strain gauges on the shaft and forming an electric bridge. Figure 1

[0003] During the helicopter test flight, the rotor shaft is subjected to not only a large tensile force but also a strong torque. The compensation ability of the T-shaped strain gauge bridge to the coupling strain caused by the torsion is poor, so that the measurement result is not completely the tensile and compressive strain, and contains a considerable proportion of torsional coupling strain, which finally leads to a large error in the measured tensile force value of the rotor shaft. SUMMARY

[0004] To solve the problem of a large error in the measured tensile force value of the rotor shaft in the prior art, the present application provides a method for eliminating the coupling of torsion to the tensile and compressive strain of a helicopter rotor shaft, which can eliminate the coupling of torsion to the tensile and compressive strain of a helicopter rotor shaft, so that the coupling degree of the torsion to the tensile and compressive strain of a helicopter rotor shaft is not greater than 5%. The method is compatible with the original test equipment and does not need to change the back-end test equipment. The rotor shaft tensile force of a helicopter test flight can be accurately measured. The technical solution is as follows:

[0005] In a first aspect, a method for eliminating the coupling of torsion to the tensile and compressive strain of a helicopter rotor shaft is provided, and the method comprises the following steps:

[0006] Step one, on one side of the helicopter rotor shaft, a strain gauge M1 is pasted on the outside of the rotor shaft along the direction of the rotor shaft. The center of the strain gauge M1 is taken as the center, and a half circle of strain gauges is uniformly pasted on the outside of the rotor shaft at every preset degree, wherein the first strain gauge and the last strain gauge are located on the same horizontal plane as M1.

[0007] Step two, on the symmetric side of the helicopter rotor shaft, a strain gauge M2 is pasted on the outside of the rotor shaft along the direction of the rotor shaft. The center of the strain gauge M2 is taken as the center, and a half circle of strain gauges is uniformly pasted on the outside of the rotor shaft at every preset degree, wherein the first strain gauge and the last strain gauge are located on the same horizontal plane as M2.

[0008] Step three, loading in the tensile and compressive direction of the rotor shaft, the tensile force is F, and the strain output of each strain gauge is measured.

[0009] Step four, loading in the torsion direction of the rotor shaft, the torque is b*F, and the strain output of each strain gauge is measured, wherein b is greater than 0 and less than 1. ​

[0010] Step 5: From the half-circle strain gauges in Step 1 and Step 2, select two strain gauges, Mi and Mk, and exhaustively calculate the coupling factor α between torsion and tension / compressive strain.

[0011] α = (Nε1+Nε2)-(Nε i +Nε k )

[0012] (Lε1+Lε2)-(Lε i +Lε k );

[0013] in,

[0014] Lε1 represents the tensile-compressive loading response of strain gauge M1, and Lε2 represents the tensile-compressive loading response of strain gauge M2.

[0015] Nε1 represents the torsional loading response of strain gauge M1, and Nε2 represents the torsional loading response of strain gauge M2.

[0016] Lε i For the tensile and compressive loading response of strain gauge Mi, Lε k The tensile and compressive loading response of strain gauge Mk

[0017] Nε i For the torsional loading response of strain gauge Mi, Nε k The torsional loading response of strain gauge Mk;

[0018] Step 6: Select two strain gauges, MX and MY, based on the coupling factor α;

[0019] Step 7: Connect strain gauges M1 and M2 with strain gauges MX and MY to form a bridge circuit to complete the rotor shaft axial force test.

[0020] Optionally, step six specifically includes:

[0021] If the minimum value of the coupling factor α is less than or equal to the threshold, select the two strain gauges corresponding to the minimum value, and name the two strain gauges MX and MY.

[0022] Furthermore, the method also includes:

[0023] If the minimum value of the influence factor α is greater than the threshold, paste another strain gauge near the two strain gauges corresponding to the minimum value, and repeat steps three, four, and five until strain gauges MX and MY that meet the requirement of less than or equal to 5% are found.

[0024] In this case, the preset degrees in steps one and two are equal and are 10°.

[0025] In step four, b is 0.75.

[0026] The threshold is 5%.

[0027] Optionally, the material testing machine is used to load the shaft force in the direction of the rotor shaft tension and compression, and to load the torque in the direction of the rotor shaft torsion.

[0028] In step seven, the strain gauges M1 and M2 and the strain gauges MX and MY are combined into a full-bridge circuit, the strain gauges M1 and M2 are the opposite arms, and the strain gauges MX and MY are the opposite arms.

[0029] The present application has at least the following beneficial effects:

[0030] 1. The torsion is decoupled from the tension and compression strain of the helicopter rotor shaft, so that the coupling degree of the torsion to the tension and compression strain of the helicopter rotor shaft is not greater than 5%;

[0031] 2. Compatible with the original test equipment, without the need to change the back-end test equipment;

[0032] 3. Accurate measurement of the rotor shaft tension of the helicopter test flight. BRIEF DESCRIPTION OF DRAWINGS

[0033] Figure 1 It is a schematic diagram of the commonly used rotor shaft tension and compression strain gauge sticking and bridge combination;

[0034] Figure 2 It is a rotor shaft strain gauge sticking position diagram for decoupling;

[0035] Figure 3 It is a strain gauge bridge combination schematic diagram after decoupling. DETAILED DESCRIPTION

[0036] The present application will be further described in detail through specific embodiments and drawings.

[0037] The present application provides a method for decoupling the torsion from the tension and compression strain of the helicopter rotor shaft, comprising the following steps:

[0038] Step one, on one side of the helicopter rotor shaft, a strain gauge M1 is pasted on the outside of the rotor shaft in the direction of the rotor shaft, with the center of the strain gauge M1 as the center, and a half circle of strain gauges is uniformly pasted on the outside of the rotor shaft at every preset degree, wherein the first strain gauge and the last strain gauge are located on the same horizontal plane as M1.

[0039] Step two, on the symmetric side of the helicopter rotor shaft, a strain gauge M2 is pasted on the outside of the rotor shaft in the direction of the rotor shaft, with the center of the strain gauge M2 as the center, and a half circle of strain gauges is uniformly pasted on the outside of the rotor shaft at every preset degree, wherein the first strain gauge and the last strain gauge are located on the same horizontal plane as M2.

[0040] Step three, loading in the direction of the rotor shaft tension and compression, the tension is F, and the strain output of each strain gauge is measured.

[0041] Step four, load in the direction of the rotor shaft torsion, torque is b*F, measure the strain output of each strain gauge, b is greater than 0 and less than 1;

[0042] Step five, in the half circle strain gauge in step one and the half circle strain gauge in step two, select two strain gauges Mi, Mk, exhaustively calculate the coupling factor α of torsion to tensile and compressive strain,

[0043] α= (Nε1+Nε2)-(Nε i +Nε k )

[0044] (Lε1+Lε2)-(Lε i +Lε k );

[0045] Wherein,

[0046] Lε1 is the tensile and compressive load response of strain gauge M1, Lε2 is the tensile and compressive load response of strain gauge M2,

[0047] Nε1 is the torsion load response of strain gauge M1, Nε2 is the torsion load response of strain gauge M2,

[0048] Lε i is the tensile and compressive load response of strain gauge Mi, Lε k is the tensile and compressive load response of strain gauge Mk,

[0049] Nε i is the torsion load response of strain gauge Mi, Nε k is the torsion load response of strain gauge Mk;

[0050] Step six, select two strain gauges MX, MY according to the coupling factor α;

[0051] Step seven, strain gauges M1, M2 and strain gauges MX, MY are combined into a bridge circuit, and the rotor shaft axial force test is completed.

[0052] In an embodiment, the specific implementation process of the present application is as follows:

[0053] 1. As shown in the figure, on one side (0°) and the symmetric side (180°) of the helicopter rotor shaft, a strain gauge M1 and a strain gauge M2 are respectively pasted along the direction of the rotor shaft, and a group of strain gauges are uniformly pasted every 10° in the horizontal direction, which are M3, M4, ··· M21, M22, M23, ··· M40 respectively; Figure 2

[0054] 2. Load in the direction of the rotor shaft tensile and compressive, tensile force is F (N), measure the strain output of each strain gauge, which is Lε1, Lε2, ··· Lε 40 ;

[0055] ​3. Load in the direction of the rotor shaft torsion, torque is 0.75*F (Nm), measure the strain output of each strain gauge, respectively Nε1, Nε2 ··· Nε 40 ;

[0056] In this embodiment, the material testing machine is used to load the shaft force in the direction of the rotor shaft tension and compression, and the torque is loaded in the direction of the rotor shaft torsion.

[0057] 4. In M3 to M40, select two strain gauges Mi and Mj, and calculate the coupling factor α of torsion to tension and compression,

[0058] α= (Nε1+Nε2)-(Nε i +Nε k )

[0059] (Lε1+Lε2)-(Lε i +Lε k );

[0060] 5. The minimum value of the coupling factor α is less than or equal to 5%, and the two strain gauges corresponding to the minimum value are selected, and the two strain gauges are MX and MY,

[0061] MX and MY can be two of M3, M4, ···, M21, or two of M22, M23, ···, M40, or MX is one of M3, M4, ···, M21, and MY is one of M22, M23, ···, M40, and the embodiments of the present application do not limit this.

[0062] In this embodiment, Lε3 and Nε3 of M3, Lε 25 and Nε 25 of M25 are substituted into the formula

[0063]

[0064] The minimum coupling factor α is obtained, and the coupling factor α is less than or equal to 5%, so MX and MY are selected as M3 and M25.

[0065] 6. The strain gauges M1 and M2 are combined with the strain gauges M3 and M25 to form a bridge circuit, as shown in Figure 3 , the tension and compression strain test of the rotor shaft is completed. The strain gauges M1 and M2 are combined with the strain gauges M3 and M25 to form a full-bridge circuit, the strain gauges M1 and M2 are opposite arms, and the strain gauges M3 and M25 are opposite arms.

[0066] The process of the rotor shaft axial force test is as follows: the strain gauge bridge circuit for the rotor shaft tension and compression force test is determined by the method, and the corresponding relationship between the strain bridge circuit output and the rotor shaft axial force is obtained through calibration. Then, the rotor load test equipment is installed on the main rotor system, the output voltage signal of the rotor shaft strain bridge circuit is collected and recorded in the helicopter flight state, and the tension and compression load of the rotor shaft in the helicopter flight state is calculated through the calibration coefficient.

[0067] In another embodiment, the present application is implemented as follows:

[0068] 1. On one side (0°) and the symmetric side (180°) of the helicopter rotor shaft, a strain gauge M1, M2 is respectively pasted along the rotor shaft direction, and a group of strain gauges M3, M4, …, M21, M22, M23, …, M40 are respectively pasted uniformly every 10° in the horizontal direction.

[0069] 2. The rotor shaft is loaded in the tension and compression direction, the tension is F (N), and the strain output of each strain gauge is measured, which is Lε1, Lε2, …, Lε 40 ;

[0070] 3. The rotor shaft is loaded in the torsion direction, the torque is 0.75*F (Nm), and the strain output of each strain gauge is measured, which is Nε1, Nε2, …, Nε 40 ;

[0071] 4. Among M3 to M40, two strain gauges Mi and Mj are selected, and the coupling factor α of torsion to tension and compression is calculated,

[0072]

[0073] 5. If the minimum value of the influence factor α is greater than 5%, strain gauges are pasted near the two strain gauges corresponding to the minimum value, and steps three, four and five are repeated until strain gauges MX and MY that meet the requirement of less than or equal to 5% are found.

[0074] In this embodiment, Lε5 and Nε5 of M5, Lε 39 and Nε 39 of M39 are substituted into the formula

[0075]

[0076] The coupling factor α is minimum, and the coupling factor α is greater than 5%, so strain gauges are pasted on the left and right sides of M5 and M39, one strain gauge is between M5 and M4, one strain gauge is between M5 and M6, one strain gauge is between M39 and M38, and one strain gauge is between M39 and M40.

[0077] Repeat step three, step four, step five until the strain gauge MX, MY meeting the requirement of less than or equal to 5% is found.

[0078] 6, the strain gauge M1, M2 and the strain gauge MX, MY are grouped into a bridge circuit, and the test of the rotor shaft tension and compression strain is completed. The strain gauge M1, M2 and the strain gauge MX, MY are grouped into a full-bridge circuit, the strain gauge M1, M2 is a pair of arms, and the strain gauge MX, MY is a pair of arms.

[0079] The above only expresses the embodiments of the present application, the description is more specific and detailed, but it cannot be understood as the limitation of the patent scope. It should be pointed out that for ordinary skilled in the art, without departing from the concept of the present application, a number of modifications and improvements can be made, which all belong to the protection scope of the present application. In addition, the part of the present application is not detailed is the conventional technology.

Claims

1. A method for releasing the torsional tension-compressive strain coupling of a helicopter rotor shaft, characterized in that, The method includes: Step 1: On one side of the helicopter rotor shaft, attach a strain gauge M1 along the direction of the rotor shaft to the outside of the rotor shaft. With the center of strain gauge M1 as the center, attach half a circle of strain gauges evenly on the outside of the rotor shaft at each preset degree. The first strain gauge and the last strain gauge are located on the same horizontal plane as M1. Step 2: On the symmetrical side of the helicopter rotor shaft, attach a strain gauge M2 along the rotor shaft direction on the outside of the rotor shaft. With the center of strain gauge M2 as the center, attach half a circle of strain gauges evenly on the outside of the rotor shaft at each preset degree. The first strain gauge and the last strain gauge are located on the same horizontal plane as M2. Step 3: Apply a load in the tensile and compressive directions of the rotor shaft, with a tensile force of F, and measure the strain output of each strain gauge; Step 4: Apply a load in the torsional direction of the rotor shaft with a torque of b*F, and measure the strain output of each strain gauge. b is greater than 0 and less than 1. Step 5: From the half-circle strain gauges in Step 1 and Step 2, select two strain gauges, Mi and Mk, and exhaustively calculate the coupling factor α between torsion and tension / compressive strain. ； in, Lε1 represents the tensile-compressive loading response of strain gauge M1, and Lε2 represents the tensile-compressive loading response of strain gauge M2. Nε1 represents the torsional loading response of strain gauge M1, and Nε2 represents the torsional loading response of strain gauge M2. Lε i For the tensile and compressive loading response of strain gauge Mi, Lε k The tensile and compressive loading response of strain gauge Mk Nε i For the torsional loading response of strain gauge Mi, Nε k The torsional loading response of strain gauge Mk; Step 6: Select two strain gauges MX and MY based on the coupling factor α: If the minimum value of the coupling factor α is less than or equal to 5%, select the two strain gauges corresponding to the minimum value, and name the two strain gauges MX and MY. Step 7: Connect strain gauges M1 and M2 with strain gauges MX and MY to form a bridge circuit to complete the rotor shaft axial force test; The method further includes: if the minimum value of the influence factor α is greater than 5%, then attach strain gauges near the two strain gauges corresponding to the minimum value, and repeat steps three, four, and five until strain gauges MX and MY that meet the requirement of less than or equal to 5% are found.

2. The method according to claim 1, characterized in that, The preset degrees in steps one and two are equal and are 10°.

3. The method according to claim 1, characterized in that, In step four, b is 0.

75.

4. The method according to claim 1, characterized in that, Axial force is applied to the rotor shaft in the tensile and compressive directions using a material testing machine, and torque is applied to the rotor shaft in the torsional direction.

5. The method according to claim 1, characterized in that, In step seven, strain gauges M1 and M2 are grouped with strain gauges MX and MY to form a full-bridge circuit, with strain gauges M1 and M2 as opposite arms and strain gauges MX and MY as opposite arms.

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