Unmanned helicopter blade lightning strike strength test verification method and system

Abstract

The application provides a unmanned helicopter blade lightning strike strength test verification method and system, and belongs to the technical field of helicopter structure strength design. The method first carries out a blade lightning current impact test and completes preparation of a blade lightning strike post-damage test piece, then determines a blade post-lightning strike residual life test load spectrum and a residual strength test load according to a blade actually measured flight load and a helicopter mission profile, carries out residual life fatigue test and residual strength test on the blade post-lightning strike test piece by simulating a helicopter blade loading and constraint mode. The loading form of the helicopter blade is complex in actual flight. The test load in the application covers all possible states of the blade actually measured flight profile, and truly simulates the loading and constraint mode of the helicopter blade, so that the residual life and residual strength of the blade post-lightning strike can be truly and effectively verified, and the safety of the blade post-lightning strike is ensured.

Description

Technical Field

[0001] This invention belongs to the field of helicopter structural strength design technology, and in particular relates to a method and system for verifying the strength of unmanned helicopter rotor blades after a lightning strike. Background Technology

[0002] In recent years, helicopter applications have become increasingly frequent. When helicopters perform high-altitude flight missions in complex weather conditions, the probability of rotor blades being struck by lightning is far higher than that of other components of the rotor system due to their large rotation radius. As a key component of the helicopter rotor system, the rotor blades bear complex aerodynamic loads, and their structural strength directly affects the flight safety of the entire helicopter. If the rotor blades fail due to structural strength failure after being struck by lightning during actual flight, it may cause serious safety accidents. Therefore, the safety of rotor blades after being struck by lightning must be considered during the helicopter development process.

[0003] Currently, helicopter rotor blades are typically made of composite materials. The damage to the blade body after being struck by lightning is difficult to accurately simulate using theoretical models. There is currently no effective modeling method to conduct an accurate theoretical analysis of the lifespan and remaining strength of rotor blades after a lightning strike. Summary of the Invention

[0004] To address the inability of related technologies to accurately analyze the lifespan and remaining strength of helicopter rotor blades after a lightning strike, this invention proposes a method and system for testing and verifying the strength of unmanned helicopter rotor blades after a lightning strike. This method can accurately and effectively verify the remaining lifespan and remaining strength of helicopter rotor blades after a lightning strike. The technical solution is as follows:

[0005] Firstly, a method for verifying the strength of unmanned helicopter rotor blades after lightning strikes is provided. First, a lightning current impact test is conducted on the rotor blades, and a test piece containing damage after lightning strikes is prepared. Then, based on the measured flight load of the rotor blades and the helicopter mission profile, the load spectrum for the remaining life test and the load for the remaining strength test of the rotor blades after lightning strikes are determined. By simulating the loading and constraint mode of the helicopter rotor blades, the remaining life fatigue test and the remaining strength test are conducted on the rotor blade test piece after lightning strikes.

[0006] Specifically, the method includes:

[0007] Step 1: Conduct a lightning current impulse test on the blades;

[0008] Step 2: Analyze the location and extent of damage to the blades after the lightning strike;

[0009] Step 3: Prepare test specimens of the propeller blades after lightning strike;

[0010] Step 4: Determine the residual strength test load after the blade is struck by lightning. The residual strength test load includes flapping moment, oscillation moment and centrifugal force.

[0011] Step 5: Determine the remaining life test load spectrum after the blade is struck by lightning. The remaining life test load spectrum includes the test load for each of the two operating conditions and the number of test load cycles for each operating condition.

[0012] Step 6: Conduct a test on the remaining life of the blades after a lightning strike;

[0013] Step 7: Conduct a residual strength test on the blades after a lightning strike;

[0014] Step 8: Analyze the effectiveness of the blade strength test after lightning strike.

[0015] Step one includes:

[0016] The location of the lightning discharge point on the blade is determined. The location of the discharge point includes the blade tip as the initial attachment area of ​​lightning and the trailing edge of the middle section of the blade airfoil as the sweep attachment area of ​​lightning.

[0017] Lightning current impulse tests were conducted on the blades in two separate lightning zones to cause lightning damage to the blade body.

[0018] Step two includes:

[0019] The damaged test specimens of propeller blades after lightning strikes were subjected to impact and ultrasonic non-destructive testing to preliminarily determine the area of ​​damage to the blade skin.

[0020] In the blade model, the skin of the damaged area is removed, and the section with the largest decrease in stiffness is used as the test monitoring area.

[0021] Step three includes:

[0022] The end of the blade after being struck by lightning is cut off, the foam is removed and filled with chopped fibers, and after curing, a metal clamp is installed to form a test specimen of the blade after being struck by lightning.

[0023] Bridge-type strain gauges are attached to both sides of the test monitoring area to measure the test load.

[0024] In step four, the first-order spectrum of the measured dynamic loads in the blade test monitoring area is sorted from largest to smallest. The measured dynamic loads include flapping loads and oscillation loads. The flapping loads include flapping dynamic loads and flapping static loads, and the oscillation loads include oscillation vibration loads and oscillation static loads. The maximum value of the flapping dynamic load is superimposed with the flapping static load to obtain the flapping bending moment of the remaining strength test load. The maximum value of the oscillation vibration load is superimposed with the oscillation static load to obtain the oscillation bending moment of the remaining strength test load. At the same time, the centrifugal force under over-torsion state is used as the centrifugal force Fc during the test.

[0025] Step five includes:

[0026] Analyze the helicopter's flight mission profile to determine the maximum loiter time t that the helicopter can still complete its flight mission and return safely after its rotor blades are struck by lightning.

[0027] The flight measured dynamic load spectrum of the propeller test monitoring area is sorted from largest to smallest, and the flight measured dynamic load spectrum is simplified into two working conditions: Working condition 1: the maximum dynamic load in the flight measured spectrum covers the first m% of the working conditions; Working condition 2: the maximum dynamic load of the remaining working conditions covers the remaining 1-m% of the working condition loads.

[0028] The number of test load cycles M1 for load condition 1 is calculated as t×K×R×60×m%. The number of test load cycles M2 for load condition 2 is calculated as follows: t×k×R×60×(1 -m%), where R is the rated speed of the helicopter rotor; K is the life dispersion coefficient.

[0029] Step six includes:

[0030] The blade root end of the test piece is fixedly installed on the support joint, and a centrifugal force Fc is applied to the loading joint end of the test piece; at the same time, an excitation force Fe is applied to adjust the rotation angle of the loading joint, so as to obtain the wagging moment and oscillation moment of the test monitoring area determined in step five.

[0031] First complete the load cycle for condition 1 in step 5, then complete the load cycle for condition 2.

[0032] After completing the prescribed number of cycles, stop the test and deload all loads to 0.

[0033] Step seven includes:

[0034] The centrifugal force Fc is increased from 0 to the maximum, and the swinging load in the test monitoring area is adjusted to the specified load determined in step four.

[0035] After completing multiple cycles, stop the test, unload all loads to 0, and inspect the test specimen.

[0036] Secondly, a system for testing and verifying the post-lightning-strength of unmanned helicopter rotor blades is provided, for use with the post-lightning-strength testing and verification method for unmanned helicopter rotor blades described in the first aspect. The system includes: a processor, a test piece, a loading device, and a bridge strain gauge.

[0037] The processor is used for:

[0038] Analyze the location and extent of damage to the blades after lightning strikes; determine the residual strength test loads for the blades after lightning strikes, which include flapping moment, oscillation moment, and centrifugal force; determine the residual life test load spectrum for the blades after lightning strikes, which includes the test loads for each of the two operating conditions and the number of test load cycles for each operating condition.

[0039] The loading device is used to fix the test specimen in place, facilitating the test;

[0040] Bridge strain gauges are used to measure test loads.

[0041] The method and system for verifying the strength of helicopter rotor blades after lightning strikes proposed in this invention can guide the entire verification process of rotor blade lightning current impulse tests, post-lightning life tests, and residual strength tests. Helicopter rotor blades are subjected to complex loads during actual flight. The test loads in this invention cover all possible states in the measured flight spectrum of the rotor blades and realistically simulate the loading and constraint methods of helicopter rotor blades. This allows for the accurate and effective verification of the residual life and residual strength of the rotor blades after a lightning strike, ensuring the safety of the rotor blades after a lightning strike. Attached Figure Description

[0042] Figure 1 A schematic flowchart of a method for verifying the strength of unmanned helicopter rotor blades after a lightning strike, provided in an embodiment of the present invention;

[0043] Figure 2 A schematic diagram of the discharge point of the blade lightning current impulse test provided in an embodiment of the present invention.

[0044] Figure 3 This is a schematic diagram of the damage location and monitoring profile of the test specimen after a lightning strike on the blade, provided for an embodiment of the present invention.

[0045] Figure 4 This is a schematic diagram of the installation and loading of the resonance method for the blade strength test after lightning strike, provided in an embodiment of the present invention.

[0046] Figure 5 This is a schematic diagram of four-point bending loading for a blade strength test after a lightning strike, provided in an embodiment of the present invention. Detailed Implementation

[0047] The present application will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0048] This invention provides a method for verifying the strength of unmanned helicopter rotor blades after a lightning strike. The method first conducts a lightning current impulse test on the rotor blades and prepares a damaged test specimen. Based on the measured flight load on the rotor blades and the helicopter mission profile, the remaining life test load spectrum and remaining strength test load of the rotor blades after the lightning strike are determined. By realistically simulating the loading and constraint conditions of the helicopter rotor blades, remaining life fatigue tests and remaining strength tests are conducted on the lightning-struck rotor blade test specimen. Figure 1 As shown, the specific steps include:

[0049] Step 1: Conduct a lightning current impulse test on the blades. This specifically includes:

[0050] 11. Determine the location of the lightning discharge point on the blade, such as... Figure 2 As shown, the discharge point locations include the blade tip as area 1A (initial lightning attachment area) and the trailing edge of the middle section of the blade airfoil as area 2A (sweeping lightning attachment area).

[0051] 12. Using the lightning current waveform requirements in ARP5412 "Aircraft Lightning Test Environment and Test Waveforms", conduct lightning current impulse tests on the blades according to the two lightning zones in step 11 to cause lightning damage to the blade body.

[0052] Step 2: Analyze the location and extent of damage to the blades after the lightning strike. This includes:

[0053] 21. Conduct impact and ultrasonic non-destructive testing on the damaged test specimens of the propeller blades after lightning strikes to preliminarily determine the area of ​​damage to the blade skin.

[0054] 22. Using the blade calculation and analysis software CPAO, the skin of the damaged area was removed from the blade model, and the section with the largest stiffness reduction was calculated and used as the test monitoring area. For example... Figure 3 As shown.

[0055] Step 3: Prepare test specimens of the blades after a lightning strike. This specifically includes:

[0056] 31. Cut off the end of the blade after the lightning strike, remove the foam and fill it with chopped fiber. After curing, install the metal clamp to form a test specimen of the blade after the lightning strike.

[0057] 32. Attach bridge-type strain gauges to both sides of the test monitoring area determined in step two to measure the test load.

[0058] Step 4: Determine the residual strength test load after the blade is struck by lightning. The residual strength test load includes flapping moment, oscillation moment and centrifugal force.

[0059] A simplified 1:1 test load spectrum block was used. The first-order spectrum of the measured dynamic load in the test monitoring area of ​​the propeller was sorted from largest to smallest. The measured dynamic load in the test included flapping load and oscillation load. The flapping load included flapping dynamic load and flapping static load. The oscillation load included oscillation vibration load and oscillation static load. The maximum value of the flapping dynamic load was superimposed with the flapping static load to obtain the flapping bending moment of the remaining strength test load. The maximum value of the oscillation vibration load was superimposed with the oscillation static load to obtain the oscillation bending moment of the remaining strength test load. At the same time, the centrifugal force under over-torsion state was used as the centrifugal force Fc during the test.

[0060] Step 5: Determine the remaining life test load spectrum for the blades after the lightning strike. The remaining life test load spectrum includes the test load for each of the two operating conditions and the number of test load cycles for each operating condition. Specifically, it includes:

[0061] 51. Analyze the profile of a helicopter performing a flight mission to determine the maximum loiter time t, in hours, during which the helicopter can continue to complete the flight mission and return safely after the rotor blades are struck by lightning.

[0062] 52. Using a simplified 1:1 test load spectrum block, the first-order spectrum of the measured dynamic load in the flight test monitoring area of ​​the propeller is sorted from largest to smallest. The first-order spectrum of the measured dynamic load in the flight is simplified into two working conditions as follows: Working condition 1: The maximum dynamic load in the measured dynamic load spectrum covers the first m% of the working conditions; Working condition 2: The maximum dynamic load of the remaining working conditions covers the remaining 1-m% of the working condition loads.

[0063] 53. Calculate the number of test load cycles M1 for condition 1 as t×K×R×60×m%. Calculate the number of test load cycles M2 for condition 2 as follows: t×k×R×60×(1 -m%), where R is the rated rotational speed of the helicopter rotor, in revolutions per minute; K is the life dispersion factor.

[0064] It should be noted that this embodiment does not limit the order of steps four and five.

[0065] Step 6: Conduct a test on the remaining life of the blades after a lightning strike.

[0066] The sequence of blade strength tests after a lightning strike is as follows: first, the remaining life test is completed, followed by the remaining strength test. Specifically, this includes:

[0067] 61. Fix the blade root end of the test piece to the support joint of the loading device, apply centrifugal force Fc to the loading joint end of the test piece; at the same time, apply excitation force Fe to adjust the rotation angle of the loading joint, so as to obtain the swinging moment and oscillation moment of the test monitoring area determined in step five.

[0068] 62. First complete the load cycle of condition 1 in step 5, then complete the load cycle of condition 2;

[0069] 63. After completing the specified number of cycles, stop the test and unload all loads to 0.

[0070] Step 7: Conduct a residual strength test on the blades after a lightning strike.

[0071] The residual strength test of blades after lightning strikes generally uses the resonance loading method, which specifically includes:

[0072] 71. Increase the centrifugal force Fc from 0 to the maximum, and adjust the swinging load in the test monitoring area to the specified load determined in step four;

[0073] 72. After completing 100 cycles, stop the test, unload all loads to 0, and inspect the test specimen.

[0074] In another embodiment, if the resonance method swinging load cannot reach the specified load, a four-point bending test method can also be used, such as... Figure 5 As shown:

[0075] The centrifugal force Fc is gradually and coordinated to the maximum in increments of no more than 10% of the load value at each level, and the waving moment and the oscillation moment are gradually and coordinated to the maximum test load in increments of no more than 10% of the load value at each level.

[0076] After loading the swinging moment and oscillation moment to 100% load value, hold the load for 30 seconds, and then unload to 0; unload the centrifugal force Fc to 0 and inspect the test specimen.

[0077] In another embodiment, after step seven, in order to analyze the effectiveness of the blade lightning strike strength test, step eight can also be performed:

[0078] Step 8: Analyze the effectiveness of the blade strength test after lightning strike. This includes:

[0079] 81. Remaining life test: If the test loading requirements (step six) are met for the number of times M1 and M2 (step five), then the remaining life test is deemed valid;

[0080] 82. Residual strength test: If the test loading requirements are met (step seven), then the residual strength test is deemed valid;

[0081] 83. Test pass criteria: If the remaining life test and the remaining strength test are valid, then the blade strength test after lightning strike is valid.

[0082] The helicopter rotor blade lightning strike strength test verification method proposed in this invention can guide the entire verification process of rotor blade lightning current impulse test and lightning strike life and residual strength test.

[0083] Helicopter rotor blades are subjected to complex loads during actual flight. The test loads in this invention cover all possible states in the measured flight spectrum of the rotor blades and realistically simulate the load and constraint methods of helicopter rotor blades. This can effectively verify the remaining life and remaining strength of the rotor blades after a lightning strike, ensuring the safety of the rotor blades after a lightning strike.

[0084] An embodiment of the present invention also provides a system for testing and verifying the post-lightning-strength of unmanned helicopter rotor blades, used in the above-described method for testing and verifying the post-lightning-strength of unmanned helicopter rotor blades. The system includes: a processor, a test piece, a loading device, and a bridge strain gauge.

[0085] The processor is used for:

[0086] The damage location and extent to the blades after lightning strikes are analyzed; the residual strength test loads after lightning strikes are determined, including flapping moment, oscillation moment, and centrifugal force; the residual life test load spectrum after lightning strikes is determined, including the test loads for each of the two operating conditions and the number of test load cycles for each operating condition; the specific execution operations of the processor can be referred to the process in the above method embodiment, and will not be repeated here.

[0087] The loading device is used to fix the test specimen in place, facilitating the test;

[0088] Bridge strain gauges are used to measure test loads.

[0089] The above description merely illustrates the embodiments of this application, and while it is quite specific and detailed, it should not be construed as limiting the scope of the patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Furthermore, any parts not detailed in this application are conventional techniques.

Claims

1. A method for verifying the strength of unmanned helicopter rotor blades after a lightning strike, characterized in that, First, a lightning current impulse test is conducted on the rotor blade, and a test specimen containing damage after a lightning strike is prepared. Then, based on the measured flight load on the rotor blade and the helicopter mission profile, the remaining life test load spectrum and remaining strength test load of the rotor blade after the lightning strike are determined. By simulating the loading and constraint mode of the helicopter rotor blade, the remaining life fatigue test and remaining strength test are conducted on the rotor blade test specimen after the lightning strike. The method specifically includes: Step 1: Conduct a lightning current impulse test on the blades; Step 2: Analyze the location and extent of damage to the blades after the lightning strike; Step 3: Prepare test specimens of the propeller blades after lightning strike; Step 4: Determine the residual strength test load after the blade is struck by lightning. The residual strength test load includes flapping moment, oscillation moment and centrifugal force. Step 5: Determine the remaining life test load spectrum after the rotor blade is struck by lightning. The remaining life test load spectrum includes the test load for each of the two operating conditions and the number of test load cycles for each operating condition. Step 5 includes: analyzing the helicopter's flight mission profile to determine the maximum loiter time t after the rotor blade is struck by lightning, allowing the helicopter to continue its flight mission and return safely; sorting the first-order spectrum of the measured dynamic load in the rotor blade test monitoring area from largest to smallest, and simplifying the first-order spectrum of the measured dynamic load into two operating conditions: Operating condition 1: the maximum dynamic load in the measured dynamic load spectrum covers the first m% of the operating conditions; Operating condition 2: the maximum dynamic load of the remaining operating conditions covers the remaining 1-m% of the operating condition load; calculating the number of test load cycles M1 for operating condition 1 as t×K×R×60×m%, and calculating the number of test load cycles M2 for operating condition 2 as t×k×R×60×(1-m%), where R is the rated speed of the helicopter rotor and K is the life dispersion factor. Step 6: Conduct a test on the remaining life of the blades after a lightning strike; Step 7: Conduct a residual strength test on the blades after a lightning strike; Step 8: Analyze the effectiveness of the blade strength test after lightning strike.

2. The method according to claim 1, characterized in that, Step one includes: The location of the lightning discharge point on the blade is determined. The location of the discharge point includes the blade tip as the initial attachment area of ​​lightning and the trailing edge of the middle section of the blade airfoil as the sweep attachment area of ​​lightning. Lightning current impulse tests were conducted on the blades in two separate lightning zones to cause lightning damage to the blade body.

3. The method according to claim 1, characterized in that, Step two includes: The damaged test specimens of propeller blades after lightning strikes were subjected to impact and ultrasonic non-destructive testing to preliminarily determine the area of ​​damage to the blade skin. In the blade model, the skin of the damaged area is removed, and the section with the largest decrease in stiffness is used as the test monitoring area.

4. The method according to claim 1, characterized in that, Step three includes: The end of the blade after being struck by lightning is cut off, the foam is removed and filled with chopped fibers, and after curing, a metal clamp is installed to form a test specimen of the blade after being struck by lightning. Bridge-type strain gauges are attached to both sides of the test monitoring area to measure the test load.

5. The method according to claim 1, characterized in that, In step four, the first-order spectrum of the measured dynamic loads in the blade test monitoring area is sorted from largest to smallest. The measured dynamic loads include flapping loads and oscillation loads. The flapping loads include flapping dynamic loads and flapping static loads, and the oscillation loads include oscillation vibration loads and oscillation static loads. The maximum value of the flapping dynamic load is superimposed with the flapping static load to obtain the flapping bending moment of the remaining strength test load. The maximum value of the oscillation vibration load is superimposed with the oscillation static load to obtain the oscillation bending moment of the remaining strength test load. At the same time, the centrifugal force under over-torsion state is used as the centrifugal force Fc during the test.

6. The method according to claim 1, characterized in that, Step six includes: The blade root end of the test piece is fixedly installed on the support joint, and a centrifugal force Fc is applied to the loading joint end of the test piece; at the same time, an excitation force Fe is applied to adjust the rotation angle of the loading joint, so as to obtain the wagging moment and oscillation moment of the test monitoring area determined in step five. First complete the load cycle for condition 1 in step 5, then complete the load cycle for condition 2. After completing the prescribed number of cycles, stop the test and deload all loads to 0.

7. The method according to claim 6, characterized in that, Step seven includes: The centrifugal force Fc is increased from 0 to the maximum, and the swinging load in the test monitoring area is adjusted to the specified load determined in step four. After completing multiple cycles, stop the test, unload all loads to 0, and inspect the test specimen.

8. A system for testing and verifying the strength of unmanned helicopter rotor blades after a lightning strike, characterized in that, The system used for verifying the post-lightning strike strength of unmanned helicopter rotor blades according to any one of claims 1 to 7 comprises: a processor, a test specimen, a loading device, and a bridge strain gauge. The processor is used for: Analyze the location and extent of damage to the blades after lightning strikes; determine the residual strength test loads for the blades after lightning strikes, which include flapping moment, oscillation moment, and centrifugal force; determine the residual life test load spectrum for the blades after lightning strikes, which includes the test loads for each of the two operating conditions and the number of test load cycles for each operating condition. The loading device is used to fix the test specimen in place, facilitating the test; Bridge strain gauges are used to measure test loads.

Images