Helicopter rotor blade and method for verifying the airworthiness compliance of the gap thereof
By conducting detailed verification of the clearance between the rotor blades and the structure, the safety hazard of rotor blade collision with the tail boom was resolved, ensuring the safety of the helicopter under various conditions and verifying its airworthiness compliance.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- CHINA HELICOPTER RES & DEV INST
- Filing Date
- 2023-11-13
- Publication Date
- 2026-07-07
AI Technical Summary
In the existing technology, the clearance between the rotor blades and the structure has not been adequately verified, which cannot ensure that the blades and tail boom are avoided in all flight conditions, thus posing a safety hazard.
By analyzing the rotor blade flapping motion and fuselage attitude, the dangerous structural parts are identified, and experimental verification is carried out under high wind conditions and typical maneuvering conditions during flight to obtain the clearance between the blades and the structure, ensuring that there is sufficient clearance between the blades and the structure under any operating condition.
It prevents rotor blades from colliding with the structure under any normal flight conditions, improving the safety level of the helicopter and ensuring that the clearance between the rotor blades and the structure meets the requirements of airworthiness regulations.
Smart Images
Figure CN117550091B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of aircraft airworthiness certification technology, specifically relating to a method for verifying the airworthiness compliance of helicopter rotor blades and their clearance. Background Technology
[0002] Clause 29.661 of the Airworthiness Regulations for Transport Category Rotorcraft (CCAR-29-R2) stipulates that there must be sufficient clearance between the rotor blades and other parts of the structure to prevent the blades from colliding with any part of the structure under any operating condition. Due to the presence of flapping limiters, blade-tail boom collisions are generally not observed during normal flight and landing. However, in unexpected situations such as strong gusts or excessive pilot maneuvering, if the design clearance between the blades and tail boom is insufficient, a collision can occur. A blade-tail boom collision typically results in the destruction of the aircraft and fatalities. Therefore, to avoid such accidents, thorough airworthiness compliance verification of rotor blade clearance is essential.
[0003] Previous type validation methods typically combined static rotor blade clearance checks with random flight tests to demonstrate conformity. This approach lacked sufficient analysis to determine the appropriate test conditions for validation and did not provide explicit insight into the clearance range between the blades and other structures. Therefore, the validation work was insufficient to demonstrate adequate rotor blade clearance, thus failing to adequately verify compliance with the requirements of 29.661 under all conditions. Summary of the Invention
[0004] To address the aforementioned issues, this invention patent proposes a method for verifying the airworthiness compliance of helicopter rotor blades and their clearance. This method obtains and ensures that there is sufficient clearance between the rotor blades and the structure under typical conditions, preventing the blades from colliding with any part of the structure under any normal flight conditions, thereby improving the safety level of the helicopter.
[0005] Firstly, this application provides a method for verifying the airworthiness compliance of helicopter rotor blade clearance, the method comprising:
[0006] Step 1: Based on the analysis of rotor blade flapping motion and fuselage attitude, determine the critical structural locations;
[0007] Step 2: For the dangerous structural parts, conduct experiments to verify the blade clearance during the rotor start-up and shutdown process of the helicopter under high wind conditions, and obtain the blade clearance test results for high wind start-up and shutdown.
[0008] Step 3: For the dangerous structural parts, conduct test flights to verify the blade clearance under typical maneuvering conditions of the helicopter during flight, and obtain the test flight results of blade clearance under typical maneuvering conditions.
[0009] Step 4: Based on the results of the high wind start-stop test and the results of the flight test under typical maneuvering conditions, determine that there is sufficient clearance between the blade and other parts of the structure to prevent the blade from colliding with any part of the structure under any operating condition.
[0010] Specifically, step 2 includes:
[0011] Step 21: Install easily breakable devices at appropriate locations on the windshield in the front fairing area and the tail boom in the rear fairing area of the fuselage structure.
[0012] Step 22: Install a wind speed measuring device at a predetermined position at the rotor height in front of the helicopter in the windward direction;
[0013] Step 23: Use an external camera to record the entire test process and obtain the external camera recording results of the blade clearance;
[0014] Step 24: Check the helicopter control stick settings. The collective pitch stick should be at the minimum pitch position, and the control stick and pedals should be in the neutral position.
[0015] Step 25: Based on the initial overall limitations of the helicopter, determine the initial wind speed limits, and blow wind in front of, behind, to the left and right of the helicopter respectively;
[0016] Step 26: After the wind speed stabilizes, start the engine according to the normal procedure and gradually increase the speed. After the rotor speed stabilizes, shut down the engine according to the normal shutdown procedure to stop the rotor.
[0017] Step 27: Check the record results of the easily broken device and the external camera to confirm whether the easily broken device has collided with the propeller blade;
[0018] Step 28: If the easily broken device does not come into contact with the blade, calculate the blade clearance test result at the location of the minimum clearance value of the dangerous structural part;
[0019] Step 29: If the test result of the blade clearance at the dangerous structural part is not less than the preset minimum clearance value, then the clearance at the dangerous structural part is sufficient.
[0020] Specifically, step 21 includes: the reference value for the height of the easily broken device is the theoretical gap value at the installation position determined by linear interpolation based on the theoretical value at the minimum gap value of the dangerous structural part.
[0021] Specifically, the preset position in front of the helicopter in the windward direction is 200-300m away from the helicopter, in order to obtain the wind speed in advance so as to start or stop the rotor.
[0022] Specifically, step 28 includes: the test results of the blade clearance at the dangerous structural part are calculated by linear interpolation based on the recording results of the external camera and the reference value of the height of the balsa wood rod.
[0023] Specifically, step 3 includes:
[0024] Step 31: Install an overload sensor at the helicopter's center of gravity to obtain the overload coefficient at the helicopter's center of gravity;
[0025] Step 32: Use an external camera to record the rotor blade motion and the clearance between it and the dangerous structural parts during the landing gear touchdown phase of the test flight of the extreme altitude-speed envelope, and obtain the recording results of the external camera.
[0026] Step 33: After the extreme altitude-speed envelope test flight mission is completed, check the dangerous structural parts of the rotor blades and tail boom and the recording results of the external camera to confirm whether the rotor blades collided with the tail boom structure.
[0027] Step 34: If the rotor blades do not collide with the tail boom structure, capture the blade clearance recorded by the external camera corresponding to the larger overload coefficient, and determine the test flight result value of the blade clearance between the rotor blades and the tail boom structure under the relatively large overload coefficient by image comparison.
[0028] Step 35: If the test flight result of the blade clearance between the blade and the tail boom structure is greater than the preset minimum clearance value, then the clearance of the dangerous structural part is sufficient.
[0029] Specifically, step 34 includes: during the ground contact process with a larger overload coefficient, the rotor blades will generate a large downward flapping due to inertia, and the gap between the blades and the fuselage will be smaller. Therefore, the ground contact situation corresponding to the larger overload coefficient is selected for blade gap analysis.
[0030] Specifically, the preset minimum gap value is 23cm.
[0031] Secondly, this application provides a helicopter rotor blade, wherein the helicopter rotor blade is implemented using the helicopter rotor blade clearance airworthiness compliance verification method described above.
[0032] In summary, this invention proposes a method for verifying the airworthiness compliance of helicopter rotor blade clearance, used to verify compliance with clause 29.661 of the airworthiness regulation. According to this method, the range of clearance values between the rotor blades and the structure under typical operating conditions can be obtained, providing a clear understanding of the clearance between the rotor blades and the structure and ensuring its adequacy. This prevents blade collisions with the structure under any normal operating conditions (even with relatively rough pilot operation), thereby improving the helicopter's safety level throughout its entire safety envelope. Attached Figure Description
[0033] Figure 1 A flowchart illustrating a helicopter rotor blade clearance airworthiness compliance verification method provided in this application. Detailed Implementation
[0034] like Figure 1 As shown, the helicopter rotor blade clearance airworthiness compliance verification method of the present invention includes the following steps:
[0035] Step 1: Based on the analysis of rotor blade flapping motion and fuselage attitude, determine the critical structural locations;
[0036] Taking into account the helicopter rotor configuration, external fuselage structure, and other specific structural features, and considering factors such as blade motion, fuselage attitude, and overload coefficient, the most likely points of collision with the rotor blades are analyzed to identify hazardous structural areas to be considered during airworthiness verification. These hazardous structural areas include the forward fairing area (including the forward fairing of the engine compartment and the windshield) and the aft fairing area (including the aft fairing of the engine compartment, exhaust pipes, and tail boom). When determining hazardous structural areas, the arrangement of external protrusions such as antennas on the aircraft should be considered.
[0037] Step 2: For the dangerous structural parts, conduct experiments to verify the blade clearance during the rotor start-up and shutdown process of the helicopter under high wind conditions, and obtain the blade clearance test results for high wind start-up and shutdown.
[0038] When the rotor is not rotating or at a low speed, the blades have a large deflection, which may cause the blades to collide with the airframe structure after being subjected to a strong gust of wind.
[0039] Specifically, step 2 includes:
[0040] Step 21: Install breakable devices at appropriate locations on the windshield in the front fairing area and the tail boom in the rear fairing area of the fuselage structure.
[0041] In practical applications, easily broken devices can be made of balsa wood or foam pads. The reference height value is the theoretical gap value at the installation position determined by linear interpolation based on the theoretical value at the minimum gap value of the dangerous structural part.
[0042] It should be noted that the appropriate location on the tail boom in the windshield and rear fairing areas is determined based on the structural shape and the feasibility of installing easily breakable devices.
[0043] Step 22: Install a wind speed measuring device at a predetermined position at the rotor height in front of the helicopter in the windward direction.
[0044] The preset position in front of the helicopter in the windward direction is 200-300m away from the helicopter, in order to obtain the wind speed in advance so as to start or stop the rotor.
[0045] Step 23: Use an external camera to record the entire test process and obtain the external camera recording results of the blade clearance.
[0046] Step 24: Check the helicopter control stick settings. The collective pitch stick should be in the minimum pitch position, and the control stick and pedals should be in the neutral position.
[0047] Step 25: Based on the initial overall limitations of the helicopter, determine the initial wind speed limits, and blow wind in front of, behind, to the left and right of the helicopter respectively.
[0048] Step 26: After the wind speed stabilizes, start the engine according to the normal procedure and gradually increase the speed. After the rotor speed stabilizes, shut down the engine according to the normal shutdown procedure to stop the rotor.
[0049] The normal procedures are the engine start-up procedure and engine shutdown procedure specified in the helicopter flight manual.
[0050] Step 27: Check the record results of the easily broken device and the external camera to confirm whether the easily broken device has collided with the propeller blade.
[0051] Step 28: If the easily broken device does not come into contact with the blade, calculate the blade clearance test result at the location of the minimum clearance value of the dangerous structural part.
[0052] Specifically, the test results of blade clearance in dangerous structural parts were calculated using linear interpolation based on the recording results from an external camera and the reference value of the height of easily broken devices.
[0053] Step 29: If the test result of the blade clearance at the dangerous structural part is not less than the preset minimum clearance value, then the clearance at the dangerous structural part is sufficient.
[0054] The preset minimum gap value is 23cm.
[0055] It should be noted that after the test, usage procedures and restrictions need to be established, and the wind speeds in each direction verified by the test should be written into the flight manual as usage restrictions during rotor start-up and shutdown.
[0056] Step 3: For the dangerous structural parts, conduct test flights to verify the blade clearance under typical maneuvering conditions of the helicopter during flight, and obtain the test flight results of blade clearance under typical maneuvering conditions.
[0057] During flight, if the rotor disc tilts severely and the fuselage cannot follow suit for some reason, a collision between the rotor blades and the fuselage may occur. Based on the analysis of different helicopter configurations and the clearance between the rotor blades and the fuselage structure under various maneuvering states within the flight envelope, typical maneuvering states include high-G ground contact flight, high-G flight, low-G or weightless flight, and engine failure leading to autorotation and descent.
[0058] For high-G ground contact flights, the event typically occurs at the low point of the extreme altitude-velocity envelope. Therefore, in conjunction with the extreme altitude-velocity envelope flight tests conducted on helicopters, blade clearance flight tests under typical maneuvering conditions should be carried out simultaneously, and the rotor blade clearance should be monitored and evaluated concurrently during the extreme altitude-velocity envelope flight tests.
[0059] Preferably, step 3 includes:
[0060] Step 31: Install an overload sensor at the helicopter's center of gravity to obtain the overload coefficient at the helicopter's center of gravity.
[0061] Step 32: Use an external camera to record the rotor blade motion and the clearance between it and the dangerous structural parts during the landing gear touchdown phase of the test flight of the extreme altitude-speed envelope, and obtain the recording results of the external camera.
[0062] It should be noted that, based on helicopter development experience and relevant accident investigation and analysis reports, the tail boom structure is the key structural component to be monitored during flight testing and verification under typical maneuvering conditions.
[0063] Step 33: After the extreme altitude-speed envelope test flight mission is completed, check the dangerous structural parts of the rotor blades and tail boom and the recording results of the external camera to confirm whether the rotor blades collided with the tail boom structure.
[0064] Step 34: If the rotor blades do not collide with the tail boom structure, capture the blade clearance recorded by the external camera corresponding to the larger overload coefficient, and determine the test flight result value of the blade clearance between the rotor blades and the tail boom structure under the relatively large overload coefficient by image comparison.
[0065] It should be noted that the extreme altitude-speed envelope test flight needs to consider different airport altitudes and different weight centers of gravity. The test flight subject includes multiple test flights. Therefore, multiple blade clearance test flight results will be obtained during the verification process. During the ground contact with a larger overload coefficient, the rotor blades will produce a larger downward flap due to inertia, and the clearance value between the blades and the fuselage will be smaller. Therefore, the ground contact situation corresponding to the larger overload coefficient is selected for blade clearance analysis.
[0066] Step 35: If the test flight result of the blade clearance between the blade and the tail boom structure is greater than the preset minimum clearance value, then the clearance of the dangerous structural part is sufficient.
[0067] The preset minimum gap value is 23cm.
[0068] Step 4: Based on the results of the high wind start-stop test and the results of the flight test under typical maneuvering conditions, determine that there is sufficient clearance between the blade and other parts of the structure to prevent the blade from colliding with any part of the structure under any operating condition.
[0069] It should be noted that if it can be demonstrated that there is sufficient clearance between the helicopter rotor blades and other parts of the structure under typical maneuvering conditions during high wind start-stop tests and flight, it is sufficient to demonstrate that the requirements of Article 29.661 of the airworthiness clause are met.
[0070] This invention patent proposes a complete method for verifying the airworthiness compliance of rotor blade clearance, points out the typical test flight conditions that should be considered when evaluating the clearance between rotor blades and the structure, and provides specific test implementation and evaluation methods.
[0071] In addition, this application provides a helicopter rotor blade, which is implemented using the helicopter rotor blade clearance airworthiness compliance verification method described above.
[0072] In summary, this invention proposes a method for verifying the airworthiness compliance of helicopter rotor blade clearance, used to verify compliance with clause 29.661 of the airworthiness regulation. This method allows for the acquisition of clearance values between the rotor blades and the structure under typical operating conditions, facilitating a clear understanding of the clearance and ensuring its adequacy. This prevents blade collisions with the structure under any normal operating conditions (even with relatively rough pilot operation), thereby improving the helicopter's safety level throughout its entire safety envelope.
Claims
1. A method for verifying the airworthiness compliance of helicopter rotor blade clearance, characterized in that, The methods include: Step 1: Based on the analysis of rotor blade flapping motion and fuselage attitude, determine the critical structural locations; Step 2: For the dangerous structural parts, conduct experiments to verify the blade clearance during the rotor start-up and shutdown process of the helicopter under high wind conditions, and obtain the blade clearance test results for high wind start-up and shutdown. Step 3: For the dangerous structural parts, conduct test flights to verify the blade clearance under typical maneuvering conditions of the helicopter during flight, and obtain the test flight results of blade clearance under typical maneuvering conditions. Step 4: Based on the results of the high wind start-stop test and the results of the flight test under typical maneuvering conditions, determine that there is sufficient clearance between the blade and other parts of the structure to prevent the blade from colliding with any part of the structure under any operating condition. Step 2 includes: Step 21: Install easily breakable devices at appropriate locations on the windshield in the front fairing area and the tail boom in the rear fairing area of the fuselage structure. Step 22: Install a wind speed measuring device at a predetermined position at the rotor height in front of the helicopter in the windward direction; Step 23: Use an external camera to record the entire test process and obtain the external camera recording results of the blade clearance; Step 24: Check the helicopter control stick settings. The collective pitch stick should be at the minimum pitch position, and the control stick and pedals should be in the neutral position. Step 25: Based on the initial overall limitations of the helicopter, determine the initial wind speed limits, and blow wind in front of, behind, to the left and right of the helicopter respectively; Step 26: After the wind speed stabilizes, start the engine according to the normal procedure and gradually increase the speed. After the rotor speed stabilizes, shut down the engine according to the normal shutdown procedure to stop the rotor. Step 27: Check the record results of the easily broken device and the external camera to confirm whether the easily broken device has collided with the propeller blade; Step 28: If the easily broken device does not come into contact with the blade, calculate the blade clearance test result at the location of the minimum clearance value of the dangerous structural part; Step 29: If the test result of the blade clearance at the dangerous structural part is not less than the preset minimum clearance value, then the clearance at the dangerous structural part is sufficient.
2. The method according to claim 1, characterized in that, Step 21 includes: The reference value for the height of the easily broken device is the theoretical gap value at the installation position determined by linear interpolation based on the theoretical value at the minimum gap value of the dangerous structural part.
3. The method according to claim 1, characterized in that, The preset position in front of the helicopter in the windward direction is 200-300m away from the helicopter, which is used to obtain the wind speed in advance so as to start or stop the rotor.
4. The method according to claim 1, characterized in that, Step 28 includes: The test results of blade clearance at the dangerous structural parts were calculated using linear interpolation based on the recording results of the external camera and the reference value of the height of the balsa wood rod.
5. The method according to claim 1, characterized in that, Step 3 includes: Step 31: Install an overload sensor at the helicopter's center of gravity to obtain the overload coefficient at the helicopter's center of gravity; Step 32: Use an external camera to record the rotor blade motion and the clearance between it and the dangerous structural parts during the landing gear touchdown phase of the test flight of the extreme altitude-speed envelope, and obtain the recording results of the external camera. Step 33: After the extreme altitude-speed envelope test flight mission is completed, check the dangerous structural parts of the rotor blades and tail boom and the recording results of the external camera to confirm whether the rotor blades collided with the tail boom structure. Step 34: If the rotor blades do not collide with the tail boom structure, capture the blade clearance recorded by the external camera corresponding to the larger overload coefficient, and determine the test flight result value of the blade clearance between the rotor blades and the tail boom structure under the relatively large overload coefficient by image comparison. Step 35: If the test flight result of the blade clearance between the blade and the tail boom structure is greater than the preset minimum clearance value, then the clearance of the dangerous structural part is sufficient.
6. The method according to claim 5, characterized in that, Step 34 includes: During a ground contact with a large overload factor, the rotor blades will exhibit significant downward flapping due to inertia, resulting in a smaller gap between the blades and the fuselage. Therefore, the ground contact scenario corresponding to a large overload factor is selected for blade gap analysis.
7. The method according to claim 6, characterized in that, The preset minimum gap value is 23cm.
8. A helicopter rotor blade, characterized in that, The helicopter rotor blades are implemented using the helicopter rotor blade clearance airworthiness compliance verification method as described in claims 1 to 7.