Method for quickly obtaining avoidance area of dual-engine civil helicopter

Abstract

The application belongs to the technical field of helicopter aerodynamic design and verification, and particularly relates to a method for quickly obtaining a dual-engine civil helicopter avoidance area, comprising the following steps: S1, obtaining a lower boundary of the helicopter avoidance area; determining a hovering low point of the avoidance area by using a real single-engine failure mode; determining an inflection point of the lower boundary of the avoidance area by using a single-engine failure training mode, and obtaining flight test data from the hovering low point to the inflection point of the lower boundary; S2, obtaining an upper boundary of the helicopter avoidance area; determining a hovering high point of the avoidance area by using the real single-engine failure mode; S3, obtaining a right boundary of the helicopter avoidance area; determining the right boundary of the avoidance area by using the single-engine failure training mode, and obtaining flight test data from the inflection point of the lower boundary to the right boundary; and S4, determining a height-velocity envelope of the helicopter as the helicopter avoidance area according to the hovering low point, the hovering high point, the inflection point of the lower boundary, the right boundary of the avoidance area, the flight test data from the hovering low point to the inflection point of the lower boundary, and the flight test data from the inflection point of the lower boundary to the right boundary.

Description

Technical Field

[0001] This invention belongs to the field of helicopter aerodynamic design and verification technology, and in particular relates to a method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter. Background Technology

[0002] The avoidance zone, also known as the altitude-velocity envelope, is usually represented by an altitude-velocity (HV) chart. It corresponds to the CCAR 27.87 altitude-velocity envelope or the CCAR 29.87 and CCAR 29.1517 extreme altitude-velocity envelope clauses. It defines the altitude and velocity envelopes that prevent safe landings when flying above ground, without power, or with one engine not operating. Under normal flying conditions and with proper flying skills, it is essential to maintain a certain clearance between the takeoff and landing tracks and the avoidance zone, such as ±5 knots at the same altitude, to ensure unobstructed takeoff routes. Clause 29.87 of the Airworthiness Regulations for Transport Category Rotarywing Aircraft (CCAR-29-R2) stipulates that helicopters must have their avoidance zone determined through flight testing and provided in their performance data. According to requirements, the altitude extrapolation from the HV test data should not exceed 2000 ft density altitude, and the weight extrapolation from the HV test data should not be to the maximum permissible weight.

[0003] For dual-engine isolated civilian helicopters, the avoidance zone is the altitude and speed envelope that prevents the helicopter from safely landing when one engine is not operating. Typically, the avoidance zone remains constant; as density altitude increases, flight weight decreases; as flight weight remains constant, the avoidance zone increases with increasing density altitude; and vice versa. Therefore, under normal circumstances, with sufficient funding and a long testing period, flight tests at airports at different altitudes can be conducted to obtain the avoidance zone that varies with density altitude and flight weight. However, avoidance zone flight tests rely on only one engine providing power. Insufficient engine power necessitates the use of emergency power from the engine or transmission, directly damaging the lifespan of the engine and transmission system, requiring a backup engine or transmission system. Furthermore, avoidance zone flight tests are high-risk, with the possibility of a hard landing during the test, potentially damaging the landing gear, tail boom structure, etc. To reduce testing costs, time, and risks... Summary of the Invention

[0004] To address the challenges of high flight test risks, high costs, long test cycles, and limited extrapolation altitude of test results in avoidance zone flight tests, this invention proposes a method for rapidly obtaining the avoidance zone for twin-engine civil helicopters. This method involves selecting an airport at a suitable altitude and the maximum flight weight for avoidance zone flight tests. Based on actual single-engine failures, key points such as the hovering low point, high point, and inflection point of the avoidance zone are quickly determined. Transitional state points are determined based on single-engine failure training modes. Through calculation and analysis, the applicable density altitude range for the avoidance zone is determined.

[0005] To achieve the above objectives, the present invention employs the following technical solution.

[0006] A method for rapidly obtaining the avoidance zone of a twin-engine civilian helicopter, the method comprising:

[0007] S1, obtain the lower boundary of the helicopter avoidance zone;

[0008] The hovering low point of the avoidance zone was determined using a real single-engine failure scenario; the inflection point of the lower boundary of the avoidance zone was determined using a single-engine failure training mode, and flight test data from the hovering low point of the avoidance zone to the inflection point of the lower boundary were obtained.

[0009] S2, obtain the upper boundary of the helicopter avoidance zone;

[0010] The hovering high point of the avoidance zone is determined by using a real single-shot failure scenario;

[0011] S3, obtain the right boundary of the helicopter avoidance zone;

[0012] The right boundary of the avoidance zone was determined by using a single-engine failure training mode, and flight test data from the inflection point of the lower boundary of the avoidance zone to the right boundary was obtained.

[0013] S4. Based on the hovering low point, hovering high point, inflection point of the lower boundary of the avoidance zone, right boundary of the avoidance zone, and flight test data from the hovering low point to the inflection point of the lower boundary of the avoidance zone and from the inflection point of the lower boundary of the avoidance zone to the right boundary, the altitude-speed envelope of the helicopter is determined as the helicopter avoidance zone.

[0014] Furthermore, following S4, the method also includes determining the applicable range of the helicopter avoidance zone:

[0015] S5, calculate the remaining power in the helicopter avoidance zone and determine the maximum density height of the helicopter avoidance zone.

[0016] Furthermore, prior to S1, the method further includes:

[0017] Determine the flight weight and center of gravity position for helicopter avoidance zone test flights;

[0018] Determine the airport altitude for helicopter avoidance zone test flights;

[0019] Determine the pilot's reaction time in the event of a single engine failure;

[0020] Determine the effectiveness of the single-shot training mode.

[0021] Furthermore, S1 specifically refers to:

[0022] S11, determine the ground clearance of the lower boundary hovering low point, hover the helicopter at a ground clearance of 1m, shut down one engine and land, during which the pilot is allowed collective pitch before touchdown;

[0023] Gradually increase the altitude until the pilot's workload becomes unacceptable or the landing gear touchdown load reaches the limit load, thereby determining the hovering low point H1 of the avoidance zone;

[0024] S12, maintaining a constant altitude, using a forward speed of 10 km / h as the step size, uses engine training mode to simulate an engine failure, during which the pilot is allowed to maintain collective pitch before touchdown;

[0025] S13, gradually increase the forward speed until the pilot's workload becomes unacceptable and the landing gear touchdown load reaches the limit load. Use this speed as the inflection point (V1, H1) of the lower boundary of the avoidance zone.

[0026] Flight test data was obtained during the S12 and S13 tests, showing the inflection point from the hovering low point to the lower boundary of the avoidance zone.

[0027] Furthermore, S2 specifically refers to:

[0028] Determine the ground clearance of the upper boundary hovering height, hover at the preset hovering ground clearance, shut down one engine and land, during which the pilot is allowed to release collective pitch to restore rotor speed, go around and accelerate to the optimal climb rate speed, with the flight trajectory ground clearance not less than 35 feet;

[0029] Gradually reduce the hovering altitude until the flight path altitude is less than 35 feet or the pilot's workload is unacceptable, and determine the hovering altitude H2 of the avoidance zone.

[0030] Furthermore, S3 specifically refers to:

[0031] S31, keep the forward flight speed V1 unchanged, take the hovering high point H2 in the avoidance zone as the initial altitude, use the engine training mode to simulate the failure of one engine, gradually reduce the altitude to the ground until the pilot's workload is unacceptable or the landing gear touchdown load reaches the limit load, and determine the right boundary point (V1, H3).

[0032] S32, gradually increase the forward flight speed, with a step size of 10 km / h. Use the engine training mode to simulate the failure of one engine. During this process, the pilot is allowed to maintain collective distance before touchdown until the pilot's workload becomes unacceptable and the landing gear touchdown load reaches the limit load. Use this speed as the inflection point (V2, H3) of the right boundary of the avoidance zone.

[0033] Flight test data from the inflection point of the lower boundary of the avoidance zone to the right boundary was obtained during the test flights of S33, S32 and S33.

[0034] Furthermore, S5 specifically refers to:

[0035] Calculate the power required for hovering in no ground effect and the actual maximum engine available power corresponding to the flight weight during the helicopter avoidance zone test flight, as well as the difference between the two, to obtain the remaining power at all test points;

[0036] The minimum residual power at all test points is taken. The power required and available for hovering in no ground effect at different density altitudes with the maximum takeoff weight of the helicopter are calculated to obtain the residual power at different density altitudes. The residual power is then compared with the minimum residual power to obtain the maximum density altitude that is not less than the minimum residual power, which is taken as the maximum density altitude of the applicable helicopter avoidance zone.

[0037] Furthermore, the flight weight for the avoidance zone test flight is determined based on the maximum takeoff weight of the helicopter. The center of gravity position of the current test flight state is determined based on the determined flight weight and the unfavorable center of gravity of the corresponding flight state. During the test, it is ensured that the flight weight does not exceed -1% to 3% of the maximum takeoff weight.

[0038] Based on the helicopter's maximum takeoff weight, calculate its service ceiling for hovering performance without ground effect, and determine the airport altitude for test flights in the avoidance zone.

[0039] This invention proposes a test flight method for verifying airworthiness compliance with the extreme altitude-speed envelope of CCAR-29-R2 Clause 29.87. According to this method, the helicopter avoidance zone can be quickly determined by conducting real single-engine failure test flights at a small number of key points, combined with engine training mode for supplementary verification, and then extended to the entire temperature envelope to obtain a helicopter avoidance zone that meets safety and operational requirements. Attached Figure Description

[0040] Figure 1 This is a schematic diagram illustrating the implementation process of the method of the present invention. Detailed Implementation

[0041] The technical solution of the present invention will be described in detail below with reference to the accompanying drawings.

[0042] This invention provides a method for rapidly obtaining the avoidance zone of a civil helicopter during test flights, comprising the following steps:

[0043] Step 1: Select the flight weight and center of gravity position for the helicopter avoidance zone test flight.

[0044] The flight weight for the avoidance zone test flight is determined based on the maximum takeoff weight of the helicopter. The center of gravity position of the current test flight state is determined based on the determined flight weight and the unfavorable center of gravity of the corresponding flight state. During the test, it is ensured that the flight weight does not exceed -1% to 3% of the maximum takeoff weight.

[0045] Step 2: Select the test flight altitude airport for the helicopter avoidance zone.

[0046] Based on the maximum takeoff weight of the helicopter, its hovering performance ceiling without ground effect is calculated, and the airport altitude for the avoidance zone test flight is determined so that the helicopter can achieve hovering without ground effect at the selected airport.

[0047] Step 3: Determine the pilot's reaction time in the event of a single engine failure.

[0048] When conducting avoidance zone tests, the pilot's reaction time in the event of a single engine failure should be clearly defined to account for the pilot's reaction time and the handling during test flights in training mode.

[0049] Step 4: Determine the effectiveness of the single-shot training mode

[0050] Before conducting avoidance zone tests, it is necessary to carry out comparative flights between single-engine training mode and actual single-engine mode to ensure the effectiveness of single-engine training mode.

[0051] Step 5: Obtain the lower boundary of the helicopter avoidance zone

[0052] S51, determine the ground clearance of the lower boundary hovering low point. Hover the helicopter at a ground clearance of 1m, shut down one engine (critical engine), and land. During this process, the pilot is allowed collective pitch before touchdown. Gradually increase the ground clearance until the pilot's workload becomes unacceptable or the landing gear touchdown load approaches the limit. The ground clearance H1 of the lower boundary hovering low point of the avoidance zone can then be determined.

[0053] S52, maintaining a constant altitude, uses a forward speed of 10 km / h as the step size and employs engine training mode to simulate the failure of one engine (critical engine). During this process, the pilot is allowed to maintain collective pitch before touchdown.

[0054] S53, gradually increase the speed to V1, or when the pilot's workload becomes unacceptable or the landing gear touchdown load approaches the limit, use this speed as the inflection point (V1, H1) of the lower boundary of the avoidance zone.

[0055] The lower boundary test flight data points were obtained during the test flights of S52 and S53;

[0056] Step 6: Obtain the upper boundary of the helicopter avoidance zone

[0057] Determine the ground clearance of the upper boundary hovering high point, hover at a relatively high ground clearance, shut down one engine (critical engine) and land, during which the pilot is allowed to release collective pitch to restore rotor speed, go around and accelerate to the optimal climb rate speed, with the flight path at a ground clearance of not less than 35 feet.

[0058] Gradually reduce the hovering altitude until the flight path altitude is less than 35 feet or the pilot's workload becomes unacceptable. This will determine the hovering altitude H2 at the upper boundary of the avoidance zone.

[0059] Step 7: Obtain the right boundary of the helicopter avoidance zone

[0060] Keep the forward flight speed V1 constant, and take the hovering height H2 determined in step 6 as the initial height. Use the engine training mode to simulate the failure of one engine (critical engine), and gradually reduce the altitude until the pilot's workload is unacceptable or the landing gear touchdown load is close to the limit, and determine the right boundary point (V1, H3).

[0061] Gradually increase the forward flight speed, using a step size of 10 km / h. Simulate the failure of one engine (critical engine) using engine training mode. During this process, allow the pilot to maintain collective distance before touchdown until the pilot's workload becomes unacceptable and the landing gear touchdown load approaches the limit. Use this speed as the inflection point (V2, H3) of the right boundary of the avoidance zone.

[0062] The right boundary test flight data point is obtained during the test flight in step 7;

[0063] For the points (V1, H1) and (V2, H3) determined in steps 5 and 7, take a landing flight with one engine (critical engine) shut down using a forward flight speed of 5 km / h as the step size, verify the right boundary of the helicopter avoidance zone, and ensure that the pilot's workload is acceptable and the landing gear touchdown load is within the limits.

[0064] Step 8: Obtain the helicopter avoidance zone

[0065] The flight test data points obtained in steps 5 to 7 are statistically analyzed, and linear fitting and connection are performed on segments to obtain a preliminary altitude-velocity envelope. The envelope is then adjusted to ensure that the test points for real single-engine failure flight verification are within the envelope range and to ensure the continuity of the envelope. Finally, the altitude-velocity envelope (avoidance zone) is obtained.

[0066] Step 9: Calculate the remaining power in the helicopter avoidance zone

[0067] The remaining power for all test points can be obtained by calculating the power required for hovering in no ground effect and the actual maximum engine power available at the points on the altitude-velocity envelope obtained in steps 5 to 7, as well as the difference between the two.

[0068] Step 10: Determine the maximum density altitude of the applicable helicopter avoidance zone.

[0069] Take the minimum residual power of all test points in step 9, calculate the power required and available for hovering in no ground effect at different density altitudes for the maximum takeoff weight of the helicopter, so as to obtain the residual power at different density altitudes, and compare it with the minimum residual power in the test to obtain the maximum density altitude that is not less than the minimum residual power, which is taken as the maximum density altitude of the applicable helicopter avoidance zone.

[0070] Example: This invention discloses a test flight method for rapidly obtaining the avoidance zone of a civil helicopter, comprising the following steps:

[0071] Determine the altitude of the test airport in the avoidance zone: Calculate the hovering performance of the helicopter at its maximum takeoff weight to determine the appropriate altitude of the test airport in the avoidance zone;

[0072] Flight test verification of the lower boundary of the avoidance zone (see Figure 1 Hover the helicopter at a height of 1m above the ground, shut down one engine (the critical engine), and land, allowing the pilot to maintain collective distance before touchdown. Gradually increase the altitude until the pilot's workload becomes unacceptable or the landing gear touchdown load approaches the limit, and determine the hovering low point altitude H1 at the lower boundary of the avoidance zone.

[0073] Keeping the altitude H1 constant, and using the forward speed in increments of 10 km / h, simulate the failure of one engine (critical engine) using engine training mode. During this process, the pilot is allowed to maintain collective pitch before touchdown. Gradually increase the speed to V1, or until the pilot's workload becomes unacceptable and the landing gear touchdown load approaches the limit, and determine the inflection point (V1, H1) at the lower boundary of the avoidance zone.

[0074] Flight test verification of the upper boundary of the avoidance zone (see Figure 1 Hover at a relatively high altitude, shut down one engine (the critical engine) and land. During this process, the pilot is allowed to release collective pitch to restore rotor speed. Accelerate to VY (optimal climb rate) for the go-around, with the flight path at an altitude of at least 35 feet above the ground. Gradually decrease the altitude until the flight path is less than 35 feet above the ground or the pilot's workload becomes unacceptable. The hovering high point at the upper boundary of the avoidance zone, H2, can then be determined.

[0075] Flight test verification of the right boundary of the avoidance zone (see Figure 1 ): Keep the forward flight speed V1 constant, and take the hovering height H2 above the upper boundary as the initial height. Use the engine training mode to simulate the failure of one engine (critical engine), and gradually reduce the altitude above the ground until the pilot's workload is unacceptable or the landing gear touchdown load is close to the limit, and determine the right boundary inflection point (V2, H3).

[0076] Between points (V1, H1) and (V2, H3), with a forward speed of 5 km / h as the step size, land with one engine (critical engine) shut down to verify the right boundary of the avoidance zone.

[0077] Determine the helicopter avoidance zone (see Figure 1 Connect the key points such as the lower boundary (0, H1) and (V1, H1), the right boundary (V2, H3) and (V2, H2), and the hovering high point (0, H2) of the upper boundary of the avoidance zone to determine the helicopter avoidance zone, and calculate the applicable altitude-temperature envelope of the helicopter avoidance zone.

[0078] This invention proposes a method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter during flight testing. The avoidance zone is simplified into several key points, thereby reducing the difficulty of flight testing. A specific verification method is also provided. Finally, the remaining power is used to extend the avoidance zone determined by the flight test to the full altitude-temperature envelope.

Claims

1. A method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter, characterized in that, The method includes: S1, obtain the lower boundary of the helicopter avoidance zone; The hovering low point of the avoidance zone was determined using a real single-engine failure scenario; the inflection point of the lower boundary of the avoidance zone was determined using a single-engine failure training mode, and flight test data from the hovering low point of the avoidance zone to the inflection point of the lower boundary were obtained. S2, obtain the upper boundary of the helicopter avoidance zone; The hovering high point of the avoidance zone is determined by using a real single-shot failure scenario; S3, obtain the right boundary of the helicopter avoidance zone; The right boundary of the avoidance zone was determined by using a single-engine failure training mode, and flight test data from the inflection point of the lower boundary of the avoidance zone to the right boundary was obtained. S4. Based on the hovering low point, hovering high point, inflection point of the lower boundary of the avoidance zone, right boundary of the avoidance zone, and flight test data from the hovering low point to the inflection point of the lower boundary of the avoidance zone and from the inflection point of the lower boundary of the avoidance zone to the right boundary, the altitude-speed envelope of the helicopter is determined as the helicopter avoidance zone.

2. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 1, characterized in that, Following S4, the method further includes determining the applicable range of the helicopter avoidance zone: S5, calculate the remaining power in the helicopter avoidance zone and determine the maximum density height of the helicopter avoidance zone.

3. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 1, characterized in that, Before S1, the method further includes: Determine the flight weight and center of gravity position for helicopter avoidance zone test flights; Determine the airport altitude for helicopter avoidance zone test flights; Determine the pilot's reaction time in the event of a single engine failure; Determine the effectiveness of the single-shot training mode.

4. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 1, characterized in that, S1 specifically refers to: S11, determine the ground clearance of the lower boundary hovering low point, hover the helicopter at a ground clearance of 1m, shut down one engine and land, during which the pilot is allowed collective pitch before touchdown; Gradually increase the altitude until the pilot's workload becomes unacceptable or the landing gear touchdown load reaches the limit load, thereby determining the hovering low point H1 of the avoidance zone; S12, maintaining a constant altitude, using a forward speed of 10 km / h as the step size, uses engine training mode to simulate an engine failure, during which the pilot is allowed to maintain collective pitch before touchdown; S13, gradually increase the forward speed until the pilot's workload becomes unacceptable and the landing gear touchdown load reaches the limit load. Use this speed as the inflection point (V1, H1) of the lower boundary of the avoidance zone. Flight test data was obtained during the S12 and S13 tests, showing the inflection point from the hovering low point to the lower boundary of the avoidance zone.

5. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 1, characterized in that, S2 specifically refers to: Determine the ground clearance of the upper boundary hovering height, hover at the preset hovering ground clearance, shut down one engine and land, during which the pilot is allowed to release collective pitch to restore rotor speed, go around and accelerate to the optimal climb rate speed, with the flight trajectory ground clearance not less than 35 feet; Gradually reduce the hovering altitude until the flight path altitude is less than 35 feet or the pilot's workload is unacceptable, and determine the hovering altitude H2 of the avoidance zone.

6. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 1, characterized in that, S3 specifically refers to: S31, keep the forward flight speed V1 unchanged, take the hovering high point H2 in the avoidance zone as the initial altitude, use the engine training mode to simulate the failure of one engine, gradually reduce the altitude to the ground until the pilot's workload is unacceptable or the landing gear touchdown load reaches the limit load, and determine the right boundary point (V1, H3). S32, gradually increase the forward flight speed, with a step size of 10 km / h. Use the engine training mode to simulate the failure of one engine. During this process, the pilot is allowed to maintain collective distance before touchdown until the pilot's workload becomes unacceptable and the landing gear touchdown load reaches the limit load. Use this speed as the inflection point (V2, H3) of the right boundary of the avoidance zone. Flight test data from the inflection point of the lower boundary of the avoidance zone to the right boundary was obtained during the test flights of S33, S32 and S33.

7. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 2, characterized in that, S5 specifically refers to: Calculate the power required for hovering in no ground effect and the actual maximum engine available power corresponding to the flight weight during the helicopter avoidance zone test flight, as well as the difference between the two, to obtain the remaining power at all test points; The minimum residual power at all test points is taken. The power required and available for hovering in no ground effect at different density altitudes with the maximum takeoff weight of the helicopter are calculated to obtain the residual power at different density altitudes. The residual power is then compared with the minimum residual power to obtain the maximum density altitude that is not less than the minimum residual power, which is taken as the maximum density altitude of the applicable helicopter avoidance zone.

8. The method for rapidly obtaining the avoidance zone of a twin-engine civil helicopter according to claim 3, characterized in that, The flight weight for the avoidance zone test flight is determined based on the maximum takeoff weight of the helicopter. The center of gravity position of the current test flight state is determined based on the determined flight weight and the unfavorable center of gravity of the corresponding flight state. During the test, it is ensured that the flight weight does not exceed -1% to 3% of the maximum takeoff weight. Based on the helicopter's maximum takeoff weight, calculate its service ceiling for hovering performance without ground effect, and determine the airport altitude for test flights in the avoidance zone.

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