A method for testing stall speed of turboprop aircraft

Abstract

This invention belongs to the field of flight testing, specifically relating to a flight test method for determining the stall speed of a turboprop aircraft, applicable to stall speed flight tests of propeller aircraft. The method determines the test conditions according to the sequence of flap configuration, aircraft weight, and engine status. By changing the engine status in a gradual and progressive manner, the flight test risks of propeller aircraft stall speed are comprehensively identified. A reasonable test sequence and risk mitigation measures are established to effectively reduce flight test risks, providing strong support for the qualification and certification flight tests of propeller aircraft stall speed.

Description

Technical Field

[0001] This invention belongs to the field of flight testing, specifically relating to a flight test method for the stall speed of a turboprop aircraft, applicable to flight tests of propeller aircraft stall speed. Background Technology

[0002] Stall issues have always been a hot topic, a focal point, and a difficult problem in the development of civil aircraft. It is one of the most critical factors affecting flight safety and is closely watched by industry, airworthiness authorities, and customers. Stall speed has a significant impact on many performance parameters affecting aircraft certification, such as airport length and takeoff speed specifications. Stall characteristics are studied to determine the aircraft's handling qualities during stall maneuvers, aiming for a low probability of unintended stalls. The goal is to allow pilots to recover safely and quickly from unintentional stalls without requiring any special piloting skills. Therefore, achieving both good stall characteristics and a low stall speed is a goal for civil aircraft development both domestically and internationally.

[0003] This invention provides a stall speed test method for turboprop aircraft, which supports the airworthiness certification or testing process of turboprop aircraft. Summary of the Invention

[0004] The purpose of this invention is to propose a test flight method for determining the stall speed of a propeller aircraft, which is of great significance for reasonably avoiding test flight risks and improving test flight efficiency.

[0005] The technical solution of the present invention:

[0006] A test flight method for stall speed of a turboprop aircraft, the method comprising:

[0007] Step 1: Determine the test conditions, using the front limit of the center of gravity envelope as the test conditions. The test conditions include flap configuration, aircraft weight, and engine status.

[0008] Step 2: Determine the aircraft's weight as the first weight, set the aircraft to the prescribed takeoff configuration, take off according to the takeoff procedure, and fly to the designated airspace as planned;

[0009] Step 3: At a given flight altitude, extend the tow cone to a specified length. The tow cone can obtain an accurate static pressure value at the specified length without being affected by turbulence. The given flight altitude is within the flight envelope.

[0010] Step 4: Set the aircraft's flap configuration to the first flap configuration;

[0011] Step 5: Set the aircraft's engine status to the first engine state under the first flap configuration. Trim the aircraft at the given speed and in the first engine state, and perform stable straight flight for 30 seconds. The given speed is a speed point between 1.13 times the stall speed and 1.3 times the stall speed. The first engine state is the idle power state under the first flap configuration.

[0012] Step 6: Decelerate the aircraft at a rate not greater than 1 kn / s using only longitudinal control until the test pilot clearly determines that the aircraft has stalled, then end the maneuver and record the speed at the moment of stall.

[0013] Step 7: Repeat steps 5 and 6, 4-8 times;

[0014] Step 8: Set the engine state in Step 5 to other engine states corresponding to the first flap configuration, repeat Steps 5 to 7 to traverse all engine states under the first flap configuration, and obtain the stall speed at the time of stall under the first flap configuration and other engine states; fit the stall speed at the time of stall under all engine states under the first flap configuration to obtain the first weight and the stall speed under the first flap configuration in the unpowered state.

[0015] Step 9: Set the flap configuration of the aircraft to other flap configurations. Repeat steps 4 to 8, traverse all engine states under other flap configurations, obtain the stall speed under all engine states under other flap configurations, and perform fitting to obtain the stall speed under the first weight and other flap configurations in the powerless state.

[0016] Step 10: Set the aircraft weight from Step 2 to another weight, and repeat Steps 2-9 to obtain the stall speed under no-power conditions for all flap configurations under other weights.

[0017] Furthermore, in step 1, the test conditions are determined as follows:

[0018] 1) Select flap configuration. Since different flap configurations may result in different stall phenomena, a comprehensive judgment should be made based on the results of wind tunnel tests and model free flight tests before testing. The configuration with smaller lift coefficient change with angle of attack should be started.

[0019] 2) Determine the aircraft weight based on the flap configuration, in ascending order of weight;

[0020] 3) The engine status sequence is from smallest to largest.

[0021] Furthermore, in step 6, when the test pilot clearly determines that the aircraft has stalled, specifically: when the inherent flight characteristics show the pilot a clearly identifiable aircraft stall phenomenon, the aircraft is considered to have stalled. The aircraft stall phenomenon includes: 1) the presence of any abnormal nose pitch; 2) the presence of any uninstructed nose pitch that foreshadows a stall; 3) the presence of any uninstructed lateral or directional movement; 4) the aircraft exhibiting a flutter of an amplitude and severity that would prevent the completion of a maneuver; 5) the pitch control reaches the post-stop point, and the control devices cannot further increase the pitch attitude after holding that position for 2 seconds before the recovery begins.

[0022] Furthermore, before step 1, the following steps are also included: completing emergency off-aircraft system tests and ground drills for the unit to ensure that the system is working properly.

[0023] Furthermore, before step 1, the process includes: completing an in-flight engine restart test before the stall test flight and developing a detailed in-flight restart procedure; step 6, in the event of an in-flight engine failure, performing an in-flight engine restart according to the detailed in-flight restart procedure developed before the stall test flight, and safely ending the test flight mission.

[0024] Furthermore, before step 1, the process includes: completing a test flight of the aircraft's unpowered glide characteristics before the stall test flight and formulating an air glide emergency landing plan; in step 6, if the engine fails to start in the air and the detailed in-flight restart procedure formulated before the stall test flight cannot be followed, the aircraft will be maneuvered back to the airfield and landed according to the formulated air glide emergency landing plan, thus ending the test.

[0025] Furthermore, before step 1, the process includes conducting engine characteristic flight tests under conditions of high angle of attack and high sideslip angle to ensure that the engine operates normally under these conditions.

[0026] Furthermore, before step 1, the test flight must be completed to ensure that the aircraft's fuel and pressurization capabilities are normal under negative overload conditions.

[0027] Furthermore, before step 1, the aircraft characteristics test flight is completed under high pitch angle, high roll angle and negative overload conditions to ensure that the aircraft characteristics are normal under these conditions.

[0028] Beneficial effects:

[0029] This method provides a flight test procedure for the stall speed of propeller aircraft, comprehensively identifies the flight test risks of propeller aircraft stall speed, and formulates a reasonable test sequence and risk degradation measures to effectively reduce flight test risks. It can provide strong support for the qualification flight test and certification flight test of propeller aircraft stall speed. Detailed Implementation

[0030] A test flight method for stall speed of a turboprop aircraft according to an embodiment of the present invention includes:

[0031] Step 1: Determine the test conditions, using the front limit of the center of gravity envelope as the test conditions. The test conditions include flap configuration, aircraft weight, and engine status.

[0032] The test conditions are determined as follows:

[0033] 1) Select flap configuration. Since different flap configurations may result in different stall phenomena, a comprehensive judgment should be made based on the results of wind tunnel tests and model free flight tests before testing. The configuration with smaller lift coefficient change with angle of attack should be started.

[0034] 2) Determine the aircraft weight based on the flap configuration, in ascending order of weight;

[0035] 3) The engine status sequence is from smallest to largest;

[0036] Step 2: Determine the aircraft's weight as the first weight, set the aircraft to the prescribed takeoff configuration, take off according to the takeoff procedure, and fly to the designated airspace as planned;

[0037] Step 3: At a given flight altitude, extend the tow cone to a specified length. The tow cone can obtain an accurate static pressure value at the specified length without being affected by turbulence. The given flight altitude is within the flight envelope.

[0038] Step 4: Set the aircraft's flap configuration to the first flap configuration;

[0039] Step 5: Set the aircraft's engine status to the first engine state under the first flap configuration. Trim the aircraft at the given speed and in the first engine state, and perform stable straight flight for 30 seconds. The given speed is a speed point between 1.13 times the stall speed and 1.3 times the stall speed. The first engine state is the idle power state under the first flap configuration.

[0040] Step 6: Decelerate the aircraft at a rate not greater than 1 kn / s using only longitudinal control until the test pilot clearly determines that the aircraft has stalled, then end the maneuver and record the speed at the moment of stall.

[0041] Step 7: Repeat steps 5 and 6, 4-8 times;

[0042] Step 8: Set the engine state in Step 5 to other engine states corresponding to the first flap configuration, repeat Steps 5 to 7 to iterate through all engine states under the first flap configuration, and obtain the stall speed under the first flap configuration and other engine states; fit the stall speeds under the first weight and the first flap configuration in the unpowered state to obtain the stall speed. Step 9: Set the flap configuration of the aircraft to other flap configurations, repeat Steps 4 to 8, iterate through all engine states under other flap configurations, obtain the stall speeds under all engine states under other flap configurations, and fit the stall speeds under the first weight and other flap configurations in the unpowered state.

[0043] Step 10: Set the aircraft weight from Step 2 to another weight, and repeat Steps 2-9 to obtain the stall speed under no-power conditions for all flap configurations under other weights.

[0044] In step 6, when the test pilot clearly determines that the aircraft has stalled, specifically when the inherent flight characteristics clearly indicate a stall phenomenon to the pilot, the aircraft can be considered to have stalled. These phenomena can occur individually or in combination: 1) any abnormal nose pitch; 2) any uninstructed nose pitch that foreshadows a stall; 3) any uninstructed lateral or directional movement; 4) the aircraft exhibiting a flutter of amplitude and severity that prevents the completion of a maneuver; 5) pitch control reaches the stop point, and the control devices remain in that position for a brief period (2 seconds) before the recovery begins, after which the pitch attitude cannot be further increased.

[0045] Stall speed is an important parameter characterizing the aerodynamic characteristics of an aircraft and defining the minimum permissible operating speed. Obtaining stall speed for flight testing carries a very high risk. Therefore, complete risk identification and the development of risk mitigation measures are necessary conditions to ensure the safe and smooth conduct of flight testing.

[0046] This embodiment describes risk identification and risk mitigation measures for stall speed test flights of turboprop aircraft:

[0047] Risk identification:

[0048] 1) During a stall, the aircraft may become uncontrollable or experience a deep stall;

[0049] 2) It may cause abnormal engine operation or engine shutdown, thus requiring the aircraft to operate with emergency power.

[0050] 3) May cause problems with the aircraft's fuel and lubrication systems;

[0051] 4) May cause problems with the operation of other aircraft systems.

[0052] Risk degradation measures:

[0053] The principle for changing the engine state in step 5 is to proceed gradually and approach the target step by step: first fly at a slow speed, then fly with power stall.

[0054] Before step 1, complete the emergency off-aircraft system test and the unit ground drill to ensure that the system is working properly;

[0055] Before step 1, the following steps are also included: completing an in-flight engine start-up test before the stall test flight and developing a detailed in-flight start-up procedure;

[0056] Step 6: If the engine fails in the air, perform an in-flight engine restart according to the detailed in-flight restart procedure established before the stall test flight, and safely end the test flight mission.

[0057] Before step 1, the following steps are also included: completing the unpowered glide characteristic test flight before the stall test flight and formulating an air glide emergency landing plan;

[0058] Step 6: If the engine fails to restart in the air, and the detailed in-flight restart procedure prepared before the stall test flight is not followed, then the aircraft shall be maneuvered back to the airfield and landed according to the prepared glide landing plan, thus ending the test.

[0059] Before step 1, the following steps are also included: conducting engine characteristic flight tests under conditions of high angle of attack and high sideslip angle to ensure that the engine works normally under these conditions;

[0060] During the stall test flight in steps 5 and 6, engine parameters are monitored in real time, and any abnormalities are reported immediately.

[0061] Before step 1, the following steps are also included: completing negative overload test flights to ensure that the aircraft's fuel and pressurization capabilities are normal under negative overload conditions;

[0062] Before step 1, the aircraft characteristics test flight is completed under high pitch angle, high roll angle and negative overload conditions to ensure that the aircraft characteristics are normal under these conditions.

[0063] Example

[0064] Taking a specific test flight as an example, the detailed implementation method for testing the stall speed of a propeller-driven aircraft is as follows:

[0065] 1) Follow the normal procedure to start the engine, check the operation of each system, and confirm that the flight control is in forced ground mode. Use the water ballast system to adjust the aircraft's center of gravity to 23.8%; perform a three-way control check of the neutral and extreme positions, and taxi out after confirming that everything is normal.

[0066] 2) The aircraft taxis to the takeoff line and takes off according to normal procedures;

[0067] 3) Once the aircraft reaches the target airspace, use the water ballast system to adjust the aircraft's center of gravity to the forward limit;

[0068] 4) The length of the drag cone is 75 meters;

[0069] 5) Trim the aircraft to the required configuration, speed, and altitude, and maintain stable straight flight for 30 seconds;

[0070] 6) Adjust the engine thrust to the required level, and decelerate the aircraft at a rate not exceeding 1 kn / s until the aircraft stalls. The test pilot then maneuvers the aircraft to recover from the stall.

[0071] 7) Alternate between slow speed and power-driven conditions to ensure that the test weights are close;

[0072] 8) Retrieve the drag cone after the test;

[0073] 9) The aircraft lands normally and taxis to the designated position. Then, the power to the test system is turned off and the engine is shut down.

Claims

1. A test flight method for determining the stall speed of a turboprop aircraft, characterized in that, The method includes: Step 1: Determine the test conditions, using the front limit of the center of gravity envelope as the test conditions. The test conditions include flap configuration, aircraft weight, and engine status. Step 2: Determine the aircraft's weight as the first weight, set the aircraft to the prescribed takeoff configuration, take off according to the takeoff procedure, and fly to the designated airspace as planned; Step 3: At a given flight altitude, extend the tow cone to a specified length. The tow cone can obtain an accurate static pressure value at the specified length without being affected by turbulence. The given flight altitude is within the flight envelope. Step 4: Set the aircraft's flap configuration to the first flap configuration; Step 5: Set the aircraft's engine status to the first engine state under the first flap configuration. Trim the aircraft at the given speed and in the first engine state, and perform stable straight flight for 30 seconds. The given speed is a speed point between 1.13 times the stall speed and 1.3 times the stall speed. The first engine state is the idle power state under the first flap configuration. Step 6: Decelerate the aircraft at a rate not greater than 1 kn / s using only longitudinal control until the test pilot clearly determines that the aircraft has stalled, then end the maneuver and record the speed at the moment of stall. Step 7: Repeat steps 5 and 6, 4-8 times; Step 8: Set the engine state in Step 5 to other engine states corresponding to the first flap configuration, repeat Steps 5 to 7 to traverse all engine states under the first flap configuration, and obtain the stall speed at the first flap configuration and other engine states; fit the stall speed at the first weight and the stall speed in the unpowered state under the first flap configuration. Step 9: Set the flap configuration of the aircraft to other flap configurations. Repeat steps 4 to 8, iterate through all engine states under other flap configurations, obtain the stall speed under all engine states under other flap configurations, and perform fitting to obtain the stall speed under the first weight and the unpowered state under other flap configurations. Step 10: Set the aircraft weight from Step 2 to another weight, and repeat Steps 2-9 to obtain the stall speed under no-power conditions for all flap configurations under other weights.

2. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, In step 1, the test conditions are determined, specifically as follows: 1) Select flap configuration. Since different flap configurations may result in different stall phenomena, a comprehensive judgment should be made based on the results of wind tunnel tests and model free flight tests before testing. The configuration with smaller lift coefficient change with angle of attack should be started. 2) Determine the aircraft weight based on the flap configuration, in ascending order of weight; 3) The engine status sequence is from smallest to largest.

3. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, In step 6, when the test pilot clearly determines that the aircraft has stalled, specifically when the inherent flight characteristics show the pilot a clearly identifiable stall phenomenon, the aircraft is considered to have stalled. The stall phenomenon includes: 1) any abnormal nose pitch; 2) any uninstructed nose pitch that foreshadows a stall; 3) any uninstructed lateral or directional movement; 4) the aircraft exhibiting a flutter of an amplitude and severity that would prevent the completion of a maneuver; 5) the pitch control reaches the stop point, and the control devices cannot further increase the pitch attitude after holding that position for 2 seconds before the recovery begins.

4. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, Before step 1, the following steps are also included: completing emergency off-aircraft system tests and ground drills for the unit to ensure that the system is working properly.

5. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, Before step 1, the process also includes: completing an in-flight engine restart test before the stall test flight and developing a detailed in-flight restart procedure; in step 6, if the engine fails in the air, the engine is restarted in the air according to the detailed in-flight restart procedure developed before the stall test flight, and the test flight mission is safely completed.

6. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, Before step 1, the test also includes: completing the test flight of the aircraft's unpowered glide characteristics before the stall test flight and formulating an air glide emergency landing plan; Step 6, once the engine stops in the air and the detailed in-flight restart procedure formulated before the stall test flight fails to start the engine, the aircraft is then operated to return to the airfield and land according to the formulated air glide emergency landing plan, thus ending the test.

7. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, Before step 1, the process also includes: conducting engine characteristic flight tests under conditions of high angle of attack and high sideslip angle to ensure that the engine is working normally under these conditions.

8. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, Before step 1, the test flight also includes completing a negative overload test flight to ensure that the aircraft's fuel and pressurization capabilities are normal under negative overload conditions.

9. The test flight method for determining the stall speed of a turboprop aircraft according to claim 1, characterized in that, Before step 1, the aircraft characteristics test flight is also completed under high pitch angle, high roll angle and negative overload conditions to ensure that the aircraft characteristics are normal under these conditions.