Trial flight method for stall speed of turboprop aircraft

Abstract

The invention belongs to the field of test flight, and particularly relates to a test flight method for a stall speed of a turboprop aircraft, which is suitable for a stall speed flight test of the turboprop aircraft. The test condition is determined according to the sequence of the flap configuration, the aircraft weight and the engine state, the test flight risk of the stall speed of the propeller-driven aircraft is comprehensively recognized according to the principle of gradual approaching in the engine state changing process, the reasonable test sequence and risk degradation measures are formulated, the test flight risk can be effectively reduced, and the test efficiency is improved. And powerful support can be provided for qualified stall speed certification test flight and identification test flight of the propeller-driven aircraft.

Description

Technical Field

[0001] The invention belongs to the field of flight testing, and in particular relates to a flight testing method for the stall speed of a turboprop aircraft, which is suitable for a stall speed flight test of a propeller aircraft. Background Art

[0002] The stall problem has always been a hot, focal and difficult issue in the development of civil aircraft models. It is one of the most important factors affecting flight safety and has received close attention from the industry, airworthiness authorities and customers. Stall speed has an important impact on many performance parameters that affect aircraft qualification, such as airport length and take-off speed schedule. Stall characteristics are used to study the handling quality of the aircraft during stall maneuvers, hoping to have a smaller probability of accidental stall. If a stall occurs, it is hoped that the pilot can recover safely and quickly from an unintentional stall without requiring any special driving skills. Therefore, obtaining good stall characteristics and a smaller stall speed at the same time is the goal of domestic and foreign civil aircraft model development.

[0003] The invention discloses a stall speed flight test method for turboprop aircraft, which is used for supporting the airworthiness certification or test evaluation process of turboprop aircraft. Summary of the invention

[0004] The purpose of the invention is to provide a stall speed test flight method for 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 method for testing the stall speed of a turboprop aircraft, the method comprising:

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

[0008] Step 2: Determine the weight of the aircraft 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, the drag cone is released to a specified length, and an accurate static pressure value can be obtained when the drag cone is not affected by turbulence at the specified length, and the given flight altitude is within the flight envelope;

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

[0011] Step 5: Setting the engine state of the aircraft to the first engine state under the first flap configuration, trimming the aircraft at a given speed and in the first engine state, and performing 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; wherein the first engine state is the idle power state under the first flap configuration,

[0012] Step 6: Use only longitudinal control to decelerate the aircraft at a rate not exceeding 1 kn / s until the test pilot clearly determines that the aircraft is stalling. Then, terminate the maneuver and record the speed at the moment of stalling.

[0013] Step 7: Repeat steps 5 to 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 speed at the stall moment under the first flap configuration and other engine states; fit the speed at the stall moment under all engine states under the first flap configuration to obtain the stall speed under the first weight and the first flap configuration in the power-free state;

[0015] Step 9: Set the flap configuration of the aircraft to other flap configurations and repeat steps 4 to 8, traverse all engine states under other flap configurations, obtain the speed at the stall moment under all engine states under other flap configurations, and perform fitting to obtain the stall speed under the first weight and no-power state under other flap configurations;

[0016] Step 10: Set the aircraft weight in step 2 to other weights and repeat steps 2-9 to obtain the stall speed in the power-off state in all flap configurations at other weights.

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

[0018] 1) Select the flap configuration. Since aircraft with different flap configurations may have different performances in stalling, a comprehensive judgment should be made based on the results of wind tunnel tests and model free flight tests before the test. The configuration with the smallest change in lift coefficient with angle of attack should be selected.

[0019] 2) Determine the aircraft weight based on the flap configuration, with the weight order from small to large;

[0020] 3) The order of engine status is from small to large.

[0021] Further, in step 6, when the test pilot clearly determines that the aircraft is stalled, specifically: when the inherent flight characteristics show the pilot a clearly identifiable aircraft stall phenomenon, the aircraft is considered to have stalled, and the aircraft stall phenomenon includes: 1) any abnormal nose pitch; 2) any uncommanded nose pitch that indicates a stall; 3) any uncommanded lateral movement or heading movement; 4) the aircraft experiences buffeting of an amplitude and severity that would prevent the completion of the maneuver; 5) the pitch control reaches the aft stop point, and the control cannot further increase the pitch attitude after remaining in this position for 2 seconds before the start of recovery.

[0022] Furthermore, before step 1, it also includes: completing the emergency exit system test and the crew ground drill to ensure that the system works normally.

[0023] Furthermore, before step 1, it also includes: completing the engine air start test before the stall test flight and formulating a detailed air start procedure; step 6, once the engine stops in the air, the engine air start is performed according to the detailed air start procedure formulated before the stall test flight, and the test flight mission is safely completed.

[0024] Furthermore, before step 1, it also includes: completing a test flight of the aircraft's unpowered descent characteristics before the stall test flight, and formulating an air taxiing forced landing plan; step 6, once the engine stops in the air and the engine cannot be started according to the detailed air start procedure formulated before the stall test flight, the aircraft is maneuvered to return to the field for landing according to the formulated air taxiing forced landing plan, thereby ending the test.

[0025] Furthermore, before step 1, it also includes: completing an engine characteristic flight test under conditions of a large angle of attack and a large sideslip angle to ensure that the engine operates normally under this state.

[0026] Furthermore, before step 1, it also includes: completing a negative overload test flight to ensure that the aircraft's fuel supply and pressure supply capabilities are normal under negative overload conditions.

[0027] Furthermore, before step 1, it also includes: completing an aircraft characteristic test flight under conditions of a large pitch angle, a large roll angle and negative overload to ensure that the aircraft characteristics under this state are normal.

[0028] Beneficial effects:

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

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

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

[0032] Determine the test conditions, specifically:

[0033] 1) Select the flap configuration. Since aircraft with different flap configurations may have different performances in stalling, a comprehensive judgment should be made based on the results of wind tunnel tests and model free flight tests before the test. The configuration with the smallest change in lift coefficient with angle of attack should be selected.

[0034] 2) Determine the aircraft weight based on the flap configuration, with the weight order from small to large;

[0035] 3) The order of engine status is from small to large;

[0036] Step 2: Determine the weight of the aircraft 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, the drag cone is released to a specified length, and an accurate static pressure value can be obtained when the drag cone is not affected by turbulence at the specified length, and the given flight altitude is within the flight envelope;

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

[0039] Step 5: Setting the engine state of the aircraft to the first engine state under the first flap configuration, trimming the aircraft at a given speed and in the first engine state, and performing 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; wherein the first engine state is the idle power state under the first flap configuration,

[0040] Step 6: Use only longitudinal control to decelerate the aircraft at a rate not exceeding 1 kn / s until the test pilot clearly determines that the aircraft is stalling. Then, terminate the maneuver and record the speed at the moment of stalling.

[0041] Step 7: Repeat steps 5 to 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 traverse all engine states under the first flap configuration, and obtain the speed at the stall moment under the first flap configuration and other engine states; fit the speed at the stall moment under all engine states under the first flap configuration to obtain the stall speed under the first weight and the first flap configuration in the power-free state; Step 9: Set the flap configuration of the aircraft to other flap configurations and repeat steps 4 to 8, traverse all engine states under other flap configurations, obtain the speed at the stall moment under all engine states under other flap configurations, and fit to obtain the stall speed under the first weight and other flap configurations in the power-free state;

[0043] Step 10: Set the aircraft weight in step 2 to other weights and repeat steps 2-9 to obtain the stall speed in the power-off state in all flap configurations at other weights.

[0044] In step 6, the airplane is considered to be stalled when the test pilot clearly determines that the airplane is stalled, specifically when the inherent flight characteristics indicate to the pilot clearly discernible signs of the airplane stalling. These signs may occur singly or in combination: 1) any abnormal nose pitch; 2) any uncommanded nose down that indicates a stall; 3) any uncommanded lateral or directional motion; 4) the airplane experiences buffeting of such magnitude and severity that it would prevent completion of the maneuver; and 5) the pitch control reaches the aft stop and cannot be further increased in pitch attitude after the controls remain in that position for a brief period (2 seconds) before recovery is initiated.

[0045] Stall speed is an important parameter that characterizes the aerodynamic characteristics of an aircraft and limits the minimum allowable operating speed. The risk of obtaining a stall speed flight test is very high. Therefore, complete risk identification and formulation of risk mitigation measures are necessary guarantees for the safe and smooth conduct of the flight test.

[0046] In this embodiment, the risk identification and risk reduction measures of the turboprop aircraft stall speed test flight are as follows:

[0047] Risk Identification:

[0048] 1) During the stall process, the aircraft may be out of control or in a deep stall;

[0049] 2) May cause abnormal engine operation or engine shutdown, resulting in the aircraft requiring emergency power supply;

[0050] 3) May cause problems with the aircraft fuel and lubricating oil systems;

[0051] 4) It may cause problems with other aircraft systems.

[0052] Risk Mitigation Measures:

[0053] The principle of changing the engine state in step 5 is to proceed step by step: first fly at an idle speed, then fly at a power stall;

[0054] Before step 1, complete the emergency exit system test and crew ground drill to ensure that the system works properly;

[0055] Prior to step 1, it also includes: completing the engine air start test before the stall test flight and formulating a detailed air start procedure;

[0056] Step 6: Once the engine stops in the air, start the engine in the air according to the detailed air start procedure formulated before the stall test flight to safely complete the test flight mission.

[0057] Before step 1, it also includes: completing the aircraft's unpowered gliding characteristics test flight before the stall test flight and formulating an air-gliding forced landing plan;

[0058] Step 6: Once the engine stops in the air and fails to start according to the detailed air start procedure prepared before the stall test flight, the aircraft is maneuvered to return to the field and land according to the prepared air taxi landing plan to end the test.

[0059] Prior to step 1, the following steps are also required: completing an engine characteristic test flight under conditions of a large angle of attack and a large sideslip angle to ensure that the engine operates normally under this condition;

[0060] During the stall test in steps 5 and 6, monitor the engine parameters in real time and report any abnormalities immediately;

[0061] Before step 1, it also includes: completing a negative overload test flight to ensure that the aircraft's fuel supply and pressure supply capabilities are normal under negative overload conditions;

[0062] Before step 1, it also includes: completing the aircraft characteristic test flight under large pitch angle, large roll angle and negative overload conditions to ensure that the aircraft characteristics are normal under this state.

[0063] Example

[0064] Taking a certain test flight as an example, the specific implementation method of the stall speed test flight of a propeller aircraft is as follows:

[0065] 1) Complete engine start-up according to normal procedures, check the working conditions of each system, and confirm that the flight control is in forced ground mode. Use the water counterweight system to adjust the center of gravity of the aircraft to 23.8%; check the neutral position and extreme position of the three-way control, and slide out after confirming that it is normal;

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

[0067] 3) The aircraft reaches the target airspace and uses the water ballast system to adjust the aircraft's center of gravity to the front limit;

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

[0069] 5) The aircraft flies steadily and straight for 30 seconds according to the required configuration, speed and altitude trim;

[0070] 6) Adjust the engine thrust to the required state, control the aircraft to decelerate at a deceleration rate not greater than 1 kn / s until the aircraft stalls, and the test pilot controls the aircraft to recover from the stall;

[0071] 7) The slow-speed state and the power-on state are performed alternately to ensure that the test weight is close;

[0072] 8) After the test, retract the cone;

[0073] 9) The aircraft makes a normal approach and landing, taxis to the designated location, then turns off the power of the test system and shuts down the vehicle.

Claims

1. A method for testing the stall speed of a turboprop aircraft, characterized in that: The method comprises: Step 1: Determine the test conditions, taking the front limit of the center of gravity envelope as the test condition. The test conditions include flap configuration, aircraft weight, and engine status. Step 2: Determine the weight of the aircraft 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, the drag cone is released to a specified length, and an accurate static pressure value can be obtained when the drag cone is not affected by turbulence at the specified length, and the given flight altitude is within the flight envelope; Step 4: Set the flap configuration of the aircraft to the first flap configuration; Step 5: Setting the engine state of the aircraft to the first engine state under the first flap configuration, trimming the aircraft at a given speed and in the first engine state, and performing 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; wherein the first engine state is the idle power state under the first flap configuration, Step 6: Use only longitudinal control to decelerate the aircraft at a rate not exceeding 1 kn / s until the test pilot clearly determines that the aircraft is stalling. Then, terminate the maneuver and record the speed at the moment of stalling. Step 7: Repeat steps 5 to 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 speed at the stall moment under the first flap configuration and other engine states; fit the speed at the stall moment under all engine states under the first flap configuration to obtain the stall speed under the first weight and the first flap configuration in the power-free state; Step 9: Set the flap configuration of the aircraft to other flap configurations and repeat steps 4 to 8, traverse all engine states under other flap configurations, obtain the speed at the stall moment under all engine states under other flap configurations, and perform fitting to obtain the stall speed under the first weight and no-power state under other flap configurations; Step 10: Set the aircraft weight in step 2 to other weights and repeat steps 2-9 to obtain the stall speed in the power-off state in all flap configurations at other weights.

2. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: In step 1, determine the test conditions, specifically: 1) Select the flap configuration. Since aircraft with different flap configurations may have different performances in stalling, a comprehensive judgment should be made based on the results of wind tunnel tests and model free flight tests before the test. The configuration with the smallest change in lift coefficient with angle of attack should be selected. 2) Determine the aircraft weight based on the flap configuration, with the weight order from small to large; 3) The order of engine status is from small to large.

3. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: In step 6, the airplane is considered to have stalled when the test pilot clearly determines that the airplane is stalled, specifically when the inherent flight characteristics indicate to the pilot a clearly discernible stall of the airplane, which includes: 1) any abnormal nose-up; 2) any uncommanded nose-down that would indicate a stall; 3) any uncommanded lateral or directional motion; 4) the airplane experiences buffeting of such magnitude and severity that it would prevent completion of the maneuver; and 5) the pitch control reaches the aft stop and the pitch attitude cannot be further increased after the control remains in that position for 2 seconds before recovery is initiated.

4. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: Before step 1, it also includes: completing the emergency exit system test and crew ground drill to ensure that the system works properly.

5. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: Before step 1, it also includes: completing the engine air start test before the stall test flight and formulating a detailed air start procedure; step 6, once the engine stops in the air, the engine air start is performed according to the detailed air start procedure formulated before the stall test flight, and the test flight mission is safely completed.

6. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: Before step 1, it also includes: completing the aircraft's unpowered descent characteristics test flight before the stall test flight and formulating an air taxiing forced landing plan; step 6, once the engine stops in the air and the engine cannot be started according to the detailed air start procedure formulated before the stall test flight, the aircraft is maneuvered to return to the field for landing according to the formulated air taxiing forced landing plan to end the test.

7. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: Before step 1, it also includes: completing the engine characteristic test flight under high angle of attack and high sideslip angle conditions to ensure that the engine works normally under this condition.

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

9. The turboprop aircraft stall speed test flight method according to claim 1, characterized in that: Before step 1, it also includes: completing the aircraft characteristic test flight under large pitch angle, large roll angle and negative overload conditions to ensure that the aircraft characteristics are normal under this state.