A method for verifying the airworthiness compliance of unusable fuel quantities in transport-type rotorcraft

Abstract

This invention discloses a method for verifying the airworthiness compliance of unusable fuel quantities in transport-type rotorcraft, comprising the following steps: Step 1. Simulating the aircraft to obtain the unusable fuel quantity under simulation conditions; Step 2. Conducting laboratory tests on the aircraft to obtain the unusable fuel quantity under test conditions; verifying the unusable fuel quantity under simulation conditions using the unusable fuel quantity under test conditions to ensure that the simulation value is greater than or equal to the test value; Step 3. Conducting flight tests on the aircraft to obtain the unusable fuel quantity under flight test conditions; verifying the unusable fuel quantity under simulation conditions using the unusable fuel quantity under flight test conditions to ensure that the simulation value is greater than or equal to the flight test value; Step 4. Determining the simulation value that satisfies the conditions of Steps 2 and 3 as the final unusable fuel quantity. This invention provides strong guidance for the airworthiness certification of transport-type rotorcraft and can effectively verify the unusable fuel quantity of transport-type rotorcraft.

Description

Technical Field

[0001] This invention belongs to the field of aircraft certification technology and relates to a method for verifying the airworthiness compliance of unavailable fuel quantities for transport-type rotorcraft. Background Technology

[0002] Unusable fuel quantity is a value that must be determined for the airworthiness certification of civil rotorcraft. Section 29.959 of the Airworthiness Regulations for Transport Category Rotorcraft (CCAR-29) stipulates that the unusable fuel quantity in each fuel tank must be determined to be no less than the following quantity: the fuel quantity in the tank at the moment when abnormal engine operation begins under the most unfavorable fuel supply conditions for all scheduled operations and maneuvers requiring fuel from that tank. Furthermore, Section 29.1337(b)(1) stipulates that each fuel gauge must be calibrated so that during level flight, when the remaining fuel in the tank equals the unusable fuel quantity determined according to Section 29.959, its reading is "zero". Therefore, the accurate determination of the unusable fuel quantity for a helicopter is directly related to its flight safety.

[0003] Because China's civil aircraft airworthiness certification work started relatively late, especially for transport-category rotorcraft, very few models have obtained airworthiness certification. Regarding airworthiness verification methods for unusable fuel quantities in transport-category rotorcraft, no specific test methods and technical solutions have been found in the literature. Currently, requirements for unusable fuel quantities are usually only implemented through bench tests in fixed attitudes or flight tests in small attitudes, which cannot comprehensively verify the unusable fuel quantity values ​​under the most unfavorable fuel supply conditions. Summary of the Invention

[0004] Objective: To provide an airworthiness verification method for unusable fuel quantities in transport-class rotorcraft that meets the requirements of CCAR 29.959, for verifying the unusable fuel quantities in transport-class rotorcraft. This invention provides strong guidance for airworthiness certification of transport-class rotorcraft and can effectively verify the unusable fuel quantities in transport-class rotorcraft.

[0005] Technical solution: A method for verifying the airworthiness compliance of unusable fuel quantities in transport-type rotorcraft, comprising the following steps:

[0006] Step 1. Simulate the aircraft to obtain the amount of unusable fuel under simulated conditions;

[0007] Step 2. Conduct laboratory tests on the aircraft to obtain the amount of unusable fuel under test conditions; use the amount of unusable fuel under test conditions to verify the amount of unusable fuel under simulation conditions, ensuring that the simulation value is greater than or equal to the test value.

[0008] Step 3. Conduct a test flight of the aircraft to obtain the amount of unavailable fuel under test flight conditions; use the amount of unavailable fuel under test flight conditions to verify the amount of unavailable fuel under simulation conditions, ensuring that the simulation value is greater than or equal to the test flight value.

[0009] Step 4. Determine the simulation value that satisfies the conditions in Steps 2 and 3 as the final unusable fuel quantity.

[0010] In the aforementioned method for verifying the airworthiness compliance of unusable fuel quantities for transport-type rotorcraft, the specific process of step 1 is as follows:

[0011] Step 1.1 Determine the fuel tank attitude: Analyze the aircraft's operating envelope and attitude during flight;

[0012] Step 1.2 Perform simulation analysis of unusable fuel quantity: Using the installation point of the booster pump as the projection point, vertically raise a certain height at the projection point to simulate the "effective fuel suction point" of the booster pump. Then, construct a cutting plane passing through the "effective fuel suction point" to cut the fuel entity. The cut fuel entity is the unusable fuel quantity in the simulation state.

[0013] Step 1.3 Perform simulations on each fuel tank as described above to determine the amount of unusable fuel in each fuel tank under simulation conditions.

[0014] In the aforementioned method for verifying the airworthiness compliance of unusable fuel quantities for transport-type rotorcraft, the generation of the cutting plane is performed according to the following steps:

[0015] Create a horizontal plane as a "reference plane" through the "effective oil absorption point";

[0016] The pitch axis is a horizontal straight line parallel to the effective oil suction point.

[0017] The straight line parallel to the heading at the "effective oil intake point" is the "roll axis";

[0018] The "reference plane" is obtained by adjusting the pitch angle with the "pitch axis" as the axis;

[0019] The "pitch plane" is obtained by adjusting the roll angle around the "roll axis".

[0020] In the aforementioned method for verifying the airworthiness compliance of unusable fuel quantities for transport-class rotorcraft, the process of cutting the fuel entity with a cutting plane is as follows:

[0021] Based on the pitch and roll range of the determined fuel tank attitude, select an appropriate step size, cut the fuel tank, establish the relationship between the unusable fuel quantity of each fuel tank and the aircraft attitude, and determine the most unfavorable fuel supply condition and the unusable fuel quantity under the flight attitude.

[0022] In the aforementioned method for verifying the airworthiness compliance of unusable fuel quantities for transport-type rotorcraft, the specific process of step 2 is as follows:

[0023] Step 2.1 Test Preparation Stage: Based on the configuration of the aircraft's fuel system, prepare the test bench equipment, fuel measurement equipment, and refueling equipment; select the roll and pitch angles for the test;

[0024] Step 2.2 Test Phase: Adjust the angle of the test bench according to the pitch and roll attitude angle determined in the early stage of the test, and inject fuel into the test fuel tank; then, open the fuel cut-off valve and all fuel booster pumps to drain the fuel in the tank; when no more fuel can be drained from the tank, turn off the fuel booster pump, restore the test bench to the horizontal position, drain the remaining fuel in each tank, and record it. The remaining fuel is the amount of unusable fuel in each tank under the test state.

[0025] Step 2.3 Test Result Processing: Compare the unusable fuel quantity in each fuel tank under test conditions with the unusable fuel quantity under simulation conditions to determine that the simulation results are more conservative than the laboratory results.

[0026] In the aforementioned method for verifying the airworthiness compliance of unusable fuel quantities for transport-type rotorcraft, step 3 is as follows:

[0027] Step 3.1 Analysis of the most critical fuel tank: Compare the differences in the local shape, size and internal equipment layout of the fuel supply tanks in the fuel tanks, and finally determine the most critical fuel tank used for flight test verification;

[0028] Step 3.2 Flight Attitude Selection: Based on the location of the most critical fuel tank, analyze the impact of left and right turns on the amount of unusable fuel to determine the turning direction; at the same time, based on the actual test flight data of the aircraft, select the maximum feasible roll angle as the turning bank.

[0029] Step 3.3 Flight Test Procedure: Start the engine normally and conduct the flight test in the selected flight test attitude; when the engine supplied by the most critical fuel tank malfunctions, shut down the engine and the fuel booster pump in the most critical fuel tank to ensure that the fuel in the most critical fuel tank is not affected by the fuel level in other fuel tanks; land, shut down the other engines, ensure that the fuel in the most critical fuel tank is not affected by the fuel level in other fuel tanks, release the remaining fuel in the most critical fuel tank, and record the remaining fuel level, which is the unusable fuel level in the flight test state;

[0030] Step 3.4 Flight Test Result Processing: Compare the unavailable fuel quantity under flight test conditions with the unavailable fuel quantity under simulation conditions of the corresponding flight attitude to determine that the simulation results are more conservative than the flight test results.

[0031] In the aforementioned method for verifying the airworthiness compliance of unavailable fuel quantities for transport-class rotorcraft, after shutting down other engines, the method of keeping the fuel booster pumps in other fuel tanks running while shutting down the fuel booster pump in the most critical fuel tank ensures that the fuel in the most critical fuel tank is not affected by the fuel quantity in other fuel tanks.

[0032] In the aforementioned method for verifying the airworthiness compliance of unavailable fuel quantity for transport-type rotorcraft, in step 1.1, when the flight manual imposes restrictions on the flight attitude after a low fuel level warning, the unavailable fuel quantity under the restricted attitude is taken as one of the analysis factors.

[0033] Beneficial Effects: This invention provides an airworthiness compliance verification method for verifying the amount of unusable fuel under CCAR 29.959, specifically for verifying the amount of unusable fuel in transport-class rotorcraft. This invention establishes a complete, detailed, and implementable method for verifying the amount of unusable fuel in rotorcraft, which not only fully verifies airworthiness requirements and ensures safety, but also reduces flight test cycles, lowers verification costs, and reduces risky procedures, thus mitigating flight test risks. This invention provides strong guidance for airworthiness certification of transport-class rotorcraft and can effectively verify the amount of unusable fuel in transport-class rotorcraft. Attached Figure Description

[0034] Figure 1 This is a flowchart of the present invention. Detailed Implementation

[0035] Example 1. A method for verifying the airworthiness compliance of unusable fuel quantities in transport-type rotorcraft, participating in... Figure 1 The specific steps are as follows:

[0036] Step 1: Simulation Analysis of Unavailable Fuel Quantity

[0037] Step 1.1 Determine the fuel tank attitude

[0038] Analyze the possible operating envelope and aircraft attitude under maneuvering flight conditions of the model, including the dynamic maneuvering effects that may be encountered such as sideslip, go-around pull-up, and acceleration. This generally includes cruise attitude, end-of-flight attitude, and stable flight attitude. In addition, if the flight manual restricts the flight attitude after a low fuel warning, the amount of unusable fuel under the restricted attitude should also be considered.

[0039] Step 1.2: Simulation analysis of unavailable fuel quantity.

[0040] The engine fuel inlet is divided into a stable fuel intake region and an unstable fuel intake region. According to CCAR 29.959, the region below the fuel level when the engine first shows signs of instability is considered the unstable fuel intake region. When the fuel level at the booster pump inlet is below this level, the booster pump will be unable to continue supplying the engine with sufficient flow and pressure to support normal engine operation. According to airworthiness regulations, when the booster pump's fuel supply pressure is unstable, the remaining fuel in the tank is unusable, and the fuel level is a certain distance above the inlet. Therefore, using the booster pump mounting point as a projection point, a vertical height is raised from the projection point to simulate the booster pump's "effective fuel intake point." Then, a cutting plane passing through the "effective fuel intake point" is constructed to cut the fuel sample; the resulting fuel sample represents the unusable fuel quantity in the simulation. This "certain height" is determined according to the booster pump's user manual.

[0041] The cutting plane is generated according to the following steps:

[0042] Create a horizontal plane as a "reference plane" through the "effective oil absorption point";

[0043] The pitch axis is a horizontal straight line parallel to the effective oil suction point.

[0044] The straight line parallel to the heading at the "effective oil intake point" is the "roll axis";

[0045] The "reference plane" is obtained by adjusting the pitch angle with the "pitch axis" as the axis;

[0046] The "pitch plane" is obtained by adjusting the roll angle around the "roll axis".

[0047] Based on the determined pitch and roll range of the fuel tank attitude, an appropriate step size is selected to cut the fuel tank, establishing the relationship between the unusable fuel quantity in each fuel tank and the aircraft attitude, and determining the most unfavorable refueling condition and the unusable fuel quantity under the flight attitude. If the unusable fuel quantity is reduced by restricting the flight attitude, the unusable fuel quantity under the restricted attitude should be considered. The step size is the angle between two adjacent cutting planes within the pitch and roll range of the fuel tank attitude.

[0048] Step 1.3 Perform simulations on each fuel tank as described above to determine the amount of unusable fuel in each fuel tank under simulation conditions.

[0049] Step 2 Laboratory Test

[0050] Step 2.1 Experimental Preparation Stage

[0051] Based on the fuel system configuration of the target aircraft model, prepare the test bench equipment, fuel measurement equipment, refueling equipment, and other necessary instruments and equipment for the test. Select the roll and pitch angles for the test; these angles can be combined with the angles used in simulation analysis.

[0052] Step 2.2 Experimental Phase

[0053] Adjust the angle of the test bench according to the pitch and roll attitude angle determined in the early stage of the test, inject an appropriate amount of fuel into the test tank, open the fuel cut-off valve and all fuel booster pumps to drain the fuel in the tank, turn off the fuel booster pumps when no more fuel can be drained, restore the test bench to the horizontal position, release the fuel in each tank into the measuring cup, and record the amount of fuel released from each tank (i.e. the amount of unusable fuel).

[0054] Step 2.3 Processing of Experimental Results

[0055] The unusable fuel quantity values ​​of each fuel tank obtained in the laboratory were compared with the simulation analysis results to determine that the simulation results are more conservative than the laboratory results (i.e., the unusable fuel quantity values ​​obtained by simulation are not less than the unusable fuel quantity values ​​obtained in the laboratory).

[0056] Step 3 Flight Test

[0057] Step 3.1: The most critical fuel tank analysis

[0058] Based on the working principle of the rotorcraft's fuel system and the fuel tank configuration, auxiliary fuel tanks and direct engine fuel supply tanks were determined. Auxiliary fuel tanks do not directly supply fuel to the engine; therefore, a malfunction in the tank itself or its internal equipment does not directly affect engine fuel supply, but may only slightly affect the amount of available fuel (or prevent the pilot from accurately judging the remaining fuel level), and does not directly impact flight safety. Direct engine fuel supply tanks, on the other hand, directly affect flight safety due to the amount of fuel they contain. Therefore, the most critical fuel tank for flight testing should be selected from the direct engine fuel supply tanks. By comparing the differences in the local shape, size, and internal equipment layout of the direct engine fuel supply tanks, the most critical fuel tank for flight testing was ultimately determined.

[0059] Step 3.2 Flight Attitude Selection

[0060] According to CCAR 29.959, for fuel tanks, unusable fuel quantity refers to the amount of fuel in the tank at the moment when engine operation begins to deteriorate under the most unfavorable fuel supply conditions for all planned operations and maneuvers requiring fuel from that tank, or, for delivery tanks, the amount of fuel when the flow of fuel into the receiving tank is interrupted. The most unfavorable fuel supply conditions include not only extreme situations unlikely to be encountered during normal operation, but also a thorough analysis of the possible operating envelope of the helicopter model and the attitudes (including pitch and roll) of any maneuvers that may occur within that envelope, to determine the unusable fuel quantity in each tank under various attitudes. For storage tanks or tanks limited to use during cruise flight, the flight state may generally be limited to level flight or hovering under center-of-gravity conditions that would produce (as determined by inspection) the maximum unusable fuel quantity. For fuel tanks that directly supply fuel to the engine, the flight state also includes takeoff and landing using the expected stable pitch attitude, as well as hovering and level flight, taking into account the adverse effects of possible extreme lateral center-of-gravity changes.

[0061] The determination of the flight attitude for unavailable fuel levels primarily considers flight safety and feasibility, and aims to verify the maximum unavailable fuel level under expected maneuvering flight conditions within the operational envelope. Considering that near-ground hovering and level flight are both steady-state flights, although the helicopter will experience a certain roll angle due to extreme lateral center of gravity, factors such as fuel level angle and fuel sloshing caused by maneuvering flight have not been fully verified. Laboratory test results for the fuel system largely cover these two flight states, and further verification through flight testing is unnecessary. The level circling flight state fully considers factors such as roll angle and maneuvering flight conditions. Based on the location of the most critical fuel tank, the impact of left and right circling on the unavailable fuel level is analyzed to determine whether to choose a left or right circling flight attitude. As for the circling bank angle, the maximum feasible roll angle should be selected based on the actual flight test data of the target aircraft. During flight testing, in the event of engine malfunction, the "landing with stable pitch attitude" procedure should be executed according to the flight manual's emergency procedures. The above flight test states represent the most severe unavailable fuel level flight conditions.

[0062] Step 3.3 Flight Test Procedure

[0063] The rotorcraft is ballasted to minimum weight. The most critical fuel tank is filled with the fuel required for the test. The fuel levels in other main fuel tanks should be sufficient to ensure flight safety, and these tanks should be isolated from the most critical tank to prevent fuel from flowing into it. The engines are started normally, and flight tests are conducted at the selected test attitude. If the engine supplied by the most critical fuel tank malfunctions, the engine and the fuel booster pump in the most critical fuel tank are shut down to ensure the fuel level in the most critical tank is not affected by the fuel levels in other tanks. The aircraft lands, the other engines are shut down, and necessary measures are taken to ensure the fuel level in the most critical fuel tank is not affected by the fuel levels in other tanks (e.g., keeping the fuel booster pumps in other tanks operational if possible). The fuel in the most critical fuel tank is quickly drained, and the amount drained is recorded.

[0064] Step 3.4 Processing of Flight Test Results

[0065] The recorded attitude of the rotorcraft and the amount of fuel released from the most critical fuel tank when the engine malfunctioned were compared with the attitude and unusable fuel amount corresponding to the simulation analysis. It was determined that the simulation results were more conservative than the flight test results (i.e., the unusable fuel amount obtained from the simulation was greater than the amount of fuel released from the most critical fuel tank during the flight test).

[0066] Step 4: Determining the final amount of unusable fuel

[0067] Through comparative analysis of simulation analysis, laboratory test and flight test results, it can be seen that the unusable fuel quantity obtained from simulation analysis is the most conservative (i.e. the largest unusable fuel quantity). Therefore, the unusable fuel quantity obtained from simulation analysis is finally determined as the unusable fuel quantity value of the target aircraft model.

Claims

1. A method for verifying the airworthiness compliance of unusable fuel quantities in a transport-type rotorcraft, characterized in that, Includes the following steps: Step 1. Simulate the aircraft to obtain the amount of unusable fuel under simulated conditions: Analyze the aircraft's operating envelope and attitude during flight; Using the booster pump installation point as the projection point, a certain height is raised vertically at the projection point to simulate the booster pump's "effective oil suction point". Then, a cutting plane passing through the "effective oil suction point" is constructed to cut the fuel entity. The cut fuel entity is the unusable fuel quantity in the simulation state. The steps for generating the cutting plane are as follows: Create a horizontal plane as a "reference plane" through the "effective oil absorption point"; The "pitch axis" is a horizontal straight line parallel to the "effective oil suction point"; The straight line parallel to the heading at the "effective oil intake point" is the "roll axis"; The "reference plane" is obtained by adjusting the pitch angle with the "pitch axis" as the axis; The "pitch plane" is obtained by adjusting the roll angle with the "roll axis" as the axis; Step 2. Conduct laboratory tests on the aircraft to obtain the amount of unusable fuel under test conditions; use the amount of unusable fuel under test conditions to verify the amount of unusable fuel under simulation conditions, ensuring that the simulation value is greater than or equal to the test value; the method for determining the amount of unusable fuel under test conditions is as follows: Based on the configuration of the aircraft's fuel system, prepare the test bench equipment, fuel measurement equipment, and refueling equipment; select the roll and pitch angles for the test. Adjust the angle of the test bench according to the pitch and roll attitude angle determined in the early stage of the test, and inject fuel into the test fuel tank; then, open the fuel cut-off valve and all fuel booster pumps to drain the fuel in the tank; when no fuel can be drained from the tank, turn off the fuel booster pump, restore the test bench to the horizontal position, drain the remaining fuel in each tank and record it. The remaining fuel is the amount of unusable fuel in each tank under the test state. Step 3. Conduct a test flight of the aircraft to obtain the amount of unavailable fuel under test flight conditions; use the amount of unavailable fuel under test flight conditions to verify the amount of unavailable fuel under simulation conditions, ensuring that the simulation value is greater than or equal to the test flight value. Step 4. Determine the simulation value that satisfies the conditions in Steps 2 and 3 as the final unusable fuel quantity.

2. The method for verifying the airworthiness compliance of unusable fuel quantity for transport-type rotorcraft according to claim 1, characterized in that, The process of the cutting plane cutting the fuel substance is as follows: Based on the pitch and roll range of the determined fuel tank attitude, select an appropriate step size, cut the fuel tank, establish the relationship between the unusable fuel quantity of each fuel tank and the aircraft attitude, and determine the most unfavorable fuel supply condition and the unusable fuel quantity under the flight attitude.

3. The method for verifying the airworthiness compliance of unusable fuel quantity for transport-type rotorcraft according to claim 1, characterized in that, Step 3 is as follows: Step 3.1 Analysis of the most critical fuel tank: Compare the differences in the local shape, size and internal equipment layout of the fuel supply tanks in the fuel tanks, and finally determine the most critical fuel tank used for flight test verification; Step 3.2 Flight Attitude Selection: Based on the location of the most critical fuel tank, analyze the impact of left and right turns on the amount of unusable fuel to determine the turning direction; at the same time, based on the actual test flight data of the aircraft, select the maximum feasible roll angle as the turning bank. Step 3.3 Flight Test Procedure: Start the engine normally and conduct the flight test in the selected flight test attitude; when the engine supplied by the most critical fuel tank malfunctions, shut down the engine and the fuel booster pump in the most critical fuel tank to ensure that the fuel in the most critical fuel tank is not affected by the fuel level in other fuel tanks; land, shut down the other engines, ensure that the fuel in the most critical fuel tank is not affected by the fuel level in other fuel tanks, release the remaining fuel in the most critical fuel tank, and record the remaining fuel level, which is the unusable fuel level in the flight test state; Step 3.4 Flight Test Result Processing: Compare the unavailable fuel quantity under flight test conditions with the unavailable fuel quantity under simulation conditions of the corresponding flight attitude to determine that the simulation results are more conservative than the flight test results.

4. The method for verifying the airworthiness compliance of unusable fuel quantities for transport-type rotorcraft according to claim 3, characterized in that, After shutting down other engines, the method of keeping the fuel booster pumps in other fuel tanks running while shutting down the fuel booster pump in the most critical fuel tank is adopted to ensure that the fuel in the most critical fuel tank is not affected by the fuel level in other fuel tanks.

5. The method for verifying the airworthiness compliance of unusable fuel quantity for transport-type rotorcraft according to claim 1, characterized in that, When analyzing the aircraft's operating envelope and attitude during flight, if the flight manual imposes restrictions on the flight attitude after a low fuel warning, the amount of unusable fuel under the restricted attitude is considered as one of the analysis factors.

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