Flight test method for unavailable fuel quantity of civil propeller single-shot aircraft

Abstract

The invention discloses a test flight method for the unavailable fuel quantity of a civil propeller single-shot aircraft. The test flight method comprises the steps that safety measures for test flight of the unavailable fuel quantity of the single-shot aircraft are determined; key discrimination parameters are captured in a ground test, and safety data are obtained; performing safety risk analysis on the test flight of the unavailable oil amount, and establishing corresponding risk solution measures for a risk analysis conclusion; according to the geometrical shape of the examination oil tank and the position of an oil suction port, a flight test subject of the unavailable oil amount is formulated; based on the formulated test flight subjects, test flight of unavailable oil is carried out, and test flight of only one test flight subject is carried out in each test flight; and after each test flight is finished, measuring the unavailable oil amount of the airplane examination oil tank, and obtaining the most unfavorable oil amount in the test flight process according to the unavailable oil amount of each test flight subject. According to the technical scheme provided by the invention, the airworthiness certification problem of a civil propeller single-engine aircraft fuel system non-fuel-consumption test flight subject is solved.

Description

Technical Field

[0001] The present invention relates to the field of, but is not limited to, civil aircraft airworthiness certification flight test technology, and in particular to a flight test method for unusable fuel quantity of a civil propeller single-engine aircraft. Background Art

[0002] For civil small transport aircraft, Section 23.959 of the "Normal Category Airplane Airworthiness Regulations" (CCAR-23) requires that the unusable fuel quantity in each fuel tank must be less than the following amount of fuel: for all scheduled operations and maneuvers requiring fuel from the tank, under the most unfavorable fuel supply conditions, the amount of fuel in the tank when the engine begins to operate abnormally, without considering the failure of fuel system components.

[0003] Since the unusable fuel test flight of the aircraft fuel system has a significant impact on the safety of civil aircraft, however, there is currently no systematic test flight verification of the unusable fuel volume of the fuel system of civil propeller single-engine aircraft. As a result, in the airworthiness certification of the unusable fuel test flight subject of this type of aircraft, there are generally problems such as complex actual operations, unclear operating procedures, and unclear test flight risk mitigation measures. Summary of the invention

[0004] Purpose of the present invention: In order to solve the above technical problems, an embodiment of the present invention provides a flight test method for unusable fuel quantity of a civil propeller single-engine aircraft, so as to solve the airworthiness certification problem of the flight test subject of unusable fuel quantity of the fuel system of a civil propeller single-engine aircraft.

[0005] Technical solution of the present invention: The embodiment of the present invention provides a flight test method for unusable fuel quantity of a civil propeller single-engine aircraft, comprising:

[0006] Step 1: Determine the safety measures for single-engine aircraft to conduct test flights without using fuel according to the structural characteristics of the aircraft fuel tank and the fuel supply characteristics of the fuel system;

[0007] Step 2: Conduct a ground test of the unusable oil volume based on the safety measures determined in step 1, capture key discrimination parameters in the ground test, and obtain safety data;

[0008] Step 3: Conduct a safety risk analysis on the unusable fuel test flight, including the risk of engine shutdown in mid-air, inaccurate test operation nodes, and inaccurate test data;

[0009] Step 4: Establish corresponding risk mitigation measures based on the risk analysis conclusions obtained in step 3;

[0010] Step 5, formulate the test flight subjects with unusable fuel quantity according to the geometric shape and fuel inlet position of the assessment fuel tank;

[0011] Step 6, based on the test flight subjects determined in step 5, conduct a test flight with unusable fuel, and conduct only one test flight subject in each test flight; wherein the test flight subjects include at least one of the following subjects: stable level flight, climb, descent and sideslip, and the sideslip includes coordinated sideslip, right side sliding turn, and sideslip with slope limit;

[0012] Step 7: After each test flight, measure the unusable fuel volume of the aircraft test tank, and obtain the most unfavorable fuel volume during the test flight based on the unusable fuel volume of each test flight subject.

[0013] Optionally, in the above-mentioned flight test method for unusable fuel quantity of a civil propeller single-engine aircraft, step 1 comprises:

[0014] Step 11, according to the overall configuration of the aircraft fuel tank, determine that the assessment fuel tanks participating in the unusable fuel quantity test flight include: a fuel transfer tank, or a fuel transfer tank and a fuel supply tank;

[0015] Step 12, for the asymmetric fuel tank, connect the main fuel pump to the test fuel tank to use it as the test fuel tank for the unavailable fuel test flight; connect the auxiliary fuel pump to another fuel tank to build an auxiliary fuel system as a safety fuel tank for the unavailable fuel test flight, and add auxiliary fuel supply pipelines to connect the test fuel tank and the safety fuel tank to the engine inlet end respectively, forming a safety measure for the asymmetric fuel tank;

[0016] Step 13, for the symmetrically configured fuel tanks, one side of the fuel tank is used as a test tank, and the other side of the fuel tank is used as a safety tank to conduct an unusable fuel volume test flight test, thereby forming a safety measure for the symmetrical fuel tanks.

[0017] Optionally, in the above-mentioned test flight method for unusable fuel quantity of a civil propeller single-engine aircraft, for the safety measures of the symmetrical fuel tanks determined in step 1, step 2 includes:

[0018] Step 22, performing a ground test of the unusable oil volume on the assessment oil tank;

[0019] Add fuel close to the unusable amount of fuel to the test tank, add a preset amount of fuel to the safety tank, set the fuel selector to the test tank position, start the engine normally and perform ground work until one of the fault phenomena such as engine speed drop, fuel flow drop, and engine shaking occurs for the first time. After the engine is shut down, obtain the fuel amount value of the test tank as the unusable fuel amount of the test tank in the ground test.

[0020] Optionally, in the above-mentioned test flight method for the unusable fuel quantity of a civil propeller single-engine aircraft, for the safety measures of the asymmetric fuel tank determined in step 1, the step before step 22 includes:

[0021] Step 21, performing a ground test on the auxiliary fuel system;

[0022] Add a preset amount of fuel to the test fuel tank and the safety fuel tank respectively, select the auxiliary fuel pump, and start the engine normally through the auxiliary fuel system and then warm it up; after the warm-up is completed, switch the main fuel pump to work, and the engine will work stably for a preset time in the small, medium and large states respectively; switch the auxiliary fuel pump to work, and the engine will work stably for a preset time in the small, medium and large states respectively, and shut down the engine normally; verify the reliability of the auxiliary fuel pump's fuel supply, and verify the engine's ground starting capability under the auxiliary fuel pump's fuel supply conditions.

[0023] Optionally, in the above-mentioned flight test method for the unusable fuel quantity of a civil propeller single-engine aircraft, after step 22, the method further includes:

[0024] Step 23, obtaining parameter change characteristics of the engine and the fuel system during the process of exhaustion of available fuel according to the test data of step 22;

[0025] Step 24, based on multiple characteristics of engine failure caused by interruption of fuel supply in the fuel system, the characteristics that first cause failure of each type of engine are determined through ground tests on different types of engines, and the parameters corresponding to the characteristics are used as key judgment parameters, and the specific values ​​of the decrease and fluctuation of the parameters corresponding to the characteristics are used as safety data.

[0026] Optionally, in the above-mentioned test flight method for unusable fuel quantity of a civil propeller single-engine aircraft, the safety analysis in step 3 includes:

[0027] Risk 1: Through the analysis of the aircraft configuration and fuel system configuration, as well as the safety measures determined in step 1, if the fuel selector valve is not switched to the safety tank in time, there will be a risk of engine shutdown in the air due to the failure to supply fuel to the safety tank and the auxiliary fuel system in time;

[0028] Risk 2: Through the analysis of flight meteorological conditions, turbulent weather will cause aircraft fluctuations. The fluctuation of the oil level will give the illusion that the fuel system cannot absorb oil, resulting in the risk of inaccurate test points and inaccurate test data during the test.

[0029] Optionally, in the above-mentioned test flight method for unusable fuel quantity of a civil propeller single-engine aircraft, the risk mitigation measures established in step 4 include:

[0030] Risk mitigation measures for risk 1 include:

[0031] Design a taxiing forced landing simulation plan according to the taxiing ratio and altitude loss of the test flight, and conduct a simulated taxiing approach and landing test flight to verify the taxiing forced landing simulation plan; then, perform an engine air start test flight;

[0032] Risk mitigation measures for Risk 2 include: in view of the impact of turbulent weather on the operational test points, setting the unavailable fuel test flight to be carried out in airspace with smooth airflow.

[0033] Optionally, in the above-mentioned test flight method for unusable fuel quantity of a civil propeller single-engine aircraft, the method of formulating the test flight subjects in step 5 is:

[0034] Based on a variety of pre-set flight test subjects, according to the geometric shape of the test fuel tank and the position of the fuel suction port, the most unfavorable fuel supply condition for the current fuel system is selected to formulate the flight test subject with unusable fuel volume.

[0035] Optionally, in the above-mentioned test flight method for unusable fuel quantity of a civil propeller single-engine aircraft, the manner of implementing the test flight for each test flight subject in step 6 includes:

[0036] Stable level flight: add the unusable fuel value obtained close to the ground to the test tank, add as much fuel as possible to the safety tank, place the aircraft fuel selector on the test tank, use the engine at maximum cruise power, and perform stable level flight until the engine speed drops, the fuel flow drops, the fuel supply pressure drops, or the engine shakes. Then switch the fuel selector to the safety tank, descend normally, and measure the unusable fuel in the test tank after landing.

[0037] Climb: Add the unusable fuel value obtained close to the ground to the test tank, add as much fuel as possible to the safety tank, place the aircraft fuel selector in the test tank, take off normally, and climb continuously at the speed under the best climb angle after takeoff until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc., quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel amount in the test tank after landing;

[0038] Descending: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to the unusable fuel, the aircraft descends at the maximum allowable speed until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc., then quickly switch the fuel selector to the safety tank, level the aircraft, and descend normally. After landing, measure the unusable fuel amount in the test tank.

[0039] The test flight of the sideslip subject includes:

[0040] Coordinated sideslip: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, the aircraft will perform coordinated sideslip flight until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine jitter, etc., quickly switch the fuel selector to the safety tank, level the aircraft, and descend normally. After landing, measure the unusable fuel amount in the test tank.

[0041] Right-side sliding turn: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, keep the wings level and fly a right-side sliding turn until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc. Quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel in the test tank after landing.

[0042] Slip with limit slope: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, the aircraft is in left rudder state with full rudder, and the right wing sinks 5°~7° until one of the following phenomena occurs: engine speed drops, fuel flow drops, fuel supply pressure drops, or engine shakes. Quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel in the test tank after landing.

[0043] Optionally, in the above-mentioned test flight method for unusable fuel quantity of a civil propeller single-engine aircraft, the unusable fuel quantity test flight in step 7 includes:

[0044] According to the unusable fuel volume measured after the flight test in step 6, the maximum value of the unusable fuel volume measured after the flight test of each flight test subject is selected as the unusable fuel volume value of the civil propeller single-engine aircraft.

[0045] Beneficial effects of the present invention: An embodiment of the present invention provides a method for testing the unusable fuel quantity of a civil propeller single-engine aircraft, by determining safety measures for the unusable fuel quantity test flight of the single-engine aircraft; conducting a ground test of the unusable fuel quantity based on the safety measures, capturing key discrimination parameters in the ground test, and obtaining safety data; conducting a safety risk analysis on the unusable fuel quantity test flight, and establishing corresponding risk mitigation measures for the risk analysis conclusions; formulating test flight subjects for the unusable fuel quantity according to the geometric shape of the assessment fuel tank and the position of the oil suction port; conducting a test flight for the unusable fuel quantity based on the formulated test flight subjects, and conducting a test flight for only one test flight subject in each test flight; after each test flight, measuring the unusable fuel quantity of the aircraft assessment fuel tank, and obtaining the most unfavorable fuel quantity during the test flight according to the unusable fuel quantity of each test flight subject.

[0046] The technical solution provided by the embodiment of the present invention establishes a method for testing the unusable fuel quantity of civil propeller aircraft. It is the first time in China to concretize and detail the method for testing the unusable fuel quantity of civil propeller aircraft, fill the shortcomings of missing design simulations, reduce the number of test flights, reduce the risk of test flights, and improve the efficiency of test flights. The test flight method of the invention can be applied to the airworthiness certification test flights of small civil aircraft applicable to 23 parts such as civil practical and normal types, and has important guiding significance for the reasonable avoidance of the risk of unusable fuel test flights of small civil aircraft in my country and the promotion of test flight work. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The accompanying drawings are used to provide a further understanding of the technical solution of the present invention and constitute a part of the specification. Together with the embodiments of the present application, they are used to explain the technical solution of the present invention and do not constitute a limitation on the technical solution of the present invention.

[0048] Figure 1 A flow chart of a method for testing the unusable fuel quantity of a civil propeller single-engine aircraft provided in an embodiment of the present invention;

[0049] Figure 2 A schematic diagram of a test flight subject with unusable fuel volume formulated in Example 1 of the present invention;

[0050] Figure 3 A schematic diagram of the test flight subjects of the unusable fuel quantity formulated in Example 2 of the present invention. DETAILED DESCRIPTION

[0051] In order to make the purpose, technical solution and advantages of the present invention more clear, the embodiments of the present invention will be described in detail with reference to the accompanying drawings. It should be noted that the embodiments and features in the embodiments of the present application can be combined with each other arbitrarily without conflict.

[0052] As explained in the above background technology, the unusable fuel test flight of the aircraft fuel system has an important impact on the safety of civil aircraft. However, there is currently no systematic test flight verification for the unusable fuel volume of the fuel system of civil propeller single-engine aircraft, which leads to the airworthiness certification of the unusable fuel volume test flight subject of this type of aircraft. There are generally problems such as complex actual operation, unclear operation procedures, and unclear test flight risk mitigation measures.

[0053] In view of the above problems, an embodiment of the present invention provides a flight test method for the unusable fuel quantity of a civil propeller single-engine aircraft, which is specifically an airworthiness verification method for the unusable fuel quantity subject of the fuel system of a civil propeller single-engine aircraft.

[0054] The present invention provides the following specific embodiments which can be combined with each other. The same or similar concepts or processes may not be described in detail in some embodiments.

[0055] Figure 1 A flowchart of a method for testing the unusable fuel quantity of a civil propeller single-engine aircraft provided in an embodiment of the present invention. The method for testing the unusable fuel quantity of a civil propeller single-engine aircraft provided in an embodiment of the present invention comprises the following steps:

[0056] Step 1: Determine the safety measures for single-engine aircraft to conduct test flights without using fuel according to the structural characteristics of the aircraft fuel tank and the fuel supply characteristics of the fuel system;

[0057] Step 2: Conduct a ground test of the unusable oil volume based on the safety measures determined in step 1, capture key discrimination parameters in the ground test, and obtain safety data;

[0058] Step 3: Conduct a safety risk analysis on the unusable fuel test flight, including the risk of engine shutdown in mid-air, inaccurate test operation nodes, and inaccurate test data;

[0059] Step 4: Establish corresponding risk mitigation measures based on the risk analysis conclusions obtained in step 3;

[0060] Step 5, formulate the test flight subjects with unusable fuel quantity according to the geometric shape and fuel inlet position of the assessment fuel tank;

[0061] Step 6, based on the test flight subjects determined in step 5, conduct a test flight with unusable fuel, and conduct only one test flight subject in each test flight; wherein the test flight subjects include at least one of the following subjects: stable level flight, climb, sideslip and glide, and the sideslip includes coordinated sideslip, right side sliding turn, and sideslip with slope limit;

[0062] Step 7: After each test flight, measure the unusable fuel volume of the aircraft test tank, and obtain the most unfavorable fuel volume during the test flight based on the unusable fuel volume of each test flight subject.

[0063] In an implementation of the embodiment of the present invention, the implementation of the above step 1 may include:

[0064] First, according to the overall configuration of the aircraft fuel tank, it is determined that the assessment tanks participating in the unusable fuel quantity test flight include: the fuel transfer tank, or the fuel transfer tank and the fuel supply tank;

[0065] For example, by observing and evaluating the overall configuration of the aircraft's fuel tank, when there is only one fuel supply tank and the amount of oil is smaller than that of the entire aircraft's fuel tank, the fuel supply tank can be ignored and the fuel transfer tank can be directly evaluated.

[0066] Secondly, if the fuel tank configuration has more than 2-3 fuel tanks, each fuel tank in the fuel system is equipped with a fuel supply pump. The main fuel pump is connected to the test tank to serve as a test tank for the test flight with unavailable fuel volume; the auxiliary fuel pump is connected to another fuel tank to build an auxiliary fuel system, which serves as a safety tank for the test flight with unavailable fuel volume; in the onboard layout, auxiliary fuel supply pipelines are added to connect the test tank and the safety tank to the engine inlet respectively, forming a safety measure for asymmetric fuel tanks.

[0067] Furthermore, if the fuel tank configuration only has two fuel tanks, and the two fuel tanks are of symmetrical configuration, and there is only one fuel supply pump in the fuel system, then one side of the fuel tank will be used as a test tank, and the other side of the fuel tank will be used as a safety tank for unusable fuel volume test flight assessment, forming a safety measure for symmetrical fuel tanks.

[0068] In one implementation of the embodiment of the present invention, the implementation method of the ground test in the above step 2 is:

[0069] If the safety measure of using an asymmetric fuel tank is determined in step 1, the ground test of step 2 includes the following test contents:

[0070] Step 21, conducting a ground test on the auxiliary fuel system;

[0071] If it is determined in step 1 that the aircraft adopts the method of adding an auxiliary fuel system as a safety measure, that is, the safety measure of adopting an asymmetric fuel tank, after the auxiliary fuel system modification is successful, a ground test of the auxiliary fuel system function inspection is to be carried out.

[0072] The specific test method is: add an appropriate amount of fuel to the test tank and the safety tank (for example, add the amount of fuel that can be used for the normal operation of the engine), select the auxiliary fuel pump, and after the engine is started normally through the auxiliary fuel system, warm up the engine according to the engine operating procedure; after the warm-up is completed, switch the main fuel pump to work, and the engine works stably for 1 minute in the small, medium and large states respectively; then, switch the auxiliary fuel pump to work, and the engine works stably for 1 minute in the small, medium and large states respectively; then shut down the engine normally; in the above process, verify the reliability of the auxiliary fuel pump's fuel supply, and verify the engine's ground starting ability under the auxiliary fuel pump's fuel supply conditions.

[0073] Step 22, performing a ground test of the unusable oil volume on the assessment oil tank;

[0074] Add fuel close to the unusable amount of fuel to the test tank, add an appropriate amount of fuel to the safety tank, and set the fuel selector to the test tank position; start the engine normally, and carry out ground work after starting until a feature of engine failure appears for the first time. Then shut down the engine or switch the fuel selector to the safety tank and then shut down the vehicle, drain the oil through the drain valve of the test tank, and record the amount of oil after draining, thereby obtaining the unusable fuel amount of the test tank under ground conditions.

[0075] It should be noted that if the safety measure of adopting a symmetrical fuel tank is determined in step 1, then the ground test in step 2 only includes the test content of step 22 above.

[0076] Furthermore, in this implementation, after the ground test is completed in the above step 2, the following steps may also be performed:

[0077] Step 23, based on the test data of step 22, observe and obtain the parameter change characteristics of the engine and the fuel system during the process of exhaustion of available fuel.

[0078] Step 24, according to the Advisory Circular (AC23-16A), it can be determined that the engine failure caused by the interruption of fuel supply in the fuel system has the following characteristics:

[0079] a) Unstable engine speed;

[0080] b) Engine power decreases;

[0081] c) The fuel pressure drops below the minimum value within the safety range;

[0082] d) Fuel flow fluctuations.

[0083] Through ground tests on different types of engines, it is determined which of the above four characteristics appears first. The corresponding parameters of the characteristics that first cause failure of each type of engine are used as key judgment parameters, and the specific values ​​of the decline and fluctuation of the corresponding parameters of the characteristics are used as safety data.

[0084] In one implementation of the embodiment of the present invention, the method of performing safety risk analysis on the unavailable fuel test flight in the above step 3 includes:

[0085] Risk 1: Based on the aircraft configuration and fuel system configuration, as well as the safety measures determined in step 1, if the fuel selector valve is not switched to the safety tank in time, there will be a risk of engine shutdown in the air due to untimely fuel supply from the safety tank and the auxiliary fuel system.

[0086] Risk 2: According to the analysis of flight meteorological conditions, turbulent weather will cause aircraft fluctuations. The fluctuation of the oil level will give the illusion that the fuel system cannot absorb oil, resulting in the risk of inaccurate test point operation and inaccurate test data during the test.

[0087] In one implementation of the embodiment of the present invention, the method of establishing risk mitigation measures based on the risk analysis conclusion in step 4 includes:

[0088] In this step, formulate corresponding mitigation measures based on the risk analysis conclusions of step 3. In view of the phenomenon of engine stalling in the air, an air start test flight needs to be carried out before the unusable fuel test flight;

[0089] In order to prevent the failure of air start during the actual test flight, an air-slip forced landing simulation test flight is required to be arranged before the air-start test flight. The air-slip forced landing simulation plan is designed according to the air-slip ratio and altitude loss of the test flight, and a simulated air-slip approach and landing test flight is carried out to verify the air-slip forced landing simulation plan, thus completing the air-slip forced landing simulation test flight; subsequently, the engine air-start test flight is carried out.

[0090] In view of the impact of turbulent weather on the operational test points, the test flight without available fuel is required to be conducted in airspace with smooth airflow.

[0091] In an implementation case of the present invention, for a small civil transport aircraft, AC-23-16A provides several recommended test flight subjects:

[0092] a) Stable level flight: The engine is cruising at maximum continuous power (rated power);

[0093] b) Climb: With maximum climb power, the aircraft climbs at a speed corresponding to the best climb angle;

[0094] c) Climbing under single engine failure conditions: When one engine fails, the other engine uses the maximum climb power and the aircraft climbs at the best climb rate;

[0095] d) Glide down to land.

[0096] In actual flight test work, it is necessary to formulate test flight subjects with unusable fuel volume based on the geometric shape of the test fuel tank and the position of the fuel suction port, and select the most unfavorable fuel supply conditions for the current fuel system.

[0097] Example 1: Figure 2 As shown, it is a schematic diagram of the test flight subject of the unusable fuel amount formulated in Example 1 of the present invention. When the oil suction port is located at the lower right side of the fuel tank, the fuel supply state is relatively unfavorable during the gliding state.

[0098] Example 2: Figure 3 As shown, it is a schematic diagram of the test flight subject of the unusable fuel quantity formulated in Example 2 of the present invention. When the oil suction port is located at the lower left of the fuel tank, the fuel supply state is relatively unfavorable during the climbing state.

[0099] In one implementation of the embodiment of the present invention, the flight test is performed in step 6 as follows:

[0100] Carry out the test flight according to the test flight subjects selected in step 5. In the test flight of this step, at least one of the following test flight subjects is selected for test flight, and the test flight method of each test flight subject is as follows:

[0101] Stable level flight: add the unusable fuel value obtained close to the ground to the test tank, add as much fuel as possible to the safety tank, place the aircraft fuel selector on the test tank, use the engine at maximum cruise power, and perform stable level flight until the engine speed drops, the fuel flow drops, the fuel supply pressure drops, or the engine shakes. Then switch the fuel selector to the safety tank, descend normally, and measure the unusable fuel in the test tank after landing.

[0102] Climb: Add the unusable fuel value obtained close to the ground to the test tank, add as much fuel as possible to the safety tank, place the aircraft fuel selector in the test tank, take off normally, and climb continuously at the speed under the best climb angle after takeoff until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc., quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel amount in the test tank after landing;

[0103] Descending: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to the unusable fuel, the aircraft descends at the maximum allowable speed until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc., then quickly switch the fuel selector to the safety tank, level the aircraft, and descend normally. After landing, measure the unusable fuel amount in the test tank.

[0104] Coordinated sideslip: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, the aircraft will perform coordinated sideslip flight until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine jitter, etc., quickly switch the fuel selector to the safety tank, level the aircraft, and descend normally. After landing, measure the unusable fuel amount in the test tank.

[0105] Right-side sliding turn: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, keep the wings level and fly a right-side sliding turn until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc. Quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel in the test tank after landing.

[0106] Slip with limit slope: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, the aircraft is in left rudder state with full rudder, and the right wing sinks 5°~7° until one of the following phenomena occurs: engine speed drops, fuel flow drops, fuel supply pressure drops, or engine shakes. Quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel in the test tank after landing.

[0107] In one implementation of the embodiment of the present invention, the specific implementation of the above step 7 includes:

[0108] According to the unusable fuel volume measured after the flight test in step 6, the maximum value of the unusable fuel volume measured after the flight test of each flight test subject is selected as the unusable fuel volume value of the aircraft.

[0109] The embodiment of the present invention provides a method for testing the unusable fuel quantity of a civil propeller single-engine aircraft. The method comprises the following steps: determining safety measures for the unusable fuel quantity test flight of the single-engine aircraft; conducting a ground test of the unusable fuel quantity based on the safety measures, capturing key discrimination parameters in the ground test, and obtaining safety data; conducting a safety risk analysis on the unusable fuel quantity test flight, and establishing corresponding risk mitigation measures for the risk analysis conclusions; formulating test flight subjects for the unusable fuel quantity according to the geometric shape of the assessment fuel tank and the position of the fuel suction port; conducting a test flight for the unusable fuel quantity based on the formulated test flight subjects, and conducting a test flight for only one test flight subject in each test flight; measuring the unusable fuel quantity of the aircraft assessment fuel tank after each test flight, and obtaining the most unfavorable fuel quantity during the test flight according to the unusable fuel quantity of each test flight subject.

[0110] The technical solution provided by the embodiment of the present invention establishes a method for testing the unusable fuel quantity of civil propeller aircraft. It is the first time in China to concretize and detail the method for testing the unusable fuel quantity of civil propeller aircraft, fill the shortcomings of missing design simulations, reduce the number of test flights, reduce the risk of test flights, and improve the efficiency of test flights. The test flight method of the invention can be applied to the airworthiness certification test flights of small civil aircraft applicable to 23 parts such as civil practical and normal types, and has important guiding significance for the reasonable avoidance of the risk of unusable fuel test flights of small civil aircraft in my country and the promotion of test flight work.

[0111] Although the embodiments disclosed in the present invention are as above, the contents are only embodiments adopted to facilitate understanding of the present invention and are not intended to limit the present invention. Any technician in the field to which the present invention belongs can make any modifications and changes in the form and details of implementation without departing from the spirit and scope disclosed in the present invention, but the patent protection scope of the present invention shall still be subject to the scope defined in the attached claims.

Claims

1. A flight test method for unusable fuel quantity of a civil propeller single-engine aircraft, characterized in that: include: Step 1: Determine the safety measures for single-engine aircraft to conduct test flights without using fuel according to the structural characteristics of the aircraft fuel tank and the fuel supply characteristics of the fuel system; Step 2: Conduct a ground test of the unusable oil volume based on the safety measures determined in step 1, capture key discrimination parameters in the ground test, and obtain safety data; Step 3: Conduct a safety risk analysis on the unusable fuel test flight, including the risk of engine shutdown in mid-air, inaccurate test operation nodes, and inaccurate test data; Step 4: Establish corresponding risk mitigation measures based on the risk analysis conclusions obtained in step 3; Step 5, formulate the test flight subjects with unusable fuel quantity according to the geometric shape and fuel inlet position of the assessment fuel tank; Step 6, based on the test flight subjects determined in step 5, conduct a test flight with unusable fuel, and conduct only one test flight subject in each test flight; wherein the test flight subjects include at least one of the following subjects: stable level flight, climb, descent and sideslip, and the sideslip includes coordinated sideslip, right side sliding turn, and sideslip with slope limit; Step 7: After each test flight, measure the unusable fuel volume of the aircraft test tank, and obtain the most unfavorable fuel volume during the test flight based on the unusable fuel volume of each test flight subject.

2. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 1, characterized in that: The step 1 comprises: Step 11, according to the overall configuration of the aircraft fuel tank, determine that the assessment fuel tanks participating in the unusable fuel quantity test flight include: a fuel transfer tank, or a fuel transfer tank and a fuel supply tank; Step 12, for the asymmetric fuel tank, connect the main fuel pump to the test fuel tank to use it as the test fuel tank for the unavailable fuel test flight; connect the auxiliary fuel pump to another fuel tank to build an auxiliary fuel system as a safety fuel tank for the unavailable fuel test flight, and add auxiliary fuel supply pipelines to connect the test fuel tank and the safety fuel tank to the engine inlet end respectively, forming a safety measure for the asymmetric fuel tank; Step 13, for the symmetrically configured fuel tanks, one side of the fuel tank is used as a test tank, and the other side of the fuel tank is used as a safety tank to conduct an unusable fuel volume test flight test, thereby forming a safety measure for the symmetrical fuel tanks.

3. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 2, characterized in that: For the safety measures of the symmetrical oil tank determined in step 1, step 2 includes: Step 22, performing a ground test of the unusable oil volume on the assessment oil tank; Add fuel close to the unusable amount of fuel to the test tank, add a preset amount of fuel to the safety tank, set the fuel selector to the test tank position, start the engine normally and perform ground work until one of the fault phenomena such as engine speed drop, fuel flow drop, and engine shaking occurs for the first time. After the engine is shut down, obtain the fuel amount value of the test tank as the unusable fuel amount of the test tank in the ground test.

4. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 3, characterized in that: For the safety measures of the asymmetric fuel tank determined in step 1, the step 22 includes: Step 21, performing a ground test on the auxiliary fuel system; Add a preset amount of fuel to the test fuel tank and the safety fuel tank respectively, select the auxiliary fuel pump, and start the engine normally through the auxiliary fuel system and then warm it up; after the warm-up is completed, switch the main fuel pump to work, and the engine will work stably for a preset time in the small, medium and large states respectively; switch the auxiliary fuel pump to work, and the engine will work stably for a preset time in the small, medium and large states respectively, and shut down the engine normally; verify the reliability of the auxiliary fuel pump's fuel supply, and verify the engine's ground starting capability under the auxiliary fuel pump's fuel supply conditions.

5. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 3, characterized in that: After step 22, the method further includes: Step 23, obtaining parameter change characteristics of the engine and the fuel system during the process of exhaustion of available fuel according to the test data of step 22; Step 24, based on multiple characteristics of engine failure caused by interruption of fuel supply in the fuel system, the characteristics that first cause failure of each type of engine are determined through ground tests on different types of engines, and the parameters corresponding to the characteristics are used as key judgment parameters, and the specific values ​​of the decrease and fluctuation of the parameters corresponding to the characteristics are used as safety data.

6. The flight test method for the unusable fuel quantity of a civil propeller single-engine aircraft according to claim 5, characterized in that: The safety analysis in step 3 includes: Risk 1: Through the analysis of the aircraft configuration and fuel system configuration, as well as the safety measures determined in step 1, if the fuel selector valve is not switched to the safety tank in time, there will be a risk of engine shutdown in the air due to the failure to supply fuel to the safety tank and the auxiliary fuel system in time; Risk 2: Through the analysis of flight meteorological conditions, turbulent weather will cause aircraft fluctuations. The fluctuation of the oil level will give the illusion that the fuel system cannot absorb oil, resulting in the risk of inaccurate test points and inaccurate test data during the test.

7. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 6, characterized in that: The risk mitigation measures established in step 4 include: Risk mitigation measures for risk 1 include: Design a taxiing forced landing simulation plan according to the taxiing ratio and altitude loss of the test flight, and conduct a simulated taxiing approach and landing test flight to verify the taxiing forced landing simulation plan; then, perform an engine air start test flight; Risk mitigation measures for Risk 2 include: in view of the impact of turbulent weather on the operational test points, setting the unavailable fuel test flight to be carried out in airspace with smooth airflow.

8. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 5, characterized in that: The method of formulating the flight test subjects in step 5 is: Based on a variety of pre-set flight test subjects, according to the geometric shape of the test fuel tank and the position of the fuel suction port, the most unfavorable fuel supply condition for the current fuel system is selected to formulate the flight test subject with unusable fuel volume.

9. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to claim 8, characterized in that: The method of implementing the flight test for each flight test subject in step 6 includes: Stable level flight: add the unusable fuel value obtained close to the ground to the test tank, add as much fuel as possible to the safety tank, place the aircraft fuel selector on the test tank, use the engine at maximum cruise power, and perform stable level flight until the engine speed drops, the fuel flow drops, the fuel supply pressure drops, or the engine shakes. Then switch the fuel selector to the safety tank, descend normally, and measure the unusable fuel in the test tank after landing. Climb: Add the unusable fuel value obtained close to the ground to the test tank, add as much fuel as possible to the safety tank, place the aircraft fuel selector in the test tank, take off normally, and climb continuously at the speed under the best climb angle after takeoff until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc., quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel amount in the test tank after landing; Descending: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to the unusable fuel, the aircraft descends at the maximum allowable speed until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc., then quickly switch the fuel selector to the safety tank, level the aircraft, and descend normally. After landing, measure the unusable fuel amount in the test tank. The test flight of the sideslip subject includes: Coordinated sideslip: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, the aircraft will perform coordinated sideslip flight until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine jitter, etc., quickly switch the fuel selector to the safety tank, level the aircraft, and descend normally. After landing, measure the unusable fuel amount in the test tank. Right-side sliding turn: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, keep the wings level and fly a right-side sliding turn until one of the following phenomena occurs: engine speed drop, fuel flow drop, fuel supply pressure drop, engine shaking, etc. Quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel in the test tank after landing. Slip with limit slope: Add the unusable fuel value obtained close to the ground to the test tank, and add as much fuel as possible to the safety tank. When the test tank is close to unusable fuel, the aircraft is in left rudder state with full rudder, and the right wing sinks 5°~7° until one of the following phenomena occurs: engine speed drops, fuel flow drops, fuel supply pressure drops, or engine shakes. Quickly switch the fuel selector to the safety tank, level the aircraft, descend normally, and measure the unusable fuel in the test tank after landing.

10. The flight test method for unusable fuel quantity of a civil propeller single-engine aircraft according to any one of claims 1 to 9, characterized in that: The unusable fuel test flight in step 7 includes: According to the unusable fuel volume measured after the flight test in step 6, the maximum value of the unusable fuel volume measured after the flight test of each flight test subject is selected as the unusable fuel volume value of the civil propeller single-engine aircraft.

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