A test flight method for a civilian single-engine propeller aircraft with unusable fuel capacity

Abstract

This invention discloses a flight test method for unusable fuel quantities in a civil propeller-driven single-engine aircraft, comprising: determining safety measures for flight tests with unusable fuel quantities; capturing key discrimination parameters and acquiring safety data during ground tests; conducting safety risk analysis on flight tests with unusable fuel quantities and establishing corresponding risk mitigation measures based on the risk analysis conclusions; formulating flight test subjects for unusable fuel quantities based on the geometry of the test fuel tank and the location of the fuel inlet; conducting flight tests with unusable fuel quantities based on the formulated flight test subjects, with only one flight test subject conducted in each flight test; measuring the unusable fuel quantity in the aircraft's test fuel tank after each flight test, and obtaining the most unfavorable fuel quantity during the flight test based on the unusable fuel quantity of each flight test subject. The technical solution provided by this invention solves the airworthiness certification problem of flight test subjects for unusable fuel quantities in the fuel system of civil propeller-driven single-engine aircraft.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of civil aircraft airworthiness certification test flight technology, and particularly to a test flight method for a civil propeller-driven single-engine aircraft that does not use fuel. Background Technology

[0002] For civil small transport aircraft, Clause 23.959 of the Normal Category Airworthiness Regulations (CCAR-23) requires that the amount of unusable fuel in each fuel tank must be less than the following amount: the amount of fuel in the tank when the engine begins to malfunction under the most unfavorable fuel supply conditions for all scheduled operations and maneuvers that require fuel from the tank, regardless of the failure of fuel system components.

[0003] Because unavailable fuel levels in aircraft fuel systems have a significant impact on civil aviation safety, there is currently no systematic flight test verification for unavailable fuel levels in the fuel systems of civil propeller-driven single-engine aircraft. As a result, the airworthiness certification of unavailable fuel level flight test subjects for this type of aircraft generally suffers from problems such as complex actual operation, unclear operation procedures, and unclear flight test risk mitigation measures. Summary of the Invention

[0004] The purpose of this invention is to solve the above-mentioned technical problems. This invention provides a method for test flights of unavailable fuel quantities for civil propeller-driven single-engine aircraft, in order to solve the airworthiness certification problem of test flights of unavailable fuel quantities in the fuel system of civil propeller-driven single-engine aircraft.

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

[0006] Step 1: Based on the structural characteristics of the aircraft fuel tank and the fuel supply characteristics of the fuel system, determine the safety measures for test flights of single-engine aircraft with unusable fuel quantities.

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

[0008] Step 3: Conduct a safety risk analysis on the test flight with unavailable fuel. The analysis reveals risks including: engine in-flight shutdown, inaccurate test operation points, 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: Based on the geometry of the test fuel tank and the location of the fuel inlet, formulate test flight subjects for unusable fuel volumes;

[0011] Step 6: Based on the test flight subjects established in Step 5, conduct test flights with no available fuel. Only one test flight subject will be conducted in each test flight. The test flight subject includes at least one of the following subjects: stable level flight, climb, glide and sideslip, and the sideslip includes coordinated sideslip, right sidelip turn and extreme sideslip with bank angle.

[0012] Step 7: After each test flight, measure the amount of unusable fuel in the aircraft's test fuel tank, and obtain the most unfavorable fuel level during the test flight based on the amount of unusable fuel for each test flight subject.

[0013] Optionally, in the test flight method for a single-engine civil propeller aircraft with unusable fuel as described above, step 1 includes:

[0014] Step 11: Based on the overall configuration of the aircraft fuel tanks, determine the test fuel tanks that will participate in the unavailable fuel test flight, including: fuel transfer tank, or fuel transfer tank and fuel supply tank.

[0015] Step 12: For the asymmetric fuel tank configuration, the main fuel pump is connected to the test fuel tank to serve as the test fuel tank for flight testing with unavailable fuel. The auxiliary fuel pump is connected to another fuel tank to build an auxiliary fuel system, which serves as the safety fuel tank for flight testing with unavailable fuel. The test fuel tank and the safety fuel tank are connected to the engine inlet end by adding auxiliary fuel supply lines to form a safety measure for the asymmetric fuel tank.

[0016] Step 13: For symmetrical fuel tank configurations, one side of the fuel tank is used as the test fuel tank, and the other side is used as the safety fuel tank for unusable fuel quantity test flights, thus forming a safety measure for symmetrical fuel tanks.

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

[0018] Step 22: Conduct a ground test on the test fuel tank with unusable fuel volume;

[0019] Add fuel close to the unusable amount to the test fuel tank and add the preset amount of fuel to the safety fuel tank. Set the fuel selector to the test fuel tank position. After the engine is started normally, perform ground work until the first fault phenomenon of engine speed drop, fuel flow drop, or engine vibration occurs. After the engine is turned off, obtain the fuel level value of the test fuel tank, which is used as the unusable fuel level of the test fuel tank in the ground test.

[0020] Optionally, in the test flight method for unusable fuel quantities for a single-engine civil propeller aircraft as described above, for the safety measures of the asymmetric fuel tank determined in step 1, the following is included before step 22:

[0021] Step 21: Conduct ground tests on the auxiliary fuel system;

[0022] Preset fuel quantities were added to both the test fuel tank and the safety fuel tank. The auxiliary fuel pump was selected, and the engine was started normally through the auxiliary fuel system. After the engine was warmed up, the main fuel pump was switched on, and the engine was allowed to operate stably for a preset time under low, medium, and high fuel pressure conditions. The auxiliary fuel pump was then switched on, and the engine was allowed to operate stably for a preset time under low, medium, and high fuel pressure conditions. The engine was then shut down normally. The reliability of the auxiliary fuel pump's fuel supply was verified, as well as the engine's ground starting capability under auxiliary fuel pump supply conditions.

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

[0024] Step 23: Based on the test data from Step 22, obtain the parameter change characteristics of the engine and fuel system during the process of exhausting available fuel;

[0025] Step 24: Based on multiple characteristics of engine failure caused by fuel system interruption, ground tests on different types of engines are conducted to identify the characteristics that first cause failure in each type of engine. The parameter corresponding to this characteristic is used as the key discrimination parameter, and the specific values ​​of the decrease and fluctuation of the parameter corresponding to this characteristic are used as safety data.

[0026] Optionally, in the test flight method for a single-engine civil propeller aircraft with unusable fuel quantities as described above, the safety analysis in step 3 includes:

[0027] Risk 1: Based on the analysis of the aircraft configuration and fuel system configuration, as well as the safety measures determined in step 1, if the fuel selection valve does not switch to the safety fuel tank in time, there is a risk of engine in-flight shutdown due to untimely fuel supply from the safety fuel tank and auxiliary fuel system.

[0028] Risk 2: Analysis of flight weather conditions reveals that turbulent weather can cause aircraft fluctuations, and fluctuations in the fuel level can create the illusion that the fuel system cannot draw fuel, leading to inaccurate operation of test points and inaccurate test data during the test.

[0029] Optionally, in the test flight method for unusable fuel quantities for a single-engine civil propeller aircraft as described above, step 4, which establishes risk mitigation measures, includes:

[0030] Risk mitigation measures for Risk 1 include:

[0031] A simulated glide landing approach was designed based on the glide ratio and altitude loss from the test flight, and a simulated glide approach and landing test flight was conducted to verify the glide landing approach simulation scheme; subsequently, an engine in-flight start test flight was performed.

[0032] The risk mitigation measures for risk 2 include: to address the impact of turbulent weather on the operational test site, setting the test flights with unavailable fuel to be conducted in airspace with stable airflow.

[0033] Optionally, in the above-described method for test flights of a single-engine civil propeller aircraft without available fuel, the method for determining the test flight subjects in step 5 is as follows:

[0034] Based on a variety of pre-set test flight subjects, and according to the geometry of the test fuel tank and the location of the fuel inlet, the test flight subjects with unusable fuel quantities are selected under the most unfavorable fuel supply conditions for the current fuel system.

[0035] Optionally, in the flight test method for a single-engine civil propeller aircraft with unusable fuel as described above, the method for conducting flight tests for each flight test item in step 6 includes:

[0036] Stable level flight: The test fuel tank is filled with the unavailable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. The aircraft fuel selector is placed in the test fuel tank, and the engine is at maximum cruise power. The aircraft is in stable level flight until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. At this point, the fuel selector is switched to the safety fuel tank, and the aircraft descends normally. After landing, the unavailable fuel level in the test fuel tank is measured.

[0037] Climb: Add the unavailable fuel level obtained near the ground to the test fuel tank, add as much fuel as possible to the safety fuel tank, place the aircraft fuel selector in the test fuel tank, and take off normally. After takeoff, the aircraft climbs continuously at the speed at the optimal climb angle until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. Quickly switch the fuel selector to the safety fuel tank, level off, and descend normally. After landing, measure the unavailable fuel level in the test fuel tank.

[0038] Descent: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft descends at the maximum permissible speed until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels off, and descends normally. After landing, the unusable fuel level in the test fuel tank is measured.

[0039] The test flights for the sideslip maneuver included:

[0040] Coordinated sideslip: The test fuel tank is filled with unusable fuel obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to unusable fuel, the aircraft performs coordinated sideslip flight until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this time, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels up, and descends normally. After landing, the unusable fuel in the test fuel tank is measured.

[0041] Right-side taxi turn: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft keeps the wings level and flies in a right-side taxi turn until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels up, and descends normally. After landing, the unusable fuel level in the test fuel tank is measured.

[0042] Extreme sideslip with bank angle: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft's left rudder is at full rudder position, and the right wing drops 5° to 7° until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels off, and the descent proceeds normally. After landing, the unusable fuel level in the test fuel tank is measured.

[0043] Optionally, in the flight test method for unusable fuel quantities for a single-engine civil propeller aircraft as described above, step 7 of conducting flight tests with unusable fuel quantities includes:

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

[0045] The beneficial effects of this invention are as follows: This invention provides a method for test flights of unusable fuel quantities for a single-engine propeller aircraft. The method involves determining safety measures for test flights of unusable fuel quantities; conducting ground tests based on these safety measures, capturing key discrimination parameters and obtaining safety data during the ground tests; performing safety risk analysis on unusable fuel quantity test flights, and establishing corresponding risk mitigation measures based on the risk analysis conclusions; formulating test flight subjects for unusable fuel quantities based on the geometry of the test fuel tank and the location of the fuel inlet; conducting test flights of unusable fuel quantities based on the formulated test flight subjects, with only one test flight subject conducted per test flight; measuring the unusable fuel quantity in the aircraft's test fuel tank after each test flight, and obtaining the most unfavorable fuel quantity during the test flight based on the unusable fuel quantity of each test flight subject.

[0046] The technical solution provided by this invention establishes a method for test flights of civil propeller-type aircraft with unusable fuel. For the first time in China, this method concretizes and details the test flight method for civil propeller-type aircraft with unusable fuel, fills the gaps in design simulation, reduces the number of test flights, lowers test flight risks, and improves test flight efficiency. The test flight method of this invention can be applied to the airworthiness certification test flights of small civil aircraft applicable to 23 parts of civil practical and normal categories. It has important guiding significance for the reasonable avoidance of test flight risks with unusable fuel for small civil aircraft in my country and for promoting test flight work. Attached Figure Description

[0047] The accompanying drawings are provided to further understand the technical solutions of the present invention and constitute a part of the specification. They are used together with the embodiments of this application to explain the technical solutions of the present invention and do not constitute a limitation on the technical solutions of the present invention.

[0048] Figure 1 A flowchart illustrating a test flight method for a single-engine, civil propeller aircraft with unusable fuel quantities, provided as an embodiment of the present invention;

[0049] Figure 2 This is a schematic diagram of the flight test subjects with unavailable fuel quantities as specified in Example 1 of this invention;

[0050] Figure 3 This is a schematic diagram of a test flight course with unavailable fuel volume as specified in Example 2 of this invention. Detailed Implementation

[0051] To make the objectives, technical solutions, and advantages of the present invention clearer, the embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be noted that, unless otherwise specified, the embodiments and features described in this application can be arbitrarily combined with each other.

[0052] As explained in the background section, flight testing with unavailable fuel levels in an aircraft's fuel system has a significant impact on the safety of civil aircraft. However, there is currently no systematic flight test verification for unavailable fuel levels in the fuel systems of single-engine propeller aircraft. This leads to common problems in the airworthiness certification of this type of aircraft, such as complex actual operations, unclear operating procedures, and unclear risk mitigation measures.

[0053] To address the aforementioned issues, this invention provides a flight test method for unavailable fuel quantities in a civil propeller-driven single-engine aircraft. Specifically, this method is an airworthiness verification method for unavailable fuel quantities in the fuel system of a civil propeller-driven single-engine aircraft.

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

[0055] Figure 1 This is a flowchart illustrating a flight test method for a single-engine, civil propeller aircraft with unusable fuel quantities, provided by an embodiment of the present invention. The flight test method for a single-engine, civil propeller aircraft with unusable fuel quantities, provided by an embodiment of the present invention, includes the following steps:

[0056] Step 1: Based on the structural characteristics of the aircraft fuel tank and the fuel supply characteristics of the fuel system, determine the safety measures for test flights of single-engine aircraft with unusable fuel quantities.

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

[0058] Step 3: Conduct a safety risk analysis on the test flight with unavailable fuel. The analysis reveals risks including: engine in-flight shutdown, inaccurate test operation points, 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: Based on the geometry of the test fuel tank and the location of the fuel inlet, formulate test flight subjects for unusable fuel volumes;

[0061] Step 6: Based on the test flight subjects established in Step 5, conduct test flights with no available fuel. Only one test flight subject will be conducted in each test flight. The test flight subject includes at least one of the following subjects: stable level flight, climb, sideslip and glide, and the sideslip includes coordinated sideslip, right-side turn, and extreme sideslip with bank angle.

[0062] Step 7: After each test flight, measure the amount of unusable fuel in the aircraft's test fuel tank, and obtain the most unfavorable fuel level during the test flight based on the amount of unusable fuel for each test flight subject.

[0063] In one implementation of this invention, step 1 may include:

[0064] First, based on the overall configuration of the aircraft fuel tanks, the test fuel tanks for unavailable fuel quantity flight tests are determined to include: fuel transfer tanks, or fuel transfer tanks and fuel supply tanks.

[0065] For example, by observing and evaluating the overall configuration of the aircraft's fuel tanks, if there is only one fuel supply tank and the amount of fuel is relatively small compared to the total fuel tank capacity, the fuel supply tank can be ignored, and the fuel delivery tank can be evaluated directly.

[0066] Secondly, if the fuel tank configuration has 2-3 or more 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 fuel tank, which serves as the test fuel tank for flight testing when the fuel quantity is unavailable. The auxiliary fuel pump is connected to another fuel tank to form an auxiliary fuel system, which serves as the safety fuel tank for flight testing when the fuel quantity is unavailable. In the aircraft layout, auxiliary fuel supply lines are added to connect the test fuel tank and the safety fuel tank to the engine inlet, forming a safety measure for asymmetric fuel tanks.

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

[0068] In one implementation of this invention, the ground test in step 2 is carried out as follows:

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

[0070] Step 21: Conduct ground tests on the auxiliary fuel system;

[0071] If step 1 determines that the aircraft will use an auxiliary fuel system as a safety measure, i.e., an asymmetric fuel tank system, then a ground test to check the auxiliary fuel system's functionality must be conducted after the auxiliary fuel system modification is successful.

[0072] The specific test method is as follows: Add an appropriate amount of fuel (e.g., enough fuel for normal engine operation) to both the test fuel tank and the safety fuel tank. Select the auxiliary fuel pump and, after the engine starts normally through the auxiliary fuel system, warm it up according to the engine operating procedure. After warming up, switch to the main fuel pump, and the engine runs stably for 1 minute each at low, medium, and high speeds. Then, switch to the auxiliary fuel pump, and the engine runs stably for 1 minute each at low, medium, and high speeds. Finally, shut down the engine normally. During the above process, verify the reliability of the auxiliary fuel pump's fuel supply and the engine's ground starting capability under auxiliary fuel pump supply conditions.

[0073] Step 22: Conduct a ground test on the test fuel tank with unusable fuel volume;

[0074] Add fuel close to the unusable level to the test fuel tank and an appropriate amount to the safety fuel tank. Set the fuel selector to the test fuel tank position. Start the engine normally and perform ground work until the first sign of engine failure appears. Then, shut off the engine or switch the fuel selector to the safety fuel tank and shut off the engine. Drain the fuel through the drain valve of the test fuel tank and record the amount of fuel drained. This will give you the amount of unusable fuel in the test fuel tank under ground conditions.

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

[0076] Furthermore, after completing the ground test in step 2 above, this implementation method can also perform the following steps:

[0077] Step 23: Based on the test data from Step 22, observe and obtain the parameter changes of the engine and fuel system during the process of exhausting available fuel.

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

[0079] a) Engine speed is unstable;

[0080] b) Engine power decreases;

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

[0082] d) Fluctuations in fuel flow rate.

[0083] By conducting ground tests on different types of engines, it is determined which of the above four characteristics appears first. The parameter corresponding to the characteristic that first causes failure in each type of engine is used as the key discrimination parameter, and the specific value of the decrease and fluctuation of the parameter corresponding to the characteristic is used as safety data.

[0084] In one implementation of this invention, step 3 above, which involves conducting a safety risk analysis on test flights with unavailable fuel, includes the following methods:

[0085] Risk 1: Depending on the aircraft configuration and fuel system configuration, as well as the safety measures determined in step 1, if the fuel selection valve does not switch to the safety fuel tank in time, there is a risk of engine in-flight shutdown due to untimely fuel supply from the safety fuel tank and auxiliary fuel system.

[0086] Risk 2: Based on the analysis of flight meteorological conditions, turbulent weather can cause aircraft fluctuations, and fluctuations in the fuel level can create the illusion that the fuel system cannot draw fuel, resulting in the risk of inaccurate operation of test points and inaccurate test data during the test.

[0087] In one implementation of this invention, step 4 above, which involves establishing risk mitigation measures based on the risk analysis conclusions, includes the following methods:

[0088] Based on the risk analysis conclusions in Step 3, this step involves formulating corresponding mitigation measures. For the issue of engine in-flight shutdown, an in-flight restart test flight must be conducted before a test flight with unavailable fuel.

[0089] To prevent in-flight start failure during actual test flights, a simulated glide landing test flight must be arranged before the in-flight start test flight. The glide landing simulation scheme is designed according to the glide ratio and altitude loss of the test flight, and a simulated glide approach and landing test flight is conducted to verify the glide landing simulation scheme, thus completing the glide landing simulation test flight. Subsequently, the engine in-flight start test flight is carried out.

[0090] To address the impact of turbulent weather on operational test sites, test flights must be conducted in airspace with stable airflow when fuel is unavailable.

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

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

[0093] b) Climb: The aircraft climbs at the speed corresponding to the optimal climb angle with maximum climb power;

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

[0095] d) Glide landing.

[0096] In actual test flights, it is necessary to select the most unfavorable fuel supply conditions for the current fuel system and formulate test flight subjects with unusable fuel quantities based on the geometry of the test fuel tank and the location of the fuel inlet.

[0097] Example 1: such as Figure 2 The diagram shown is a schematic of a test flight subject with unusable fuel volume as specified in Example 1 of this invention. When the fuel inlet is located at the lower right of the fuel tank, the fuel supply is less favorable during the descent.

[0098] Example 2: such as Figure 3 The diagram shown is a schematic of a test flight subject with unusable fuel volume as specified in Example 2 of this invention. When the fuel inlet is located at the lower left of the fuel tank, the fuel supply is less favorable during the climb.

[0099] In one implementation of this invention, step 6 of the above-mentioned test flight is performed as follows:

[0100] Conduct test flights according to the test flight subjects selected in step 5. In this step, select at least one of the following test flight subjects for test flight, and the test flight methods for each subject are as follows:

[0101] Stable level flight: The test fuel tank is filled with the unavailable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. The aircraft fuel selector is placed in the test fuel tank, and the engine is at maximum cruise power. The aircraft is in stable level flight until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. At this point, the fuel selector is switched to the safety fuel tank, and the aircraft descends normally. After landing, the unavailable fuel level in the test fuel tank is measured.

[0102] Climb: Add the unavailable fuel level obtained near the ground to the test fuel tank, add as much fuel as possible to the safety fuel tank, place the aircraft fuel selector in the test fuel tank, and take off normally. After takeoff, the aircraft climbs continuously at the speed at the optimal climb angle until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. Quickly switch the fuel selector to the safety fuel tank, level off, and descend normally. After landing, measure the unavailable fuel level in the test fuel tank.

[0103] Descent: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft descends at the maximum permissible speed until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels off, and descends normally. After landing, the unusable fuel level in the test fuel tank is measured.

[0104] Coordinated sideslip: The test fuel tank is filled with unusable fuel obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to unusable fuel, the aircraft performs coordinated sideslip flight until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this time, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels up, and descends normally. After landing, the unusable fuel in the test fuel tank is measured.

[0105] Right-side taxi turn: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft keeps the wings level and flies in a right-side taxi turn until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels up, and descends normally. After landing, the unusable fuel level in the test fuel tank is measured.

[0106] Extreme sideslip with bank angle: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft's left rudder is at full rudder position, and the right wing drops 5° to 7° until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels off, and the descent proceeds normally. After landing, the unusable fuel level in the test fuel tank is measured.

[0107] In one implementation of this invention, step 7 is specifically implemented as follows:

[0108] Based on the unavailable fuel quantity measured after the flight test in step 6, the maximum unavailable fuel quantity measured after the completion of each flight test subject is selected as the unavailable fuel quantity value of the aircraft.

[0109] The method for test flights of unusable fuel quantity for single-engine propeller aircraft provided in this invention involves: determining safety measures for test flights of unusable fuel quantity; conducting ground tests of unusable fuel quantity based on safety measures, capturing key discrimination parameters and obtaining safety data during ground tests; performing safety risk analysis on unusable fuel quantity test flights and establishing corresponding risk mitigation measures based on the risk analysis conclusions; formulating test flight subjects for unusable fuel quantity based on the geometry of the test fuel tank and the location of the fuel inlet; conducting test flights of unusable fuel quantity based on the formulated test flight subjects, with only one test flight subject conducted in each test flight; measuring the unusable fuel quantity in the aircraft's test fuel tank after each test flight, and obtaining the most unfavorable fuel quantity during the test flight based on the unusable fuel quantity of each test flight subject.

[0110] The technical solution provided by this invention establishes a method for test flights of civil propeller-type aircraft with unusable fuel. For the first time in China, this method concretizes and details the test flight method for civil propeller-type aircraft with unusable fuel, fills the gaps in design simulation, reduces the number of test flights, lowers test flight risks, and improves test flight efficiency. The test flight method of this invention can be applied to the airworthiness certification test flights of small civil aircraft applicable to 23 parts of civil practical and normal categories. It has important guiding significance for the reasonable avoidance of test flight risks with unusable fuel for small civil aircraft in my country and for promoting test flight work.

[0111] While the embodiments disclosed in this invention are as described above, they are merely illustrative of the embodiments to facilitate understanding of the invention and are not intended to limit the invention. Any person skilled in the art to which this invention pertains may make any modifications and variations in the form and details of the implementation without departing from the spirit and scope disclosed herein; however, the scope of patent protection for this invention shall still be determined by the scope defined in the appended claims.

Claims

1. A test flight method for a single-engine, civil propeller-driven aircraft without using a certain amount of fuel, characterized in that, include: Step 1: Based on the structural characteristics of the aircraft fuel tank and the fuel supply characteristics of the fuel system, determine the safety measures for test flights of single-engine aircraft with unusable fuel quantities. Step 2: Conduct a ground test on unusable oil volume based on the safety measures determined in Step 1, capture key discrimination parameters and obtain safety data during the ground test; Step 3: Conduct a safety risk analysis on the test flight with unavailable fuel. The analysis reveals risks including: engine in-flight shutdown, inaccurate test operation points, and inaccurate test data. Step 4: Establish corresponding risk mitigation measures based on the risk analysis conclusions obtained in Step 3; Step 5: Based on the geometry of the test fuel tank and the location of the fuel inlet, formulate test flight subjects for unusable fuel volumes; Step 6: Based on the test flight subjects established in Step 5, conduct test flights with no available fuel. Only one test flight subject will be conducted in each test flight. The test flight subject includes at least one of the following subjects: stable level flight, climb, glide and sideslip, and the sideslip includes coordinated sideslip, right sidelip turn and extreme sideslip with bank angle. Step 7: After each test flight, measure the amount of unusable fuel in the aircraft's test fuel tank, and obtain the most unfavorable fuel level during the test flight based on the amount of unusable fuel for each test flight subject.

2. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 1, characterized in that, Step 1 includes: Step 11: Based on the overall configuration of the aircraft fuel tanks, determine the test fuel tanks that will participate in the unavailable fuel test flight, including: fuel transfer tank, or fuel transfer tank and fuel supply tank. Step 12: For the asymmetric fuel tank configuration, the main fuel pump is connected to the test fuel tank to serve as the test fuel tank for flight testing with unavailable fuel. The auxiliary fuel pump is connected to another fuel tank to build an auxiliary fuel system, which serves as the safety fuel tank for flight testing with unavailable fuel. The test fuel tank and the safety fuel tank are connected to the engine inlet end by adding auxiliary fuel supply lines to form a safety measure for the asymmetric fuel tank. Step 13: For symmetrical fuel tank configurations, one side of the fuel tank is used as the test fuel tank, and the other side is used as the safety fuel tank for unusable fuel quantity test flights, thus forming a safety measure for symmetrical fuel tanks.

3. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 2, characterized in that, Regarding the safety measures for the symmetrical fuel tanks determined in step 1, step 2 includes: Step 22: Conduct a ground test on the test fuel tank with unusable fuel volume; Add fuel close to the unusable amount to the test fuel tank and add the preset amount of fuel to the safety fuel tank. Set the fuel selector to the test fuel tank position. After the engine is started normally, perform ground work until the first fault phenomenon of engine speed drop, fuel flow drop, or engine vibration occurs. After the engine is turned off, obtain the fuel level value of the test fuel tank, which is used as the unusable fuel level of the test fuel tank in the ground test.

4. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 3, characterized in that, For the safety measures for the asymmetric fuel tank determined in step 1, the steps preceding step 22 include: Step 21: Conduct ground tests on the auxiliary fuel system; Preset fuel quantities were added to both the test fuel tank and the safety fuel tank. The auxiliary fuel pump was selected, and the engine was started normally through the auxiliary fuel system. After the engine was warmed up, the main fuel pump was switched on, and the engine was allowed to operate stably for a preset time under low, medium, and high fuel pressure conditions. The auxiliary fuel pump was then switched on, and the engine was allowed to operate stably for a preset time under low, medium, and high fuel pressure conditions. The engine was then shut down normally. The reliability of the auxiliary fuel pump's fuel supply was verified, as well as the engine's ground starting capability under auxiliary fuel pump supply conditions.

5. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 3, characterized in that, After step 22, the method further includes: Step 23: Based on the test data from Step 22, obtain the parameter change characteristics of the engine and fuel system during the process of exhausting available fuel; Step 24: Based on multiple characteristics of engine failure caused by fuel system interruption, ground tests on different types of engines are conducted to identify the characteristics that first cause failure in each type of engine. The parameter corresponding to this characteristic is used as the key discrimination parameter, and the specific values ​​of the decrease and fluctuation of the parameter corresponding to this characteristic are used as safety data.

6. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 5, characterized in that, The security analysis in step 3 includes: Risk 1: Based on the analysis of the aircraft configuration and fuel system configuration, as well as the safety measures determined in step 1, if the fuel selection valve does not switch to the safety fuel tank in time, there is a risk of engine in-flight shutdown due to untimely fuel supply from the safety fuel tank and auxiliary fuel system. Risk 2: Analysis of flight weather conditions reveals that turbulent weather can cause aircraft fluctuations, and fluctuations in the fuel level can create the illusion that the fuel system cannot draw fuel, leading to inaccurate operation of test points and inaccurate test data during the test.

7. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 6, characterized in that, Step 4 involves establishing risk mitigation measures, including: Risk mitigation measures for Risk 1 include: A simulated glide landing approach was designed based on the glide ratio and altitude loss from the test flight, and a simulated glide approach and landing test flight was conducted to verify the glide landing approach simulation scheme; subsequently, an engine in-flight start test flight was performed. The risk mitigation measures for risk 2 include: to address the impact of turbulent weather on the operational test site, setting the test flights with unavailable fuel to be conducted in airspace with stable airflow.

8. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 5, characterized in that, The method for determining the test flight subjects in step 5 is as follows: Based on a variety of pre-set test flight subjects, and according to the geometry of the test fuel tank and the location of the fuel inlet, the test flight subjects with unusable fuel quantities are selected under the most unfavorable fuel supply conditions for the current fuel system.

9. The test flight method for a single-engine civil propeller aircraft with unusable fuel capacity according to claim 8, characterized in that, The methods for conducting test flights for each test flight subject in step 6 include: Stable level flight: The test fuel tank is filled with the unavailable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. The aircraft fuel selector is placed in the test fuel tank, and the engine is at maximum cruise power. The aircraft is in stable level flight until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. At this point, the fuel selector is switched to the safety fuel tank, and the aircraft descends normally. After landing, the unavailable fuel level in the test fuel tank is measured. Climb: Add the unavailable fuel level obtained near the ground to the test fuel tank, add as much fuel as possible to the safety fuel tank, place the aircraft fuel selector in the test fuel tank, and take off normally. After takeoff, the aircraft climbs continuously at the speed at the optimal climb angle until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. Quickly switch the fuel selector to the safety fuel tank, level off, and descend normally. After landing, measure the unavailable fuel level in the test fuel tank. Descent: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft descends at the maximum permissible speed until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels off, and descends normally. After landing, the unusable fuel level in the test fuel tank is measured. The test flights for the sideslip maneuver included: Coordinated sideslip: The test fuel tank is filled with unusable fuel obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to unusable fuel, the aircraft performs coordinated sideslip flight until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this time, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels up, and descends normally. After landing, the unusable fuel in the test fuel tank is measured. Right-side taxi turn: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft keeps the wings level and flies in a right-side taxi turn until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, engine vibration, etc. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels up, and descends normally. After landing, the unusable fuel level in the test fuel tank is measured. Extreme sideslip with bank angle: The test fuel tank is filled with the unusable fuel level obtained near the ground, and the safety fuel tank is filled with as much fuel as possible. When the test fuel tank is close to the unusable fuel level, the aircraft's left rudder is at full rudder position, and the right wing drops 5° to 7° until one of the following phenomena occurs: engine speed decreases, fuel flow decreases, fuel supply pressure decreases, or engine vibration occurs. At this point, the fuel selector is quickly switched to the safety fuel tank, the aircraft levels off, and the descent proceeds normally. After landing, the unusable fuel level in the test fuel tank is measured.

10. The test flight method for a single-engine civil propeller aircraft with unusable fuel quantity according to any one of claims 1 to 9, characterized in that, Step 7, which involves conducting test flights with unavailable fuel, includes: Based on the unusable fuel quantity measured after the flight test in step 6, the maximum unusable fuel quantity measured after the completion of each flight test subject is selected as the unusable fuel quantity value of the civil propeller single-engine aircraft.

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