Method for determining longitudinal motion stability of water surface aircraft taking off and landing on wave water surface

Abstract

The embodiment of the application discloses a method for determining longitudinal motion stability of a water surface aircraft in wave water surface taking-off and landing, comprising: carrying out model test based on determined test parameters, collecting trim angle time history data, and recording motion state of a scaled model in the model test process, drawing a response curve by using the filtered trim angle time history data, and analyzing the form of the trim angle response curve to obtain a trim angle fluctuation amplitude, a fluctuation period and a fluctuation angular rate, compiling a motion stability statistical table in combination with the motion stability determined by shooting, and finally drawing a two-parameter motion stability determination criterion graph capable of reflecting a motion stability region of the water surface aircraft in the wave water surface taking-off and landing process. The technical scheme provided by the embodiment of the application solves the problem that the existing longitudinal motion stability analysis method and determination criterion of the water surface aircraft in the still water surface are difficult to be applied to the determination of the longitudinal motion stability of the water surface aircraft in the wave water surface.

Description

Technical Field

[0001] This invention relates to, but is not limited to, the field of aircraft on water... and particularly to a method for determining the longitudinal motion stability of a waterborne aircraft taking off and landing on a wave-like surface. Background Technology

[0002] The motion stability of a water-based aircraft during its movement on the water surface is an important indicator for evaluating its performance.

[0003] The conventional method for determining the motion stability of a surface aircraft during still water movement is as follows: Model tests are conducted to verify whether the aircraft's pitch angle changes smoothly during constant speed motion. If the pitch angle fluctuates by more than 2°, the state is considered unstable; if the fluctuation is less than or equal to 2°, the state is considered stable. The longitudinal control surfaces of the test model are adjusted to change the taxiing pitch angle until the model exhibits unstable motion. This determines the upper and lower stability boundaries of the aircraft at that speed. Repeating the above steps at different test speeds yields the complete range of stability boundaries for the aircraft.

[0004] However, when a surface-to-water aircraft takes off and lands on wavy water, its pitch angle always fluctuates within a certain amplitude and period due to the interference of the waves. The magnitude and period of this fluctuation are influenced by many factors such as wave height, wavelength, speed, and aircraft configuration. Existing methods and criteria for analyzing the longitudinal motion stability of surface-to-water aircraft in still water are no longer applicable, and publicly available information does not describe methods and criteria for determining the longitudinal motion stability of surface-to-water aircraft during takeoff and landing on wavy water. Summary of the Invention

[0005] The purpose of this invention is to provide a method for determining the longitudinal motion stability of a surface vehicle taking off and landing on wavy water, thereby solving the problem that existing methods and criteria for analyzing and determining the longitudinal motion stability of surface vehicles in still water are difficult to apply to determining the longitudinal motion stability of surface vehicles on wavy water.

[0006] The technical solution of the present invention: The embodiments of the present invention provide a method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water, comprising:

[0007] Step 1: Determine the model test parameters for conducting regular wave towing tests on scaled-down model water tanks of water surface aircraft;

[0008] Step 2: Based on the model test parameters confirmed in Step 1, conduct a regular wave towing test of the scaled-down model of the water surface aircraft in a water tank, and collect pitch angle time history data during the model test, and photograph the motion state of the scaled-down model during the model test.

[0009] Step 3: Filter the pitch angle time history data obtained from the model test in Step 2;

[0010] Step 4: Select the pitch angle time history data within the filtered uniform velocity segment, plot the pitch angle response curve with time as the horizontal axis and the pitch angle of the experimental scaled-down model as the vertical axis, and analyze the shape, pitch angle fluctuation amplitude, and fluctuation period of the pitch angle response curve.

[0011] Step 5: Calculate the pitch angle fluctuation rate using the pitch angle fluctuation amplitude and fluctuation period from Step 4;

[0012] Step 6: Determine the motion stability based on the motion state of the scaled-down model;

[0013] Step 7: Based on different test conditions, and combined with the amplitude of pitch angle fluctuation, fluctuation period, fluctuation angular rate, and motion stability judgment results, compile a motion stability statistical table for the scaled-down test model.

[0014] Step 8: Based on the motion stability statistics table obtained in Step 7, draw a two-parameter motion stability judgment criterion diagram. The pitch angle fluctuation amplitude criterion and pitch angle fluctuation angular rate criterion obtained from the two-parameter motion stability judgment criterion diagram are used to reflect the motion stability region of the water surface aircraft during take-off and landing on the wave surface.

[0015] Optionally, in the method for determining the longitudinal motion stability of a water surface vehicle taking off and landing on wavy water as described above, the model test parameters to be determined and their confirmation methods before conducting the model test in step 1 include:

[0016] Step 11, the method for determining the wave height h in the model test is as follows:

[0017]

[0018] Where H is the meaningful wave height of the sea waves corresponding to the takeoff and landing of the actual aircraft, and λ is the scale value of the scaled model, that is, the size ratio between the actual aircraft and the scaled model.

[0019] Step 12, the method for determining the wavelength of the model test is as follows: select no less than 4 wavelengths with approximately equal intervals between the minimum wavelength and the maximum wavelength; wherein, the minimum wavelength is less than 1 times the length of the test model hull, and the maximum wavelength is greater than 4 times the length of the test model hull;

[0020] Step 13, the method for determining the model test speed is as follows: between 0 and the takeoff speed of the test model from the water, select no less than 5 test speeds at approximately equal intervals.

[0021] Optionally, in the method for determining the longitudinal motion stability of a water surface vehicle taking off and landing on wavy water as described above, the model test process in step 2 includes:

[0022] In the towed pool, the scaled-down test model is made to move at a constant speed in regular waves of the selected wave height and wavelength at each selected test speed. The time history data of the pitch angle of the scaled-down test model during the constant speed motion is collected, and the motion state of the scaled-down test model is recorded using a high-definition camera.

[0023] Optionally, in the method for determining the longitudinal motion stability of a water surface vehicle taking off and landing on wavy water, as described above,

[0024] The high-definition camera is mounted on the side of the scaled-down test model on the trailer. The position of the high-definition camera is at the same front-to-back and vertical position as the center of gravity of the scaled-down test model.

[0025] Optionally, in the method for determining the longitudinal motion stability of a water surface vehicle taking off and landing on wavy water, as described above,

[0026] The filtering frequency in step 3 is 9.5 times the encounter frequency of the scaled-down experimental model.

[0027] Optionally, in the method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water, as described above, the method for analyzing the response curve in step 4 includes:

[0028] For pitch angle response curves in highly regular, relatively regular, or irregular states, different analysis strategies are used to derive the pitch angle fluctuation amplitude and fluctuation period.

[0029] Optionally, in the method for determining the longitudinal motion stability of a water surface vehicle taking off and landing on wavy water as described above, step 5 calculates the pitch angle fluctuation rate by dividing twice the pitch angle fluctuation amplitude α by the pitch angle fluctuation period T, expressed by the formula:

[0030]

[0031] Optionally, in the method for determining the longitudinal motion stability of a water surface aircraft taking off and landing on wavy water as described above, the method for determining motion stability in step 6 is as follows:

[0032] Based on the video analysis of the motion state of the scaled-down experimental model, the following judgment criteria were established:

[0033] The stability of motion is determined for the scaled-down experimental model that is always moving in water.

[0034] For the experimental scaled-up model to briefly jump off the water surface, and for the experimental scaled-up model to maintain a basically stable longitudinal axis during the jump off the water surface, the state determination position motion stability is achieved.

[0035] If a scaled-down experimental model jumps off the water surface and exhibits a jumping wave phenomenon, or if the longitudinal axis of the scaled-down experimental model fluctuates significantly during the jumping process, it is considered to be in an unstable state.

[0036] Optionally, in the method for determining the longitudinal motion stability of a water surface aircraft taking off and landing on wavy water as described above, step 8 includes:

[0037] Step 81: Plot a scatter plot with the pitch angle fluctuation amplitude as the abscissa and the pitch angle fluctuation angular rate as the ordinate;

[0038] Step 82: Determine the minimum fluctuation amplitude and minimum angular rate corresponding to the state points of all unstable motions. Draw two straight lines parallel to the horizontal and vertical coordinate axes through these points. The pitch angle fluctuation amplitude and fluctuation angular rate corresponding to these two straight lines are the pitch angle fluctuation amplitude criterion and the pitch angle fluctuation angular rate criterion, respectively.

[0039] The regions enclosed by the two straight lines and the horizontal and vertical coordinate axes are considered stable regions, while regions outside the stable regions are considered unstable regions.

[0040] The beneficial effects of this invention are as follows: This invention provides a method for determining the longitudinal motion stability of a surface vehicle taking off and landing on wavy water. Specifically, it analyzes the longitudinal motion stability of a surface vehicle during takeoff and landing on wavy water based on a "two-parameter determination criterion." Since different configurations of surface vehicles take off and land in waves of different heights, the values ​​of the "two-parameter determination criterion" (the two parameters include: pitch angle fluctuation amplitude and pitch angle fluctuation rate) are usually different. This invention provides a "two-parameter determination criterion" with pitch angle fluctuation amplitude and pitch angle fluctuation rate as input variables. In the determination process, a model test is first conducted based on the determined test parameters. Pitch angle time history data is collected, and the motion state of the scaled-down model during the model test is recorded. The response curve is plotted using the filtered pitch angle time history data, and the shape of the pitch angle response curve is analyzed to obtain the pitch angle fluctuation amplitude, fluctuation period, and fluctuation angular rate. Combined with the motion stability determined by the photographs, a motion stability statistical table is compiled. Finally, a two-parameter motion stability determination criterion diagram that can reflect the motion stability region of the surface vehicle during takeoff and landing on wavy water is drawn. The technical solution provided by the embodiments of the present invention can obtain a relatively accurate criterion for judging the longitudinal motion stability of a surface aircraft when it moves on a wave of a certain wave height. Attached Figure Description

[0041] 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.

[0042] Figure 1A schematic diagram showing the pitch angle and stability boundary of an aircraft gliding on the water surface;

[0043] Figure 2 A flowchart illustrating the method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water, as provided in an embodiment of the present invention.

[0044] Figure 3 This is a schematic diagram showing that the pitch angle response curve in an embodiment of the present invention is in a very regular state;

[0045] Figure 4 This is a schematic diagram showing that the pitch angle response curve is in a relatively regular state in an embodiment of the present invention;

[0046] Figure 5 This is a schematic diagram showing that the pitch angle response curve is irregular in an embodiment of the present invention;

[0047] Figure 6 This is a schematic diagram of a typical motion stability state determined using the judgment criteria provided in the embodiments of the present invention;

[0048] Figure 7 This is a schematic diagram of a typical motion instability state determined using the judgment criteria provided in the embodiments of the present invention;

[0049] Figure 8 This is a schematic diagram of a two-parameter longitudinal motion stability determination criterion formed using the longitudinal motion stability determination method provided in this embodiment of the invention. Detailed Implementation

[0050] 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.

[0051] As explained in the background section, the motion stability of a surface-to-water vehicle (STOVL) during its movement on water is a crucial performance indicator. Currently, there are well-established methods and criteria for assessing the motion stability of STOVLs on calm water, typically based on the amplitude of fluctuations in the pitch angle. However, due to the interference of waves, the pitch angle of the STOVL always fluctuates within a certain amplitude and period, the magnitude of which is influenced by numerous factors such as wave height, wavelength, speed, and flight configuration.

[0052] During takeoff and landing on wave-like water, the water surface acts as a soft support. Simultaneously, due to the changing aerodynamic and hydrodynamic forces acting on the aircraft with its speed, the aircraft's longitudinal pitch attitude (roll angle) is constantly changing. When the roll angle is too large or too small, the aircraft will experience longitudinal instability, thus jeopardizing its operational safety. In other words, the longitudinal motion of a water-surface aircraft has upper and lower stability boundaries. Stability can only be maintained when the aircraft's attitude lies within these boundaries. This range is the stable range of the water-surface aircraft's roll angle. The area above the upper boundary and the area below the lower boundary represent the upper and lower unstable regions, respectively. Figure 1 The diagram shows the pitch angle and stability boundary of an aircraft gliding on the water surface. Therefore, during takeoff and landing of a waterplane, the pilot must adjust the longitudinal control surfaces of the aircraft according to its condition to ensure that the pitch angle remains within a stable range.

[0053] To address the aforementioned problems, embodiments of the present invention provide a method for determining the longitudinal motion stability of a surface vehicle taking off and landing on wavy water. Specifically, it proposes a two-parameter determination criterion and method for determining the longitudinal motion stability of a surface vehicle taking off and landing on wavy water. By using the method and criteria provided in the embodiments of the present invention, the motion stability of a surface vehicle during its movement on wavy water can be determined.

[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] According to the research and analysis of the researchers of this invention, the longitudinal motion stability of a water surface aircraft during takeoff and landing on wavy water is mainly affected by the magnitude and rate of pitch angle fluctuation. Both excessively large pitch angle fluctuations and excessively rapid fluctuations can affect the longitudinal motion stability of the aircraft. Therefore, this invention proposes a "dual-parameter judgment criterion" with pitch angle fluctuation amplitude and pitch angle fluctuation rate as input variables.

[0056] Different configurations of water surface aircraft take off and land in waves of different heights. The values ​​of the "dual-parameter judgment criteria" may be different, but the stability of water surface aircraft taking off and landing in waves can be determined by using the longitudinal motion stability determination method for water surface aircraft taking off and landing in waves provided by this invention.

[0057] Figure 2 This is a flowchart illustrating a method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water, as provided in an embodiment of the present invention. Figure 2 As shown, the longitudinal motion stability determination method for wave surface rise and fall provided in this embodiment of the invention is performed through the following steps:

[0058] Step one: Before conducting the regular wave towing test of the scaled-down model of the water-based aircraft, it is necessary to first determine the various test parameters used for the model test, specifically including the following parameters:

[0059] (1) The method for determining the wave height (denoted as h) of the model test is as follows: 1.32 times the meaningful wave height (denoted as H) of the sea waves corresponding to the take-off and landing of the actual aircraft, divided by the scale of the scaled model (i.e., the size ratio between the actual aircraft and the scaled model, denoted as λ), and then divided by 2, and h is calculated by the following formula (1):

[0060]

[0061] (2) The method for determining the wavelength of the model test is as follows: the minimum wavelength should be smaller than 1 times the length of the test model hull, and the maximum wavelength should be larger than 4 times the length of the test model hull. At least 4 wavelengths should be selected with approximately equal intervals between the minimum and maximum wavelengths.

[0062] (3) The method for determining the test speed of the model is as follows: between 0 and the takeoff speed of the test model from the water, select no less than 5 test speeds at approximately equal intervals.

[0063] Step two: After confirming the model test parameters for the regular wave towing test of the scaled-down model of the water-based aircraft, the model test is carried out. The test process and method for the regular wave towing test of the scaled-down model of the water-based aircraft are described below:

[0064] In the towed pool, the scaled-down test model is made to move at a constant speed in regular waves of the selected wave height and wavelength at each selected test speed. The pitch angle time history data of the scaled-down test model during the constant speed movement is collected, and the motion state of the scaled-down test model is recorded using a high-definition camera (the high-definition camera is installed on the front side of the scaled-down test model on the trailer, and the position of the high-definition camera is basically at the same front-back and vertical position as the center of gravity of the scaled-down test model).

[0065] Step 3: After completing the model test, the collected pitch angle time history data is filtered, and the filtering frequency is 9.5 times the encounter frequency of the scaled-down model.

[0066] Step four: After filtering, select the pitch angle time history data within the uniform velocity segment, and plot the pitch angle response curve with time as the horizontal axis and the pitch angle of the scaled-down experimental model as the vertical axis. Analyze the shape, fluctuation amplitude, and period of the curve. The analysis method is as follows:

[0067] (1) For a very regular pitch angle response curve, read the average of the maximum and minimum pitch angle values. The difference between the two is the pitch angle fluctuation amplitude (denoted as α). Select a certain number of response cycles for the total time to calculate the pitch angle fluctuation period (denoted as T). Figure 3 The diagram shown is a schematic representation of a pitch angle response curve in an embodiment of the present invention, where the curve is in a highly regular state.

[0068] (2) For a relatively regular pitch angle response curve, select a response period with a large fluctuation range to calculate the average of the maximum and minimum pitch angle fluctuations respectively. The difference between the two is the pitch angle fluctuation amplitude. The theoretical encounter period of the model is calculated using the test wavelength and test speed as the pitch angle fluctuation period. Figure 4 The diagram shown is a schematic representation of a relatively regular pitch angle response curve in an embodiment of the present invention.

[0069] (3) For irregular pitch angle response curves, select 2-3 response periods with large fluctuation ranges to calculate the average of the maximum and minimum pitch angle fluctuations respectively. The difference between the two is the pitch angle fluctuation amplitude. Using the test wavelength and test speed, combined with the test video recording, determine the number of jump waves in the model, and calculate the actual encounter period of the model as the pitch angle fluctuation period. Figure 5 The figure shown is a schematic diagram of the pitch angle response curve being irregular in an embodiment of the present invention.

[0070] Step 5: Based on the above analysis results, calculate the pitch angle fluctuation rate (denoted as ) using the pitch angle fluctuation amplitude and fluctuation period. The calculation method is to divide twice the amplitude of the pitch angle fluctuation α by the fluctuation period T, which can be expressed by the formula:

[0071]

[0072] Step 6: Determine the motion stability based on the motion state of the scaled-down model. The determination method is as follows: Analyze the motion state of the scaled-down model based on the video recording. If the scaled-down model remains in the water throughout the entire process, it is considered motion stable. If the scaled-down model briefly jumps out of the water and its longitudinal axis remains basically stable during the jump, it is considered motion stable. If the scaled-down model jumps out of the water and exhibits wave-jumping behavior (i.e., directly jumping over waves), or if its longitudinal axis fluctuates significantly during the jump, it is considered motion unstable.

[0073] like Figure 6 The diagram shown is a typical motion stability state determined using the judgment criteria provided in the embodiments of the present invention. Figure 6Figure a shows the aircraft at its minimum pitch angle, figure b shows the aircraft pitching up, figure c shows the aircraft reaching its peak pitch angle, and figure d shows the aircraft pitching down.

[0074] like Figure 7 The diagram shown is a typical motion instability state determined using the judgment criteria provided in the embodiments of the present invention. Figure 7 Image a shows the plane crashing against the waves; image b shows the plane raising its head; image c shows the plane jumping out of the water; image d shows the plane briefly flying in the air; image e shows the plane falling back into the water; and image f shows the front of the plane touching the water.

[0075] Step 7: Compile a motion stability statistics table. The compilation method is as follows: Based on different test conditions, combined with the pitch angle fluctuation amplitude, fluctuation period, fluctuation angular rate, and motion stability judgment results analyzed above, compile a motion stability statistics table for the scaled-down test model, as shown in Table 1 below.

[0076] Table 1. Statistics on Motion Stability

[0077]

[0078] Step 8: Draw the two-parameter motion stability criterion diagram;

[0079] The plotting method in this step is explained as follows: Based on the above motion stability statistics table, a scatter plot is drawn with the pitch angle fluctuation amplitude as the abscissa and the pitch angle fluctuation angular rate as the ordinate. Unstable motion state points are marked with a distinct and eye-catching color. The minimum fluctuation amplitude and minimum angular rate corresponding to each unstable motion state point are identified. Two straight lines are drawn parallel to the abscissa and ordinate axes through these points. The pitch angle fluctuation amplitude and fluctuation angular rate corresponding to these two lines are the pitch angle fluctuation amplitude criterion and the pitch angle fluctuation angular rate criterion, respectively. The envelope region formed by these two lines and the abscissa and ordinate axes is the stable region; the region outside the stable region is the unstable region. Figure 8 The diagram shown is a schematic of a two-parameter longitudinal motion stability determination criterion formed using the longitudinal motion stability determination method provided in this embodiment of the invention. Figure 8 The specific illustration shows the stability criteria for the AG600 aircraft in a 2-meter wave, where the pitch angle fluctuation amplitude criterion is 9.8° and the pitch angle fluctuation angular rate criterion is 9° / s.

[0080] The longitudinal motion stability determination method for a surface-to-water vehicle (SUV) taking off and landing on wavy water provided in this invention embodiment specifically analyzes the longitudinal motion stability of the SUV during takeoff and landing on wavy water based on a "two-parameter determination criterion." Since different configurations of SUVs take off and land in waves of varying heights, the values ​​of the "two-parameter determination criterion" (the two parameters include: pitch angle fluctuation amplitude and pitch angle fluctuation rate) are usually different. This invention embodiment provides a "two-parameter determination criterion" with pitch angle fluctuation amplitude and pitch angle fluctuation rate as input variables. During the determination process, a model test is first conducted based on determined experimental parameters. Pitch angle time-history data is collected, and the motion state of a scaled-down model during the model test is recorded. A response curve is plotted using the filtered pitch angle time-history data, and the shape of the pitch angle response curve is analyzed to obtain the pitch angle fluctuation amplitude, fluctuation period, and fluctuation angular rate. A motion stability statistical table is compiled based on the motion stability determined by the photographs, and finally, a two-parameter motion stability determination criterion diagram is drawn that reflects the motion stability region of the SUV during takeoff and landing on wavy water. The technical solution provided by the embodiments of the present invention can obtain a relatively accurate criterion for judging the longitudinal motion stability of a surface aircraft when it moves on a wave of a certain wave height.

[0081] 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 method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water, characterized in that, include: Step 1: Determine the model test parameters for conducting regular wave towing tests on scaled-down model water tanks of water surface aircraft; Step 2: Based on the model test parameters confirmed in Step 1, conduct a regular wave towing test of the scaled-down model of the water surface aircraft in a water tank, and collect pitch angle time history data during the model test, and photograph the motion state of the scaled-down model during the model test. Step 3: Filter the pitch angle time history data obtained from the model test in Step 2; Step 4: Select the pitch angle time history data within the filtered uniform velocity segment, plot the pitch angle response curve with time as the horizontal axis and the pitch angle of the scaled-down experimental model as the vertical axis, and analyze the shape, pitch angle fluctuation amplitude, and fluctuation period of the pitch angle response curve. Step 5: Calculate the pitch angle fluctuation rate using the pitch angle fluctuation amplitude and fluctuation period from Step 4; Step 6: Determine the motion stability based on the motion state of the scaled-down model; Step 7: Based on different test conditions, and combined with the amplitude of pitch angle fluctuation, fluctuation period, fluctuation angular rate, and motion stability judgment results, compile a motion stability statistical table for the scaled-down test model. Step 8: Based on the motion stability statistics table obtained in Step 7, draw a two-parameter motion stability judgment criterion diagram. The pitch angle fluctuation amplitude criterion and pitch angle fluctuation angular rate criterion obtained from the two-parameter motion stability judgment criterion diagram are used to reflect the motion stability region of the water surface aircraft during take-off and landing on the wave surface.

2. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 1, characterized in that, Before conducting the model experiment in step 1, the required model experiment parameters and their verification methods include: Step 11, the method for determining the wave height h in the model test is as follows: ； Where H is the meaningful wave height of the sea waves corresponding to the takeoff and landing of the actual aircraft, and λ is the scale value of the scaled model, that is, the size ratio between the actual aircraft and the scaled model. Step 12, the method for determining the wavelength of the model test is as follows: select no less than 4 wavelengths with approximately equal intervals between the minimum wavelength and the maximum wavelength; wherein, the minimum wavelength is less than 1 times the length of the test model hull, and the maximum wavelength is greater than 4 times the length of the test model hull; Step 13, the method for determining the model test speed is as follows: between 0 and the takeoff speed of the test model from the water, select no less than 5 test speeds at approximately equal intervals.

3. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 2, characterized in that, The model experiment process in step 2 includes: In the towed pool, the scaled-down test model is made to move at a constant speed in regular waves of the selected wave height and wavelength at each selected test speed. The time history data of the pitch angle of the scaled-down test model during the constant speed motion is collected, and the motion state of the scaled-down test model is recorded using a high-definition camera.

4. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 3, characterized in that, The high-definition camera is mounted on the side of the scaled-down test model on the trailer. The position of the high-definition camera is at the same front-to-back and vertical position as the center of gravity of the scaled-down test model.

5. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 1, characterized in that, The filtering frequency in step 3 is 9.5 times the encounter frequency of the scaled-down experimental model.

6. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 1, characterized in that, The methods for analyzing the response curve in step 4 include: For pitch angle response curves in highly regular, relatively regular, or irregular states, different analysis strategies are used to obtain the pitch angle fluctuation amplitude and fluctuation period.

7. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 1, characterized in that, The method for calculating the pitch angle fluctuation rate in step 5 is as follows: twice the pitch angle fluctuation amplitude α divided by the pitch angle fluctuation period T, expressed by the formula:

8. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 1, characterized in that, The method for determining motion stability in step 6 is as follows: Based on the video analysis of the motion state of the scaled-down experimental model, the following judgment criteria were established: The stability of motion is determined for the scaled-down experimental model that is always moving in water. For the experimental scaled-up model to briefly jump off the water surface, and for the experimental scaled-up model to maintain a basically stable longitudinal axis during the jump off the water surface, the state determination position motion stability is achieved. If a scaled-down experimental model jumps off the water surface and exhibits a jumping wave phenomenon, or if the longitudinal axis of the scaled-down experimental model fluctuates during the jumping process, it is considered to be in an unstable state.

9. The method for determining the longitudinal motion stability of a surface aircraft taking off and landing on wavy water as described in claim 1, characterized in that, Step 8 includes: Step 81: Plot a scatter plot with the pitch angle fluctuation amplitude as the abscissa and the pitch angle fluctuation angular rate as the ordinate; Step 82: Determine the minimum fluctuation amplitude and minimum angular rate corresponding to the state points of all unstable motions. Draw two straight lines parallel to the horizontal and vertical coordinate axes through these points. The pitch angle fluctuation amplitude and fluctuation angular rate corresponding to these two straight lines are the pitch angle fluctuation amplitude criterion and the pitch angle fluctuation angular rate criterion, respectively. The regions enclosed by the two straight lines and the horizontal and vertical coordinate axes are considered stable regions, while regions outside the stable regions are considered unstable regions.

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