A method and device for measuring motion of an externally suspended rotorcraft

Abstract

This invention provides a method and apparatus for measuring the motion of an external sling load on a rotorcraft. The invention employs strain testing, calculating the load on the external sling load using load strain calibration coefficients, calculating the angle of the external sling rope based on directional, lateral, and vertical loads, and then obtaining the angular rate and acceleration by differentiating the rope angle over time, thereby deriving the relative motion of the external sling load relative to the sling point. This invention provides a technical means for accurately measuring the three-dimensional motion trajectory and motion parameters of an external sling load. The provided nonlinear load strain calibration method improves measurement accuracy. Furthermore, the apparatus can be modularly designed, making installation convenient, highly accurate, and versatile.

Description

Technical Field

[0001] This invention belongs to the field of aviation technology, and in particular relates to a method and device for measuring the motion of an externally suspended rotorcraft. Background Technology

[0002] External sling load capability is one of the main strengths of helicopters, and it has become one of the most common modes of transport for helicopters. The status and value of helicopters have been repeatedly proven by their sling load capabilities. People began using helicopters for external sling load transport as early as the 1950s. With its flexible maneuverability and the fact that it does not require a dedicated airport, helicopters play an increasingly important role in the helicopter industry. When performing external sling load transport, helicopters can transport large volumes of cargo without considering the helicopter's own loading capacity or the cargo's shape. They are not constrained by local geographical conditions or traffic situations, and can transport cargo to remote locations inaccessible by conventional means of transport. Furthermore, they can deliver cargo precisely and quickly, greatly expanding the transport range, reducing time, accelerating project progress, and improving economic efficiency.

[0003] When a helicopter takes off with a sling load, the additional aerodynamic and inertial loads generated during normal sling load flight will couple with the helicopter's motion, altering its flight dynamics. If the pilot is unaware of these changes in load and fails to adjust flight attitude in time, flight stability will be affected. In the event of engine failure, the helicopter is prone to entering a danger zone (avoidance zone) determined by the combination of altitude and speed, leading to a safety accident. Upon arrival at the destination, due to ground effect and other environmental influences, the pilot needs to concentrate on controlling the helicopter, especially in solo pilot situations, leaving little time to focus on the deployment of the sling load. Therefore, during the helicopter design phase, it is necessary to establish a complete helicopter external sling load model coupled with a flight dynamics model to analyze the characteristics under different flight conditions.

[0004] Accurate measurement of the motion of external slings on helicopters provides experimental data for flight test corrections and verification in establishing high-confidence flight dynamics models of helicopter / sling combinations. Due to the relative motion and mutual coupling between the helicopter and the external sling, and the relatively large size of the sling, which involves complex torsional and oscillating motions, accurately measuring the three-dimensional motion trajectory and motion parameters of the external sling has always been an unsolved problem. Summary of the Invention

[0005] To address the challenge of measuring the three-dimensional motion trajectory and motion parameters of external slings, this invention provides a method and device for measuring the motion of external slings on rotorcraft based on strain testing. By adding a portable strain measurement device and load calibration coefficients, the loads in three different directions corresponding to the aircraft coordinate system are obtained. Angles can be obtained through trigonometric function calculations, and the corresponding angular velocity and velocity can be obtained by differentiating with respect to time. This method meets the relative motion measurement requirements for external sling motion parameters during helicopter flight testing, ensuring the flight safety of the helicopter sling. The technical solution is as follows:

[0006] Firstly, a method for measuring the motion of an external suspension on a rotorcraft is provided. This method employs strain testing, calculates the load on the external suspension using load strain calibration coefficients, calculates the angle of the external suspension rope based on the heading, lateral, and vertical loads, and then obtains the angular rate and acceleration by differentiating the rope angle over time, thereby deriving the relative velocity and relative acceleration of the external suspension relative to the suspension point.

[0007] Optionally, the method includes:

[0008] Step 1: Install strain gauges at the connection point between the helicopter and the external suspension beam;

[0009] Step 2: Install a data acquisition system on the helicopter fuselage;

[0010] Step 3: With the helicopter off-pilot, apply loads fx, fy, and fz along the heading, lateral, and vertical directions respectively at the connection point between the helicopter and the external sling. The data acquisition system collects the strain data of the strain components.

[0011] Step 4: Process the strain data from Step 3 to obtain the load strain coefficient matrix K;

[0012] Step 5: While the helicopter is in flight, the data acquisition system collects strain data from the strain components;

[0013] Step 6: Based on the load strain coefficient matrix K in Step 4 and the strain data collected in Step 5, the extended least squares method is used to inverse the loads to obtain the actual loads Fx, Fy and Fz in the heading, lateral and vertical directions.

[0014] Step 7: Based on the actual loads Fx, Fy, and Fz obtained in Step 6, and combining the trigonometric projection relationship between the three forces, the rope angle is obtained;

[0015] Step 8: Take the time derivative of the rope angle obtained in Step 7 to find the angular velocity and acceleration of the rope, and then multiply it by the rope length to derive the relative velocity and relative acceleration of the external suspension relative to the suspension point.

[0016] In step 1, the number of strain gauge components is ≥6. To improve accuracy, each strain gauge component uses a full bridge or a half bridge.

[0017] To avoid being affected by fuselage overload, the strain gauge assembly in step 1 should not be located on the fuselage load-bearing frame beam, but above the external sling point, on the fuselage connecting rod beam.

[0018] Among them, the vertical load satisfies: fz ≥ 2 times the maximum external suspension design weight Mg; considering the difference between tensile and compressive loads and strain coefficients, the yaw load satisfies: -0.5Mg ≤ fx ≤ 0.5Mg; the lateral load satisfies: -0.5Mg ≤ fy ≤ 0.5Mg.

[0019] In step 4, considering the difference between tensile and compressive loads and strain coefficients, a quadratic curve is used to represent the load-strain relationship to reduce errors:

[0020] εi=k11*Fx 2 +k12*Fx+k13*Fy 2 +k14*Fy+k15*Fz 2 +k15*Fz,

[0021] The corresponding rectangular shape is:

[0022]

[0023] The calculated load strain coefficient matrix K is as follows:

[0024]

[0025] in,

[0026] εi represents the strain value of the bridge at the i-th measuring point acquired in step 3.

[0027] ki1 is the heading calibration load fx 2 The influence coefficient of the strain component at the i-th measuring point;

[0028] ki2 is the influence coefficient of the heading calibration load fx on the strain of the strain component at the i-th measuring point;

[0029] ki3 is the lateral calibration load fy 2 The influence coefficient of the strain component at the i-th measuring point;

[0030] ki4 is the influence coefficient of the lateral calibration load fy on the strain of the strain component at the i-th measuring point;

[0031] ki5 is the vertical calibration load fz 2 The influence coefficient of the strain component at the i-th measuring point;

[0032] ki6 is the influence coefficient of the vertical calibration load fz on the strain of the strain component at the i-th measuring point.

[0033] In step 6, the extended least squares method is used to inverse the loads to obtain the actual loads Fx, Fy, and Fz borne by the external suspension. The calculation formula is as follows:

[0034]

[0035] INV indicates matrix inversion, []' indicates matrix transpose, εi is the strain value of the strain component; Fx is the actual load in the heading direction of the external sling, Fy is the actual load in the lateral direction, Fz is the actual load in the vertical direction; kn1 indicates the number of strain components with subscript n.

[0036] In step 7, the rope angles include: heading angle θ1 and yaw angle. Based on Fx, Fy, and Fz obtained in step 6, and combining the trigonometric projection relationships between the three forces, the rope angle is calculated using the following formula:

[0037]

[0038] In step 8, the rope angle obtained in step 7 is differentiated over time to determine the relative velocity and acceleration of the outer suspension relative to the suspension point.

[0039] The formula for calculating the relative velocity of the external suspension relative to the suspension point is:

[0040]

[0041] The formula for calculating the relative acceleration of the external suspension relative to the suspension point is:

[0042]

[0043] Where l is the length of the rope. Let k be the relative velocity of the heading at time k. Let k be the lateral relative velocity. Let k be the vertical relative velocity at time k; Δt be the sampling interval. Let k be the relative acceleration in the heading direction at time k. Let k be the lateral relative acceleration. Let k be the vertical relative acceleration at time k.

[0044] Secondly, a motion measurement device for an external suspension of a rotorcraft is provided, comprising: a strain component, a data acquisition system, and a processor; the strain component is located at the connection between the helicopter and the external suspension beam and is used to measure strain data;

[0045] The data acquisition system is connected to the strain assembly and is used to acquire strain data from the strain assembly.

[0046] The processor is used for:

[0047] The strain data is processed to obtain the load strain coefficient matrix K;

[0048] Based on the load strain coefficient matrix K and the strain data, the extended least squares method is used to inverse the loads to obtain the actual loads Fx, Fy and Fz in the heading, lateral and vertical directions.

[0049] Based on the actual loads Fx, Fy, and Fz in the heading, lateral, and vertical directions, and combined with the trigonometric projection relationship between the three forces, the rope angle is obtained;

[0050] By differentiating the rope angle over time, the angular velocity and acceleration of the rope are obtained. Then, by multiplying by the rope length, the relative velocity and relative acceleration of the external suspension relative to the suspension point are derived.

[0051] The beneficial effects of this invention are at least as follows:

[0052] This invention provides a method and device for measuring the motion of an external suspension of a rotorcraft based on strain testing. It provides a technical means for accurately measuring the three-dimensional motion trajectory and motion parameters of the external suspension. At the same time, this invention provides a load strain nonlinear calibration method, which can greatly improve accuracy. In addition, this device can adopt a modular design, which is convenient to install, has high accuracy, strong versatility, and good economic benefits. Attached Figure Description

[0053] Figure 1 This is a schematic diagram illustrating the definition of the helicopter body axis and the suspension attitude of the present invention;

[0054] Figure 2 This is a diagram showing the device composition of the present invention;

[0055] Figure 3 This is a full-bridge strain composition diagram of the present invention;

[0056] Figure 4 This is a diagram of the test acquisition system of this invention;

[0057] Figure 5 This is a schematic diagram of the external suspension heading calibration loading of the present invention;

[0058] Figure 6 This is a schematic diagram of the lateral load calibration curve of the present invention;

[0059] Figure 7 This is a schematic diagram of the load identification curve of the present invention;

[0060] Figure 8 This is the heading angle recognition curve of the present invention. Detailed Implementation

[0061] The present invention will now be described in further detail with reference to specific embodiments and accompanying drawings.

[0062] The generalized coordinates (suspension attitude angles) for measuring suspension displacement are defined within the helicopter body axis, such as... Figure 1 As shown, θ1 and These are respectively called the back yaw angle (heading angle) and side yaw angle of the sling, and are denoted by vectors.

[0063] The external sling joint is fixed to the lower middle part of the fuselage. During flight, due to gravity, drag and the movement of the external sling, random loads are generated. The external sling load is transmitted to the fuselage through the rope along the rope direction. It can be decomposed into yaw load Fx, vertical load Fz and lateral load Fy. These loads cause strain in the fuselage structure.

[0064] The coordinates of the suspended center of mass with the suspension point as the origin are:

[0065]

[0066] In the formula, r1 is the distance from the center of gravity of the aircraft to the mounting point on the aircraft body;

[0067] Considering the resultant force F of the external suspension position and the external suspension load L The directions are exactly the same, and the directional load Fx, vertical load Fz, and lateral load Fy are the resultant force F. L The relationship is as follows:

[0068]

[0069] The relationship between the strain εi at each measuring point of the structure and the load F can be expressed by a linear equation: εi=k11*F,

[0070] This invention considers the difference in load-strain coefficients under tensile and compressive loads, and uses a quadratic curve to give the calibration curve εi=k11*F 2 +k12*F,

[0071] Structural strain follows the principle of linear superposition, that is, when the structure is subjected to yaw load, vertical load and lateral load simultaneously, the strain value at each measuring point is a linear superposition of the strain when these loads act alone.

[0072] The relationship between the strain εi of the bridge at the i-th measuring point of the externally suspended load-bearing structure and the load can be expressed by a nonlinear equation:

[0073] εi=k11*Fx 2 +k12*Fx+k13*Fy 2 +k14*Fy+k15*Fz 2 +k15*Fz

[0074] εi represents the strain value of the bridge at the i-th measuring point, written in rectangular form as follows:

[0075]

[0076] Strain was tested at various measuring points during flight. Given the information, the heading load, vertical load, and lateral load can be obtained using the extended least squares method.

[0077] This invention arranges multiple strain bridges in the main load-bearing points connected within the fuselage to test strain values ​​during flight. Combining this with a calibration coefficient matrix, the least squares method is used to obtain the external sling load. Trigonometric functions are used to solve for the heading and yaw angles, and then the angles are solved over time to obtain the relative velocity and relative acceleration of the external sling motion. The method of this invention mainly includes: ① strain testing; ② a data acquisition system; ③ a calibration coefficient and load decoupling algorithm; and ④ an angle-based algorithm. See details below. Figure 1 .

[0078] 1) Multiple strain test points are arranged in the main load-bearing point connected structure within the machine body.

[0079] Strain gauges convert the relative deformation of the test piece into a change in resistance. Each test point uses a full-bridge or half-bridge strain gauge to improve accuracy. Considering the X, Y, and Z directions, the number of test points is ≥6. The strain gauge mainly consists of four parts: grid wire, substrate, capping layer, and leads. The grid wire, also called the sensitive grid, is the main factor determining the performance of the strain gauge.

[0080] 2) Data Acquisition System

[0081] A strain gauge strain measurement system generally consists of four parts: a sensor (a Wheatstone bridge composed of strain gauges), a signal conditioner (mainly composed of an excitation source and a signal amplifier), a data acquisition and recording system, and its software system.

[0082] 3) Calibration coefficients and load decoupling algorithm

[0083] At the external hanging ring position, fix one angle steel with two bolts, then use three aluminum levers to form a two-stage lever system, and finally combine them into a loading point. Measure the static bending strain under positive loading by applying static loads of 0.1mg, 0.2mg, 0.4mg...1.0mg along the heading using a hand-operated hoist; measure the static bending strain under negative loading by applying static loads of -0.1mg, -0.2mg, -0.4mg...-1.0mg fx along the heading using a hand-operated hoist.

[0084] After load calibration, load-strain relationship curves were obtained. This invention considers the difference in load-strain variation coefficients under tensile and compressive loads, and uses a quadratic curve to give the calibration curve. Each calibration test was repeated 3 times, and k11 and k12 were calculated using the least squares method.

[0085] εi x=k11*fx 2 +k12*fx

[0086] The static bending strain under positive lateral loading was measured by applying static loads of 0.1mg, 0.2mg, 0.4mg...1.0mg laterally using a hand-operated hoist; the static bending strain under negative lateral loading was measured by applying static loads of -0.1mg, -0.2mg, -0.4mg...-1.0mg laterally using a hand-operated hoist. Similarly, k13 and k14 were calculated.

[0087] By applying static loads fz in the vertical direction in successive increments of -0.3mg, -0.6mg, -0.9mg...3.0mg using a hand-operated hoist, the static bending strain under positive vertical loading is measured, and k15 and k16 are calculated accordingly.

[0088] At this point, the linear superposition relationship between the strain at each measuring point of the structure and the multiple loads can be expressed by a linear equation:

[0089] εi=k11**fx 2 +k12*fx+k13*fy 2 +k14*fy+k15*fz 2 +k16*fz

[0090] εi represents the strain value of the bridge at the i-th measuring point, which can be written in matrix form as follows:

[0091]

[0092] 4) Identify external suspended loads through strain:

[0093] The strain at each measuring point is tested during flight, requiring a measuring point count of n≥6, within the load-strain calibration coefficient matrix. Given the information, the heading load Fx, vertical load Fz, and lateral load Fy can be obtained using the extended least squares method, with the following formula:

[0094]

[0095] Where INV represents matrix inversion, and []' represents matrix transpose;

[0096] εi is the strain value of the strain component;

[0097] Fx is the yaw load of the external suspension, Fy is the lateral load, and Fz is the vertical load;

[0098] kn1 represents the number of strain gauge components with subscript n.

[0099] 5) Calculate the relative motion of the external suspension using structural load relationships:

[0100] The yaw load Fx, vertical load Fz, and lateral load Fy, along with the resultant force F L The projection formula:

[0101]

[0102] From the above formula, we can derive:

[0103] θ1=acos(Fz / F L )

[0104]

[0105] The relative position vector of the external suspension:

[0106]

[0107] By differentiating the position vector using the differential formula, the relative velocity can be obtained, and the discrete form can be expressed as follows:

[0108]

[0109] By differentiating the velocity vector using the differential formula, the relative acceleration can be obtained, and the discrete form can be expressed as follows:

[0110]

[0111] For example, in one embodiment, the helicopter has a maximum external sling load of 3600 kg and an external sling length of 3 m. Above the external sling point, six sets of full-bridge strain gauges are arranged on the fuselage connecting beam. Figure 3 A testing system was added, using the general-purpose UMA2000 data acquisition unit to collect PCM signals. An MDR data logger was used for data recording and real-time display monitoring. A B-code generator was added to output IRIG-B120 clock codes for time synchronization with the UMA2000 airborne data acquisition unit. The airframe testing system uses a 28V power supply with a power consumption not exceeding 700W. Its test acquisition components are described below. Figure 4 .

[0112] Calibration was performed according to the plan. See the schematic diagram for the external suspension lateral calibration loading. Figure 5 The calibration results are shown below. Figure 6 The equation for the lateral load calibration curve is obtained as: y = 1E-13x² + 1E-08x + 2E-05;

[0113] The calculation was performed according to the external suspension motion measurement method of the present invention, and the resulting curve is shown in the figure. Figure 7 It is the heading angle identification curve.

[0114] The above description merely illustrates embodiments of the present invention and is quite specific and detailed; however, it should not be construed as limiting the scope of the patent. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these all fall within the scope of protection of the present invention. Furthermore, any parts of the present invention not described in detail are conventional techniques.

Claims

1. A method of measuring the motion of an external suspension of a rotary wing aircraft, characterized by, The relative speed and relative acceleration of the external sling relative to the sling point are derived by using the strain test method, calculating the external sling load by using the load strain calibration coefficient, calculating the rope angle of the external sling according to the heading, lateral and vertical loads, and time-deriving the rope angle to obtain the angular rate and acceleration rate. The method comprises: Step 1, arranging a strain assembly at the position of the connecting rod beam of the helicopter and the external sling; Step 2, adding a data acquisition system to the helicopter body; Step 3, under the condition that the helicopter is not running, applying loads fx, fy and fz along the heading, lateral and vertical directions respectively at the connecting point of the helicopter and the external sling, and collecting strain data of the strain assembly by the data acquisition system; Step 4, processing the strain data in Step 3 to obtain a load strain coefficient matrix K; Step 5, collecting strain data of the strain assembly by the data acquisition system under the condition that the helicopter is running; Step 6, obtaining actual loads Fx, Fy and Fz in the heading, lateral and vertical directions by using the extended least square method to inverse according to the load strain coefficient matrix K in Step 4 and the strain data collected in Step 5; Step 7, obtaining the rope angle by combining the actual loads Fx, Fy and Fz obtained in Step 6 and the trigonometric projection relationship among the three forces; Step 8, time-deriving the rope angle obtained in Step 7 to obtain the angular rate and acceleration rate of the rope, and multiplying the rope length to derive the relative speed and relative acceleration of the external sling relative to the sling point.

2. The method of claim 1, wherein, The number of strain assemblies arranged in Step 1 is greater than or equal to 6, and each strain assembly uses a full bridge or a half bridge.

3. The method of claim 1, wherein, The strain assembly arranged in Step 1 is arranged above the sling point of the external sling and on the connecting rod beam of the helicopter body.

4. The method of claim 1, wherein, In Step 3, the vertical load satisfies fz≥2 times the maximum external sling design weight Mg, the heading load satisfies -0.5Mg≤fx≤0.5Mg, and the lateral load satisfies -0.5Mg≤fy≤0.5Mg.

5. The method of claim 1, wherein, In Step 4, the load strain relationship is represented by a quadratic curve as follows: ， The load strain coefficient matrix K obtained by calculation is as follows: wherein, represents the strain value 2 of the bridge of the i-th measurement point collected in step 3, represents the strain value 2 of the bridge of the i-th measurement point collected in step 3, ki1is the heading calibration load fx 2 ki1is the heading calibration load fx 2 ki1is the heading calibration load fx 2 ki1is the heading calibration load fx 2 ki1is the heading calibration load fx <000000 ki2 is the influence coefficient of the heading calibration load fx on the strain of the strain assembly of the i th measuring point; ki3 is the lateral calibration load fy 2 ki3 is the lateral calibration load fy 2 ki3 is the lateral calibration load fy 2 ki3 is the lateral calibration load fy 2 ki3 is the lateral calibration load fy <000000 ki4 is the influence coefficient of the lateral calibration load fy on the strain of the strain assembly of the i th measuring point; ki5is the vertical calibration load fz 2 ki5is the vertical calibration load fz ki5is the vertical calibration load fz ki6 is the influence coefficient of the vertical calibration load fz on the strain of the strain assembly of the i th measuring point.

6. The method of claim 1, wherein, In Step 6, the actual loads Fx, Fy and Fz borne by the external sling are obtained by using the extended least square method to inverse, and the calculation formula is as follows: INV denotes matrix inversion, and []' denotes matrix transposition. Fx is the actual load in the fore-aft direction, Fy is the actual load in the lateral direction, and Fz is the actual load in the vertical direction; kn1 denotes the number of strain components with subscript n.

7. The method of claim 1, wherein, In step 7, the rope angle includes: a heading angle and a yaw angle , according to Fx, Fy and Fz obtained in step 6, combined with the trigonometric projection relationship among the three forces, the rope angle is calculated according to the following formula:

8. The method of claim 1, wherein, In Step 8, the relative speed and relative acceleration of the external sling relative to the sling point are obtained by time-deriving the rope angle obtained in Step 7, The calculation formula of the relative speed of the external sling relative to the sling point is as follows: The calculation formula of the relative acceleration of the external sling relative to the sling point is as follows: wherein, is the length of the rope, is the relative velocity in the heading direction at time k, is the relative velocity in the lateral direction at time k; is the relative velocity in the vertical direction at time k. Δt is the sampling interval; is the relative acceleration in the heading direction at time k, is the relative acceleration in the lateral direction at time k, is the relative acceleration in the vertical direction at time k.

9. An external-hung motion measurement device for a rotary wing aircraft, comprising: It comprises: a strain assembly, a data acquisition system and a processor; the strain assembly is located at the position of the connecting rod beam of the helicopter and the external sling and is used for measuring strain data; the data acquisition system is connected with the strain assembly and is used for collecting strain data of the strain assembly; the processor is used for: processing the strain data to obtain a load strain coefficient matrix K; According to the load strain coefficient matrix K and the strain data, the actual loads Fx, Fy and Fz in the heading direction, lateral direction and vertical direction are obtained by using the extended least square method inverse; According to the actual loads Fx, Fy and Fz in the heading direction, lateral direction and vertical direction, and the trigonometric projection relationship among the three forces, the rope angle is obtained; The time derivative of the rope angle is calculated to obtain the angular velocity and acceleration of the rope, which are then multiplied by the length of the rope to derive the relative velocity and acceleration of the outer hanging relative to the hanging point.

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