Active air refueling route planning method

Abstract

The invention provides an active air refueling route planning method, and belongs to the field of aircraft flight control, and the method comprises the steps: a refueling machine sets a predicted meeting point on a fixed route of a receiver aircraft, and the meeting point is solved in a manner that the refueling machine flies to the predicted meeting point in a Dubins shortest path to be combined with the receiver aircraft; judging whether the solved meeting point is on a specified straight line section of the horse race, if so, enabling the refueling machine to fly according to a Dubins path navigation point, and if not, moving the meeting point to a starting point of the specified straight line section, and obtaining a circling route after the refueling machine reaches the meeting point; and calculating a straight flight path after the refueling machine and the oil receiver are combined until refueling is completed and the refueling machine is separated from the oil receiver. According to the invention, the unmanned aerial vehicle which flies according to a fixed air route and has a relatively low intelligent level can be ensured to realize an active aerial refueling task of the refueling machine on the unmanned aerial vehicle, and meanwhile, a refueling meeting point is set on a specified edge of an air route of the refueling aircraft, so that the safety and reliability of aerial refueling are improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of aircraft flight control, and particularly relates to an active in-air refueling route planning method. Background Art

[0002] During the long-distance flight and complex mission execution of aircraft, in-air refueling technology, as a core guarantee means for extending the endurance time and expanding the operation range, has important application value. Traditional in-air refueling operations rely on manual control methods. Operators need to ensure the docking of the receiver aircraft and the tanker through visual observation, and the receiver aircraft actively approaches the tanker to complete in-air refueling. This mode has significant limitations that the operation accuracy is restricted by environmental factors (such as weather, light, etc.) and human factors, and it is difficult to meet the requirements of high docking accuracy.

[0003] With the intelligent development of intelligent unmanned systems and the performance improvement of detection devices (including radars, optical sensors, laser rangefinders), autonomous in-air refueling of unmanned tankers has gradually become possible. For example, Chinese Patent with the publication number CN105302158B provides a method for autonomous in-air refueling of unmanned aerial vehicles. In this method, the tanker flies along a fixed route and waits for the unmanned aerial vehicle to approach for refueling. After receiving the in-air refueling command, the receiver unmanned aerial vehicle autonomously flies to the tanker to complete the rendezvous mission and then conducts docking refueling. However, the current commonly used unmanned aerial vehicles have a low level of intelligence. At the same time, due to the payload limitations and cost control requirements of the receiver unmanned aerial vehicle, in actual applications, the receiver unmanned aerial vehicle cannot well perform the task of flying to the refueling position along the route calculated in real time. Summary of the Invention

[0004] Aiming at the above deficiencies of existing in-air refueling of unmanned aerial vehicles, the present invention sets the unmanned aerial vehicle as the receiver on a fixed route (racecourse route), the tanker actively flies towards the receiver's route, and realizes the refueling route planning of the tanker through corresponding path planning methods. Further, in the refueling route planning, the present invention also considers the safe refueling route of the receiver on the fixed route, and sets the refueling rendezvous point of the tanker and the receiver on a specified side of the receiver's route, so as to realize safe and reliable refueling of the unmanned aerial vehicle.

[0005] To achieve the above object, the technical solution provided by the present invention is:

[0006] Provided is an active in-air refueling route planning method, including the following steps:

[0007] Step 1, the tanker obtains the racecourse route information and the current position information of the receiver unmanned aerial vehicle to be refueled, sets the obtained current position of the receiver unmanned aerial vehicle as the expected rendezvous point, and the time for the receiver unmanned aerial vehicle to move to the expected rendezvous point in the station-centered coordinate system is t R1, where the racetrack route includes two arcs and two straight lines that form a circle, and the two arcs are opposite to each other, and the two straight lines are opposite to each other;

[0008] Step 2, calculate the time t required for the refueling aircraft to fly to the predicted rendezvous point at a speed v along the Dubins shortest path T ; If the difference between t T1 and t T1 is within the set rendezvous time difference threshold range, then update the predicted rendezvous point along the route direction of the receiver aircraft according to the set step length until the difference between t R1 and t T1 is within the set rendezvous time difference threshold range, and then output the Dubins path navigation point; R1

[0009] Step 3, determine whether the predicted rendezvous point is on the specified side, where the specified side is the straight line segment closer to the refueling aircraft in the racetrack route; if it is determined that the predicted rendezvous point is on the specified side, then the refueling aircraft selects the current predicted rendezvous point as the rendezvous point, and the refueling aircraft tracks the Dubins path navigation point and flies to the selected rendezvous point; if it is determined that the predicted rendezvous point is not on the specified side, then the refueling aircraft selects the starting point of the specified side as the rendezvous point, and the time for the receiver aircraft to move to the selected rendezvous point is t R2 , the refueling aircraft flies to the selected rendezvous point according to the Dubins path navigation point and hovers for several circles at the rendezvous point, where the starting point of the specified side refers to the point where the receiver aircraft enters the straight line segment along the route direction, and the hovering path is calculated as follows:

[0010] The first step is to recalculate the time t required for the refueling aircraft to reach the selected rendezvous point according to the Dubins path T2 ;

[0011] The second step is to calculate the extra distance that the refueling aircraft needs to fly: S more =(t T2 -t R2 )*v T ;

[0012] The third step is to calculate the hovering path of the refueling aircraft, including the number of hovering circles and the hovering radius:

[0013]

[0014] In the formula, r min is the minimum turning radius of the refueling aircraft, and round(·) represents rounding down; if the number of hovering circles n more =0, then use the method of increasing the hovering radius to ensure that the refueling aircraft and the receiver aircraft arrive at the rendezvous point at the same time; if n more ≠0, then calculate the turning radius:

[0015] ​Step 4: The fuel tanker flies along the direct flight path to refuel the receiver aircraft. Meanwhile, it determines whether there are still receiver aircraft that need to be refueled. If there are, after completing the refueling and detaching from the current receiver aircraft, the above process is repeated. If not, it returns to the set position.

[0016] Further, in Step 1, the obtained route information and current position information of the receiver aircraft are in the geographic coordinate system, and their information in the local-level coordinate system is obtained through coordinate transformation. The coordinate transformation process is as follows:

[0017] Step 1: Convert the coordinates of the target point P from the geographic coordinate system to the geodetic rectangular coordinate system:

[0018]

[0019] In the formula, (L, B, H) are the coordinates of the target point P in the geographic coordinate system, where L is the geodetic longitude, B is the geodetic latitude, and H is the geodetic height; (X, Y, Z) are the coordinates of the target point P in the geodetic rectangular coordinate system; N is the radius of curvature of the prime vertical of the ellipsoid; e is the first eccentricity of the ellipsoid.

[0020] Step 2: Convert the coordinates of the target point P from the geodetic rectangular coordinate system to the local-level coordinate system:

[0021]

[0022] In the formula, (x, y, z) are the coordinates of point P in the local-level coordinate system with the local-level origin P0 as the coordinate origin; (X o , Y0, Z0) are the coordinates of the local-level origin P0 in the geographic coordinate system, and (L0, B0, H0) are the coordinates of the local-level origin P0 in the geographic coordinate system.

[0023] Further, in Step 1, the time t for the receiver aircraft to move to the predicted rendezvous point in the local-level coordinate system R1 is calculated as follows:

[0024]

[0025] In the formula, (x R , y R ) are the position coordinates of the receiver aircraft, (x exp , y exp ) are the coordinates of the predicted rendezvous point, and v R is the flight speed of the receiver aircraft.

[0026] Further, the set range of the rendezvous time difference threshold is from 0 to 2 seconds.

[0027] Further, the method for the fuel tanker to calculate the Dubins path includes the following steps:

[0028] In the first step, perform a standard transformation to obtain the standardized starting and ending coordinates and the straight-line distance between the starting and ending points.

[0029] In the second step, use the obtained standardized starting and ending point information to calculate the lengths of six Dubins paths from the starting point to the ending point.

[0030] In the third step, select the Dubins path with the shortest path length among the six paths and perform waypoint sampling on the horizontal plane.

[0031] In the fourth step, calculate the height difference and determine whether the climbing or descending requirements can be met based on the maximum climbing rate; if it is determined that it can be met, perform Dubins three-dimensional path calculation in a uniform climbing manner, and if it is determined that it cannot be met, perform Dubins three-dimensional path calculation in an ascending spiral or descending spiral manner.

[0032] The advantages of the present invention are as follows:

[0033] 1. For the active in-air refueling route planning method proposed by the present invention, considering that the intelligent level of the unmanned aerial vehicle is relatively low and it cannot perform the in-air refueling task according to the planned route well, the receiver is set to fly a fixed route of a racecourse loop, and the tanker actively flies towards the receiver's route and refuels after rendezvous. First, the tanker sets a predicted rendezvous point on the receiver's fixed route, then solves the rendezvous point in the way that the tanker flies to the predicted rendezvous point along the Dubins shortest path to rendezvous with the receiver, and then determines whether the solved rendezvous point is on the specified straight line segment of the racecourse loop. If it is, the tanker flies according to the Dubins path navigation points; if not, the rendezvous point is moved to the starting point of the specified straight line segment, and the hovering route of the tanker after reaching the rendezvous point is obtained. Then, calculate the straight flight path after the tanker and the receiver rendezvous until the refueling is completed and the tanker disengages from the receiver. Therefore, the present invention can ensure that an unmanned aerial vehicle with a relatively low intelligent level flying along a fixed route can achieve the active in-air refueling task by the tanker. At the same time, setting the refueling rendezvous point on the specified side of the receiver's route improves the safety and reliability of in-air refueling.

[0034] 2. In the present invention, if there are still receivers that need to be refueled, after the tanker completes the refueling of the current receiver and disengages from it, it continues to perform the refueling operation, which can achieve the route planning for the tanker to perform in-air refueling on multiple receivers in one flight and perform multiple refuelings on a single receiver, thereby improving the in-air refueling efficiency and saving refueling costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] Through the following description with reference to the drawings, the above and / or other features and advantages of the present invention will become more readily understood. In the drawings:

[0036] Figure 1It is the calculation flow chart of the rendezvous point in the active in-air refueling route planning method of the present invention;

[0037] Figure 2 It is a schematic diagram of the coordinate system conversion method in the present invention. (a) is the geographic coordinate system and the geodetic rectangular coordinate system, and (b) is the geodetic rectangular coordinate system and the station-centered coordinate system;

[0038] Figure 3 It is a schematic diagram of coordinate transformation in the Dubins path calculation in the present invention;

[0039] Figure 4 It is a schematic diagram of the Dubins path in the present invention;

[0040] Figure 5 It is a schematic diagram of the RSR path in the present invention;

[0041] Figure 6 It is a schematic diagram of the ascending spiral in the present invention;

[0042] Figure 7 It is the process of the present invention for active in-air refueling of two receiver aircraft;

[0043] Figure 8 It is the in-air refueling route planning result in the example of the present invention. Detailed implementation manners

[0044] The present invention will be described in detail below with reference to the accompanying drawings by means of exemplary embodiments of the present invention. It should be noted that the following detailed description of the present invention is for illustrative purposes only and does not limit the present invention.

[0045] Considering that the intelligent level of the unmanned aerial vehicle is relatively low and it cannot perform the in-air refueling task according to the planned route well, the present invention sets the receiver aircraft to a fixed route of a running horse circle route, and the tanker actively flies towards the receiver aircraft's route. After rendezvous, refueling is carried out, thereby providing an active in-air refueling route planning method. In the present invention, the receiver aircraft's route is set in the form of a running horse circle, that is, there are two arc sides and two straight sides. During in-air refueling, it is hoped to always be on the safer straight side. In addition, due to the low intelligence of the receiver aircraft and its flight along a fixed route, it is impossible to achieve rendezvous by adjusting the receiver aircraft, and it is necessary to actively increase the flight time of the tanker to achieve rendezvous between the tanker and the receiver aircraft.

[0046] Refer to Figure 1 , the active in-air refueling route planning method provided by the present invention may include the following steps:

[0047] Step S1, the tanker obtains the running horse circle route information and the current position information of the receiver aircraft to be refueled, sets the obtained current position of the receiver aircraft as the predicted rendezvous point, and the time for the receiver aircraft to move to the predicted rendezvous point in the station-centered coordinate system is tR1 , where the racecourse route includes two arcs and two straight lines that form a circle, and the two arcs are opposite to each other, and the two straight lines are opposite to each other;

[0048] Step S2, calculate the time t required for the refueling aircraft to fly to the predicted rendezvous point at a speed v along the Dubins shortest path T ; If the difference between t T1 and t T1 is within the set rendezvous time difference threshold range, then update the predicted rendezvous point along the route direction of the receiver aircraft according to the set step length until the difference between t R1 and t T1 is within the set rendezvous time difference threshold range, and then output the Dubins path navigation point; R1

[0049] Step S3, determine whether the predicted rendezvous point is on the specified side, where the specified side is the straight line segment closer to the refueling aircraft in the racecourse route; if it is determined that the predicted rendezvous point is on the specified side, the refueling aircraft will select the current predicted rendezvous point as the rendezvous point, and the refueling aircraft will fly to the selected rendezvous point by tracking the Dubins path navigation point; if it is determined that the predicted rendezvous point is not on the specified side, the refueling aircraft will select the starting point of the specified side as the rendezvous point, and the time for the receiver aircraft to move to the selected rendezvous point is t R2 , the refueling aircraft will fly to the selected rendezvous point according to the Dubins path navigation point and circle several times at the rendezvous point, where the starting point of the specified side refers to the point where the receiver aircraft enters the straight line segment along the route direction, and the circling path is calculated as follows:

[0050] First step, recalculate the time t required for the refueling aircraft to reach the selected rendezvous point according to the Dubins path T2 ;

[0051] Second step, calculate the extra distance that the refueling aircraft needs to fly: S more = (t T2 - t R2 ) * v T ;

[0052] Third step, calculate the circling path of the refueling aircraft, including the number of circling turns and the circling radius:

[0053]

[0054] In the formula, n more is the number of circling turns, r min is the minimum turning radius of the refueling aircraft, and round(·) represents rounding down; if n more = 0, then use the method of increasing the circling radius to ensure that the refueling aircraft and the receiver aircraft arrive at the rendezvous point at the same time; if n more ≠ 0, then calculate the turning radius:

[0055] Step S4, the fuel dispenser flies along the direct flight path and refuels the receiver aircraft. Meanwhile, it determines whether there are still receiver aircraft that need to be refueled. If there are, after completing the refueling and detaching from the current receiver aircraft, the above process is repeated. If not, it returns to the set position.

[0056] In step 1, the obtained route information and current position information of the receiver aircraft are in the geographic coordinate system and need to be converted to the information in the local-level coordinate system through coordinate transformation. The input coordinates (longitude, latitude, and altitude) in the geographic coordinate system are converted to the coordinates (x, y, z) in the local-level coordinate system to facilitate the use of the subsequent route planning algorithm. The geographic coordinate system is first converted to the geodetic rectangular coordinate system, and then the geodetic rectangular coordinate system is converted to the local-level coordinate system.

[0057] As Figure 2 shown in (a) of g , the origin of the geographic coordinate system is selected at the center of the earth. The Z g axis is defined as the earth's axis of rotation, and the positive direction is from the center of the earth to the north pole; the X g axis is defined in the equatorial plane, and it is the axis from the center of the earth to the Greenwich meridian; the Y g axis is determined by the right-hand rule from the X g axis and the Z

[0058]

[0059] axis. Assume the coordinates of the target point P in the geographic coordinate system are (L, B, H), where L is the geodetic longitude, B is the geodetic latitude, and H is the geodetic altitude. The coordinate position of the target point P in the geodetic rectangular coordinate system is (X, Y, Z). Then the position transformation relationship between the geographic coordinate system and the geodetic rectangular coordinate system is:

[0060] As Figure 2 shown in (b) of o , the origin of the local-level coordinate system is defined at the center of mass of the vehicle; the N axis is in the direction of the geographic north compass (north); the E axis is in the direction of the earth's rotation tangent (east); the D axis is in the direction from the center of mass of the vehicle to the center of the earth. The conversion between the geodetic rectangular coordinate system and the local-level coordinate system is mainly achieved through the rotation matrix and the translation matrix. Since the coordinates in the geodetic rectangular coordinate system are relatively large values, which are not convenient for spatial calculations, a local-level point needs to be selected so that the geographic coordinates to be converted are relatively small values. Assume the coordinates of the local-level origin P0 in the geographic coordinate system are (L0, B0, H0), and the corresponding coordinates in the geodetic rectangular coordinate system are (X o , Y0, Z0). Then, when converting the coordinates in the geodetic rectangular coordinate system to the local-level coordinate system with P0 as the coordinate origin, the coordinate transformation matrix S is:

[0061]

[0062] Then the calculation formula for the coordinates (x, y, z) of the target point P=(X, Y, Z) in the local-level coordinate system with P0 as the coordinate origin is as follows:

[0063]

[0064] Thus, the coordinate transformation of the coordinate point P is completed.

[0065] According to the present invention, in step 1, the time t for the receiver aircraft to move to the expected rendezvous point in the local-level coordinate system R1 is calculated as follows:

[0066]

[0067] In the formula, (x R , y R ) are the position coordinates of the receiver aircraft, (x exp , y exp ) are the coordinates of the expected rendezvous point, and v R is the flight speed of the receiver aircraft. It should be understood that in order to achieve refueling after rendezvous, the flight speed of the receiver aircraft is equal to that of the tanker aircraft.

[0068] For the Dubins path calculation method used in route planning, it provides an optimal forward path in the case of no obstacles. Specifically, it includes:

[0069] The first step is to perform a standard transformation:

[0070] Referring to Figure 3 , assume that in the OXY coordinate system, the starting point is the current position of the tanker aircraft, with coordinates s(x i , y i , α i ), and the end point is the expected rendezvous point or the selected rendezvous point, with coordinates g(x g , y g , β g ). First, perform a coordinate transformation to translate the starting point to the origin of the O'X'Y' coordinate system, and then rotate the OXY coordinate system by an angle θ so that the X-axis of the OXY coordinate system is parallel to the X'-axis of the O'X'Y' coordinate system. Then the end point also falls on the X'-axis. The coordinates of the starting point and the end point in the O'X'Y' coordinate system become s(0, 0, α) and g(d, 0, β) respectively, where:

[0071]

[0072] d = D / R (7)

[0073] α = (α i-θ) mod{2π} (8)

[0074] β = (β g -θ) mod{2π} (9)

[0075] Wherein, mod{·} represents taking the remainder, D represents the straight-line distance between the starting point and the ending point before normalization, R represents the turning radius of the fuel tanker, and d represents the straight-line distance between the starting point and the ending point after normalization;

[0076] Second step, using the obtained starting point and ending point information after normalization, calculate the lengths of six Dubins paths from the starting point to the ending point:

[0077] Referring to Figure 4 , there are a total of six Dubins paths, namely LSL, RSR, RSL, LSR, RLR, and LRL, where L represents a left turn, S represents a straight line, and R represents a right turn;

[0078] As Figure 5 shown, taking the RSR path as an example, the trajectory length is calculated as follows:

[0079]

[0080] Wherein, t rsr represents the length of the first curved segment in the RSR path, p rsr represents the length of the straight-line segment in the RSR path, and q rsr represents the length of the second curved segment in the RSR path;

[0081] Therefore, the total trajectory length of the RSR path is:

[0082] L rsr = t rsr + p rsr + q rsr = α - β + p rsr (13)

[0083] Third step, select the Dubins path with the shortest path length among the six paths and sample waypoints on the horizontal plane;

[0084] Fourth step, calculate the height difference and determine whether the climbing or descending requirement can be met according to the maximum climbing rate; if it is determined that it can be met, the Dubins three-dimensional path calculation is carried out in a uniform climbing manner, and if it is determined that it cannot be met, the Dubins three-dimensional path calculation is carried out in an ascending spiral or descending spiral manner. The spiral schematic diagram is as Figure 6 shown.

[0085] In step S4, the direct flight path consists of two segments. The first segment is the flight maintenance segment, and the function of this segment is to ensure that the tanker and the receiver have the same speed and the same heading. After passing the verification, it will continue to enter the in-air refueling stage. The second segment is the in-air refueling segment. To ensure the safety of in-air refueling, in-air refueling needs to be carried out under straight flight conditions. Therefore, the distance of this segment can be determined by the product of the refueling duration and the flight speed.

[0086] Since the coordinates required by the tanker flight control are in the geodetic coordinate system, it is necessary to perform another coordinate transformation to convert the coordinates in the local-level coordinate system obtained in the above process into the geodetic coordinate system. This transformation process is the inverse operation of the above geodetic coordinate system to the local-level coordinate system, mainly including converting the local-level coordinate system to the geodetic rectangular coordinate system and converting the geodetic rectangular coordinate system to the geodetic coordinate system.

[0087] Since the coordinate transformation matrix S obtained above is an orthonormal matrix, it has the following properties:

[0088] S -1 =S T (14)

[0089] Therefore, the local-level coordinate system can be converted to the geodetic rectangular coordinate system through the inverse operation of the matrix:

[0090]

[0091] The conversion of the geodetic rectangular coordinate system to the geodetic coordinate system is mainly achieved by solving the inverse transformation of formula (1). The inverse transformation corresponding to formula (1) is:

[0092]

[0093] Now refer to Figure 7 The process of active in-air refueling of two receivers using the method provided by the present invention is described. Among them, the tanker refuels each receiver twice.

[0094] As shown in (a) of the figure, the tanker obtains the circle information of the receiving aircraft and sets the current position of the first receiving aircraft as the expected meeting point; then as shown in (b), the expected meeting point is updated and finally determined; then as shown in (c), the tanker determines that the expected meeting point is on the specified edge, selects it as the meeting point, and flies to the expected meeting point according to the Dubins shortest path; then as shown in (d), the tanker meets the first receiving aircraft at the expected meeting point, enters the straight path and performs aerial refueling on the straight path; then as shown in (e), the tanker completes the aerial refueling mission for the first receiving aircraft and prepares to separate from the first receiving aircraft; then as shown in (f), the current position of the second receiving aircraft is set as the expected meeting point; then as shown in (g), the expected meeting point is updated and finally determined; then as shown in (h), the tanker determines that the expected meeting point is on the specified edge, selects it as the meeting point, and then flies to the expected meeting point according to the Dubins shortest path; Then, as shown in (i), the tanker meets the second receiving aircraft at the expected meeting point, enters a straight path and performs aerial refueling on the straight path; then, as shown in (j), the tanker completes the aerial refueling mission for the second receiving aircraft, prepares to separate from the second receiving aircraft, and sets the current position of the first receiving aircraft as the expected meeting point; then, as shown in (k), the expected meeting point is updated and finally determined; then, as shown in (l), since it is determined that the expected meeting point is not on the specified edge, the expected meeting point is moved to the starting point of the specified edge; then, as shown in (m), the tanker flies to the expected meeting point according to the Dubins shortest path; then, as shown in (n), the tanker enters a circling path at the expected meeting point, circling and waiting for the first receiving aircraft; then, as shown in (o), the tanker meets the first receiving aircraft at the expected meeting point, enters a straight path and performs aerial refueling on the straight path, and then repeats (e) to (j) to complete the aerial refueling mission for the second receiving aircraft.

[0095] As described above, according to the present invention, the fuel tanker sets a predicted rendezvous point on the fixed route of the receiver aircraft, and then solves the rendezvous point in the way that the fuel tanker flies to the predicted rendezvous point along the Dubins shortest path to rendezvous with the receiver aircraft. Then, it is judged whether the solved rendezvous point is on the specified straight line segment of the racecourse. If it is, the fuel tanker flies according to the navigation points of the Dubins path. If not, the rendezvous point is moved to the starting point of the specified straight line segment, and the hovering route after the fuel tanker reaches the rendezvous point is obtained. Then, the straight flight path after the fuel tanker and the receiver aircraft rendezvous is calculated until the refueling is completed and the fuel tanker disengages from the receiver aircraft. Therefore, the present invention can ensure that an unmanned aerial vehicle with a relatively low level of intelligence flying along a fixed route can achieve the active in-air refueling task of the fuel tanker. At the same time, setting the refueling rendezvous point on the specified side of the receiver aircraft's route improves the safety and reliability of in-air refueling. In addition, the present invention can realize the route planning for the fuel tanker to refuel multiple receiver aircraft in one flight and to refuel a single receiver aircraft multiple times, thereby improving the in-air refueling efficiency and saving the refueling cost.

[0096] Next, the active in-air refueling route planning method provided by the present invention will be further described with reference to an example.

[0097] In this example, the starting coordinate points of the four points of the racecourse, the fuel tanker, and the two receiver aircraft are coordinates in the geodetic coordinate system (longitude, latitude, and altitude). First, coordinate transformation is performed on them to convert them into the local coordinate system. The coordinate values in each coordinate system during this process are shown in Table 1.

[0098] Table 1

[0099]

[0100]

[0101] Then, the predicted rendezvous points of the fuel tanker and the receiver aircraft are calculated. One fuel tanker refuels two receiver aircraft, so a total of two predicted rendezvous points need to be calculated. The coordinates of the calculated predicted rendezvous points in the local coordinate system are shown in Table 2.

[0102] Table 2

[0103]

[0104] Next, it is calculated whether hovering and turning radius are required. After calculation, hovering is not required for refueling both receiver aircraft. When refueling Receiver Aircraft One, the turning radius of the fuel tanker is 16835 m. When refueling Receiver Aircraft Two, the turning radius of the fuel tanker is 3035 m.

[0105] Simulate the entire in-air refueling process, and the in-air refueling route of the fuel tanker obtained is as Figure 8As shown in the figure. In the figure, the red aircraft is the refueling aircraft, and the blue aircraft are the refueled aircraft, with two refueled aircraft. The beam in front of the refueling aircraft is a schematic diagram of the radar, and the radar detection range is about 40 km. In this figure, the flight paths of section ① and section ③ are the results of flight path planning based on Dubins paths. The rendezvous point of the refueling aircraft and the first refueled aircraft is at the intersection of the flight path of section ① and the straight side of the racecourse. The flight path of section ② is the straight flight path when the refueling aircraft refuels the first refueled aircraft. The rendezvous point of the refueling aircraft and the second refueled aircraft is at the intersection of the flight path of section ③ and the straight side of the racecourse. The flight path of section ④ is the straight flight path when the refueling aircraft refuels the second refueled aircraft.

[0106] After the flight path calculation of the first refueled aircraft is completed, it is necessary to predict the position of the second refueled aircraft to facilitate the calculation of the flight path for aerial refueling of the second refueled aircraft. In the simulation, the second refueled aircraft flew for 442.27 s when the first refueled aircraft completed aerial refueling. Therefore, it is calculated that when the first refueled aircraft completed aerial refueling, the coordinates of the second refueled aircraft in the station-centered coordinate system were (54450.8282, 49997.2600, 8999.9885).

[0107] Perform coordinate transformation according to formula (16) to convert the station-centered coordinate system into the geographical coordinate system, and use the navigation points of longitude, latitude, and altitude in the geographical coordinate system as the input of the flight control system. The waypoints of the planned active aerial refueling flight paths for the two refueled aircraft are shown in Table 3.

[0108] Table 3

[0109]

[0110] It can be seen that this example realizes the active aerial refueling of two refueled aircraft flying along a fixed flight path, and verifies the effectiveness of the active aerial refueling flight path planning method proposed by the present invention.

[0111] Finally, it should be noted that the features mentioned and / or shown in the above description of the exemplary embodiments of the present invention can be combined in the same or similar manner into one or more other embodiments, combined with the features in other embodiments or replace the corresponding features in other embodiments. The technical solutions obtained through such combination or replacement should also be regarded as being included within the protection scope of the present invention.

Claims

1. An active in-air refueling route planning method, characterized in that It includes the following steps: Step 1: The fuel dispenser obtains the racecourse route information and the current position information of the refueling receiver aircraft to be refueled, sets the obtained current position of the receiver aircraft as the predicted rendezvous point, and the time for the receiver aircraft to move to the predicted rendezvous point in the station-centered coordinate system is t R1 , where the racecourse route includes two arcs and two straight lines that form a circle, and the two arcs are opposite to each other, and the two straight lines are opposite to each other; Step 2: Calculate the shortest path of the tanker along the Dubins path at speed v T The time required to fly to the estimated rendezvous point t T1 If t T1 With t R1 If the difference between the two is within the set rendezvous time difference threshold, the estimated rendezvous point is updated along the route direction of the receiving aircraft according to the set step length until t T1 With t R1 When the difference between them is within the set rendezvous time difference threshold, the Dubins path navigation point is output; Step 3: Determine whether the predicted rendezvous point is on the specified side, where the specified side is the straight line segment closer to the refueling aircraft in the racecourse flight path; if it is determined that the predicted rendezvous point is on the specified side, the refueling aircraft selects the current predicted rendezvous point as the rendezvous point, and the refueling aircraft tracks the Dubins path navigation point and flies to the selected rendezvous point; If it is determined that the predicted rendezvous point is not on the specified side, the tanker selects the starting point of the specified side as the rendezvous point, and the time for the receiver aircraft to move to the selected rendezvous point is t R2 , the tanker navigates to the selected rendezvous point according to the Dubins path navigation points and hovers several circles at the rendezvous point. The starting point of the specified side refers to the point where the receiver aircraft enters the straight line segment along the flight path. The hovering path is calculated as follows: First step, recalculate the time t for the fuel dispenser to reach the selected rendezvous point according to the Dubins path T2 ; Step 2: Calculate the extra distance the fuel dispenser needs to fly: S more =(t T2 -t R2 )*v T ; The third step: Calculate the hovering path of the refueling aircraft, including the number of hovering circles and the hovering radius: where r min is the minimum turning radius of the fuel tanker, and round(·) represents rounding down; if the number of turning circles n more = 0, then the method of increasing the turning radius is used to ensure that the fuel tanker and the receiver reach the rendezvous point simultaneously; if n more ≠ 0, then calculate the turning radius: Step 4: The refueling aircraft flies along the straight flight path and refuels the receiver aircraft. At the same time, it determines whether there are still receiver aircraft that need to be refueled. If so, after completing the refueling and detaching from the current receiver aircraft, the above process is repeated. If not, it returns to the set position.

2. The active in-air refueling route planning method according to claim 1, characterized in that In Step 1, the information of the receiver aircraft flight path and the current position information obtained are in the geographical coordinate system, and the information in the local geodetic coordinate system is obtained through coordinate transformation. The coordinate transformation process is as follows: The first step: Convert the coordinates of the target point P from the geographical coordinate system to the geodetic rectangular coordinate system: In the formula, (L, B, H) are the coordinates of the target point P in the geographical coordinate system, L is the geodetic longitude, B is the geodetic latitude, and H is the geodetic height; (X, Y, Z) are the coordinates of the target point P in the geodetic rectangular coordinate system; N is the radius of curvature of the prime vertical of the ellipsoid; e is the first eccentricity of the ellipsoid; The second step: Convert the coordinates of the target point P from the geodetic rectangular coordinate system to the local geodetic coordinate system: where (x, y, z) are the coordinates of point P in the station-centered coordinate system with the station-centered origin P0 as the coordinate origin; (X o , Y0, Z0) are the coordinates of the station-centered origin P0 in the geodetic coordinate system, and (L0, B0, H0) are the coordinates of the station-centered origin P0 in the geodetic coordinate system.

3. The active in-air refueling route planning method according to claim 1 or 2, characterized in that, In step 1, the time t for the receiver aircraft to move to the predicted rendezvous point in the local-level coordinate system is calculated as follows: R1 The calculation is as follows: Wherein, (x R , y R ) are the position coordinates of the fuel receiver aircraft, (x exp , y exp ) are the coordinates of the expected rendezvous point, and v R is the flight speed of the fuel receiver aircraft.

4. The active in-air refueling route planning method according to claim 1 or 2, characterized in that, Set the range of the rendezvous time difference threshold to 0 to 2 seconds.

5. The active in-air refueling route planning method according to claim 1 or 2, characterized in that, The method for the refueling aircraft to calculate the Dubins path It includes the following steps: The first step: Perform a standard transformation. Translate and rotate the starting point to the origin through coordinate transformation to obtain the standardized starting point and ending point coordinates and the straight-line distance between the starting point and the ending point; The second step: Use the obtained standardized starting point and ending point information to calculate the lengths of six Dubins paths from the starting point to the ending point; The third step: Select the Dubins path with the shortest path length among the six paths and sample waypoints on the horizontal plane; The fourth step: Calculate the height difference and determine whether the climb or descent requirements can be met according to the maximum climb rate; if it is determined that it can be met, the Dubins three-dimensional path is calculated in a uniform climbing manner. If it is determined that it cannot be met, the Dubins three-dimensional path is calculated in a rising spiral or descending spiral manner.

Images