M-shaped synchronous unfolding device for a cylindrical unmanned aerial vehicle wing

Abstract

The application discloses a novel M-shaped synchronous unfolding device for a barrel launching unmanned aerial vehicle wing, and relates to the technical field of unmanned aerial vehicles. The wing bearing plate comprises a cartridge positioning device, a boss, a circular arc groove, an inner wing shaft, a transmission gear shaft, an inner wing spring pin hole and a rectangular block. The folded wing group comprises an inner wing, an outer wing, a tooth, a stepped shaft, a torsional spring and an outer wing spring pin. The toothed end of the inner wing is a root part and is fixed on the inner wing shaft. The inner wing spring pin hole is arranged at the horizontal center line of the non-toothed end of the inner wing and is matched with the lower end of the torsional spring. The outer wing spring pin is arranged at a point of the horizontal center line of the outer wing and is matched with the lower end of the torsional spring. The gear unfolding mechanism comprises two transmission gears, a rack, a rack transmission rod and a cartridge. The application is beneficial to the miniaturization of the barrel launching unmanned aerial vehicle and facilitates transportation and launching in various environments.

Description

Technical Field

[0001] This invention relates to the field of unmanned aerial vehicle (UAV) technology, particularly the field of UAV wing rotation technology, and specifically to a folding wing unfolding pivot mechanism. Background Technology

[0002] Foldable-wing drones have the advantages of small size and easy portability when folded. Furthermore, swarm drones have become a hot topic, with most swarm drones launched via catapults, cannons, or aerial launch. To meet the requirements of cannon launch, most cannon-launched swarm drones use foldable wings. The synchronous deployment mechanism of the folding wings is a key technology for this type of aircraft.

[0003] The design of the folding wing pivot mechanism is a technical challenge. The mechanism requires that the folding size of the wing be small enough for easy transport and launch, that the pivot mechanism can quickly and reliably complete the synchronous deployment of the left and right wings in a very short time, and that the position be locked when the wings are deployed. Summary of the Invention

[0004] The purpose of this invention is to provide a tube-launched unmanned aerial vehicle (UAV) wing M-shaped synchronous deployment device.

[0005] The technical solution to achieve the purpose of this invention is: a cannon-launched UAV wing M-shaped synchronous deployment device, comprising a wing support plate, a pair of folding wing assemblies, and a gear deployment mechanism, wherein:

[0006] The wing bearing plate includes a gunpowder cartridge positioning device, a boss, an arc groove, an inner wing shaft, a transmission gear shaft, an inner wing spring pin hole, and a rectangular block; the gunpowder cartridge positioning device and the boss are located at the axis of the wing bearing plate; the transmission gear shaft, the inner wing shaft, and the rectangular block are symmetrically arranged on both sides of the boss from the inside to the outside, and the axes of the transmission gear shaft and the inner wing shaft are located on the same plane; an arc groove coaxial with the inner wing shaft is provided on the outer side of the inner wing shaft;

[0007] The folding wing assembly includes an inner wing, an outer wing, teeth, a stepped shaft, a torsion spring, and an outer wing spring pin. The stepped shaft serves as a rotation axis, and a torsion spring is mounted on it. One end of the inner wing has teeth, while the other end is toothless. The toothed end of the inner wing forms the root and is fixed to the inner wing shaft. An inner wing spring pin is located at the horizontal centerline, with its lower end embedded in an arc groove. An inner wing torsion spring hole is located at the horizontal centerline of the toothless end, engaging with the lower end of the torsion spring. The upper surface of the inner wing shaft is in close contact with the stepped shaft and does not rotate relative to it. An outer wing spring pin is located at a point on the horizontal centerline of the outer wing, with its lower end in contact with the plane of the stepped shaft. An outer wing torsion spring hole is located on the horizontal centerline of the outer wing, further away from the outer wing rotation axis than the outer wing spring pin, engaging with the upper end of the torsion spring. The lower surface of the outer wing shaft is in close contact with the stepped shaft and will rotate relative to it.

[0008] The gear deployment mechanism includes two transmission gears, a rack, a rack transmission rod, and a gunpowder cartridge. The transmission gears have transmission gear bearings at both the top and bottom to ensure normal rotation. The rack is placed on the boss of the wing bearing plate. Teeth on both sides of the rack mesh with the transmission gears, and the other side of the transmission gear meshes with the teeth on the outer circumferential surface of the inner wing. The rack transmission rod at the tail of the rack is inserted into the gunpowder cartridge fixed on the bearing plate. The gunpowder cartridge is fixed on the wing bearing plate by a gunpowder cartridge positioning device.

[0009] Furthermore, the rectangular block has an elastic rubber block on the inner wing shaft edge as an energy-absorbing buffer. When the wing rotates to a limited position, the wing abuts against the energy-absorbing buffer.

[0010] Furthermore, the starting point of the arc groove is located on the wing bearing plate below the centerline of the inner wing, with an outward rotation angle of 90°. At the end of the arc groove, there is an inner wing spring pin hole. When the inner wing is unfolded to 90°, the inner wing stops moving when it abuts against the rectangular block, and the inner wing spring pin slides into the inner wing spring pin hole at the end of the arc groove, thereby achieving the limiting of the inner wing.

[0011] Furthermore, the inner wing is also equipped with an inner wing bearing, an inner wing cover plate, and an inner wing bolt arranged from bottom to top along the rotation axis of the inner wing. The inner wing is fixed to the inner wing axis by the inner wing cover plate and the inner wing bolt, and inner wing bearings are arranged above and below it to ensure that the inner wing can rotate normally when subjected to lift.

[0012] Furthermore, the outer wing is also equipped with an outer wing bearing, an outer wing cover plate, and an outer wing bolt arranged from bottom to top along the rotation axis of the outer wing. The outer wing bolt and the outer wing cover plate connect the outer wing to the stepped shaft, and the outer wing bearing is provided between the outer wing cover plate and the outer wing to ensure that the outer wing can rotate normally when subjected to lift.

[0013] Furthermore, the stepped shaft is also equipped with a spring pin recess for the outer wing. When the outer wing is extended to 180°, the torsion spring stops pulling the outer wing, and the spring pin of the outer wing slides into the spring pin recess in the stepped shaft, thereby achieving the limiting of the outer wing.

[0014] Furthermore, a weight-reducing groove is provided between the boss and the gunpowder cartridge positioning device on the wing bearing plate.

[0015] Furthermore, the transmission gear bearing (5), transmission gear (3), transmission gear bearing (5), transmission gear cover plate (31), and transmission gear screw (24) are arranged from bottom to top with the transmission gear shaft (26) as the axis to achieve stable transmission during the unfolding process of the transmission gear (3).

[0016] Furthermore, the drone is in a folded state when launched from the outer shell. The unfolding of the inner and outer wings is restricted by the shell wall. After launch, the drone separates from the missile body and detonates the gunpowder in the gunpowder cartridge, causing the inner wings to unfold. At the same time, the torsion spring causes the inner and outer wings to move relative to each other, causing the wing assembly to unfold in an M-shape. When all four wings are unfolded, they are on the same straight line.

[0017] Compared with the prior art, the significant advantages of this invention are:

[0018] The two-section deployment allows the wing to be folded to half the length of a single-section deployment, resulting in a shorter wing mechanism compared to a single-section deployment, which facilitates the optimization of the internal structure of the launcher.

[0019] After the external cartridge case restraints the wings, the inner wing deployment section is driven by the propellant in the cartridge, which moves the rack and pinion mechanism, causing the transmission gears on both sides to rotate. This rotation of the transmission gears then drives the teeth on the outer circumference of the left and right inner wings to rotate synchronously, achieving simultaneous deployment of both wings. The left and right wings use independent rotation axes, which simplifies the connection compared to a coaxial deployment mechanism and ensures reliable connection at the wing root. The rack and pinion transmission method is more compact and provides smoother rotation compared to using torsion springs at the root. The outer wing deployment section is driven by torsion springs, causing it to deploy in the opposite direction to the rotation of the inner wing, resulting in an M-shaped deployment of both wings and ensuring that the deployment of the left and right wings does not interfere with each other.

[0020] Except for the use of electronic devices to detonate the gunpowder, the rest are purely mechanical mechanisms. Apart from the electromagnet, the invention consists of purely mechanical components, which have a simple structure, low failure rate, high reliability, and are easy to use. Attached Figure Description

[0021] Figure 1 This is a schematic diagram of the folded state of the wing of the present invention.

[0022] Figure 2 This is a schematic diagram of the M-shaped unfolding process of the present invention.

[0023] Figure 3 This is a schematic diagram of the fully deployed state of the present invention.

[0024] Figure 4 This is a schematic diagram of the outer wing deployment device of the present invention without a torsion spring.

[0025] Figure 5 This is a schematic diagram of the torsion spring installation of the present invention.

[0026] Figure 6 A schematic diagram of the installation of the inner wing spring pin in this invention.

[0027] Figure 7 This is a schematic diagram of the wing support plate of the present invention.

[0028] In the diagram: 1. Rectangular block; 2. Inner wing tooth; 3. Transmission gear; 4. Boss; 5. Transmission gear bearing; 51. Inner wing bearing; 6. Inner wing cover plate; 7. Arc groove; 8. Wing bearing plate; 9. Inner wing; 10. Outer wing; 11. Torsion spring; 12. Inner wing torsion spring hole; 13. Outer wing bearing; 14. Powder cartridge; 15. Powder cartridge positioning device; 16. Rack; 17. Outer wing cover plate; 18. Inner wing bolt; 19. Inner wing shaft; 20. Inner wing spring pin hole; 21. Outer wing torsion spring hole; 22. Outer wing spring pin recess; 23. Outer wing spring pin; 24. Transmission gear screw; 25. Stepped shaft; 26. Transmission gear shaft; 27. Weight reduction groove; 28. Inner wing spring pin; 29. ​​Outer wing bolt; 30. Rack drive rod; 31. Transmission gear cover plate. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0030] Please see Figures 1-7 A novel cannon-launched UAV wing M-shaped synchronous deployment device includes a wing support plate 8, a folding wing assembly, and a gear deployment mechanism; combined with Figure 7 The wing support plate 8 includes a gunpowder cartridge positioning device 15, a boss 4, an arc groove 7, an inner wing shaft 19, a transmission gear shaft 26, an inner wing spring pin hole 20, and a rectangular block 1. The wing support plate 8 has the inner wing shaft 19 and the transmission gear shaft 26 as its front side. The gunpowder cartridge positioning device 15 and the boss 4 are symmetrically arranged along the axis of the wing support plate 8. The transmission gear shaft 26 and the inner wing shaft 19 are symmetrically arranged on both sides of the boss 4 along the axis of the wing support plate 8. The axes of the transmission gear shaft 26 and the inner wing shaft 19 are located on the same plane. The rectangular block 1 is provided next to the inner wing shaft, and the arc groove 7 is coaxial with the inner wing shaft. The inner wing spring pin hole 20 is located at the end of the arc groove 7.

[0031] Preferably, the wing bearing plate 8 has a weight reduction groove 27 between the boss 4 and the gunpowder cartridge positioning device 15.

[0032] Combination Figures 4-5The folding wing assembly includes an inner wing 9, an outer wing 10, teeth 2, a stepped shaft 25, a torsion spring 11, an inner wing bearing 51, an inner wing cover plate 6, an inner wing bolt 18, an outer wing bearing 13, an outer wing cover plate 17, an outer wing bolt 29, and an outer wing spring pin 23. The stepped shaft 25, from bottom to top, engages with the toothless side of the inner wing 9, the torsion spring 11, and the outer wing 10. The inner wing 9, from bottom to top, has an inner wing bearing 51 and an inner wing cover plate arranged around its rotation axis. Plate 6, inner wing bolt 18; outer wing 10 is arranged from bottom to top with the rotation axis of outer wing 10 as the axis, outer wing bearing 13, outer wing cover plate 17, outer wing bolt 29, outer wing spring pin 23 is set on the horizontal center line of outer wing next to the rotation axis of outer wing, and the lower end of the outer wing spring pin 23 is in contact with the stepped shaft 25; the upper surface of the shaft part of inner wing 9 is in close contact with the stepped shaft 25 and does not rotate relative to it, and the lower surface of the shaft part of outer wing 10 is in close contact with the stepped shaft 25.

[0033] Combination Figures 1-3 The gear deployment mechanism includes two transmission gears 3, a rack 16, a rack transmission rod 30, and a gunpowder cartridge 14. The transmission gears 3 have transmission gear bearings 5 ​​at both the top and bottom to ensure normal rotation. The rack 16 is placed on the boss 4 of the wing support plate 8. The rack 16 has teeth on both sides that mesh with the transmission gears 3. The rack transmission rod 30 at the tail of the rack 16 is inserted into the gunpowder cartridge 14 which is fixed on the wing support plate 8. The gunpowder cartridge 14 is fixed on the wing support plate 8 by a gunpowder cartridge positioning device 15.

[0034] Preferably, the transmission gear bearing (5), transmission gear (3), transmission gear bearing (5), transmission gear cover plate (31), and transmission gear screw (24) are arranged from bottom to top with the transmission gear shaft (26) as the axis, so as to achieve stable transmission during the unfolding process of the transmission gear (3).

[0035] To drive the gunpowder cartridge 14 to move linearly, the gunpowder cartridge 14 is fixed to the wing bearing plate 8 by the gunpowder cartridge positioning device 15. When deployed, the gunpowder in the gunpowder cartridge 14 explodes, causing the rack 16 to move linearly.

[0036] Combination Figures 1-3 The inner wing 9 is a machined part, including teeth 2, an inner wing spring pin 28, and an inner wing torsion spring hole 12. The inner wing spring pin 28 is located at the horizontal centerline of the toothed end of the outer circumference of the inner wing 9, with its lower end embedded in an arc groove 7. The inner wing torsion spring hole 12 is located at the horizontal centerline of the other end of the inner wing 9, engaging with the lower end of the torsion spring 11. The geared end of the outer circumference of the inner wing 9 forms its root, which is fixed to the inner wing shaft 19 by the inner wing cover plate 6 and inner wing bolts 18. Inner wing bearings 51 are arranged above and below it to ensure that the inner wing 9 can rotate normally under lift.

[0037] To drive the inner wings 9 to rotate and open, teeth 2 are arranged on an arc segment exceeding 1 / 4 of the circumference of the outer circumference of the left and right inner wings 9. A transmission gear 3 is arranged between the two inner wing pivots, meshing with the inner wing teeth 2. A rack 16 is mounted on a boss 14 of the wing support plate 8 and can slide along the length of the boss 14. The linear motion of the rack 16 drives the transmission gear 3 to rotate, which in turn drives the inner wings 9 to rotate, thus opening the inner wings 9. The rotation angle is 0-90°.

[0038] like Figures 4-5 The stepped shaft 25 is used as the rotation axis. Countersunk screws 30 are used to connect the inner wing and the stepped shaft 25. The outer wing bolts 29 and the outer wing cover plate 17 are used to connect the outer wing 10 and the stepped shaft 25. An outer wing bearing 13 is provided between the outer wing cover plate 17 and the outer wing 10 to ensure that the outer wing 10 can rotate normally when subjected to lift.

[0039] To drive the outer wing 10 to rotate and open, a torsion spring 11 is provided in the middle section of the stepped shaft 25. The upper end of the torsion spring 11 is bent and fixed to the torsion spring hole 12 of the outer wing, and the lower end is bent and fixed to the torsion spring hole 21 of the inner wing.

[0040] like Figures 2-3 As described above, after the cartridge case is removed, it starts to rotate simultaneously with the inner wing 9. The inner and outer wings rotate in opposite directions, and the outer wing rotates at an angle of 0-180°, thereby achieving the deployment of the M-shaped wing.

[0041] To achieve locking after wing deployment, the inner wing 9 has a toothed end with an inner wing spring pin 28, the lower end of which is embedded in the arc groove 7. The inner wing spring pin 28 rotates with the inner wing 9, with a rotation angle of 0-90°. The arc groove 7 has an inner wing spring pin hole 20 at the end of the rotation. When the inner wing spring pin 28 rotates to the end, its head enters the inner wing spring pin hole 20 to achieve inner wing locking.

[0042] Combination Figure 4 The middle section of the stepped shaft 25 is parallel to the inner wing 9 and is located at a point on the axis away from the inner wing 9. There is an outer wing spring pin pit 22. The outer wing 10 is provided with an outer wing spring pin 23 on its side. When the outer wing 10 rotates, the outer wing spring pin 23 rotates accordingly. After rotating 180°, it slides into the outer wing spring pin pit 22, thereby locking the inner and outer wings together.

[0043] When all four wings are deployed, they are aligned in a straight line.

[0044] Combination Figure 7 The wing bearing plate 8 is characterized in that there is a rectangular block 1 on the inner wing shaft side edge, and the rectangular block 1 has an elastic rubber block of appropriate thickness as an energy-absorbing buffer. When the wing rotates to a limited position, the wing abuts against the energy-absorbing buffer, thereby achieving energy absorption and buffering when the wing is fully deployed.

[0045] This invention employs a two-stage deployment mechanism, reducing the wing's folded length to half that of a single-stage deployment. Compared to a single-stage deployment mechanism, this shorter wing length facilitates optimization of the projectile's internal structure. The left and right wings utilize independent rotation axes, simplifying the connection compared to coaxial deployment mechanisms and ensuring reliable connection at the wing root. The transmission is achieved through a rack and pinion mechanism, resulting in a more compact structure and smoother rotation compared to using torsion springs at the root. The outer wing deployment section is driven by torsion springs, unfolding in the opposite direction to the inner wing's rotation, creating an M-shape and preventing interference between the left and right wing deployments. Except for the electronic components required for detonating the propellant, the entire invention is purely mechanical. Apart from the electromagnet, the other purely mechanical components result in a simple structure, low failure rate, high reliability, and ease of use, representing an optimization and improvement for UAV wing deployment mechanisms.

[0046] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Those skilled in the art can still make modifications to the foregoing technical solutions or equivalent substitutions for some of the technical features. Any modifications made without departing from the spirit and scope of the present invention should fall within the protection scope of the present invention.

Claims

1. A cannon-launched UAV wing M-shaped synchronous deployment device, characterized in that, Includes wing support plate (8), a pair of folding wing assemblies, and a gear deployment mechanism, wherein: The wing support plate (8) includes a gunpowder cartridge positioning device (15), a boss (4), an arc groove (7), an inner wing shaft (19), a transmission gear shaft (26), an inner wing spring pin hole (20), and a rectangular block (1). The gunpowder cartridge positioning device (15) and the boss (4) are located at the axis of the wing support plate. The transmission gear shaft (26), the inner wing shaft (19), and the rectangular block (1) are symmetrically arranged on both sides of the boss (4). The axes of the transmission gear shaft (26) and the inner wing shaft (19) are located on the same plane. The transmission gear shaft (26) is closest to the boss (4), the inner wing shaft (19) is centered to the boss (4), and the rectangular block (1) is furthest from the boss (4). An arc groove (7) coaxial with the inner wing shaft is provided on the outer side of the inner wing shaft (19). The folding wing assembly includes an inner wing (9), an outer wing (10), teeth (2), a stepped shaft (25), a torsion spring (11), and an outer wing spring pin (23). The stepped shaft (25) serves as a rotation axis, on which the torsion spring (11) is mounted. One end of the inner wing (9) is provided with teeth (2), while the other end is toothless (2). The toothed end of the inner wing (9) is the root, fixed to the inner wing shaft (19). An inner wing spring pin (28) is set at the horizontal centerline, with the lower end of the inner wing spring pin (28) embedded in an arc groove (7). The toothless end of the inner wing (9) is provided at the horizontal centerline. The inner wing torsion spring hole (12) is fitted with the lower end of the torsion spring (11), and the upper surface of the inner wing (9) shaft is in close contact with the lower surface of the middle section of the stepped shaft (25) without relative rotation; an outer wing spring pin (23) is set at a point on the horizontal centerline of the outer wing (10), and its lower end is in contact with the plane of the stepped shaft (25). An outer wing torsion spring hole (21) is set on the horizontal centerline of the outer wing (10) at a distance from the outer wing rotation axis than the outer wing spring pin (23), and it is fitted with the upper end of the torsion spring (11). The lower surface of the outer wing (10) shaft is in close contact with the upper surface of the middle section of the stepped shaft (25) and relative rotation occurs. The gear deployment mechanism includes two transmission gears (3), a rack (16), a rack transmission rod (30), and a gunpowder cartridge (14). The transmission gears (3) are equipped with transmission gear bearings (5) on both the top and bottom to ensure normal rotation of the transmission gears (3). The rack (16) is placed on the boss (4) of the wing support plate (8). The rack (16) has teeth on both sides that mesh with the transmission gears (3). The other side of the transmission gears (3) meshes with the teeth (2) on the outer peripheral surface of the inner wing (9). The rack transmission rod (30) at the tail of the rack is inserted into the gunpowder cartridge (14) fixed on the support plate. The gunpowder cartridge (14) is fixed on the wing support plate (8) by the gunpowder cartridge positioning device (15).

2. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, The rectangular block (1) is located on the inner wing shaft side edge. The rectangular block (1) has an elastic rubber block as an energy-absorbing buffer. When the wing rotates to a limited position, the wing abuts against the energy-absorbing buffer.

3. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, The starting point of the arc groove (7) is located on the wing support plate (8) below the centerline of the inner wing, and rotates outward at an angle of 90°. There is an inner wing spring pin hole (20) at the end of the arc groove. When the inner wing (9) is unfolded to 90°, the inner wing (9) stops moving when it touches the rectangular block (1), and the inner wing spring pin (28) slides into the inner wing spring pin hole (20) at the end of the arc groove, thereby achieving the limiting of the inner wing (9).

4. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, The inner wing (9) is also equipped with an inner wing bearing (51), an inner wing cover plate (6), and an inner wing bolt (18) arranged from bottom to top with the rotation axis of the inner wing (9) as the axis. The inner wing (9) is fixed to the inner wing shaft (19) by the inner wing cover plate (6) and the inner wing bolt (18). The inner wing bearing (51) is arranged above and below it to ensure that the inner wing (9) can rotate normally when subjected to lift.

5. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, The outer wing (10) is arranged from bottom to top with the rotation axis of the outer wing (10) as the axis, and also includes an outer wing bearing (13), an outer wing cover plate (17), and an outer wing bolt (29). The outer wing bolt (29) and the outer wing cover plate (17) connect the outer wing (10) and the stepped shaft (25). The outer wing bearing (13) is set between the outer wing cover plate (17) and the outer wing (10) to ensure that the outer wing (10) can rotate normally when subjected to lift.

6. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, The stepped shaft (25) is also provided with an outer wing spring pin pit (22). When the outer wing (10) is extended to 180°, the torsion spring (11) stops pulling the outer wing (10), and the outer wing spring pin (23) slides into the outer wing spring pin pit (22) in the stepped shaft, thereby realizing the limiting of the outer wing (10).

7. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, The wing bearing plate (8) has a weight reduction groove (27) between the boss (4) and the gunpowder cartridge positioning device (15).

8. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, With the transmission gear shaft (26) as the axis, the transmission gear bearing (5), transmission gear (3), transmission gear bearing (5), transmission gear cover plate (31), and transmission gear screw (24) are arranged from bottom to top to achieve stable transmission during the unfolding process of the transmission gear (3).

9. The tube-launched UAV wing M-shaped synchronous deployment device according to claim 1, characterized in that, When the UAV is launched with the shell, it is in a folded state. The unfolding of the fold between the inner wing (9) and the outer wing (10) is restricted by the shell wall. After launch, the UAV separates from the shell and detonates the gunpowder in the gunpowder cartridge (14) to unfold the inner wing (9). At the same time, the torsion spring (11) causes the inner wing (9) and the outer wing (10) to move relative to each other, so that the wing assembly unfolds in an M shape. When the four wings are unfolded, the four wings are on the same straight line.

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