A counter-rotating propeller with double-degree-of-freedom foldable blades

Abstract

The present invention belongs to the field of propeller propellers. It relates to a counter-rotating propeller propeller with blades that can be folded in two degrees of freedom. After adopting the folding mechanism of the present invention, the folding blades are respectively close to the shell and the tail cone. Compared with the non-foldable type, the outer width diameter of the propeller can be reduced by more than 40%, reaching the required diameter of the storage space. The folding first-stage blades and the folding second-stage blades are folded forward and backward respectively, each close to the shell and the tail cone to avoid mutual interference. The blades can be unfolded around the horizontal axis, and the horizontal axis can rotate in the double fan-shaped slide groove. This single-structure double-degree-of-freedom cooperation mode realizes the minimum folding of the blades. The telescopic door enables the folding blades to open in one direction, and cooperates with the outer end cover to form an approximately complete spherical shell, reducing the flow resistance of the folding mechanism during the flight of the propeller. At the same time, the folding mechanism realizes the double-degree-of-freedom rotation of the propeller, meets the demand for changing the angle of attack of the blade airflow, and ensures the propulsion efficiency of the counter-rotating propeller propeller.

Description

Technical Field

[0001] The present invention belongs to the field of propeller fan propellers and relates to a counter-rotating propeller fan propeller with double-degree-of-freedom foldable blades. Background Art

[0002] Turboprop engines have the advantage of low fuel consumption, turbofan engines have the advantage of high flight speed, and propfan engines combine the advantages of both. The use of counter-rotating propellers can improve the overall flight performance of aircraft. Currently, the mainstream counter-rotating propellers often use non-foldable blades, and their typical structure is as follows: Figure 1 As shown, it includes a housing, a primary shaft, a secondary shaft, a fixed primary blade, a primary hub, a fixed secondary blade, a secondary hub and a tail cone. The two shafts drive the two hubs to rotate respectively, so as to transfer the shaft power output from the engine (not shown) to the two-stage fixed blades. The fixed blades are fixed to the propeller hub at an installation angle that meets the aerodynamic performance, and the rotation generates thrust to push the aircraft forward. Aircraft generally increase the propeller diameter and increase the windward area under the condition that the material strength allows, in order to pursue higher thrust and economy. However, various aircraft on aircraft carriers, missiles in the bomb bay, and drones in the launcher have special requirements for their storage space in the non-working state. Too long blades will increase the required storage space, increasing the difficulty and cost of installation, transportation, and storage. Therefore, it is necessary to fold the blades so that the diameter of the space occupied by the aircraft in the storage state is smaller than the required storage space diameter. However, the cross-section of the fan blade is an airfoil, which gradually becomes thinner and smaller from the root to the tip, has a certain angle of twist, and is overall swept-back saber-shaped. Therefore, the minimum storage cannot be achieved by simply rotating around a single axis, that is, bending in only one direction cannot make it fit tightly against the shell and the hub.

[0003] Some propeller-fan propellers use multiple hinges or complex electric devices to achieve double-degree-of-freedom folding of the propeller-fan blades, that is, from folding to opening and rotating around the propeller's own axis. However, the complex folding mechanism increases the number of parts and reduces the safety of the propeller during operation. At the same time, more parts increase the weight of the propeller, resulting in a decrease in the thrust-to-weight ratio of the propeller, which greatly restricts the installation and operation of the propeller-fan propeller. Therefore, the problem of double-degree-of-freedom minimum folding of the propeller-fan propeller blades is raised. The present invention proposes a single-structure double-degree-of-freedom rotating blade technology to solve the above problem. Summary of the invention

[0004] In order to solve the problem that the propeller takes up too much space and the blades are difficult to store, a counter-rotating propeller propeller with double-degree-of-freedom foldable blades was invented. The propeller can rotate from the folded state to the unfolded state, and the blades can rotate around their own axis and change the airflow angle of attack with a single structure.

[0005] The technical solution adopted by the present invention is:

[0006] The present invention has a particularity - the first-stage rotor and the second-stage rotor have similarities, but some structures are different. Therefore, the following description will first be described in detail using the first stage as an example, and the second stage is the same as the first stage, but the structure that is different from the first stage will be described separately.

[0007] A contra-rotating propeller propeller with double-degree-of-freedom foldable blades, as shown in FIGS. 2 and 3, comprises a housing, a primary rotating shaft, a secondary rotating shaft, a primary hub, a secondary hub, a primary folding mechanism, a primary foldable blade assembly, a secondary foldable blade assembly, a secondary folding mechanism and a tail cone, wherein the number of the primary folding mechanism is consistent with the number of the primary foldable blade assembly, which can be 6 to 10. The number of the secondary folding mechanism is consistent with the number of the secondary foldable blade assembly, which can be 5 to 8, and the number of the secondary foldable blade assembly must be equal to or less than the number of the primary foldable blade assembly.

[0008] The shell is a part of the aircraft, as shown in Figure 2, and serves to connect the aircraft and the propeller, wrap the propeller, and make the airflow smooth. The primary shaft and the secondary shaft are hollow shafts, which drive the primary hub and the secondary hub to rotate respectively under the drive of the engine. The primary hub and the secondary hub connect the two-stage shaft and the base, and transmit the shaft power output by the engine to the primary foldable blade assembly and the secondary foldable blade assembly. The tail cone, as part of the propeller fairing shape, plays a role in reducing resistance.

[0009] The primary folding mechanism and the secondary folding mechanism are semi-ellipsoidal as a whole, and the enlarged views of area I in the unfolded and folded states of the fan blades are shown in Figures 4 and 4 respectively. The main structure includes a base, an outer end cover, a telescopic door, a locking pin, a straight spring, a locking pin slot, a fastening screw, a locking washer and an inner end cover. The primary foldable fan blade assembly belongs to the primary folding mechanism, including foldable primary fan blades, a primary longitudinal axis, and a primary transverse axis. The secondary foldable fan blade assembly belongs to the secondary folding mechanism, including foldable secondary fan blades, a secondary longitudinal axis, and a secondary transverse axis.

[0010] Now combined Figure 5The assembly diagram of the foldable fan blade and folding mechanism is used to illustrate the overall structure of the first-level folding mechanism and the assembly relationship between the various parts: the locking pin is inserted into the locking pin groove at the center of the base with the straight spring. The first-level longitudinal axis is placed in the longitudinal axis storage groove on the base, and the first-level transverse axis is placed in the half double-sector groove of the base, and the foldable first-level fan blade is close to the shell. At the same time, the locking pin is inserted into the folding locking pin hole on the first-level transverse axis under the push of the straight spring preload. The hole is a spherical crown-shaped pit smaller than the hemisphere. The inner end cover is placed on the base so that the inner end cover longitudinal axis slide groove is aligned with the longitudinal axis storage groove, and the half double-sector groove on its inner surface cooperates with the half double-sector groove on the base to form a complete double-sector slide groove, which wraps the first-level transverse axis and completes the assembly of the first-level foldable fan blade assembly. The arc-shaped spring is installed in the inner end cover telescopic door groove on the outer surface of the inner end cover. The telescopic door is placed on the telescopic door slot of the inner end cover, and the four anti-drop pins are inserted into the four anti-drop pin holes in the telescopic door. The outer end cover is placed on the base and the inner end cover, so that the longitudinal axis slide groove of the outer end cover is aligned with the longitudinal axis slide groove of the inner end cover, and the telescopic door slot of the outer end cover cooperates with the telescopic door slot of the inner end cover to form a complete telescopic door slide groove. The length of the anti-drop pin is greater than the anti-drop pin hole, and the excess part extends into the anti-drop pin slide groove in the telescopic door slot of the outer end cover to complete the assembly of the telescopic door. The five fastening screws cooperate with the anti-loosening washers and the five through holes of the outer end cover, and are inserted into the fastening screw holes in the form of five non-uniformly distributed blind holes on the outer circle of the circumference of the base, and the above parts are fixed to the base to complete the assembly of the first-level folding mechanism. The second-level folding mechanism is the same as the first-level, and the multiple folding structures in the first-level rotor and the second-level rotor are also the same.

[0011] The first-stage foldable fan blade assembly includes a foldable first-stage fan blade, a first-stage longitudinal axis and a first-stage transverse axis. The cross-section of the foldable first-stage fan blade is an airfoil, which gradually becomes thinner and smaller from the root to the tip, and has a certain angle of twist, and is overall in a swept saber shape. The first-stage longitudinal axis connects the foldable first-stage fan blade and the first-stage transverse axis, transmits the engine torque to the foldable first-stage fan blade to do work on the airflow, and bears the centrifugal load and bending moment generated when the fan blade rotates. When working, the foldable first-stage fan blade absorbs the shaft work transmitted by the engine and rotates, generating thrust that is transmitted to the propeller through the outer end cover, the inner end cover, the first-stage transverse axis, the locking pin, the base and the first-stage hub, as shown in Figure 2. The second stage is the same as the first stage.

[0012] The primary longitudinal axis is a column with a runway-shaped cross section. When the propeller is in the folded state, the primary longitudinal axis is placed in the longitudinal axis storage groove on the base. The pre-compressed straight spring in the locking pin groove pushes the locking pin into the folding locking pin hole on the primary transverse axis. The hole is a spherical crown-shaped pit smaller than a hemisphere. By cooperating with the spherical surface of the locking pin head, a locking force is provided for the folding primary blade to ensure that it is fixed in the folded position when the propeller is stationary and rotating at a low speed, preventing it from opening due to gravity, small centrifugal force or vibration, so that the folding primary blade and the folding secondary blade are respectively close to the shell and the tail cone, as shown in Figure 4 (b) and Figure 6 (b), completing the locking of the primary folding mechanism in the folded state. After the rotation speed of the primary shaft exceeds the critical speed, the critical speed range is 600rpm~1000rpm, the primary folding mechanism will release the locking state and perform the double-degree-of-freedom rotation of the blade, that is, the primary longitudinal axis deflection and the primary transverse axis deflection. When the primary longitudinal axis deflects, that is, the primary longitudinal axis and the folding primary blade rotate around the primary transverse axis, the telescopic door is first pushed open, and then slides along the complete longitudinal axis slide groove formed by the inner end cover longitudinal axis slide groove and the outer end cover longitudinal axis slide groove on the inner and outer end covers, so that the folding primary blade transitions from the folded state to the unfolded state, completing the rotation of the blade unfolding freedom, which is the first degree of freedom. The secondary and primary are the same.

[0013] The primary horizontal axis is a cylinder with spherical surfaces at both ends. After the primary longitudinal axis reaches the maximum expansion position, the primary horizontal axis is deflected immediately, that is, the primary horizontal axis and the folding primary blade rotate around the primary longitudinal axis, and slide along the double fan-shaped slide groove formed by the base and the inner end cover, so that the folding primary blade can rotate around its own axis to meet the change of the airflow angle of attack, and complete the rotation of the blade's own axis freedom, which is the second degree of freedom. The horizontal axis sweep angle is determined according to the airflow angle of attack at the design point, and the general value range is 35° to 55°, as shown in Figure 6 (a) and Figure 6 (b). When the propeller is in the expanded state, that is, after the primary blade 17 completes the rotation of two degrees of freedom, the locking pin enters the expansion locking pin hole of the primary horizontal axis under the push of the straight spring, and the locking pin uses the cooperation of the quadrangular prism surface to prevent the blade from rotating around the horizontal axis and the longitudinal axis. And due to the centrifugal force and the tightening force of the straight spring, the locking pin cannot be disengaged from the folding locking pin hole, making the unfolding process of the folding first-stage fan blade irreversible, avoiding the fan blade rebound caused by aerodynamic force. As shown in Figures 4 and 6, the first-stage folding mechanism is locked in the unfolded state. The second stage is the same as the first stage.

[0014] The telescopic door is a two-piece spherical fan-shaped door, both of which have the function of one-way opening, that is, the primary longitudinal axis can push the door open from folding to unfolding, but cannot be reversed. The telescopic door is matched with an arc-shaped spring in a compressed state and placed in the telescopic door slot of the outer end cover and the telescopic door slot of the inner end cover to form a complete telescopic door slide slot, and can slide in the telescopic door slide slot along the moving direction of the telescopic door. The sliding direction is an arc shape, and the angle range corresponding to the axis is 50° to 70°. At the same time, a total of 4 anti-drop pin holes are opened along the diameter direction of the telescopic door spherical surface, and 4 anti-drop pins are inserted into the 4 anti-drop pin holes. The length of the anti-drop pin is greater than the anti-drop pin hole, and the excess part thereof extends into the anti-drop pin slide slot in the telescopic door slot of the outer end cover, and can slide in the anti-drop pin slide slot with the sliding of the telescopic door. Its rotation direction and angle range are consistent with the telescopic door to prevent the telescopic door from falling off the slot. When the propeller is in a working state, the primary rotating shaft and the secondary rotating shaft drive the primary wheel hub and the secondary wheel hub to rotate. As the speed of the first-stage shaft increases, the centrifugal force on the first-stage foldable fan blade assembly also increases. When the speed exceeds the critical speed, the critical speed range is 600rpm~1000rpm, and the centrifugal force on the first-stage foldable fan blade assembly exceeds the preload force of the straight spring, the first-stage longitudinal axis pushes open the telescopic door, and at the same time drives the first-stage horizontal axis to push the locking pin into the locking pin groove, releasing the locking state of the first-stage foldable fan blade assembly. At this time, the telescopic door is pushed open by the first-stage longitudinal axis relying on the inclined surface at the bottom, and then, under the guidance of the anti-drop pin, it is retracted into the telescopic door slide groove along the moving direction of the telescopic door, revealing a complete longitudinal axis slide groove composed of the outer end cover longitudinal axis slide groove and the inner end cover longitudinal axis slide groove. When the first-stage longitudinal axis reaches the maximum expansion position, the telescopic door is pushed by the arc-shaped spring, cooperates with the anti-drop pin and the anti-drop pin slide groove to close along the moving direction of the telescopic door, and forms an approximately complete spherical shell with the outer end cover, such as Figure 7 As shown, the reverse movement of the folding first-stage fan blades is prevented, and the flow resistance of the first-stage folding mechanism in the propeller during flight is reduced. While the telescopic door is closed, the first-stage horizontal axis further slides along the double-fan-shaped slide groove, completes the rotation direction around the longitudinal axis, and reaches the final working position of full expansion, as shown. Figure 7 The dotted line fan blades are shown. The second level is the same as the first level.

[0015] The present invention realizes the double-degree-of-freedom rotation of the propeller with a simple folding mechanism, solving the problem that the propeller occupies too much space and the blades are difficult to store. The primary longitudinal axis cooperates with the longitudinal axis slide groove to realize the rotation of the blade expansion freedom (first degree of freedom), and the primary transverse axis cooperates with the double fan-shaped slide groove to realize the rotation of the blade's own axis freedom (second degree of freedom). The rotation of the two degrees of freedom realizes the spatial expansion of the blade from the minimum storage state to the working state. The locking pin cooperates with the straight spring and the folding locking pin hole on the primary transverse axis to complete the locking of the primary folding mechanism in the folded state; and cooperates with the expansion locking pin hole to complete the locking of the primary folding mechanism in the expanded state. The telescopic door cooperates with the arc-shaped spring and the telescopic door slide groove to make the expansion sliding of the primary longitudinal axis irreversible; at the same time, it reduces the flow resistance of the folding mechanism during the propeller's flight. The various components cooperate with each other and work together to make the propeller propeller fly efficiently and safely. The second level is the same as the first level.

[0016] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0017] 1. Small storage space

[0018] Propeller diameter of a non-foldable counter-rotating propeller fan (typical value) 400mm), which is larger than the required diameter of the storage space (typical value After adopting the folding mechanism of the present invention, the folding blades are respectively close to the housing and the tail cone. Compared with the non-foldable type, the outer diameter of the propeller can be reduced by more than 40%, reaching the required diameter of the storage space.

[0019] 2. Minimum folding

[0020] The folding first-stage blades and the folding second-stage blades are folded forward and backward respectively, each close to the shell and the tail cone to avoid mutual interference. The blades can be unfolded around the horizontal axis, and the horizontal axis can rotate in the double fan-shaped slide. This single-structure dual-degree-of-freedom coordination method achieves the minimum folding of the blades.

[0021] 3. High propulsion efficiency

[0022] The telescopic door allows the folding blades to open in one direction, and cooperates with the outer end cover to form a nearly complete spherical shell, reducing the flow resistance of the folding mechanism during the propeller flight. At the same time, the folding mechanism realizes the double-degree-of-freedom rotation of the propeller, meeting the requirements for changing the angle of attack of the blade airflow and ensuring the propulsion efficiency of the counter-rotating propeller propeller.

[0023] 4. High reliability

[0024] The present invention realizes multiple functions with a simple single structure, wherein the primary longitudinal axis and the primary transverse axis respectively cooperate with the longitudinal axis slide groove and the double fan-shaped slide groove to realize the double-degree-of-freedom rotation of the fan blade. At the same time, it plays the role of transmitting aerodynamic torque; the locking pin provides a locking force for the folding primary fan blade, making the unfolding process of the folding primary fan blade irreversible. At the same time, the primary longitudinal axis and the primary transverse axis of the fan blade are prevented from rotating, completing the fixed locking of the folding primary fan blade in the static state and the working state of the propeller. The second level is the same as the first level. Compared with the propeller using multiple hinges or complex electric devices, the number of parts is reduced, and the reliability of the propeller changing from the storage state to the running state is improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Cross-sectional view of a counter-rotating propeller with non-foldable blades;

[0026] Figure 2 (a) is a front view of the propeller with the blades deployed;

[0027] Figure 2(b) is a side view of the propeller with the blades deployed;

[0028] Figure 3 AA section view of the propeller with the blades deployed;

[0029] Fig. 4 (a) is a partial cross-sectional view of region I in the unfolded state of the folding mechanism;

[0030] Fig. 4(b) is a partial cross-sectional view of region I of the folding mechanism in the folded state;

[0031] Figure 5 Schematic diagram of the assembly of the foldable fan blades and the folding mechanism;

[0032] Fig. 6 (a) is a cross-sectional view of the BB portion of the folding mechanism when the folding mechanism is in the unfolded state;

[0033] Figure 6(b) is a cross-sectional view of the BB section of the folding machine in the folded state;

[0034] Figure 7 Schematic diagram of the two-degree-of-freedom deployment process of the propeller blades;

[0035] Figure 8 Blade profile and velocity triangle diagram of the elementary level at the mid-diameter of the fan blade.

[0036] In the figure: 1, housing; 2, primary shaft; 3, secondary shaft; 4, fixed primary blade; 5, primary hub; 6, fixed secondary blade; 7, secondary hub; 8, tail cone; 9, primary folding mechanism; 10, primary foldable blade assembly; 11, secondary foldable blade assembly; 12, secondary folding mechanism; 13, base; 14, outer end cover; 15, telescopic door; 16, locking pin; 17, foldable primary blade; 18, primary longitudinal axis; 19, primary transverse axis; 20, foldable secondary blade; 21, secondary longitudinal axis; 22, secondary transverse axis; 23, straight spring; 24, locking pin groove; 25 , fastening screws; 26, anti-loosening washers; 27, inner end cover; 28, longitudinal axis storage slot; 29, fastening screw holes; 30, double fan-shaped slide slots; 31, folding locking pin holes; 32, unfolding locking pin holes; 33, telescopic door slots for outer end cover; 34, anti-drop pin slide slots; 35, longitudinal axis slide slots for outer end cover; 36, anti-drop pins; 37, anti-drop pin holes; 38, longitudinal axis slide slots for inner end cover; 39, telescopic door slots for inner end cover; 40, arc-shaped springs; 41, primary rotor; 42, secondary rotor; 43, rotation direction around the horizontal axis; 44, rotation direction around the longitudinal axis; 45, telescopic door movement direction; 46, propeller fan diameter 47. Storage space diameter 48. Horizontal sweep angle DETAILED DESCRIPTION

[0037] The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. The following is a detailed description of a counter-rotating propeller propeller with double-degree-of-freedom foldable blades in conjunction with the accompanying drawings.

[0038] A contra-rotating propeller with double-degree-of-freedom foldable blades comprises a housing 1, a primary shaft 2, a secondary shaft 3, a primary hub 5, a secondary hub 7, eight primary folding mechanisms 9, eight primary foldable blade assemblies 10, six secondary foldable blade assemblies 11, six secondary folding mechanisms 12 and a tail cone 8, as shown in FIG2 . The assembly process of the primary folding mechanism 9 and the secondary folding mechanism 12 is as follows: Figure 5 shown.

[0039] The shell 1 is a part of the aircraft, connecting the aircraft and the propeller, and wrapping the propeller to make the airflow passing through the propeller smooth.

[0040] When the propeller is in the non-operating storage state, the eight folding primary blades 17 are all close to the housing 1, and the six folding secondary blades 20 are all close to the tail cone 8. The primary longitudinal axis 18 is stored in the longitudinal axis storage groove 28, and the pre-compressed straight spring 23 in the locking pin groove 24 pushes the locking pin 16 into the folding locking pin hole 31 on the primary transverse axis 19, providing a locking force for the folding primary blades 17, ensuring that they are fixed in the folded position when the propeller is stationary and rotating at a low speed, preventing them from opening due to gravity, small centrifugal force or vibration, such as Figure 4(b) and 6(b) The second stage is similar to the first stage, and the multiple folding structures in the first stage rotor and the second stage rotor are also the same.

[0041] When the propeller is in working state, such as when various aircraft on the aircraft carrier take off, missiles are launched from the bomb bay, and drones are ejected from the launcher. The primary shaft 2 and the secondary shaft 3 drive the primary hub 5 and the secondary hub 7 to rotate, and the two-stage rotors 41 and 42 rotate in opposite directions. Under the engine idling condition, when the rotation speed of the primary shaft 2 is within 800rpm and the rotation speed of the secondary shaft 3 is within 700rpm, the folding primary blade 17 and the folding secondary blade 20 are locked by the locking pin 16 and blocked by the telescopic door 15 and will not unfold. With the increase of the rotation speed of the primary shaft 2 and the secondary shaft 3, when the rotation speed exceeds 800rpm and 700rpm respectively, the centrifugal force on the primary foldable blade assembly 10 and the folding secondary blade 20 exceeds the preload elastic force of the straight spring 23, and the telescopic door 15 is pushed open by the primary longitudinal shaft 18 relying on the inclined surface at the bottom. The primary longitudinal shaft 18 drives the primary transverse shaft 19 to push the locking pin 16 into the locking pin groove 24. The locking pin 16 moves downward by 6 mm to release the locking state of the first-stage foldable fan blade assembly 10. The telescopic door 15 cooperates with the anti-drop pin slide 34 and the anti-drop pin 36 to rotate along the telescopic door slide formed by the outer end cover telescopic door slot 33 and the inner end cover telescopic door slot 39, and rotates 60° along the telescopic door moving direction 45 to the maximum open position. The arc-shaped spring 40 is in a compressed state. At this time, the telescopic door 15 is retracted into the telescopic door slide, revealing a complete longitudinal axis slide composed of the outer end cover longitudinal axis slide 35 and the inner end cover longitudinal axis slide 38. The first-stage longitudinal axis 18 rotates 90° along the longitudinal axis slide in the expansion direction 43, and the foldable first-stage fan blade 17 reaches the maximum expansion position, completing the rotation of the fan blade expansion freedom (the first degree of freedom). Subsequently, the folding first-stage fan blade 17, under the action of the aerodynamic circulation torque, drives the first-stage longitudinal axis 18 and the first-stage transverse axis 19 to rotate 45° along the rotation direction 44 around the longitudinal axis, and the second-stage transverse axis 22 to rotate 39°, completing the rotation of the fan blade's own axial freedom (the second degree of freedom) to reach the final fully unfolded working position. At this time, the telescopic door 15, under the push of the arc-shaped spring 40, cooperates with the anti-slip pin 36 and the anti-slip pin slide 34 to rotate 60° along the telescopic door moving direction 45 and then closes. It forms an approximately complete spherical shell with the outer end cover 14 to prevent the reverse movement of the folding first-stage fan blade 17 and reduce the flow resistance of the first-stage folding mechanism 9 in the propeller during flight, such as Figure 7 As shown. Then, the locking pin 16 moves upward 12 mm under the push of the straight spring 23 and enters the expansion locking pin hole 32 of the primary horizontal axis 19. The locking pin 16 uses the cooperation of the quadrangular prism surface to prevent the fan blade from rotating around the horizontal axis and the longitudinal axis. And due to the centrifugal force and the tightening force of the straight spring 23, the locking pin 16 cannot be disengaged from the expansion locking pin hole 32, making the expansion process of the foldable primary fan blade 17 irreversible, avoiding the fan blade rebound caused by aerodynamic force, and completing the locking of the primary folding mechanism 9 in the expanded state, as shown in FIG. Figure 4(a) and 6(a)As shown. The same is true for the first and second level rotors, and the multiple folding structures in the first and second level rotors are also the same.

[0042] At this time, the propeller is flying stably in the air. The primary shaft 2 and the secondary shaft 3 drive the primary hub 5 and the secondary hub 7 to rotate stably, and transmit the shaft work output by the engine to the foldable primary blades 17 and the foldable secondary blades 20. The two-stage foldable blades rotate in opposite directions to do work on the airflow. The blade shape and velocity triangle at the middle diameter are shown as follows: Figure 8 As shown: the first-stage propeller fan takes in air axially, and the air velocity increases and has a certain degree of rotation after the air passes through the first-stage propeller fan to do work; the airflow with pre-rotation directly flows into the second-stage propeller fan, and the work capacity of the second-stage propeller fan can be increased due to the increase in torque. The air velocity continues to increase after passing through the second-stage propeller fan, and the airflow angle continues to deflect, and finally discharged along the axial direction of the propeller. The thrust generated is transmitted to the propeller through the outer end cover 14, the inner end cover 27, the first-stage longitudinal axis 18, the second-stage longitudinal axis 21, the first-stage hub 5 and the second-stage hub 7, so that the aircraft can fly stably.

Claims

1. A contra-rotating propeller with blades that can be folded in two degrees of freedom, characterized in that: It comprises a housing (1), a primary rotating shaft (2), a secondary rotating shaft (3), a primary wheel hub (5), a secondary wheel hub (7), a primary folding mechanism (9), a primary foldable fan blade assembly (10), a secondary foldable fan blade assembly (11), a secondary folding mechanism (12) and a tail cone (8); the number of the primary folding mechanisms (9) is the same as that of the primary foldable fan blade assembly (10); the number of the secondary folding mechanisms (12) is the same as that of the secondary foldable fan blade assembly (11); Furthermore, the number of the secondary foldable fan blade assemblies (11) must be equal to or less than the number of the primary foldable fan blade assemblies (10); The primary folding mechanism (9) and the secondary folding mechanism (12) are semi-ellipsoidal in shape as a whole. The primary folding mechanism (9) comprises a base (13), an outer end cover (14), a telescopic door (15), a locking pin (16), a straight spring (23), a locking pin slot (24), a fastening screw (25), a locking washer (26) and an inner end cover (27). The primary foldable fan blade assembly (10) belongs to the primary folding mechanism (9) and comprises a foldable primary fan blade (17), a primary longitudinal axis (18) and a primary transverse axis (19). The secondary foldable fan blade assembly (11) belongs to the secondary folding mechanism (12), and the secondary foldable fan blade assembly (11) comprises a foldable secondary fan blade (20), a secondary longitudinal axis (21) and a secondary transverse axis (22). The locking pin (16) cooperates with the straight spring (23) to be inserted into the locking pin groove (24) at the center of the base (13); the primary longitudinal axis (18) is placed in the longitudinal axis storage groove (28) on the base (13), and the primary transverse axis (19) is placed in the half double fan-shaped groove of the base (13), and the foldable primary fan blade (17) is close to the shell (1); at the same time, the locking pin (16) is inserted into the folding locking pin hole (31) on the primary transverse axis (19) under the push of the pre-tightening force of the straight spring (23). The hole is a spherical crown-shaped pit smaller than a hemisphere; the inner end cover (27) is placed on the base (13), so that the inner end cover longitudinal axis slide groove (38) is aligned with the longitudinal axis storage groove (28), and the half double fan-shaped groove on its inner surface cooperates with the half double fan-shaped groove on the base (13) to form a complete double fan-shaped slide groove (30), wrapping the first-level horizontal axis (19), completing the assembly of the first-level foldable fan blade assembly (10); the arc-shaped spring (36) is installed in the inner end cover telescopic door groove (39) on the outer surface of the inner end cover (27); the telescopic door (1 5) is placed on the telescopic door slot (39) of the inner end cover, and the anti-drop pin (36) is inserted into the anti-drop pin hole (37) in the telescopic door (15); the outer end cover (14) is placed on the base (13) and the inner end cover (27), so that the outer end cover longitudinal axis slide groove (35) is aligned with the inner end cover longitudinal axis slide groove (38), and the outer end cover telescopic door slot (33) and the inner end cover telescopic door slot (39) cooperate to form a complete telescopic door slide groove; the anti-drop pin (36) is longer than the anti-drop pin hole (37), and the excess portion extends into the outer end cover telescopic door slot (33 ) in the anti-drop pin slide groove (34) to complete the assembly of the telescopic door (15); the fastening screw (25) cooperates with the anti-loosening washer (26) and the through hole of the outer end cover (14), and is inserted into the fastening screw hole (29) in the form of 5 non-uniformly distributed blind holes opened along the outer circumference of the base (13), and the above-mentioned parts are fixed to the base (13) to complete the assembly of the first-level folding mechanism (9); the second-level folding mechanism (12) is the same as the first level, and the multiple folding structures in the first-level rotor (41) and the second-level rotor (42) are also the same; The first-stage foldable fan blade assembly (10) comprises a foldable first-stage fan blade (17), a first-stage longitudinal axis (18) and a first-stage transverse axis (19); the cross section of the foldable first-stage fan blade (17) is an airfoil, the airfoil gradually becomes thinner and smaller from the root to the tip, has a certain angle of twist, and is in a swept saber shape as a whole; the first-stage longitudinal axis (18) connects the foldable first-stage fan blade (17) and the first-stage transverse axis (19), transmits the engine torque to the foldable first-stage fan blade (17) to perform work on the airflow, and bears the centrifugal load and bending moment generated when the fan blade rotates; when working, the foldable first-stage fan blade (17) absorbs the shaft work transmitted by the engine and rotates, generating thrust that is transmitted to the propeller through the outer end cover (14), the inner end cover (27), the first-stage transverse axis (19), the locking pin (16), the base (13) and the first-stage hub (5).

2. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 1, characterized in that: The primary longitudinal axis (18) is a column with a runway-shaped cross section; when the propeller is in a folded state, the primary longitudinal axis (18) is placed in a longitudinal axis receiving groove (28) on the base (13); a pre-compressed straight spring (23) in the locking pin groove (24) pushes the locking pin (16) into a folding locking pin hole (31) on the primary transverse axis (19); the hole is a spherical crown-shaped pit smaller than a hemisphere, and through cooperation with the spherical surface of the head of the locking pin (16), a locking force is provided for the folding primary fan blade (17), ensuring that it is fixed in a folded position when the propeller is stationary and rotating at a low speed, preventing it from opening due to gravity, small centrifugal force or vibration, so that the folding primary fan blade (17) and the folding secondary fan blade (20) are respectively close to the shell (1) and the tail cone (8), completing the locking of the primary folding mechanism (9) in the folded state.

3. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 1 or 2, characterized in that: The first-level transverse axis (19) is a cylinder with spherical surfaces at both ends; after the first-level longitudinal axis (18) reaches the maximum expansion position, the first-level transverse axis (19) is deflected immediately, that is, the first-level transverse axis (19) and the foldable first-level fan blade (17) rotate around the first-level longitudinal axis (18), slide along the double fan-shaped slide groove (30) formed by the base (13) and the inner end cover (27), so that the foldable first-level fan blade (17) can rotate around its own axis to meet the change of the airflow angle of attack, and complete the rotation of the fan blade's own axis degree of freedom, the fan blade's own axis degree of freedom is the second degree of freedom; the transverse axis sweep angle is determined according to the airflow angle of attack at the design point.

4. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 3, characterized in that: The horizontal sweep angle ranges from 35° to 55°.

5. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 1 or 2, characterized in that: The telescopic door (15) is in the form of two spherical sectors, both of which have the function of opening in one direction, that is, the primary longitudinal axis (18) can push the door open when it is folded to unfolded, but cannot be opened in the reverse direction; the telescopic door (15) cooperates with the arc-shaped spring (40) in a compressed state and is placed in the telescopic door groove (33) of the outer end cover and the telescopic door groove (39) of the inner end cover to form a complete telescopic door slide groove.

6. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 5, characterized in that: The telescopic door (15) has four anti-dropout pin holes (37) in the diameter direction of the spherical surface, and four anti-dropout pins (36) are inserted into the four anti-dropout pin holes (37); the anti-dropout pin (36) is longer than the anti-dropout pin hole (37), and the protruding portion thereof extends into the anti-dropout pin slide groove (34) in the telescopic door groove (33) of the outer end cover, and can slide in the anti-dropout pin slide groove (34) along with the sliding of the telescopic door (15), and the rotation direction and angle range thereof are consistent with those of the telescopic door, so as to prevent the telescopic door (15) from falling out of the groove.

7. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 5, characterized in that: The telescopic door (15) cooperates with the arc-shaped spring (40) in a compressed state and is placed in a complete telescopic door slide groove formed by the telescopic door groove (33) of the outer end cover and the telescopic door groove (39) of the inner end cover, and can slide in the telescopic door slide groove along the telescopic door moving direction (45), and the sliding direction is an arc shape, and the angle range corresponding to the axis is 50° to 70°.

8. A counter-rotating propeller with double-degree-of-freedom foldable blades as claimed in claim 1, 2, 4, 6 or 7, characterized in that: The number of the first-level folding mechanisms (9) is consistent with the number of the first-level foldable fan blade assemblies (10), which is 6 to 10; the number of the second-level folding mechanisms (12) is consistent with the number of the second-level foldable fan blade assemblies (11), which is 5 to 8.

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