WO2024093481A1 - Variable-rotating-speed rotor blade, coaxial unmanned helicopter, and single-rotor unmanned helicopter - Google Patents

Abstract

A variable-rotating-speed rotor blade, a coaxial unmanned helicopter, and a single-rotor unmanned helicopter. The variable-rotating-speed rotor blade comprises: a blade root (10), a blade middle section (20), and a blade tip (30) which are connected in sequence. A pitch curve L of the variable-rotating-speed rotor blade comprises a root pitch section L1, a middle pitch section L2, and a tip pitch section L3 respectively corresponding to the blade root (10), the blade middle section (20), and the blade tip (30); a pitch corresponding to a point connecting the middle pitch section L2 to the tip pitch section L3 is used as a standard pitch L4; a pitch corresponding to each point in the tip pitch section L3 is less than the standard pitch L4. The blade tip (30) of the variable-rotating-speed rotor blade has a large negative torsion, and the angle of attack of a blade element is small, so that in a cyclic pitch changing process, the blade tip (30) can generate a large change in the lift coefficient, thereby improving the cyclic pitch changing control capacity.

Description

Variable speed rotor blades, coaxial unmanned helicopters and single rotor unmanned helicopters Technical Field

The present invention relates to the field of aircraft, and in particular to a variable speed rotor blade, a coaxial unmanned helicopter and a single-rotor unmanned helicopter.

Background technique

Coaxial helicopters have the advantages of small size, no tail rotor, high hovering efficiency, etc., and are the most suitable layout form for lightweight and miniaturized unmanned helicopters. Lightweight and miniature coaxial drones have certain advantages over multi-rotor drones in terms of portability, both in civil and military applications.

However, the variable speed rotor blades of the light and micro coaxial UAVs in the prior art have a weak control torque under the effect of only cyclic pitch variation.

Summary of the invention

The main purpose of the present invention is to provide a variable speed rotor blade, a coaxial unmanned helicopter and a single-rotor unmanned helicopter to solve the problem of weak control torque of the variable speed rotor blade in the prior art under the action of only cyclic pitch change.

In order to achieve the above-mentioned purpose, according to one aspect of the present invention, there is provided a variable speed rotor blade, comprising: a blade root, a blade middle section and a blade tip connected in sequence, the pitch curve L of the variable speed rotor blade comprising a root pitch segment L1, a middle pitch segment L2 and a tip pitch segment L3 corresponding to the blade root, the blade middle section and the blade tip respectively, the pitch corresponding to the connection point of the middle pitch segment L2 and the tip pitch segment L3 is used as the standard pitch L4, and the pitch corresponding to each point in the tip pitch segment L3 is smaller than the standard pitch L4.

In one embodiment, the tip corresponding to the outermost side of the blade tip has a maximum negative twist c, which is the difference between the pitch of the tip corresponding to the outermost side of the blade tip and the standard pitch L4, and the maximum negative twist c is between 1.6 inches and 2.2 inches.

In one embodiment, the tip pitch segment L3 includes a first straight line segment L5. The slope is between -10 and -20, and the pitch corresponding to the end of the first straight line segment L5 is the pitch of the tip corresponding to the outermost side of the blade tip.

In one embodiment, the tip pitch segment L3 further includes a first arc transition segment L6 connected between the end of the middle pitch segment L2 and the starting end of the first straight segment L5.

In one embodiment, the pitch corresponding to each point in the middle pitch section L2 is greater than the standard pitch L4.

In one embodiment, the connection point between the root and the middle section of the blade has a maximum positive twist d, which is the difference between the pitch corresponding to the connection point between the root and the middle section of the blade and the standard pitch L4, and the maximum positive twist d is between 0.2 inches and 1.1 inches.

In one embodiment, the middle pitch segment L2 includes a second straight line segment L7, the slope of the second straight line segment L7 is less than 0 and greater than or equal to -0.9, the pitch corresponding to the end of the second straight line segment L7 is the standard pitch L4, and the difference between the pitch corresponding to the starting end of the second straight line segment L7 and the standard pitch L4 is between 0.15-0.25.

In one embodiment, the middle pitch segment L2 further includes a second arc transition segment L8 connected between the end of the root pitch segment L1 and the starting end of the second straight segment L7.

In one embodiment, the portion of the variable speed rotor blade with a relative radius between 0 and 0.27 is the overhang e, the portion of the variable speed rotor blade with a relative radius between 0.27 and 0.4 corresponds to the blade root, the portion of the variable speed rotor blade with a relative radius between 0.4 and 0.75 corresponds to the middle section of the blade, and the portion of the variable speed rotor blade with a relative radius between 0.75 and 1 corresponds to the blade tip.

In one embodiment, the maximum value of the blade element angle of attack at the blade root is between 16° and 25°.

In one embodiment, the pitch axis L9 of the variable speed rotor blade is between the first 35% and 47% of the average chord length of the variable speed rotor blade.

In one embodiment, the airfoil of the variable speed rotor blade is an airfoil with a Reynolds number less than or equal to 10 ⁶ .

In one embodiment, the projection of the variable speed rotor blade in the reference plane is used as the blade plane. shape, the leading edge of the blade plan shape includes the root leading edge projection, the middle section leading edge projection and the tip leading edge projection corresponding to the blade root, the blade middle section and the blade tip respectively, the trailing edge of the blade plan shape includes the root trailing edge projection, the middle section trailing edge projection and the tip trailing edge projection corresponding to the blade root, the blade middle section and the blade tip respectively, the root leading edge projection and the root trailing edge projection are parallel to the pitch axis L9, the middle section leading edge projection and the tip leading edge projection are swept backward, the middle section trailing edge projection and the tip trailing edge projection are swept forward, and the forward sweep angle of the tip trailing edge projection is smaller than the forward sweep angle of the middle section trailing edge projection.

In one embodiment, the blade tip leading edge projection includes a third straight line segment and a third arc transition segment sequentially connected in a direction from the blade root to the blade tip.

According to another aspect of the present invention, there is provided a coaxial unmanned helicopter, comprising: variable speed rotor blades, wherein the variable speed rotor blades are the variable speed rotor blades mentioned above.

In one embodiment, the rotor solidity of the coaxial unmanned helicopter ranges from 0.98 to 1.1.

According to the last aspect of the present invention, there is provided a single-rotor unmanned helicopter, comprising: a variable speed rotor blade, wherein the variable speed rotor blade is the variable speed rotor blade mentioned above.

In one embodiment, the rotor solidity of the single-rotor unmanned helicopter ranges from 0.49 to 0.55.

By applying the technical solution of the present invention, the pitch corresponding to each point in the tip pitch section L3 is smaller than the standard pitch L4, that is, the tip of the variable speed rotor blade has a larger negative twist and the blade element angle of attack is smaller, which makes the tip of the blade produce a larger change in lift coefficient during the cyclic pitch change, that is, a larger lift difference. Such a lift difference provides the torque of the cyclic pitch change of the aircraft in forward flight, so the larger lift difference can improve the control ability of the cyclic pitch change.

In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which constitute a part of the present invention, are used to provide a further understanding of the present invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute improper limitations of the invention. In the accompanying drawings:

FIG1 is a schematic diagram showing a three-dimensional structure of an embodiment of a variable speed rotor blade according to the present invention, wherein FIG1 shows blade elements at different radii;

FIG2 shows the blade plane shape of the variable speed rotor blade of FIG1 ;

FIG3 shows the blade plane shape of the variable speed rotor blade of FIG1 ;

FIG4 is a schematic diagram showing a pitch curve L of the variable speed rotor blade of FIG1 ;

FIG5 shows a pitch distribution diagram of the variable speed rotor blade of FIG1 after the coordinate system is transformed;

FIG6 shows a lift coefficient curve corresponding to the airfoil of the variable speed rotor blade of FIG1 and other low Reynolds number airfoils;

FIG7 shows a polar curve diagram corresponding to the airfoil of the variable speed rotor blade of FIG1 and other low Reynolds number airfoils;

FIG8 shows an example rotor chord length distribution diagram of the variable speed rotor blade of FIG1 ;

FIG9 shows a distribution diagram of the vertical component of the slipstream at 0.65R downstream of the rotor blade disk of the variable speed rotor blade of FIG1 ;

FIG. 10 shows a curve diagram of the installation angle of the variable speed rotor blade of FIG. 1 ; and

FIG. 11 shows a design flow chart of the variable speed rotor blades of FIG. 1 .

The above drawings include the following reference numerals:
10. Blade root; 11. Projection of the leading edge of the blade root; 12. Projection of the trailing edge of the blade root; 20. Middle section of the blade; 21.
Projection of the leading edge of the middle section; 22, projection of the trailing edge of the middle section; 30, blade tip; 31, projection of the leading edge of the blade tip; 311, the third straight line segment; 312, the third arc transition segment; 32, projection of the trailing edge of the blade tip.

Detailed ways

It should be noted that, in the absence of conflict, the embodiments of the present invention and the features in the embodiments can be combined with each other. The present invention will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

In order to make those skilled in the art better understand the scheme of the present invention, the following will be combined with the present invention to The drawings in the examples clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

It should be noted that the terms "first", "second", etc. in the specification and claims of the present invention and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the terms used in this way can be interchanged where appropriate, so as to describe the embodiments of the present invention described herein. In addition, the terms "including" and "having" and any variations thereof are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

It should be noted that the terms used herein are only for describing specific embodiments and are not intended to limit the exemplary embodiments according to the present application. As used herein, unless the context clearly indicates otherwise, the singular form is also intended to include the plural form. In addition, it should be understood that when the terms "comprise" and/or "include" are used in this specification, it indicates the presence of features, steps, operations, devices, components and/or combinations thereof.

In order to solve the above problems, as shown in Figures 1, 4 and 5, the variable speed rotor blade of this embodiment includes: a blade root 10, a blade middle section 20 and a blade tip 30 connected in sequence, and the pitch curve L of the variable speed rotor blade includes a root pitch segment L1, a middle pitch segment L2 and a tip pitch segment L3 corresponding to the blade root 10, the blade middle section 20 and the blade tip 30 respectively. The pitch corresponding to the connection point of the middle pitch segment L2 and the tip pitch segment L3 is used as the standard pitch L4, and the pitch corresponding to each point in the tip pitch segment L3 is smaller than the standard pitch L4.

By applying the technical solution of this embodiment, the pitch corresponding to each point in the tip pitch section L3 is smaller than the standard pitch L4, that is, the tip of the variable speed rotor blade has a larger negative twist and the blade element angle of attack is smaller, which makes the tip of the blade generate a larger lift coefficient during the periodic pitch change process. Such a lift difference provides a moment of cyclic pitch change in the forward flight of the aircraft, so a larger lift difference can improve the control ability of cyclic pitch change.

As shown in FIG4 , in this embodiment, the tip corresponding to the outermost side of the blade tip 30 has a maximum negative twist c, which is the difference between the pitch of the tip corresponding to the outermost side of the blade tip 30 and the standard pitch L4, and the maximum negative twist c is between 1.6 inches and 2.2 inches. If the maximum negative twist c is too small, the improvement in lift difference is not obvious, and the improvement in the control ability of cyclic pitch change is limited. If the maximum negative twist c is too large, the blade efficiency will be lost. Preferably, in this embodiment, the maximum negative twist c is 2 inches.

As shown in FIG4 , in this embodiment, the tip pitch segment L3 includes a first straight segment L5, the slope of the first straight segment L5 is between -10 and -20 (i.e., linear negative torsion), and the pitch corresponding to the end of the first straight segment L5 is the pitch of the tip corresponding to the outermost side of the blade tip 30. The above structure makes the slope of the first straight segment L5 larger, so that the blade element angle of attack is smaller, and further increases the lift difference, thereby improving the control ability of cyclic pitch change. It should be noted that if the slope of the first straight segment L5 is too small, it will affect the control ability of cyclic pitch change, and if the slope of the first straight segment L5 is too large, the blade efficiency will be lost.

Preferably, in this embodiment, the slope of the first straight line segment L5 is -14.2. It should be noted that when adjusting the blade element angle of attack, only the maximum negative twist amount c or only the slope of the first straight line segment L5 can be adjusted, or the maximum negative twist amount c and the first straight line segment L5 can be adjusted in combination. Compared with the two, the maximum negative twist amount c has a greater impact on the blade element angle of attack.

As shown in Figure 4, in this embodiment, the tip pitch segment L3 also includes a first arc transition segment L6 connected between the end of the middle pitch segment L2 and the starting end of the first straight segment L5. The above structure prevents the blade element angle of attack from changing suddenly, which is beneficial to subsequent lofting modeling.

As shown in FIG4 , in this embodiment, the pitch corresponding to each point in the middle pitch section L2 is greater than the standard pitch L4, that is, the middle section 20 of the blade is positively twisted. Specifically, the closer to the blade root 10, the greater the pitch. At a certain speed, the closer to the blade root 10, the smaller the linear velocity, and the closer to the blade tip 30, the larger the linear velocity. Since the linear velocity at the blade root 10 is small, the lift is insufficient, so We increase the positive twist in the middle pitch section L2 connected to the blade root 10 in order to increase the angle of attack and thus enhance the lift.

As shown in FIG4 , in this embodiment, the connection point between the blade root 10 and the blade middle section 20 has a maximum positive twist d, which is the difference between the pitch corresponding to the connection point between the blade root 10 and the blade middle section 20 and the standard pitch L4, and the maximum positive twist d is between 0.2 inches and 1.1 inches. If the maximum positive twist d is too small, the blade element angle of attack does not increase significantly, resulting in an insignificant lift effect. If the maximum positive twist d is too large, the resistance at the blade root 10 increases, which in turn causes the blade root 10 to stall. Preferably, in this embodiment, the maximum positive twist d is 1 inch.

It should be noted that, in this embodiment, the transitional modification is performed from the root of the propeller root 10 to the maximum pitch.

It should also be noted that, as shown in Figures 2, 4 and 9, the blade root 10 and the blade midsection 20 are twisted, so that the vertical component of the slipstream downstream of the impeller disk is relatively evenly distributed from the blade root to 80% of the relative radius (r/R), thereby improving the efficiency of hovering and low-speed forward flight. It should be noted that R is the distance between the center of rotation O and the tip of the blade tip 30. The axis where the center of rotation O is located is the axis of rotation Q.

As shown in FIG4 , in this embodiment, the middle pitch segment L2 includes a second straight segment L7, the slope of the second straight segment L7 is less than 0 and greater than or equal to -0.9 (i.e., linear negative torsion), the pitch corresponding to the end of the second straight segment L7 is the standard pitch L4, and the difference between the pitch corresponding to the starting end of the second straight segment L7 and the standard pitch L4 is between 0.15-0.25. The above structure makes the second straight segment L7 as close to the standard pitch L4 as possible, thereby effectively inheriting the variable speed advantage of the standard pitch propeller. Preferably, the difference between the endpoint of L7 and L4 is 0.2.

As shown in Figure 4, in this embodiment, the middle pitch segment L2 also includes a second arc transition segment L8 connected between the end of the root pitch segment L1 and the starting end of the second straight segment L7. The above structure prevents the blade element angle of attack from changing suddenly, which is beneficial to subsequent lofting modeling.

It should be noted that the variable speed rotor blade has nonlinear negative torsion as a whole. However, its overall size is small, and it is easy to manufacture using a composite material molding process, which is not difficult.

As shown in Figures 2 to 4, in this embodiment, the portion of the variable speed rotor blade with a relative radius between 0 and 0.27 is the overhang e, the portion of the variable speed rotor blade with a relative radius between 0.27 and 0.4 corresponds to the blade root 10, the portion of the variable speed rotor blade with a relative radius between 0.4 and 0.75 corresponds to the blade middle section 20, and the portion of the variable speed rotor blade with a relative radius between 0.75 and 1 corresponds to the blade tip 30. As shown in Figure 10, at the blade tip 30, the range of its installation angle from the relative radius 0.75 to the outermost side is 7.7 to 2.8 degrees. If the rotor is subjected to a cyclic pitch change of ±10 degrees. The blade element angle of attack range of the blade tip 30 is between -7.2 and 17.7. According to Figure 6, in a cyclic pitch change, the blade tip portion will produce a larger lift coefficient change, that is, a larger lift difference. Such a lift difference provides a torque for the cyclic pitch change of the rotorcraft forward flight.

It should be noted that, as shown in FIG. 2 , the overhang e is the distance between the center of rotation O and the vertical hinge P of the variable speed rotor blade.

It should also be noted that FIG. 10 shows the installation angle curve of the variable speed rotor blade, which can be obtained by the pitch curve L of FIG. 4 and the formula The relative radius of each blade element is r ₁ , the pitch is a ₁ , and the installation angle is α. The blade element installation angle curve is calculated through the pitch curve L, and then the plotting is performed.

In this embodiment, the maximum value of the blade element angle of attack of the blade root 10 is between 16° and 25°. Too small a blade element angle of attack will result in insufficient lift, while too large a blade element angle of attack will increase the resistance of the blade root 10, leading to stall. Preferably, in this embodiment, the maximum blade element angle of attack is not necessarily at the maximum pitch. The maximum value of the blade element angle of attack is 18.5°, at the relative radius r/R=0.35.

As shown in Figure 2, in this embodiment, the pitch axis L9 of the variable speed rotor blade is between the first 35% and 47% of the average chord length of the variable speed rotor blade. It should be noted that the above description refers to that in the direction from the leading edge to the trailing edge of the variable speed rotor blade, a point within the first 35% to 47% of the average chord length of the variable speed rotor blade is used as a reference point, and the pitch axis L9 is perpendicular to the chord length and passes through the reference point. The above structure makes the pitch axis L9 near the aerodynamic center, so that the torque around the pitch axis L9 generated during the pitch change process is small, thereby reducing the load on the pitch change mechanism. Preferably, in this embodiment In the figure, the pitch axis L9 of the blade is located at the front 46% of the average chord length.

After long-term research, the inventor found that the main reason for the insufficient endurance of light and micro coaxial drones is that the rotor blades are mostly model-grade blades, and the airfoils are mostly symmetrical airfoils without optimized design, resulting in low hovering efficiency and not suitable for variable speed control.

To solve the above problem, in this embodiment, the airfoil of the variable speed rotor blade is an airfoil with a Reynolds number less than or equal to 10 ^6. Preferably, in this embodiment, the airfoil of the variable speed rotor blade is NACA3412. Of course, in other embodiments, the airfoil of the variable speed rotor blade may also be an airfoil with a low Reynolds number such as Eppler387 or A18. The following is a detailed description of the airfoil selection method:

When selecting an airfoil, the lift coefficient curves and polar curves of several target airfoils should be compared. First, the lift coefficient should have a larger angle of attack at the maximum lift coefficient. As shown in Figure 6 (lift curve), the angle of attack of the NACA3412 airfoil at the maximum lift coefficient is greater than that of the other two airfoils. Secondly, the polar curve should have a larger opening, that is, at a smaller drag coefficient, there is a larger range of lift coefficient variation. As shown in Figure 7 (polar curve), the polar curve of the NACA3412 airfoil has a larger opening. Therefore, this embodiment selects the NACA3412 airfoil as the airfoil for the variable speed rotor blade.

As shown in Figures 2 and 3, in this embodiment, the projection of the variable speed rotor blade in the reference plane is used as the blade plane shape, and the leading edge of the blade plane shape includes a root leading edge projection 11, a middle section leading edge projection 21 and a tip leading edge projection 31 corresponding to the blade root 10, the blade middle section 20 and the blade tip 30 respectively, and the trailing edge of the blade plane shape includes a root trailing edge projection 12, a middle section trailing edge projection 22 and a tip trailing edge projection 32 corresponding to the blade root 10, the blade middle section 20 and the blade tip 30 respectively, the root leading edge projection 11 and the root trailing edge projection 12 are parallel to the variable pitch axis L9, the middle section leading edge projection 21 and the tip leading edge projection 31 are swept backward, the middle section trailing edge projection 22 and the tip trailing edge projection 32 are swept forward, and the forward sweep angle of the tip trailing edge projection 32 is smaller than the forward sweep angle of the middle section trailing edge projection 22. Under the combined effect of the above-mentioned special blade plan shape and the corresponding pitch curve, the difference in the vertical component of the slipstream downstream of the impeller disk can be reduced, so that the distribution of the vertical component of the slipstream downstream of the impeller disk from the root to 80% of the relative radius (r/R) is relatively uniform, thereby improving the efficiency of hovering and low-speed forward flight.

It should be noted that, as shown in FIG. 8 , the chord length of the blade gradually decreases from the blade root 10 to the blade tip 30 , which helps to reduce the rotor drag and blade tip loss.

As shown in Fig. 3, in this embodiment, the blade tip leading edge projection 31 includes a third straight line segment 311 and a third arc transition segment 312 sequentially connected in the direction from the blade root 10 to the blade tip 30. The above structure reduces the chord length of the variable speed rotor blade, thereby reducing resistance; on the other hand, it has the effect of reducing noise.

FIG11 shows a design flow chart of the variable speed rotor blades of this embodiment.

The present application also provides a coaxial unmanned helicopter. According to an embodiment of the coaxial unmanned helicopter (not shown in the figure), the coaxial unmanned helicopter includes a variable speed rotor blade, and the variable speed rotor blade is the above-mentioned variable speed rotor blade. Since the above-mentioned variable speed rotor blade has a strong control torque under the action of only cyclic pitch change, the coaxial unmanned helicopter having the same also has the above-mentioned advantages.

In this embodiment, the rotor solidity of the coaxial unmanned helicopter ranges from 0.98 to 1.1. Specifically, the solidity is the ratio of the vertical projection area of a pair of blades to the area of the propeller disc. When the solidity is within this range, the rotor efficiency of the coaxial unmanned helicopter is the highest and the flight time is the longest.

The present application also provides a single-rotor unmanned helicopter. According to an embodiment of the single-rotor unmanned helicopter (not shown in the figure), the single-rotor unmanned helicopter includes a variable speed rotor blade, and the variable speed rotor blade is the above-mentioned variable speed rotor blade. Since the above-mentioned variable speed rotor blade has a strong control torque under the action of only cyclic pitch change, the single-rotor unmanned helicopter having the same also has the above-mentioned advantages.

In this embodiment, the rotor solidity of the single-rotor unmanned helicopter ranges from 0.49 to 0.55. When the solidity is within this range, the rotor efficiency of the single-rotor unmanned helicopter is the highest and the flight time is the longest.

Unless otherwise specifically stated, the relative arrangement of the components and steps, numerical expressions and numerical values described in these embodiments do not limit the scope of the present invention. At the same time, it should be understood that for ease of description, the sizes of the various parts shown in the drawings are not drawn according to the actual proportional relationship. The techniques, methods and equipment known to ordinary technicians in the relevant fields may not be discussed in detail, but where appropriate, the techniques, methods and equipment should be regarded as part of the authorized specification. In all examples shown and discussed herein, any specific values should be interpreted as merely exemplary and not as limiting. Therefore, other examples of the exemplary embodiments may have different values. It should be noted that similar reference numerals and letters represent similar items in the following figures, and therefore, once an item is defined in one figure, it does not need to be further discussed in subsequent figures.

For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

In the description of the present invention, it is necessary to understand that the directions or positional relationships indicated by directional words such as "front, back, up, down, left, right", "lateral, vertical, perpendicular, horizontal" and "top, bottom" are usually based on the directions or positional relationships shown in the drawings. They are only for the convenience of describing the present invention and simplifying the description. Unless otherwise specified, these directional words do not indicate or imply that the devices or elements referred to must have a specific direction or be constructed and operated in a specific direction. Therefore, they cannot be understood as limiting the scope of protection of the present invention. The directional words "inside and outside" refer to the inside and outside relative to the contours of each component itself.

The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims (18)

1. A variable speed rotor blade, characterized in that it comprises: a blade root (10), a blade middle section (20) and a blade tip (30) connected in sequence, wherein a pitch curve L of the variable speed rotor blade comprises a root pitch section L1, a middle pitch section L2 and a tip pitch section L3 corresponding to the blade root (10), the blade middle section (20) and the blade tip (30) respectively, a pitch corresponding to a connection point between the middle pitch section L2 and the tip pitch section L3 is used as a standard pitch L4, and pitches corresponding to various points in the tip pitch section L3 are all smaller than the standard pitch L4.
2. The variable speed rotor blade according to claim 1 is characterized in that the tip corresponding to the outermost side of the blade tip (30) has a maximum negative twist c, and the maximum negative twist c is the difference between the pitch of the tip corresponding to the outermost side of the blade tip (30) and the standard pitch L4, and the maximum negative twist c is between 1.6 inches and 2.2 inches.
3. The variable speed rotor blade according to claim 1 is characterized in that the tip pitch segment L3 includes a first straight line segment L5, the slope of the first straight line segment L5 is between -10 and -20, and the pitch corresponding to the end of the first straight line segment L5 is the pitch of the tip corresponding to the outermost side of the blade tip (30).
4. The variable speed rotor blade according to claim 3 is characterized in that the tip pitch segment L3 also includes a first arc transition segment L6 connected between the end of the middle pitch segment L2 and the starting end of the first straight line segment L5.
5. The variable speed rotor blade according to claim 1 is characterized in that the pitch corresponding to each point in the middle pitch section L2 is greater than the standard pitch L4.
6. The variable speed rotor blade according to claim 5 is characterized in that the connection point between the blade root (10) and the blade middle section (20) has a maximum positive twist d, and the maximum positive twist d is the difference between the pitch corresponding to the connection point between the blade root (10) and the blade middle section (20) and the standard pitch L4, and the maximum positive twist d is between 0.2 inches and 1.1 inches.
7. The variable speed rotor blade according to claim 5 is characterized in that the middle pitch segment L2 includes a second straight line segment L7, the slope of the second straight line segment L7 is less than 0 and greater than or equal to -0.9, the pitch corresponding to the end of the second straight line segment L7 is the standard pitch L4, and the difference between the pitch corresponding to the starting end of the second straight line segment L7 and the standard pitch L4 is between 0.15-0.25.
8. The variable speed rotor blade according to claim 7 is characterized in that the middle pitch segment L2 also includes a second arc transition segment L8 connected between the end of the root pitch segment L1 and the starting end of the second straight line segment L7.
9. The variable speed rotor blade according to claim 1 is characterized in that the portion of the variable speed rotor blade with a relative radius between 0 and 0.27 is the overhang e, the portion of the variable speed rotor blade with a relative radius between 0.27 and 0.4 corresponds to the blade root (10), the portion of the variable speed rotor blade with a relative radius between 0.4 and 0.75 corresponds to the blade middle section (20), and the portion of the variable speed rotor blade with a relative radius between 0.75 and 1 corresponds to the blade tip (30).
10. The variable speed rotor blade according to claim 1 is characterized in that the maximum value of the blade element angle of attack of the blade root (10) is between 16° and 25°.
11. The variable speed rotor blade according to claim 1 is characterized in that the pitch axis L9 of the variable speed rotor blade is between the first 35% and 47% of the average chord length of the variable speed rotor blade.
12. The variable speed rotor blade according to claim 1 is characterized in that the airfoil of the variable speed rotor blade is an airfoil with a Reynolds number less than or equal to 10 ⁶ .
13. The variable speed rotor blade according to any one of claims 1 to 12, characterized in that the projection of the variable speed rotor blade in the reference plane is used as the blade plane shape, the leading edge of the blade plane shape includes a root leading edge projection (11), a middle section leading edge projection (21) and a tip leading edge projection (31) corresponding to the blade root (10), the blade middle section (20) and the blade tip (30), respectively, and the trailing edge of the blade plane shape includes a blade root leading edge projection (11), a middle section leading edge projection (21) and a blade tip leading edge projection (31) corresponding to the blade root (10), the blade middle section (20) and the blade tip (30), respectively. The blade tip (30) corresponds to a blade root trailing edge projection (12), a middle section trailing edge projection (22) and a blade tip trailing edge projection (32), wherein the blade root leading edge projection (11) and the blade root trailing edge projection (12) are parallel to the pitch axis L9, the middle section leading edge projection (21) and the blade tip leading edge projection (31) are swept backward, the middle section trailing edge projection (22) and the blade tip trailing edge projection (32) are swept forward, and the forward sweep angle of the blade tip trailing edge projection (32) is smaller than the forward sweep angle of the middle section trailing edge projection (22).
14. The variable speed rotor blade according to claim 13 is characterized in that the blade tip leading edge projection (31) includes a third straight line segment (311) and a third arc transition segment (312) connected in sequence in a direction from the blade root (10) to the blade tip (30).
15. A coaxial unmanned helicopter comprises: a variable speed rotor blade, wherein the variable speed rotor blade is the variable speed rotor blade according to any one of claims 1 to 14.
16. The coaxial unmanned helicopter according to claim 15 is characterized in that the rotor solidity of the coaxial unmanned helicopter ranges from 0.98 to 1.1.
17. A single-rotor unmanned helicopter, comprising: a variable speed rotor blade, characterized in that The variable speed rotor blade is the variable speed rotor blade described in any one of claims 1 to 14.
18. The single-rotor unmanned helicopter according to claim 17 is characterized in that the rotor solidity of the single-rotor unmanned helicopter ranges from 0.49 to 0.55.