HIGH-EFFICIENCY PROPELLER FOR AIRCRAFT

Abstract

An improved efficiency propeller for aircraft includes a blade structure mounted onto a propeller hub, a servo unit, and a cantilevered base. A distinctive feature of the invention is that the blade structure includes a main mast, which is mounted onto a propeller hub and forms the spine of the leading edge of the blade structure, and at least one secondary mast aligned with the main mast, and turning spacers with struts fitted with a strut are mounted onto the main mast, and the struts are covered by lateral pieces of a skin module, and the overlapping and flexible lateral piece of the skin module form a skin.

Claims

1. A propeller for aircraft, comprises a blade structure mounted onto a propeller hub, a servo unit, and a cantilevered base, wherein the blade structure comprises a main mast, at least one secondary mast, and spacers, wherein the main mast is mounted onto the propeller hub and forms a spine of a leading edge of the blade structure, and the at least one secondary mast is mounted onto and aligned with the main mast, and the at least one secondary mast turns the spacers, the spacers comprise struts and are mounted onto the main mast, and the struts are covered by lateral pieces of a skin module, and the lateral pieces of the skin module are overlapping and flexible, and form a skin.

2. The propeller according to claim 1, wherein the at least one secondary mast is mounted onto a secondary mast base piece movable around an axis of rotation of the propeller hub, and the at least one secondary mast is connected to a tilting hub of spaced battens.

3. The propeller according to claim 1, wherein the struts embrace in a fork-like manner the at least one secondary mast, wherein the struts are turnable by the at least one secondary mast.

4. The propeller according to claim 1, wherein an axis of the main mast is parallel to the leading edge of the blade structure, the main mast and parts of the spacers mounted onto the main mast are covered by frontal pieces of the skin module, the frontal pieces of the skin module are connected to the lateral pieces of the skin module, and the lateral pieces of the skin module and the frontal pieces of the skin module form a modular unit of the skin.

5. The propeller according to claim 1, wherein the lateral pieces of the skin module are connected to each other so that the lateral pieces move relative to each other, the lateral pieces of the skin module are connected to at least one neighbouring spacers of the spaces so that each of the lateral pieces of the skin module is fixed onto the struts of the at least one of the spacers, each of the lateral pieces of the skin module is assigned to the struts of a neighbouring spacer so that the neighbouring spacer and each of the lateral pieces move relative to each other, each of the lateral pieces of the skin module crosses, at least in part, a parallel line following an axis of the struts, wherein the parallel line is an intersecting line of a first plane and a second plane, the first plane crosses the axis of the struts and is perpendicular to a surface of the blade structure, and the second plane is a plane of the surface of the blade structure.

6. The propeller according to claim 1, wherein the further away from the propeller hub, the smaller a diameter of a cross-section of the main mast and the at least one secondary mast becomes.

7. The propeller according to claim 1, wherein the main mast is connected to the propeller hub through a hub of first spaced battens, a gear fixed to a hub of second spaced battens is associated to the hub of the first spaced battens, and a rack and a slider plate are associated to the gear fixed to the hub of the second spaced battens.

8. The propeller according to claim 1, wherein the blade structure is fitted with a flexible blade tip element, and the lateral pieces of the skin module are fitted with aerodynamic elements of aerodynamic profile trimming.

9. The propeller according to claim 1, wherein the skin is not fully closed.

10. The propeller according to claim 1, wherein the propeller hub is hollow, the cantilevered base is standing and is fixed to a hydraulic cylinder through the propeller hub and the blade structure is connected to the cantilevered base with a bearing located in the propeller hub.

11. The propeller according to claim 2, wherein an axis of the main mast is parallel to the leading edge of the blade structure, the main mast and parts of the spacers mounted onto the main mast are covered by frontal pieces of the skin module, the frontal pieces of the skin module are connected to the lateral pieces of the skin module, and the lateral pieces of the skin module and the frontal pieces of the skin module form a modular unit of the skin.

12. The propeller according to claim 3, wherein an axis of the main mast is parallel to the leading edge of the blade structure, the main mast and parts of the spacers mounted onto the main mast are covered by frontal pieces of the skin module, the frontal pieces of the skin module are connected to the lateral pieces of the skin module, and the lateral pieces of the skin module and the frontal pieces of the skin module form a modular unit of the skin.

13. The propeller according to claim 2, wherein the lateral pieces of the skin module are connected to each other so that the lateral pieces move relative to each other, the lateral pieces of the skin module are connected to at least one neighbouring spacers of the spaces so that each of the lateral pieces of the skin module is fixed onto the struts of the at least one of the spacers, each of the lateral pieces of the skin module is assigned to the struts of a neighbouring spacer so that the neighbouring spacer and each of the lateral pieces move relative to each other, each of the lateral pieces of the skin module crosses, at least in part, a parallel line following an axis of the struts, wherein the parallel line is an intersecting line of a first plane and a second plane, the first plane crosses the axis of the struts and is perpendicular to a surface of the blade structure, and the second plane is a plane of the surface of the blade structure.

14. The propeller according to claim 3, wherein the lateral pieces of the skin module are connected to each other so that the lateral pieces move relative to each other, the lateral pieces of the skin module are connected to at least one neighbouring spacers of the spaces so that each of the lateral pieces of the skin module is fixed onto the struts of the at least one of the spacers, each of the lateral pieces of the skin module is assigned to the struts of a neighbouring spacer so that the neighbouring spacer and each of the lateral pieces move relative to each other, each of the lateral pieces of the skin module crosses, at least in part, a parallel line following an axis of the struts, wherein the parallel line is an intersecting line of a first plane and a second plane, the first plane crosses the axis of the struts and is perpendicular to a surface of the blade structure, and the second plane is a plane of the surface of the blade structure.

15. The propeller according to claim 4, wherein the lateral pieces of the skin module are connected to each other so that the lateral pieces move relative to each other, the lateral pieces of the skin module are connected to at least one neighbouring spacers of the spaces so that each of the lateral pieces of the skin module is fixed onto the struts of the at least one of the spacers, each of the lateral pieces of the skin module is assigned to the struts of a neighbouring spacer so that the neighbouring spacer and each of the lateral pieces move relative to each other, each of the lateral pieces of the skin module crosses, at least in part, a parallel line following an axis of the struts, wherein the parallel line is an intersecting line of a first plane and a second plane, the first plane crosses the axis of the struts and is perpendicular to a surface of the blade structure, and the second plane is a plane of the surface of the blade structure.

16. The propeller according to claim 2, wherein the further away from the propeller hub, the smaller a diameter of a cross-section of the main mast and the at least one secondary mast becomes.

17. The propeller according to claim 3, wherein the further away from the propeller hub, the smaller a diameter of a cross-section of the main mast and the at least one secondary mast becomes.

18. The propeller according to claim 4, wherein the further away from the propeller hub, the smaller a diameter of a cross-section of the main mast and the at least one secondary mast becomes.

19. The propeller according to claim 5, wherein the further away from the propeller hub, the smaller a diameter of a cross-section of the main mast and the at least one secondary mast becomes.

20. The propeller according to claim 2, wherein the main mast is connected to the propeller hub through a hub of first spaced battens, a gear fixed to a hub of second spaced battens is associated to the hub of the first spaced battens, and a rack and a slider plate are associated to the gear fixed to the hub of the second spaced battens.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0029] The invention is presented in more detail using drawings of possible implementation forms.

[0030] On the attached drawings,

[0031] FIG. 1 shows a schematic drawing of the blade structure with breakouts,

[0032] FIG. 2 shows a schematic drawing of the skeleton of the blade structure,

[0033] FIG. 3 shows a folding drawing of the cover of the blade structure,

[0034] FIG. 4 shows a front-view drawing of an implementation form of the propeller with an eccentric propeller hub,

[0035] FIG. 5 shows a side view of FIG. 4,

[0036] FIG. 6 shows an A-A section of FIG. 7,

[0037] FIG. 7 shows a side view drawing of the propeller structure fitted with an eccentric propeller hub,

[0038] FIG. 8 shows a C-C section of FIG. 9,

[0039] FIG. 9 shows the drawing of a longitudinal section of the hydraulic cylinder of the propeller,

[0040] FIG. 10 shows a B-B section of FIG. 11,

[0041] FIG. 11 shows a side view drawing of the propeller structure fitted with a concentric propeller hub,

[0042] FIG. 12 shows a drawing of a blade end,

[0043] FIG. 13 shows a drawing of an implementation form of the blade structure with aerodynamic profile parts,

[0044] FIG. 14 shows a blade section with profile parts.

DETAILED DESCRIPTION OF THE EMBODIMENTS

[0045] FIG. 1 shows a shape-changing blade structure 11. It shows the main mast 1, the secondary masts 2, the eccentric propeller hub 3, the secondary mast base pieces 17, the axis of rotation 4 of the turning secondary masts 2, the axis of rotation 9 of the propeller hub 3 and the propeller, the mast base 8 that fixes the main mast 1, and the spacers with struts 5 located on the main mast 1 that form a unit with the fork-like struts 16. Lateral piece of skin module 6 are located on the struts 16, and, together with the frontal pieces of skin module 18, they form the skin 15. The lateral pieces of skin module 6 are made of a bendable and flexible material, such as a composite Kevlar material, and are suitably covered by teflon. FIG. 1 also shows the parallel line 7 and the leading edge 10.

[0046] The main mast 1 is fixed to the propeller hub 3 through the mast base 8, and they rotate together. As an example, the bases of three secondary masts 2 of different length are fixed into the secondary mast base piece 17. The secondary mast base piece 17 can turn in a fan-like manner around the mast base 8 and the identical fixed axis having an axis of rotation 4 located between the stud forming part of the propeller hub 3. The main mast 1 is located as close as possible to the leading edge 10; in fact, it forms the spine of the leading edge 10 by way of the spacers with struts 5 and the frontal pieces of skin module 18. The spacers with struts 5 are connected to the main mast 1 by such means, e.g., bearings, that allow displacement relative to the main mast 1 only in a plane perpendicular to the main mast 1 along the main mast 1 as axis.

[0047] FIG. 2 shows the main mast 1, the secondary masts 2, the mast base 8 of the main mast 1, the spacer with struts 5, the propeller hub 3, the axis of rotation 4 of the secondary masts, and the strut 16 of the spacers with struts 5. The struts 16 of the spacer with struts 5 has the following distinctive features: [0048] they determine the aerodynamic characteristics of sections of the blade structure 11; [0049] they determine the planform of the blade structure 11; [0050] they drive the displaceable secondary mast 2; [0051] they hold the lateral pieces of skin module 6.

[0052] The smoothness of the surface of the blade structure 11 may be improved by increasing the number of the spacers with struts 5, by refining the modular distribution, and structural deviation from the ideal blade arch line may be reduced.

[0053] The larger the distance from the propeller hub 3, the smaller the diameter of the cross-section of the main mast 1 and/or the secondary masts 2 becomes. However, in another implementation form, the diameters remain unchanged. The profile of the blade structure 11 may be further shaped and refined by using a conic skeleton. Thus, the skin 15 sections can become thinner and thinner approaching the blade ends of the blade structure 11, which reduces weight and allows for a more even distribution of mechanical tension.

[0054] With a view to ensuring the feasibility of various blade planforms (e.g., long, narrow), further displaceable blade support rods (without own drive) may be installed in the blade structure 11 in addition to the two main skeleton components, i.e., the main mast 1 and one secondary mast 2 identified as a minimum requirement. More than two secondary masts 2 need to be applied in all situations where the planform of the blade limits the length of the strut 16 of the spacer with struts 5. In such situations, the strut 16 cannot reach the secondary masts 2 displaced by the servo unit 13 (presented on FIG. 5; internal structure shown on FIG. 7) over a given radius value.

[0055] The mast-like rods perform passive movement, i.e., they are not displaced, are moved and adjusted appropriately by the spacers with struts 5 that are close to the axis of rotation 4 of the secondary masts 2 and reach the secondary masts 2. As the blade radius increases, the regulatory role of the secondary masts 2 is always taken over by the rod that performs passive movements closest to the leading edge 10. The necessary number and individual length of the mast-like rods that perform passive movement are determined by the stiffness/rigidity requirements of the blade structure 11 and the blade planform to be achieved.

[0056] FIG. 3 shows the “folding plan” of the lateral pieces of skin module 6 located on the struts 16. The lateral pieces of skin module 6 are fitted with strut sockets 14 that can be pulled onto the strut 16.

[0057] The lateral pieces of skin module 6 are responsible for transforming the necessarily changing configuration defined only by its main points by the main mast 1, the secondary masts 2, and the struts 16 of the spacers with struts 5 into a blade surface that is aerodynamically efficient at all times, so that, in the meantime, they do not hinder the free movement of the secondary masts 2 and struts 16 working in the internal layers of the blade.

[0058] One side of the lateral piece of skin module 6 is connected to the spacer with struts 5 so that the strut socket 14 located in the blade skin lateral piece of skin module 6 fits onto the fork-like branch of the strut 16, and the lateral piece of skin module 6 surrounds the strut 16 from all directions. The lateral piece of skin module 6 thus pulled on is connected to the strut 16 without any displacement. If necessary, the rigidity of the fixing can be increased by gluing, moulding, or another similar method.

[0059] At the same time, the neighbouring blade skin lateral pieces of skin module 6 are connected to each other so that they remain displaceable relative to each other. The blade skin lateral pieces of skin module 6 are also connected to each other, so that they remain displaceable relative to each other: they can move and slide on each other and relative to each other. The recommended arrangement of the modular skin elements 23 is similar to the arrangement of scales of fish or roof tiles, where the elements are connected to each other by partial overlapping, but they are not fixed to each other. The lateral piece of skin module 6 is located next to the neighbouring strut 16 so that it embraces it in a cloak-like manner from two directions (from the directions of the two external sheets of the propeller blade).

[0060] The lateral pieces of skin module 6 are connected to each other so that they can move relative to each other, and the lateral pieces of skin module 6 are connected to at least two neighbouring spacers with struts 5 (with the exception of the outmost spacer with struts 5 in radial direction, which is necessarily connected to only one piece) so that each lateral piece of skin module 6 is fixed onto the strut 16 of at least one spacer with struts 5, while the same lateral piece of skin module 6 is assigned to the strut 16 of at least one neighbouring spacer with struts 5 so that the neighbouring spacer with struts 16 and the lateral piece of skin module 6 can move relative to each other. The lateral piece of skin module 6 crosses, at least in part, the parallel line 7 following the axis of the strut 16 which parallel line 7 is the line of intersection of, on the one hand, the plane that crosses the axis of the given neighbouring strut 16 and is perpendicular to the surface of the blade structure 11 and, on the other hand, the plane of the surface of the blade structure 11.

[0061] The number and size of the interconnected lateral pieces of skin module 6 forming the modular skin 15 can be determined freely. This also means that the length of the struts 16, i.e., the radius of the propeller and the size of the blade surface, can be increased as necessary.

[0062] It is irrelevant from the perspective of aerodynamics whether the skin 15 of the propeller is hermetically sealed or not. Drag and efficiency of the propeller is mostly determined by the entirety of surface parts having an influence of airflow. Whether or not parts of the skin 15 are connected to each other in a hermetically sealed manner is irrelevant from this perspective. This recognition makes it possible to overcome the professional prejudice concerning bag-like covers, as described as part of the state of the art, and allows us to implement a more advantageous modular skin 15.

[0063] FIG. 4 shows, as an example, the frontal view of a propeller with an eccentric propeller hub 3. It shows the secondary masts 2 opened in a fan-like manner, the modular unit of skin 23 formed by the lateral piece of skin module 6 and the frontal piece of skin module 18, and the skin 15 formed by the modular units of skin 23. FIG. 4 also shows the outline of the known propeller cone 19 of the propellers.

[0064] FIG. 5 shows a side-view of the servo unit 13, the surrounding propeller cone 19, the propeller hub 3, and the cantilevered base 21 with a shortened structure. In this situation, the blades are shown in feathered position of blade 22. The internal skeleton is moved by the servo unit 13, which also includes the hydraulic cylinder 24, by moving the secondary masts 2. The movements causing the blade structure 11, 22 to change its shape may be controlled via remote control through controllers located in the skeleton according to the wishes of the pilot, or they may be controlled by an automatic regulator system.

[0065] FIG. 7, and FIG. 6 showing the A-A section thereof, shows an implementation form of a hydraulic power transmission solution. FIG. 6 shows the eccentric propeller hub 3, the gear fixed to the hub of spaced batten 30, the slider plate 31, the rack 32, the hub of spaced batten 29, and the main mast 1. FIG. 7 also shows the secondary masts 2, the cantilevered base 26 and its piston 25, the driving gear 34, the gear 35, and the aircraft body 44 of the aircraft or drone. Our implementation forms include three secondary masts 2 for each blade structure 11, but their number may change from one to more pieces, depending on the size and shape of the blades. On FIG. 7, a hydraulic cylinder 24, located in a central position and operating in two directions, serves as power transmission source for moving internal skeleton of the blade structure 11 and the struts 16 forming a single part with the spacer with struts 5. The piston 25 of the hydraulic cylinder 24 ends in an accurately formed external edge, the surface of which is suitable for leading the rollers 33 that move at high speed. The hydraulic cylinder 24 is fixed onto the cantilevered base 26 that is connected to the aircraft body, and it is not involved in the rotating movement of the propeller.

[0066] The cantilevered base 26 needs to be solid enough to transmit all pushing, pulling, and bending force that arises between the propeller and the aircraft body. The cantilevered base 26 is not exposed to any twisting force, as it is transmitted by the driving gear 34. The blade structures 11 are installed into the hollow eccentric propeller hub 3, which is mounted onto the cantilevered base 26 through bearings 27. Thus, the twisting torque required for rotating the blades are transmitted from the driving motor to the eccentric propeller hub 3 through the driving gear 34 and the large gear 35. As pulling and pushing forces also arise on the blade structures 11, the bearing 27 is also capable of transmitting such forces, meaning that the bearing 27 is a ball or inverted tapered roller bearing.

[0067] This design of the hydraulics makes it possible to control and operate deformation of any number of torsion blade structures 11 using a single central hydraulic cylinder 24. With a view to twisting the rotating blade structures 11, the displacement of the non-rotating piston 25 needs to be transmitted to the main mast 1 and secondary masts 2 of the blades. In this implementation form, a transmission chain including rollers 33, steel slider plates 31, racks 32, and a suitably converted hub of spaced batten 29 is used for that purpose.

[0068] The characteristics of the hub of spaced batten 29 include the followings: [0069] it can rotate around the main mast 1 freely; [0070] it includes a lower geared part; [0071] it does not include any lateral piece of skin module 6; [0072] it is responsible for tilting the secondary masts 2 exactly in the angle specified by the pilot or the regulating system; [0073] it has a rigid build.

[0074] In normal operation, the blade structures 11 perform rotating movements, while the cantilevered base 26 and the hydraulic cylinder 24 remain in a stationary position relative to the aircraft body. The slider plates 31 rotate with the blade structures 11 and hold onto the edge of the piston 25 using their openings fitted with rollers. The notches cut into the hollow and eccentric propeller hub 3 form a rail and allow the slider plates 31 to move in an axial direction. The connection fitted with rollers and the axially free movement allowed in the notches make it possible for the slider plates 31 to follow the axial displacement of the piston 25 continuously.

[0075] The rack 32 parts fixed onto the slider plates 31 are connected to the gears on base-facing part of the hub of spaced batten 29. Thus, the hub of spaced batten 29 is forced to follow the movement of the slider plates 31 around the main mast 1 as axis. The struts 16, which turn in a plane that is perpendicular to the main mast 1, not only tilt and turn the secondary masts 2 around their axis of rotation, but also fix them in their new position.

[0076] The secondary masts 2, driven by the hub of spaced batten 29, open and close in a fan-like manner, as they are allowed to do so by their arrangement and the position of their axis of rotation. The purpose of the arrangement is to ensure that the useful blade surface created primarily by the main mast 1 and the secondary masts 2 (i.e., the internal skeleton) with the support of the spacers with struts 5, the lateral pieces of skin module 6, and the frontal pieces of skin module 18 can form slices with radially adjusting angles that follow the radial distribution of resultant wind at all times (i.e., dynamically), creating a twist altogether.

[0077] FIG. 8 shows a hydraulic cylinder 24, while FIG. 9 shows a C-C section of the hydraulic cylinder 24 shown on FIG. 8 and the intersected eccentric propeller hub 28. FIG. 9 also shows the piston 25, the bearing 27, the cantilevered base 26, and the aircraft body 44.

[0078] FIGS. 10 and 11 show implementation forms that are similar to those presented on FIGS. 6 and 7, respectively, but in this implementation form, the hollow propeller hub is a concentric propeller hub 36. FIG. 10 shows the secondary mast 2, the cantilevered base 26, the slider plate 31, the rack 32, the propeller hub 36, and the secondary mast base ring 38. Furthermore, FIG. 11 also shows the main mast 1, the rollers 33, the spacers 37, the hub of spaced batten 29, the gear 35, the driving gear 34, and the aircraft body 44. The secondary mast 2 is inserted either into an eccentric propeller hub 3 at the secondary mast base piece 17, or into a concentric propeller hub 36 at the ring-shaped secondary mast base piece 38. The main difference between the cantilevered base 21 and the cantilevered base 26, as well as the concentric propeller hub 28 and the propeller hub 36, as shown on FIG. 5, is that the cylindric sections are longer in the implementation form using the cantilevered base 26 and the concentric propeller hub 36.

[0079] The implementation forms of the eccentric propeller hub 3, 28 and the propeller hub 36 have advantages and disadvantages, as follows. When an eccentric solution is used, the axis of rotation 4 of the turning axis of the secondary masts 2 shown on FIG. 1 is parallel to the axis of rotation 9 of the propeller; when a concentric solution is used, the two axes of rotation 4, 9 are one and the same.

[0080] An eccentric solution offers a propeller hub 3 that is easier to repair and maintain, but the mathematical error (i.e., the difference between the curves) may not reach zero. This means that efficiency may degrade at lower speeds at the base of the blades; however, a braking air-wing mode cannot appear in either scenario. When a concentric solution is used, the curves, i.e., the direction of speed vectors and the chord lines of the blade structure sections, are 100% identical in terms of mathematics in the entire radius range. For this reason, this solution provides the greatest possible improvement in efficiency. However, a disadvantage is that the entire propeller needs to be disassembled to repair the blade structure 11. When an eccentric solution is used, the secondary masts 2 (FIG. 1) are supported by the secondary mast base pieces 17; when a concentric solution is used, the secondary masts 2 are supported by the ring-shaped secondary mast base rings 38 shown on FIGS. 10 and 11.

[0081] FIG. 12 shows the end of the blade structure 11. It shows the main mast 1, the secondary masts 2, and the blade tip element 20. The blade tip element 20 is made of an elastic material and is in part self-adjusting. The blade tip element 20 participates in influencing vortices at the tip of the blades, thereby influencing the degree of loss at the tip of the blades.

[0082] FIG. 13 shows an implementation form of the blade structure 11. FIG. 13 indicates the locations to fix aerodynamic trimming pieces 43 where the elements of aerodynamic profile trimming 41, shown on FIG. 14, may be placed. FIG. 14 shows the outline of the section according to NACA 0012, as well as the blade section untrimmed 39, the elements of aerodynamic profile trimming 41, and the aerodynamically trimmed blade section 42. The element of aerodynamic profile trimmings 41 may be placed onto the lateral pieces of skin module 6 in strips, meaning that they are in similar positions on each lateral piece of skin module 6, and they exert similar and optimized aerodynamic effect on the blade structure 11.

[0083] The invention has numerous advantages. It is advantageous that it is interchangeable with currently used propeller structures. This is achieved by using only one hydraulic cylinder for each propeller. It is possible to avoid extreme speed values for the blade tips that might approach or exceed the speed of sound. This ensures quieter operation and can improve safety. It is not necessary for the skin to be hermetically sealed, so more advantageous propeller structures can be formed.

[0084] The aerodynamic phenomena characteristic of stalling can be avoided along the surface of the propeller, and, overall, it allows the propeller to be operated at maximum or near-maximum efficiency in a wider speed range.

[0085] By providing a better approach to optimal twisting, the propeller implemented according to the invention outperforms propellers representing the state of the art in terms of power/efficiency. It is not forced to rotate the blade tips at a speed close to or above the speed of sound, thus avoiding modes of operation with increased losses. The blade angle can be regulated in a wide range without the blades spinning out of the wind (partially or completely), i.e., stalling or braking flight as a windmill.

[0086] A propeller fitted with blades according to the invention is able to avoid stalling/windmilling modes in a wider range, and its performance will be greater than that of similar rigid-blade propellers.

[0087] The blades according to the invention are capable of providing the same or better performance at higher speeds by operating at lower blade tip speeds but with greater twist. This means less noise and greater efficiency compared to solutions representing the state of the art.

[0088] For blades according to the invention, the blade angle (the angle of adjustment of the sections, i.e., the angle between the section chord and the plane of rotation) is minimal at a higher degree of twisting. Reducing the twist gradually means increasing the blade angles; in practice this may be expedient e.g., at acceleration. The proposed design ensures that the adjustment angle distribution of the sections (along the radius) is approximately equal to the angle of the resultant airflow along the blade (resultant airflow) with the plane of rotation. The blade angles can be increased or decreased as necessary or desirable while performing manoeuvres. The angles of each chord line vary not only with respect to the plane of rotation, but also with respect to each other. The latter means twisting.

[0089] Using the proposed torsional propeller blades, a mathematical analytical match can be achieved between the direction of the chord lines of the blade sections and the direction of the resulting wind, at approximately all velocity and all radius values. This allows the blade angle to be optimal over a wide range of ADVANCE RATIO, which ensures high efficiency over a wide range of ADVANCE RATIO even at moderate rotary speed. Propeller efficiency is close to the theoretical maximum over a very wide range of selected cruising speeds.

[0090] A further advantage of the modular skin is that it takes advantage of the dominant, quasi-constant directions of flow measured on the surface of the propeller blade, and the individual deformation of the elements is minimal. This allows the modular skin to follow the deformations of the skeleton with low friction and without increasing the elastic resistance to movement of the skeleton elements, while keeping the outer surface of the propeller blade close to the aerodynamic optimum. The modular skin is easier to implement and has better manufacturability in comparison to deformable skins representing the state of the art.

[0091] Increasing efficiency results in fuel savings. If allowed by the engine power of the aircraft, the entire subsonic speed range can be flown with the same propeller, including both take-off efficiency (short and normal runways), comfortable manoeuvres, and flight stability at top speed.

[0092] An unexpected economic advantage, which also reduces production time, is that the production of blades in their contemporary complex spatial shape (e.g., 3D design/milling) becomes unnecessary. It is advantageous for both construction (including design and sizing) and manufacturing technology that most of the design work can be done in a plane (2D).

[0093] For electric aircraft, the more favourable (softer) torque characteristics and better controllability of electric motors are more pronounced in the wide working range of propellers fitted with blades according to the invention, and the number of available drive/steering optimum points increases. The given battery capacity, which is still generally a bottleneck today, allows a greater flight range when aircraft are driven with more efficient propellers.

[0094] The primary field of application of the invention is driving subsonic transport aircraft and drones. In addition to the above examples, the invention can be implemented in other forms within the scope of protection.