WO2010114387A1

WO2010114387A1 - Magnetically mounted rotor

Info

Publication number: WO2010114387A1
Application number: PCT/NO2010/000122
Authority: WO
Inventors: Petter Muren; Pål SANDBERG
Original assignee: Prox Dynamics As
Priority date: 2009-03-30
Filing date: 2010-03-24
Publication date: 2010-10-07
Also published as: NO330283B1; NO20091279L

Abstract

The present invention discloses a rotor assembly that enables a rotor to be magnetically mounted on a rotor shaft. The thrust from the rotor is transmitted to the shaft by magnets, while mechanical members transfer torque from the shaft to the rotor. If the rotor blades hit an obstacle the magnetic forces will no longer be able to hold the rotor in place and it will disconnect from the shaft.

Description

Magnetically Mounted Rotor

Field of the invention

The present invention relates to thrust generating rotors and to rotary wing aircrafts such as helicopters. In particular it relates to a rotor being mounted to a rotor shaft by magnets. It also relates to rotors that will automatically disconnect from the shaft if the rotor blades hit an obstacle.

Background of the invention

Typically, rotary wing aircrafts such as helicopters are sustained by a rotor, rotating about a vertical rotor shaft, generating lift or upward thrust.

In small radio controlled (RC) helicopters the rotor is normally fixed to a rotor shaft hub with one or more screws . Sometimes the rotor blades can swing back and forth about a single mounting screw positioned in the inner part of the blades, close to the rotor shaft. If the blades hits something while the rotor is spinning this can help reduce the damage to the blades and to the rest of the aircraft. However, even if the blades are free to swing in the horizontal plane they are often damaged by the slightest contact with an obstacle. Often, the blades, the hub and the rotor shaft are damaged if this happens. Should the helicopter experience a more severe crash, the rotor blades and several other parts are always damaged and must be replaced.

To optimize performance or to alter the characteristics of a RC helicopter it is often necessary to change to a new rotor. This normally takes a long time and involves precise work and difficult adjustments.

On this background it is believed that a system allowing easy replacement of rotors would be of great interest. If such a system also could disconnect the rotor from the aircraft in the event of a crash, expensive repairs and a lot of work could be avoided. A system like this could even be used to remove the rotor from the aircraft for normal storage and allow for easy transportation.

There is therefore believed to be a need for a rotor assembly comprising a rotor that can easily be disconnected and reconnected to the rotor shaft hub. The present invention aims at fulfilling this need. In the prior art of rotary wing aircrafts no such system have been described or demonstrated.

Summary of the invention

The present invention aims at fulfilling the need for a very simple and low cost way of replacing the rotor of a rotary wing aircraft by using magnets to hold the rotor.

In the preferred embodiment of the present invention a rotor has two small permanent magnets placed in a central part of the rotor, close to the rotational axis of the rotor shaft. These magnets magnetically interact with another set of magnets mounted in a rotor shaft hub. The magnets primarily secure the rotor in the axial direction transmitting thrust from the rotor to the rotor shaft. Torque from the shaft to the rotor is transmitted via a set of mechanical torque transmitting members. In the preferred embodiment of the present invention the torque is transmitted via two pins placed on the hub. They are extending upwards, in the axial direction of the shaft. The two pins interact with two holes positioned in the central part of the rotor. The pins and the holes are positioned with a small but substantial radial distance from the central axis of the rotor shaft in order to transmit as high torque with as low force as possible.

During operation the magnets holds the rotor on to the rotor shaft hub, while the pins in the hub interacting with the holes in the rotor, transfer torque from the shaft. Because the magnets only transmit thrust and no torque they can be much weaker than would have been the case if they should also transmit torque. The relatively weak magnetic force enables the rotor to disconnect from the shaft (hub) immediately if the rotor blades should hit an obstacle. This way both the rotor and the rest of the aircraft can avoid being damaged in case of a small crash or if an object comes in contact with the spinning rotor. This function will also make any small rotary aircraft utilizing the present invention much safer during operation.

Assembling the rotor is very easy. As soon as the rotor is placed close to its correct position the magnetic forces and the pin and hole combination tends to line up the rotor correctly and snap it in place .

Several alternative configurations of magnets and mechanical torque members within the scope of the present invention are described and discussed.

Brief description of the drawings

The following detailed description of the preferred embodiment is accompanied by drawings in order to make it more readily understandable. In the drawings:

Figure 1 is a perspective view of a disassembled rotor assembly comprising a rotor and a rotor shaft with a pivoting hub.

Figure 2 is a perspective view of a rotor assembly comprising a rotor and a rotor shaft with a pivoting hub.

Figure 3a is a top view and 3b is a side view of the rotor assembly from figure 2.

Figure 4 is a perspective view of an alternative rotor assembly comprising a rotor and a rotor shaft with a rigid hub.

Figure 5 is a perspective view of an alternative rotor assembly comprising a rotor and a rotor shaft with a rigid hub.

Figure 6 is a perspective view of the rotor shaft and hub from an alternative embodiment of the present invention.

Figure 7 is a perspective view of the rotor shaft and hub from an alternative embodiment of the present invention.

Figure 8 is a perspective view of the rotor shaft and hub from an alternative embodiment of the present invention. Detailed description of the preferred embodiment

In the following the present invention will be discussed and the preferred embodiment described by referring to the accompanying drawings. Alternative embodiments will also be discussed; however, people skilled in the art will realize other applications and modifications within the scope of the invention as defined in the enclosed independent claims.

In Figure 1, 2 and 3 the preferred embodiment of a rotor assembly according to the present invention is shown. The rotor assembly (10) comprises a rotor (20) with a central part (22), a pivoting hub (23) and a rotor shaft (24) .

The rotor (20) has two generally horizontal rotor blades (21) arranged as a pair with the tip of the blades pointing in opposite directions. The inner end of each blade is connected to a common central part (22) of the rotor with a predefined pitch angle of about 15 degrees. The pitch angles of both the blades are fixed with respect to the central part (22) and thereby with respect to each other. The central part (22) of the rotor is flat and has a wider area near the rotational axis (A) of the rotor. This flat wider area extends out from the center in a direction that is perpendicular to both the shaft (24) and to the longitudinal direction of the rotor blades (21) and it gives room for two permanent magnets (25) and two holes (27) . These upper magnets (25) are positioned close to the rotational axis (A) while the holes (27) are positioned further out. They are lined up perpendicular to the longitudinal direction of the blades (21) .

When the rotor assembly (10) is assembled, the central part (22) of the rotor is lined up with and mounted on to a pivoting hub (23) . The pivoting hub (23) holds two lower permanent magnets (26) and two pins (28) . The pins (28) are positioned so they directly line up with the holes (27) in the rotor (20) . When the two pins (28) mates with the two holes (27) , the rotor (20) is correctly positioned with respect to the rotor shaft (24) . Torque from the spinning rotor shaft (24) is transmitted to the rotor (20) by these pins and holes. The pins (28) and the holes (27) are positioned with a small but substantial radial distance from the central axis (A) of the rotor shaft (24) in order to transmit as high torque with as low force as possible. Directly inside the pins (28), each of the two lower magnets (26) are positioned. They line up with the upper magnets (25) and are oriented with their magnetic poles so they attract the upper magnets (25) .

The rotor shaft (24) extends upwards and ends in a wider part (31) which at its top holds two tube-shaped members (32) . The holes of the tube-shaped members (32) are lined up with each other and with the pivoting axis (B) . The pivoting axis (B) is perpendicular to the rotor shaft axis (A) and parallel to the longitudinal direction of the rotor blades (21). The two tube-shaped members (32) are positioned to each side of the rotor shaft axis (A) to give room for the pivoting hub (23) between them. The lower end of the pivoting hub (23) has a pivot hole with the same inner diameter as the two tube- shaped members (32) . The pivoting hub (23) and the rotor shaft (24) are connected together by a pivot pin (33) . The pin (33) goes trough the pivot hole in the lower part of the pivoting hub (23) and the two tube-shaped members (32) to form a hinge, enabling the rotor (20) to pivot along its longitudinal direction (parallel to axis B) . This hinge, will via the pivot pin (33) transmit both torque and thrust between the rotor (20) and the rotor shaft (24) .

When the rotor assembly (10) of the preferred embodiment of the present invention is used in a helicopter, the aircraft is controlled by cyclically changing the pitch angle of the rotor blades (21) . These cyclical changes of the pitch angle are normally controlled via a so-called swash plate (not shown) and a pitch link (not shown) . The pitch link normally extends vertically parallel to the rotor shaft (24) and at its top end it is connected to a pitch arm (29) part of the pivoting hub (23) . When the pitch link is moved up or down as indicated by vertical arrow (D) the pivoting hub (23) will rotate about the pivot axis (B) . Because the rotor (20) is mounted onto the pivoting hub (23) it will follow the rotating arrow (c) when the pitch link moves along vertical arrow (D) .

During normal operation, when an aircraft with a rotor assembly (10) according to the present invention flies and maneuvers, the force between the upper magnets (25) in the rotor (20) and the lower magnets (26) in the pivoting hub (23) should be just strong enough to match the thrust from the rotor (20) plus the dynamic forces from cyclic changes of pitch angles. The magnetic strength of the magnets (25,26) should be optimized according to the expected thrust and dynamic loads. Typically the magnets (25,26) should be strong enough to (in total) match a force about 3 times the weight of the aircraft for a rotary wing aircraft and about 2 times the weight in case of a fixed wing aircraft. If the magnets (25,26) are stronger the rotor (20) might not disconnect properly in a crash. To disconnect as intended any additional forces due to a crash or because the rotor blades (21) hit an object should pull or tilt the rotor (20) such that the magnets (25,26) separate. When the rotor (20), or at least one side of the rotor (20), has been lifted from the pivoting hub (23) the pins (28) will no longer remain in the holes (27) . At this point the shaft (24) is not able to transmit torque to the rotor (20) and the rotor (20) will quickly swing or pull away from the pivoting hub (23). The magnets (25,26) are no longer lined up and the rotor (20) is completely disconnected from the aircraft without being damaged.

To mount the rotor (20) back on to the aircraft again is a very quick and easy operation. Simply line up the rotor (20) over the pivoting hub (23), enter the pins (28) into the holes (27) in the central part

(22) of the rotor (20) and let the magnets (25,26) snap the rotor

(20) on to the aircraft again.

Figure 4 shows an alternative embodiment of the present invention. This rotor assembly (40) is almost identical to the preferred rotor assembly (20) but without a pivoting hub. If the rotor assembly (40) is to be used in a fixed wing aircraft or in a 4-rotor X-shaped aircraft there are no need for cyclic pitch control of the rotor blades (41), therefore the fixed hub (43) is mounted directly onto the rotor shaft (44) . The magnetic function and the way of transmitting torque is identical to the preferred rotor assembly

(10) . The central part (42) holds a set of upper magnets (45) and two holes. The fixed hub holds a set of lower magnets and two pins (48).

Figure 5 shows an alternative embodiment of the present invention. In this rotor assembly (50) the pins (58) are moved from the fixed hub (53) to the central part (52) of the rotor. The pins are still extending in a direction parallel to the rotor shaft, but in stead of pointing up, the pins are now pointing down, facing the two holes (57) in the fixed hub (53) .

In this alternative rotor assembly (50) only one upper magnet (55) positioned in the very center of the rotor and one lower magnet (56) in the center of the fixed hub (53) is used. In this case the single magnets (56,57) should be twice as strong as the double set of magnets used in the previous embodiments discussed above. Yet another version of the rotor assembly (50) can be realized by replacing one of the permanent magnets (55,56) with a material that is not a permanent magnet but still have magnetic properties. Typically one of the permanent magnets could be replaced by iron or soft steel or other materials that will magnetically interact with a permanent magnet.

Finally Figure 6, 7 and 8 shows examples of other ways of designing rotor shaft hubs according to the present invention. Here only the hub part is shown, but it will be obvious to anyone skilled in the art that these hubs may be combined in different ways or used as pivoting hubs.

In Figure 6 the 4-armed fixed hub (63) uses a combination of pins (68), holes (67) and magnets (66). In Figure 7 the circular fixed hub (73) has a square mechanical member (78) extending upwards. This square member (78) is meant to mate with a similar square hole in the central part of a corresponding rotor. Only one lower magnet (76) is used and it is positioned in the centre of the hub. In Figure 8 an alternative circular fixed hub (83) with a square center positioned hole (87) and a single magnet (86) is shown.

The figures of embodiments with fixed hubs only show two-bladed rotors. It will, however, be obvious to anyone skilled in the art that a rotor with any number of blades may be used. The present invention would also be useful in many other applications. It may advantageously be utilized in all applications wherein a thrust generating rotor should be non-permanently mounted on a shaft.

While the preferred embodiment of the present invention have been described and certain alternatives suggested, it will be recognized by people skilled in the art that other changes may be made to the embodiments of the invention without departing from the broad, inventive concepts thereof. It should be understood, therefore, that the invention is not limited to the particular embodiments disclosed but covers any modifications which are within the scope and spirit of the invention as defined in the enclosed independent claims .

Claims

Patent claimsPatent claims

1. A rotor assembly including a rotor shaft, a rotor adjusted to generate thrust, and a hub mounted on top of the rotor shaft, characterized in

at least one first magnetic member provided on the central part of the rotor, at least one second magnetic member provided on the hub, whereby the first and the second magnetic members interact to magnetically connect the rotor to the rotor shaft, thereby transmitting thrust from the rotor to the rotor shaft.

2. A rotor assembly according to claim 1 wherein the first magnetic member and the second magnetic member both are permanent magnets.

3. A rotor assembly according to claim 1 wherein the first magnetic member is a permanent magnet and where the second magnetic member is not a permanent magnet.

4. A rotor assembly according to claim 1 wherein the first magnetic member is not a permanent magnet and where the second magnetic member is a permanent magnet.

5. A rotor assembly according to claim 1, the rotor assembly further comprising at least two torque transmitting members for transmitting torque from a rotor shaft to the rotor.

6. A rotor assembly according to claim 5, wherein a first torque transmitting member is placed in the central part of the rotor and a second torque transmitting member is placed in the hub mounted on the shaft, whereby said torque transmitting members are further adapted to mechanically interact to transmit torque from the shaft to the rotor.

7. A rotor assembly according to claim 6, wherein the first torque transmitting members employs a hollow part and where the second torque transmitting member extends out from the hub in a direction parallel to the shaft.

8. A rotor assembly according to claim 6, wherein the first torque transmitting members extends out from the central part of the rotor in a direction parallel to the shaft and where the second torque transmitting member employs a hollow part.

9. A rotor assembly according to claim 1 wherein a magnetic force that is acting between the magnetic members is strong enough to transmit thrust from the rotor to the shaft whereby if the rotor hits an object, additional forces that are created will disconnect the rotor from the shaft.

10. A rotor assembly according to claim 1, wherein the at least one first magnetic member is placed in the central part of the rotor and the at least one second magnetic member is placed in the hub mounted on the shaft, and where at least one first torque transmitting member is placed in said central part of the rotor and at least one second torque transmitting member is placed in the hub, said first and second torque transmitting members being adapted to mechanically interact to transmit torque from the shaft to the rotor and said first and second magnetic members being adapted to magnetically interact in order to connect the rotor to the shaft, whereby thrust from the rotor is transmitted to the rotor shaft when the shaft and the rotor is rotating.

11. A rotor assembly according to claim 1, wherein the rotor is a two-bladed rotor, at least two magnetic members adapted to transmit thrust from said rotor to a rotor shaft and at least two torque transmitting members adapted to transmit torque from the rotor shaft to the rotor, said rotor assembly further comprises an upper hub pivotally connected to the rotor shaft via a pivot pin being held by a lower hub mounted on the rotor shaft, said pivot pin having an axis perpendicular to the rotor shaft and parallel to the rotor, whereby the rotor can pivot about said axis in order to change pitch angles.