Helicopter rotor

A rotor for a helicopter, having a drive shaft rotating about a first axis; a hub angularly integral with the drive shaft about the first axis; and at least two blades projecting from the hub on opposite sides of the first axis and elongated along respective second axes crosswise to the first axis; each blade is movable with respect to the hub and to the other blade about a respective third axis crosswise to the respective second axis; the rotor has at least two dampers for damping oscillation of respective blades about the respective third axes, and which have respective first portions movable integrally with the respective blades about the respective third axes; and the dampers have respective second portions connected elastically to the respective first portions and functionally to each other.

The present invention relates to a helicopter rotor.

BACKGROUND OF THE INVENTION

Helicopters are known comprising a fuselage; a main rotor fitted to the top of a central portion of the fuselage; and an antitorque tail rotor for counteracting the torque transmitted by the main rotor to the fuselage.

Articulated main rotors and/or antitorque rotors are also known.

Articulated rotors comprise a drive shaft that rotates about a first axis; a hub that rotates integrally with the drive shaft about the first axis; and a number of blades projecting from the hub along respective second axes radial with respect to the first axis.

Each blade can rotate with respect to the hub about the respective second axis to adjust its angle of attack with the airstream, and is free to oscillate about the hub about a respective third axis to perform a so-called flapping movement. More specifically, each third axis is crosswise to the first axis and to the second axis of the relative blade.

Each blade is free to oscillate with respect to the hub and the other blades about a respective fourth axis, parallel to the first axis, to perform a so-called “lead-lag movement”.

A need is felt to damp vibration induced by lead-lag motion of the blades, using damping devices whose damping action is affected as little as possible by centrifugal force, so they are effective over a wide range of blade rotation speeds about the first axis, and a wide range of damping device positions along the second axes of the relative blades.

A need is also felt within the industry to damp vibration induced by lead-lag motion of the blades, using damping devices as lightweight and compact as possible.

Finally, a need is felt to damp vibration induced by lead-lag motion of the blades, using damping devices that require no operating fluid, e.g. oil, to function correctly, so as to simplify damping device construction and maintenance.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a helicopter rotor designed to meet at least one of the above requirements cheaply and easily.

According to the present invention, there is provided a helicopter rotor as claimed in the attached claims.

DETAILED DESCRIPTION OF THE INVENTION

Number1inFIG. 1indicates a helicopter substantially comprising a fuselage2with a nose5; a main rotor3on top of fuselage2; and an antitorque tail rotor4fitted to a fin projecting from fuselage2at the opposite end to nose5.

More specifically, main rotor3provides helicopter1with the lift and thrust required to lift and propel helicopter1respectively, while rotor4exerts force on the fin to generate a torque reaction on fuselage2to balance the torque exerted on fuselage2by main rotor3, and which would otherwise rotate fuselage2about an axis A.

Rotor3is articulated, and substantially comprises (FIGS. 2 and 3):a drive shaft10which rotates anticlockwise about axis A in the top plan views inFIGS. 2 and 3;a hub11fitted to shaft10to rotate integrally with shaft10about axis A; anda number of—in the example shown, five—blades12(FIG. 3) projecting from hub11on the opposite side to axis A, and elongated along respective axes B crosswise to axis A.

More specifically, hub11comprises a body16defining a cylindrical through seat17housing drive shaft10; and a tubular portion13, which is radially outwards of cylindrical body16with respect to axis A, has a curved polygonal profile, and is connected to body16by a number of angularly equally spaced spokes14radial with respect to axis A.

In other words, hub11has a number of through seats15open parallel to axis A, equally spaced about axis A, and through which to fasten respective blades12.

More specifically, each seat15is bounded circumferentially by two adjacent spokes14, is bounded by body16radially inwards with respect to axis A, and is bounded by tubular portion13radially outwards with respect to axis A.

Each blade12comprises a main body18(only shown partly in the drawings) defining the helicopter lift/thrust surfaces; and a coupling19bolted to the radially inner end30of body18with respect to axis A, and which connects blade12to hub11.

Coupling19of each blade12is substantially C-shaped, and comprises two parallel arms20, between which end30of body18of blade12is fixed; and a connecting portion21connecting arms20and which engages a respective seat15in hub11.

Coupling19of each blade12is hinged to hub11with the interposition of an elastomeric bearing25.

Each bearing25allows relative blade12to rotate about respective axis B to adjust its angle of attack with respect to the airstream; to rotate with respect to hub11and the other blades12about a respective axis C, parallel to and at a distance from axis A, to perform the so-called lead-lag movement; and to rotate about a respective axis D, perpendicular to axis A and crosswise to respective axis C, to perform the so-called flapping movement.

Axes B, C and D, about which each blade12rotates, all converge at one point.

Each blade12comprises an appendix23which is eccentric with respect to respective axis B, projects from a radially inner end of body18of blade12with respect to axis A, and is acted on by a control member to rotate blade12about respective axis B and so adjust the angle of attack with respect to the airstream.

Appendix23comprises two walls26having first ends32spaced apart parallel to axis A, and second ends33, opposite ends32, joined to each other. More specifically, ends32of walls26are fixed to end30of body18of relative blade12.

On the side facing axis A, walls26of each appendix23are connected by a further wall.

Appendixes23project from relative bodies18on the same side of relative blades12with respect to relative axes B.

Rotor3advantageously comprises a number of dampers40for damping oscillation of relative blades12about respective axes C, and which comprise respective portions41movable integrally with relative blades12about respective axes C; and respective portions42connected functionally to one another and elastically to respective portions41.

More specifically (FIGS. 2 and 3), each damper40is made of elastomeric material, and comprises a quantity of metal material embedded inside the elastomeric material, so each damper40is elastically deformable under load.

Each damper40is housed between walls26of appendix23of respective blade12, and is substantially cylindrical about an axis E parallel to axis C of respective blade12.

More specifically, each damper40comprises:two bases43located at opposite ends along axis E, and which define portion41of damper40and are each fixed to a respective wall26of appendix23; anda lateral surface44interposed axially between bases43with respect to axis E.

More specifically, each portion42in turn comprises a first and second area46a,46bdefined by respective separate areas of surface44of damper40.

Each area46bis interposed between axis A and axis D of relative damper40, and each area46ais located to the side of axis B of relative blade12.

Axis B of each blade12extends through relative area46b, but not through relative area46a.

More specifically, the lines joining the barycentres of areas46a,46bof each damper40to relative axis E and drawn radially to axis E form an angle ranging between ninety and a hundred and thirty-five degrees.

Rotor3comprises a number of—in the example shown, five—rods45alternating with blades12and relative dampers40.

Each rod45is preferably made of rigid material, and connects area46aof one damper40to area46bof the adjacent damper40.

More specifically, each rod45comprises two axial ends47,48housing respective pin joints50,49, which define respective seats engaged by respective threaded pins55,54projecting respectively from area46aof one damper40and area46bof the adjacent damper40.

End48of each rod45is interposed between axis A and axis D of relative damper40, and end47is located to one side of axis B of relative blade12.

Joints50,49allow pins55,54to adjust position in a plane perpendicular to axis A.

The dot-and-dash line60inFIG. 4indicates the angular displacement of a damper40about relative axis E as a function of angular displacement of relative blade12about relative axis C and in the opposite direction to rotation of hub11about axis A. In other words, dot-and-dash line60relates to lag movement of relative blade12.

The continuous line61inFIG. 4indicates the elastic angular displacement of a damper40about relative axis E as a function of rigid angular displacement of relative blade12about relative axis C and in the same direction as rotation of hub11about axis A. In other words, continuous line61relates to lead movement of relative blade12.

FIG. 4shows the effectiveness of each damper40in damping lead-lag oscillations of relative blade12of rotor3over the full range of rotation angles of blade12with respect to corresponding axis C.

FIG. 4also shows clearly how elastic twisting of damper40increases proportionally alongside a variation in rotation of blade12about relative axis D.

Rotation of hub11in turn rotates blades12as a whole about axis A.

Blades12are normally subjected to different aerodynamic loads having different components in a direction parallel to axis A, and which tilt blades12with respect to hub11about respective axes D, thus resulting in a flapping movement of blades12.

The flapping movement of each blade12alters the distance between the barycentre of the blade and axis A.

To maintain its angular momentum with respect to axis A, each blade12rotates about respective axis C to increase its rotation speed with respect to axis A when its barycentre moves towards axis A. That is, each blade performs a lead movement.

Conversely, each blade12rotates about respective axis C to reduce its rotation speed with respect to axis A when its barycentre moves away from axis A. That is, each blade performs a lag movement.

Continual periodic oscillation of blades12about respective axes C produces vibration that is damped by dampers40.

More specifically, at a given instant in time, as a result of the different speeds with respect to the airstream, blades12tilt at respective different angles with respect to hub11about respective axes D, so each blade12has a respective lead or lag angle about respective axis C and with respect to the other blades12.

Operation of rotor3is described below with reference to one blade12and respective damper40.

Portion41of damper40rotates integrally with blade12about axis C; area46aof damper40moves integrally with area46bof one of the two adjacent dampers40, by means of relative rod45; and area46bof damper40moves integrally with area46aof the other of the two adjacent dampers40, by means of relative rod45.

Areas46a,46bof portion42of damper40therefore move elastically towards or away from portion41, thus producing elastic twisting of damper40about relative axis E, which, together with the internal damping of damper40, damps vibration of blade12about axis C.

Number3′ inFIG. 5indicates as a whole a helicopter rotor in accordance with a different embodiment of the present invention. Rotor3′ is similar to rotor3and therefore only described as regards the differences between the two, using the same reference numbers, where possible, for corresponding or equivalent parts of rotors3,3′.

Rotor3′ differs from rotor3by areas46a,46bof each damper40being defined by one half of surface44facing away from axis A.

In other words, areas46a,46bof each damper40are located on the opposite side of relative axis D to axis A.

Rods45′ differ from rods45by extending entirely on the opposite side of axes E of relative dampers40with respect to axis A.

The dot-and-dash line60′ inFIG. 6indicates elastic angular displacement of a damper40of rotor3′ about relative axis E as a function of angular displacement of relative blade12about relative axis C and in the opposite direction to rotation of hub11about axis A. In other words, dot-and-dash line60′ relates to lag movement of blade12.

The continuous line61′ inFIG. 6indicates elastic angular displacement of a damper40of rotor3′ about relative axis E as a function of rigid angular displacement of relative blade12about relative axis C and in the same direction as rotation of hub11about axis A. In other words, continuous line61′ relates to lead movement of blade12.

FIG. 6shows the effectiveness of each damper40in damping lead-lag oscillations of relative blade12of rotor3′ over the full range of rotation angles of blade12with respect to corresponding axis C.

FIG. 6also shows clearly how elastic twisting of damper40increases proportionally alongside a variation in rotation of blade12about relative axis D.

Operation of rotor3′ is the same as that of rotor3, and therefore not described in detail.

The advantages of rotor3,3′ according to the present invention will be clear from the above description.

In particular, lead-lag oscillation of blades12is damped by relative dampers40twisting elastically about relative axes E, which means, unlike dampers with pistons moving radially to axis A, damping performance of dampers40is unaffected by centrifugal force and therefore effective over a wide range of rotation speeds of shaft10about axis A.

Moreover, unlike oil-operated dampers, for example, rotor3,3′ provides for damping oscillation induced by lead-lag movement of blades12about relative axes C with no hydraulic components required.

As such, rotor3,3′ not only greatly reduces vibration associated with lead-lag movement of blades12, but is also extremely easy to construct and/or maintain.

Finally, given the light weight and compactness of dampers40, the overall weight of rotor3,3′ is greatly reduced with no impairment in the effectiveness of dampers40.

Clearly, changes may be made to rotor3,3′ as described and illustrated herein without, however, departing from the protective scope as defined in the accompanying Claims.

In particular, rotor3,3′ may be employed as a tail rotor of helicopter1.