GB2280162A - Rigid/articulated helicopter rotor hub. - Google Patents

Abstract

A rigid/articulated helicopter rotor hub in which the blades (100, 110 fig 2) extend, 500, or retract, 600, from and to the rotor hub (15, 35 fig 3) at their roots. The extension/retraction serves to vary the stiffness of the blade/hub attachment. When the rotor is at rest or at low rotational speeds the blades are retracted and faces 306 and 310 lock together to hold the blades fixed to the hub at a designated pitch angle. As the rotor speed increases the rotor blades are gradually automatically extended due to centrifugal effects overcoming the retracting forces of a retracting mechanism such as a pressurised pneumatic cylinder (410 fig 7). Flapping and feathering of the blades may be permitted by flexible straps (345 fig 7) while lead and lag motions may be provided through a pivot block (330 fig 7). The hub may be used with aileron controlled rotor blades or with swash plate mechanisms. The hub may also be used with co-axial rotors (figs 1 to 3). <IMAGE>

Description

RIGID/ARTICULATED HUB This invention relates to a helicopter equipped with a bearingless rotor hub.

Rotating wing aircraft are well known e.g. helicopters, and comprise a fuselage with an overhead driven blade assembly, known as a rotor head. The rotor head comprises a series of rotor blades attached to a hub. Beneath the rotor hub is a swash-plate mechanism for controlling and varying the angular pitch of each blade, this is a mechanical system which when operating re-acts against the airframe or chassis of the aircraft, causing vibration.

In order to remove this re-action between airframe and rotor and remove the complex swash-plate mechanism, aileron equipped rotor blades are used as described in UK PhEENi' GB 2090214B Controlling Helicopter Rotors.

Rotor hub design follows three paths. These being 'rigid' and 'articulated', whilst the 'semi-rigi;d' rotor is a combination of both types, and attempts to combine the best characteristics of each , these being the reduced maintenance of the rigid rotor combined with the reduced gyroscopic couple of the articulated head, with mixed success.

The rigid/articulated hub is a bearingless rigid hub, which will provide a fully articulated action. Two straps retain each blade, and they are flexible in both flapping and feathering actions, whilst lead/lag movement is provided by a pivot equipped with damping.

The RAH features retracting blades and straps, which extend at or about flying speeds of blade rotation. During non-flyirg speeds of blade rotation air rotor stopped conditions, the blades retract, causing each blade to be pulled onto a matching and locating face on the rotor hub, thereby locking the blade (at a designated pitch angle) rigidly to the hub and preventing its movement in the 3 axes used during flight. Retracting the blades and locking them to the hub, removes the need for extra rigidity in present hub design. This extra rigidity is necessary to provide support for the blades when static, and during non-flying speeds. of blade rotation, resulting in greater rigidity than necessary for flying speeds of operation.

The excess rigidity of conventional rigid rotors is well known, and seriously compromises their design and performance.

Use of the RAR will make possible a rigid hub/blade joint optimised purely for the flight regime, deriving a higher proportion of its stiffness from centrifugal loads, than at present. This will reduce the gyroscopic couple, and in so doing -reduce vibration and increase flight comfort. Blade sailing will also be prevented by locking the blades at sub-flying speeds of rotation.

Other advantages of the RAH will be the removal of the complex stressing problems associated with rigid rotor hub arms, making possible a lighter hub.

Blade design will be simplified by the reduction of the spanwise stiffness presently equired, made possible by the i:-creased flexibility of the hub joint, and by use of aileron controlled blades it wi- 1 be possible to remove pitch control inputs at the hub. This will remove pitch change moments on te aircraft structure, with a reduction in vibration.

The bear less design of the RAH will reduce maintanance requirements to the rotor hub.

According to the present invention there is provided a helicopter rotor hub, shown in co-axial contra-rotating configuration, characterized in that the hub hinge mechanism is retractable at low speeds of rotation and extendableat higher speeds of rotation, this being achieved by autonatic means through the use of interconnected pressurized cylinders in each hub arm, and attached to each hub/blade hinge mechanism being centrifugally operated at the higher speeds of blade rotation, and providing a rotor hub with a hub/blade hinge mechanism of variable rigidity.

A specific embodiment of the invention will now be described by way of example with reference to the accompanying drawings in which: Fig. 1 shows in orthographic projection, a plan view of the co-axial rotor hubs assembled with top cover removed; Fig. 2 shows in orthographic projection a side view section, of the co-axial rotor hubs with air supply ducting and fibre optic lines; Fig. 3 shows in exploded perspective, the component build and assembly of the co-axial rotor hubs; Fig. 4 shows in 'ghosted' perspective, the inter-rotor air supply duct; Fig. 5 shows in perspective the lead/lag pivot and blade anchorage block; Fig. 6 shows in perspective, a typical hub assembled with blade root locating shroud cut through-and 'ghosted for clarity;; Fig. 7 shows in perspective, the working components of the retracting mechanism assembled, but separate from the hub, with fibre optic tube and interconnecting pressure line.

Referring to the drawings, the rigid/articulated hub shown in Figs 1,2,3 and 6 is constructed around a two piece hub case assembly, in a co-axial application using two separate hub case assemblies, these being an upper hub assembly 15, comprising an upper hub case half 20 and a lower hub case half 30 with integral drive shaft 31, and a lower hub assy 35, comprising an upper hub case half 40 and a lower hub case half 50 with integral drive shaft 51.

Each hub ass 15 and 35 is supplied with air 10 provided by compressor means on the helicopter. The air 10 is delivered through the air-passages 60, provided within drive shaft 51 to pressurize the lower hub assembly 35, the air 10 is then supplied from this assembly through air-supply holes 12 and 14 and via air-supply duct 55, shorn in Ftg. 4, to supply the upper hub assembly 15 with air 10 through air-supply holes 18, to pressurize the upper hub assembly 15 in the same manner as hub assembly 35.

The pressurization of hub assemblies 15 and 35 ensures the supply of air 10 to rotor blades 100 and 110 on their respective hub assemblies 15 and 35, to provide pneumatic actulon means for the opto-eumatic actuators on each blade.

The supply of optical signalling to each blade is provided through fibre optic signal lines 200 and 205 contained and carried within drive shafts 31 and 51, these are provided with connectors 210 and 220 in each hub 15 and 35, and these attach to matching connectors 211 and 221 integral with fibre optic line 300 on rotor blades 100 and 110, to provide suitable light (optical) carrying transmission means to opto-pneumatic actuators on each rotor blade 100 and 110.

Shown in Figs 1,2 and 3 and detailed in Figs 5,6 and 7 is the blade retraction mechanism used in hub assemblies 15 end 35.

This consists of a gas filled retraction cylinder assembly 400; comprising cylinder 410, cylinder rod 420 and blade extension stop 430. Attached to this assembly is the retraction slide assembly 320; comprising retraction/pivot slide 325, lead/lag pivot and blade anchorage block 330, friction block 340(to permit vertical/flapping movement of) blade retaining straps 345, and pinch-block 350. The pinch-block 350 is used to clamp the fibre optic signal line 300 trom rotor blades 100 and 110, this passes through the slide assembly 320 and retraction cylinder assembly 400, to fibre optic connection means 211 and 221 in hub assemblies 15 and 35 respectively.

Retraction cylinder assembly 400 is pressurized to pull the blade retraction slide assembly 320, in and towards the hub centre, this action is shown by arrow 600, whilst its opposite action 500 is variable and is created centrifugally, by the action of hub rotation,causing the rotor blades 100 and 110 to exert a force in the direction of arrow 500 to pneumatic cylinders 410, this cause's further compression of their gas and in so doing, permits rotor blades 100 and 110 to extend at a predetermined rotor hub R.P.M. . The resultant movement between -actions 500 and 600 is shown as 550 in Fig6 1 and 7.

Equal pressure distribution between retraction cylinder assemblies 400 is provided through pressure line 370, which interconnects with each retraction cylinder 410, thereby ensuring even blade extension (500) and retraction (600!, also provided on toes line is a pressure test point and re-charge valve 360 shown in Figs 1 and 7 to facilitate system pressure check and 'top ups'.

Shown in Fig 6 is the blade root locating shroud 305 and 308 attached to and integral with blades 100 and '10 respectively, n extended tflying' position. Tn retracted position the face 306 locates onto a matching face 310 provided on the arm OT 15 and 35, locating the blade in a fixed nosit on, when not required for fliht, and is shown in this position in Figs 1 and 2.

Shown also in Fig G is pressure retaining gaiter 105, provided to contact pneumatic supply 10 -ro: holes 14, trough the locating shrouds 305 and 308 and the rotor blades 100 and .110 structure 115, to the opto-pneumatic actuators on the rotor blades.

Claims (13)

1 A rigid/articulated helicopter or autogyro rotor hub characterized in that hub root stiffness and hingeing at the blades attachment point, is controllably varied by extension or retraction of said blade root attachments.

2 A rigid/articulated hub as claimed in claim 1, wherein blade extension and retraction is controlled centrifugally, by speed of hub rotation.

3 A rigid/articulated hub as claimed in claims 1 and 2 wherein blade extension and retraction is achieved by reaction of centrifugal load upon a pressurized cylinder mechanism.

4 A rigid/articulated hub as claimed in claim 1, wherein blade extension and retraction is achieved by mechanical means, through use of an electrical motor.

5 A rigid/articulated hub as claimed in claim 1, wherein blade extension and retraction is achieved by hydraulic means.

6 A rigid/articulated hub as claimed in claims 1 and 2 wherein blade extension and retraction is achieved by spring tensioning mechanism.

7 A rigid/articulated hub as claimed in claim 1, wherein blade root hingeing is achieved by use of blade retaining straps.

8 A rigid/articulated hub as claimed in claims 1 and 7 wherein fore and aft (lead/lag) blade movement is provided by pivotally mounting the blade attachment straps.

9 A rigid/articulated hub as claimed in claim 1 and 2 wherein blade pitch (feathering) is achieved by flexion of the blade retaining strap or straps.

10 A rigid/articulated hub as claimed in claims 1 and 2 wherein1 blade feathering is achieved by swash-plate mechanism.

11 A rigid/articulated hub as claimed in claims 1 and 2, wherein, blade feathering is achieved without hub mechanics, eg swash-plate mechanismtand attendant mechanical reaction.

12 A rigid/articulated helicopter or autogyro rotor hub, as claimed in claims 1 to 6 and characterized, in that the force applied for retraction of the hub roots and attached blades may be divided equally between each hub, by mechanical, pneumatic, hydraulic or electrical/electronic means or other.

13 A rigid/articulated helicopter or autogyro rotor hub, substantially as described with reference to Figs 1 to 7 of the accompanying drawings.