GB2251896A

GB2251896A - A propeller mounting arrangement

Info

Publication number: GB2251896A
Application number: GB9026473A
Authority: GB
Inventors: Terence John Dix
Original assignee: Smiths Aerospace Gloucester Ltd
Current assignee: Smiths Aerospace Gloucester Ltd
Priority date: 1990-12-05
Filing date: 1990-12-05
Publication date: 1992-07-22
Anticipated expiration: 2010-12-05
Also published as: GB2251896B; GB9026473D0

Abstract

A propeller blade shank 3 is releasably located within a hub 1, provided with an inner bearing race insert 11 and an outer bearing race insert 12. The shank 3 is provided with bearing races 5, 6 and bearings 7, 8 are disposed between these races and the race inserts 11, 12. The bearings 7, 8 are given a preload by rotating a ring nut 15 in screw threaded engagement with the outer race insert 12 and the preload is maintained by a locking plate 18. By providing the races as removable inserts a blade of the propeller may be removed for servicing without the requirement for complete dismantling of the hub 2 and the hub 2 may be machined as a single component. In an alternative arrangement (figure 4), rotation of an outer insert is transmitted via dogs to an inner insert in screw threaded engagement with a member secured to the hub thereby to pre-load the bearing arrangements. <IMAGE>

Description

PROPELLER ARRANGEMENT This invention relates to a propeller arrangement particularly but not exclusively a variable pitch propeller arrangement for use in aircraft.

Such propellers are usually formed from a number of propeller blades each being located by a radially inner end, called a shank, in a barrel of a hub of the propeller. In order to locate the shanks within the hub barrel, the hub is made in separable halves. This is necessary in order to allow the insertion of bearings between races on the shank and races on the hub. The bearings permit movement of the blade so that its pitch can be varied. In order to replace a blade that has been lost or damaged, the two halves of the hub must be separated which disturbs the other propeller blades and their bearings.

According to the invention there is provided a propeller arrangement comprising a blade a radially innermost end of which forms a shank having bearing races; a hub having a hub barrel within which the shank is releasably located; radially inner and outer race inserts interposed between the hub barrel and the shank; bearings interposed between the shank races and the race inserts; blade retaining means in engagement with the inner race insert and the hub barrel to prevent radially outwards movement of the blade; and bearing loading means adapted to cooperate with the outer race insert and the hub to urge the race inserts radially apart so loading the bearings.

By providing the races as inserts it is possible for the propeller blade shank to be located within the hub barrel without the requirement to split the hub. The hub may therefore be machined as one piece which eliminates the problem of matching the hub halves. Blades may therefore be removed and replaced without disturbing the other blades of the propeller which significantly simplifies servicing and reduces the time required to carry out a service.

Specific embodiments of the invention will now be described, by way of example only, with reference to the drawings in which: Figure 1 shows a propeller arrangement in accordance with the invention; Figure 2 shows a partial section through a blade barrel shown in Figure 1; Figure 3 shows a plan view of a locking plate; and Figure 4 shows an alternative embodiment of the invention.

With reference to Figure 1, a propeller arrangement comprises a hub 1 of aluminium having a hub barrel 2 into which a propeller blade shank 3 is located. At the front of the hub 1 is an access hole 4 which in use is covered by a cover plate. The shank 3 has a radially inner race 5 and outer race 6 as shown in Figure 2. These races extend about the periphery of the shank 3 to provide a bearing surface for inner and outer roller bearings two of which 7 and 8 are shown in the figure. The bearings are clipped into cages 9 and 10 and also make contact with inner and outer race inserts 11 and 12 respectively. The race inserts have mutually engaging dogs 13 and are in threaded engagement with a blade retaining nut 14 and a ring nut 15. Between the ring nut 15 and the outer edge of the hub barrel 2 is positioned a lock plate 16.The ring nut 15 is fixed to the hub barrel 2 by bolts one of which is shown and labelled 17 in the figure. The blade retaining nut 14 is prevented from rotating relative to the inner race insert 11 by retaining pins one of which is shown and labelled 18. The race inserts 11, 12, the ring nut 15 and the blade retaining nut 14 are made of steel with the race inserts 11, 12 being case hardened.

Between the barrel 2 and the blade retaining nut 14 and the race inserts 12 and 11 is located liner 19 of plastics material.

The arrangement is assembled in the following manner. The retaining nut 14 is assembled into hub barrel 2 through the access hole 4 and secured in place by the locating pins 18. The liner 19 is then located in the hub barrel 2. Next the ring nut 15 and the lock plate 16 are slipped along the shank 3. The race 6 is assembled onto shank 3 and the roller bearings 8 are clipped into cage 9 and placed onto race 6. The upper insert 12 is then slipped over shank 3 followed by the lower insert 11, and both collapsed axially together. Race 5 is then assembled onto shank 3 along with roller bearings 7 and cage 10. The two race inserts 11 and 12 are then moved axially apart to engage the bearings 6 and 7, and the plastic washer 21 is placed between the two inserts 11 and 12 to hold them apart in contact with the bearings.

The shank of the blade with the bearing on it is then inserted into the hub barrel 2 and screwed tightly into insert 14 using a C spanner on dogs 20 which rotates both inserts 11, 12 together because of their mutually engaging dogs 13. A preload is produced in the threaded engagement between the lower race insert 11 and the retaining nut 14 by tightening against one another of the cooperating shoulders 25 therebetween. This preload is necessary to prevent fatigue stresses in the threads. The locking plate 16 is then slipped back down the blade and over the threaded portion of the outer insert 12.

The locking plate 16 is shown in greater detail in Figure 3 and has a plurality of bolt holes and three equispaced locking tabs 22. The tabs 22 locate in recesses formed in the periphery of outer race insert 12 and serve when bolted to the hub barrel 2 to prevent rotation of the outer race insert 12. The ring nut 15 is then threaded onto the outer race insert 12 and torqued to the required tightness. The tightening action acts to withdraw the outer race insert 12 from the barrel 2 but is prevented from doing so by the bearing 8 and the inclined face 23. There is therefore a force exerted on the shank 3 which acts to withdraw the shank 3 from the barrel 2. This force is resisted by the bearing 7 and the lower race insert 11.It can be seen that by the tightening action of the ring nut 16, the bearings 7 and 8 are preloaded, that is, they have a load applied before operation of the completed propeller. This preload has been found desirable for propellers to prevent the blade wobbling relative to the hub 1 during some flight conditions.

Once the correct amount of preload has been applied to the bearings 7 and 8 bolts are passed through the ring nut 15 and the locking plate 16 to engage threaded holes in the hub barrel 2 to complete the assembly.

In an alternative embodiment of the invention shown in Figure 4, assembled in a similar manner to the first embodiment, the outer race insert has been configured to provide a land 24 which abuts against the barrel 2. In this case the preload is brought about by rotation of the outer race insert which by virtue of the dog arrangement causes corresponding rotation of the inner race insert causing it to move downwards to load the bearings.

Claims

1. A propeller arrangement comprising a blade a radially innermost end of which forms a shank having bearing races; a hub having a hub barrel within which the shank is releasably located; radially inner and outer race inserts interposed between the hub barrel and the shank; bearings interposed between the shank races and the race inserts; blade retaining means in engagement with the inner race insert and the hub barrel to prevent radially outwards movement of the blade; and bearing loading means adapted to cooperate with the outer race insert and the hub to urge the race inserts radially apart so loading the bearings.

2. An arrangement as claimed in claim 1 in which the hub is substantially a one piece hub.

3. An arrangement as claimed in claims 1 or 2 further comprising a locking means arranged to prevent movement of the outer race insert'after loading of the bearings.

4. An arrangement as claimed in claim 3 wherein the locking means comprises an annular plate having engagement means for engaging the outer race and a plurality of bolt holes by means of which the plate is fixed to the hub so preventing movement of the outer race insert relative to the hub.

5. An arrangement as claimed in claim 4 wherein the engagement means comprises at least one radially, inwardly extending projection which engages with a recess in the outer race insert.

6. An arrangement substantially as hereinbefore described with reference to the drawing.