GB2254893A

GB2254893A - A variable pitch propeller assembley.

Info

Publication number: GB2254893A
Application number: GB9208376A
Authority: GB
Inventors: Michael Poucher
Original assignee: Smiths Aerospace Gloucester Ltd
Current assignee: Smiths Aerospace Gloucester Ltd
Priority date: 1991-04-18
Filing date: 1992-04-16
Publication date: 1992-10-21
Also published as: GB9108313D0; GB9208376D0

Abstract

The invention provides a variable pitch propeller assembly for use with at least one propeller blade 4. The assembly comprises a hub 1 defining at least one propeller barrel 2 for receiving a shank 3 of the blade 4. With the hub 1 is located an hydraulically operated pitch setting means 5, 11, 12 defining a radially opening circumferential recess 10 within which an inner end (comprising a roller 7 on a pin 6) engages such that axial motion of the pitch setting means 5, 11, 12 causes rotation of the shank 3 about a pitch change axis 20 within the barrel 2. A defining wall 9 of the recess 10 is provided with a cut out alignable with a corresponding inner end 6, 7 of the shank 3 by rotation of the pitch setting means 5, 11, 12 and through which the inner end 6, 7 may pass to allow extraction of the pitch setting means 5, 11, 12 for servicing. This reduces the time for servicing of the pitch setting means since none of the propeller blades require removal. <IMAGE>

Description

A VARIABLE PITCH PROPELLER ASSEMBLY This invention relates to a variable pitch propeller assembly of the type comprising a hub defining barrels within which propeller blades are located and pitch setting means movably located within the hub which engages with the propeller blades to rotate them within the barrels varying the propeller pitch.

In the operation of aircraft fitted with such propellers it is necessary to regularly inspect the assembly and to carry out maintenance at set service intervals. Additionally damage to the assembly can occur between the service intervals which also requires attention. Some service operations will require complete disassembly. For instance, where the pitch setting means requires attention all the propeller blades will have to be removed to allow the mechanism to be withdrawn from the hub.

According to the invention there is provided a variable pitch propeller assembly having an axis of rotation, for use with at least one propeller blade, comprising a hub defining at least one propeller barrel for receiving a shank of the blade and pitch setting means located, at least in part, within the hub defining a radially opening recess within which an inner end of the shank engages such that axial motion of the pitch setting means causes rotation of the shank within the barrel to vary the propeller pitch, a defining wall of the recess being provided with a cut out alignable with a corresponding inner end of the shank by rotation of the pitch setting means and through which the inner end may pass alloying the pitch setting means to be withdrawn from the hub.

By providing a cut out in a defining wail of the recess the pitch setting means may be removed without having to remove the propeller blade.

Hence the time required to service the pitch setting means is greatly reduced. Considering that the invention may be used with propeller assemblies having a number of blades it will be realised that the invention offers a very significant reduction in servicing time. Where more than one propeller blade is used a corresponding number of recesses and cut outs will be required. By cut out it is meant an opening in the defining wall whether made in a cutting operation or otherwise for example during forging or casting.

Preferably, the pitch setting means may comprise a hydraulically actuatable piston although it may be possible to use electromechanical means to effect the axial displacement.

Preferably, means are provided to prevent rotation of the pitch setting means. This will prevent the pitch setting means rotating unintentionally and possibly disengaging the blade shanks which may be hazardous especially if it were to occur in flight.

Preferably, the inner end comprises a roller which engages the recess wall. This is preferred since it will ensure smooth variation in the pitch of the blade.

Whilst it is envisaged that an individual recess may be provided for engaging an end of each propeller blade, preferably a single peripheral channel will be provided a defining wall of which engages all of the blades. This is preferable for it allows the channel to be formed in one machining operation. The cut outs will be formed in the defining wall of the channel.

A specific embodiment of the invention will now be described, by way of example only, with reference to the drawings in which: Figure 1 shows a variable pitch propeller assembly in accordance with the invention; and Figure 2 is a view along line II--I of Figure 1.

With reference to Figure 1, a propeller assembly comprises a one piece aluminium hub 1 defining a number of angularly disposed barrels one of which is shown in the figure and labelled 2. Within the barrel 2 is located a shank 3 of a propeller blade 4. The propeller blade 4 is retained within the barrel 2 by a bearing arrangement (not shown).

The blade 4 engages with pitch setting means comprising a crosshead 5, by means of a pin 6 and roller 7. The pin 6 is fixed to the shank 3 and thus the pin 6 and roller 7 form the inner end of the shank 3. The roller 7 abuts with walls 8 and 9 of a generally circumferential U-shaped peripheral channel 10. The crosshead 5 has a cylindrical axially extending tubular portion 11 which terminates in a piston head 12.

Along the axis of the tubular portion 11 are located coaxial beta tubes 13 and 14 which supply hydraulic fluid to either side of the piston head 12. The piston head 12 can therefore be made to move in an axial direction within a cylinder 15 terminated by an end cap 16 by pumping fluid along the beta tubes 13, 14. The crosshead 5 is fixed angularly relative to the cylinder 15 by means of an anti-torque pin 17 which engages holes 18 and 19.

The anti-torque pin 17 prevents rotational movement of the crosshead 5 until bolts 22 and 23 are released.

The cylinder end cap 16, the cylinder 15, the piston head 12, the beta tubes 13 and 14, the crosshead 5 and the anti-torque pin 17 together form a module which sets the pitch of the propeller blades in the following manner.

Oil is pumped via the beta tube 13 to the right hand side of the piston head 12 causing it to be displaced together with the crosshead 5 to the left in the figure. As it moves, the anti-torque pin 17 passes through the hole 19 in the crosshead 5. Movement of the crosshead 5 causes movement of the roller 7 because of the abutting wall 9. The pin 6 and roller 7 are axially offset on the shank 3 and accordingly the movement causes rotation of the blade 4 about the pitch change axis 20 normal to the axis of rotation of the propeller assembly, changing the pitch of the propeller to a fine pitch.

To reverse the change, oil is pumped via beta tube 14 to the left hand side of the piston head 12 causing it to be displaced to the right. The wall 8 then forces the roller 7 and pin 6 to the right causing the blade 4 to rotate back to a coarse pitch setting.

A rear view of the crosshead 5 is shown in figure 2 and it can be seen that the rear wall 9 is provided with hemispherical cut-outs 21. In order to withdraw the pitch setting module from the hub 1, bolts 22 and 23 are removed and the module rotated through about 30 until the cut-outs 21 are aligned with rollers 7. The module can then be removed and serviced or replaced as required.

The module is replaced by aligning the cut-outs 21 with the rollers 7 and pushing the cartridge further into the hub 1 until the channel wall 8 abuts each roller 7. The cartridge is then rotated through 30 and the bolts 22 and 23 replaced.

Claims

1. A variable pitch propeller assembly having an axis of rotation, for use with at least one propeller blade, comprising a hub defining at least one propeller barrel for receiving a shank of the blade and pitch setting means located, at least in part, within the hub defining a radially opening recess within which an inner end of the shank engages such that axial motion of the pitch setting means causes rotation of the shank within the barrel to vary the propeller pitch, a defining wall of the recess being provided with a cut out alignable with a corresponding inner end of the shank by rotation of the pitch setting means and through which the inner end may pass allowing the pitch setting means to be withdrawn from the hub.

2. An assembly as claimed in claim 1 wherein the pitch setting means comprises a hydraulically actuable piston.

3. An assembly as claimed in claims 1 or 2 wherein anti-rotation means are provided to prevent rotation of the pitch setting means.

4. An assembly as claimed in any preceding claim wherein the radially opening recess comprises a single peripheral channel a defining wall of which engages the inner end of the or each blade.

5. An assembly as claimed in any preceding claim wherein the inner end of the shank comprises a roller.

6. A variable pitch propeller assembly as hereinbefore described with reference to and as illustrated by the drawings.

7. A pitch setting means for use in an assembly as claimed in any of claims 1 to 6.