The present invention relates to ring seals, in particular, ring seals having a plurality of sealing lands.

Multi-landed sealing rings are known, for example, as disclosed in British patent application No. GB-A-2163498. Known ring seals suffer problems of intermittent or poor sealing contact when subjected to shocks and vibrations. Such problems typically arise in the field of aeronautics particularly in hubs of aircraft propellers.

The present invention provides an assembly comprising relatively rotating and vibrating parts and a sealing ring for sealing between the parts, the sealing ring having a plurality of sealing lands, the shape and configuration of the lands being selected so that frequencies of natural resonant vibration of the ring and/or lands are not frequencies of vibration applied to the ring in use. Increasing the thickness of a sealing land has the effect of increasing its resonant frequency. Furthermore, the height of the sealing lands determines the squash force, i.e. pre-compression, which the ring will experience when forced into position between the rotating parts. Increasing the pre-compression has the effect of increasing the resonant frequency of the land away from the frequency or range of frequencies to be avoided.

The resilience of the material of which the sealing land is

made can also be selected so as to ensure that the resonant frequency of the sealing ring and its lands take the desired values.

The preferred sealing ring is shaped, configured, and pre- stressed in si tu, so that its resonant frequencies are well away from the frequencies of vibration of the rotating parts occurring during constant running. The resonant frequencies of the ring can also be selected so as to be away from the vibration frequencies occurring during start-up and/or shut¬ down of a propeller.

The preferred sealing ring has both outwardly-directed lands and inwardly-directed lands. There are more lands in one direction than the other. Preferentially, there is a greater number of lands directed outwardly, ensuring that the sealing ring rotates with the rotating outer part. Furthermore, having fewer inwardly-directed lands ensures that there is reduced friction and wear between the relatively rotating sealing ring and the inner part.

The more central of the outwardly-directed sealing lands preferably has a reduced height compared to the outer ones. In consequence, the more central land or lands are less pre- stressed than the outer inwardly-directed lands when the sealing ring is fitted between propeller parts. This has the advantage of making the more central land or lands less likely to collapse, and so provides a sealing ring of increased

stability. Furthermore, having a central land or lands of reduced height ensures there is less friction against the propeller outer part. This is advantageous because lubricant is less likely to reach the central lands than the outer lands.

A preferred embodiment of the invention will now be described by way of example with reference to the drawings, in which:

Figure 1 is a side view of a sealing ring according to the present invention;

Figure 2 is a cross-sectional view along the line A-A shown in Figure 1;

Figure 3 is an enlarged cross-sectional view of part of the ring as shown in Figure 2; and

Figure 4 is an enlarged cross-section view, showing dimensions, of the ring part shown in Figure 3.

As shown in the figures, the sealing ring 1, which of rubber material, includes three outwardly-directed sealing lands 2,4,6 and two inwardly-directed sealing lands 3,5. Thus the sealing ring 1 has an approximate -shaped cross-section. The heights of the sealing lands 2,3,4,5,6 are chosen so that the sealing ring 1 is appropriately pre-stressed when placed in situ between relatively rotating aircraft propeller parts. Specifically, the ring is held within a groove of an outer

propeller part and the inner propeller part is a rotating shaft around which the sealing ring is positioned. The outer part is a socket of a propeller hub and the inner part is a propeller blade shank. More specifically the socket is a blade root which fits in a hub port of the hub. The heights of the lands 2,3,4,5,6 are selected so that the sealing ring is appropriately pre-stressed between the inner and outer parts when placed in si tu . This ensures that the resonant frequencies of the lands and ring are displaced from the usual frequencies of vibration of the propeller in use.

The thicknesses of the lands are also selected so as to be tuned away from resonance. Furthermore, the material from which the sealing ring is made is also selected so as to have an appropriate elasticity such that the ring is tuned away from resonance.

The preferred sealing ring 1 is designed for use in a propeller having a constant running speed of about 1000 revolutions per minute. Thus vibrations occur primarily at 1000/60 = 16.6667Hz. The sealing ring 1 is such that the natural resonant frequencies of the sealing ring and lands are away from this frequency or harmonics thereof.

The preferred sealing ring 1 has an inner diameter of between 125.15mm and 126.35mm when unstressed. With reference to Figure 4, other angles and dimensions of the unstressed sealing ring are as follows. In Figure 4, a R prefix to a value

denotes that the value is a radius of curvature.

Angles/ ⁰

a ₁ 10° a ₂ 9° a ₃ 18°

Dimensions/mm

Radii of Curvature/mm

0.90 0.35

R _c 0.75 R _Λ 0.75

In further embodiments of the invention, the sealing ring may be coated with tape or epoxy resin so as to provide desired frictional and wear properties .

Having three outwardly-directed sealing lands ensures good axial stability. The central land 4 is of a high reduced relative to the height of the outer lands 2,6. In consequence, the central land 4 is less stressed in use than the outer lands 2,6, so as to prevent the sealing ring collapsing under high stress. Furthermore, there is less friction between the central sealing land 4 and the outer propeller part than between the outer sealing lands 2,6 and the outer propeller part. This prevents wear of the central land 4, particularly as lubricant is more likely to reach the outer lands 2,6 and the central land 4.

Having fewer inwardly-directed lands 3 , 5 than outwardly- directed lands 2,4,6 provides less friction between the inner propeller part and the sealing ring 1, than the outer propeller part and the sealing ring 1. The sealing ring thus rotates with the outer part. Alternatively, a sealing ring can be provided with more inwardly-directed lands, for example, if it is intended that the sealing ring 1 should rotate with the inner propeller part.

In the preferred embodiment, the two inwardly-directed lands 3,5 are shaped so that under stress they will deform outwards rather than inwards. The region 7 of the sealing ring 1

between these two inwardly-directed lands 3,5 is shaped so as to be able to resist tensile forces. In consequence, the sealing ring 1 is resistant to damage under high stress.

The present invention is based on the realisation that a sealing ring can be provided which has its resonant frequencies tuned away from the vibrational frequencies that the ring is likely to experience in use. In consequence, many technical solutions and practical advantages will be become evident.