GB2365085A

GB2365085A - Protecting aircraft brake assemblies

Info

Publication number: GB2365085A
Application number: GB0017619A
Authority: GB
Inventors: Philip Arnold Swales
Original assignee: Dunlop Aerospace Ltd
Current assignee: Dunlop Aerospace Ltd
Priority date: 2000-07-18
Filing date: 2000-07-18
Publication date: 2002-02-13
Also published as: GB0017619D0; GB2369866A; GB0112062D0

Abstract

A shielding means 14 for protecting sensitive parts of an aircraft brake assembly from harmful liquids, e.g.runway de-icers, splashed on to the assembly is positioned, in use, in the likely path of splashed liquid and comprises an annular body of porous material sandwiched between two plates 14 with marginal portions 16 of the body exposed. Each plate, which may be of steel or ceramic material, is built up of three sections to allow for movement caused by differential expansion, and the shielding means is secured to the assembly by rivets 17.

Description

<Desc/Clms Page number 1> SHIELDED AIRCRAFT BRAKE ASSEMBLY Runway de-icers are used at airports during the winter months to ensure that the runway surfaces are maintained free of ice in the interest of aircraft safety. De- icers based on glycol liquids and urea have traditionally been used. These materials have been found to present a hazard to the environment (see Jane's Airport Review July/August 1996, page 42) and more environmentally benign formulations have recently been introduced based on acetates and formates. It has been realised that exposure of carbon-carbon composites, e.g. brake discs, to contaminants such as runway de-icers and aircraft cleaning fluids can cause an increase in the oxidation rate of the composite at temperatures above about 450'C. There has been a marked increase in the oxidation rate since the introduction of environmentally friendly runway de-icers. A small amount of oxidation causes a dramatic reduction in the material strength and can even result in the failure of drive tenons, especially from the stator discs. Oxidation weight loss of only 5% can result in a loss of strength of approximately 25%. Carbon-carbon composite materials will oxidise at temperatures above 450'C in the absence of contact with de-icer or cleaning solutions but the oxidation rate is controlled by anti-oxidative protection applied to discs and is not found to be a problem during the service life of the brake. The relationship between the oxidation problem and de-icers is evidenced by the fact that the problem is worse in winter months than in summer months and in the case of aircraft regularly operating out of airports in cold climates.

Carbon-carbon composite brake discs are exposed to the runway de-icer spray as the aircraft takes off, lands and during taxiing. The spray runs into the brake assembly after splashing onto the exposed parts of the brake, such as the cylinder block, or spray containing the de-icer can be drawn into the brake by the airflow caused by cooling fans that cool the brakes after landing. The de-icer solution can seep into pores within the composite where it dries onto the material when the discs are at an elevated temperature, thereby contaminating them. This contamination can then act as a catalyst to accelerate oxidation at temperatures in excess of about 450'C, resulting in a reduction in service life of the brake discs. It is one object of the invention to provide means to ameliorate or avoid the reduction in service life of carbon-carbon composite brake discs which results from contact with substances such as de-icers and cleaners that are used in airports. In one aspect therefore, the invention provides an aircraft brake assembly incorporating components which are sensitive to heat and to contact with substances present in runway de-icer compositions, cleansing fluids and like liquids characterised by shielding means mounted on the outside of the assembly at a location which will not substantially increase the temperature of the heat sensitive components and which is arranged to receive and retain such liquids. In one preferred embodiment the shielding means comprises a porous member positioned in the likely path of splashed liquid. Preferably, the porous member is mounted in a support with a p6rtion of the porous member exposed.

The porous member may be made from a wide range of liquid absorbing materials such as sponges, felts, matting, fabrics or the like. The porous member can be made up of a single piece or a number of sections. The porous member could be a single layer or made with multiple layers,which may be the same or different. As the porous member is positioned on an outside surface of the brake it does not reach the high temperatures experienced by discs located in the centre of the brake. However, it is important that the material selected for the porous member is compatible with the service environment and service conditions. In one preferred feature the porous member is impregnated with reagents to neutralise or fix the substances in place. The shielding means may be used to protect any suitable component. Typically the sensitive components are carbon brake discs arranged in a heat stack. In such a case the shielding member is mounted on the exterior surface of one end of the stack, e.g. on the pressure stator. A shielding member may be present at each end. In one preferred structure an annular layer of porous member is mounted between two plates dimensioned to leave an exposed area of the porous member. Plates between which the porous member is contained could be of a metallic material such as steel or of ceramic or other material compatible with the service environment and service conditions. Preferably the plates are arranged in sections which may be relatively moveable to allow for mismatching thermal rates of expansion. The plates need not be flat as stiffening webs or cooling fins could be incorporated. The plates, especially the outer plate, could be solid, relieved with holes or in the form of a mesh. Means may be present, e.g. wiper means or

walls including channels and ducts may be shaped to direct splashed liquids on to the porous member. The porous member held to one plate or between such plates could be attached to the outside (pressure) face of the pressure stator by fastening means such as riveting or by the use of joining techniques such as bonding. In a variation the porous member is attached to any other conveniently located component, at one or both ends of the chassis. In another aspect the invention provides a method of shielding the components of an aircraft brake assembly which are sensitive to heat and to contact with substances present in runway de-icer compositions, cleaning fluids and like liquids, the method comprising mounting shielding means on the outside of the assembly at a location which will not substantially increase the temperature of the heat sensitive components and which will cause the shielding means to receive and retain such liquids. Preferably the method includes the step of mounting a porous member in the likely splash path of the liquid. It has been found that by using the invention i.e. incorporating a porous member into the brake assembly splashed de-icer or similar solution can be absorbed into the porous material before it comes into contact with the brake discs. During service the heat of the brake during landing cycles dries the porous member to leave a residue in an otherwise dry porous member, allowing the porous member to again absorb liquids on repeated exposure. The porous member would be

changed during routine servicing of the brake with the porous member, or the assembly containing the plates being replaced. It is important that the porous member contained within the shield is exposed at a position where contaminants will be encountered, In brakes fitted with cooling fans this position will be within the flow of air into the brake when the fan is operative. In order that the invention may be well understood it will now be described with reference to the accompanying diagrammatic drawings in which: Figure 1 is an end elevation of one end stator of the brake assembly of the invention; Figure 2 is a side elevation of the absorbent layers; Figure 3 is a sectional view of the assembly; and Figure 4 is a partial sectional view drawn to an enlarged scale. A typical brake assembly I has the usual annular heat stack of interleaved stator and rotor discs made of carbon-carbon composite. A shield assembly 10 is mounted on the exterior surface at an end (or both ends) of the stack; as shown in Figure 1 the assembly is mounted on the pressure stator 11. The assembly comprises an annular body 12 smaller in diameter than the pressure stator 11 and having radially spaced apart castellations 13. The body 12 is formed of a liquid absorbant material which can withstand the conditions of use, e.g. SAVERUARD E GLASS NEEDLEMAT NGM-06-120. A plate 14 of the same general shape is fitted over each side of the body 12, and its castellations 15 are

dimensioned to leave a marginal portion 16 of the body exposed. The plate is built up of three sections adjacent ends of which overlap, as shown, to allow for movement caused by differential thermal expansion, The plates 14 and body 12 are held to the pressure stator 11 by rivets 17. In use, any liquid sprayed on to the brake assembly will reach the exposed margins 16 of the absorbent material and will be retained there, so being kept away from the carbon-carbon composite discs. As the brakes heat up, the heat will cause the liquid to evaporate from the absorbent material leaving the contaminant solids behind. The material is then free to take up more liquid. On servicing the porous member will be replaced. The invention is not limited to a shield of the size or position shown and a shield covering a larger portion of the pressure stator disc outer face is envisaged.

Claims

CLAIMS 1. An aircraft brake assembly incorporating components which are sensitive to heat and to contact with substances present in runway de-icer compositions, cleansing fluids and like liquids characterised by shielding means mounted on the outside of the assembly at a location which win not substantially increase the temperature of the heat sensitive components and which is arranged to receive and retain such liquids.
2. An assembly according to Claim 1, wherein the shielding means comprises a porous member positioned in the likely path of splashed liquid.
3. An assembly according to Claim 2, wherein the porous member is mounted in a support dimensioned to leave a portion of the porous member exposed to the likely path of splashed liquid.
4. An assembly according to Claim 2 or 3, wherein the porous member is made of felt, a zeohte, matting, fabric or the like.
5. An assembly according to any of Claims 2 to 4, wherein the porous member is impregnated with reagents to neutralise or fix the substances.
6. An assembly according to any preceding Claim, wherein the sensitive components are carbon-carbon brake discs arranged in a heat stack.

<Desc/Clms Page number 8>
7. An assembly according to Claim 6, wherein the shielding member is mounted on the exterior surface of one end of the stack, e.g. on the pressure stator, at a location where it will experience heat generated by the brake in use.
8. A method of shielding the components of an aircraft brake assembly which are sensitive to heat and to contact with substances present in runway de- icer compositions, cleaning fluids and Eke liquids, the method comprising mounting shielding means on the outside of the assembly at a location which will not substantially increase the temperature of the heat sensitive components and which will cause the shielding means to receive and retain such liquids.
9. A method according to Claim 8, including the step of mounting the shielding means in the likely splash path of the liquid.
10. A method according to Claim 8, including the step of moving the shielding means in the path of flow of air into the brake assembly having fan cooling means.