Stock material or miscellaneous articles – Structurally defined web or sheet – Honeycomb-like
Patent
1986-09-02
1988-04-05
Epstein, Henry F.
Stock material or miscellaneous articles
Structurally defined web or sheet
Honeycomb-like
156292, 428408, B32B 312
Patent
active
047358416
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to panels for nacelles intended to house aircraft engines, and more particularly transport aircraft engines, and which have detachable parts constituting what is generally called the cowling.
The cowling of an aircraft engine must be constructed in such a manner as to ensure the continuity of shape of the nacelle, to withstand aerodynamic forces, to be insensitive to the various fluids originating from the engine, and, in the case of an engine fire, to contain the fire before the extinguishers are operated. With regard to this last point, the standard FAR 25 stipulates resistance of the cowling to a flame at a temperature of 1100.degree. C. for 15 minutes.
Up to the present time this requirement could be met only by metals which withstand high temperatures, such as stainless steels or titanium, whereas light alloys or composite materials containing an epoxy resin were suitable only with the addition of protectors of refractory materials or intumescent paints, the end result being that the cowlings were heavy and costly.
SUMMARY OF THE INVENTION
The present invention makes it possible to produce cowlings of composite material which have no protection and are therefore lighter and less expensive, and which have satisfactory resistance to fire.
According to a first characteristic of the invention the sandwich panels constituting the cowlings are composed of coverings of carbon fibres impregnated with phenol resin and joined together by a honeycomb core which may be of glass fibres, likewise impregnated with phenol resin.
It has in fact been found that in order to form the outer and inner coverings of a panel which has to satisfy the conditions defined above it was advantageous to use carbon fibres which have higher resistance to temperature than glass fibres or fibres of the material known as "KEVLAR" and higher mechanical resistance than refractory fibres, such as silica for example.
The carbon fibres are preferably used in the form of woven fabrics to constitute the coverings, as woven fabrics make it possible to obtain coverings whose resistance in the event of fire is better than that of nonwoven fibres, which are torn away.
The phenol resin used to impregnate such woven fabrics may be the resin available on the market under the trade mark "Brochier 200", which is almost completely insensitive to fire.
For the purpose of joining the coverings and the interposed honeycomb, it is advantageous to use an epoxy adhesive, which will be deposited in the form of a film on the coatings before they are joined to the honeycombs.
According to another feature of the invention the outer coating and the inner coating are treated separately in such a manner that the outer coating will be as fluidtight as possible, but that the inner coating will be porous.
The phenol resin used for impregnating the carbon fabric constituting the base of each of the coatings gives off gases during its polymerization under heat.
This being so, the outer coating will be baked in an autoclave, first in vacuo in order to eliminate as much as possible the gases given off, and then in the final phase of the baking it will be subjected to heavy pressure in order to close the pores, so that the residual gas will remain in the coating in the form of fine included bubbles.
For the inner coating the polymerization will also be effected by baking in an autoclave, but without the application of a vacuum, and in such a manner that most of the pores remain open. This porosity of the inner coating prevents it from bursting through the action of the abrupt rise in temperature caused by the fire.
It is advantageous to complete the production of the inner covering by adding a coating of low melting metal sprayed onto the inwardly facing surface of this covering, and also a coating of cellulose paint in order that this covering may be fluidtight under normal operating conditions, but will become porous again in the event of fire, through the disappearance of the paint and the immediate melting of the meta
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Avions Marcel Dassault-Breguet Aviation
Epstein Henry F.
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