Electricity: electrical systems and devices – Discharging or preventing accumulation of electric charge – Structurally combined with building or vehicle
Patent
1982-09-30
1984-10-23
Moose, Jr., Harry E.
Electricity: electrical systems and devices
Discharging or preventing accumulation of electric charge
Structurally combined with building or vehicle
244 1A, H05F 102
Patent
active
044791631
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to aircraft lightning protection systems and more particularly to lightning protection structures for composite structural components having fasteners.
It is known that the present planned graphite epoxy composite structural components to be used on aircraft will be subjected to natural lightning strike discharges. The most severe strikes will be limited to structures located at or near the aircraft protuberances (wing tips, stabilizer tips, vertical tips, rudder, elevators, ailerons, some engine cowlings, etc.). These locations are designated Zone 1 and will be subjected to the initial attachment of the lightning channel. The initial attachment lightning strike is characterized by a fast rise, high peak current (2.times.10.sup.5 amp) and a large energy transfer (2.times.10.sup.6 amp.sup.2 sec). It can create severe structural damage to unprotected graphite epoxy structure (much more so compared to aluminum structure). Other parts of the structure will be subjected to lesser discharges, called swept stroke lightning. These areas are designated Zone 2 and are located aft of the initial attachment points. Particularly sensitive areas are integral fuel tanks and pressurized sections. Punctures cannot be tolerated in either area but fasteners penetrating the skin and protruding into a fuel tank area have been shown to constitute a fuel ignition source even without a skin puncture. Unprotected fasteners are a preferred attachment point for the lightning and spark because the energy cannot be distributed fast enough into the surrounding graphite epoxy material (due to its low thermal and electrical conductivity). The test criteria for Zone 2 also contains a fast rise current but with a 1.times.10.sup.5 amp peak and an energy transfer of 0.25.times.10.sup.6 amp.sup.2 sec.
Representative of the prior art literature is U.S. Pat. No. 3,755,713, assigned to The Boeing Company. Knitted wire mesh is utilized in U.S. Pat. No. 3,755,713 in contrast to preferred embodiments of the present invention which utilize nickel-plated graphite fibers. A decorative layer is shown in the reference patent, thereby providing insufficient coverage for fastener heads. Further, in U.S. Pat. No. 3,755,713 there is no insulation between the fasteners and the structure since the reference structure is fiberglass and therefore nonconductive.
Heretofore, lightning protection material most commonly utilized for non-metallic structures is aluminum. The aluminum is normally applied as a flame spray, a woven screen, a foil or a plating. Such prior method works satisfactorily when the structure is a dielectric such as fiberglass or kevlar epoxy. However, aluminum is galvanically incompatible with graphite epoxy forming the composite structures in accordance with the present preferred embodiments. If not isolated from the graphite epoxy, the aluminum will corrode; if isolated, the aluminum loses its effectiveness as a protection system (no electrical path).
As a consequence of the preceding, it is an object of the present invention to provide a more compatible protection system for graphite epoxy structures to prevent future maintenance problems with the protection system.
It is a further object of the present invention to provide woven outer layer structures for composite structural components which include interwoven nickel-plated graphite fibers.
It is yet a further object of the present invention to provide plating of fiber tows as a function of protection desired, e.g., Zone 1 or Zone 2, in the outer layer of fabric for the structural component requiring lightning protection.
A full understanding of the present invention, and of its further objects and advantages and the several unique aspects thereof, will be had from the following description when taken in conjunction with the accompanying drawing in which:
FIG. 1 is cross-sectional view of a composite structure including fasteners showing the present nickel-plated graphite fiber lightning protection;
FIG. 2 is a further embodiment of the present invention showi
REFERENCES:
patent: 3755713 (1973-08-01), Paszkowski
patent: 3989984 (1976-11-01), Amason et al.
Bannink, Jr. Engbert T.
Olson Glenn O.
DeVogel Nicolaas
Donahue Bernard A.
Gardner Conrad O.
Moose Jr. Harry E.
The Boeing Company
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