Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B64—AIRCRAFT; AVIATION; COSMONAUTICS
  • B64D—EQUIPMENT FOR FITTING IN OR TO AIRCRAFT; FLIGHT SUITS; PARACHUTES; ARRANGEMENT OR MOUNTING OF POWER PLANTS OR PROPULSION TRANSMISSIONS IN AIRCRAFT
  • B64D45/00—Aircraft indicators or protectors not otherwise provided for
  • B64D45/02—Lightning protectors; Static dischargers

Definitions

• This specification generally relates to protecting composite structures from lightning strikes, and more particularly, to an appliqu ⁇ for protecting composite aircraft from lightning strikes.
• a lightning strike to unprotected components, embedded in, passing through or attached to the CRFP aircraft skin that is generally 35-40% resin does not dissipate as readily as in metal.
• a lightning strike can cause considerable damage to the CRFP aircraft skin, even destroying critical portions of the aircraft.
• temperature drives the damage level.
• the discharge current through composite skin resistance dissipates a burst of energy that causes the carbon fibers to become very hot, so much so, that the skin temperature becomes much hotter in a CRFP structure than in a state of the art aluminum skin.
• the temperature may exceed the CRFP resin pyrolization temperature, causing the resin to vaporize, turning some of it from a solid to a gas.
• the exterior CFRP structure must withstand not only the initial lightning strike, but also at least one hundred kiloamperes (10OkA) of discharge current without adverse affects or impact to safety-of-flight.
• composite structure aircraft must have some protection, especially at exposed skin fasteners, and especially at fuel and hydraulic couplings in the fuel tank to minimize this sparking.
• this protection is economically feasible, in its initial application, in its effectiveness for minimizing resulting damage and, in subsequent consequent repair or replacement, both for continued aircraft flightworthiness and to meet economic repair targets.
• An embodiment reduces lightning strike damage to aircraft and in particular, fuel tank sparking from lightning strikes to composite surfaces.
• an embodiment simplifies protecting composite aircraft and in particular wing fuel tanks from lightning strikes, and simplifies repairing of damage to the aircraft lightning strike protection system.
• embodiments include a lightning protection system in a lightning protection appliqu ⁇ , an aircraft including the lightning protection system and method of protecting an aircraft from lightning strikes.
• a dielectric ply is fixed (e.g., bonded) above and completely covers metallic skin fasteners.
• a conductive ply is fixed (e.g., bonded) above and completely covers the dielectric ply and extends to an external connection, e.g., to a platform ground. The conductive ply directs lightning discharge current away from critical areas.
• Both plies may be adhesively backed and sequentially pressed into place.
• a preferred lightning protection appliqu ⁇ provides flexibility in lightning protection design without increasing aircraft weight appreciably and with superior performance and protection.
• Appliqu ⁇ dielectric and conductor layers are simply sequentially pressed in place on the skin to avoid adding an embedded conductive layer or requiring a conductive surface protection layer for a CFRP skin.
• a preferred lightning protection system simplifies aircraft skin design while reducing weight.
• cost savings are realized from simple dielectric and conductor layer manufacturing requirements, as well as maintenance simplicity.
• age may make removal increasingly difficult, an entire preferred appliqu ⁇ may be replaced by peeling the old ply( ⁇ lies) off and pressing a new one(s) in place.
• Figure 1 shows an example of an aircraft skin cross section through the wing with lightning protection appliqu ⁇ (LPA) according to an advantageous embodiment the present invention.
• LPA lightning protection appliqu ⁇
• Figure 2 shows an example of a preferred LPA attached to the wing of an aircraft. DESCRIPTION OF PREFERRED EMBODIMENTS
• Figure 1 shows an example of a lightning protection system according to a advantageous embodiment in a cross section 100 of an aircraft.
• the cross section 100 is taken through the composite skin 102, e.g., a Carbon Fiber Reinforced Plastic (CFRP) skin, of the aircraft wing, protected by a preferred embodiment Lightning Protection Applique " (LPA) 104.
• the composite skin 102 is fastened to a rib (metal or CFRP) 106 or similarly to a spar (CFRP), by skin fasteners 108 extending through the skin 102 and shear tie flange 107, held in place by collars or nuts 110.
• the cross section 100 is part of a fuel tank of a wing section.
• a preferred LPA 104 may be used to protect any composite structure surface area where metal is exposed at the skin surface and so, is exposed to similar lightning threat levels, including other areas of a composite aircraft.
• the lightning protection appliqu ⁇ 102 includes a dielectric ply 112 electrically isolating and insulating the skin fasteners 108, e.g., from a lightning strike, and a conductive ply 114 diverting electrical energy from such a lightning strike away from the isolated skin fasteners 108.
• the conductive ply 114 extends at least 1.0" (2.54cm) beyond the dielectric ply 112 at the skin fasteners 108, in this example to a ground contact 116, e.g., a bolt or rivet, that is separated from the skin fasteners 108 and located away from the fuel tank.
• the ground contact 116 is connected to a platform ground 118 and held in place by suitable attachment 120, e.g., a nut.
• suitable attachment 120 e.g., a nut.
• the conductive ply 114 is selected large enough that the lightning strike current dispersed around the surface of the structure to what are non-critical areas and without connecting the conductive ply 114 to platform ground 118.
• the dielectric ply 112 may be, for example, a suitable electrically insulating or dielectric film 112D of an appropriate thickness, e.g., 0.003" to 0.010" (0.076-0.254mm) and an attachment backing 112 A, e.g., of pressure sensitive adhesive, preferably, 0.002" (0.050mm) thick.
• a suitable electrically insulating or dielectric film 112D of an appropriate thickness, e.g., 0.003" to 0.010" (0.076-0.254mm) and an attachment backing 112 A, e.g., of pressure sensitive adhesive, preferably, 0.002" (0.050mm) thick.
• the specific material selected for electrically insulating dielectric film 112D depends on the intended installation conditions and the system's design.
• the selected insulating material may be a film of a fluoropolymer such as for example polytetrafluoroethylene (PTFE); or a terpolymer of tetrafluoroethylene, hexafluoropropylene, and vinylidene fluoride (THV); or fluorinated ethylene propylene (FEP); or perfluoroalkoxytetrafluoroethylene (PFA).
• PTFE polytetrafluoroethylene
• TSV vinylidene fluoride
• FEP fluorinated ethylene propylene
• PFA perfluoroalkoxytetrafluoroethylene
• polyester, polyimide, or polyurethane films may be more appropriate to facilitate paint adhesion.
• the conductive ply 114 in this example includes a conductive center layer 114C sandwiched between and encapsulated by a protective surface layer 114S and an attachment backing 114A.
• the conductive center layer 114C includes a 0.001" to 0.004" (0.025 - 0.102mm) thick metallic layer (solid or mesh) incorporated in an adhesive.
• the preferred protective surface layer 114S provides the conductive center layer 114C with partial environmental protection and promotes primer/top coat adhesion for subsequent painting, if necessary.
• the preferred protective surface layer 114S is 0.002" to 0.004" (0.051 - 0.102mm) thick electrically insulating film, that may be the same material as electrically insulating film 112D in the dielectric play 112.
• the attachment backing 114A may be a layer of pressure sensitive adhesive, 0.002" to 0.008" (0.051 - .203mm) thick. Both attachment backing 112A and 114A provide adhesion for attaching the respective ply 112, 114 to the underlying structure, i.e., CFRP skin, and/or the dielectric ply 112.
• the metallic layer in conductive center layer 114C may be incorporated in the same adhesive material.
• a sealant may be applied along the edges of the plies 112, 114, e.g., to prevent chemical/environmental erosion.
• the dielectric ply 112 is applied in a strip to the skin 102 covering all skin fasteners 108 in the area of exposure. If applicable, the dielectric ply 112 also covers any other exposed surface metal features. Since the dielectric ply strip 112 may be limited to only the area around surface metal such as skin fasteners 108, the strip 112 provides a significant weight saving over a more encompassing approach. Examples of such encompassing approaches include, for example. Published U.S. Patent Application No. 20050181203, entitled “Applique " " to Diane C. Rawlings et al., and Published U.S. Patent Application No. 20050150596 entitled "Methods and Materials for Reducing Damage from Environmental Electromagnetic Effects" to Terrence G.
• Vargo et al. both of which are assigned to the assignee of the present invention and incorporated herein by reference.
• the overlap distance that the dielectric layer strip 112 must overlap surface metal depends on the skin resistance and the level of desired protection. However, preferably, for a state of the art CFRP and for a one hundred kiloampere (10OkA) lightning strike, the overlap is at least 1.8" (4.57cm) to sufficiently isolate metallic surface features.
• the conductive ply 114 has significantly greater area coverage than the dielectric layer strip 112 and is applied directly over the dielectric layer strip 112 and CFRP skin 102.
• the preferred conductive ply 114 may cover the entire structure (e.g., aircraft or other composite structure) or only selected sections of the structure (e.g., selected sections of a composite wing or fuselage), e.g., for weight reduction.
• the conductive ply 114 provides a high current path to the platform ground 118 that directs current from lightning strikes away from the isolated skin fasteners 108 and through grounding studs 116 and nuts 120. So, the grounding studs 116 also must be spaced adequately away from the skin fasteners 108, depending upon skin 102 resistance and desired protection level. Thus, the conductive ply 114 overlaps and completely covers a significantly greater area than the dielectric ply 112.
• a preferred lightning protection appliqu ⁇ 104 is capable of successfully meeting the lightning protection requirements for lightning strike zone 2 (10OkA) as set forth in SAE International standard No. ARP5412.
• FIG 2 shows an example of an aircraft 120 with a preferred lightning protection appliqu ⁇ (e.g., the LPA 104 of Figure 1) fixed to the skin 102 of the wing, e.g., over metal features on the wing.
• the metal features may be fasteners at the fuel tank.
• the preferred conductive ply provides this external high current path, it is unnecessary to add weight to the CFRP skin by including a conductive surface protection layer.
• the preferred embodiment lightning protection appliqu ⁇ 104 which contains the lightning discharge protection, avoids the substantial weight of including a conductive surface protection layer.
• a preferred lightning protection applique 104 may be applied post-assembly after fastener installation and is easily inspected, maintained and replaced as necessary.
• the preferred lightning protection appliqu ⁇ 104 may also be uniquely configured/designed to satisfy the Electromagnetic Effect (EME) requirements for a particular lightning zone.
• EME Electromagnetic Effect
• the dielectric layer (112D, 114D in Figure 1) thicknesses and the conductive element (114C in Figure 1) thickness can be selected accordingly to satisfy the particular lightning protection requirement level of each particular lightning zone.
• the preferred lightning protection applique provides flexibility in lightning protection design without increasing aircraft weight appreciably and with superior performance and protection. Instead of adding an embedded conductive layer or requiring a conductive surface protection layer for a CFRP skin, the dielectric and conductor layers are simply sequentially pressed in place on the skin.
• the present invention simplifies aircraft skin design while reducing weight.
• cost savings are realized from simple dielectric and conductor layer manufacturing requirements, as well as maintenance simplicity.
• An entire appliqu ⁇ may be replaced by just peeling the old ply(plies) off and pressing a new one(s) in place.

Landscapes

• Engineering & Computer Science (AREA)
• Aviation & Aerospace Engineering (AREA)
• Laminated Bodies (AREA)
• Elimination Of Static Electricity (AREA)
• Thermistors And Varistors (AREA)

Priority Applications (3)

Applications Claiming Priority (2)

Publications (1)

Family

ID=38349516

Family Applications (1)

Country Status (6)

Cited By (4)

Families Citing this family (46)

Citations (3)

Family Cites Families (14)

• 2006
  • 2006-03-29 US US11/277,888 patent/US7277266B1/en not_active Expired - Lifetime
• 2007
  • 2007-03-29 EP EP07754453.4A patent/EP2004490B1/en active Active
  • 2007-03-29 PT PT77544534T patent/PT2004490E/pt unknown
  • 2007-03-29 ES ES07754453.4T patent/ES2560863T3/es active Active
  • 2007-03-29 JP JP2009503033A patent/JP5097768B2/ja active Active
  • 2007-03-29 WO PCT/US2007/007936 patent/WO2007123700A1/en not_active Ceased

Patent Citations (3)

Also Published As

Similar Documents

Legal Events