GB1580321A

GB1580321A - Lightning diverter strip and method of manufacturing the same

Info

Publication number: GB1580321A
Application number: GB2346478A
Authority: GB
Original assignee: Dayton Granger Aviation Inc
Current assignee: Dayton Granger Aviation Inc
Priority date: 1977-08-09
Filing date: 1978-05-26
Publication date: 1980-12-03
Also published as: FR2400245A1; FR2400245B1; JPS5429500A; JPS6055358B2; CA1106438A

Description

(54) LIGHTNING DIVERTER STRIP AND METHOD OF MANUFACTURING THE SAME (71) We, DAYTON-GRANGER AVIATION, INC., a corporation organised and existing under the laws of the State of Florida, United States of America, of 812, Northwest First Street, Fort Lauderdale, Florida 33302 United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to aircraft lightning protection and more particularly to an improved lightning diverter strip for aircraft, and a method of making the same.

It is well known that aircraft, when flying in the vicinity of thunderstorms, are subject to lightning strikes. Various points and regions of the aircraft extremities are subject to the form- ation of streamers prior to the actual lightning strike. It is also known that the lightning strike will occur when a leader connects up with one of the streamers, and the resulting current can reach as high as 200,000 amperes. While the aluminium aircraft skin is seldom subject to severe lightning damage by reason of its electrical conductivity, lightning attachments at certain critical points, for example, the radome section, are to be avoided due to the likelihood of damage to the electrical equipment.

Lightning diverter strips have been devised in the past for application to aircraft structural surfaces for the purpose of providing a non-destructive, electrically-conductive path to protect the underlying structure from direct lightning attachments. For example, thin metal foil strips and solid metal bars have been used to divert the charge. In addition, a series of closely spaced metal discs or dots have been applied to flexible strip material. In such instances, metal disks of 1/10 inch diameter have been bonded to a substrate, and the latter has been fixed by an epoxy adhesive to the outer surface of the radome to provide an ionized conductive path.While such an arrangement has been successful, it is of relatively high cost, and the relatively large discs absorb a great deal of heat and occasionally these discs have been known to explode and shoot out like pellets, especially if they are spaced too far apart. Also, the size of the discs adversely affects the radio frequency absorption of the strip.

According to one aspect of the present invention there is provided a lightning diverter strip for aircraft, for conducting lightning-induced electrical currents and thereby protecting vulnerable aircraft components such as radomes and the like, comprising a substrate of flexible dielectric tape having a first surface which, in use of the strip, is the inner surface of the tape and is applied to the aircraft component to be protected, and a second surface which, in use of the strip, is the outer surface of the tape, on which is provided a flexible epoxy binder, a conductive metal powder substantially uniformly deposited along the second surface of said tape, and bonded thereto by said binder, said powder having a particle density to provide a high DC resistance while forming a conductive path for electrical currents induced by lightning.

In one embodiment, the lightning diverter strip consists of a supporting substrate comprising a light, thin dielectric tape of film strip formed from a plastics material of the polyester tape, and a substantially uniformly dispersed powdered metal applied to the second or outer surface of the tape and bonded thereto by a suitable flexible epoxy.

Finely powdered aluminium is used as the conductive metal and is distributed substantially uniformly along the surface of the tape, in such a manner that a direct current conductive path is not formed. Thus, the finished lightning diverter strip will have a very high resistance so that it will read essentially as an open circuit to DC voltage. The particles are dispersed in sufficiently close fashion that the strip is essentially a short circuit to lightning currents and is also transparent to rf.

energy. Since the aluminium particles are of small size, very little energy is absorbed in the particles and physical damage due to lightning attachments is held to a minimum. The particle themselves, since they are very close together appear to the lightning as a large number of series-connected tiny capacitors which guide the lightning strike to the fuselage.

The tape is preferably formed from polyethylene terephalate. The lightning diverter strip is conveniently applied, by the first or inner surface of the tape, to the aircraft surface to be protected using a suitable epoxy cement.

From another aspect, the invention provides a method of manufacturing a lightning diverter strip, which includes: a) applying a curable epoxy to a surface of a length of thin dielectric tape, b) substantially uniformly applying particles of a conductive metal powder to the epoxy with a particle density such as to provide a high DC resistance while forming a conductive path for lightning-induced currents, and c) curing said epoxy to bind the metal particles to the tape.

In order that the invention may be more readily understood, reference will now be made to the accompanying drawings, in which: Figure 1 is a perspective view of the nose of the aircraft showing a radome as having lightning diverter strips embodying the invention applied thereto; Figure 2 is a perspective view, partially broken away, of a lightning diverter strip embodying the invention; Figure 3 is a transverse section, on a larger scale, through the strip shown in Figure 2; and Figure 4 shows the strips as applied to the canopy and vertical stabilizer surfaces of an aircraft.

Referring to the drawings which illustrate a preferred embodiment, a typical aircraft is shown at 10 as having a radome 11 which is to be protected by the lightning diverter strips 12.

As shown, the strips 12 will commonly lead along the surface of the part to be protected and will terminate at or near the skin of the aircraft.

The strip is illustrated in Figures 2 and 3 as including a base or substrate formed of polyester tape 15 having a first, inner or lower surface 16 adapted to be applied directly to the aircraft component to be protected and bonded thereto by a suitable epoxy cement.

The tape 15 is preferably a dielectric material such as thin polyethylene terephalate tape sold under the Registered Trade Mark "Mylar".

Preferably, this material is about 4 mils in thickness, although the thickness, width, and length are not critical.

Aheat curable flexible epoxy binder 18 is uniformly applied to the second, outer or upper surface of the tape 15.

A conductive metal powder 20 is uniformly deposited along the upper surface of the epoxy binder 18. The epoxy binder binds the metal powder to the tape 15. While many different conductive metal powders may be used, it is preferable to employ finely divided aluminium.

The aluminium particles are deposited sparsely along the binder 18 on the tape 15.

Preferably, an atomizer-grade powder is used which is 99.5% pure aluminium, with a particle size or diameter of 13 + 3 microns. The powder is uniformly dispersed along the epoxy binder 18 with an approximate density of 300,000 particles per square centimeter. The actual density is not critical and may be 100,000 particles per square centimeter, or lower. The individual particles are of such a small physical mass that very little energy is absorbed within the particles. Thus, physical damage to the diverter strip 12 due to lightning attachment is held to a minimum. For the best results, the aluminium particles are deposited sparsely along the binder 18 on the tape 15. Preferably, the powdered aluminium particles are deposited on the binder 18 before it is cured and thus become embedded into the exposed surface of the binder.An excess of particles may be deposited on the uncured binder, and the excess particles removed, for example, by shaking or brushing the strip after curing, so that only the attached or embedded particles remain. While the individual aluminium particles may touch each other, nevertheless a DC conductive path is not formed in view of the fact that the aluminium particles have a microscopically thin coating of aluminium oxide on their outer surfaces, and aluminium oxide is essentially a non-conductive or a dielectric material. Therefore, the strip will read, after curing, as an essentially open DC circuit or will present a very high resistance to DC voltage.

While the strip reads as an open circuit to DC voltage, it will be substantially transparent to rf. frequencies, and provides a low impedence path at the frequencies of the lightning strike.

Since the particles are close together, the strip appears to the lightning as a large series of very small capacitors guiding the strike to the conductive skin of the aircraft.

The finished diverter strip is very thin, is light in weight, and is flexible. The tape 15 forming the base or substrate may for example be 3/8' wide, and any length. It is easily cut by scissors to a desired length. For the purpose of illustration, the thicknesses shown in Figure 3 have been greatly exaggerated. Further, the particles of the aluminium powder 20 are actually slightly embedded within the epoxy binder 18 and are permanently attached to the tape 15. The diverter strip 12 has high resistance to errosion and damage due to air currents and the impact of rain on the exposed surface. Since the strip is flexible and thin, it is easy to apply, and it is relatively inexpensive to manufacture as compared to prior devices. It does not adversely affect the operation of radar and has low aerodynamic drag. It has little or no maintenance requirements and is capable of taking repeated lightning strikes without severe degradation.

Of course, the strip 12 may be used wherever lightning protection on an aircraft is desired. In Figure 4, ajet aircraft 30 is shown as having a plastic canopy 32 protected by a strip 12. A vertical stabilizer has fiber glass leading edges 35 which are also protected by strips 12.

While the lightning diverter strip herein described, and its method of manufacture, constitute preferred embodiments of this inven tlon, it is to be understood that various modifications may be made without departing from the scope of the invention as defined in the

Claims

appended claims. WHAT WE CLAIM IS:

1. A lightning diverter strip for aircraft, for conducting lightning-induced electrical currents and thereby protecting vulnerable aircraft components such as radomes and the like, comprising a substrate of flexible dielectric tape having a first surface, which, in use of the strip, is the inner surface of the tape and is applied to the aircraft component to be protected, and a second surface which, in use of the strip, is the outer surface of the tape, on which is provided a flexible epoxy binder, a conductive metal powder substantially uniformly deposited along the second surface of said tape, and bonded thereto by said binder, said powder having a particle density to provide a high DC resistance while forming a conductive path for electrical currents induced by lightning.

2. A lightning diverter strip as claimed in claim 1, in which the conductive metal powder is aluminium.

3. A lightning diverter strip as claimed in claim 2, in which said aluminium powder is finely divided aluminium in which the particles have a size of approximately 13 microns and are deposited with a density within the range of 100,000 to 300,000 particles per square centimeter.

4. A lightning diverter strip as claimed in claim 1, 2 or 3, in which said tape is formed from a dielectric plastics material of the polyester type.

5. A lightning diverter strip as claimed in claim 4, in which said tape is formed of polyethylene terephalate.

6. A method of manufacturing a lightning diverter strip, which includes: a) applying a curable epoxy to a surface of a length of thin dielectric tape, b) substantially uniformly applying particles of a conductive metal powder to the epoxy with a particle density such as to provide a high DC resistance while forming a conductive path for lightning-induced currents, and c) curing said epoxy to bind the metal particles to the tape.

7. A method as claimed in claim 6, wherein the conductive metal powder is finely divided aluminium powder, the particles of which are approximately 13 microns in size and are deposited with a particle density which is within the range of 100,000 to 300,000 particles per square centimeter.

8. A method as claimed in claim 6 or 7, wherein the dielectric tape is formed from a plastics material of the polyester type.

9. A method as claimed in claim 6, 7 or 8, in which the thickness of the tape is about 4 mils.

10. The metliods of manufacturing lightning diverter strips substantially as hereinbefore described with reference to the accompanying drawings.

11. Lightning diverter strips made by the method claimed in any of claims 6 to 10.

12. Lightning diverter strips substantially as hereinbefore described with reference to the accompanying drawings.

13. An aircraft provided with a lightning diverter strip, or lightning diverter strips, as claimed in any of claims 1 to 5, 11 or 12.