Apparatus and method for effecting repair to damaged non-stressed aircraft structure

A apparatus and method for effecting repair to damaged, nonstressed aircraft structure is described. A sheet of material comprised of woven glass cloth impregnated with a resin cured under temperature and pressure forms the basic patch. One side of the patch has a Tedlar.RTM. overlay attached to the sheet face in the preferred embodiment. This patch material meets the Federal Aviation Regulations (FAR 25.855) which is required to provide for fire resistant material on transport aircraft. A pressure sensitive film is bonded to the side opposite the Tedlar.RTM. overlay. This combination of glass sheet and pressure sensitive film is pressure bonded to the damaged structure and further held in place by mechanical fasteners which can withstand a temperature of at least 1,700 degrees Fahrenheit. One of the primary applications of this invention is in the cargo liner repair of transport aircraft. A fire in the cargo bay must be contained in that area and not allowed to spread to the aircraft due to a damaged cargo liner.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention pertains to an apparatus and method for effecting repairs to 
damaged, nonstressed aircraft structure. More specifically, this invention 
provides a repair to damaged, nonstressed aircraft structure that will 
withstand a burn requirement established by the Federal Aviation 
Regulation (FAR 25.855). 
2. Description of the Prior Art 
There are damaged, non-stressed structures in specific parts of transport 
aircraft that must be repaired immediately to prevent loss of life and 
property in the event of a catastrophic situation such as a fire. One such 
structure is the cargo bay of a transport aircraft. Cargo bays contain a 
cargo bay liner that is made from high impact resistant and fire resistant 
material. These cargo liners take considerable abuse from the loading and 
off loading of cargo at every aircraft terminal. Invariably, in time, a 
sharp object of cargo will puncture a hole in the liner or damage the 
liner such that the liner integrity is in question. The FAA regulation 
effective March, 1991 states that as soon as the damage is discovered, a 
repair must be made prior:to the next flight. This repair must provide the 
same burn resistance as the original liner had before the damage. The 
present invention provides this requirement and can be installed in less 
than 20 minutes, which can be accomplished, most of the time, between 
flights. 
There are several repair devices and methods available for various types of 
damaged to aircraft structure. One such method is found in U.S. Pat. No. 
4,517,038, which describes a method of repairing ballistic damage to 
stressed structure. This patent descries a sandwich material of metal, 
nylon and armid cloth which are heated and fused together to form a strong 
patch that may be bent to shape like the surface of an airfoil. The patch 
is then bonded and riveted in place. 
Another repair apparatus is described in U.S. Pat. No. 4,858,853. This 
patent describes a stack of thin flexible metal plates with adhesive 
applied therebetween. The plates are bent to shape and bolted onto the 
outside of the aircraft structure. Obviously this is a field repair 
because a plate bolted on the outside of a wing would cause drag and flow 
disturbance. 
U.S. Pat. No. 4,759,812 discloses a method and apparatus for effecting 
field repairs in stress carrying structures. This patent describes a patch 
using two thin metal sheets bent to shape with one part of VELCRO.RTM. 
bonded to each side. The metal sheets have a resin impregnating the 
VELCRO.RTM. and when the resin hardens, the patch becomes stiff. 
U.S. Pat. No. 3,470,048 describes a method of patching metal car bodies 
using a metal patch bonded to the body with pressure sensitive film. No 
mechanical fasteners are used as in the present invention. 
U.S. Pat. No. 4,707,391 describes a vehicle body surface repair assembly 
for automobiles and uses a perforated thin metal or plastic plate. This 
plate is placed over the damaged part and fiberglass mesh is placed over 
the plate. Fiberglass body surface repair compound such as Bondo.RTM. is 
forced in the mesh and perforated plate to better support the repair. 
U.S. Pat. No. 3,850,718 uses a metal patch with a thin layer of high 
density foam bonded to one side. A pressure sensitive adhesive is bonded 
to the foam which is then applied to the damaged area. This patch finds 
application in truck trailers and sea going cargo containers. 
From the foregoing, the need should be appreciated for a repair patch that 
will meet the burn requirement of FAR 25.855. The present invention, which 
is fire resistant, will not loose its integrity even if the adhesive, 
which is fire retardant, does not hold the patch in place. The fasteners, 
which will withstand a temperature of at least 1,700 degrees Faherinheit 
will hold the patch in place and prevent the fire from reaching the 
aircraft structure. Accordingly, a fuller understanding of the invention 
may be obtained by refering to the summary of the invention, and the 
detailed description of the preferred embodiment, in addition to the scope 
of the invention defined by the claims taken in conjunction with the 
accompanying drawings. 
SUMMARY OF THE INVENTION 
It is the object of the present invention to provide an apparatus and 
method for effecting a repair to a damaged, non-stressed transport 
aircraft structure. 
It is another object of this invention to provide an apparatus and method 
for effecting a repair to a damaged, non-stressed aircraft structure of a 
transport aircraft. 
It is a further object of this invention to provide an apparatus and method 
for effecting a repair to a damaged, non-stressed transport aircraft 
structure that will meet the Federal Aviation Regulations (FAR 25.855). 
It is yet another object of this invention to provide an apparatus and 
method for effecting a repair to a damaged, non-stressed transport 
aircraft structure that contains fire resistant mechanical blind 
fasteners. 
Briefly, in accordance with this invention, there is provided a glass cloth 
material impregnated with a resin and cured under heat and pressure. A 
pressure sensitive film is bonded to one side of the cured glass cloth to 
form a patch. The patch is placed over the damaged area and pressure is 
applied to the patch to form an air tight seal. Mechanical fasteners of 
the blind type are placed around the edge of the patch and tightened to 
form a firm mate. In the preferred embodiment, the cured glass cloth has a 
Tedlar.RTM. overlay bonded to one side. In addition, the pressure 
sensitive film is fire retardant and the blind fasteners can withstand a 
temperature of at least 1,700 degrees fahrenheit. The present invention is 
simple, reliable and inexpensive to manufacture. It is estimated that a 
repair can be made to a non-stressed transport aircraft structure in less 
than 20 minutes.

DESCRIPTION OF THE PREFERRED EMBODIMENT 
Turning now to FIG. 1 there is shown a non-stressed aircraft structure 
generally shown at 10 having a damaged area 11. The structure can either 
be metallic or non-metallic, however, in the preferred embodiment the 
structure is non-metallic material. The non-metallic structure 12 as shown 
in FIG. 1 must be a structure capable of receiving a high impact without 
damage and must be able to meet the Federal Aviation Regulation (FAR) 14 
CFR Part 25, Amendment No. 25-60, Paragraph 25.855 (a-1)(1) and Part III 
of Appendix F, Oil Burner Test Requirement. An example of non-stressed, 
non-metallic structure in transport aircraft that must meet the burn test 
requirement given above, is the cargo bay of these aircraft. If a fire 
starts in the cargo bay, it must be contained in that bay and not travel 
to other parts of the aircraft which would result in obvious disastrous 
results. Most cargo bays of transport aircraft are made of fiberglass and 
have a covering of Tedlar.RTM. which provides an appealing appearance and 
texture. Tedlar.RTM. is a trade name of E. I. DuPont de Nemours and 
Company, Inc., Wilmington, Del., for a polyvinylfluoride type of 
fluorocarbon film. Some of the older transport aircraft, however, do not 
have a Tedlar.RTM. covering over the non-metallic structure. 
FIG. 2 shows that composition of the layers of material 13 that is used for 
patching the damaged structure. The basic material is cured glass cloth 14 
that is composed of plies of woven glass, impregnated with a thermosetting 
resin and cured with the application of heat and pressure. In the 
preferred embodiment, the thermosetting resin is a phenolic resin, 
however, a polyester or a epoxy resin may be used with equally successful 
results. A cured laminate made from woven glass cloth impregnated with a 
phenolic resin and having a Tedlar.RTM. overlay may be purchased from M. 
C. Gill of El Monte, Calif. under the trade name of Gilfab 1167, which is 
incorporated herein by reference. FIG. 2 also shows the Tedlar overlay 20 
which is bonded to the glass cloth 14 when the laminate is used to 
fabricate patch 22. The cured laminate having a Tedlar.RTM. overlay bonded 
thereto is at least 0.010 inches thick in the preferred embodiment wherein 
the Tedlar.RTM. overlay prior to being bonded to the laminate is at least 
1 mil thick. The cured laminate with the Tedlar.RTM. bonded thereto as 
described above is also fire resistant and meets the Federal Aviation 
Requirements (FAR 25.855) which is the same as that described for the 
structure 12. FIG. 2 also shows a pressure sensitive adhesive film 16 
having a release liner 18. (For illustration purposes, the release liner 
18 has been removed from the pressure sensitive adhesive film 16.) The 
release liner 18 is a thin film of plastic that is placed on the pressure 
sensitive adhesive film 16 to preserve the adhesive capability, however in 
some embodiments paper may be used. The pressure sensitive film side 
without the release liner is pressure bonded to the cured glass cloth side 
without the Tedlar.RTM. overlay. The release liner 18 will be removed just 
prior to placing the patching material 13 over the damaged area 11. The 
pressure sensitive adhesive film 16 in the preferred embodiment is fire 
retardant and non-hardening and is an acrylic base film although a rubber 
base film can be used with equally successful results. The preferred 
embodiment pressure sensitive adhesive film 16 can be purchased from E & H 
Laminating and Slitting Company, Paterson, N.J. designated as E&H 775-3FR3 
non-supported, standard bonding film and is incorporated herein by 
reference. The preferred embodiment pressure sensitive adhesive film 16 is 
at least 1.0 mils thick. 
Turning now to FIG. 3 there is shown a shaped patch 22 fastened to a 
damaged structure 12 by mechanical fasteners 24 that are capable of 
withstanding a temperature of at least 1,700 degrees fahrenheit. The patch 
22 shown in FIG. 3 has had the release liner 18 removed from the pressure 
sensitive film 16 and the patch 22 is carefully placed over the damaged 
area 11 on structure 12. Pressure is applied to patch 22 until an air 
tight seal is obtained between structure 12 and patch 22. The overlap of 
patch 22, or the distance from the edge of the damaged area 11 to the edge 
of patch 22 is at least 1 inch. Mechanical fasteners 24 are placed through 
drilled holes of appropriate diameter wherein the distance the mechanical 
fasteners 24 are placed from the edge of patch 22 may vary from 1/8 inch 
to 2 inches. This spacing will be determined by the size of the patch and 
the severity of the damaged section 11. The spacing between the mechanical 
fasteners 24 is at least 0.75 inches. In the preferred embodiment the 
mechanical fasteners 24 are of the blind type which have a low clamp up 
force and therefore provides a low preload force. The blind mechanical 
fasteners 24 having a self-restraining pin also have a large bearing area 
for the manufactured head and blind side upset. In the preferred 
embodiment, the blind mechanical fastener 24 is a blind fastener made of 
monel metal which is capable of withstanding a temperature of at least 
1,700 degrees fahrenheit. A monel metal blind mechanical fastener that can 
be used in the present invention may be purchased from Cherry Aerospace, 
Torrance, Calif. as Part No. CR8M83 which is incorporated herein by 
reference. 
Turning now to FIG. 4 there is seen a cross section of a patch 22 attached 
to structure 12 with the pressure sensitive adhesive film 16 therebetween. 
The hole and fastener spacing in between blind mechanical fasteners 24 in 
FIG. 4 is at least 0.75 inches. 
FIG. 5 shows a cross section of a patch 22 across the damage portion 11 of 
structure 12. The blind mechanical fasteners in FIGS. 4 and 5 are shown in 
upset condition. The heads and upset portion of the blind mechanical 
fasteners 24 are shown with a large bearing area which is required in the 
present invention for non-metallic structure 12 and patch 22. Also shown 
in FIG. 5 is the pressure sensitive adhesive film which provides an air 
tight seal between the structure 12 and the patch 22 when pressure is 
applied to patch 22. 
The application of patch 22 is simple and easy for a non-skilled worker to 
apply. The area of the structure 12 surrounding the damaged area 11 is 
thoroughly cleaned with a non-flamable degreasing solvent. The area of 
structure 12 around the damaged area 11 is then wiped clean and dry with a 
lint free cloth. The patch 22 including the pressure sensitive film 16 
attached to patch 22 and with the release liner 18 removed is then 
carefully placed over the damaged area 11 of structure 12 and pressure 
applied to the patch 22 until an air tight seal is obtained between the 
patch 22 and structure 12. Appropriate diameter holes are drilled with a 
drill bit (not shown) that shall not exceed 0.25 inches measured from the 
drill chuck end to the end of the drill bit. The diameter of the blind 
mechanical fasteners shall be at least 1/8 inch in diameter. Once the 
holes (not shown) with the proper spacing and with the proper distance 
from the patch edge are completed, the appropriate blind fasteners 24 are 
inserted in the holes and a blind mechanical fastener hand tool (not 
shown) is used to upset the blind mechanical fasteners 24 to provide a 
firm, air tight seal between the patch 22 and the structure 12. 
Thus, it is apparent that there has been provided in accordance with this 
invention an apparatus and method for effecting repair to damaged, 
non-stressed transport aircraft structure that fully satisfied the 
objectives, aims, and advantages set forth above. While the invention has 
been described in conjunction with specific embodiments thereof, it is 
evident that many alternatives, modifications, and variations will be 
apparent to those skilled in the art in light of the aforegoing 
description. Accordingly, it is intended to embrace all such alternatives, 
modifications, and variations that fall within the spirit and scope of the 
appended claims.