Method and apparatus for sealing an aircraft penetration

A penetration seal (12) is provided including a flexible patch (14) having adhesive (20) applied to one of the patch's first and second face surfaces (16), (18). An opening (22) is formed in the patch (14) of a size predetermined to fit a particular penetration (24). The opening (22) is slightly smaller than the cross-sectional shape of the penetration (24). In addition, a method of sealing the space (28) between an aircraft penetration (24) and surrounding insulation material (26) is provided. The method includes providing a seal (12) having a patch (14) with first and second face surfaces (16), (18), an opening (22) in the patch (14), and adhesive (20) applied to the first face surface (16). The method further includes applying the patch (14) to the penetration and insulation material by passing the penetration (24) through the opening (22) at the first face and pressing the first face surface (16) to the insulation material (26). In preferred embodiments, the method includes removing the seal (12) and the surrounding insulation material (26) as an assembly from the penetration and reapplying it at a later time.

FIELD OF THE INVENTION 
The present invention relates to methods and apparatus for sealing adjacent 
surfaces, and more particularly, to methods and apparatus for sealing 
aircraft penetrations that protrude from various blanketed aircraft 
structures. 
BACKGROUND OF THE INVENTION 
Current commercial aircraft fuselages are built by interconnecting a number 
of structural members, such as longitudinal stringers and circular frames 
(labeled 10 in the attached FIGURES). A metal skin is attached to the 
outside of the stringers to form the fuselage exterior surface. Various 
system components (e.g., electrical wires, heating ducts, etc.) are then 
attached to the inboard surfaces of the structural members using system 
supports. The system supports generally consist of brackets, fittings, 
standoffs, and the like. 
Insulation blankets are placed over the frames to insulate the fuselage 
interior from the low temperatures present at high altitudes. Often, the 
system supports have portions that must extend beyond the thickness of the 
insulation. To accommodate these portions, the insulation material is cut 
and fitted around the protruding portion. Because the system supports are 
said to "penetrate" the insulation layer, the supports are generally 
referred to as "penetrations". As used herein, the word "penetrations" is 
meant to indicate any component (system support or otherwise) that 
penetrates the insulation layer and thus requires an opening to be formed 
in the layer. Lastly, lightweight decorative panels are installed over the 
insulation and all protruding penetrations. The decorative panels form the 
interior walls of the cabin. 
During flight, moist cabin air tends to migrate behind the decorative 
panels, through the openings in the insulation at the penetrations, and 
outward to the inside of the inboard surface of the skin. At high 
altitudes, the ambient temperature is well below freezing and thus makes 
the skin very cold. Once the moist air reaches the skin, the moisture 
condenses and freezes onto the skin. 
When the aircraft reaches a lower altitude (and a commensurate higher skin 
temperature), this frost melts. The runoff accumulates on the outboard 
side of the insulation blankets. The intended location for this liquid 
runoff is to remain behind the insulation blankets where gravity will 
cause the liquid to migrate to exit drains that are located in the bottom 
of the fuselage. Due to the high number of provisions and the associated 
penetrations extending through the insulation blankets, however, the 
condensation run-off can sometimes find its way through to the cabin. The 
run-off may eventually drip onto passengers or cargo. (This dripping of 
liquid in the cabin is sometimes referred to as "rain in the plane".) The 
situation is exacerbated by the sheer number of penetrations in a typical 
aircraft, e.g., one thousand or more is not uncommon. This cycle of 
freezing and melting has occurred in aircraft for many years, going back 
at least to the start of pressurized, high-altitude aircraft flight. 
Some aircraft designs use foam patches that are custom-shaped to fit around 
each penetration in order to cover the space between the penetration and 
the insulation blanket. The foam patches rely on their stiffness and a 
unique installation technique in order to cover the space. Although the 
foam patches are helpful in reducing the size of each opening, they are 
not designed to form a water-tight seal. In addition, they are difficult 
and time consuming to install. 
Other aircraft use a paste or sealant material applied around each 
penetration joint opening. This method has the obvious drawbacks of being 
labor intensive and potentially heavy. In addition, it is important to be 
able to remove both the insulation material and seal during maintenance 
inspections. A sealant material cannot be removed and then reused, and as 
a result, fresh sealant must be applied. 
Yet other aircraft seal off the space between the penetration and the 
insulation material by applying blanket tape around each penetration. 
Blanket tape, however, is not elastic, so penetrations having odd shapes 
are difficult and labor intensive to seal with blanket tape. Also, a 
blanket tape seal cannot be reused. 
Therefore, a need exists for an improved method and apparatus for sealing 
the space between an aircraft penetration and surrounding insulation 
blanket material. The optimum seal should stop moist air from passing 
behind aircraft insulation and prevent fluid from passing back into the 
cabin. Further, the ideal seal should be lightweight, easy to install, 
durable, removable, flexible, able to accommodate odd shapes, and 
effective against transference of liquid and liquid vapor. 
SUMMARY OF THE INVENTION 
In accordance with the present invention, an aircraft penetration seal for 
sealing the open space between a penetration and surrounding insulation 
material is provided. The seal includes a patch having an opening through 
which the penetration may be inserted and an adhesive attached to one side 
of the patch. In preferred embodiments, the patch is formed from an 
elastic material, e.g., neoprene, silicone, elastomeric polyurethane, etc. 
The patch is preferably between about 0.005 inches to 0.100 inches thick. 
The adhesive is preferably formed from acrylic, silicone, or a synthetic 
rubber based water resistant pressure sensitive material. 
In accordance with other aspects of this invention, the patch opening is of 
a size slightly smaller than the cross-sectional area of the penetration. 
During use, the edges of the opening form a lip surrounding the exterior 
surface of the penetration. Preferred opening shapes include a circle, a 
rectangle with rounded corners, and a pair of slots with rounded ends. 
Where a particular penetration has a concave cross-section (e.g., an 
L-shaped cross-section), a filler material is provided and inserted into 
the concave surface portion. The opening in the patch contacts the filler 
at the location of the concavity so as to form a tight seal. Fillers are 
formed from various materials including nomex felt treated with an 
antifungal solution. 
In accordance with further aspects of this invention, a method of sealing a 
space between an aircraft penetration and surrounding insulation material 
is provided. The method includes providing a flexible patch having first 
and second face surfaces, an opening in the patch, and adhesive on the 
first face surface. The method further includes applying the patch to the 
penetration by passing the penetration through the opening at the first 
face and pressing the adhesive first face surface to the surrounding 
insulation material to seal the space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
In general, a penetration seal 12 formed in accordance with the present 
invention includes a flexible patch 14 having first and second face 
surfaces 16, 18. An adhesive 20 is attached to the first face surface 16. 
An opening 22 is formed in the patch 14 of a size predetermined to fit a 
particular aircraft penetration 24. In use, the penetration 24 is inserted 
through the opening 22 and the adhesive surface 16 is pressed to 
insulation material 26 surrounding the penetration 24. 
The penetration seal 12 of the present invention is particularly useful in 
sealing the space or joint 28 between the insulation material 26 and the 
penetration 24. The space 28 is the result of an opening 29 formed in the 
insulation material to accommodate the penetration. Example aircraft 
penetrations include electrical wiring, electrical ground blocks, tie rod 
fittings, etc. These penetrations penetrate the insulation material in a 
manner that forms a potential path for moisture and condensation. 
In more detail, the patch 14 is formed from a material that is elastic, 
i.e., it may be stretched and yet return to a shape similar to its 
original shape. Example materials include elastomers in general, as well 
as flexible memory metal alloys. Elastomers that may be used with the 
present invention include neoprene, silicone, elastomeric polyurethane, 
etc. Preferred patch materials include aliphatic elastomeric polyurethane. 
It is important that the material also be durable. During production, 
workers must be able to quickly apply the seal 12. If the patch material 
is not durable, then the worker may inadvertently tear or puncture the 
seal on the penetration 24 during seal installation. In addition, more 
durable materials will resist tears and cracks during aircraft loading and 
vibrations and also during aircraft maintenance inspections. Lastly, the 
patch material should be moisture-resistant, and preferably moisture 
proof, so that moisture does not pass through the patch. 
Correspondingly, the patch thickness will depend on the patch material 
being used. For example, if a less durable patch material is being used, 
then the patch 14 should be correspondingly thicker. For example, silicone 
rubber material would preferably be sized at about 0.020 inches thick. 
Likewise, if the material is highly durable, then less thickness will be 
required. For example, a seal using elastomeric polyurethane patch 
material would preferably be sized at about 0.014 inches thick. In 
general, the patch thickness is between about 0.005 to 0.100 inches. 
Referring to FIGS. 3, 6, and 9, the platform size and shape of the seal 12 
should be large enough that the opening 22 is relatively small by 
comparison. This provides a large sticking area to attach to the 
insulation material 26, making it unlikely that the seal 12 will split 
apart if subjected to large loads or vibrations and ensuring that all 
spaces between the insulation material 26 and the penetration 24 are 
sealed. The opening 22 is located roughly in the center of the seal 
planform. 
The adhesive 20 is composed of a pressure-sensitive material that is 
initially removable, but when allowed to cure, is strongly adhesive. 
Therefore, the cured adhesive 20 keeps the patch 14 attached to the 
insulation material 26 at all times. During maintenance inspections, the 
insulation material 26 and seal 12 are pulled away as a single unit in 
order to reveal the structure and the penetration. After the combination 
of seal 12 and insulation material 26 are removed, they should be capable 
of being re-installed onto the penetration and structure, preferably 
multiple times, before showing signs of wear or tearing. The adhesives may 
be provided with a disposable release liner (not shown) that can be 
conveniently pulled away prior to installation of the patch. 
The adhesives are preferably formed from flame retardant permanent acrylic. 
A preferred seal embodiment is formed from item number D-9215FR produced 
by the Patco Corp. at P.O. Box 1200, Bristol, R.I. 02809-0995. This is a 
transparent flame retardant aliphatic polyurethane material. Item number 
814 (adhesive backed clear aromatic polyurethane material) of the same 
producer has also yielded good results. 
Still referring to FIGS. 3, 6, and 9, the opening 22 is shaped similar to 
the shape being sealed, only slightly smaller in size. How much smaller is 
a function of the elasticity and durability of the materials being used. 
The ideal fit should allow the operator to install the seal 12 quickly and 
easily, and should form a slight outward lip 30 about the penetration 24 
as shown in FIG. 10. This lip 30 is important in ensuring a good seal 
about the penetration 24. Therefore, the patch material must be able to 
withstand being formed into a lip 30 without tearing or separating from 
the penetration 24. 
Referring to FIGS. 4-6, the size of opening 22 will also depend on the 
shape of the penetration 24. In general, the present invention seal 12 
works best with penetrations that do not have significantly larger 
cross-sections at their unattached ends when compared to the cross-section 
at the intended seal location. It is difficult to get the seal 12 around 
an enlarged end portion, which increases the likelihood of ripping the 
opening 22. The tie rod fitting of FIGS. 4 and 5 is an example of an 
acceptable size difference between the circular head of the fitting 
flanges and their smaller sized necks. 
The openings 22 may be any shape, though it is preferred to use only 
outwardly curved or straight shapes. Since the patch material will 
stretch, a single cutout size may be used to fit more than one 
cross-section size and shape of penetration, provided the proper tight 
seal is formed and provided the hole will stretch without degrading. 
Therefore, in FIG. 3, the opening is circular to fit a penetration having 
a circular cross-section. The same opening size may be used to fit a 
larger circular penetration cross-section so long as the opening does not 
tear or become overly stressed. In a similar manner, in FIG. 9, the 
opening is circular to fit a somewhat triangular combination of 
penetration and filler (described below). This attribute results in being 
able to produce only a few patch geometries to cover thousands of 
penetrations. 
In FIG. 6 the opening is actually two openings, each being elongated 
rectangles or slots with rounded ends. Alternatively, the opening may be a 
slit, though, tear stop holes are recommended to be formed at each slit 
end. The diameter of the tear stop holes should be as small as possible 
while still preventing tearing of the seal during installation and/or 
removal. 
As will be appreciated from viewing FIGS. 1-9, the cross-sectional shape of 
the penetrations at the location of the seal 12 preferably contains only 
convex shapes. By "convex" what is meant is that in drawing a line from 
any point about the exterior of the shape to any other point about the 
exterior of the shape, the line will fall entirely within the 
cross-sectional area of the penetration (including an exterior surface). 
By contrast, concave shapes are those shapes in which some portion of the 
line passes outside of the cross-sectional area. 
Referring to FIG. 7, there shown in perspective view is an L-shaped 
bracket. The cross-sectional shape of the L is a concave shape since a 
line from end-to-end would pass outside of the cross-sectional area of the 
L. To compensate for the corner, a small filler 32 is positioned in the 
corner at the location along the penetration where the seal 12 will be 
positioned. 
Selection as to the type of filler and the type of filler material will 
vary depending on the application. For example, the filler may be formed 
by bonding a substance directly to the penetration. Preferably, the filler 
is separable, though, to allow for easy repair. Example materials include 
Teflon, paper, fiber, plastic, felt, etc. A preferred filler material is 
lightweight nomex felt that has been treated with an antifungal solution. 
Such a felt is formed from thin paper that is rolled to form the 
appropriate filler thickness. A preferred filler material of this type is 
item number B3652-93F produced by Albany International Research at 777 
West Street, P.O. Box 9114, Mansfield, Mass. 02048-9114. This particular 
paper is 0.09 inches thick and is rolled into a filler of 1 inch diameter. 
In FIG. 8, the filler 32 is shown held in place using an encircling tie 34 
that is provided for installation purposes. Referring to FIG. 9, the 
resulting cross-sectional shape of the combined bracket and filler 32 is 
positive or convex. Referring to FIG. 8, the resulting configuration shows 
the seal 12 tightly sealing the bracket and the filler 32. 
In addition to the above sealing apparatus, a method of sealing the space 
28 between an aircraft penetration 24 and surrounding insulation material 
26 is provided. The purpose of sealing the space 28 is to prohibit 
moisture from passing through the space 28. The method includes providing 
a seal 12 having a patch 14 with first and second face surfaces 16, 18, an 
opening 22 in the patch 14, and adhesive 20 applied to the first face 
surface 16. The opening 22 is sized smaller than the cross-sectional area 
of the penetration 24 to be sealed. The method further includes applying 
the patch 14 to the penetration by passing the penetration 24 through the 
opening 22 from the first face side and pressing the first face 16 to the 
surrounding material 26. In preferred embodiments, the method further 
includes removing the seal 12 and the insulation material 26 as a single 
unit and reapplying them at a later time. 
As will be appreciated from reading the above, the benefits of the present 
invention are many. The seal 12 does not absorb moisture and hence will 
not become saturated. There are no messy chemicals or bonding putty to 
handle during the manufacturing assembly process. Pre-cut seal details are 
installed quickly. The elastic patch 14 fits tightly around penetration 
features and effectively blocks the path of moist cabin air from migrating 
behind the insulation material thereby reducing the amount of frost build 
up. The seal further prevents any condensate liquid runoff from entering 
back into the cabin area. Also, due to the fact that a single cutout size 
22 will stretch to fit more than one cross-section of penetration, only a 
few patch geometries are necessary to cover thousands of penetrations. 
While the preferred embodiment of the invention has been illustrated and 
described, it will be appreciated that various changes can be made therein 
without departing from the spirit and scope of the invention as defined by 
the appended claims.