Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
ELECTRICAL ISOLATOR FITTING
TECHNICAL FIELD
[0001] The application relates generally to electrically-isolating attachments
and, more
particularly, to an electrical isolator fitting for an aircraft wing.
BACKGROUND
[0002] Aircraft fuel tanks which are located on the wing have internal
metallic ribs which
define and extend through the fuel tank. Throughout the fuel tank structure
run multiple
systems including fuel, electric and hydraulic for conveying system
requirements to
various locations. Aircraft certification standards require that lightning
which may strike
the external surface of the wing and which may be transmitted to the metallic
rib be
isolated so that the electrical current of the lightning strike cannot create
an ignition
source to the fuel inside the fuel tank by arcing to nearby metallic structure
or systems.
It may also be necessary to provide an electrical bonding path for other
electrical
discharges, such as static and electrical currents generated by fuel sloshing
in the fuel
tank, fluids flowing through metallic piping, faults, or shorts in the
aircraft electrical
system..
SUMMARY
[0003] In one aspect, there is provided an aircraft wing, comprising: a fuel
tank defined
between ribs and a skin of the wing, at least one of the ribs being metallic
and defining
a first side and a second side, the at least one rib having an opening wall
delimiting an
opening in the at least one rib extending between the first and second sides;
and an
isolator fitting, comprising; a first isolator mounted to the at least one rib
and having a
first isolator opening; a second isolator mounted to the at least one rib and
having a nut
housing segment defining a second isolator opening; and a conduit extending
between
a first end and a second end, and a nut mounted about an outer surface of the
conduit
and abutted against the first isolator, the conduit extending through the
opening of the
at least one rib and through the first and second isolator openings, the nut
disposed
within the nut housing segment of the second isolator to position the nut
housing
1
CA 3054217 2019-09-03
segment between the nut and the opening wall of the at least one rib, a
tracking
distance being defined between the outer surface of the conduit and the
opening wall to
electrically insulate the conduit from the at least one rib.
[0004] In an embodiment of the aircraft wing, the second isolator abuts
against the first
side of the at least one rib, and the first isolator abuts against the second
isolator on the
first side of the at least one rib.
[0005] In an embodiment of the aircraft wing, a gap is defined between the
opening
wall of the at least one rib and the nut, the nut housing segment of the
second isolator
being disposed within the gap and spaced apart from both the opening wall and
the nut.
[0006] In an embodiment of the aircraft wing, a sealant is disposed in the gap
between
the nut housing segment and the nut.
[0007] In an embodiment of the aircraft wing, the second isolator includes a
flange
segment extending outwardly from the nut housing segment and mounted to the at
least one rib, the nut housing segment having an axial portion extending from
the flange
segment and being positioned in the opening between the nut and the opening
wall of
the at least one rib, the nut housing segment having a radial portion
extending from the
axial portion to a distal end having a second applicator opening wall
delimiting the
second applicator opening.
[0008] In an embodiment of the aircraft wing, the tracking distance is defined
along at
least a surface defined by the axial portion and the radial portion.
[0009] In an embodiment of the aircraft wing, the flange segment of the second
isolator
is disposed between the first isolator and the first side of the at least one
rib, the flange
segment abutting against a first side of the first isolator and the nut
abutting against the
first side of the first isolator.
[0010] In an embodiment of the aircraft wing, the conduit is metallic and has
a
permanent nut fixedly attached to the outer surface and a threaded segment
extending
along a length of the outer surface, the nut mounted to the threaded segment
and
2
CA 3054217 2019-09-03
spaced apart from the permanent nut to define an isolator gap, a portion of
the first
isolator being positioned in the isolator gap between the nut and the
permanent nut.
[0011] In an embodiment of the aircraft wing, the aircraft wing further
comprises a
plurality of fluid pipe segments, one of the fluid pipe segments being mounted
to the
outer surface of the first end of the conduit on the first side of the at
least one rib, and
another one of the fluid pipe segments being mounted to the outer surface of
the
second end of the conduit on the second side of the at least one rib.
[0012] In an embodiment of the aircraft wing, the first isolator and the
second isolator
are configured to dissipate electrical charge into the at least one rib.
[0013] In an embodiment of the aircraft wing, the at least one rib and the
first and
second isolators include aligned fastener openings spaced apart from the
opening of
the at least one rib, and the isolator fitting further comprises fasteners
extending
through the aligned fastener openings between the first and second sides of
the at least
one rib.
[0014] In an embodiment of the aircraft wing, the at least one rib is a baffle
rib, the
aircraft wing further comprising a fluid pipe extending between the ribs, the
fluid pipe
being mounted to the baffle rib with the isolator fitting, the fluid pipe
being mounted to at
least another one of ribs with a moveable isolating bracket.
[0015] In an embodiment of the aircraft wing, the first and second isolators
are made of
polyetheretherketone.
[0016] In an embodiment of the aircraft wing, the tracking distance is at
least 0.5
inches.
[0017] In another aspect, there is provided an isolator fitting positionable
about an
opening in a metallic rib of an aircraft wing, the isolator fitting
comprising: a first isolator
mountable to the rib to position a first isolator opening in alignment with
the opening of
the rib; a second isolator mountable to the rib and having a nut housing
segment
defining a second isolator opening to be positioned in alignment with the
opening of the
rib; and a conduit extending between a first end and a second end, and a nut
3
CA 3054217 2019-09-03
mountable about an outer surface of the conduit to abut against the first
isolator and
mount the conduit thereto, the conduit being positionable to extend through
the opening
of the rib and through the first and second isolator openings to position the
nut within
the nut housing segment of the second isolator such that the nut housing
segment is
positioned between the nut and the rib.
[0018] In an embodiment of the isolator fitting, the second isolator is
abuttable against
a first side of the rib, and the first isolator is abuttable against the
second isolator on the
first side of the rib.
[0019] In an embodiment of the isolator fitting, the second isolator includes
a flange
segment extending outwardly from the nut housing segment and mountable to the
rib,
the nut housing segment having an axial portion extending from the flange
segment and
being positionable between the nut and the opening of the rib, the nut housing
segment
having a radial portion extending from the axial portion to a distal end
having a second
applicator opening wall delimiting the second applicator opening.
[0020] In an embodiment of the isolator fitting, the flange segment of the
second
isolator is positionable between the first isolator and a first side of the
rib, the flange
segment being abuttable against a first side of the first isolator, and the
nut being
abuttable against the first side of the first isolator.
[0021] In an embodiment of the isolator fitting, the conduit is metallic and
has a
permanent nut fixedly attached to the outer surface and a threaded segment
extending
along a length of the outer surface, the nut being mountable to the threaded
segment to
be spaced apart from the permanent nut to define an isolator gap, a portion of
the first
isolator being positionable in the isolator gap between the nut and the
permanent nut.
[0022] In an embodiment of the isolator fitting, the first and second
isolators are
configured to dissipate electrical charge into the rib.
[0023] In an embodiment of the isolator fitting, the first and second
isolators include
aligned fastener openings spaced apart from the first and second isolator
openings, and
the isolator fitting further comprises at least one fastener being extendable
through the
aligned fastener openings.
4
,
CA 3054217 2019-09-03
[0024] In an embodiment of the isolator fitting, the first and second
isolators are made
of polyetheretherketone.
[0025] In a further aspect, there is provided a method of electrically
insulating and
supporting a fluid pipe from a metallic rib of an aircraft wing, the method
comprising:
mounting a first isolator about a conduit to extend the conduit through a
first isolator
opening of the first isolator; securing the first isolator to the conduit by
tightening a nut
about an outer surface of the conduit to abut the first isolator; mounting a
second
isolator about the conduit to at least partially enclose the nut such that the
nut is housed
within a segment of the second isolator, the segment defining a second
isolator
opening; securing the first and second isolators to the metallic rib to
support the conduit
therefrom such that the conduit extends through an opening in the metallic rib
and
through the first and second isolator openings; and mounting the fluid pipe to
the
conduit.
[0026] In an embodiment of the method, securing the first and second isolators
to the
metallic rib includes abutting the second isolator against a first side of the
rib, and
abutting the first isolator against the second isolator on the first side of
the rib.
[0027] In an embodiment of the method, securing the first and second isolators
to the
metallic rib includes forming a gap between the rib and the nut, the segment
of the
second isolator being disposed within the gap and spaced apart from both the
rib and
the nut.
[0028] In an embodiment of the method, the method further comprises filling
the gap
with a sealant.
[0029] In an embodiment of the method, mounting the fluid pipe includes
mounting a
first fluid pipe segment to a first end of the conduit, and mounting a second
fluid pipe
segment to a second end of the conduit opposite to the first end.
[0030] In an embodiment of the method, the method further comprises
transferring an
electrical charge from the first and second isolators to the rib.
CA 3054217 2019-09-03
[0031] In an embodiment of the method, the method further comprises arresting
sliding
movement of the conduit along a direction parallel to an axis of the opening
in the rib.
DESCRIPTION OF THE DRAWINGS
[0032] Reference is now made to the accompanying figures in which:
[0033] Fig. 1 is a schematic tridimensional view of an aircraft;
[0034] Fig. 2 is a top view of a wing of the aircraft shown in Fig. 1, showing
a fuel tank
and ribs;
[0035] Fig. 3 is a perspective view of one of the ribs shown in Fig. 2, the
rib having
isolator fittings;
[0036] Fig. 4A is a perspective, cross-sectional view of one of the isolator
fittings shown
in Fig. 3, taken along the line IVA-IVA;
[0037] Fig. 4B is an exploded view of the isolator fitting shown in Fig. 4A;
[0038] Fig. 4C is a cross-sectional view of a fastener of the isolator fitting
of Fig. 4A;
[0039] Fig. 4D is another cross-sectional view of the isolator fitting of Fig.
4A, shown
with a sealant;
[0040] Fig. 5A is a perspective view of a first isolator of the isolator
fitting of Fig. 4A;
[0041] Fig. 5B is another perspective view of the first isolator of Fig. 5A;
[0042] Fig. 6A is a perspective view of a second isolator of the isolator
fitting of Fig. 4A;
[0043] Fig. 6B is another perspective view of the second isolator of Fig. 6A;
[0044] Fig. 7 is a perspective view of a conduit of the isolator fitting of
Fig. 4A;
[0045] Fig. 8 is a top view of a wing of the aircraft shown in Fig. 1, showing
a fuel tank,
ribs, and fluid pipes;
6
CA 3054217 2019-09-03
[0046] Fig. 9A is a perspective, cross-sectional view of an isolator fitting
having a first
isolator according to another embodiment of the present disclosure; and
[0047] Fig. 9B is an exploded view of the isolator fitting shown in Fig. 9A.
DETAILED DESCRIPTION
[0048] Referring to the drawings and more particularly to Fig. 1, an aircraft
is shown at
1, and is generally described to illustrate some components for reference
purposes in
the present disclosure. The aircraft 1 has a fuselage 2 having a fore end and
an aft end,
with a cabin generally located between the cockpit and the tail assembly. A
tail
assembly comprises a vertical stabilizer 3 with a rudder, and horizontal
stabilizers 4
with elevators. The tail assembly has a fuselage-mounted tail, but other
configurations
may also be used for the aircraft 1, such as cruciform, T-tail, etc. Wings 5
project
laterally from the fuselage 2. The aircraft 1 has engines 6 mounted to the
wings 5 in the
depicted embodiment, although for other aircraft they can be supported by the
fuselage
2. The aircraft 1 is shown as a jet-engine aircraft, but may also be a
propeller aircraft. It
is also understood that the aircraft 1 can be a business aircraft, alternately
it can be any
other type of aircraft, including, but not limited to, a commercial aircraft
or a military
aircraft.
[0049] Fig. 2 shows part of one of the wings 5 of the aircraft 1. The wing 5
has an airfoil
body 5A whose acting surfaces are defined by a skin 5B of the wing 5 being
formed
about an internal frame 7 or structure of the wing 5. The airfoil body 5A
extends along a
longitudinal axis of the aircraft 1 between a leading edge 5C of the wing 5,
and a trailing
edge 5D of the wing 5. The airfoil body 5A extends along a spanwise axis of
the wing 5,
or along a lateral axis of the aircraft 1, between a root (not shown in Fig.
2) of the airfoil
body 5A and a tip 5E of the airfoil body 5A. A span of the wing 5 is defined
between the
root and the tip 5E. The internal frame 7 of the wing 5 includes any suitable
arrangement of spars, ribs, stringers, and other members. In Fig. 2, the
internal frame 7
includes a front spar 8A and a rear or aft spar 8B, which are interconnected
by multiple
transverse ribs 9. In the depicted embodiment, the skin 5B of the wing 5
includes
carbon fibre and has stringers. The front and aft spars 8A,8B are also made
from
composite, non-metallic materials such as carbon fibre, and the ribs 9 are
metallic.
7
CA 3054217 2019-09-03
Other constructions for the wing 5 are possible and within the scope of the
present
disclosure.
[0050] The wing 5 includes an internal and integral fuel tank 11. The fuel
tank 11 is a
void in the wing 5 that is defined and delimited by some of the ribs 9 and the
skin 5B of
the wing 5. In the depicted embodiment, the fuel tank 11 is delimited by upper
and
lower composite skins 5B, composite front and aft spars 8A,86 and metallic
ribs 9.
These components provide the boundary to form the integral fuel tank 11 as an
internal
structure of the wing 5. Fig. 2 shows that the fuel tank 11 is delimited by an
outboard rib
9A and an inboard rib 9B, and has a baffle rib 9C disposed between the
outboard and
inboard ribs 9A,9B. The fuel tank 11 may be delimited by other components of
the
internal frame 7. For example, the fuel tank 11 may be defined by fore/aft
boundary
walls provided by the front and rear spars 8A,8B. The baffle rib 90 may have
holes
extending through the baffle rib 9C to allow for the passage of fuel within
the fuel tank
11 through the baffle rib 9C. The baffle rib 9C may have additional holes to
allow for
systems penetration and support. The baffle rib 9C has a first side 12A facing
toward
the tip 5E of the wing 5, and a second side 12B facing toward the root of the
wing 5.
Other configurations for the fuel tank 11 are possible and within the scope of
the
present disclosure. The fuel tank 11 may extend between many different ribs 9,
and the
wing 5 may also have a dry bay and collector tank between some of the ribs 9.
The
wing 5 typically has lines or conduits running through it as part of fuel,
hydraulics and
electrical systems. The lines or conduits run through the wing 5 and are
structurally
supported by brackets attached to the ribs 9.
[0051] Fig. 3 shows part of the baffle rib 9C in greater detail. The baffle
rib 90 is
metallic. In the depicted embodiment, the baffle rib 90 is formed from
aluminum by
machining, although other metal materials or combinations of materials may
also be
used. The baffle rib 9C has holes 13 which permit the penetration of the lines
or
conduits of the various systems. The baffle rib 9C has other apertures
extending
through the baffle rib 9C from the first to second sides 12A,12B. The baffle
rib 9C has
inner openings 14 extending between the first and second sides 12A,12B. The
openings 14 are defined and delimited by an opening wall 14A. The opening wall
14A is
8
CA 3054217 2019-09-03
positioned in the body of the baffle rib 9C, between upper and lower
extremities of the
baffle rib 9C.
[0052] Isolator fittings 20 are provided in some of the openings 14 of the
baffle ribs 9C.
Metallic fluid pipes 15 are mounted to the isolator fittings 20 on the first
side 12A and
the second side 12B of the baffle rib 9C, in order to convey a fluid within
the fluid pipes
15 through the baffle rib 9C to some other part of the aircraft 1. As will be
better
appreciated from the description provided below, each isolator fitting 20 is a
component
or an assembly that secures the fluid pipes 15 to the baffle rib 9C while
electrically
isolating the fluid pipes 15 from lightning current extending through the
baffle rib 9C and
enabling electrostatic discharge from the fluid pipes 15 into the baffle rib
9C. Each
isolator fitting 20 helps to break up or interrupt the fluid pipes 15 into
metallic fluid pipe
segments 15A that are less long, and thus less likely to move during aircraft
flight, by
providing a fixed point of attachment to the baffle rib 9C. Each isolator
fitting 20 also
helps to provide electrical insulation to prevent electric charge from being
transferred to
fuel inside the fuel tank 11, and to the fluid inside the fluid pipes 15. Each
isolator fitting
20 also helps to provide a static discharge or dissipation of built-up
electrical charges to
the baffle rib 9C, and ultimately to the wing 5 and electrical ground of the
aircraft 1.
Although the openings 14 and the isolator fittings 20 are sometimes described
herein in
relation to the baffle rib 9C, the openings 14 may be present, and the
isolator fittings 20
may be used, on other ribs 9. Therefore, the term "rib 9" will be used herein
to generally
denote the structure in which the openings 14 are formed, and to which the
isolator
fittings 20 are attached.
[0053] Figs. 4A and 4B show one of the isolator fittings 20. The isolator
fitting 20
includes a first isolator 22 and a second isolator 24. The first isolator 22
is any suitable
gasket, bracket, or other mount which helps to attach the isolator fitting 20
to the rib 9,
and which helps to electrically insulate components of the isolator fitting 20
from the rib
9, as described in greater detail below. The first isolator 22 is mounted to
the rib 9 on its
first side 12A. In the depicted embodiment, the first isolator 22 is mounted
indirectly to
the rib 9, and the second isolator 24 is sandwiched between the first isolator
22 and the
first side 12A of the rib 9. In an alternate embodiment, the first isolator 22
is mounted
directly to one of the first and second sides 12A,12B of the rib 9. The first
isolator 22
9
CA 3054217 2019-09-03
has a first isolator opening 22A which is aligned with the opening 14 in the
rib 9. In the
depicted embodiment, the first isolator opening 22A is substantially coaxial
with the
opening 14. An axis of the first isolator opening 22A is substantially
collinear with an
axis 14B of the opening 14 in the rib 9. The first isolator 22 may assume any
suitable
shape or form to achieve such functionality. In the depicted embodiment, the
first
isolator 22 is triangular in shape, and the first isolator opening 22A is a
substantially
central opening. Alternative shapes for the first isolator 22 are also
possible.
[0054] The second isolator 24 is also any suitable gasket, bracket, or other
mount
which also helps to electrically insulate components of the isolator fitting
20 from the rib
9. The second isolator 24 is mounted to the rib 9 on its first side 12A. In
the depicted
embodiment, the second isolator 24 is mounted directly to the first side 12A
of the rib 9.
The second isolator 24 is therefore mounted to the same first side 12A of the
rib 9 as
the first isolator 22. In an alternate embodiment, the second isolator 24 is
mounted
directly to the second side 12B of the rib 9.
[0055] The second isolator 24 has a nut housing segment 25. The nut housing
segment 25 is a portion of the second isolator 24 which encloses and houses a
metallic
nut 28 when installed. As will be described in greater detail below, the nut
housing
segment 25 provides a barrier between the nut 28 and the opening wall 14A of
the rib 9
to help electrically insulate the nut 28 from an electrical discharge
emanating from the
rib 9. The nut housing segment 25 has a second isolator opening 24A which is
substantially aligned with the opening 14 in the rib 9, and with the first
isolator opening
22A. In the depicted embodiment, the second isolator opening 24A is
substantially
coaxial with the opening 14. An axis of the second isolator opening 24A is
substantially
collinear with the axis 14B of the opening 14 in the rib 9. The second
isolator 24 may
assume any suitable shape or form to achieve the functionality ascribed
thereto herein.
In the depicted embodiment, the second isolator 24 is triangular in shape, and
the
second isolator opening 24A is a substantially central opening. Alternative
shapes for
the second isolator 24 are also possible.
[0056] Still referring to Figs. 4A and 4B, the isolator fitting 20 also
includes a conduit
30. The conduit 30 is a hollow pipe or tube. The conduit 30 is a metallic
component in
CA 3054217 2019-09-03
the depicted embodiment, and is a hydraulic bulkhead connector. The conduit 30
is
made from a corrosion-resistant steel (GRES) or aluminum alloy. The conduit 30
made
from CRES may be anodized and passivated. The conduit 30 made from aluminum is
chemical film treated. The conduit 30 is non-metallic or composite in an
alternate
embodiment. The fluid pipe segments 15A are mounted to opposite first and
second
ends 32A,32B of the conduit 30. The conduit 30 is externally swaged to the
fluid pipe
segments 15A in the depicted embodiment. The conduit 30 helps to convey fluid
between the fluid pipe segments 15A. In the depicted embodiment, the first end
32A of
the conduit 30 is located on the first side 12A of the rib 9, and the second
end 32B of
the conduit 30 is located on the second side 12B of the rib 9. The conduit 30
has an
axis which is co-linear with the axis 14B of the opening 14 in the rib 9, and
with the axes
of the first and second isolator openings 22A,24A. The conduit 30 has an axis
which is
co-linear with the axes of the pipe segments 15A.
[0057] The conduit 30 is a separate component from the first and second
isolators
22,24. The conduit 30 is mounted to the first isolator 22 and is thus
supported from the
rib 9 because the first isolator 22 is itself mounted to the rib 9. Many
configurations for
mounting the conduit 30 to the first isolator 22 are possible and within the
scope of the
present disclosure. In Fig. 4A, for example, the conduit 30 has a permanent
nut 33
secured to an outer surface 34 of the conduit 30. The permanent nut 33 is
fixed in place
on the outer surface 34 of the conduit 30, and does not displace relative to
an axis of
the conduit 30. The permanent nut 33 protrudes radially outwardly (i.e. away
from the
axis 14B of the opening 14) from the outer surface 34. The conduit 30 also has
a
threaded segment 35 extending along a length of the outer surface 34. The
threaded
segment 35 is spaced apart in an axial direction from the permanent nut 33 to
define an
isolator gap 36. The isolator gap 36 is configured to receive a portion of the
first isolator
22.
[0058] To mount the conduit 30 to the first isolator 22, and thus to the rib
9, the conduit
30 is inserted through the first isolator opening 22A in order to position a
radially-inner
portion (i.e. closer to the axis 14B of the opening 14) of the first isolator
22 in the
isolator gap 36. The nut 28 is then tightened along the threaded segment 35 of
the
conduit 30 until it abuts against the radially-inner portion of the first
isolator 22. The nut
11
CA 3054217 2019-09-03
28 secures the radially-inner portion of the first isolator 22 in the isolator
gap 36, and
"jams" the radially-inner portion of the first isolator 22 against the
permanent nut 33,
thereby securing the conduit 30 to the first isolator 22. Once the nut 28 is
installed, the
second isolator 24 is then slid over the second end 32B of the conduit 30. The
first and
second isolators 22,24 are placed against the first side 12A of the rib 9 such
that the
second isolator 24 is sandwiched between the first isolator 22 and the first
side 12A of
the rib 9. Then, both the first and second isolators 22,24 are secured to the
rib 9 with
fasteners 39, thereby allowing the conduit 30 to be supported from the rib 9.
In the
depicted embodiment, and as shown in Fig. 4B, washers 37 are positioned
between the
permanent nut 33 and the radially-inner portion of the first isolator 22, and
between the
nut 28 and the radially-inner portion of the first isolator 22, to further
improve the
frictional engagement of the nut 28 with the radially-inner portion of the
first isolator 22.
On one of its sides, the first isolator 22 includes a washer rib 22B to
circumscribe the
washer 37 in the depicted embodiment.
[0059] The first isolator 22 is made from a first material, and the second
isolator 24 is
made from a second material. The first material and the second material
function to
impede or prevent the conductance of electricity from the rib 9 through the
first and
second isolators 22,24, to the conduit 30, and to the fluid pipe segments 15A.
The
electrical resistance of the first material and the second material is greater
than the
electrical resistance of the metallic conduit 30. The electrical resistance of
the first
material and of the second material is also greater than the electrical
resistance of the
rib 9 and of the fluid pipe segments 15A. The first and second materials are
configured
to electrically insulate the metallic conduit 30 from the rib 9 to prevent the
conductance
of electrical current thereto. The first and second materials are also
configured to slowly
discharge or dissipate an electrical charge to the rib 9, as described in
greater detail
below. The first and second materials therefore provide electrical insulation
for relatively
high voltage, high current lightning strikes, but are still electrically
conductive for
relatively low voltage, low current electrostatic charge build up. According
to a specific
embodiment, the first and second materials are the same. The first material
and the
second material have approximately the same electrical resistance value, where
the
electrical resistance value is typically measured in ohms (0). In an alternate
embodiment, the first material and the second material may be different and
have
12
CA 3054217 2019-09-03
different electrical resistance values. In such an alternate embodiment, the
electrical
resistance value of one of the first material and the second material is less
than the
electrical resistance value of the other material.
[0060] In the depicted embodiment, the first material and the second material
have the
same base material. The first material and the second material are both made
from
polyetheretherketone (PEEK). PEEK is normally not electrically-conductive, but
may be
made more conductive if desired. PEEK may therefore be used because it is non-
conductive, but still able to discharge electrostatic build-up. In some
embodiments, the
PEEK of the first and second materials may be made more conductive in order to
impart some conductivity to the first and second materials of the first
isolator 22 and the
second isolator 24, respectively. In such a situation, a conductive additive
may be
added to the non-conductive PEEK to provide enhanced electrical conductivity,
or to
control the electrical resistance from the conduit 30 to the rib 9 via the
first and second
isolators 22,24 so that the electrical resistance is within a permissible
range. Some non-
limitative examples of conductive additives for the PEEK include ground metal
particles,
carbon black, or other suitable conductive matter. The enhanced electrical
conductivity
of the first and second isolators 22,24 may allow an electrostatic charge to
be
dissipated through the first and second materials, into the rib 9, and onwards
to the
electrical ground of the aircraft 1. Another possibility for the first and
second materials
includes polyphenylene sulfide (PPS). In the depicted embodiment, the first
and second
materials have the same concentration of conductive additives, such that the
first
material and the second material have approximately the same electrical
resistance
value.
[0061] In an alternate embodiment, the first material and the second material
are made
from different base materials. In another alternate embodiment, the PEEK of
the first
material is made more conductive than the PEEK of the second material in order
to
impart more conductivity to the first material of the first isolator 22 than
to the second
material of the second isolator 24. In such an embodiment, the conductive
additive is
added to the non-conductive PEEK to provide enhanced electrical conductivity,
or to
control the electrical resistance from the conduit 30 to the rib 9 via the
first isolator 22
so that the electrical resistance is within a permissible range. In this
alternate
13
CA 3054217 2019-09-03
embodiment, the electrical resistance value of the first material is less than
the electrical
resistance value of the second material.
[0062] Referring to Fig. 4A, when mounted to the rib 9, the conduit 30 extends
through
the opening 14 of the rib 9, and also extends through the first and second
isolator
openings 22A,24A. After the nut 28 has been tightened against the radially-
inner portion
of the first isolator 22, the second isolator 24 is placed over the second end
32B of the
conduit 30 such that the nut 28 is disposed within the nut housing segment 25
of the
second isolator 24. The nut housing segment 25 in the depicted embodiment is
made
from the same second material as the rest of the second isolator 24. The nut
housing
segment 25 at least partially encloses the nut 28, and the nut housing segment
25 is
positioned between the nut 28 and the opening wall 14A of the rib 9. When
mounted to
the rib 9, the isolator fitting 20 helps to define a tracking distance D. The
tracking
distance D is the distance separating the rib 9 from an electrically-
conductive
component, such as the metallic nut 28 or the metallic conduit 30. The
tracking distance
D helps to electrically insulate the nut 28 and the conduit 30, and the fluid
pipe
segments 15A mounted thereto as well as their fluid contents, from electrical
discharges emanating from the rib 9, such as for example during a lightning
strike on
the wing 5. By spacing the metallic conduit 30 apart from the metallic rib 9
across the
tracking distance D, and by shielding the nut 28 with the electrically-
insulating second
material of the nut housing segment 25, the isolator fitting 20 helps to
decrease the
likelihood that an electrical spark or discharge will be conveyed from the
opening wall
14A of the metallic rib 9 to the metallic conduit 30. The isolator fitting 20
therefore helps
to provide electrical isolation of metallic fluid pipes 15 from the metallic
wing ribs 9,
thereby helping to improve lightning strike protection for the fuel tank 11.
[0063] Still referring to Fig. 4A, the tracking distance D is defined between
the outer
surface 34 of the conduit 30 and the opening wall 14A of the metallic rib 9.
The
presence of the electrically-insulating nut housing segment 25 contributes to
increasing
the tracking distance D by forming an electrically-insulating barrier between
the nut 28
and the opening wall 14A. If the nut housing segment 25 were not present to
shield the
nut 28, the tracking distance D would be smaller, and an electrical discharge
from the
14
CA 3054217 2019-09-03
rib 9 would have a much smaller distance to jump or arc across the opening 14
in the
rib 9 to impact the conduit 30.
[0064] Different configurations of the second isolator 24 and its nut housing
segment
25 are possible to achieve the electrical isolation effect described above.
One such
configuration is shown in Fig. 4A, where the second isolator 24 includes a
flange
segment 24B which extends radially outwardly from the nut housing segment 25.
The
flange segment 24B is mounted to the first side 12A of the rib 9, and is
sandwiched
between one side of the first isolator 22 and the rib 9. The nut 28 is also
abutted against
the same side of the first isolator 22 as the flange segment 24B. The nut
housing
segment 25 has an axial portion 25A which is substantially aligned with the
axis 14B of
the opening 14 in the rib 9, and with the axis of the second isolator opening
24A. The
axial portion 25A is positioned in the opening 14 of the rib 9. The axial
portion 25A is
transverse to the flange segment 24B. The axial portion 25A extends in a
direction
parallel to the axis 14B from the flange segment 24B, and is positioned
between the nut
28 and the opening wall 14A of the rib 9 to shield the nut 28 as described
above. The
nut housing segment 25 also has a radial portion 25B which has an orientation
being
substantially radial to the axis 14B of the opening 14, and to the axis of the
second
isolator opening 24A. The radial portion 25B is transverse to the axial
portion 25A, and
is parallel to the flange segment 24B. The radial portion 25B extends from the
axial
portion 25A along a radial direction toward the conduit 30 to a distal end 25C
of the nut
housing segment 25. The distal end 25C has a second applicator opening wall
24C
which delimits and defines the second applicator opening 24A. The radial
portion 25B of
the nut housing segment 25 helps to block migration of the nut 28 in a
direction parallel
to the axis 14B along the outer surface 34 of the conduit 30. The radial
portion 25B
helps to prevent rotation of the nut 28 about the outer surface 34 which might
cause
loosening of the nut 28 and affect the mounting of the conduit 30 to the first
isolator 22.
The axial portion 25A forms an electrically-insulating barrier between the nut
28 and the
opening wall 14A of the rib 9. It will therefore be appreciated that the
second isolator 22
is a PEEK fitting which helps to provide tracking protection between the fluid
pipe
segments 15A and the metallic rib 9, and also helps to provide secondary
locking
features to prevent the nut 28 from loosening.
CA 3054217 2019-09-03
[0065] Still referring to Fig. 4A, a gap 27 is defined between the opening
wall 14A of the
rib 9 and the nut 28. The gap 27 has an annular shape which has a radially-
inner
boundary defined by the surface of the nut 28, and a radially-outer boundary
defined by
the opening wall 14A. The nut housing segment 25, and in particular the axial
portion
25A thereof, is disposed within the gap 27. The axial portion 25A of the nut
housing
segment 25 is spaced apart from both the opening wall 14A and the nut 28. The
presence of the gap 27 helps to increase the tracking distance D between the
opening
wall 14A and the outer surface 34 of the conduit 30, and thus helps to further
electrically
insulate the metallic conduit 30 from the metallic rib 9. In the depicted
embodiment, the
tracking distance D is the combined length of the following segments: a first
segment
starting at the opening wall 14A to the radially-outer surface of the axial
portion 25A, a
second segment along the radially-outer surface of the axial portion 25A, a
third
segment along an outer surface of the radial portion 25B to the second
applicator
opening wall 24C, and a fourth segment from the second applicator opening wall
24C to
the outer surface 34 of the conduit 30. The tracking distance D includes the
gap 27. The
tracking distance D is greater than a thickness of the gap 27. In the depicted
embodiment, the tracking distance D is at least 0.5 inches.
[0066] Still referring to Figs. 4A and 4B, the first and second isolators
22,24 also help to
space the fasteners 39, which secure the first and second isolators 22,24 to
the rib 9,
from another metal component such as the nut 28, the conduit 30 or the rib 9
itself. In
the depicted embodiment, the first and second isolators 22,24 have a
triangular shape,
and the fasteners 39 extend through the first and second isolators 22,24 at
the corners
of the triangular first and second isolators 22,24. The fasteners 39 are
therefore spaced
apart an appropriate tracking distance D from the permanent nut 33, the nut
28, the
outer surface 34 of the conduit 30, and the metallic surface of the rib 9,
such that the
first and second isolators 22,24 contribute to providing an adequate tracking
distance D
between the fasteners 39 and another metal component.
[0067] Referring to Fig. 4C, each of the rib 9, the first isolator 22, and the
second
isolator 24 have aligned fastener openings 38. The fastener openings 38 are
through
passages in the rib 9 and the first and second isolators 22,24 that are
configured to
receive the fasteners 39 to mount the first and second isolators 22,24 to the
rib 9. Each
16
CA 3054217 2019-09-03
of the first and second isolators 22,24 has three fastener openings 38 in the
depicted
embodiment (see Figs. 4A and 4B), although more or fewer fastener openings 38
are
possible. The fastener openings 38 are separate and distinct from the opening
14, and
from the first and second isolator openings 22A,24A, and the fastener openings
38 are
spaced apart therefrom. Each fastener 39 extends through the aligned fastener
openings 38 between the first and second sides 12A,12B of the rib 9. Each
fastener 39
in Fig. 4C is a bolt with a metallic shaft 39A, a metallic head 39B, and a
metallic nut
39C. The metallic head 39B is abutted against one side of the first isolator
22 on the
first side 12A of the rib 9, and the metallic nut 39C is abutted against the
second side
12B of the rib 9.
[0068] In the depicted embodiment, the first and second isolators 22,24 are
configured
to dissipate electrical charge into the rib 9 through a conductive path
defined along the
fasteners 39. An ignition risk within aircraft fuel tanks 11 is electrostatic
discharge. As
fuel is pumped into the fuel tank 11, the surface of the fuel may become
charged, and
this charge could accumulate on the fluid pipes 15, either by direct contact
with the fuel
or by inducing voltage in the fluid pipes 15 across an air gap. The rib 9 is
configured to
provide multiple paths for this charge to dissipate. As explained above, a
conductive
additive is added to the non-conductive PEEK of the first and second materials
of the
first and second isolators 22,24 to provide enhanced electrical conductivity
to the first
and second isolators 22,24. The concentration of the conductive additive in
the first and
second materials is selected so that the path of least electrical resistance
between the
outer surface 34 of the conduit 30 and the rib 9 has a resistance below a
maximum
resistance value (to ensure that current can flow between the fluid pipes 15
and the rib
9 via the first and second isolators 22,24 and the fasteners 39 to dissipate
any
electrostatic charges) and above a minimum resistance value (to ensure that
the first
and second isolators 22,24 still provide sufficient electrical insulation
against a lighting
strike). The charge being dissipated through the first isolator 22, the second
isolator 24,
and the fasteners 39 slowly flows back into the rib 9 and into the ground path
of the
wing 5.
[0069] Fig. 4D is another cross-sectional view of the rib 9 and the isolator
fitting 20. A
sealant 40 is applied over some of the components of the isolator fitting 20.
The sealant
17
CA 3054217 2019-09-03
40 helps to plug gaps between the isolator fitting 20 and the rib 9 to make
the mounting
of the isolator fitting 20 impermeable to fuel within the fuel tank 11. For
example, the
sealant 40 is applied as a fillet seal between the rib 9 and the first and
second isolators
22,24, over the metallic head 39B of the fastener 39, between the washer rib
22B and
the permanent nut 33, and over the metallic nut 39C. The sealant 40 is also
disposed in
the gap 27 between the nut housing segment 25 and the nut 28, and in this
location
may help prevent or reduce rotational loosening of the nut 28. The sealant 40
is
disposed between the axial and radial portions 25A,25B of the nut housing
segment 25,
and the outer surface 34 and nut 28. The sealant 40 may be an aerospace grade,
fuel
tank sealant. In the depicted embodiment, the sealant 40 is electrically non-
conductive
and may contribute to preventing spark ignition. The sealant 40 also has
resistive
properties to the fuel in the fuel tank 11. Examples of a suitable sealant 40
include AC-
370 Aerospace Sealant commercialised by 3MTm, and PR-1776M Class B Low Weight
Fuel Tank Sealant commercialised by PPGTM. The sealant 40 may also help with
corrosion protection.
[0070] Fig. 5A shows the first isolator 22 from a first side 22C, and Fig. 5B
shows the
first isolator 22 from a second side 22D. In the depicted embodiment, the
first isolator
22 is triangular in shape, and the first isolator opening 22A is a central
opening. On the
first side 22C, the washer rib 22B is configured to circumscribe the washer
37. The
fastener openings 38 are through passages between the first and second sides
22C,22D of the first isolator 22.
[0071] Figs. 6A and 6B show the second isolator 24 from both sides. In the
depicted
embodiment, the second isolator 24 is triangular in shape, and the second
isolator
opening 24A is a central opening. The flange segment 24B extends radially
outwardly
from the axial portion 25A of the nut housing segment 25. The axial portion
25A
extends to the radial portion 25B. The radial portion 25B extends from the
axial portion
25A along a radial direction toward the distal end 25C and the second
applicator
opening wall 24C. The fastener openings 38 are through passages through the
second
isolator 24.
18
CA 3054217 2019-09-03
[0072] Fig. 7 shows the conduit 30 extending between its first and second ends
32A,32B. The permanent nut 33 is secured to the outer surface 34 of the
conduit 30.
The permanent nut 33 is fixed in place on the outer surface 34 of the conduit
30, and
does not displace relative to an axis 30A of the conduit 30. The threaded
segment 35 is
spaced apart in a direction along the axis 30A from the permanent nut 33 to
define the
isolator gap 36.
[0073] Referring to Fig. 8, an interior of the wing 5 is shown. The fuel tank
11 is defined
between multiple ribs 9, including the baffle rib 9C. The ribs 9 extend
between the
leading and trailing edges 5C,5D of the wing 5, and are mounted to the front
and aft
spars 8A,8B. The wing 5 includes a plurality of the fluid pipe segments 15A.
One of the
fluid pipe segments 15A is mounted to the first end 32A of the conduit 30 on
the first
side 12A of the baffle rib 9C (see Fig. 3). Another one of the fluid pipe
segments 15A is
mounted to the second end 32B of the conduit 30 on the second side 12B of the
baffle
rib 9C. The fluid pipe 15 is collectively defined by its fluid pipe segments
15A, and
extends between the ribs 9. At least two of the fluid pipe segments 15A are
mounted to
the baffle rib 9C with the isolator fitting 20 disclosed herein. For the
remainder of the
ribs 9, the fluid pipe segments 15A are mounted thereto with other types of
fittings, such
as a moveable isolating bracket 120 that do not fix the pipe segments 15A to
the rib 9
and instead permit the pipe segments 15A to move relative to the rib 9. The
wing 5 is
thus provided with an arrangement of fittings 20,120 for mounting the fluid
pipe
segments 15A to the ribs 9. In Fig. 8, the arrangement of fittings 20,120
includes a fixed
metallic bracket 120 at the rib 9D, three movable isolating brackets 120 at
each of the
ribs 9E,9F,9G, and the fixed isolator fitting 20 at the baffle rib 9C. This
configuration of
the fittings 20,120 results in the elimination of a path for electrical
current along the fluid
pipe 15 between at least three ribs 9, because one of the ribs 9 (e.g. the
baffle rib 9C in
the depicted embodiment) is electrically isolated. Other arrangements of the
fittings
20,120 are possible and within the scope of the present disclosure.
[0074] Figs. 9A and 9B show another embodiment of the first isolator 122. The
first
isolator 122 does not include a washer rib 22B. The first isolator 122
includes a washer
recess 122B which extends inwardly from the first side 122C of the first
isolator 122.
19
CA 3054217 2019-09-03
The washer recess 122B is configured to receive therein one of the washers 37
and to
circumscribe the washer 37.
[0075] Referring to Fig. 4A, there is also disclosed a method of electrically
insulating
and supporting the fluid pipe 15 from the metallic rib 9. The method includes:
mounting
the first isolator 22 about the conduit 30 to extend the conduit 30 through
the first
isolator opening 22A. The method also includes securing the first isolator 22
to the
conduit 30 by tightening the nut 28 about the outer surface 34 of the conduit
30 to abut
against the first isolator 22. The method also includes mounting the second
isolator 24
about the conduit 30 to at least partially enclose the nut 28 such that the
nut 28 is
housed within a segment, such as the nut housing segment 25, of the second
isolator
24. The method also includes securing the first and second isolators 22,24 to
the
metallic rib 9 to support the conduit 30, such that the conduit 30 extends
through the
opening 14 in the metallic rib 9 and through the first and second isolator
openings
22A,24A. The method also includes mounting the fluid pipe 15 to the conduit
30. The
method may include arresting sliding movement of the conduit 30 along a
direction
parallel to the axis 14B of the opening 14. This may be achieved from the
mounting of
the conduit 30 to the first isolator 22, which reduces or prevents a sliding
axial relative
movement between the conduit 30 and the rib 9. A rotational movement of the
conduit
30 about the axis 14B of the opening 14 is also prevented by engagement of the
nut 28
with the radial portion 25B of the nut housing segment 25.
[0076] In light of the preceding, it will be appreciated that the components
of the
isolator fitting 20 are relatively inexpensive, relatively easy to source, and
relatively
easy to assembly to mount the isolator fitting 20 to the rib 9. The size of
some of the
components of the isolator fitting 20, such as the first and second isolator
openings
22A,24A, may be modified to cater to different diameters of fluid pipe
segments 15A.
[0077] The above description is meant to be exemplary only, and one skilled in
the art
will recognize that changes may be made to the embodiments described without
departing from the scope of the invention disclosed. For example, although the
isolator
fitting 20 is disclosed herein being mounted to the rib 9 of an aircraft wing
5, it will be
appreciated that the isolator fitting 20 may be mounted to other components
and
CA 3054217 2019-09-03
structures to support and electrically insulate fluid tubing. Therefore, the
present
disclosure does not limit the isolator fitting 20 to being used only with ribs
9 of an
aircraft wing 5. Still other modifications which fall within the scope of the
present
invention will be apparent to those skilled in the art, in light of a review
of this
disclosure, and such modifications are intended to fall within the appended
claims.
21
CA 3054217 2019-09-03
