Note: Descriptions are shown in the official language in which they were submitted.
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Determinant Wins Assembiv
This invention relates to a method and apparatus for inexpensively
manufacturing major airplane assemblies to dose tolerances, and more
particularly,
to a method and apparatus for assembling wing skins, spars, n'bs and other
oomponer~ with unpreoedant~ad predate to produos a wing having dose
conformance to the original engineering configuration, while significantly
reducing
tooling expense.
t3acicaround of the invention
Conventional manufacturing techniques for assembling cbmponents and
subassemblies to produce airplane wings to a apediied contour rely on fixtured
"hardpoiM" tooling techniques utilizing floor assembly jigs and terr~pietes to
locate and
2o temporarily fasten detailed struc~urai parts together to locate the parts
correctly
relstnro to one another. This traditional tooling concept usually requires
primary
assembly toots for each subassembly producx~d, and two lads wing major
assembly
tools (left and right) for flnai assembly of the subassemblies into a
completed wing. '
Assembly tooling is intended to acanetely retied the original er~ginearing
25 design of the product, but there are many steps between the original design
of the
product and the final marnrfact~ of the tool, so it is trot unu~,tai that the
tool as
finally manufactun3d produces mtssized wings or wing components that would be
outside of the dimensional tolerances of the original wing or w~ component
design
unless extensive, time consuming end costly hand work is applied to correct
the
30 tooling-induced errors. More seriously, a tool that was originally bulit
wlthln
toi~ancs can distort out of tolerance from the hard use it typically receives
in the
factory. Moreover, dimensional variations caused by temperature d~tanges in
the
factory can produce a variation in the final part dimensions as produced on
the tool,
particxrlarly when a large difference in the coefficient of themnat expansion
exists
35 between the tooling material ~d the wing material, as in the usual case
where the
fooling is made of steel and the wing components are made of aluminum or
titanium.
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Since dimensions in airplane construction are often controlled to within
0.005",
temperature induced dimensional variations can be significant.
Hand drilling of the part on the tool can produce holes that are not perfectly
round or normal to the part surface when the drill is presented to the part at
an angle
that is slightly nonperpendicular to the part, and also when the drill is
plunged into
the part with a motion that is not perfectly linear. Parts can shift out of
their intended
position when they are fastened in non-round hales, and the nonuniform hole-to-
fastener interterence in a non-round hole or a hole that is axially skewed
from the
hole in the mating part lacks the strength and fatigue durability of round
holes drilled
normal to the part surface. The tolerance buildup on the wing subassemblies
can
result in significant growth from the original design dimensions, particularly
when the
part is located on the tool at one end of the part, forcing all of the part
variation in
one direction instead of centering it over the true intended position.
Wing components are typically fastened together with high interference
fasteners
andlor fasteners in cold worked holes. interference fasteners, such as rivets
and lock
- bolts, and cold working of a fastener hole, both create a pattern of stress
in the metal
around the hole that improves the fatigue life of the assembled joint, but a
long line of
such stress patterns causes dimensional growth of the assembly, primarily in
the
longitudinal direction, and also can cause an elongated part to warp, or
"banana", along
its length. Attempts to restrain the assembly to prevent such distortion are
generally
fruitless, so the most successful technique to date has been to attempt to
predict the
extent of the distortion and account for it in the original design of the
parts, with the
intent that the assembly will distort to a shape that is approximately what is
called for in
the design. However, such predictions are only approximations because of the
naturally occurring variations in the installation of fasteners and the cold
working of
holes, so there is often a degree of unpredictability in the configuration of
the final
assembly. A process for nullifying the effects of the distortion in the
subassemblies
before they are fastened into the final assembly has long been sought and
would be of
significant value in wing manufacturing, as well as in the manufacture of
other parts of
3 0 the airplane.
Wing major tooling is expensive to build and maintain within tolerance, and
requires a long lead time to design and build. The enormous cost and Tong lead
time
to build wing major tooling is a profound deterrent to redesigning the wing of
an
existing model airplane, even when new developments in aerodynamics are made,
because the new design would necessitate rebuilding all the wing major tools
and
some or all of the wing component tooling.
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The capability of quickly designing and building custom wings for airline
customers having particular requirements not met by existing airplane models
would
give an airtrame manufacturer an enormous competitive advantage. Currently,
that
capability does not exist because the cost of the dedicated wing major tooling
and
the factory floor space that such tooling would require make the cost of
"designer
wings" prohibitively expensive. However, if the same tooling that is used to
make
the standard wing for a particular model could be quickly and easily converted
to
building a custom wing meeting the particular requirements of a customer, and
then
converted back to the standard model or another custom wing design, airplanes
'i 0 could be offered to customers with wings optimized specifically to meet
their specific
requirements. The only incremental cost of the new wing would be the
engineering
and possibly some modest machining of headers and other low cost tooling that
would be unique to that wing design
The disadvantages of manufacturing processes using hard tooling are inherent.
Although these disadvantages can be minimized by rigorous quality control
techniques, they will always be present to some extent in the manufacture of
large
mechanical structures using hard tooling. A determinant assembly process has
been
developed and is in production for airplane fuselage manufacture, replacing
hardpoint
tooling with self locating detail parts that determine the configuration of
the assembly
2o by their own dimensions and certain coordinating features incorporated into
the design
of the parts. This new process, shown in U. S. Patent No. 5,560,102 entitled
"Panel
and Fuselage Assembly" by Micale and Strand, has proven to produce far more
accurate assemblies with much less rework. Application of the determinant
assembly
process in airplane wing manufacture should yield a better process that
eliminates or
minimizes the use of hard tooling while increasing both the production
capacity of the
factory and increasing the quality of the product by reducing part variability
while
reducing the casts of production and providing flexibility in making fast
design changes
available to its customers. These improvements would be a great boon to an
airtrame
manufacturers and ifs customers and would improve the manufacturer's
competitive
position in the marketplace. The present invention is a significant step
toward such a
process.
Summary of the Invention
Accordingly, it is an object of this invention to provide a method of
manufacturing large and heavy assemblies, such as airplane wings, from
flexible
and semi-flexible parts and subassemblies in accordance with an original
engineering design, free from reliance on conventions! "hardpoint" tooling to
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determine the placement of the parts relative to one another and the contour
of the
assembly.
Another object of the invention is to provide a method of manufacturing
airplane
wings using intrinsic features of the component parts to allow them to self
locate and
determine assembly dimensions and contours rather than using the dimensions
and
contours of conventional tooling to determine assembly dimensions and
contours.
It is yet another object of this invention to provide a system for
manufacturing
airplane wings that is inherently more accurate than the prior art and
produces
structures in which the parts are consistently located more accurately on the
structure with closer conformance to the tolerance specified by the
engineering
design.
It is yet a further object of the invention to provide a system for
manufacturing
airplane wings that is faster and less expensive than the prior art
traditional
techniques and requires less factory space and is less dependent upon the
skill of
workers to produce parts within the engineering tolerances specified.
- Still a further object of this invention is to provide a method and
apparatus
which facilitates the manufacturing of subassemblies with a precision and
repeatability that enables airplane wings to be built within tolerance
specified in the
original engineering wing design.
Another still further object of the invention is to provide a method for
building
airplane wings having a sequence of operations arranged to apply critical
features to
the detail parts or subassemblies after the wing or wing component has been
distorted
by operations that distort the wing or component, such as interference
fasteners.
Yet another still further object of the invention is to provide a method of
assembling a major assembly from distorted parts or subassemblies by
accommodating
their distortion with a probing routine that creates partial digital
representation of the
distorted part or subassembly, and compares it to the space in which it is to
fit, then
produces a best-fit orientation for the distorted part or assembly to minimize
the effects
of the distortion.
3o It is yet another still further object of the invention to provide a
process for
manufacturing an airplane wing wherein only the key characteristics of the
components
and the wing are controlled, and they are controlled only for as Tong as they
are
important, and then they are allowed to vary after they are no longer
important.
These and other objects of the invention are attained in a system for
assembling
wings and other large, heavy assemblies from flexible and semi-flexible
subassemblies
using a method that utilizes spatial relationships between key features of
detail parts
or subassemblies as represented by coordination features such as holes and
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machined surtaces drilled or machined into the parts and subassemblies by
accurate
numerically controlled machine tools using digital data from original
engineering
product definition, thereby making the components and subassemblies themselves
intrinsically determinant of the dimensions and contour of the wing.
5
Description of the Drawings
The invention and its many attendant objects and advantages will become better
understood upon reading the following detailed description of the preferred
embodiment
in conjunction with the following drawings, wherein:
Fig. 1 is a top level schematic diagram of an assembly process for airplane
wings in accordance with this invention;
Figs. 2A-2F are schematic views of certain milestone steps in the process
according to this invention for assembling components and subassemblies info a
wing box in accordance with this invention;
Fig. 3 is a perspective view of a portion of a wing majors assembly cell in
accordance with this invention;
Fig. 4 is a perspective view one of the headers shown in the wing majors
assembly cell Fig. 3;
Fig. 5 is a schematic view of a computer architecture and process for
converting data from a digital product definition to instruction in a machine
toot
controller for pertorm certain assembly operations;
Fig. 6 is a sectional elevation showing a rib fastened between spars in an
airplane wing made in accordance with this invention;
Fig. 7 is an eniarged view of a junction between a stringer, a wing skin, a
rib
and a spar in a section of a wing made in accordance with this invention;
Fig. 8 is a sectional elevation of a side-of body connection between a wing
and
an airplane fuselage in accordance with this invention;
Fig. 8A is a perspective view of the inboard end of a wing made in accordance
with this invention showing the side-of body fitting;
Fig. 9 is a sectional elevation of a partially assembled wing box showing the
spars bridged by top and bottom wing panels with attached stringers, but
omitting
the ribs for clarity of illustration;
Fig. 10 is a perspective view of a completely assembled wing box according to
this invention, omitting the side-of body web to shown the interior of the
wing box;
Fig. 11 is an enlarged perspective view of the inboard end of the wing box
shown in Fig. 10;
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Fig. 12 is an elevation, partly in section, of an edge gauge/clamp for
positioning a spar relative to the edge of a wing panel and clamping it in
position;
Fig. 13 is an elevation of a temporary spar support used in the process of
this
invention;
Fig. 14 is an exploded view of a wing box made in accordance with this
invention, showing a shear tied rib fastened between two spars with the wing
panels
exploded away;
Fig. 15 is a perspective view of a wing box in phantom, showing the placement
of engine strut fittings to the wing box;
Figs. 16 and 17 are elevation and plan views of flap supports attached to the
rear spar and the lower wing panel;
Fig. 18 is a schematic elevation of a process for mounting aileron hinge ribs
to
the rear spar;
Fig. 19 is a schematic illustration of a spar-based wing assembly process in
~ 5 accordance with this invention with the wing waterline oriented in the
vertical
position during assembly; and
Fig. 20 is a sectional end elevation of an apparatus for assembling wings
using
a spar-based horizontal assembly process.
2o Descriation of the Preferred Embodiment
The invention is described as applied to a preferred embodiment, namely, a
process of assembling airplane wings. However, it is contemplated that this
invention
has general application to the assembly of parts into major assemblies where
adherence
to a specified set of dimensional tolerances is desired, particularly- where
some or all of
25 the parts and subassemblies are flexible or semi-flexible.
Referring now to the drawings, wherein Pike reference characters designate
identical or corresponding parts, and more particularly to Fig. 1 thereof, top
level
schematic diagram illustrates the major process steps in the determinant wing
assembly
process according to this invention. The process begins with building the
major
30 components of the wing, including upper and lower wing panels 30 and 32, a
rear spar
34 and a front spar 36, and in-spar ribs 38. The major components are brought
together on a computer numerically controlled machine tool 40 and assembled as
a
wing in the horizontal position, as illustrated in Fig. 2, on a series of
holding fixtures 42
mounted on a bed 44 of the machine tool 40. The lower wing panel 32 is
positioned on
35 the holding fixtures 40, and the spars 34 and 36 are positioned adjacent
trailing and
leading edges of the lower wing panel 32. The ribs 38 are positioned between
the
spars 34 and 36 and are fastened to the spars and to the lower wing panel 32,
and the
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spars 32 and 34 are also fastened to the lower wing panel 32. Three engine
strut
fittings 46 are fastened to the underside of the wing box with fasteners
extending
ttuough the lower wing skin and into internal load fittings 48 fastened to the
designated
ribs, and a bearing 50 for a landing gear link 52 is attached to the rear
spar. The wing
is dosed out by fastening the upper wing panel 30 to the front and rear spars
and to the
ribs 38. The process for pertonning these steps is described in detail below.
Conventional fasteners are contemplated for use in the preferred embodiment.
These conventional fasteners, such es rivets, bolts, lock bolts, Hi-Locks and
the like
are widely used in the aerospace industry, and are well understood and
reliable.
However, this invention is not restricted to the use of conventional fasteners
and is
fully compatible with the use of advanced fastening techniques such as co-
curing and
other bonding techniques for thermoset composite parts, induction welding of
thermoplastic parts, as described in United States Patent No. 5,486,684
entitled
"Multipass Induction Heating for Thermoplastic Welding" filed by Peterson et
al., and
i 5 friction welding of metallic parts as described in a PCT International
Publication No.
WO 93/10935, published June 10, 1993 when these processes become sufficiently
understood, reliable and proven for use in flight critical hardware.
The tooling, such as the holding fixtures 42, used in the process is primarily
for
supporting the components and parts for drilling and machining by the machine
toot
40, such as a Henri Line' gantry mounted 5-axis toot, or a Cincinnati Milacron
vertical
tower 5~-axis machine tool. Other machine tools of similar capabilities could
also be
used. The required capabilities are precision and repeatability in spindle
positioning,
which in this application is about 10.005", and operation under control of a
machine
controller that can be programmed to incorporate digital product definition
data
originating from an engineering authority for the wing and wing components, so
that
coordination features specified by the digital product definition can be
placed
accurately and repeatably by the machine tool 40. These two capabilities
enable the
machine tool 40 to apply coordination features, such as coordination holes and
machined coordination surfaces, to parts, components and assemblies at
precisely
3 0 accurate positions specified in the digital product definition. These
coordination
features are used to position parts and components relative to each other
where they
are pinned and fastened, thereby eliminating or drastically reducing the need
for
fixed hard tooling that previously was used to located the parts and
components
relative to each other. The coordination features thus determine the relative
position
of the parts and components that comprise the assembly, and thereby determine
the
sire and shape of the assembly, independently of any tooling.
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8
WING PANEL BUILD-UP
Wing panel build-up begins with erection of the haiding fixtures 42 on the
machine
tool bed 44. Ttte holding fuctures 42 can be any of a multitude of designs
that will
support several wing skin planks 54 which together make up the lower wing skin
56.
The planks 54 are supported in generally horizontal or lying down position,
with the
lower surface, or "outer mold line" conforming to the wing panel q~ofile speed
in the
engineering design. The preferred embodiment of a set of holding fixtures 42
is shown
in Fig. 3. Each holding fixture inGudes a sturdy base structure 58 supporting
a header
60 ~on which the wing planks 54 lie, with their outer surtaces in contact with
a contact
pad fit on the top of the header 60. The contact pad 62 is a strip of durable,
non-
abrasive material s~h as ultra high density polyethylene, polyurethane, or
Teflori which
will support the wing planks 54 without deflection under compression, but will
not scratch
the su<face coating on the wing skin planks 54. After the holding fuctures 42
are
mounted for the first time on the machine tool bed 44, the machine tool 40 is
used to
machine the contact pads 62 to the exact contour specified by the engineering
design,
using the data from the digital product definition.
The digital definition is the ultimate engineering authority for the product,
in
this case, a particular model airplane. ft exists on a master computer 64 in a
computer-
aided design program as a digital model 86 which includes all the dimensions,
tolerances, materials and processes that completely define the product. The
dimensional data from the model 66 is provided in a file to an NC programmer
who uses
it to create a dateset 68 and machine instnrctions, such as cutter type and
size, feed
speeds, and other information used by a controller of the machine tool 40 to
control the
operation of the tool. The dataset and machine instructions are launched in a
post
processor 70 where they are converted to a machine readable file 72 that is
transmitted
to a data management system 74 where it is stored for use by the machine tool
controllers ?8. On demand, the fife 72 is transmitted over phone lines 76 or
other known
means of communication to !he machine tool controller 78 for use by the
controller in
operating the machine tool 40.
3o The file 72 in the data management system 74 is used to program the machine
tool
controller 78 to direct the ms~chine tool 40 to drill coordination holes and
fastener holes
and other precision machining and positioning operations described below. The
machine tool 40 also drills holes into the headers 60 for three precision
drilled bushings
80 into which are set precision ground alignment pins 82 for positioning the
wing skin
planks 54 at a known position on the headers 64. The position is not critical
so the
accuracy of the wing is not dependent on the accuracy of the registry of the
wing skin
planks 54 on the headers 60 since the ptanks are probed for their actual
position on the
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headers fi0 using a contact probe 84 mounted on the machine tool 40. A vacuum
source 88 is energized to create a auction in a series of suction cups 88 on
the headers
60 to secure the wing skin planks 54 in position against the contact pads 62
on the
headers 60, and the contact probe 84 is moved by the machine tool 40 to probe
the key
coordination features on the wing skin planks 54. A suitable probe for this
purpose
would be a Renishaw contact probe Model No. RW486 made by the Renishaw Company
in Onendagua, New York, although other probes available from other sources
could also
be used.
After probing of the key coordination features on the wing skin planks 54 to
determine the actual position of the planks on the headers 80, the machine
control
program is updated or normalized to synchronize the data set from the digital
product
definition with the actual position of the wing skin planks 54 on the headers
60. The
machine program is now initiated to drill coordination holes in the inboard
end of the
wing skin planks 54 common to coordination holes drilled in the inboard end of
a
series of longitudinal wing stringers 90. The stringers 90 extend
longitudinally, or
span wise along the wing and serve to conned the several wing skin planks 54
into a
single wing panel 32, and also to stiffen the panel. They also serve as the
connecting stnx~ure between the in-spar ribs 38 and the wing skin 56, as
discussed
in more detail below. The stringers 90 are located spanwise on the planks 54
via the
2o coordination holes, and the floating ends of the stringers 90 are located
chordwise by
the machine tool 40 as it progresses down the plank, drilling and fastening as
it goes.
The machine tool 40 can use a simple pin to engage the side of the stringer to
position it chordwise, or can use a centering mechanism as shaw~n in United
States
Patent No. 5,299,894 or United States Patent No. 5,477,596 both by Peter
McCowin.
To ensure that the stringers 90 intersect the ribs 38 at position: within the
designated tolerance limits, so that the wing panel 30 may be fastened to the
ribs 38
without the use of shims and without stressing the wing panel, the stringers
90 must
be fastened to the wing skin planks 54 accurately and consistently. The
determinant assembly process is a capable process that enables the use of
3o statistical process control to detect a trend toward an out of tolerance
condition
before bad wing panels 32 are produced so that corrective action may be taken.
Accuracy of wing panel fabrication insures that the wing components will come
together as intended without prestressing the parts and without cosmetic
impertections, and that the assembled wing will function aerodynamically as
designed. Accurate placement of the stringers 90 on the wing panels 30 and 31
makes it possible to use smaller "pad-ups" or thicken areas on the chords 92
of the
ribs 38 and stringers where the stringers are bolted to the rib chords 92, as
shovim in
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Figs. 6 and 7, instead of the wide area pad-ups used conventionally to
accommodate the variation in stringer placement. Smaller pad-ups reduces the
weight of the rib chords and stringers and increases the load carrying
capacity of
the airplane.
5 Coordination holes are drilled in the stringers 90 at the inboard end.
Preferably, the coordination holes are drilled when the stringers are
initially
fabricated, but they may also be drilled afterward on a dedicated fudure or
even on
the same machine tool 40 on the same or similar holding fixtures 42 before the
wing
skirt planks 54 are laid in place. The specked locations of the stringer
fastener
10 hoiea, at which the stringers will be riveted to the wing skin planks, are
in the
machine tool control program, having been previously down-loaded from the data
base on which the digital product definition resides. The machine tool program
directs the drill head to the specified locations for these fastener holes,
typically at
one or more of the positions where rivets will be installed to secure the
stringers to
the wing skin planks to form the wing panels. The stringers can be drilled on
a
machine tool other than the machine tool 40, whereon the wing skin planks are
positioned and drilled, but doing so introduces a possible source of errs.
The stringers are fastened to the wing skin planks 54 to secure them together
in
a correctly assembled lower wing panel 32, but the final fastening of the
stringers 90
2 o to the wing skin planks 54 must be done before the assembly is a completed
wing
parwl. Numerous wing panel riveting machines are known which can pertorm the
c~illlng and riveting operations with the required accuracy and ~nsistency of
quality.
One such machine is illustrated in United States Patent No. 5,727,300 entitled
"Fastener Ver~cation System" filed on February 7, 1995 by Hanks et at. Another
such machine is the yoke wing riveter shown United States patent number
5,033,174.
In addition, it is contemplated that the riveting of the stringers could be
done on the
same header 60s using upper and lower gantry mounted drilUrivet units, such as
the
structure shown in United States Patent No. 5,231,747.
After all the rivets holding the stringers 90 to the wing skin planks 54 are
installed,
tt~ wing skin is repositioned on the holding fixtures 42 by use of
coordination holes 94 in
the wing panel 30 and the alignment pins 82 on the headers 60. Several
reference
surfaces on the wing panel 30, such as tool balls or reference pins 96
installed in
accurately drilled holes in the wing panel, are probed with the probe 84 in
the machine
tool 40 to determine the actual position of the wing panel 32 on the holding
fixtures 42,
and the machine program is normalized with the actual position of the wing
panel 32 on
the fuctures 42. A mill cutter is mounted in the machine too! 40 and the wing
pane! is
trimmed to the exact edge dimensions specified in the digital product
definition to ensure
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that the dimensions on the wing are as specified, despite growth in length and
width
because of the numerous rivets installed during the riveting of the stringers
90 to the wing
skin 32. This step is in accordance with one of the principles of the
invention, namely,
that the application of critical self tooling features in the parts and
assemblies are
postponed until after the part is distorted by upstream processes. That is,
edge
machining and other trimming operations could have been performed before
fastening
the stringers 90 to the wing skin planks 54, but doing so would have required
an
estimation of the anticipated growth that the assembly would undergo during
riveting.
These estimations can be quite accurate and have been made successfully for
many
years, but there is always a slight unpredictability factor because of the
variation in the
parameters of the process for installation of rivets, lack bolts, Hi-locks and
other
interference fasteners, such as exact hole diameter or hole roundness because
of drill bit
wear, slight variations in the countersink depth of the rivet hole because of
the machine
settings, and slight variations in rivet diameter. Even when these parameters
are all well
within tolerance, the variations in the rivet interference they produce in the
installed rivet
- can accumulate in a large part such as a wing panel to produce variation in
the assembly
dimensions that can be significant. The effects of these variations can be
eliminated by
scheduling the application of critical features on the parts and assemblies
after the
distortion by assembly and manufacturing processes such as installing
interterence
2o fasteners, heat treating, and shot peening.
As shown in Figs. 8 and 8A, a T-chord 100 is positioned on the inboard edge of
the
tower wing panel 32 by aligning coordination holes accurately drilled in an
outboard
flange 102 of the T-chord with corresponding coordination holes drilled in the
inboard
edge of the wing panel. Accurate placement of the T-chord is important
because, in part,
it determines the position of the wing on the airplane, and also because a
vertical flange
104 on the T-chord must align in a flat vertical plane with corresponding
flanges on other
wing structure, to be described below, for attachment of a side-of body web
106. The
web is sealed to the flanges and is the inboard structure of the wing fuel
tank, so the
flanges must align with a small tolerance for proper fitting of the side-of-
body web 106.
A paddle fitting 108 is positioned over the T-chord flange 102 by aligning
coordination holes predrilled in the paddle fitting with the aligned
coordination holes
through the T-chord flange and wing skin. The T-chord and paddle fitting are
clamped in
place using temporary fasteners through the coordination holes, and full sized
fastener
holes are drilled through the assembly. A series of vertical vanes 110 on the
paddle
fitting is positioned to lie flush against a flat face an each of the lower
wing stringers 90,
and is clamped thereto and back drilled with full sized fastener holes. The
paddle fitting
708 and T-chord 100 are disassembled and deburred, and the holes are
coldworked to_
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12
improved their fatigue life, since the T-chord and paddle fitting are part of
the connection
of the wing to the wing stub in the airplane fuselage, and the connection
experiences
high stress and fluctuating loads. The T-chord 100 is coated with sealant and
is attached
to the inboard edge of the lower wing pane! 32 with bolts 112.
The upper wing panel 30 is the last major subassembly to be added to the wing
box,
and is installed only after the lower wing box has been built. However, the
upper wing
panel 30 may be built in parallel with the lower, wing panel 32, or whenever
the
scheduling best coincides with the availability of manpower. The upper wing
panel 30 is
very' similar in its constnrdion and assembly processes to that of the lower
wing panel 32,
so it will not be separately described. One exception is the design of the
component,
called a "double-plus chord" 118, by which the wing is attached at its upper
wing panel
30 to the wing stub (not shown) in the airplane fuselage. The double-plus
chord 116,
also shown in Fig. 8, has upper and lower vertical flanges 118 and 120 which
are
fastened to the fuselage skin 122 and to the side-of-body web 106,
respectively, when
5 the wing is attached to the airplane. Two additional vertically spaced
sideways proj~ting
flanges 124 and 126 on each side of the double-plus chord 116 engage the wing
stub on
the inboard side and rooeive the inboard end of the upper wing panel 30 on the
outboard
side of the double-plus chord. Coorclination holes drilled through the upper
wing skin
and the stringers 90 at the inboard end align with corresponding coordination
holes
drilled in the sideways projecting flanges 126 to position the upper side of
the wingbox
properly when it is attached to the wing stub.
In-spar ribs 38 are fabricated and brought to the wing major assembly area for
assembly into the wing. Ribs 38 are of basically two types: machined ribs and
built-up
ribs. Machined ribs are machined out of a solid slab of aluminum and slave the
benefit
of greater dimensional accuracy. However, until the advent of high speed
machining
which makes possible the machining of thin walled stmctures without the
problem of
distortion due to localized heating from the cxrtter, it had been necessary to
make the
structure heavier than required by engineering analysis for anticipated loads,
to prevent
heat distortion of the thin walls. The greater weight and the greater cost of
the
machined components has delayed the acceptance of monolithic madlined ribs and
other components, but new procedures are being developed to solve the problems
that
will permit wider use of these components in airplane structures.
Built-up ribs 214, shown in Figs. 6 and 7, are made using the determinant
assembly processes of this invention by a process similar to that used to make
wing
spars, disclosed in our companioh application enticed °Determinant Spar
Assembly"
filed concurrently herewith issued as United States Patent No. 6,170,157.
A rib web 2i6 is cut from a sheet of aluminum using a machine tool such as
CA 02242868 2004-11-09
wo ~r3s~~ rc~rius~ro~sso
13
a gantry-mounted machine tool programmed to drive a cutter around the profile
of the
rib web 218. The rib web profile data is input to the machine tool drive
program from
the engineering authority responsible for the digifal product d~nition for the
wing and
the ribs. The position of upper and lower rib chords 218 and 220 on the rib
web 216
determine the height profile of the rib 214 and hence the chord-wise profile
of the
wing, so they must be acxurateiy positioned on the rib web 216. The rib d~ords
are
accurately positioned on the rib web 214 using an accurate positioning and
clamping
technique such as that shown in the aforesaid PCT Application entitled
"Determinant
Spar Assembly" issued as U.S. Patent No 6,170,157 . Fastener holes are drilled
through
1 o the clamped rib web 216 and rib chords 218 and 220 and intertererrce
fasteners are
inserted and severed. After the fasteners are secured and the rib is fully
distorted by
the interterenoe fasteners, the rib web 216 is end trimmed to the designated
length.
Coordination holes are drilled in the two ends of the rib 214 for fastening to
the rib
posts 204 on the wing spars. The locations of the rib post coordination holes
are
accurately set using a machine tool such as machine tool 40 having a
controller
programmed with the coordination hole locations from the digital rib
definition.
Phenolic washers 222 shown in Fig. 7 are bonded to the rib chords 218 and 220
at the positions of contact between the rib chords and the stringers 90. These
washers are made slightly thicker than needed and are machined to the correct
thickness by the machine tool ~ which the ribs are made, or another machine
tool of
suitable accuracy, to give the ribs 38 the correct height as designated in the
digital
parts definition of the ribs. The phenolic washers 222 form a bearing surtace
between
the ribs 38 and the stringers 90 to accommodate relative movement between the
ribs
38 and the wing panels 30 and 32 when the wing flexes during flight. The
washer in
this bonded applk~tion also serves as a pad of sacrificial material that can
be
trimmed to make the height of the ribs 38 exactly as specified in the digital
parts
definition of the rii~.
wng major assembly is pertonmed on the holding fixtures 42 after the stringers
90
are all fastened to the wing panel 30. The wing panel is placed, stringer side
up, on the
holding failures 42 and moved into position to align at least one coordination
hole in the
wing panel with a corresponding location hole in one of the headers 60.
Conveniently,
the wing panel 30 can be floated on an air cushion by connecting a source of
air
pressure to the lines in the headers 60 that normally supply vacuum to the
suction cups
88. When the wing panel 30 is positioned accurately on the headers 60, an
index pin is
inserted through the coordination Hole or holes in the wing panes and headers
60, and
the vacuum cups 88 are connected to the vacuum source 190 to pull the wing
panel 30
against the contact pads 62 on the headers 60 end hold it searrely in place.
r CA 02242868 1998-07-13
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14
The wing panel 32, when positioned and secured to the headers 60, is probed
with the touch sensitive probe 84 to locate the coordinating features such as
the tool
ball or features machined into the wing panel, such as coordination holes. The
predetermined locations of the features which are probed on the panel 30 were
recorded in the digital part definition, and the actual locations as probed
are
compared with the predetermined locations. The machine program is normalized
to
conform to the actual position of the panel on the headers 60 so that
subsequent
operations are pertormed accurately on the panel at its actual position.
A program in the controller of the machine tool 40 is initiated to drive a
machining cutter around the edges of the wing panel to net trim the panel 32
to
size. Pertorming this net trim operation after all the stringer fasteners have
been
installed, instead of beforehand, eliminates the size distorting effect of the
many
stringer fasteners, so the dimension of the wing panel 30 is precisely as
specified
in the product definition.
Attaching the Spars and Ribs
The machine tool controller 78 is programmed with the locations of
coordination
holes at the inboard ends of the front and rear spars 36 and 34, and holes in
the
stringers 90 of the lower wing panel 32 for rib-to-stringer bolts, and the
machine tool
drills these holes, after which the gantry is withdrawn. Sealant is applied to
the
bottom chord of one of the spars, and the spar is placed on the edge of the
wing
panel with the inboard coordination hole aligned with a coordination hole
drilled in
the wing panel. The other end of the spar is accurately positioned relative to
the
edge of the wing panel using one or more gauge/clamps 224, shown in Fig. 12,
that
are accurately machined for that purpose. A second coordination hole at the
outboard end of the wing panel could also have been used, but it is the edge
relationship between the spar and the wing panel that is important at this
point, not
the length of the spar. A principle of the invention is to control dimensions
that are
important, but only while they are important; the spar length is not important
at this
stage of the assembly, so only the edge relationship of the spar to the wing
panel is
controlled. A coordination hole, which would have to register lengthwise of
the spar
as well as chord-wise from the edge of the wing panel 30, has an unnecessary
required degree of precision, so the edge gauges are preferred over a
coordination
hole for the outer end of the spar.
The gauge/clamps 224 shown in Fig. 12 each include a body 226 having an
upturned flange 228 at one end and a shoulder 230 intermediate the body 226.
The
upturned flange 228 has an end facing surface 232 that is accurately ground to
CA 02242868 1998-07-13
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match the angle of the spar web 132, and the shoulder 230 is accurately ground
so
that the distance between the facing surFace 232 and the shoulder is exactly
the
same as the desired distance between the rear surface of the spar web 132 and
the
trailing edge of the wing panel 32 at the position set for that gauge/clamp
224. A
5 temporary fastener such as the cleco fastener 234 illustrated in Fig. 20
fastens the
gauge/clamp 224 to the lower edge of the spar 34 through a hole drilled
through the
upturned flange 228 and through the web 132 and lower chord 136 of the spar
34.
After the spar 34 is pinned to the inboard end of the lower wing panel 32 and
positioned in the approximate position relative to the edge of the wing panel,
the
10 gauge/c(amps 224 are attached to the lower edge of the spar 34 and the
shoulder
230 is snugged against the trailing edge of the lower wing panel 32. A screw
236 in
the end of a pivotally mounted arm 238 of a toggle clamp 240 is tightened
against the
underside of the wing panel 32 to secure the clamp to the wing panei~32 and
hold the
spar 34 down against the upper surface of the wing skin 56.
~ 5 Either the front spar 36 or rear spar 34 could be placed first on the wing
panel 32.
In this first embodiment, the rear spar 34 is placed first as a matter of
convenience, but
in a production operation wherein the front spar 36 is attached with the
leading edge
fittings already attached, it may be desirable to attach the front spar first
while
supporting the forward cantilevered weight of the leading edge fittings with
jib cranes.
The first-attached spar is secured in place by clamps and/or temporary
fasteners
such clew removable fasteners. tf the front spar with leading edge fittings is
attached
first, temporary spar supports such as the triangular structures 242 shown in
Fig. 13
are pinned to the rib posts 204 and clamped to stringers 90 on the Lower wing
panel 32
to react the overturning moment exerted by the weight of the leading edge
fittings, and
to hold the spar in position during rib placement.
Certain of the ribs 38 are placed on the stringers 90 and are pinned to the
rib
posts 204 through the coordination holes predrilled in the rib posts 204 and
the ends
of the ribs 38. These are the ribs that would be difficult to maneuver into
position
between the front and rear spars 34 and 32 after both front and rear spars are
attached to the wing pane! 32. Sealant is now applied to the bottom chord of
the other
spar and it is laid on the wing panel 32 adjacent the other edge, and the
coordination
hole in the inboard end of that spar is aligned and pinned to the
corresponding
coordination hole in the wing panel 32. The ends of the ribs 38 already in
place are
pinned to the rib posts 204 of the second spar, and that spar is clamped in
place at the
position determined by the length of the ribs 38. The other ribs 38 are all
placed
between the spars and are pinned in place to the spars on their respective rib
posts
204.
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16
The ribs are fastened to the rib posts by clamping the ribs to the rib posts
and
removing the coordination pins or temporary fasteners one by one, then
drilling and
reaming the alipr~d coordination holes to full size for insertion of the
permanent
fasteners. Atteniatively, the coordination holes could be drilled at nearly
full size so
they merely need be teemed in an operation that is quick and produces quality
holes for the fasteners. As the fastening of the ribs to the spar rib posts
proceeds,
the temporary spar supports 242 are removed..
The accurate placement of the spars on the edges of the wing panel, and the
accurate attachment of the ribs to the rib posts on the spars ensures that the
wing box,
formed of the spars, ribs and two wing panels, will be made accurately in
accordance
with the digital wing product definition. Variations in the dimensions of wing
boxes
made using prior art processes caused difficulties in mounting the control
surface
strudures such as leading edge slats and trailing edge flaps, and also caused
difficukies in attaching the wing to the airplane. These difficulties are
largely
eliminated with wing boxes made in accordance with this invention because of
the
smelt tolerances to which assembly dimensions can be held. The ability to
produce
wings to designated engineering tolerances enables for the first time the use
of
advanced tolerancing techniques in wing manufaduring, suds as that disclosed
in PCT
Application No. PCTIUS96J10757 by Atkinson, Miller and Scholz entitled
"Statistical
Toleranang" issued as U.S. Patent 5,956,251. Economies achieved in the factory
by reduction
or elimination of rework alone may justify the capital cost of the equipment
used to practice
this invention and scrapping the conventional wing majors assembly tooling.
Rib bolt fasteners 244 shown in fig. 7 are inserted in predrilled holes
through
the stringer p~-ups and phenolic washers 222 and the rib chord flanges. If the
bonded phenolic washers are used, as in the preferred embodiment, they have
already been machined to the con ed height. tf not, separate phenolic washers
can
be inserted befinreen the stringer pad-ups and the rib chord before the rib
bolts 244
are inserted. The holes predriUed in the rib chord flanges and the stringer
pad-ups
are slip fit hoses to allow limited slip betvveen the rib 38 and the stringer
90 on the
wing panes 30 when the wing flexes in flight, so the tolerances on these rib
bolt
fastener holes can be somewhat more relaxed than the tolerances on the
coordination holes which determine part positions in the assembly.
With the spars 36 and 34, and ribs 38 fastened together and aligned properly
on the lower wing panel 32, the spars are now temporarily fastened in place.
Clamps are applied, which preferably are part of the edge gauges 224 that set
the
position of the spars relative to the leading and trailing edges of the wing
panel 32,
as shown in Fig. 12. The Gamps generate suffiicient interfacial pressure
between
CA 02242868 1998-07-13
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17
the spar lower chord 136 and the wing panel 32 to prevent interlaminar burrs
firom
intruding in the spar/panel intertace. Such burrs would interfere with a
proper
junction between the spar and the wing panel 32 and be very difficult to
remove
because ofi the sealant in the intertace. Holes are drilled for temporary
fasteners
which are inserted to hold the spar in place during the permanent fasteners
installation. The temporary fastener holes are drilled undersized so that as
the full
sized fastener holes are drilled, any creep in dimensions due to distortion
from
insertion of interference fasteners will be removed. Other techniques for
holding the
spars in place while they are being fastened could also be used in place of
the
1 o temporary fasteners.
The spars are now fastened with permanent fasteners in place on the edges of
the wing panel 32. The machine tool 40 drills holes in bottom filange 144 ofi
the
tower the spar chord 136 from the lower surface or skin side. If the
particular
machine toot 40 being used is not able to drill from below, it is directed to
drill
accurate picot holes from above, which pilot holes are used to guide the
drilling and
_ countersinking ofi fastener holes from below by conventional power tools.
Fasteners
are inserted and tightened as the drilling proceeds, so any differential
length growth
between the spar and the wing pane( is washed-out as the fastening proceeds
along
the length of the spar. Fasteners are not inserted in the holes adjacent high
stress
areas such as the engine strut fittings, landing gear attachment fittings, and
the
side-of body rib because these holes are designated for cold working and it is
inadvisable to cold work holes in the presence of wet sealant. The holes to be
coldworked are left until later after the sealant has cured. Use of
interference
fasteners with a radiused lead-in minimizes the need for cold working the
holes.
After the sealant is cured, these holes in high stress areas are cold worked,
reamed
and countersunk and the fasteners are installed and tightened.
Next, the shear tied ribs 38' are fastened to the lower wing panel 32. As
shown in Fig. 14, the shear tied ribs 38' have projections 246 that extend
between
the stringers and terminate in flanges or contact pads 248 that engage and are
3o fastened to the underside ofi the wing skin 56. Pilot holes, predrilled in
the pads 248
during fabrication of the shear tied ribs, are used by the mechanic for back
drilling
through the wing skin 56. It is not necessary to back drill at every pad since
the
purpose is to fix the position of the shear tied ribs which are flexible and,
even
though fixed at their ends at the rib posts 204 in the spars, can be flexed
substantially in the spanwise direction until they are fixed in place to the
stringers 90
and/or the wing skin 56. Temporary fasteners are installed to hold the shear
tied rib
38' in place while the permanent countersunk fastener holes are drilled from
the
CA 02242868 2002-10-30
18
underside, that is, from the skin side up through the shear tie pad 248. The
permanent fastener holes can be drilled by a counterbalanced ground based
drilling
unit operated by a mechanic, or preferably are drilled by a machine tool that
probes
the location of the pilot holes drilled at selected shear tie pads to
normalize the
s digital data from the product definition data set with the actual position
of the shear
tie ribs as indicated by the pilot holes. The machine tool then drills and
countersinks
the permanent fastener holes. Prior to installation of the fasteners, the
mechanic
runs a "chip chaser", a thin blade-like toot, through the interface between
the shear
tie rib pads and the wing skin to remove any chips or burrs that may have
intruded
~o into that interface during the drilling. The fasteners are inserted from
the skin side
and secured by a mechanic on the inside who installs and tightens nuts or
collars on
the fasteners and tightens them with the appropriate power tool.
As shown in Fig. 15, three strut fittings 250 are positioned on the underside
of the
lower wing panel 32 at the engine strut position and are indexed by way of
coordination
15 holes predrilled in the strut fitting 250 to coordination holes drilled in
the wing panel
with the machine tool 40. Internal load fittings 252 are attached to the ribs
38 by way
of accurately drilled coordination holes predrilled during rib fabrication,
and the strut
fittings 250 are attached to the internal load fittings 252 by fasteners which
extend
through holes in wing skin 56 and aligned holes through the foot of the
internal load
ao fitting 252. The forward two strut fittings are fastened to the bottom spar
chord by
fasteners extending through holes drilled accurately by the machine tool 40
using
digital product definition data to inform the controller 78 of the machine
tool 40 as to
the locations of those fastener holes. It is important that the strut fittings
250 be
accurately placed on the wingbox since they support the fuse pins which carry
the
as engine strut on the wing, and the axis of the fuse pin bores 253 must be
properly
aligned to ensure a trouble-free connection of the engine to the wing. The
accurate
drilling of the coordination holes using data from the digital wing product
definition from
the ultimate engineering authority ensures that the engine strut fittings 250
will be
accurately positioned, thereby eliminating or minimizing any down stream
problems
3 o that would have been produced by mispositioned strut fittings. Temporary
fasteners
are inserted in some of the aligned coordination holes to hold the engine
strut fittings
and internal load fittings in position while permanent fastener holes are
drilled. The
drilling can be done by hand held power drills, but preferably is done with
the machine
tool 40. If the holes are to be cold worked, the strut fitting is removed,
deburred and
35 the fastener holes in the wing panel, the ribs, and the strut fitting 250
are coldworked
and reamed. Faying surface sealant is applied and the strut fitting is
returned to its
place and the fasteners are inserted and tightened by the mechanic.
CA 02242868 1998-07-13
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19
As shown in Figs. 16 and 17, flap reaction fittings 254 are attached to the
underside of the lower wing panel 32 by aligning coordination holes predrilked
in the
flap reaction fittings 254 and corresponding coordination holes in the wing
panel,
drilled from above by the machine tool 40. These coordination holes can be
full sized
fastener holes since they are not used as pilot holes for back drilling or as
temporary
fastener holes. The holes are cold worked and reamed, and the fasteners are
installed
and tightened to secure the fkap reaction fittings in place. Corresponding
flap support
fittings 256 are attached to the rear spar 34 during spar build-up by aligning
coordination holes 257 predrilled in the flap support fittings 256 and the
spar web 132
and fastening them together in the aligned position.
Wing close-out involves attachment of the upper wing panel 30 to the wing box
frame. Sealant is applied to the flanges of the upper spar chords 134, and the
upper
wing panel 30 is lifted by crane and lowered onto the assembled spars and ribs
of the
lower wing box assembly. The upper wing panel 30 is indexed to the inboard end
of
the spars by way of a coordination hole predrilied into the inboard end of the
wing
- panel 30 during panel build-up, and a corresponding coordination hole
drilled into the
inboard end of the spar, preferably in the terminal end fitting 206 during
spar build-up.
Another pair of coordination features on the upper wing panel 30 and the kower
wing
box assembly are positioned relative to each other to fix the position of the
upper wing
panel 30 uniquely on the lower wing box assembly. This other pair of
coordination
features could be coordination holes in the edge of the upper wing panel and
in the
upper spar chord 134 of the front or rear spar 36 or 34 or, preferably, a
coordination
surface on the front edge of the upper wing panel and the corresponding edge
of the
front spar, positioned relative to each other with an edge locator tool and
clamp like
the gauge/clamp 224 shown in Fig. 12.
The proper positioning of the upper wing panel 30 on the lower wing box
ensures that the vertical flange 120 of the double plus chord 116 on the
inboard
edge of the upper wing panel 30 aligns in a vertical plane with the vertical
flange
104 of the T-chord 100 on the inboard edge of the lower wing panel 32, and
also
with the inward flanges on the terminal end fittings 206 on the front and rear
spars
36 and 34. The alignment of these four flanges ensures that the side-of body
rib
web 106 wil( lie flat against all four flanges and will seal reliably and
permanently
thereto when it is attached.
The upper wing panel 30 is clamped in its properly indexed position using
edge clamps like the clamps 224 shown in Fig. 12 or the like. Rib bolts 244
are
inserted through predrilled holes in the upper rib chords and the stringers
90, as
shown in Fig. 7. Because the wing box is now closed by the upper wing panel
30,
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access to the interior of the wing box is through the access openings 258 in
the
lower wing panel 32. A small mechanic crawls into the wing box through the
access
opening 258 between each rib and inserts a rib bolt 244 into the aligned holes
in the
upper rib chords and the stringers 90, and tightens the bolts. The accurate
control
5 over the position of the stringers 90 when the wing panels are built up
makes it
possible for the rib bolt holes to be predrilled and line up with the rib bolt
holes in
the stringers 90 when the upper wing panel is properly positioned on the lower
wing
box, thereby eliminating the need for drilling the rib bolt holes from inside
the wing
box, and also making possible the use of much smaller rib and stringer pad-ups
10 where they are fastened together by the rib bolts. Predrilling the rib bolt
holes also
has the benefit of accurately locating the midportion of the rib, which is
somewhat
flexible, properly along the stringers 90 spanwise on the wing.
With the upper wing panel 3D now firmly fastened to the ribs 38 and clamped
to the spars 34 and 36, temporary pilot holes are drilled by the mechanic
using a
15 hand held power drill from the inside of the wing box up through shear tie
flanges
- 260 at the top of the rib posts 204 and through the wing skin. Reaction
force is
exerted by the machine tool 40 during the back drilling to prevent the upper
wing
panel 30 from being lifted off the upper spar chord 134 by the force exerted
on the
drill during drilling of the pilot holes. Temporary fasteners are installed in
the pilot
20 holes to hold the wing panel 30 firmly against the spar chord 134 white the
permanent fastener holes are being drilled so that no chips or burrs intrude
into the
interface between the spar chord and the upper wing panel. The exact control
of the
rib height and profile by controlling the position of the rib chords on the
rib webs
ensures that the height and contour of the ribs and the spar chords correspond
closely so that the stringers 90 of the wing panel lies on the rib chords and
the wing
skin lies smoothly over the spar chords without any discontinuity that would
require
shimming.
The machine tool 40 is directed to the spar-to-wing panel fastener locations
using data from the digital wing product definition which specifies the
locations and
sizes of the fasteners. The fastener holes should be exactly normal to the
surface of
the wing skin so that the countersink axis is also normal to the wing skin at
the
fastener location. A conical head fastener inserted in a fastener hole
properly
drilled normal to the surface of the wing skin at the fastener location will
lie in the
countersink with its head flush with the surface of the wing skin. Such a
fastener in
a non-normal fastener hole would have one edge of the fastener's conical head
protruding from the countersink, and the opposite edge recessed below the
surface.
There is almost nothing that can make a fastener improperly installed in this
way
CA 02242868 2004-11-09
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a1
acceptable. Shaving the head removes the protruding edge, but leaves that side
of
the head too narrow. The recessed edge of the head remains recessed and
shaving or sanding the wing scaface is not an acoe~ble fa. To ensure that the
fastener holes ere drilled rxxrnel to the wing surtace, a self-normalizing
drill head
may be used, as shown in U.S. Patent Application No. 08!785,821 filed on
January 8.
1997 by Gregory Clark entitled "Self Normalizing Drill Head" issued as U.S.
Patent 5,848,859.
The machine tool 40 drills and countersinks the faster holes and inserts the
fasfeners. A mechanic inside the wing box installs the nuts or collars end
tightens
the fasteners with a power tool ss the fasteners are inserted. The holes arse
drilled
1 o and countersunk in the wing skin, and the holes extend thro<rgh the top
flange on
the far chord. A pressure foot on the drill head exerts a press-up force to
assist
the clamps end the temporary fasteners in maintaining the pressure at the
interface
between the wing akin and the spar ids to prevent chips and burFS from
ir>tnrd'mg
into that interface. The press-up force also assists in squeezing out any
excess
sealant resulting in very little sealant on the chips, so they may be vacuumed
away
without fouttng the chip vsystwn with sealant. Tarr~porary fasteners may be
inatslied in the hole$ that requiro coldworWng until the sealant cures, after
which the
holes may be ooidworked and reamed, and the permanent fasteners installed.
The upper wing panel 30 is fastened to the shear tied ribs 38' as shown in
Fig.
ac 14 by drilling fastener holes from above the wing skin With the machine
tool 40,
using the digital product definition to inform the machine tool controller of
the
ioc~tion of the shear tie pads 248 Wider the upper wing skin. Because of the
flexibility of the rtes, it may be desirable for a medianic to bade drill
pilot holes
through predrilled pilot holes in selected shear tie pads 248 and install
index head
talc fasteners ~ fix the position of the intermediate portions of the shear
tie ribs 38'
flexing in the spanvwse d~e~ion. The machine toot 40 can the probe for
the index heads of the tads fasteners and normalize the machine tool program
with
the actual position of the shear tied ribs 38' based on the position of the
index
heads. The mechir~e toot 40 drills and countersinks full sized fastener holes
from
3o above the upper wing skin while a mechanic inside the wing boot urns a chip
chaser
befiveen the shear tie pads 248 and the inside surtace of the wing skin. The
machine tool 40 insane the fastener while the mechanic inside the wing box
places
the nuts or collars and ~ the boles with the appropriate ptool.
Aileron hinge ribs 1 ~ are attached to the rear spar 34 for supporting an
aileron hinge rod in bushings spaced to the rear of the rear spar. !t is
important for
the smooth and trouble free operation of the aileron that the bushings in the
ends of
the aileron hinge ribs be aligned accurately on a single axis parallel to the
rear spar.
CA 02242868 2002-10-30
22
Because of the length of the aileron hinge ribs 130, a small discrepancy in
its
placement is magnified to a large deviation from the intended position of the
hinge
bushing at the end of the hinge rib. It was found that, even when the aileron
hinge ribs
were attached with the best possible accuracy while the spar 34 was being
built up, the
s small distortion that was produced during final wing box assembly was
sufficient to
create unacceptable displacements of the ends of the hinge ribs so that they
were no
longer axially aligned. Therefore, in the practice of this invention, the
attachment of the
hinge ribs is scheduled for an assembly stage after the majority of the
distorting events
are finished.
io Another factor influencing the positional accuracy of the hinge bushing on
the
installed hinge rib 130 is the effect that minute variations of positioning of
the proximal
end, or attaching end, of the aileron hinge rib 130 have on the position of
the hinge
bushing. Even when coordination holes are drilled very accurately in the spar
web and
in the proximal end of the aileron hinge rib, very small local variations in
the flatness of
15 the facing surfaces, variations in the perpendicularly of the hinge rib to
its distal end
mounting plate, and other small such variations can have a significant effect
on the
position in space of the hinge bushing after the rib is attached to the rear
spar.
To avoid all these problems in accordance with this invention, the hinge
bushing
in the end of the hinge rib 130 is set at its critical position in space, and
the hinge rib is
2o attached to the spar where it contacts the spar web. This simply avoids the
difficulties
of trying to control all the factors that influence the position of the hinge
bushing in
space. The controller 78 of the machine tool 40 directs the machine tool 40 to
position
a mounting pin 262, held by the machine tool 40 as shown in Fig. 18, in space
at the
position to the rear of the rear spar specified by the digital product
definition as the
as location of the hinge bushing. The hinge bushing in the distal end of one
of the hinge
ribs is slipped onto the mounting pin 262, locating it accurately in spaced at
its position
specified by the digital product definition, and the proximal end of the hinge
rib is
attached to the spar web at the position determined by the position in space
of the
hinge bushing.
3o The side-of-body web 106 is positioned on the vertical flange 120 of the
double-
plus chord 116 and the vertical flange 104 of T-chord 100, and on the two
sideways
flanges on the spar terminal end fitting 207 using coordination holes
predrilled into the
side-of-body web 106 and the four flanges, as shown in Figs. 8 and 8A.
Temporary
fasteners are installed to hold the side-of-body web 106 in place while full
size fastener
35 holes are drilled through the web and the four flanges. The web 106 is
removed and
the holes deburred, and the faying surface of the web is coated
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with sealant. The coated web is replaced on the fiianges and fasteners are
inserted
through the holes. A mechanic inside the wingbox installs nuts or collars on
the
fasteners and tightens them with the appropriate power tool.
The determinant assembly process is not limited to assembly of the major
components in the horizontal or lying down position, illustrated in Fig. 3,
with the
waterline of the wing lying horizontally. Another assembly orientation is the
spar-
based vertical or "on-edge" orientation, with the waterline of the wing
oriented
vertically as shown in Fig. 19, using the rear spar as the base member on
which the
assembly is built. The rear spar is supported on a spar support structure 264
with
the spar web in the horizontal position. This embodiment uses the rear spar
34' as
the base sub-assembly to which the ribs and wing skins are attached. The spar
support structure 264 holds the rear spar accurately to its theoretical shape
while
the assembly process proceeds. Ribs 38 are located to the rear spar 34' by
aligning
coordination holes in the ribs that are common to the rib posts 204. Temporary
~ 5 supports are attached to stabilize the ribs 38 until they are attached to
the front spar
36'. A series ofi holding fixtures 266 is provided to hold the front spar 36'
at the
theoretical waterline position relative to the rear spar 34'. The holding
fixtures 266
permit adjustment of the firont spar 36' up and down since the distance
between the
rib coordination holes determines the chordwise distance between the firont
and rear
20 spars, just is it does fior the embodiment of Fig. 1. After all the
fasteners are
installed to secure the ribs to the spars, the temporary rib supports are
removed.
The upper wing panel is positioned against the inner wing structure and
accurately positioned in place by inserting alignment pins through a
coordination
hole in the inboard end of the wing panel. This coordination hole is common to
the
25 inboard end of the rear spar 34'. Outboard and intermediate secondary index
holes
in the rear spar provide additional location but are allowed to have some
misalignment in the span-wise direction, for example, by using dififerential
undersized holes or a slot in one part. Wing panel fixturing is designed to
support
the weight of the wing panel since the alignment pins through the coordination
holes
30 would not normally be designed to support a load of that magnitude. Since
the
panel fiixture is not the sole authority for wing panel location, it is
provided with
adjustment mechanisms such as independent jacks and the like to facilitate
alignment of the coordination holes in the wing panel and the spars.
After the wing panel is strapped or pulled against the ribs and front spar,
full-
35 sized fastener holes are match drilled in the wing skin, the spar and the
ribs. The
shape of the wing is determined by the shape and placement ofi the ribs. The
wing
skin is allowed to conform to the ribs by starting from the rear spar and
wrapping the
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wing skin around the ribs by progressively installing fasteners until the wing
skin
meets the front spar. No coordination holes common to the front spar and the
leading edge of the wing skin are needed, and the wing design allows a small
payoff
between the fixed leading edge and the wing skin.
After the fastener holes are drilled, the wing panel is separated from the
ribs
and spars and is beburred, cleaned, lay sealed and relocated against the ribs
and
spars. Fasteners are installed and tightened as described earlier. A
numerically
controlled track drill, machine tool or the like is used to drill holes in the
skin
common to the spar, thereby eliminating the use of drill templates now in
common
1 o use in conventional wing manufacturing facilities. The lower skin is
located and
indexed to the rear spar just as the upper skin was. Nacelle, landing gear,
flap
tracks and other major fittings are located using light weight tools that pin
to
localized key coordination holes in the skin.
A spar based horizontal assembly technique is illustrated in Fig. 20. This
technique allows access to both top and bottom sides of the wing and
potentially
could permit simultaneous operations on both sides for faster throughput and
higher
production rates.
The front and rear spars 34 and 36 are mounted on and supported by spar
supports 270 and 272 carried by fixed upright columns 275. The spar supports
270
and 272 slide laterally in guides or linear bearings in the columns 275 to
accommodate different sizes of wing for different model airplanes. The lateral
freedom of movement also allows the spars to self-adjust to the lateral
spacing
between spars determined by the coordination holes drilled in the ends of the
in-
spar ribs.
Two laterally spaced rails 277 are mounted on rigid longitudinal beams 279
supported atop the columns 275. An upper gantry 280 is mounted far
longitudinal
traversing movement on the rails 277 under control of the controller 78 by
traversing
motors 282. A laterally traversing plate 286 mounted on rails 288 fastened to
the
gantry 280 is driven by engagement of a bail nut 290 with a ball screw. The
bail
screw 292 is driven by a servomotor mounted behind the plate 286 under control
of
the controller 78. A vertical arm 295 mounted on linear bearings and driven by
a
drive motor has a wrist 297 that can tilt to a desired angle and can rotate
about the
vertical axis of the arm 295. The wrist has a gripper that accepts a
mechanical and
power connection for an end effector so the arm 295 can position an end
effector at
the desired locations for drilling, hole measuring and conditioning, and
fastener
insertion.
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A lower gantry 300 is mounted for longitudinal movement on rails 302 mounted
on a shoulder 304 adjacent the inside edges of the columns 275. The gantry 300
has an arm 308 which is mounted like the arm 295, except the operating end is
at
the top end instead of the bottom end as for the arm 295 of the gantry 280.
5 Otherwise, the gantries 280 and 300 are basically the same.
In operation, the spars 34 and 36 are loaded onto the spar supports 272 and
the ribs are indexed to the rib posts on the spar and fastened thereto by
temporary
fasteners through the coordination holes. The upper and lower gantries are
used to
drill the fastener holes, and the ribs are removed, deburred and sealant is
applied to
10 the faying surfaces common to the rib posts. The ribs are repositioned and
the end
effector on the gantries 280 and 300 inserts the fasteners which are secured
by
workers following behind the gantries.
After all the ribs are attached, the lower gantry 300 is moved to a parking
position at one end of its longitudinal travel beyond the wing position, and a
lower
~ 5 wing panel 32 is transported by crane to a gurney supported on the same
rails 302,
- and moved into position beneath the spars 34 and 36 and the in-spar ribs 38
on the
gurney. The lower wing panel 32 is elevated to the undersurtace of the spars
34
and 3E and the in-spar ribs 38 with a series of vertically telescoping
supports and is
indexed to the spars by alignment of predrilled coordination holes in the
panel 32
2o and the spars 34 and 36. The wing panel is temporarily secured in place
with straps
around each rib and the vertically telescoping supports are retracted,
clearing the
way for the lower gantry 300 to move in and begin drilling fastener holes for
attaching the wing panel 32 to the spars and ribs. The upper gantry arm 295
can be
positioned opposite to the arm 308 to provide a reaction clamping force to
prevent
25 the feed force on the drill in the end effector in the arm 308 from lifting
the rib or
spar chord flanges away from the wing panel 32 when the drill breaks through
the
wing panel, which could allow interlaninar burrs to intrude between the
surfaces. It
is thus possible to apply sealant when the wing panel 32 is first positioned
since
there is no need for the usual deburring step.
After the lower wing panel 32 is attached, the upper gantry 280 is moved to a
parking position beyond the wing position and upper wing panel 30 is
transported by
overhead crane directly to its intended position on the spars and ribs. The
upper
wing panel 30 is indexed to its correct position by aligned coordination holes
predrilled in the wing panel and drilled in the spars 34 and 36 by an end
effector
held by the gantry arm 295. Index pins in the aligned coordination holes lock
the
wing panel in the proper position, and the gantry arm 295 moves to the
positions
designated by the machine program 68 to drill fastener holes. Depending on the
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26
stiffness of the spar chord flanges and the rib chord flanges and the drilling
parameters, such as feed force, it may be necessary to deburr the fastener
holes by
lifting the wing panel 30 high enough to open access to the underside of the
wing
panel 30 and the top side of the spar and rib chords for the debarring
operation.
Sealant is applied and the panel is repositioned and the fasteners are
inserted and
secured as explained above.
End trimming of the spars and wing panels can be performed with roofer
cutters in end effectors held by the arms 295 and 308. Coordination holes for
the
other components mentioned above are drilled by the gantry end effectors for
'! 0 attachment after removal from the apparatus. The aileron hinge ribs can
be
attached using pins held at the correct point in space by the gantry end
effectors.
It is contemplated that two support fixtures shown in Fig. 20 could be
positioned end-to-end so that the gantry positioner/machine tools could be at
one
end working on assembling the wing while workers are at the other end removing
an
assembled wing and setting up the components for the next wing to be
assembled.
A system is thus disclosed which is usable for assembling airplane wing
subassemblies into a full airplane wing with a high degree of precision and
repeatability. The determinant assembly concept embodied in this disclosure
utilizes
the spatial relationships between key features of detail parts and
subassemblies, as
defined in the digital design and represented by coordination holes and other
coordination features put into the parts and subassemblies by a numerically
controlled
tool, using original part design data from the engineering authority, to
control the
relative location of detail parts in subassemblies and the relative
relationship of
subassemblies to each other, making the parts and subassemblies self locating.
This
concept eliminates the need for traditional hard tooling used for decades in
the airframe
industry and for the first time enables assembly of large, heavy, flexible and
semi-
flexible mechanical structures wherein the contour of the structure and the
relative
dimensions within the structure are determined by the parts themselves rather
than the
tooling.
Freed in this way from dependence on fixed tooling, the wing can now be built
to
accommodate distortion created by manufacturing processes, such as
interference
fasteners and cold working, so that attachment of critical features on the
wing at
precisely accurate positions specified by the engineering design can be
scheduled in
the manufacturing process after distortion by the upstream processes which
would
have affected their position or orientation on the wing. The factory can now
manufacture wings of any shape and size for which engineering data is
provided,
within the physical range of the CNC machine tools, and do so faster and with
far
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27
greater precision than was possible with fixed tooling. The cost of building
and
maintaining the conventional wing component and wing major tooling, and the
factory
floor space for such fixed tooling, no longer need be amortized and factored
into the
price of the airplane, and it is now possible to build wings customized to
meet the
particular requirements of particular customers.
Obviously, numerous modifications and variations of the system disclosed
herein will occur to those skilled in the art in view of this disclosure.
Therefore, it is
expressly to be understood that these modifications and variations, and the
equivalents thereof, will be considered to be within the spirit and scope of
the
invention as defined in the following claims, wherein we claim:
