Note: Descriptions are shown in the official language in which they were submitted.
CA 02554189 1997-03-21
Determinant Wind Assembly
Technical Field
This invention relates to a method and apparatus for inexpensively
manufacturing
to major airplane assemblies to close tolerances, and more particularly, to a
method and
apparatus for assembling wing skins, spars, ribs and other components with
unprecedented precision to produce a wing having close conformance to the
original
engineering configuration, while significantly reducing tooling expense.
~5 Background of the Invention
Conventional manufacturing techniques for assembling components and
subassemblies to produce airplane wings to a specified contour rely on
fixtured
"hardpoint" tooling techniques utilizing floor assembly jigs and templates to
locate and
temporarily fasten detailed structural parts together to locate the parts
correctly relative
zo to one another. This traditional tooling concept usually requires primary
assembly tools
for each subassembly produced, and two large wing major assembly tools (left
and right)
for final assembly of the subassemblies into a completed wing.
Assembly tooling is intended to accurately reflect the original engineering
design
of the product, but there are many steps between the original design of the
product and
z5 the final manufacture of the tool, so it is not unusual that the tool as
finally
manufactured produces missized wings or wing components that would be outside
of
the dimensional tolerances of the original wing or wing component design
unless
extensive, time consuming and costly hand work is applied to correct the
tooling-
induced errors. More seriously, a tool that was originally built within
tolerance can
3o distort out of tolerance from the hard use it typically receives in the
factory. Moreover,
dimensional variations caused by temperature changes in the factory can
produce a
variation in the final part dimensions as produced on the tool, particularly
when a large
difference in the coefficient of thermal expansion exists between the tooling
material
and the wing material, as in the usual case where the tooling is made of steel
and the
35 wing components are made of aluminum or titanium. Since dimensions in
airplane
construction are often controlled to within 0.005", temperature induced
dimensional
variations can be significant.
CA 02554189 1997-03-21
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 holes, and the nonuniform hole-to-fastener
interference 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
so 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
and/or 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
i5 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
2o 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
a5 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 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 long lead time to
build
3 o 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.
The capability of quickly designing and building custom wings for airline
35 customers having particular requirements not met by existing airplane
models would
give an airframe manufacturer an enormous competitive advantage. Currently,
that
capability does not exist because the cost of the dedicated wing major tooling
and the
CA 02554189 1997-03-21
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
s the standard model or another custom wing design, airplanes 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 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
ao 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 costs
of production
and providing flexibility in making fast design changes available to its
customers. These
improvements would be a great boon to an airframe manufacturers and its
customers and
as 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
30 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 conventional "hardpoint" tooling to 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
35 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.
CA 02554189 1997-03-21
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
to 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
15 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
a o 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.
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 long as they
are important,
a s 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
machined
3 o surfaces 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.
CA 02554189 1997-03-21
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 into 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
15 data from a digital product definition to instruction in a machine tool
controller for
perform 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 enlarged view of a junction between a stringer, a wing skin, a
rib and a
z o 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;
z5 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;
s o Fig. 11 is an enlarged perspective view of the inboard end of the wing box
shown
in Fig. 10;
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
3 s invention;
CA 02554189 1997-03-21
6
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
s 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;
to Fig. 19 is a schematic illustration of a spar-based wing assembly process
in
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.
Description 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
2o set of dimensional tolerances is desired, particularly- where some or all
of the parts and
subassemblies are flexible or semi-flexible.
Referring now to the drawings, wherein like 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
as this invention. The process begins with building the major 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
3o tool 40. The lower wing panel 32 is positioned on 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 spars 32 and 34 are also fastened to the
lower wing
panel 32. Three engine strut fittings 250 are fastened to the underside of the
wing box
35 with fasteners extending through the lower wing skin and into internal load
fittings 48
fastened to the designated ribs, and a bearing 208 for a landing gear link 212
is attached
to the rear spar, along with a forward trunnion fitting 210, as shown in Fig.
10. The wing is
CA 02554189 1997-03-21
closed out by fastening the upper wing panel 30 to the front and rear spars
and to the ribs
38. The process for performing these steps is described in detail below.
Conventional fasteners are contemplated for use in the preferred embodiment.
These conventional fasteners, such as rivets, bolts, lock bolts, Hi-Locks and
the like are
s 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 Patent No. 5,486,684 entitled "Multipass Induction Heating for
Thermoplastic Welding" filed by Peterson et al., and 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
tool 40,
such as a Henri Line' gantry mounted 5-axis tool, 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 ~0.005", and operation under control of a machine
controller
ao 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,
25 to parts, components and assemblies at precisely 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
3 o features thus determine the relative position of the parts and components
that comprise
the assembly, and thereby determine the size and shape of the assembly,
independently of any tooling.
WING PANEL BUILD-UP
35 Wing panel build-up begins with erection of the holding fixtures 42 on the
machine
tool bed 44. The holding fixtures 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
CA 02554189 1997-03-21
are supported in generally horizontal or lying down position, with the lower
surface, or
"outer mold line" conforming to the wing panel profile specified in the
engineering design.
The preferred embodiment of a set of holding fixtures 42 is shown in Fig. 3.
Each holding
fixture includes a sturdy base structure 58 supporting a header 60 on which
the wing planks
54 lie, with their outer surfaces in contact with a contact pad 62 on the top
of the header 60.
The contact pad 62 is a strip of durable, non-abrasive material such as ultra
high density
polyethylene, polyurethane, or TefIonT"" which will support the wing planks 54
without
deflection under compression, but will not scratch the surface coating on the
wing skin
planks 54. After the holding fixtures 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 product definition is the ultimate engineering authority for the
product, in
this case, a particular model airplane. It exists on a master computer 64 in a
computer-
aided design program as a digital model 66 which includes all the dimensions,
tolerances,
~5 materials and processes that completely define the product. The dimensional
data from the
model 66 is provided in a file to an NC programmerT"" who uses it to create a
dataset 68
and machine instructions, 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
2o 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 78. On demand, the file 72 is
transmitted
over phone lines 76 or other known means of communication to the machine tool
controller
78 for use by the controller in operating the machine tool 40.
The file 72 in the data management system 74 is used to program the machine
tool
as controller 78 to direct the machine 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 60. The position is not critical so the accuracy of
the wing is not
3o dependent on the accuracy of the registry of the wing skin planks 54 on the
headers 60
since the planks are probed for their actual position on the headers 60 using
a contact
probe 84 mounted on the machine tool 40. A vacuum source 86 is energized to
create a
suction 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
35 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.
CA 02554189 1997-03-21
RW486T"" 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 60, 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
to along the wing and serve to connect the several wing skin planks 54 into a
single wing
panel 32, and also to stiffen the panel. They also serve as the connecting
structure
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 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 shown in Patent No. 5,299,894 or Patent No. 5,477,596,
both
by Peter McCowin.
To ensure that the stringers 90 intersect the ribs 38 at positions within the
ao 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 statistical
process
control to detect a trend toward an out of tolerance condition before bad wing
panels 32
as 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 imperfections, and that the
assembled
wing will function aerodynamically as designed. Accurate placement of the
stringers 90
on the wing panels 30 and 32 makes it possible to use smaller "pad-ups" or
thicken
3 o areas on the chords 218 of the ribs 38 or 216 and stringers where the
stringers are
bolted to the rib chords 92, as shown in 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.
35 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 fixture or even on the same
machine tool
CA 02554189 1997-03-21
40 on the same or similar holding fixtures 42 before the wing skin planks 54
are laid in
place. The specified locations of the stringer fastener holes, 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
to of error.
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 to the
wing skin planks 54 must be done before the assembly is a completed wing
panel.
Numerous wing panel riveting machines are known which can perform the drilling
and
riveting operations with the required accuracy and consistency of quality. One
such
machine is illustrated in Patent No. 5,727,300 entitled "Fastener Verification
System"
filed on February 7, 1995 by Hanks et al. Another such machine is the yoke
wing riveter
shown in U.S. patent number 5,033,174 issued to Peter Zieve. In addition, it
is
contemplated that the riveting of the stringers could be done on the same
header 60s
2o using upper and lower gantry mounted drill/rivet units, such as the
structure shown in
U.S. Patent No. 5,231,747.
After all the rivets holding the stringers 90 to the wing skin planks 54 are
installed, the
wing skin is repositioned on the holding fixtures 42 by use of coordination
holes in the wing
panel 30 and the alignment pins 82 on the headers 60. Several reference
surfaces on the
as wing panel 30, such as tool balls or reference pins 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 fixtures 42. A
mill cutter is
mounted in the machine tool 40 and the wing panel is trimmed to the exact edge
dimensions
3o specified in the digital product definition to ensure 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.
35 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
CA 02554189 1997-03-21
11
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, lock bolts, Hi-locks and other
interference fasteners,
such as exact hole diameter or hole roundness because of drill bit wear,
slight variations in
s 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
to features on the parts and assemblies after the distortion by assembly and
manufacturing
processes such as installing interference 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
lower 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
15 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
a o 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
25 assembly. A series of vertical vanes 110 on the paddle fitting is
positioned to lie flush
against a flat face on each of the lower wing stringers 90, and is clamped
thereto and back
drilled with full sized fastener holes. The paddle fitting 108 and T-chord 100
are
disassembled and deburred, and the holes are coldworked to improved their
fatigue life,
since the T-chord and paddle fitting are part of the connection of the wing to
the wing stub in
3 o 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 panel 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
35 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
construction and assembly processes to that of the lower wing panel 32, so it
will not be
CA 02554189 1997-03-21
12
separately described. One exception is the design of the component, called a
"double-plus
chord" 116, 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
s and to the side-of-body web 106, respectively, when the wing is attached to
the airplane.
Two additional vertically spaced sideways projecting flanges 124 and 126 on
each side of
the double-plus chord 116 engage the wing stub on the inboard side and receive
the inboard
end of the upper wing panel 30 on the outboard side of the double-plus chord.
Coordination
holes drilled through the upper wing skin and the stringers 90 at the inboard
end align with
to 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 have the
benefit of
15 greater dimensional accuracy. However, until the advent of high speed
machining which
makes possible the machining of thin walled structures without the problem of
distortion
due to localized heating from the cutter, 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
2 o components has delayed the acceptance of monolithic machined 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,
25 disclosed in our companion application entitled "Determinant Spar Assembly"
filed
concurrently herewith issued as U.S. patent 6,170,157. A rib web 216 is cut
from a sheet
of aluminum using a machine tool such as a gantry-mounted machine tool
programmed
to drive a cutter around the profile of the rib web 216. The rib web profile
data is input to
the machine tool drive program from the engineering authority responsible for
the digital
3o product definition 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 accurately positioned on the
rib web 216.
The rib chords are accurately positioned on the rib web 214 using an accurate
positioning and clamping technique such as that shown in the aforesaid PCT
Application
35 entitled "Determinant Spar Assembly" issued as U.S. patent 6,170,157.
Fastener holes
are drilled through the clamped rib web 216 and rib chords 218 and 220 and
interference
fasteners are inserted and secured. After the fasteners are secured and the
rib is fully
CA 02554189 1997-03-21
13
distorted by the interference 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
s 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 on 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 surface 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
application also serves as a pad of sacrificial material that can be trimmed
to make the
15 height of the ribs 38 exactly as specified in the digital parts definition
of the ribs.
Wing major assembly is performed 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 fixtures 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
zo 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 panel and headers 60, and the
vacuum cups 88
are connected to the vacuum source 190 to pull the wing panel 30 against the
contact
25 pads 62 on the headers 60 and hold it securely in place.
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
3 o 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
performed accurately on the panel at its actual position.
A program in the controller of the machine tool 40 is initiated to drive a
35 machining cutter around the edges of the wing panel to net trim the panel
32 to size.
Performing this net trim operation after all the stringer fasteners have been
installed,
instead of beforehand, eliminates the size distorting effect of the many
stringer
CA 02554189 1997-03-21
14
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
to 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
zo 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
match
a 5 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 temporary
fastener
such as the cleco fastener 234 illustrated in Fig. 20 fastens the gauge/clamp
224 to the
30 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
gauge/clamps 224 are attached to the lower edge of the spar 34 and the
shoulder 230
35 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
CA 02554189 1997-03-21
of the wing panel 32 to secure the clamp to the wing panel 32 and hold the
spar 34
down against the upper surface of the wing skin 56.
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
s 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 cleco removable fasteners. If the front spar with leading edge fittings
is attached
to 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
15 204 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 panel
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
a o 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.
z5 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 aligned coordination holes to full size for insertion of the
permanent
fasteners. Alternatively, the coordination holes could be drilled at nearly
full size so
they merely need be reamed in an operation that is quick and produces quality
holes
3 o 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
35 the digital wing product definition. Variations in the dimensions of wing
boxes made using
prior art processes caused difficulties in mounting the control surface
structures such as
leading edge slats and trailing edge flaps, and also caused difficulties in
attaching the
CA 02554189 1997-03-21
16
wing to the airplane. These difficulties are largely eliminated with wing
boxes made in
accordance with this invention because of the small 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
s manufacturing, such as that disclosed in PCT Application No. PCT/US96/10757
by
Atkinson, Miller and Scholz entitled "Statistical Tolerancing" 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.
to Rib bolt fasteners 244 shown in Fig. 7 are inserted in predrilled holes
through the
stringer pad-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 correct height. If not, separate phenolic washers can be
inserted
between the stringer pad-ups and the rib chord before the rib bolts 244 are
inserted.
15 The holes predrilled in the rib chord flanges and the stringer pad-ups are
slip fit holes to
allow limited slip between the rib 38 and the stringer 90 on the wing panel 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.
zo 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 clamps generate sufficient interfacial pressure between the spar lower
chord
z5 136 and the wing panel 32 to prevent interlaminar burrs from intruding in
the spar/panel
interface. Such burrs would interfere with a proper junction between the spar
and the
wing panel 32 and be very difficult to remove because of the sealant in the
interface.
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
3o 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 temporary fasteners.
The spars are now fastened with permanent fasteners in place on the edges of
35 the wing panel 32. The machine tool 40 drills holes in bottom flange 144 of
the lower
the spar chord 136 from the lower surface or skin side. If the particular
machine tool 40
being used is not able to drill from below, it is directed to drill accurate
pilot holes from
CA 02554189 1997-03-21
17
above, which pilot holes are used to guide the drilling and countersinking of
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
panel 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
to 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 fastened to
the
15 underside of 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
z o 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 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
a s machine toot that probes the location of the pilot holes drilled at
selected shear tie pads
to normalize the 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 tool, through the interface
between the
3o shear tie rib pads and the wing skin to remove any chips or burrs that may
have
intruded 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
35 lower wing panel 32 at the engine strut position and are indexed by way of
coordination
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
CA 02554189 1997-03-21
18
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
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 engine strut on the
wing, and the
axis of the fuse pin bores 253 must be properly aligned to ensure a trouble-
free
to 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 that would have been produced by
mispositioned strut fittings. Temporary fasteners are inserted in some of the
aligned
15 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 the fastener holes in the wing
panel, the ribs,
and the strut fitting 250 are coldworked and reamed. Faying surface sealant is
applied
2o and the strut fitting is returned to its place and the fasteners are
inserted and tightened by
the mechanic.
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 predrilled in the
flap reaction
fittings 254 and corresponding coordination holes in the wing panel, drilled
from above by
z s 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 flap
reaction fittings in place. Corresponding flap support fittings 256 are
attached to the rear
spar 34 during spar buildup by aligning coordination holes 257 predrilled in
the flap
3o 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
35 wing box assembly. The upper wing panel 30 is indexed to the inboard end of
the spars
by way of a coordination hole predrilled 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
CA 02554189 1997-03-21
19
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 lower 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.
to 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
is of these four flanges ensures that the side-of-body rib web 106 will 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.
a o Because the wing box is now closed by the upper wing panel 30, 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 over the position of the
stringers 90
as 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 where they are fastened together by the
rib
3 o 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 30 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
hand
35 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
CA 02554189 1997-03-21
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 holes to hold the
wing panel
firmly against the spar chord 134 while the permanent fastener holes are being
drilled so that no chips or burrs intrude into the interface between the spar
chord and
s 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.
to 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 acceptable. Shaving the head
2o 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
surface
is not an acceptable fix. To ensure that the fastener holes are drilled normal
to the
wing surface, 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-
25 Normalizing Drill Head" issued as U.S. patent 5,848,859.
The machine tool 40 drills and countersinks the fastener holes and inserts the
fasteners. A mechanic inside the wing box installs the nuts or collars and
tightens the
fasteners with a power tool as the fasteners are inserted. The holes are
drilled and
countersunk in the wing skin, and the holes extend through the top flange on
the spar
3o chord. A pressure foot on the drill head exerts a press-up force to assist
the clamps
and the temporary fasteners in maintaining the pressure at the interface
between the
wing skin and the spar chords to prevent chips and burrs from intruding 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
fouling the chip vacuum system with sealant. Temporary fasteners may be
installed in
the holes that require coldworking until the sealant cures, after which the
holes may be
coldworked and reamed, and the permanent fasteners installed.
CA 02554189 1997-03-21
21
The upper wing panel 30 is fastened to the shear tied ribs 38' as shown in
Fig. 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
location of the
shear tie pads 248 under the upper wing skin. Because of the flexibility of
the ribs, it
s may be desirable for a mechanic to back drill pilot holes through predrilled
pilot holes in
selected shear tie pads 248 and install index head tack fasteners to fix the
position of
the intermediate portions of the shear tie ribs 38' against flexing in the
spanwise
direction. The machine tool 40 can then probe for the index heads of the tack
fasteners and normalize the machine tool program with the actual position of
the shear
to tied ribs 38' based on the position of the index heads. The machine tool 40
drills and
countersinks full sized fastener holes from above the upper wing skin while a
mechanic
inside the wing box runs a chip chaser between the shear tie pads 248 and the
inside
surface of the wing skin. The machine tool 40 inserts the fastener while the
mechanic
inside the wing box places the nuts or collars and tightens the bolts with the
appropriate
is power tool.
Aileron hinge ribs 130 are attached to the rear spar 34 for supporting an
aileron
hinge rod in bushings spaced to the rear of the rear spar. It 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.
2o 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
small distortion that was produced during final wing box assembly was
sufficient to
25 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.
Another factor influencing the positional accuracy of the hinge bushing on the
3 o 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
the facing surfaces, variations in the perpendicularly of the hinge rib to its
distal end
35 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.
CA 02554189 1997-03-21
22
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
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
s 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
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
to 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.
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
15 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
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 with sealant.
The
2o coated web is replaced on the flanges 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
25 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-
3 o 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 supports are attached to
stabilize the ribs 38 until they are attached to the front spar 36'. A series
of holding
35 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 front
spar 36' up and down since the distance between the rib coordination holes
determines
CA 02554189 1997-03-21
23
the chordwise distance between the front and rear spars, just is it does for
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
s 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
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 differential undersized holes or a
slot in one
to part. Wing panel fixturing is designed to support the weight of the wing
panel since the
alignment pins through the coordination holes would not normally be designed
to
support a load of that magnitude. Since the panel fixture 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-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 of the ribs. The wing skin
is
allowed to conform to the ribs by starting from the rear spar and wrapping the
wing skin
2o 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
25 spars and is beburred, cleaned, fay 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 use in
conventional wing
manufacturing facilities. The lower skin is located and indexed to the rear
spar just as
3 o 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
35 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
CA 02554189 1997-03-21
24
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.
s Two laterally spaced rails 277 are mounted on rigid longitudinal beams 279
supported atop the columns 275. An upper gantry 280 is mounted for
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 ball nut 290 with a ball screw. The
ball 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
15 desired locations for drilling, hole measuring and conditioning, and
fastener insertion.
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. Otherwise, the
gantries
20 280 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
25 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
wing panel 32
3o 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 undersurface of the spars 34 and 36 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 and the spars 34
and 36.
35 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
CA 02554189 1997-03-21
and ribs. The upper gantry arm 295 can be positioned opposite to the arm 308
to
provide a reaction clamping force to prevent 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
5 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
debarring 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 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.
2 o End trimming of the spars and wing panels can be performed with router
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
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.
25 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
3o 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
CA 02554189 1997-03-21
26
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.
s 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 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
2o 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:
