U.S. patent application number 09/781032 was filed with the patent office on 2001-08-16 for method of fabricating leading edge nose structures of aerodynamic surfaces.
Invention is credited to Lajain, Henri, Mertens, Josef.
Application Number | 20010013173 09/781032 |
Document ID | / |
Family ID | 7630105 |
Filed Date | 2001-08-16 |
United States Patent
Application |
20010013173 |
Kind Code |
A1 |
Mertens, Josef ; et
al. |
August 16, 2001 |
Method of fabricating leading edge nose structures of aerodynamic
surfaces
Abstract
A method of fabricating an aircraft leading edge nose structure
includes the following steps. Parallel strengthening members are
welded onto a flat planar outer skin sheet. Two forming tool
members having appropriately shaped outer contours contact the
inner surfaces of the strengthening members, and are then pivoted
and shifted toward each other so as to bend the outer skin sheet
into a parabolic shape along the curved contour defined by the
forming tool members. The resulting bent outer skin sheet with the
strengthening members welded thereon is secured into a negative
mold. To provide boundary layer suction, a perforated throttling
sheet, inner ribs, and a non-perforated inner skin sheet may be
successively secured by sealant and blind rivets onto the pre-bent
structure of the outer skin sheet and the strengthening members.
The finished structure is then removed from the mold.
Inventors: |
Mertens, Josef; (Aachen,
DE) ; Lajain, Henri; (Bremen, DE) |
Correspondence
Address: |
FASSE PATENT ATTORNEYS, P.A.
P.O. BOX 726
HAMPDEN
ME
04444-0726
US
|
Family ID: |
7630105 |
Appl. No.: |
09/781032 |
Filed: |
February 8, 2001 |
Current U.S.
Class: |
29/897.2 ;
29/448 |
Current CPC
Class: |
B64C 5/00 20130101; Y10T
29/49629 20150115; B64C 3/00 20130101; Y10T 29/49904 20150115; Y10T
29/49956 20150115; Y10T 29/49867 20150115; Y10T 29/49622 20150115;
Y10T 29/49895 20150115; Y10T 29/49869 20150115; Y10T 29/49968
20150115 |
Class at
Publication: |
29/897.2 ;
29/448 |
International
Class: |
B23P 011/02 |
Foreign Application Data
Date |
Code |
Application Number |
Feb 8, 2000 |
DE |
100 05 348.3 |
Claims
What is claimed is:
1. A method of fabricating a leading edge nose structure of an
aerodynamic surface, comprising the following steps: a) joining
plural metal strengthening members that extend in a longitudinal
direction and that are laterally spaced apart from one another onto
a flat planar metal outer skin sheet, so as to form thereof a
preliminary flat planar structure; b) after said step a), deforming
said preliminary flat planar structure by contacting and securing
at least some of said strengthening members onto a curved contour
of a positive forming tool and reconfiguring said positive forming
tool so as to increase a curvature defined by said curved contour,
and thereby bending said outer skin sheet to have an outer sheet
contour with a cross-sectional nose curvature corresponding to said
curved contour, so as to form of said preliminary flat planar
structure a preliminary curved structure; c) after said step b),
placing and securing said preliminary curved structure into a
negative form so that said outer skin sheet contacts and is
supported by a negative form surface of said negative form having a
negative contour corresponding to said outer sheet contour; and d)
after said step c), releasing and removing said positive forming
tool from said preliminary curved structure.
2. The method according to claim 1, wherein said step b) is carried
out using a bending apparatus that includes a rotatable threaded
spindle, first and second threaded guide elements which are
thread-engaged on said threaded spindle, and said positive forming
tool which includes first and second separate forming tool members
that each have a respective portion of said curved contour and that
are respectively pivotally connected to said first and second
threaded guide elements; and wherein said contacting and securing
of said strengthening members onto said curved contour of said
positive forming tool and said reconfiguring of said positive
forming tool is carried out in a stepwise progressive manner and
comprises securing two laterally outermost ones of said
strengthening members respectively to said first and second forming
tool members, rotating said threaded spindle to move said first and
second threaded guide elements linearly toward one another and
thereby pivoting said first and second separate forming tool
members relative to one another so as to increase said curvature
defined by said curved contour comprising said respective portions
of said curved contour on said first and second forming tool
members, then contacting and securing onto said first and second
forming tool members two more of said strengthening members that
are respectively inwardly adjacent to said two laterally outermost
ones of said strengthening members, and then continuing said
pivoting of said first and second forming tool members in
successive pivoting steps and successively securing inwardly
successive pairs of said strengthening members onto said first and
second forming tool members between successive ones of said
pivoting steps, while said deforming of said preliminary flat
planar structure progresses correspondingly in a stepwise
manner.
3. The method according to claim 1, wherein said step b) is carried
out so that said cross-sectional nose curvature is substantially a
parabola.
4. The method according to claim 1, wherein said step b) applies
and establishes a pre-stress in said preliminary curved structure,
and further comprising, after said step d), an additional step of
connecting form ribs crosswise across and onto said strengthening
members such that said form ribs take up said pre-stress and hold
said preliminary curved structure so as to maintain said outer
sheet contour even after removing said structure from said negative
form.
5. The method according to claim 1, wherein said positive forming
tool comprises first and second forming tool members that
respectively include first and second rigidly curved forming plates
and that are pivotable and slidable relative to each other, and
wherein said step b) comprises pivoting and sliding said first and
second forming tool members relative to each other so as to
decrease an angle between said rigidly curved forming plates and
thereby increase said curvature defined by said curved contour that
is defined along said rigidly curved forming plates and
therebetween along a parabolic curve spanning a vertex of said
angle between said rigidly curved forming plates, whereby it is
particularly a curvature of said parabolic curve that is
increased.
6. The method according to claim 1, wherein said strengthening
members include respective L-sectional profile members which each
include a main web that protrudes substantially perpendicularly
from said outer skin sheet and a stiffening flange that protrudes
from said main web substantially locally parallel to said outer
skin sheet; wherein said joining in said step a) comprises a
permanent, rigid integral material joining achieved by one of
welding, soldering and brazing; wherein said stiffening flange of
each said L-sectional profile member has a hole therein, and said
positive forming tool has holes therein; and wherein said securing
of said strengthening members onto said curved contour of said
positive forming tool comprises inserting respective assembly pins
through said holes in said stiffening flanges of said L-sectional
profile members and correspondingly through said holes in said
positive forming tool respectively aligning in registration with
said holes in said stiffening flanges.
7. The method according to claim 6, wherein said strengthening
members further include a T-sectional profile member including a
main web that protrudes substantially perpendicularly from said
outer skin sheet along a longitudinally extending centerline
thereof along a center of said cross-sectional nose curvature and a
stiffening flange that protrudes in two opposite directions from
said main web substantially locally parallel to said outer skin
sheet; wherein said joining of said T-sectional profile member in
said step a) comprises a permanent, rigid, integral material
joining achieved by one of welding, soldering and brazing; and
wherein said T-sectional profile member is not contacted and
secured onto said positive forming tool in said step b), and
instead said step b) comprises bending said outer skin sheet
adjacent to said T-sectional profile member along a free-form
parabolic curve between two respective portions of said curved
contour of said positive forming tool.
8. The method according to claim 1, wherein said outer skin sheet
is a perforated outer skin sheet; and further comprising the
following steps after said step d): e) providing pre-curved
perforated throttling sheets that have a curvature substantially
corresponding to a curvature of said strengthening members in said
step c), applying a sealant between said strengthening members and
said throttling sheets, positioning said throttling sheets onto
said strengthening members, and securing said throttling sheets
onto said strengthening members using blind rivets; f) after said
step e), providing pre-curved inner ribs that have a curvature
substantially corresponding to a curvature of said throttling
sheets, applying a sealant between said inner ribs and said
throttling sheets at least along areas of joints that extend
between adjoining ones of said throttling sheets crosswise relative
to said longitudinal direction, positioning said inner ribs onto
said throttling sheets at least along said joints to extend
crosswise relative to said longitudinal direction, and securing
said inner ribs onto said throttling sheets using blind rivets; g)
after said step f), providing plural flanged U-section members that
each include a U-channel and two flanges respectively protruding
from two edges of said U-channel, applying a sealant between said
U-channels of said U-section members and said throttling sheets,
positioning said flanged U-section members to extend in said
longitudinal direction respectively substantially along and aligned
with respective ones of said strengthening members with said
U-channels arranged on said throttling sheets while extending
through respective openings in said inner ribs, and securing said
U-channels onto said throttling sheets using blind rivets; h) after
said step g), providing pre-curved non-perforated inner skin sheets
that respectively have a curvature substantially corresponding to
respective portions of a curvature of said inner ribs, applying a
sealant between said inner skin sheets and said flanges of said
flanged U-section members, positioning said inner skin sheets
respectively onto said flanges of said flanged U-section members,
and securing said inner skin sheets respectively onto said flanges
of said flanged U-section members using blind rivets; and i) after
said step g), removing from said negative form a resultant nose
sandwich structure including at least said outer skin sheet, said
strengthening members, said throttling sheets, said inner ribs, and
said flanged U-section members.
9. The method according to claim 8, wherein said step i) is carried
out after said step h), and said resultant nose sandwich structure
further includes said inner skin sheets.
10. The method according to claim 8, wherein said step i) is
carried out before said step h), said resultant nose sandwich
structure removed from said negative form does not yet include said
inner skin sheets, and said step h) is carried out while said
resultant nose sandwich structure is out of said negative form.
11. The method according to claim 8, wherein said providing of said
pre-curved perforated throttling sheets comprises a preliminary
step of bending initially flat throttling sheets by respectively
contacting and securing said initially flat throttling sheets onto
said curved contour of said positive forming tool and reconfiguring
said positive forming tool so as to increase a curvature defined by
said curved contour and thereby bending said respective throttling
sheet to have a curvature corresponding to said curved contour, so
as to respectively form of said initially flat throttling sheets
said pre-curved perforated throttling sheets.
12. The method according to claim 1, wherein said step b) is a cold
forming step carried out at room temperature.
Description
[0001] This application is based on and claims the priority under
35 U.S.C. .sctn.119 of German Patent Application 100 05 348.3,
filed on Feb. 8, 2000, the entire disclosure of which is
incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The invention relates to a method of fabricating a leading
edge nose structure of an aerodynamic surface such as wing or a
tail fin of an aircraft. The method involves bending or forming
fuselage skin sheets and joining strengthening components onto the
skin sheets.
BACKGROUND INFORMATION
[0003] Conventional wings of known aircraft types are fabricated as
riveted and adhesively bonded aluminum constructions. The leading
edge nose structure of the tail fin of such a known aircraft
similarly is constructed of aluminum, glass fiber composites,
graphite fiber composites, or carbon fiber composites, which are
disadvantageously subject to erosion. In fabricating such known
metal structures of aerodynamic surfaces, the fuselage skin sheets
are formed over positive cores before the sheets are joined
together. Other solutions or methods of fabricating the leading
edge nose structure of an aerodynamic surface, and especially such
a leading edge nose structure that allows boundary layer control by
suction of boundary layer air through holes in the leading edge
nose structure, have not been successfully developed or brought
into practice. Nonetheless, the development of such improved
methods of fabricating such leading edge nose structures is
becoming ever more important in the field of air-craft
construction, due to the constant efforts to reduce manufacturing
costs and to improve the resulting aerodynamic structures with
regard to an improvement of the aerodynamics, a reduction of the
weight, and a resulting reduction of fuel consumption and increase
of the maximum cruise flight range of the aircraft.
[0004] Previously known constructions for leading edge structures
enabling a boundary layer suction all suffer from several common
disadvantages, which has made it impossible or impractical to carry
out such methods in large scale assembly line or series production
of aircraft components. For example, the Boeing Company
successfully tested a hybrid laminar technology in flight tests
with the Boeing 757 aircraft. In that context, the connection of
the several suction chambers was carried out by gluing or
adhesively bonding together trapezoidal shaped metal sheets with
relatively large joint surfaces on the aircraft outer skin.
[0005] Disadvantageously, the large joint surfaces of the
adhesively bonded surfaces covered a rather large proportion of the
suction holes, i.e. the aerodynamic surfaces provided with
perforated holes therein. As a result, this known joining method
has been very critically reviewed and judged, for example also with
respect to the operating life and with respect to the application
of internal pressure for cleaning and de-icing the suction
structure.
[0006] Another known fabrication method involves warm deforming and
joining of components in a vacuum soldering oven or furnace, using
negative and positive cores made of steel. In this known method,
considerable problems have arisen from the local and global
deformations which require an extremely complicated and costly
temperature control and variation. Additional difficulties have
been caused by crystal transformations in the materials during the
process. It has further been found in practice that the weight and
the stiffness of the components cannot be brought down to
acceptable values for making such a known method useful for the
series production of a high volume of components.
[0007] Another known approach was the wind tunnel model of the
so-called ELFIN II wing (an acronym for "European Laminar Flow
Investigation"), of which the components were joined together by
adhesive bonding or gluing. While the results seemed acceptable for
test purposes, such a fabrication method does not appear to be
practical for high volume series production, because high
manufacturing costs and a low operating life are expected. Also, on
technical grounds the required interior pressurization for cleaning
and for de-icing the suction structures is lacking.
SUMMARY OF THE INVENTION
[0008] In view of the above, it is an object of the invention to
provide a method of fabricating a leading edge nose structure for
an aerodynamic surface, especially for use in the manufacture of
aircraft, which is able to form almost any desired aerodynamic
contour with a high contour accuracy and true reproduction of the
desired contour, while maintaining tight construction tolerances
and achieving a high surface quality. The method particularly aims
to avoid the use of cost-intensive and complex deformation
techniques using positive mold cores or warm deformation of the
material. To the contrary, the invention aims to reduce the
manufacturing cost, effort and complexity, so as to enable the
series production of a high volume of aerodynamic surface
components. The invention further aims to avoid or overcome the
disadvantages of the prior art, and to achieve additional
advantages, as apparent from the present specification.
[0009] The above objects have been achieved according to the
invention in a method of fabricating a leading edge nose structure
of an aerodynamic surface, using a bending apparatus including two
longitudinally movable guide elements movably arranged and
supported on a threaded spindle, such that a rotation of the
threaded spindle is transferred to a sliding motion of the two
guide elements either toward each other or away from each
other.
[0010] A respective forming tool member with a defined outer
contour is articulately connected by a respective pivot joint to
each respective one of the guide elements. The method according to
the invention proceeds as follows.
[0011] Metal stringers or other profile element segments acting as
strengthening members are arranged substantially parallel to each
other and are then mechanically secured to a metal outer skin sheet
that is in a flat planar configuration. For example, the
strengthening members are laser welded or soldered onto the outer
skin sheet so that the major profile web of each strengthening
member stands substantially perpendicularly relative to the plane
of the outer skin sheet. The bending apparatus is then configured
and positioned so that the left and right forming tool members are
arranged with their outer contour surfaces respectively contacting
the back or inner contact surfaces of the strengthening members,
while extending substantially crosswise across the strengthening
members. At this point, the outer skin sheet is initially still in
a substantially flat planar configuration.
[0012] Then respective outermost ones of the strengthening members
are secured respectively to the left and right forming tool members
by respective assembly pins. Next, the bending apparatus is
operated to move the guide elements stepwise toward one another so
that the left and right forming tool members pivot and slide
relative to one another and thereby pull the outer skin sheet along
with the moving forming tool members, so as to step-wise bend the
outer skin sheet into a bent form that is generally in the shape of
a parabola on a plane substantially perpendicular to the
longitudinal extending strengthening members. This bent form of the
outer skin sheet is determined by the similarly curved outer
contour of the left and right forming tool members, against which
the inner contact edge of each strengthening member is pulled, as
well as a free-form parabolic curve of the outer skin sheet
spanning the gap between the two forming tool members following the
pivoting motion of the two forming tool members.
[0013] During this step-wise bending process, successive ones of
the strengthening members are secured to the respective forming
tool members by respective assembly pins, as each step of bending
successively brings the next successive pair of strengthening
members into contact with the forming tool members. This process is
continued until the outer skin sheet has been bent or deformed into
a curved aerodynamically contoured nose shape as seen in a
cross-section plane perpendicular to the center line of the outer
skin sheet or perpendicular to the strengthening members, in the
area of the respectively adjacent free ends of the two forming tool
members. The above described bending process is a cold bending or
cold forming process, which may be carried out at room temperature
(e.g. 60.degree. F. to 100.degree. F.).
[0014] The preliminary nose structure that has been joined together
and then flexed or bent to apply a pre-tension thereto in the above
described manner is then positioned into a negative form or mold,
which has an inner contour substantially matching and following
(while compensating tolerances) the generally parabolic curve
contour of the outer skin sheet that has been formed as described
above. Then, the two longitudinally extending edges of the outer
skin sheet are secured to prevent the deformed nose structure from
springing out of the negative form, by several securing plates
which are distributed along the longitudinally extending edges of
the negative form and which retain the edges of the outer skin
sheet. Next, the above mentioned assembly pins are removed, to
release the inner contact surfaces of the strengthening members
from the left and right forming tool members, so that the bending
apparatus can then be removed and retracted away from the nose
structure.
[0015] Further steps according to the inventive method may then be
carried out as follows, especially if the nose structure is to
provide for boundary layer suction. After the preliminary nose
structure has been arranged in the negative form or mold as
described above, perforated throttling sheets, which have been
pre-formed into a shape similar to a parabola generally matched or
adapted to the parabolic contour of the outer skin sheets, are then
arranged in a row and butted against one another in the
longitudinal direction on the inside of the preliminary nose
structure, i.e. contacting the inner contact edges of the
strengthening members, after having applied a sealant at defined
locations between the inner perforated throttling sheets and the
strengthening members, wherever required. The inner perforated
throttling sheets are then secured to the inner contact edges of
the strengthening members by respective blind rivets. The
non-abutting crosswise extending edge of the last perforated
throttling sheet in the row of these sheets ends and extends
perpendicularly above or inwardly along the skin sheet crosswise
edge, while the longitudinal edges of the throttling sheets extend
perpendicularly inwardly along the longitudinally extending edges
of the skin sheets.
[0016] Next, a plurality of inner ribs that have been previously
bent into a parabolic shape matching that of the throttling sheets,
are provided with a sealant on the back or outwardly directed
surfaces thereof and are then placed onto the inwardly facing
surface of the throttling sheets so as to extend generally
crosswise relative to the longitudinal centerline of the leading
edge nose structure. These inner ribs are then secured by
respective blind rivet connections.
[0017] Then, a plurality of flanged U-section members having a
"hat-shaped" sectional profile are provided with a sealant applied
thereto, and are arranged running substantially parallel to one
another along the longitudinal direction of the leading edge nose
structure, on the inner parabolic surface of the inner throttling
sheets, and are secured thereto by additional blind rivet
connections. Thereafter, a plurality of longitudinally extending
inner skin sheets are provided with a sealant along their
longitudinally extending edges, and then these edge portions are
arranged on the protruding flanges of the flanged U-section members
and connected thereto by additional blind rivet connections. In the
above manner, the leading edge nose sandwich structure has been
essentially completed with a sandwich construction, which is then
removed out of the negative form or mold after releasing the
securing plates.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] In order that the invention may be clearly understood, it
will now be described in connection with an example embodiment,
with reference to the accompanying drawings, wherein:
[0019] FIG. 1 is a schematic exploded perspective view of the
principle components of an aircraft fin and rudder assembly
allowing for boundary layer suction;
[0020] FIG. 2 is a sectional view of an initial planar condition of
an outer skin sheet with parallel stringers mounted thereon;
[0021] FIG. 3 is a cross-sectional view of a bending apparatus for
carrying out the cold bending of the illustrated leading edge nose
structure, according to the invention;
[0022] FIG. 4 is a sectional view of a negative mold or form with
the leading edge nose structure of FIG. 3 arranged and secured
therein;
[0023] FIG. 5 is a view similar to that of FIG. 4, but showing a
further step in which a suction air throttling sheet has been
mounted on the stringers;
[0024] FIG. 6 is a perspective view generally showing the
arrangement of FIG. 5, in a further subsequent step in which an
inner rib has been secured onto the throttling sheet;
[0025] FIG. 7 is a view generally similar to that of FIG. 6, but
showing a further subsequent step in which a flanged U-section
member has been guided through the inner rib and secured onto the
throttling sheet; and
[0026] FIG. 8 is a view generally similar to that of FIG. 7, but
showing the next subsequent step in which an inner skin sheet has
been secured onto the protruding flanges of respective adjacent
ones of the U-section members.
DETAILED DESCRIPTION OF PREFERRED EXAMPLE EMBODIMENTS AND OF THE
BEST MODE OF THE INVENTION
[0027] As shown in FIG. 1, the fin and rudder assembly 1 of an
aircraft includes a tail fin 4A with a leading edge nose 4, as well
as a fin support structure or particularly a torsion box 2, and a
rudder 3. The general structure of this fin and rudder assembly 1
can be according to any conventionally known principles and design,
but special attention will be directed herein to the leading edge
nose 4, which is actually made up of a plurality of nose portions
that are arranged one after another in the span direction, for
example an upper fin nose portion that sweeps back to the fin tip,
a lower fin nose portion that extends and merges into the fin root,
and a middle fin nose portion that extends between the upper and
lower portions. The support structure 2 is particularly a carbon
fiber reinforced composite torsion box structure 2. The above
described leading edge nose 4 is secured to the front side of the
torsion box structure 2. The rudder 3 is pivotably arranged on the
rear spar of the supporting torsion box structure 2.
[0028] The nose structure 4, or at least one of the portions
thereof, is provided with perforations through the outer skin
thereof, and air channels therein, in order to allow boundary layer
air flowing along the respective nose portion to be sucked or
suctioned off, through the perforations into the air channels
within the leading edge nose structure, especially at the areas of
the aerodynamic stagnation lines along the nose structure surface,
in order to advantageously influence the aerodynamic resistance in
these areas during flight of the aircraft. The leading edge nose
structure is further provided with suction ports or tappings to
suction and carry away the boundary layer air that has been sucked
into the air channels. These features can be according to any
conventionally known teachings.
[0029] The present inventive method of manufacturing such a leading
edge nose structure 4 will now be described in an example
embodiment with reference to the subsequent Figures. First
referring to FIG. 2, continuous metal stringers 6 or local securing
elements such as sections of stringers 6, or generally referenced
strengthening members 6, are arranged on a flat planar outer skin
sheet 5, which is, for example, made of an aluminum alloy, titanium
or a titanium alloy, or chrome nickel steel. Any conventionally
known joining techniques, such as riveting, soldering, brazing,
adhesive bonding or gluing, and welding, such as laser welding or
diffusion welding, can be used for joining the strengthening
members 6 onto the flat planar skin sheet 5. The strengthening
members 6 extend substantially parallel to one another, and
substantially parallel to a longitudinal center line of the skin
sheet 5, whereby the major webs of the strengthening members 6
protrude substantially perpendicular relative to the plane of the
outer skin sheet 5.
[0030] In order to achieve an inwardly curved, generally parabolic
bend or curved form of the nose structure, the inventive method
uses a bending apparatus 7 that comprises a two-part crank rod or
threaded spindle 73 including a left spindle part and a right
spindle part that are respectively provided with a right-hand
external threading 710 and a left-hand external threading 79 (or
vice versa), and respectively have a left-crank 72 and/or a
right-crank 71 mounted respectively on opposite ends thereof. The
threaded spindle 73 is rotatably supported at its center in a
spindle housing 78.
[0031] Two guide elements 74 and 75 are internally threaded with
respective opposite threadings, and are respectively arranged on
and engage the external threading of the left-spindle part and the
right-spindle part. Thereby, in view of the two opposite threading
directions, a rotation of the threaded spindle 73 using the
right-crank 71 and/or the left-crank 72, will respectively move the
guide elements 74 and 75 toward each other or away from each other
along the threaded spindle 73. In other words, the rotational
motion of the spindle 73 is converted via the internal threading of
the respective guide elements 74 and 75 engaging the external
threadings of the threaded spindle 73, into linear motion of the
respective guide elements 74 and 75 along the spindle 73. Rather
than the cranks 71 and 72, one or two drive motors may be provided
for rotationally driving the threaded is spindle 73.
[0032] Respective left and right pivot joints 76 and 77 are
provided on the guide elements 74 and 75, and pivotally connect
respective left and right forming tool members 9 and 10 to the
respective guide elements 74 and 75. Each of these forming tool
members 9 and 10 respectively comprises a forming rib or actually
half-rib, which may be formed with the necessary contour out of a
hardwood or the like, and may further optionally comprise
respective bending jig plates 81 and 82 secured on the outer edges
of the respective forming ribs, i.e. the edges facing outwardly
away from the threaded spindle 73 and the spindle housing 78. These
bending jig plates may be made of a chrome nickel steel or the
like, and have a curved outer contour that matches the curved
contour of the edges of the respective ribs of the left and right
forming tool members 9 and 10. These respective curved contours of
the left and right forming tool members 9 and 10 together will form
the desired generally parabolic curved contour to which the nose
structure will be bent.
[0033] To begin the bending of the preliminary nose skin structure
shown in FIG. 2, the guide elements 74 and 75 are moved to an
initial position spread widely apart from one another, with the
forming tool members 9 and 10 pivoted from the respective guide
elements inwardly toward one another (i.e. toward the center plane)
so that the outer bending jig contour surfaces thereof lie on a
flat plane. The forming tool members 9 and 10 are then brought into
contact with the contact surfaces of the stiffening flanges 63 of
at least the outermost ones of the strengthening members 6 located
farthest from the longitudinal center plane, and these outermost
ones of the strengthening members 6 are secured to the forming tool
members 9 and 10 by inserting respective assembly pins 11 through
holes 61 in the stiffening flanges 63 of the strengthening members
6, and corresponding holes in the bending plates 81 and 82 of the
forming tool members 9 and 10.
[0034] Then, the threaded spindle 73 is rotated in the appropriate
direction to move the guide elements 74 and 75 stepwise toward each
other, which pulls and pivots the forming tool members 9 and 10
away from the flat plane and successively into an ever-tighter
curvature. This correspondingly pulls and bends the outer skin
sheet 5, to bring the curved bending jig contour of the bending jig
plates 81 and 82 successively into contact with the inwardly facing
contact surfaces of the stiffening flanges 61 of successive pairs
of the strengthening members 6. As each successive strengthening
member 6 comes into firm resting contact against the respective
bending jig plate 81 and 82, a respective further assembly pin 11
is used to secure each of the strengthening members 6 to the
forming tool members 9 and 10. During this process, the outer skin
sheet 5 is successively bent into a curved generally parabolic
contour shape, as shown in FIG. 3 in an intermediate condition.
Namely, as the forming tool members 9 and 10 are pulled and pivoted
inwardly toward each other, the preliminary structure shown in FIG.
2 is pulled along with the forming tool members 9 and 10 and bent
into a contour shape adaptingly along the curved outer contour of
the bending jig plates 81 and 82 of the forming tool members 9 and
10 as well as a free-form parabolic curve of the outer skin sheet
spanning the gap between the two forming tool members following the
pivoting motion of the two forming tool members. This bending
process is continued until the ultimately desired finished curved
contour of the outer skin sheet 5 is achieved, as shown in FIG.
4.
[0035] Thereafter, the completely bent or curved outer skin sheet 5
with the strengthening members 6 joined thereon is inserted into a
negative form or mold 12 that is, for example, made of hardwood and
has an inner curved contour that matches or corresponds to the
desired finished outer contour of the leading edge nose structure
4. The preliminary bent structure of the outer skin sheet 5 with
the strengthening members 6 thereon is secured into the negative
form 12 using left and right securing plates 131 and 132 along the
outer edges of the negative form 12, so that these securing plates
131 and 132 retain the edges of the preliminary outer skin sheet
structure and prevent this structure from springing out of the
negative form 12, as shown in FIG. 4. Once the preliminary bent
structure has been secured in the negative form 12, the above
mentioned assembly pins 11 are removed, to release the bending
apparatus 7 from the preliminary bent structure, and then the
bending apparatus 7 is retracted or moved away.
[0036] The leading edge nose preliminary structure that has been
fabricated in the above manner, with the form thereof shown in FIG.
4, is suitable for any conventional leading edge nose structures of
aerodynamic surfaces in which no boundary layer suction is to as be
provided. In other words, in such an embodiment, the outer skin
sheet 5 is a solid non-perforated sheet, and there is no need of
forming internal suction channels for sucking away boundary layer
air. Thus, the resulting structure as shown in FIG. 4 can be
removed from the negative form or mold 12 and used as a leading
edge nose structure of a conventional wing, tail fin, or tail plane
leading edge of an aircraft without boundary layer suction. In this
context it is advantageous to rivet a plurality of inner form ribs
extending in the crosswise direction onto the inner surfaces of the
strengthening members 6, before removing this structure from the
negative form or mold 12, in order to take up the pre-stress forces
and hold and maintain the structure in its curved configuration
after it is removed from the negative form 12.
[0037] In contrast to the above simple embodiment, it is preferred
to provide a leading edge nose structure with perforations or the
like through which boundary layer air may be suctioned off, for
achieving a boundary layer control as described above. For such an
embodiment, the outer skin sheet is provided with numerous small
perforation holes therein at the appropriate locations. It is
further necessary to form air channels and a proper suction
distribution arrangement within the leading edge nose structure for
distributing the suction air flow along the perforated surface of
the outer skin sheet 5. To achieve this, several additional steps
are carried out after the configuration shown in FIG. 4 has been
achieved.
[0038] As a first additional step, a so-called perforated
throttling sheet 14 is to be arranged on the inner contact surface
of the stringers or other strengthening members 6. To achieve this,
plural perforated throttling sheets 14 are provided with a sealant
15 at the appropriate locations of intended contact on the
strengthening members 6, and are then arranged on the inwardly
facing contact surfaces of the strengthening members 6 in the
negative form 12. The several throttling sheets 14 are arranged
butted against one another (or slightly overlapping) in a row along
the longitudinal direction parallel to the longitudinal center line
of the outer skin sheet or of the leading edge nose structure. In
this context, the throttling sheets 14 have been bent or curved
into the appropriate generally parabolic shape, in a preceding
step, to match smoothly onto the inner parabolic curve defined by
the contact surfaces of the strengthening members 6 in the
configuration as shown in FIG. 5. The sealant 15 has been applied
at the locations of contact between the throttling sheets 14 and
the inwardly facing contact surfaces of the strengthening members
6. Additionally, blind rivets 19 are used to secure the throttle
sheets 14 onto the strengthening members 6. In this arrangement,
the free non-butting crosswise edge of the last one of the
throttling sheets 14 in the row, ends perpendicularly above the
corresponding crosswise edge of the outer skin sheet 5, while the
lengthwise edges of the throttling sheets 14 also terminate along
and perpendicularly above or inwardly from the longitudinal edges
of the outer skin sheets 5. By arranging the throttling sheets 14
with the sealant 15 in this manner, respective pre-chambers 20 for
the suction air are respectively formed and bounded between the
outer skin sheet 5 and the throttling sheets 14, and between the
respective adjacent strengthening members 6, as shown in FIG. 5
(and FIG. 6).
[0039] In a next successive step, inner ribs 16 are secured onto
the above described semi-finished sandwich structure of the outer
skin sheet 5, the strengthening members or stringers 6, and the
throttling sheets 14. This connection is also achieved with a
sealant and blind rivets, to achieve the further structure shown in
FIG. 6. In greater detail, each inner rib 16 is first formed to
match the inner parabolic curvature of the throttling sheets 14,
and then the outwardly directed contact surface of each inner rib
16 is provided with a further sealant 15. Then the respective inner
rib 16 is positioned overlappingly along a respective butting edge
joint between two adjacent throttling sheets 14, extending in the
crosswise direction. Each inner rib 16 is then additionally secured
by blind rivets onto the underlying throttling sheets 14. This
achieves the intermediate construction shown in FIG. 6.
[0040] FIG. 7 shows the result of the next step, wherein a
plurality of flanged U-section members 17 or "hat profile members"
are arranged to extend parallel to each other in the leading edge
longitudinal direction respectively through holes or notches
provided in the inner ribs 16. Each one of the flanged U-section
members 17 is arranged with the U-section standing upright on the
underlying throttling sheet 14, and the protruding flanges thereof
lying along an inner parabolic contour. Sealant 15 is provided
between the underlying throttling sheet 14 and the respective
U-section members 17, and additional blind rivets 19 secure the
U-section members 17 onto the throttling sheet 14 and/or the
underlying strengthening member 6. The boundaries of air
communication to each respective underlying air suction pre-chamber
20 are thereby defined by the locations of the U-section members
17. Namely, the U-section members 17 form boundaries of collecting
plenum chambers 21 as will be discussed further below. The ends of
the U-section members 17 terminate flush with the crosswise edges
of the underlying throttling plates 14.
[0041] Finally, in order to form the above mentioned air collecting
plenum chambers 21, a plurality of solid non-perforated metal inner
skin sheets 18 are secured and sealed with blind rivets 19 and
sealant 15 to the protruding flanges on the inner contour side of
the flanged U-section members 17. Successive inner skin sheets 18
are thereby arranged abutting one another end-to-end (or
overlapping) along the longitudinal direction along the leading
edge nose structure. A respective air collecting plenum chamber 21
is thus formed respectively between the throttling plates 14 and
the inner skin sheets 18, and respectively between neighboring ones
of the U-section members 17. By applying suction in any
conventionally known manner to these plenum chambers 21, the
suction is appropriately distributed and controlled through the
throttling sheets 14 and the outer air suction pre-chambers 20 to
the suction holes or perforations in the outer skin sheets 5. The
resulting structure and air distribution through the plenum
chambers 21 and the pre-chambers 20 can be understood from FIG.
8.
[0042] As a final step, the above described finished configuration
of the leading edge nose sandwich structure is removed from the
negative form 12 by releasing the securing plates 131 and 132. The
leading edge nose structure is now ready to be installed as a
component of an aircraft aerodynamic surface in any known
construction technique and arrangement.
[0043] Further details of the inventive method will now be
emphasized with brief additional comments. The substantially
parabolic shape of the outer skin sheets 5 is established or
determined by the substantially parabolic shape of the forming tool
members 9 and 10, or particularly the bending jig plates 81 and 82
thereof, as well as a free-form parabolic curve of the outer skin
sheet 5 spanning the gap between the two forming tool members, when
these are moved to their inwardly pivoted position. The proper or
desired curvature can thereby be achieved simply by providing the
respective required curvature for the forming tool members 9 and
10. This substantially parabolic contour is then matched by the
inner curvature of the negative form 12. Throughout this
specification it should be understood that the term "substantially
parabolic" and similar terms describing this curvature do not
necessarily require a true mathematically defined parabola, but
rather relate to any desired aerodynamically curved contour that is
suitable for a leading edge nose structure.
[0044] The above described joining of the stringers or other
strengthening members 6 onto the outer skin sheets 5 in a flat
planar configuration is carried out in any known manner to achieve
a rigid, permanent, integral material interconnection between the
strengthening members 6 and the skin sheets 5. Preferably, these
joints are achieved by soldering or welding using laser welding
technology. Also, to achieve proper airtight sealing of the several
air flow channels or passages, any known suitable sealant 15 is
preferably arranged along and between all of the joint areas, and
particularly all of the joints secured by blind rivets 19.
[0045] It is further noted that a respective one of the
strengthening members 6 positioned along the longitudinal center
line of the leading edge nose structure preferably has a
T-sectional shape while the remaining strengthening members 6 each
have an inverted L-sectional shape. This T-sectional strengthening
member 6 extends directly along the forward longitudinal edge of
the leading edge nose structure to form a symmetrical center line
of the parabolic bending or curvature by means of the forming tool
members 9 and 10. A non-symmetrical curvature may also be achieved,
as needed, by simply providing the appropriate shaped forming tool
members 9 and 10 and the negative mold 12.
[0046] As a further detail, it is noted that the throttling sheets
14 may be pre-bent or pre-curved using the same bending apparatus 7
with the same forming tool members 9 and 10, or similar forming
tool members with a slightly different matching curvature, to
provide the appropriate curvature for the throttling sheets 14 to
be arranged on the inner contour of the strengthening members 6 as
shown in FIG. 5. In this context the throttling sheets 14 can also
be connected to the forming tool members 9 and 10 using assembly
pins 11 as described above.
[0047] The removal or retraction of the bending apparatus 7 as
described above can be carried out in a stepwise or a stagewise
manner corresponding to the successive stages of assembling or
arranging the throttling sheets 14 and the ribs 16. Alternatively,
the bending apparatus 7 may be entirely withdrawn or retracted in a
single step at the stage shown in FIG. 4.
[0048] The removal of the finished leading edge nose sandwich
structure out of the negative form 12 could alternatively be
carried out before the step shown in FIG. 8, rather than after
completion of the step shown in FIG. 8.
[0049] Throughout this specification, when two components (such as
the strengthening members for example) are said to be
"substantially parallel" or even "parallel", this is not intended
to require precise parallelism, but rather only that the components
extend generally in the same direction without crossing each other,
and only within an ordinary degree of manufacturing tolerances in
the aircraft manufacturing art. For example, the stringers may
typically extend along barrel-shaped or conical or tapering curved
surfaces, but are still considered to be "substantially parallel".
The terms "perpendicular" and "substantially perpendicular" are to
be understood with a similar degree of tolerance. Similarly, when
two contours are said to "correspond" to one another, that is to be
understood as allowing for ordinary manufacturing tolerances, and
the differences in curvature that are necessary for nesting or
fitting one contour into the other.
[0050] The inventive method provides several advantages in the
field of aircraft construction. A substantially conventional nose
for aircraft wings, tail fins and tail planes, must have an
aerodynamic contour with suitable structural tolerances, and must
protect the underlying supporting structure from external damage,
as well as incorporating arrangements for deicing. Laminar suction
nose structures must additionally have a very high contour
accuracy, and make possible a complex internal structure for
achieving the suction system. The inventive method makes it
possible to construct substantially conventional nose structures,
as well as specially featured nose structures, with reduced costs,
improved erosion resistance, and relatively low weight. The cost
efficiency or economy of the present manufacturing method has been
proven in trial runs or experiments. The laminar technology
utilized according to the invention promises the highest potential
for reducing fuel consumption of commercial transport aircraft,
among all technologies that have been investigated to the present
date. In view of these advantages, the invention provides a
suitable fabrication method for the high volume series production
of laminar suction structures that may be used for the leading edge
nose structures of wings as well as empennage surfaces. All of the
requirements of the surface quality (e.g. roughness, waviness, form
or contour accuracy, etc.), the weight, the stiffness, the
protection against damage (e.g. due to bird strikes or other impact
damage), the airtight sealing, and the ease of repair, are all met
by the inventive method being used to fabricate leading edge nose
structures.
[0051] Although the invention has been described with reference to
specific example embodiments, it will be appreciated that it is
intended to cover all modifications and equivalents within the
scope of the appended claims. It should also be understood that the
present disclosure includes all possible combinations of any
individual features recited in any of the appended claims.
* * * * *