Note: Descriptions are shown in the official language in which they were submitted.
This invention relates to the design and fabrication
of airfoil shapes, and particularly to composite fiber wound
large scale wind turbine rotor blades. More particularly, the
invention provides a method ror avoiding the problem of brid-
ging which occurs when the composite fiber is wound over a
concave mandrel surface to form the airfoil shape. The fibers,
being under tension during the winding process, will not
follow a concave contour or valley of the surface9 but will
form a bridge, resulting in the occurrence of voids in the
surface which weaken the blade structure.
Techniques for fabrication of airfoils such as pro-
peller and rotor blades are well known in the art and include
the use of wood, wood la~inates, various met~ls, and more
recently composite materials such as fiberglass. Very large
rotor blades, such as those used in wind driven turbine
generators, present unique problems due to their very large
size, up to 300 feet in combined length. A preferred cost and
weight saving technique for fabricating these blades is by a
process that involves winding fibers onto a mandrel. A band
or group of parallel resin-impre~nated filarQents is wound
onto a slowly rotating mandrel. The band typically is about
2 inches wide, and composed of a plurality of rovings, each
from a separate spool. Each roving consists of a large
number of filaments, so that the band contains many
thousands of separate glass filaments. The ~ayout guide is
positioned during mandrel rotation to produce the desired
band path on the mandrel. Bridging, or winding over a concave
area of the rnandrel, does not occur on cylindrical shapes, but
can be expected on a wind turbine blade because of blade twist
and its root-to-tip thickness characteristic. With a filament
winding angle of 30 to 40 degrees, the concave shape also
- 2 -
appears along the desired band path. If a section i5 cut along
the band path, the section is bridged if there is a void
between the mandrel and the fiber or filament pulled tightly
across it.
The most visible problem caused by bridging is voids,
which weaken the structure. The voids may be -111ed with
glass and resin to make a solid structureS but this adds
substantial weight at considerable extra cost. Bridging can
produce poor fiber compaction, thus increasing the resin-to-
glass ratio and lowering its strength. Loss of fiber controlmeans that an unsupported band will tend to form a rope, or
to separate.
The angle of winding of the fibers is determined as
required by the specific shape and loads on the blade, and
the angle may be varied along the longitudinal axis of the
blade. Further, conventional winding techniques normally in-
volve multiple winding passes whereby layers oE fibers are
built up to form the airfoil. In some applications specific
portions of the airfoil or blade may contain more layers of
fibers than others, e.g., in rotor blades it is common to
apply many more la~ers of fiber to the inboard or hub end than
to the outboard end to enhance structural rigidity and to ab-
sorb loads.
In many applications a so-called winding or adapter
ring is used at the end of the blades, the fibers belng
wrapped about the ring during fabrisa'~ion and the fibers being
cut off at the end of the blade after fabrication. Again this
technique is well known.
In some applications the fibers in different passes
may be of different compositions, and different passes may
use flbers of varying t~icknesses, or different spacings,
~;~' ' .
~ - 3 -
or different angles. A common technique is to perform one
winding pass on a right-hand helical path, with the next
pass being on a left-hand helical path.
For large blades a solid surface is generally used as
the mandrel over which the fibers are wound. The mandrel
may be, for example, a plywood frame covered with wire
cloth and a plaster filler, or it may be aluminum or
plastic. In some applications a spar section is located
inside the rotor or airfoil for added strength, with mandrel
sections located adjacent the spar. Upon fabrication, the man-
drel may be removed from the inside of the airfoil, or it may
be left in place to act as a structural reinforcement.
Although the invention will be described with respect ~-
to glass fibers coated with resin or other epoxy matrixa
it is apparent that other types of fibers and/or matrices
are equally applicable, and that single or multiple fibers
may be used in practicing the invention.
Bridging may be prevented in some cases by varying
the winding angle, but this is not always practical since
changing the winding angle changes the strength and load
absorbing characteristics of the rotor. Another solution
is to modify the mandrel design, and yet another solution is
to determine in advance from the design geometry the localized
areas of the mandrel where bridging will occur, and adjust the
shape of the design geometry and the mandrel to avoid bridging.
In other words, fixing an airfoil to avoid bridging means
slightly changing the mandrel shape so it is not concave
along any band path. Airfoil changes resulting from bridge-
fixing are primarily near the trailing edge of root stations,
resulting in a negligible impact on aerodynamic performance.
4 -
It is therefore an object of this invention to pro-
vide a method which avoids or reduces bridging in the
fabrication of large scale fiber wound rotor blades.
Another object of this invention is a method for de-
termining where bridging will occur when a composite fiber
is wound over a mandre] or other contoured structure.
A further object of this invention is a method for
making minor changes in the shape of the mandrel or struc-
ture upon which a fiber composite is wound to avoid
bridging.
In accordance with the present invention, there is
provided a method for determining where bridging will occur
in the manufacture of an airfoil surface by the wind-
ing of a composite fiber material upon a mandrel, and for
modifying the contour of the mandrel airfoil surface to
eliminate bridging. The method consists of providing the mandrel
airfoil surface or defining the surface from design data in any
selected coordinate system, such as cylindrical coordinates~
and selecting representative coordinate points on the airfoil
at fixed intervals. As an illustrative example, a set of lines
denoted stringers is defined by the intersection of a plurality
of longitudinal planes, each of which is in a plane containing
the winding axis, with the mandrel surface. A plurality of
planes, which are normal to the winding axis intersect the man-
drel surface along a plurality of lines denoted sections or
stations which are transverse to the stringers. The inter-
section of the stringers and stations define a grid of coor-
dinate points on the mandrel surface. At each coordinate
point, two straight lines are constructed coincident with the
fiber winding plane, the first straight line beginning from
the selected coordinate point and extending in the direction of
fiber winding and coincident with the fiber winding plane,
- 5
and the second straight line beginning from the selected coor-
dinate point and extending coincident with the fiber winding
plane but opposite the direction of fiber winding, i.e., 180
from the direction of the first straight line. Both straight
lines are extended until they intersect either the next
adjacent stringer, or next adjacent station; either may be
selected. The two straight lines thereby connect the selected
coordinate point with the points of intersection with the
adjacent stringers, or stations. A third straight line is
constructed connecting the two points of intersection of the
first and second straight lines with the adjacent stringers or
stations with respect to their distance from the winding axis,
i.e., the points of intersection of the winding plane with the
stringers, or stations, adjacent the selected coordinate point.
The selected coordinate point is bridged if it lies closer to
the winding axis than does the third straight line. The third
line is constructed on a plot in the winding plane. Tne coor-
dinate point, if bridged, must be raised to the level of the
third straight line to avoid bridging. This method is then
repeated for each coordinate point except boundary points at
the axial ends of the airfoil. The method may be performed by
hand using standard clerical techniques, or preferably is auto-
mated by standard computer techniques. The stringers and/or
stations need not be parallel to or normal to the winding axis.
The method is adapted to any coordinate system defining the air-
foil shape, or any valid geometric description of the air-
foil surface and winding band path.
.~,
~L~6~
In accordance with a particular emhodiment of the
invention, a method of rabricating a filament wound wind
turbine blade comprises the steps of: defining a surface re-
presentative of a winding mandrel, defi.ning a plurality of
stringers along said surface~ each of said plurality of
stringers being in substantially the same direction as the axis
about which said surface is wound; defining a plurality of
stations along said surface, each of said plurality of stations
being substantially perpendicular to said plurality of stringers,
the intersection of each of said plurality of stringers and
stations defining a multiplicity of coordinate points on said
surface, said intersections forming a grid of coordinate pointsJ
and for each of said coordinate points: determining the height
of sald coordinate point from said winding axis, constructing
first and second straight line segments on said surface along
said winding path, each said straight line segment connecting
said coordinate point respectively with a point on the stringer
or station adjacent said coordinate point on opposite sides
of said coordinate point, determining the height of said coor-
dinate point from said winding axis; constructing a thirdstraight line between said connected points; determining the
presence of a concave portion of said surface by comparing the
height of said selected coordinate point from said winding axis
with the height of said third straight line from said winding
aixs, said surface being concave between said connected points
along said winding path when the height of said selected coor-
dinate point from said winding axis is less than the height of
said third straight line from said winding axis, and
correcting any determined concavities by adjusting the height of
said selected coordinate point from said winding axis to be
substantially equal to or greater than the height of said
third straight line from said winding a*is, providing a form
.~ ~ . - 7
having a surface corresponding to said corrected surface; and
winding filamentary material abou* said mandrel surface
thereby forming said filament wound blade.
In accordance with a further embodiment of the
invention, a method of fabricating a filament wound wind
turbine blade comprises the steps of: defining on a three
dimensional contoured surface of a winding mandrel, a plurality
of stringers along said surface, each of said plurality of
stringers being in substantially the sa~e direction as the axis
about which said surface is wound, defining a plurality of
stations along said surface, each of said plurality of
stations being substantially perpendicular to said plurality
of stringers, the intersection of each of said plurality of
stringers and stations defining a multiplicity of coordinate
points on said surface, said intersections forming a grid of
coordinate points, and for each of said coordinate points:
determining the height of said coordinate point from said
winding axis constructing first and second straight line seg-
ments on said surface along said winding path, each said
straight line segment connecting said coordinate point respect-
ively with a point on the stringer or station adjacent said
coordinate point on opposite sides of said coordinate point,
determining the height of said coordinate point from said
winding axis, constructing a third straight line between said
connected points, determining the presence of a concave portion
of said surface by comparing the height of said selected coor-
dinate point from said winding axis with the height of said third
straight line from said winding axis, said surface being con-
concave between said connected points along said winding path
when the height of said selected coordinate point from said wind-
ing axis is less than the height of said third straight line from
said winding axis adjusting said mandrel surface io eliminate
any concavities therein, and winding filamentary material
about said mandrel surface thereby forming said filament wound
blade~
The invention will now be described with reference
to the accompanying drawings which show a preferred form thereof
and wherein:
Fig. 1 is a perspective view of a representative
airfoil showing the winding axis, stringers and stations.
Fig. 2 is a diagrammatic plan view of the upper-sur~
face of the airfoil of Fig. 1 showing the intersection of
the stringers and stations.
Fig. 3 is a diagrammatic view taken along
section 3-3 of Fig. 2.
Fig. ~, which appears on the same sheet of draw-
ings as Fig. 1, is a schematic drawing of a computer adapted
to perform the method of this invention.
Fig. 5 is a flow chart showing the steps performed
in practicing the method of this invention using the computer
of ~'ig. 4~
When an airfoil is designed for a particular pur-
pose, such as a rotor blade to power a wind turbine, certain
constrains are inherent in the design, e~g., contour length,
aerodynamic performance, weight, load distribution, etc.
Although fabrication of the blade is also taken into account
in the design, many parameters of the design canrlot be changed
even though the particular design causes difficulties in
fabrication of the blade.
With large sca7e wind turbine blades, conventional
fabrication techniques are cost-l-y and difficult, and
it has been determined that a fiber wound blade is optimal.
g _
. ~
~6~
Winding, however, has presented unexpected difficulties due
to the bridging problem described previously. The present
invention overcomes these difficulties without the necessity
of completely redesigning the blade. That portion of the
method wherein concavities in the mandrel surface are
determined, i.e., can be performed by hand using standard
geometric procedures, but because of its iterative nature
is best adapted to computing apparatus. The method will be
described with respect to the steps involved in manually
accomplishing the result, but a computer can perform the
same steps faster and more efficiently.
Referring to Fig. 1 there is shown in perspective
a portion of a ty~ical airfoil shaped mandrel 10, such as
for a roto~ blade. While a specific sweep or contour is
not shown, it may be assumed that the cross section of the
blade 10 varies in sweep and dimension along its axial length,
the hub end generally being thicker than the outboard tip.
The method of this invention is appiicable to any conventional
aerodyna~ic airfoil shape, and in fact need not be restricted
to airfoils, but can be used for any contoured surface.
Once the blade is designed, in order to wind fibers
or filaments into the desired aerodynamic shape, it is
necessary to construct a mandrel upon which to wind the fibers.
It has been found that constructing the mandrel according to
the design normally results in difficulties in rotor blade
fabrication due to the bridging problem, and an unsatisfactory
blade results. Of course it is possible to manually inspect
the mandrel after its fabrication, such as using a straight
edge along the paths over which a fiber will be wound, and
correct any concave portions, but this solution is obviously
extremely time-consuming, and any correction to the mandrel
$
-- 10 --
~6~
will require another inspection to determine if correction of
one concave portion has produced another concave portion
when the fiber is wound in a return path.
The method of this invention uses standard geometric
techniques to determine from the design data, if any concave
portions exist in the fiber winding paths, and the shape of
the mandrel can be corrected to avoid bridging.
The blade design is often defined in cylindrical co-
ordinates, although the coordinate system is irrelevant
since it requires only simple mathematics to convert from
one coordinate system to another. Assuming a cylindrical
coordinate system, a plurality of stringers are geometric-
ally constructed, via manual or computer techniques, prefer-
ably but not necessarily in a plane which also contains
the winding axis of the blade. Three such representative
stringers are shown in Fig. 1 as stringers A, B and C, and
the stringers are in planes through the winding axis,
although it will be apparent that the actual geometric
shape and number of stringers is variable. The stringers
extend entirely about the perimeter of the airfoil. The
stringers may be at fixed intervals, such as every 5, or
may vary such as every 10 along relatively straight cross-
sections of the blade and every 1/2 along the leading
and trailing edges where greater airfoil curvature occurs.
Although each stringer is preferably, but not necessarily,
in a plane which contains the winding axis of the blade,
the stringers at their point of intersection with the air-
foil are not parallel to each other, as shown in Fig. 2,
and may in fact be curved lines depending on the airfoil
curvature. For example, a stringer along the airfoil
leading edge will curve in two dimensions as the airfoil
becomes narrower at its tip and is swept along its length.
Likewise a plurality of sections or stations are
shown in Fig. 1 denoted stations 1, 2 ... 9. Each station
lies in a plane which is commonly, but not necessarily,
normal to the winding axis 8. The number of stations will
depend on the length and curvature of the blade, a represen-
tative distance being about 5% of blade length.
Coordinate points 12 (Fig. 1) are defined at the
intersection of every stringer with every station.
The airfoil shown in Fig. 1 may include a winding
ring, also referred to as an adapter or turnaround ring.
For example, the actual blade may end at station 3, with
stations 2 and 1 being par~t of a winding ring. It is
generally necessary in practicing the invention to include
the winding ring to insure a bridge-free design of both
the airfoil and the blend area between the winding ring
and the airfoil.
The following method, performed by clerical or com-
puting techniques is repeated for every coordinate point
on the airfoil matrix except the boundary points.
With re~erence to Fig. 2, coordinate point 1~ lo-
cated at the intersection of stringer B and station 3 has
been selected. It should also be noted that Fig. 2 is a
two-dimensional top view of a selected portion of the
airfoil, and that in fact the airfoil will vary in cross
section, i.e., each point in FigO 2 will vary in height
or depth, viz., into or out of the plane of the paper, as
a function of the airfoil design.
Through the selected coordinate point 14 two planes,
16 and 18, referred to as winding planes, are constructed
at angles corresponding to the angles at which the fiber
- 12 -
a
is to be wound, Using plane 16 as illustrative, two
straig'ht lines, shown in Fig. 3 as lines 15 and 17, are
constructed coincident with winding plane 16, the first
straight line 15 beginning at coordinate point 14 and
extending until it intersects either station 4 at point B4
or stringer A at point Al shown in Fig. 2, and the second
straight line 17 beginning at coordinate point 14 and ex-
tending in plane 16 in a direction generally opposite that
of line 15 until it intersects either station 2 at point B2
or stringer C, at point Cl. It will be understood that it is
a matter of choice whether stringers or stations adjacent
the selected coordinate point are used. The lines 15 and 17
while both in winding plane 16 as defined herein, are not
generally collinear since the airfoil is a three-dimensional
surface, It should also be noted that geometric models
other than planes may be used to define the winding path,
and that this invention encompasses any geometric model.
With respect to winding plane 18, two additional
straight lines are drawn in opposite directions from co-
ordinate point 14 in the winding plane to the point of inter-
section with the adjacent stringers, or stations, these
points being shown in Fig. 2 as points A2 or D2 for one
line, and points C2 or D4 for the other line. Again, since
all points are in the same plane, the points used are a
matter of choice. For the example described herein, inter-
section with stringers will be used as the points of inter
section~
The distance of -the intersected points from the wind-
ing axis is then determined, This distance is known for
the coordinaté points. Assuming that -the lines between
adjacent coordinate points are straight lines, a third
- 13 -
5~
straight line 20 shown in Fig. 3 is defined as extending
between points Al and Cl, the relative location of the third
straight line 20 to the coordinate point 14 determining
if coordinate point 14 is bridged. Thus, if the coordinate
point is located as shown at 14, the coordinate point is
closer to the winding axis than is line 20 between points A
and Cl, and point 14 would therefore be bridged. If the
coordinate point is located as shown at 14a, the coordinate
point is located further away from the winding axis than the
line between points Al and Cl, and would not be bridged.
Any coordinate point along or above line 20 is not bridged,
while any coordinate point below line 20 is bridged.
If a coordinate point is bridged, that portion of
the mandrel surface corresponding to the point must be raised
up to the level of line 20 to avoid bridging.
Points B2 or B4 could be used in Fig. 3 rather than
Al or Cl, since all points are on the same line and in the
winding plane~
The above procedure may be then repeated using
20 points A2 or D2, and points C2 or D~, in winding plane 18
corresponding to the other defined winding direction.
The above method may then be repeated for every
non-boundary coordinate point on the airfoil matrix. This
completes one iteration of the method.
If the winding path is defined as other than a
plane, line 20 may not intersect a line extending from the
winding axis, and perpendicular thereto, through the selected
coordinate point. For the method of this invention this is
immaterial, since the relevant data is the difference, if
any, between the distance of the line 20 from the winding
axis and the distance of the coordinate point from the
winding axis.
- 14 -
As an alternatlve to examining each selected coor-
dinate point for possible bridging along both winding planes
16 and 18 and then proceeding to examine the next coordinate
point in the same manner, it may be desirable in some appli-
cations to first examine every coordinate point for bridging
in sequence along one winding path, e.g., the right-hand
helical winding path, and then reexamine the same coordinate
points for bridging in sequence along the other winding path,
e~g., the left-hand helical winding path. An advantage of
examining each coordinate point in both winding paths before
proceeding to the next coordinate point is that under certain
conditions a bridged coordinate point need not be changed.
For example, if relatively minor bridging occurs in the wind-
ing path of the first or lowest fiber, such bridging can be
ignored in some cases if the winding path of the next succeed-
ing fiber, in the opposite direction, does not bridge the
coordinate point since the lower fiber will be physically
forced down by the next succeeding fiber to contact the mandrel,
thereby eliminating the bridging problem for that coordinate
point.
If any coordinate points were raised to eliminate
bridging, it may be necessary tG perform an additional
iteration of the method to determine if raising of one coor-
dinate point has caused bridging of another coordinate point~
The number of stringers and stations, and thus the
number of coordinate points, is a design choice, and will
depend on the blade curvature, i.e., for a blade with large
pitch changes and/or sweep, it may be desirable to use more
coordinate points than with a more straightforward airfoil
shape.
I~ne method has been described with respect to
- 15 -
5~L~4
cylindrical coordinates, but is equally applicable to other
coordinate systems by simple geometric and/or mathematical
transformation oE the airfoil design data. Also, in prac-
tice, stringers and stations need not be planar nor be co-
incident with or perpendicular to the winding axis. After
elimination of bridged points, the final coordinates define
the appropriate mandrel, or templates therefor, for winding
of the airfoil.
Fig. 4 shows a typical computer for performing the
method, since the use of a computer simplifies the method
and is the best mode contemplated.
Fig. 5 shows in flow chart form the instructional
format followed in programming the computer to perform the
method of this invention. It is apparent that the method
of the invention can be implemented in accordance with the
steps of the flo~ chart using any suitable digital computer
or preprogrammed analog computer or microprocessor. The
actual program steps may be varied depending on the computer
and computer language available, and are simple mathematical
computations ~r logical steps, the implementation of which
will be apparent to those skilled in the art. In practice
the program used is Program Fl43 of the Hamilton Standard
Division of United Technologies Corporation, on an IB~
370/163 computer.
The steps could also be performed on many hand-
held commercially available calculators which preferably
perform trigonometric and logarithmic functions for ease
of computation. The computer itself forms no part oE the
present invention, and is shown merely as exemplary of the
type of apparatus commercially available on which the
invention may be practiced in its best mode.
- 16 -
Referring to Fig. 4 there are shown the basic
elements of a digital computer which may be used to
practice the invention and include an input unit 50,
for example a tape deck or punch card reader, which feeds
airfoil design data and program instructions to a memory
52 and a computation and control unit 54. After the program
instructions have been executed, output data is fed to output
unit 56 such as a printer. The memory 52 and computation
and control unit 54 communicate with each other via line 5~
as required. The computation and control unit 54 typically
contains control logic for the particular program, an in-
struction register receiving instructions from memory
comprising commands and addresses, an arithmetic unit in two-
way communication with the memory in which the commands are
executed, and an address register feeding data to memory as
requested. ~he input and output units may include peripheral
equipment to translate into and from the computer language.
Other elements of computers are well known and need not be
described iIl detail.
Fig. 5 shows in flow chart form the program steps
performed in the computer of Fig. 4, or in a similar comput-
ing apparatus. When automating the method of this invention
it is desirable to set a limit on the numerical value of
changes in the coordinate point required to avoid bridging,
i.e., if a coordinate point is bridged by only a small amount
such as .02 inches, can the bridging be ignored, or must
all coordinate points be carefully free of bridging? In
practice it is nearly impossible to construct a mandrel with
an accuracy of 0.02 in., so in fact minor bridging can
usually be ignored. Thus, block 100 of Fig. 5 contains an
instruction whereby a limiting numerical value of the change
17 -
~6~0~
in a coordinate point to avoid bridging is determined ana
stored in the computer's memory. It may be that the limiting
value is zero, i.e., no bridging is permitted. Another
approach, not shown in Figure 5, is to set a maximum number
of iterations of the method, and count each iteration, stop-
ping the program when the maximum number has been reached.
Some points may still be bridged, but the majority or at
least the largest in magnitude will have been corrected.
Likewise it may be desirable to ignore bridging by the first
fiber layer if the next layer is not bridged.
After setting the limiting numerical value of
changes in the coordinate point, the program proceeds to
block 102 where a storage register in the computer memory is
set to zero at the be~inning of each iteration of the program
for the entire mandrel. In this storage register is stored,
as the program progresses, the numerical value of the maximum
coordinate point change required to avoid bridging during one
iteration. Ultimately the value in the storage register
will be compared with the limiting value set by the instruc-
tion in block 100 to determine if the program is finished,i.e., no ~ridging has occurred, or the largest brldged coor-
dinate point is less than the limiting value, or another
iteration is necessary because the change in a coordinate
point to avoid bridging was greater than the limiting value.
The program then selects the first coordinate point,
block 104, and determines in block 106 from the design
data for the blade stored in the computer memory the numerical
value of the coordinate point~ i.e., the distance of the
selected coordinate point from the wi~ding axis. The next
step, block 108, is to compute the numerical value of the
coordinate point required to avoid bridging, i.e., compute
points Al or Cl, and B2 or B4, and also points A2 or C2,
- 18 -
~16~4
and D2 and D4, as in Fig. 2, interpolating between other
coordinate points as necessary, and then as in Fig. 3 compute
the distance the coordinate point must be from the winding
axis to avoid bridging. The design data for the coordinate
point in block 106 is then compared by the instruction in
block 110 with the value of the coordinate point to avoid
bridging performed in block 108, and if the design value is
less than the computed value, bridging will occur and the
program branches to block 112. Block 112 instructs the pro-
gram to change the design value of the coordinaLe point tothe computed value necessary to avoid bridging. The ne~t
instruction in block 114 compares the numerical value of the
change in the coordinate point to avoid bridging with the
value stored in memory by virtue of the instruction in block
102~ Since block 102 sets a storage register to zero during
each iteration, and since the first coordinate point bridged
will cause the numerical value of the change in the coordinate
point necessary to avoid bridging to be greater than zero,
this value will always be stored. For subsequent bridged
coordinate points, the numerical value of coordinate point
change may or may not be greater than the value in the storage
register. Consequently, if the change in a subsequent coor-
dinate point is greater than that in the storage register,
the program branches to block 116 which instructs the program
to store the new coordinate point change value. Ultimately
for each iteration the storage register will contain a value
equal to the largest numerical change in any coordinate point.
If the change in the coordinate point is less than the value
in the storage register, the instruction in block 116 will be
by~passed, and the program will proceed to the instruction
in block 118. Likewise if the coordinate point is not
bridged, the program will proceed from block 110 to block 118.
,~,,~ '' .
. -- 19 --
The instruction in block 118 requires an iteration of
the instructions from block ~04, so the program returns to
block 104 and selects the next coordinate point along the
same station. When all coordinate points along a station
have been examined for bridging, the program proceeds to
block 120 where it is instructed to repeat the entire pro-
cess for every station except the first and last. After
every coordinate point on the blade, except those on the
first and last stations9 has been examined for bridging,
the program proceeds to the instruction in block 122 where
the value of the largest change in any coordinate point
during the entire iteration, stored in the register, is
compared with the limit set by the instruction in block 100.
If the largest change in any coordinate point s less than
the limit, the program is ended. However, if the largest
change in any coordinate point is greater than the limit,
the program proceeds to the instruction in block 124 which
requires a return to block 102 and another iteration of the
process for the entire blade. As noted previously, a limit
may be set ~or the number of iterations.
While the winding path of the fibers has been described
as though it ~as a plane, this is not the only possible geomet-
ric model for the winding path. It is possible to define the
winding path by other geometric constructions, and therefore,
the invention is not limited to the particular coordinate system
used, or the particular geometric model used to define the
fiber winding path.
While the invention has been described with respect
to a rotor blade, it is also applicable to any contoured shape
where it is desired to avoid the bridging problem when the
- 20 -
~,~ ,.,
~.G5~4
contoured shape is wound with any material. It is also
apparent that changes and modifications may be made to
the invention without departing from its scope as defined
by the following claims.
.~ - 21 -
