NASA CASE NO.

PRINT FIG. 1

NOTICE

LAR 14004-1

The invention disclosed in this document resulted from research in aeronautical and

space activities performed under programs of the National Aeronautics and Space

Administration. The invention is owned by NASA and is, therefore, available for

licensing in accordance with the NASA Patent Licensing Regulation (14 Code of

Federal Regulations 1245.2).

To encourage commercial utilization of NASA-owned inventions, it is NASA policy to

grant licenses to commercial concerns. Although NASA encourages nonexclusive

licensing to promote competition and achieve the widest possible utilization, NASA

will provide the necessary incentive to the licensee to achieve early practical

application of the invention.

Address inquiries and all applications for license for this invention to NASA Patent

Counsel, Langley Research Center, Code 143, Hampton, Virginia 23681-0001.

Serial No.: 07/647,097

01-29/91 LaRC

(NASA-Case-LAR-I4004-1) NUMERICAL

CONTROL FABRICATION TECHNIQUE FOR

DYNAMIC COMPOSITE MODELS Patent

App|ication (NASA) IIp

N93-19024

Unclas

83/63 0149923
NUMERICAL CONTROL FABRICATION TECHNIQUE 

FOR DYNAMIC COMPOSITE MODELS 

NASA Case No. LAR 14004-1 

AWARDS ABSTRACT 

The prior art of fabricating composite dynamic models and parts is a long and tedious process 

that involves three steps. First, a wooden pattern is made using a series of templates and handcarving techniques. Next, a hand-laid fiberglass mold is created. This second step of creating the 

fiberglass mold involves three sub-steps: (a) applying to the wooden pattern a series of alternating 

layers of resin and fiberglass cloth; (b) breaking the wooden pattern apart; and (c) removing and 

discarding the wooden pattern leaving a hard fiberglass shell or mold. In the final step, the 

fiberglass mold is filled with another series of resin and fiberglass layers, and any specified 

hardware is attached. Aside from being tedious and time-consuming, the prior art suffers from 

another serious drawback. In general, dynamic models used in simulating how a vehicle or aircraft 

will respond in actual situations must necessarily meet strict tolerance specifications for the tests 

to yield realistic results. Because by using the prior art the model is entirely crafted by hand, it is 

often difficult to achieve accuracy within the desired tolerance specifications. 

In the present method of fabricating an article such as a dynamic model or a part thereof, 

a computer-driven machining means, such as a numerically controlled machine, is used to cut a 

core material, such as a rigid foam, into a desired shape and to a size specification that is slightly 

smaller than the final size desired for the article. Alternating layers of a polymer resin such as 

polyester and a reinforcing fabric such as fiberglass cloth are then applied to the surface of the core 

material, causing a build-up of layers of polymer resin and reinforcing fabric to a point at which the 

item being fabricated is oversized from that desired. Finally, a computer-driven machining means 

is used to cut the article being fabricated to exact size and shape specifications, leaving a desired 

thickness of reinforcing material. 

The present invention differs significantly from the prior art. Because the hand-carving of a 

wooden pattern is replaced by cutting a pattern with a computer-driven machining means, the 

present invention is far less time consuming and much more accurate in meeting tolerance 

specifications. Also, when two halves of an article are created and then bonded together to form 

a whole, greater symmetry can be achieved with the present invention because the same computer 

program is used to cut both halves. Furthermore, unlike the prior art, the pattern upon which the 

reinforcing fabric is laid is retained as part of the model and not discarded. 

Inventor: 

Address: 

Employer: 

John B. Kovtun 

103 Warehouse Course 

Yorktown. VA 23692 

SS: 

NASA 

- 

LaRC 

lnitial Evaluator: John Powell 

Serial No.: 071647,097 

Filed: 01 -29-91 
& .'/_,y/tc-'r/

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LAR 14004-1 -1- PATENT APPLICATION

NUMERICAL CONTROL FABRICATION TECHNIQUE

FOR DYNAMIC COMPOSITE MODELS

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Origin of the Invention

The invention described herein was made by an employee of the

United States Government and may be manufactured and used by or

for the Government of the United States of America for governmental

purposes without the payment of any royalties thereon or therefore.

Background of the Invention

1 Field of the Invention

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This invention relates to a method for fabricating articles. In

particular, the process involves manufacturing composite materials

consisting essentially of a core material and resins and reinforcing

fabric by using a computer-driven machining means and hand-laying

techniques.

1 Description of the Prior Art

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The prior art of fabricating composite dynamic models and parts

is a long and tedious process that involves three steps. First, a

wooden pattern is made using a series of templates and hand-carving

techniques. Next, a hand-laid fiberglass mold is created. This second

step of creating the fiberglass mold involves three sub-steps: (a)

applying to the wooden pattern a series of alternating layers of resin

and fiberglass cloth; (b) breaking the wooden pattern apart; and (c)

removing and discarding the wooden pattern leaving a hard fiberglass
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LAR 14004-1 -2-

shell or mold. In the final step, the fiberglass

another series of resin and fiberglass layers,

hardware is attached.

PATENT APPLICATION

mold is filled with

and any specified

Aside from being tedious and time-consuming, the prior art suffers

from another serious drawback. In general, dynamic models used in

simulating how a vehicle or aircraft will respond in actual situations

must necessarily meet strict tolerance specifications for the tests to

yield realistic results. Because by using the prior art the model is

entirely crafted by hand, it is often difficult to achieve accuracy within

the desired tolerance specifications.

U.S. Patent 4,150,084 (Arenas) uses a process of superposing a

model with a woven reinforcing fabric. Once the reinforcing fabric

hardens, the model is removed, thereby creating a mold. Resin with

or without fiberglass reinforcement is then cast into the mold.

U.S. Patent 4,687,691 (Ka_ discloses a method of fabricating

airplane composite components. The invention uses a foam core

surrounded by resin impregnated fibers. The improvement in Kavis

the joining of foam sheets by aligning a layer of honeycomb such that

its cells are perpendicular to two layers of sheet foam, thereby

improving shear strength.

The present invention differs from the prior art. Because

the hand-carving of a wooden pattern is replaced by cutting a pattern

with a computer-driven machining means, the present invention is far

less time consuming and much more accurate in meeting tolerance

specifications. Also, when two halves of an article are created and

then bonded together to form a whole, greater symmetry can be

achieved with the present invention because the same computer

program is used to cut both halves. Furthermore, unlike the prior art,

the pattern upon which the reinforcing fabric is laid is retained as part

of the model and not discarded. Although the prior art anticipates the
LAR 14004-1 -3- PATENT APPLICATION

use of a foam core reinforced by fiberglass and resin, the present

invention pertains to a combination of steps in a fabrication process,

not the use of a foam core itself.

5 Summary of the Invention

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An object of the present invention is to provide a method of

manufacturing articles, dynamic models and dynamic model parts

which involves using a computer-driven machining means, thereby

being more accurate and less time consuming than previous methods.

A further object of the present invention is to provide a method of

manufacturing articles, dynamic models and dynamic model parts

which yields greater symmetry than previous methods.

A further object of the present invention is to provide a method of

manufacturing articles, dynamic models and

which uses a core material that is retained as

A further object of the present invention is

manufacturing articles, dynamic models and

which yields a core material strengthened with

reinforcing fabric.

dynamic model parts

part of the model.

to provide a method of

dynamic model parts

a desired thickness of

To meet the foregoing and additional objects, a method of

manufacturing articles such as dynamic models and dynamic model

parts has been developed. A computer-driven machining means, such

as a numerically controlled machine, is used to cut a core material

into a desired shape and to a size specification that is slightly smaller

than the final size desired for the article. It has been found beneficial

to use foam as a core material, especially rigid foam such as

polyurethane. Alternating layers of polyester resin and a reinforcing

fabric are then applied to the surface of the core material, causing a

build-up of layers of polyester resin and reinforcing fabric to a point
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LAR 14004-1 -4- PATENT APPLICATION

at which the item being fabricated is oversized from that desired.

Polyester resin has been especially successful, although epoxy resin

and silicon will also produce satisfactory results. Similarly, fiberglass

cloth has been preferred as a reinforcing fabric, but other reinforcing

fabrics made from linen, cotton, Kevlar® aromatic polyamide and

graphite will also be satisfactory. Finally, a computer-driven

machining means is used to cut the article being fabricated to exact

size and shape specifications, leaving a desired thickness of

reinforcing material.

Brief Description of the Drawings

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The drawings illustrate the present method being used with a

numerically controlled machine to fabricate a fuselage for a dynamic

airplane model.

FIG. 1 illustrates a rough-cut blank of commercial polyurethane

foam 10 bolted to a numerical control (NC) machine table 11;

FIG. 2 shows the rough-cut blank of commercial polyurethane

foam 10 after having been cut to a finished undersized core 12;

FIG. 3 shows a layer of fiberglass and resin build-up 13 applied to

a finished undersized core 12;

FIG. 4 shows a finished machined exterior surface 14 after the

fiberglass and resin build-up 13 has been machined to exact size and

shape specifications, leaving a fiberglass skin of specified thickness;

FIG. 5 shows that extra machining may be done to meet article

design specifications, such as a slot for a wing spar 15;

FIG. 6 shows a jig 16 which is constructed to rotate the workpiece

180 °, and to locate it precisely on the NC table 11 by drilling pin holes

17 into the jig 16 and aligning the pin holes 17 with the set pins 18 of

the NC table 11;
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LAR 14004-1 -5- PATENT APPLICATION

FIG. 7 shows a finished core 19 after its has been excavated with

,the NC machine;

FIG. 8 shows that various slots and pockets can be machined for

locating hardware, such as a pocket for a balance mount 20 and a

hole for an alignment dowel 21; and

FIG. 9 shows a completed fuselage 22 after the process is

reversed and repeated for the opposite half of a fuselage core, and

two finished cores 17 are bonded together.

10 Detailed Description of the Invention

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The present invention can be explained with reference to the

drawings. The drawings illustrate the new method applied to the

fabrication of a model airplane fuselage.

As illustrated in FIG. 1, fabrication of the fuselage begins with a

rough-cut blank of commercial polyurethane foam 10 large enough to

encompass half of the fuselage structure: right, left, top, or bottom.

For constructing dynamic model aircraft, 4 lb. density polyurethane

foam has been found especially preferred. The rough-cut blank of

commercial polyurethane foam 10 is bolted to a numerical control (NC)

table 11, and a computer-generated program is operated to rough-cut

the blank to a desired shape for the exterior fuselage surface. The

rough-cut blank of commercial polyurethane foam 10 is generally cut

to be undersized by an amount equal to the thickness of a fiberglass

skin of specified thickness as shown in FIG. 4 on the finished

machined exterior surface 14. The finished undersized core 12 is

shown in FIG. 2. In a particular application, the surface of the

fuselage was cut to thirty-three thousandths of an inch below the size

desired.
LAR 14004-1 -6- PATENT APPLICATION

Next, as shown in FIG. 3, alternating layers of resin and

reinforcing fabric, preferably fiberglass cloth, are laid onto the cut

exterior surface of the finished undersized core 12 to create a

fiberglass cloth and resin build-up 13. Polyester resin has been found

5 to be preferred to other types of resins because it sets-up more

quickly. Applying a dry layer of fiberglass cloth over the surface of

the core material is preferred. Then, polyester resin is painted onto

the surface of the fiberglass cloth with a paint brush and smoothed

with a plastic squeegee. When the polyester resin becomes tacky, but

10 before it sets, another layer of fiberglass cloth is laid over the

polyester resin and all the wrinkles are smoothed out of the fiberglass

cloth. A successful way to remove wrinkles has been to use a

squeegee. This process is repeated until the desired number of layers

of fiberglass cloth and polyester resin are applied. It has been found

15 that, after cutting the surface of the core material thirty-three

thousandths of an inch below the final size desired, four layers are

preferred. Four layers of fiberglass cloth and polyester resin build

the surface of the fuselage back up thirty-thousandths of an inch, or

three-thousandths of an inch below the desired size of the finished

20 fuselage surface. Then, about twenty-thousandths of an inch of resin

is applied to the last layer of fiberglass cloth. Machining the resin

layer only, not the layers of resin and fiberglass cloth, is preferred and

results in a very hard finished surface. Once the final twentythousandths of an inch layer of polyester resin has hardened,

25 seventeen-thousandths of an inch of the final layer of resin is cut off

using the NC machine. This process leaves the finished machined

exterior surface 14 of proper size and shape. Extra machining can

also be done at this point to create slots for wing spars or stabilizers

and pockets for hardware or any other needed items. FIG. 5

30 illustrates where the typical slot for a wing spar 15 could be machined.
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LAR 14004-1 -7- PATENT APPLICATION

After one side of the half of the fuselage is completed, a jig 16 is

constructed to rotate the workpiece 180°. The construction of jigs is

well known to those skilled in the art. Generally, it is beneficial to

construct the jig 16 with a heavier density of foam than was used to

construct the fuselage. It has been found that using a 15lb. density

polyurethane foam is preferred when constructing the fuselage from

41b. foam. One way to construct a jig 16 has been to cut the surface

of a blank sheet of 15 lb. polyurethane foam to approximately fit the

contour of the fuselage. Then, a layer of tape is placed over the

model fuselage surface. The tape is sanded and washed with solvent,

such as acetone or alcohol, and then body putty is used to pot the jig

to the surface of the fuselage. Pin holes 17 are then drilled into the

jig at positions which match the location of set pins 18 of the NC table

11. The workpiece is then rotated 180°, and the drilled pin holes 17

in the jig 16 are used to align the workpiece precisely in the proper

location.

Another computer program is executed to excavate the core of the

workpiece to produce a shell. The thickness of the shell is chosen in

advance for compatibility with the fiberglass skin to furnish the

required strength, weight, and internal volume. FIG. 7 shows the

excavated core 19. During operations from this side, slots and

pockets can also be machined for bulkheads, firewalls, sting or

balance attachments mounts, hard points for locating pins, or other

hardware. FIG. 8 shows the possible locations for a pocket for a

balance mount 20 and a hole for an alignment dowel 21.

Finally, the process is inverted and repeated to fabricate the other

half of the fuselage. All hardware, stiffeners, and internal structures

are fitted and installed in one half of the excavated core 19, and then

the two halves are located and bonded together. The completed

fuselage 22 is shown in FIG. 9. The fuselage is then sanded and
LAR 14004-1 -8-

painted and ready for installation of

landing gear, or other attachments.

wings,

PATENT APPLICATION

stabilizers, canards,

What is claimed ad new and desired to be secured for Letters

Patent is:
LAR 14004-1 PATENT APPLICATION

NUMERICAL CONTROL FABRICATION TECHNIQUE

FOR COMPOSITE DYNAMIC MODELS

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Abstract of the Disclosure

In a method of fabricating an article such as a dynamic model

or a part thereof, a computer-driven machining means, such as a

numerically controlled machine, is used to cut a core material such as

a rigid foam into a desired shape and to a size specification that is

slightly smaller than the final size desired to the article. Alternating

layers of a polymer resin such as polyester and a reinforcing fabric

such as fiberglass cloth are then applied to the surface of the core

material, causing a build-up of layers of polymer resin and reinforcing

fabric to a point at which the item being fabricated is oversized from

that desired. Finally, acomputer-driven machining means is used to

cut the article being fabricated to exact size and shape specifications,

leaving a desired thickness of reinforcing material.
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FIG.7 FIG.8 FIG.9