Carve your own cowl
[[email protected]]
Control Line Aerobatics Bob Hunt
You can achieve a perfect air-intake opening by gluing to the
uncarved cowl a piece of 1/32 plywood that is cut to the desired
opening shape.
The internal parts of the front end of Bob’s Classic Caprice.
Notice the torque-box plate and diagonal pieces in the tank
compartment to which it is bolted.
ONE OF THE challenges in building a CL
Precision Aerobatics (Stunt) model (or any
other type of model for that matter) is
achieving a neat and clean air-intake-opening
shape in the cowling and ensuring that it will
stay looking neat and clean throughout the life
of the model.
The nose is a “high traffic” area; it gets a
lot of handling and is prone to minor damage
from that handling.
Getting a crisp, defined line at the cowl air
intake can be frustrating, because balsa is
generally a soft material and does not easily
hold an “edge.” I’ve come up with a method
that works for me to get this area looking the
way I want it to and then keeping it looking
good.
My models generally feature molded
fuselage shells on both top and bottom, but I
still rely on the tried-and-true method of
carving the intricate compound-curve
contours of the cowl from a solid (but light)
balsa block. I usually make a side-view
template of the cowling shape and then use
that template to mark the cowl shape on the
balsa block. I use a band saw to cut the sideview
shape, and I make certain to leave a little
extra all around for custom-fitting to the
fuselage.
Before attaching the cowl block blank to
the fuselage, I accurately clamp the spinner to
the nose ring. At this point I’ve already made
the top balsa shell flow perfectly into the
shape of the spinner and can simply match the
spinner to the top shell, to ensure proper
location on the nose ring.
The clamp I use is made from a piece of
1/2 x 3/8-inch maple engine-mount stock. I drill
a 1/4-inch-diameter hole in the center of that
piece and place it behind the nose ring. I can
then use a piece of 1/4-28 threaded rod and a
couple of 1/4-28 nuts to clamp the spinner
backplate to the nose ring.
Make sure that the nuts are tightened
securely. You don’t want the spinner to shift
during carving and sanding!
Once the cowl block is properly dry-fit to
the fuselage, I use a few “dots” of aliphatic
resin (yellow woodworker’s glue),
strategically placed around the mating
surfaces between the cowl block and the cowl
blank, to lightly secure the cowl to the
fuselage for carving. This is called “tackgluing.”
Be sure to let the tacked spots dry
thoroughly before you begin the sanding and
carving process!
May 2011 129
Installing a 1/32 plywood torque-box plate in the bottom of the tank
compartment prevents the engine’s torque from eventually
twisting the fuselage and cracking the wing/fuselage joint.
After carving and sanding, the plywood plate can be “opened”
with a rotary hand tool fitted with a drum sander. A thin, rigid
ring maintains the shape of the opening throughout the life of
the model.
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:14 AM Page 129
130 MODEL AVIATION
with a drum sander attachment to grind
through the face of the 1/32 plywood airintake-
opening plate.
Do this at the center of the plate and then
carefully open the plate until a consistent
1/16-inch rim of plywood is left on the front
of the cowl. This plywood rim will ensure
that the opening will retain its shape and
edge during the finishing phase and
throughout the life of the model.
Once the opening is cut and trimmed to
final shape, you can use round sanding
drums (such as the type used on rotary
spindle sanders) to blend the inside lip of the
cowl opening to the hollowed wall of the
cowling. I try to make the finished wall
approximately 3/16 inch thick. If it’s any
thinner, the cowl might be too fragile; it
might break under normal use.
Remove the spinner clamp and the
spinner. Mount your engine and carefully
measure for the required openings for the
exhaust outlet, glow-plug access hole (You
reading this, Buddy?), air-outlet holes, and
cowl hold-down access holes, as required. A
BMJR Model Products
• Original Design by: Jerry Stoloff, 1944
• 46" wingspan, 307 sq" wing area
• For 1/2A or Electric Texaco
• Original design by JASCO, 1952
• 32" wingspan, 170 sq” wing area
• For 1/2A Early Nostalgia
Box 1210 • Sharpes, FL 32959-1210
321-537-1159 • www.BMJRModels.com
$9200
+ postage
Send $2.00 for 2011 22 page catalog or go to www.bmjrmodels.com
STREAK SWAMI
$3600
+ postage
- SECURE SHOPPING WITH OUR ONLINE CATALOG -
www.fiberglassspecialtiesinc.com
[email protected]
Phone (479) 359-2429 Fax (479) 359-2259
Hours: Monday - Friday 9 to 5 CST
15715 Ashmore Dr., Garfield, Arkansas 72732
LARGEST
COLLECTION OF
EPOXY GLASS
COWLS & WHEEL
PANTS IN THE WORLD!
SINCE
1977!
The next step is to sand the cowling sides
to fit flush with the fuselage sides and with
the bottom block or bottom molded shell,
depending on which you use. Do not do any
“rounding,” or contouring at this time. Only
flush the sides of the cowl with the fuselage.
When everything fits flush, measure from
side to side on the bottom of the cowl block.
Scribe a centerline from the nose ring to the
aft end of the cowl using a ball-point pen.
Determine what shape you want the airintake
opening to be, and then cut a piece of
1/32 plywood to that shape—plus 1/16 inch all
around in plan form. Put a centerline on this
piece as well.
Determine where this piece should be
positioned on the front of the cowl, to give
you the proper location top to bottom of the
air-intake hole. Coat the back of the
plywood piece with medium-viscosity CA
glue and attach it to the front of the cowl
block. An accompanying photo depicts this
procedure.
Now for the fun part. Carve and sand the
cowling to fit the contours of the fuselage,
and smoothly blend the front of the block
into the contour of the spinner. Take your
time and use a variety of shapes of sanding
tools to achieve a perfectly shaped part.
This is where the art of model building is
evident. You can greatly enhance the
appearance of your model by learning to
carve and shape proficiently.
Use the Perma-Grit tools I highlighted in
the March column to smoothly blend the
hardwood areas of the plywood doublers to
the soft surrounding balsa. Try to see the
shape you want to achieve in your mind, and
then don’t stop shaping until the part
matches that image.
Once you are satisfied with the carving
and sanding job, carefully “pop” the tackglued
spots apart (you might need to
carefully insert a single-edge razor blade
between the fuselage and the cowl block to
separate the two) and remove the cowling.
The next step is to use an X-Acto router
and gouge blades to hollow the cowl block.
Before hollowing too much at the nose of
the cowl block, use a rotary hand tool fitted
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:15 AM Page 130
photo depicts how a typical finished cowling
should look.
Notice that the plywood rim defines the
opening well. This idea can be expanded to
achieve perfect fits between other parts on
the model.
For instance, if you want to mate an
airfoiled fin to the top of a fuselage block, you
need only make a template of the base of the
fin and tack-glue it to the fuselage block prior
to carving and sanding the block to its final
contour. The template will yield a “land” onto
which the fin will fit nicely.
To make the fit perfect, remove the finbase
template from the fuselage after carving
and sanding, and tack-glue it to the base of the
fin. Sand the base of the fin to match the
template, and then remove the template from
the fin’s base. The fin should match the land
on the top of the fuselage.
Think a bit and you will find many uses
for this technique in your building.
Torque-Box Plate: Since we are focusing
on the front of the airplane, I’ll pass along
another tip that will yield a stiffer and
more vibration-resistant nose area.
Many models have been designed with
open tank-compartment areas. They have
sides and a top in the tank area, but no bottom.
Because of this, the twisting moment induced
by the running engine goes all the way from
the power plant to the wing LE. That can
cause the wing-to-fuselage joint to crack at the
fillet.
I got tired of this happening to my aircraft
long ago and developed a system that forms a
rigid box after the tank is installed.
I install diagonal pieces in the four corners
at the bottom of the tank compartment. These
pieces are big enough to allow me to drill a
hole at each corner and install 4-40 blind nuts
into the diagonal pieces from above.
The diagonal plywood pieces are recessed
1/32 inch into the tank box. This allows me to
cut a piece of 1/32 plywood that will fit snugly
between the fuselage sides in that area and be
bolted down tight after the tank is installed.
There are two photos that should
clarify this process. The tank is removable
using this “torque-box plate” technique,
and the integrity of the front end is assured.
I have this system in my 10-year-old
Caprice and there are no signs of cracks at the
LE, even after hundreds of flights. Be certain
to coat the 1/32 plywood plate with epoxy, so
that the inevitable, unintentional, bath of raw
fuel doesn’t rot it away. For that same reason,
coat the entire engine bay and tank
compartment with epoxy.
I use and recommend Z-Poxy Finishing
Resin for this operation. A thin coat is all that’s
required.
Until next time, fly Stunt! MA
Sources:
Precision Aerobatics Model Pilots Association
www.control-line.org
Z-Poxy Finishing Resin:
Super Glue Corporation
(800) 538-3091
www.supergluecorp.com
May 2011 131
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:15 AM Page 131
Edition: Model Aviation - 2011/05
Page Numbers: 129,130,131
Edition: Model Aviation - 2011/05
Page Numbers: 129,130,131
Carve your own cowl
[[email protected]]
Control Line Aerobatics Bob Hunt
You can achieve a perfect air-intake opening by gluing to the
uncarved cowl a piece of 1/32 plywood that is cut to the desired
opening shape.
The internal parts of the front end of Bob’s Classic Caprice.
Notice the torque-box plate and diagonal pieces in the tank
compartment to which it is bolted.
ONE OF THE challenges in building a CL
Precision Aerobatics (Stunt) model (or any
other type of model for that matter) is
achieving a neat and clean air-intake-opening
shape in the cowling and ensuring that it will
stay looking neat and clean throughout the life
of the model.
The nose is a “high traffic” area; it gets a
lot of handling and is prone to minor damage
from that handling.
Getting a crisp, defined line at the cowl air
intake can be frustrating, because balsa is
generally a soft material and does not easily
hold an “edge.” I’ve come up with a method
that works for me to get this area looking the
way I want it to and then keeping it looking
good.
My models generally feature molded
fuselage shells on both top and bottom, but I
still rely on the tried-and-true method of
carving the intricate compound-curve
contours of the cowl from a solid (but light)
balsa block. I usually make a side-view
template of the cowling shape and then use
that template to mark the cowl shape on the
balsa block. I use a band saw to cut the sideview
shape, and I make certain to leave a little
extra all around for custom-fitting to the
fuselage.
Before attaching the cowl block blank to
the fuselage, I accurately clamp the spinner to
the nose ring. At this point I’ve already made
the top balsa shell flow perfectly into the
shape of the spinner and can simply match the
spinner to the top shell, to ensure proper
location on the nose ring.
The clamp I use is made from a piece of
1/2 x 3/8-inch maple engine-mount stock. I drill
a 1/4-inch-diameter hole in the center of that
piece and place it behind the nose ring. I can
then use a piece of 1/4-28 threaded rod and a
couple of 1/4-28 nuts to clamp the spinner
backplate to the nose ring.
Make sure that the nuts are tightened
securely. You don’t want the spinner to shift
during carving and sanding!
Once the cowl block is properly dry-fit to
the fuselage, I use a few “dots” of aliphatic
resin (yellow woodworker’s glue),
strategically placed around the mating
surfaces between the cowl block and the cowl
blank, to lightly secure the cowl to the
fuselage for carving. This is called “tackgluing.”
Be sure to let the tacked spots dry
thoroughly before you begin the sanding and
carving process!
May 2011 129
Installing a 1/32 plywood torque-box plate in the bottom of the tank
compartment prevents the engine’s torque from eventually
twisting the fuselage and cracking the wing/fuselage joint.
After carving and sanding, the plywood plate can be “opened”
with a rotary hand tool fitted with a drum sander. A thin, rigid
ring maintains the shape of the opening throughout the life of
the model.
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:14 AM Page 129
130 MODEL AVIATION
with a drum sander attachment to grind
through the face of the 1/32 plywood airintake-
opening plate.
Do this at the center of the plate and then
carefully open the plate until a consistent
1/16-inch rim of plywood is left on the front
of the cowl. This plywood rim will ensure
that the opening will retain its shape and
edge during the finishing phase and
throughout the life of the model.
Once the opening is cut and trimmed to
final shape, you can use round sanding
drums (such as the type used on rotary
spindle sanders) to blend the inside lip of the
cowl opening to the hollowed wall of the
cowling. I try to make the finished wall
approximately 3/16 inch thick. If it’s any
thinner, the cowl might be too fragile; it
might break under normal use.
Remove the spinner clamp and the
spinner. Mount your engine and carefully
measure for the required openings for the
exhaust outlet, glow-plug access hole (You
reading this, Buddy?), air-outlet holes, and
cowl hold-down access holes, as required. A
BMJR Model Products
• Original Design by: Jerry Stoloff, 1944
• 46" wingspan, 307 sq" wing area
• For 1/2A or Electric Texaco
• Original design by JASCO, 1952
• 32" wingspan, 170 sq” wing area
• For 1/2A Early Nostalgia
Box 1210 • Sharpes, FL 32959-1210
321-537-1159 • www.BMJRModels.com
$9200
+ postage
Send $2.00 for 2011 22 page catalog or go to www.bmjrmodels.com
STREAK SWAMI
$3600
+ postage
- SECURE SHOPPING WITH OUR ONLINE CATALOG -
www.fiberglassspecialtiesinc.com
[email protected]
Phone (479) 359-2429 Fax (479) 359-2259
Hours: Monday - Friday 9 to 5 CST
15715 Ashmore Dr., Garfield, Arkansas 72732
LARGEST
COLLECTION OF
EPOXY GLASS
COWLS & WHEEL
PANTS IN THE WORLD!
SINCE
1977!
The next step is to sand the cowling sides
to fit flush with the fuselage sides and with
the bottom block or bottom molded shell,
depending on which you use. Do not do any
“rounding,” or contouring at this time. Only
flush the sides of the cowl with the fuselage.
When everything fits flush, measure from
side to side on the bottom of the cowl block.
Scribe a centerline from the nose ring to the
aft end of the cowl using a ball-point pen.
Determine what shape you want the airintake
opening to be, and then cut a piece of
1/32 plywood to that shape—plus 1/16 inch all
around in plan form. Put a centerline on this
piece as well.
Determine where this piece should be
positioned on the front of the cowl, to give
you the proper location top to bottom of the
air-intake hole. Coat the back of the
plywood piece with medium-viscosity CA
glue and attach it to the front of the cowl
block. An accompanying photo depicts this
procedure.
Now for the fun part. Carve and sand the
cowling to fit the contours of the fuselage,
and smoothly blend the front of the block
into the contour of the spinner. Take your
time and use a variety of shapes of sanding
tools to achieve a perfectly shaped part.
This is where the art of model building is
evident. You can greatly enhance the
appearance of your model by learning to
carve and shape proficiently.
Use the Perma-Grit tools I highlighted in
the March column to smoothly blend the
hardwood areas of the plywood doublers to
the soft surrounding balsa. Try to see the
shape you want to achieve in your mind, and
then don’t stop shaping until the part
matches that image.
Once you are satisfied with the carving
and sanding job, carefully “pop” the tackglued
spots apart (you might need to
carefully insert a single-edge razor blade
between the fuselage and the cowl block to
separate the two) and remove the cowling.
The next step is to use an X-Acto router
and gouge blades to hollow the cowl block.
Before hollowing too much at the nose of
the cowl block, use a rotary hand tool fitted
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:15 AM Page 130
photo depicts how a typical finished cowling
should look.
Notice that the plywood rim defines the
opening well. This idea can be expanded to
achieve perfect fits between other parts on
the model.
For instance, if you want to mate an
airfoiled fin to the top of a fuselage block, you
need only make a template of the base of the
fin and tack-glue it to the fuselage block prior
to carving and sanding the block to its final
contour. The template will yield a “land” onto
which the fin will fit nicely.
To make the fit perfect, remove the finbase
template from the fuselage after carving
and sanding, and tack-glue it to the base of the
fin. Sand the base of the fin to match the
template, and then remove the template from
the fin’s base. The fin should match the land
on the top of the fuselage.
Think a bit and you will find many uses
for this technique in your building.
Torque-Box Plate: Since we are focusing
on the front of the airplane, I’ll pass along
another tip that will yield a stiffer and
more vibration-resistant nose area.
Many models have been designed with
open tank-compartment areas. They have
sides and a top in the tank area, but no bottom.
Because of this, the twisting moment induced
by the running engine goes all the way from
the power plant to the wing LE. That can
cause the wing-to-fuselage joint to crack at the
fillet.
I got tired of this happening to my aircraft
long ago and developed a system that forms a
rigid box after the tank is installed.
I install diagonal pieces in the four corners
at the bottom of the tank compartment. These
pieces are big enough to allow me to drill a
hole at each corner and install 4-40 blind nuts
into the diagonal pieces from above.
The diagonal plywood pieces are recessed
1/32 inch into the tank box. This allows me to
cut a piece of 1/32 plywood that will fit snugly
between the fuselage sides in that area and be
bolted down tight after the tank is installed.
There are two photos that should
clarify this process. The tank is removable
using this “torque-box plate” technique,
and the integrity of the front end is assured.
I have this system in my 10-year-old
Caprice and there are no signs of cracks at the
LE, even after hundreds of flights. Be certain
to coat the 1/32 plywood plate with epoxy, so
that the inevitable, unintentional, bath of raw
fuel doesn’t rot it away. For that same reason,
coat the entire engine bay and tank
compartment with epoxy.
I use and recommend Z-Poxy Finishing
Resin for this operation. A thin coat is all that’s
required.
Until next time, fly Stunt! MA
Sources:
Precision Aerobatics Model Pilots Association
www.control-line.org
Z-Poxy Finishing Resin:
Super Glue Corporation
(800) 538-3091
www.supergluecorp.com
May 2011 131
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:15 AM Page 131
Edition: Model Aviation - 2011/05
Page Numbers: 129,130,131
Carve your own cowl
[[email protected]]
Control Line Aerobatics Bob Hunt
You can achieve a perfect air-intake opening by gluing to the
uncarved cowl a piece of 1/32 plywood that is cut to the desired
opening shape.
The internal parts of the front end of Bob’s Classic Caprice.
Notice the torque-box plate and diagonal pieces in the tank
compartment to which it is bolted.
ONE OF THE challenges in building a CL
Precision Aerobatics (Stunt) model (or any
other type of model for that matter) is
achieving a neat and clean air-intake-opening
shape in the cowling and ensuring that it will
stay looking neat and clean throughout the life
of the model.
The nose is a “high traffic” area; it gets a
lot of handling and is prone to minor damage
from that handling.
Getting a crisp, defined line at the cowl air
intake can be frustrating, because balsa is
generally a soft material and does not easily
hold an “edge.” I’ve come up with a method
that works for me to get this area looking the
way I want it to and then keeping it looking
good.
My models generally feature molded
fuselage shells on both top and bottom, but I
still rely on the tried-and-true method of
carving the intricate compound-curve
contours of the cowl from a solid (but light)
balsa block. I usually make a side-view
template of the cowling shape and then use
that template to mark the cowl shape on the
balsa block. I use a band saw to cut the sideview
shape, and I make certain to leave a little
extra all around for custom-fitting to the
fuselage.
Before attaching the cowl block blank to
the fuselage, I accurately clamp the spinner to
the nose ring. At this point I’ve already made
the top balsa shell flow perfectly into the
shape of the spinner and can simply match the
spinner to the top shell, to ensure proper
location on the nose ring.
The clamp I use is made from a piece of
1/2 x 3/8-inch maple engine-mount stock. I drill
a 1/4-inch-diameter hole in the center of that
piece and place it behind the nose ring. I can
then use a piece of 1/4-28 threaded rod and a
couple of 1/4-28 nuts to clamp the spinner
backplate to the nose ring.
Make sure that the nuts are tightened
securely. You don’t want the spinner to shift
during carving and sanding!
Once the cowl block is properly dry-fit to
the fuselage, I use a few “dots” of aliphatic
resin (yellow woodworker’s glue),
strategically placed around the mating
surfaces between the cowl block and the cowl
blank, to lightly secure the cowl to the
fuselage for carving. This is called “tackgluing.”
Be sure to let the tacked spots dry
thoroughly before you begin the sanding and
carving process!
May 2011 129
Installing a 1/32 plywood torque-box plate in the bottom of the tank
compartment prevents the engine’s torque from eventually
twisting the fuselage and cracking the wing/fuselage joint.
After carving and sanding, the plywood plate can be “opened”
with a rotary hand tool fitted with a drum sander. A thin, rigid
ring maintains the shape of the opening throughout the life of
the model.
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:14 AM Page 129
130 MODEL AVIATION
with a drum sander attachment to grind
through the face of the 1/32 plywood airintake-
opening plate.
Do this at the center of the plate and then
carefully open the plate until a consistent
1/16-inch rim of plywood is left on the front
of the cowl. This plywood rim will ensure
that the opening will retain its shape and
edge during the finishing phase and
throughout the life of the model.
Once the opening is cut and trimmed to
final shape, you can use round sanding
drums (such as the type used on rotary
spindle sanders) to blend the inside lip of the
cowl opening to the hollowed wall of the
cowling. I try to make the finished wall
approximately 3/16 inch thick. If it’s any
thinner, the cowl might be too fragile; it
might break under normal use.
Remove the spinner clamp and the
spinner. Mount your engine and carefully
measure for the required openings for the
exhaust outlet, glow-plug access hole (You
reading this, Buddy?), air-outlet holes, and
cowl hold-down access holes, as required. A
BMJR Model Products
• Original Design by: Jerry Stoloff, 1944
• 46" wingspan, 307 sq" wing area
• For 1/2A or Electric Texaco
• Original design by JASCO, 1952
• 32" wingspan, 170 sq” wing area
• For 1/2A Early Nostalgia
Box 1210 • Sharpes, FL 32959-1210
321-537-1159 • www.BMJRModels.com
$9200
+ postage
Send $2.00 for 2011 22 page catalog or go to www.bmjrmodels.com
STREAK SWAMI
$3600
+ postage
- SECURE SHOPPING WITH OUR ONLINE CATALOG -
www.fiberglassspecialtiesinc.com
[email protected]
Phone (479) 359-2429 Fax (479) 359-2259
Hours: Monday - Friday 9 to 5 CST
15715 Ashmore Dr., Garfield, Arkansas 72732
LARGEST
COLLECTION OF
EPOXY GLASS
COWLS & WHEEL
PANTS IN THE WORLD!
SINCE
1977!
The next step is to sand the cowling sides
to fit flush with the fuselage sides and with
the bottom block or bottom molded shell,
depending on which you use. Do not do any
“rounding,” or contouring at this time. Only
flush the sides of the cowl with the fuselage.
When everything fits flush, measure from
side to side on the bottom of the cowl block.
Scribe a centerline from the nose ring to the
aft end of the cowl using a ball-point pen.
Determine what shape you want the airintake
opening to be, and then cut a piece of
1/32 plywood to that shape—plus 1/16 inch all
around in plan form. Put a centerline on this
piece as well.
Determine where this piece should be
positioned on the front of the cowl, to give
you the proper location top to bottom of the
air-intake hole. Coat the back of the
plywood piece with medium-viscosity CA
glue and attach it to the front of the cowl
block. An accompanying photo depicts this
procedure.
Now for the fun part. Carve and sand the
cowling to fit the contours of the fuselage,
and smoothly blend the front of the block
into the contour of the spinner. Take your
time and use a variety of shapes of sanding
tools to achieve a perfectly shaped part.
This is where the art of model building is
evident. You can greatly enhance the
appearance of your model by learning to
carve and shape proficiently.
Use the Perma-Grit tools I highlighted in
the March column to smoothly blend the
hardwood areas of the plywood doublers to
the soft surrounding balsa. Try to see the
shape you want to achieve in your mind, and
then don’t stop shaping until the part
matches that image.
Once you are satisfied with the carving
and sanding job, carefully “pop” the tackglued
spots apart (you might need to
carefully insert a single-edge razor blade
between the fuselage and the cowl block to
separate the two) and remove the cowling.
The next step is to use an X-Acto router
and gouge blades to hollow the cowl block.
Before hollowing too much at the nose of
the cowl block, use a rotary hand tool fitted
05sig5.QXD_00MSTRPG.QXD 3/23/11 10:15 AM Page 130
photo depicts how a typical finished cowling
should look.
Notice that the plywood rim defines the
opening well. This idea can be expanded to
achieve perfect fits between other parts on
the model.
For instance, if you want to mate an
airfoiled fin to the top of a fuselage block, you
need only make a template of the base of the
fin and tack-glue it to the fuselage block prior
to carving and sanding the block to its final
contour. The template will yield a “land” onto
which the fin will fit nicely.
To make the fit perfect, remove the finbase
template from the fuselage after carving
and sanding, and tack-glue it to the base of the
fin. Sand the base of the fin to match the
template, and then remove the template from
the fin’s base. The fin should match the land
on the top of the fuselage.
Think a bit and you will find many uses
for this technique in your building.
Torque-Box Plate: Since we are focusing
on the front of the airplane, I’ll pass along
another tip that will yield a stiffer and
more vibration-resistant nose area.
Many models have been designed with
open tank-compartment areas. They have
sides and a top in the tank area, but no bottom.
Because of this, the twisting moment induced
by the running engine goes all the way from
the power plant to the wing LE. That can
cause the wing-to-fuselage joint to crack at the
fillet.
I got tired of this happening to my aircraft
long ago and developed a system that forms a
rigid box after the tank is installed.
I install diagonal pieces in the four corners
at the bottom of the tank compartment. These
pieces are big enough to allow me to drill a
hole at each corner and install 4-40 blind nuts
into the diagonal pieces from above.
The diagonal plywood pieces are recessed
1/32 inch into the tank box. This allows me to
cut a piece of 1/32 plywood that will fit snugly
between the fuselage sides in that area and be
bolted down tight after the tank is installed.
There are two photos that should
clarify this process. The tank is removable
using this “torque-box plate” technique,
and the integrity of the front end is assured.
I have this system in my 10-year-old
Caprice and there are no signs of cracks at the
LE, even after hundreds of flights. Be certain
to coat the 1/32 plywood plate with epoxy, so
that the inevitable, unintentional, bath of raw
fuel doesn’t rot it away. For that same reason,
coat the entire engine bay and tank
compartment with epoxy.
I use and recommend Z-Poxy Finishing
Resin for this operation. A thin coat is all that’s
required.
Until next time, fly Stunt! MA
Sources:
Precision Aerobatics Model Pilots Association
www.control-line.org
Z-Poxy Finishing Resin:
Super Glue Corporation
(800) 538-3091
www.supergluecorp.com
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