CONTROL LINE AEROBATICS
Curt Contrata, 6783 Nightwind Cir., Orlando FL 32818; E-mail: [email protected]
line larger than the plans show, and sand
the LE true using a long T-bar sander.
Test the hinge-line fit to the TE of the
wing and work slowly until they mate
perfectly.
Some find it easier to true an edge by
applying a long strip of self-adhesive
sandpaper to the surface of a bench, and
then dragging the part across it. With that
method, one can use a square to ensure
that the part is sanded perpendicular to the
bench.
For flap and elevator horn clips, I have
been using basswood with great success.
It is lighter than plywood, easier to cut,
and much easier to blend into the balsa
flap. To cap the opening on the clip, I
used 1⁄64 plywood with the grain running
vertical. It is also a good idea to slap a cap
of basswood or plywood on the other end
of the flaps if they are not full span; it
really helps keep them from getting
rounded off during the finishing process.
Once true, mark a centerline on the LE
of the flap and mark all of the hinge
locations. Take some extra time as you
slot the flaps and wing for the hinges. Do
not rush this step, and make sure the
hinges are in the center of the wing and
the flap. If you have to fill a slot and
restart, do it. Even if you have to move all
the slots over a bit to get a fresh start, it
can be worth starting over.
To obtain a perfect hinge line, you
must recess the hinge barrels into a small
notch on the LE of the flap. This is easy to
do if you make a maple block the width of
a hinge with 120-grit sandpaper glued to
one side. Use this block to cut a notch in
Marvin Denny built this Dave Gierke-designed Classic-legal Novi IV. Denny photo.
L-R: Lew Woolard, Bill Schmidt, and Bud Burroughs with their fleet. Denny photo.
A way to attempt to keep your neighbors
happy is to run a hose from the exhaust
into an empty nut can with lots of holes in
the lid. Denny photo.
BOOKS COULD BE written describing
the many methods that have been
developed in an attempt to construct the
perfect flap for a competitive Stunt model.
The quest for a control surface that resists
twisting under loads while being as light
as possible never seems to end.
Consistent with the adage of simplicity
often being the best solution, it is tough to
beat a plain, old sheet-balsa flap. The
focus this month will be on detail-sanding
flaps to shape using the “rod method” and
reviewing a few other details of controlsurface
construction.
Begin by cutting the flaps just a pencil
October 2004 143
10sig5.QXD 7/23/04 9:29 am Page 143
144 MODEL AVIATION
the LE of the flaps at each hinge location,
and then with finer papers as the finishing
process progresses.
With all hinges in place and the flaps
temporarily mounted to the wing, there
should be no gaps at the hinge line. If you
run your fingers along the hinge line, the
top and bottom of the flaps should be in
alignment with the top and bottom of the
wing TE. If something is not right, fix it
before you move on.
With everything in alignment, the flaps
are ready for shaping. If you have never
tried using the “rod method” to shape your
flaps, you have no idea how easy it can be
to accurately shape flaps and elevators
from sheet balsa. With a bit of extra care
over the fragile ribs, you can even use this
method for sanding to shape built-up
control surfaces that are to be sheeted.
The process starts with the part laying
flat on a work surface with one metal rod
placed against the LE and a thinner metal
rod placed at the TE. With the sizes of the
rods determined by the desired thickness
of the edges on the finished part, you use a
sanding block to sand the part flush with
the two metal rods.
That sounds simple, but there is a little
more to it than that. To sand the part to
shape without a warp, it will have to be
completely sanded on one side before you
turn it over to shape the other side. Since
the part is completely shaped with a flat
sanding block, obtaining a perfect finish
will be much easier.
For this example, I will use 3⁄8 sheet
balsa to form a flap with a 3⁄8-inch-thick
LE and a 1⁄8-inch-thick TE. The rod at the
LE will be 3⁄8 inch in diameter, and the rod
at the TE will be half the thickness of the
wood plus half the desired TE final
thickness. Half of the 3⁄8-inch wood is 3⁄16
inch, plus half of the 1⁄8-inch final
thickness, or 1⁄16 inch, equals 1⁄4 inch. Or,
3⁄16 inch + 1⁄16 inch = 1⁄4 inch.
With the part flat on the work surface,
place the 3⁄8-inch-diameter rod at the LE
and the 1⁄4-inch-diameter rod along the TE.
Shape the part using a sanding block with
80-grit paper. Go lightly and let the
sandpaper do all the work. If you apply too
much pressure, you will sand a permanent
warp into the control surface.
If you go down to the metal rods with
coarse paper, you will never get the
scratches out. Keep an eye on the progress,
and switch to 110-grit paper before you go
too far. Continue to sand with little
pressure, and switch to 220- and 320-grit
as you begin to hit the metal. Finish it off
with 400-grit.
When the first side is finished, lift the
part off the board and clean away all the
dust. With the workspace clean, flip the
part over and place the 3⁄8-inch rod against
the LE. Since the TE needs to be 1⁄8-inch
thick, use a 1⁄8-inch-diameter rod at the TE
for the second side.
We stock three different styles of MK mechanical
retractable landing gear.There is the Standard
(green) set for use on .60-1.20 sized aircraft.
They feature a 3.5mm (5⁄32”) strut.There is
also the Standard (Gold) set which features a beefier mechanism
and a 4.0mm (3⁄16”) strut for 120 and larger aircraft.The Special
Gold set has struts with forward rake pre-bent and a special strut
mount to support them.These struts are also 4.0mm.
We also carry a great selection of special retract linkages
and spare struts for all of our MK retracts.
Standard Main Gear Set (Green 3.5mm) pair .................$59.95
Standard Nose Gear Set (Green 3.5mm) pair ................$47.95
Standard Main Gear Set (Gold 4.0mm) pair...................$69.95
Special Main Gear Set (Gold 4.0mm Forward Bend) pair ....$79.95
MK Super Light Wheels
with plastic hubs
50mm pair ..........$10.95
55mm pair ..........$11.95
60mm pair ..........$12.95
MK tail wheel assemblies
Tail wheel assy. ...$21.95
Tail wheel 3/4” .....$4.95
Looking for reliable retracts
and tires? Gator R/C has them!
2100 N Old Mill Rd
Brookline, MO 65619
Min. $6.50
Shipping&Handling per order
417-725-7755
www.gatorrc.com
VISA & MasterCard Welcomed!
Repeat the process as before, starting
with 80-grit paper and working toward
finer paper as you progress. I cannot stress
enough not to apply too much pressure
when sanding; it will cause deep scratches
and permanent warps. If the part has a
twist, or if the TE is inconsistent in
thickness, you used the wrong amount of
pressure when sanding.
Since this method produces a finely
sanded and perfectly shaped part,
additional sanding will not be required
across its surface except for the finish. For
this reason, it is important that the work
surface is smooth and free of glue or any
debris that may dent or scratch the part
while it is being sanded to shape; glass
works extremely well as a work surface.
This technique works best with control
surfaces that do not have elliptical TEs.
Although it is possible to use this method
when shaping parts with curved TEs, it is
best to save those for when you are
confident with the process. If the flap
outline curves slightly on the plans, leave
it squared off for the sanding step; do the
final shaping when you are finished with
the rods and the TE is being rounded off.
For this project, you will need to buy a
few sizes of steel rods at your local homesupply
store. The size needed for the LE
will be the same as the thickness of the
sheet balsa you use. For the TE, you will
have to do some math. On a 3⁄8-inch-thick
flap, steel rods that are 3⁄8 inch, 1⁄4 inch,
and 1⁄8 inch in diameter are required. For a
1⁄2-inch-thick flap, steel rods that are 1⁄2
inch, 5⁄16 inch, and 1⁄8 inch in diameter are
required.
To add the required rigidity to the control
surface, applying carbon veil with dope is the
best method I have used so far. Not only does
the carbon add incredible stiffness to the part,
it fills so quickly that it makes the finishing
process much easier. Carbon veil looks like
black silkspan and is applied dry, with dope,
over any solid surface.
There have been a couple of issues with
using the veil in this manner. The most
common complaints are about bending it
around curves and pinholes that show up
later in the finishing process.
The problem of not working around
curves is related to the type of veil you
purchase. Some kinds do not cooperate
around corners, but the softer variety will
conform to any surface. The hard type
works fine over flat surfaces and is no
different in performance. If you have the
hard variety, apply a strip of silkspan
around all of the edges first, and then use
the veil on the flat surface.
The other problem is with hundreds of
pinholes showing up during the finishing
process. Carbon veil is fragile with only
one coat of dope, and it becomes
extremely hard with three or more coats of
dope. Somewhere between fragile and rock
hard is when you must sand it.
If you sand too early, you will
immediately sand it all off. If you wait too
long, it will be too hard and you will get
pinholes. With experience, you get a feel
for when and how much to sand.
The most common places for pinholes
to appear are in areas where more than a
layer of veil has been applied. If you plan
to apply more than one layer to a surface,
it is best to apply a couple coats of dope on
the bottom layer and sand it smooth before
adding the second layer. Whichever type
of veil you have, it helps to iron it flat
before you attempt to use it. MA
10sig5.QXD 7/23/04 9:29 am Page 144
Edition: Model Aviation - 2004/10
Page Numbers: 143,144
Edition: Model Aviation - 2004/10
Page Numbers: 143,144
CONTROL LINE AEROBATICS
Curt Contrata, 6783 Nightwind Cir., Orlando FL 32818; E-mail: [email protected]
line larger than the plans show, and sand
the LE true using a long T-bar sander.
Test the hinge-line fit to the TE of the
wing and work slowly until they mate
perfectly.
Some find it easier to true an edge by
applying a long strip of self-adhesive
sandpaper to the surface of a bench, and
then dragging the part across it. With that
method, one can use a square to ensure
that the part is sanded perpendicular to the
bench.
For flap and elevator horn clips, I have
been using basswood with great success.
It is lighter than plywood, easier to cut,
and much easier to blend into the balsa
flap. To cap the opening on the clip, I
used 1⁄64 plywood with the grain running
vertical. It is also a good idea to slap a cap
of basswood or plywood on the other end
of the flaps if they are not full span; it
really helps keep them from getting
rounded off during the finishing process.
Once true, mark a centerline on the LE
of the flap and mark all of the hinge
locations. Take some extra time as you
slot the flaps and wing for the hinges. Do
not rush this step, and make sure the
hinges are in the center of the wing and
the flap. If you have to fill a slot and
restart, do it. Even if you have to move all
the slots over a bit to get a fresh start, it
can be worth starting over.
To obtain a perfect hinge line, you
must recess the hinge barrels into a small
notch on the LE of the flap. This is easy to
do if you make a maple block the width of
a hinge with 120-grit sandpaper glued to
one side. Use this block to cut a notch in
Marvin Denny built this Dave Gierke-designed Classic-legal Novi IV. Denny photo.
L-R: Lew Woolard, Bill Schmidt, and Bud Burroughs with their fleet. Denny photo.
A way to attempt to keep your neighbors
happy is to run a hose from the exhaust
into an empty nut can with lots of holes in
the lid. Denny photo.
BOOKS COULD BE written describing
the many methods that have been
developed in an attempt to construct the
perfect flap for a competitive Stunt model.
The quest for a control surface that resists
twisting under loads while being as light
as possible never seems to end.
Consistent with the adage of simplicity
often being the best solution, it is tough to
beat a plain, old sheet-balsa flap. The
focus this month will be on detail-sanding
flaps to shape using the “rod method” and
reviewing a few other details of controlsurface
construction.
Begin by cutting the flaps just a pencil
October 2004 143
10sig5.QXD 7/23/04 9:29 am Page 143
144 MODEL AVIATION
the LE of the flaps at each hinge location,
and then with finer papers as the finishing
process progresses.
With all hinges in place and the flaps
temporarily mounted to the wing, there
should be no gaps at the hinge line. If you
run your fingers along the hinge line, the
top and bottom of the flaps should be in
alignment with the top and bottom of the
wing TE. If something is not right, fix it
before you move on.
With everything in alignment, the flaps
are ready for shaping. If you have never
tried using the “rod method” to shape your
flaps, you have no idea how easy it can be
to accurately shape flaps and elevators
from sheet balsa. With a bit of extra care
over the fragile ribs, you can even use this
method for sanding to shape built-up
control surfaces that are to be sheeted.
The process starts with the part laying
flat on a work surface with one metal rod
placed against the LE and a thinner metal
rod placed at the TE. With the sizes of the
rods determined by the desired thickness
of the edges on the finished part, you use a
sanding block to sand the part flush with
the two metal rods.
That sounds simple, but there is a little
more to it than that. To sand the part to
shape without a warp, it will have to be
completely sanded on one side before you
turn it over to shape the other side. Since
the part is completely shaped with a flat
sanding block, obtaining a perfect finish
will be much easier.
For this example, I will use 3⁄8 sheet
balsa to form a flap with a 3⁄8-inch-thick
LE and a 1⁄8-inch-thick TE. The rod at the
LE will be 3⁄8 inch in diameter, and the rod
at the TE will be half the thickness of the
wood plus half the desired TE final
thickness. Half of the 3⁄8-inch wood is 3⁄16
inch, plus half of the 1⁄8-inch final
thickness, or 1⁄16 inch, equals 1⁄4 inch. Or,
3⁄16 inch + 1⁄16 inch = 1⁄4 inch.
With the part flat on the work surface,
place the 3⁄8-inch-diameter rod at the LE
and the 1⁄4-inch-diameter rod along the TE.
Shape the part using a sanding block with
80-grit paper. Go lightly and let the
sandpaper do all the work. If you apply too
much pressure, you will sand a permanent
warp into the control surface.
If you go down to the metal rods with
coarse paper, you will never get the
scratches out. Keep an eye on the progress,
and switch to 110-grit paper before you go
too far. Continue to sand with little
pressure, and switch to 220- and 320-grit
as you begin to hit the metal. Finish it off
with 400-grit.
When the first side is finished, lift the
part off the board and clean away all the
dust. With the workspace clean, flip the
part over and place the 3⁄8-inch rod against
the LE. Since the TE needs to be 1⁄8-inch
thick, use a 1⁄8-inch-diameter rod at the TE
for the second side.
We stock three different styles of MK mechanical
retractable landing gear.There is the Standard
(green) set for use on .60-1.20 sized aircraft.
They feature a 3.5mm (5⁄32”) strut.There is
also the Standard (Gold) set which features a beefier mechanism
and a 4.0mm (3⁄16”) strut for 120 and larger aircraft.The Special
Gold set has struts with forward rake pre-bent and a special strut
mount to support them.These struts are also 4.0mm.
We also carry a great selection of special retract linkages
and spare struts for all of our MK retracts.
Standard Main Gear Set (Green 3.5mm) pair .................$59.95
Standard Nose Gear Set (Green 3.5mm) pair ................$47.95
Standard Main Gear Set (Gold 4.0mm) pair...................$69.95
Special Main Gear Set (Gold 4.0mm Forward Bend) pair ....$79.95
MK Super Light Wheels
with plastic hubs
50mm pair ..........$10.95
55mm pair ..........$11.95
60mm pair ..........$12.95
MK tail wheel assemblies
Tail wheel assy. ...$21.95
Tail wheel 3/4” .....$4.95
Looking for reliable retracts
and tires? Gator R/C has them!
2100 N Old Mill Rd
Brookline, MO 65619
Min. $6.50
Shipping&Handling per order
417-725-7755
www.gatorrc.com
VISA & MasterCard Welcomed!
Repeat the process as before, starting
with 80-grit paper and working toward
finer paper as you progress. I cannot stress
enough not to apply too much pressure
when sanding; it will cause deep scratches
and permanent warps. If the part has a
twist, or if the TE is inconsistent in
thickness, you used the wrong amount of
pressure when sanding.
Since this method produces a finely
sanded and perfectly shaped part,
additional sanding will not be required
across its surface except for the finish. For
this reason, it is important that the work
surface is smooth and free of glue or any
debris that may dent or scratch the part
while it is being sanded to shape; glass
works extremely well as a work surface.
This technique works best with control
surfaces that do not have elliptical TEs.
Although it is possible to use this method
when shaping parts with curved TEs, it is
best to save those for when you are
confident with the process. If the flap
outline curves slightly on the plans, leave
it squared off for the sanding step; do the
final shaping when you are finished with
the rods and the TE is being rounded off.
For this project, you will need to buy a
few sizes of steel rods at your local homesupply
store. The size needed for the LE
will be the same as the thickness of the
sheet balsa you use. For the TE, you will
have to do some math. On a 3⁄8-inch-thick
flap, steel rods that are 3⁄8 inch, 1⁄4 inch,
and 1⁄8 inch in diameter are required. For a
1⁄2-inch-thick flap, steel rods that are 1⁄2
inch, 5⁄16 inch, and 1⁄8 inch in diameter are
required.
To add the required rigidity to the control
surface, applying carbon veil with dope is the
best method I have used so far. Not only does
the carbon add incredible stiffness to the part,
it fills so quickly that it makes the finishing
process much easier. Carbon veil looks like
black silkspan and is applied dry, with dope,
over any solid surface.
There have been a couple of issues with
using the veil in this manner. The most
common complaints are about bending it
around curves and pinholes that show up
later in the finishing process.
The problem of not working around
curves is related to the type of veil you
purchase. Some kinds do not cooperate
around corners, but the softer variety will
conform to any surface. The hard type
works fine over flat surfaces and is no
different in performance. If you have the
hard variety, apply a strip of silkspan
around all of the edges first, and then use
the veil on the flat surface.
The other problem is with hundreds of
pinholes showing up during the finishing
process. Carbon veil is fragile with only
one coat of dope, and it becomes
extremely hard with three or more coats of
dope. Somewhere between fragile and rock
hard is when you must sand it.
If you sand too early, you will
immediately sand it all off. If you wait too
long, it will be too hard and you will get
pinholes. With experience, you get a feel
for when and how much to sand.
The most common places for pinholes
to appear are in areas where more than a
layer of veil has been applied. If you plan
to apply more than one layer to a surface,
it is best to apply a couple coats of dope on
the bottom layer and sand it smooth before
adding the second layer. Whichever type
of veil you have, it helps to iron it flat
before you attempt to use it. MA
10sig5.QXD 7/23/04 9:29 am Page 144