“IT’S WHAT YOU learn after you know it all that really counts.” I
wish I could remember who taught me that. It may be from the writings
of Dave Thornburg or perhaps spoken by one of the philosopher fliers
I’ve had the good fortune to fly with and learn from.
I had intended to write this column detailing my method of
installing aileron control linkages, thinking that since I had done it 70
or more times I had the routine down and would able to bestow my
wisdom on the readership—especially those with less time at the
building bench.
But, alas and alack, my 71st aileron installation proved to have a
crucial flaw. Following is the story of how the linkage was built and
how the flaw was discovered and rectified.
First I’ll cover how I’ve been happily installing single-servo aileron
control linkages throughout the years. The Power Scale Soaring Slope
sailplane under construction is the Leading Edge Gliders 60-inch-span
P-63 Kingcobra.
This installation uses one servo to control two ailerons via torque
rods and wire control linkages—a common geometry in sailplanes with
wingspans of 50 inches or less: low- and high-wing mounts. The goal
is to have a tight, strong, accurate linkage that will last for the life of
the airframe.
I find it easier and more convenient to
install the pair of linkages before the wing
halves are joined. In this case the spars have
been set into the EPP-foam wing halves, the
spruce sub-TE sticks installed and sanded.
I dug into the scrap box to find hard-balsa
aileron stock for the short centerline TE
pieces; they will receive quite a bit of
handling, and the harder material resists nicks
and dings better than the light balsa I prefer for
the rest of the aileron.
Following are the steps I used to fit these
aileron control linkages.
1) Cut the pair of centerpieces of aileron
stock to length. They need to be sized to fit
from the wing centerline out to the end of the
tubes holding the torque rods. The kit maker
may specify this length in the instructions.
Plane and sand these pieces to the correct
thickness.
2) Draw centerlines on all four parts: the
two short pieces of aileron stock and the sub-
Leading Edge Gliders’ P-63 Kingcobra in “Pinball Squadron” aerial
gunnery training target scheme. Photo by Alex Paul.
The underside of one aileron linkage on the Kingcobra.
[[email protected]]
Radio Control Slope Soaring Dave Garwood
Installing aileron control linkages
Aileron-linkage mounting components on the Kingcobra, ready for
installation. The text details this process.
Luminaries at the Leading Edge Gliders shop (L-R): Joe Chovan, Alex Paul, Ed Berris,
Mike Bailey, Pat McCleave, Jack Cooper.
February 2006 137
TE stock where the torque tubes will be
located. These serve as guides to carve halfround
slots in the sub-TE and in the TE stock
to enclose the torque-rod holder tubes.
3) Carve the half-round slots with a hobby
knife or a roto-tool. Work slowly and
carefully. If you use a knife, remember that a
sharp blade is safer than a dull one; less
pressure is needed to make the cut, reducing
the hazard if the knife slips. Be sure to hold
the part and the knife so that the knife will not
cause injury if it does slip.
4) Finish shaping the slots with a small
round file, trial-fitting the parts often to see
when the slots are just deep enough to fit in
place with the torque-rod tubes inside.
5) Final-shape and sand all four of the
wing TE pieces: the short pieces to be
mounted as TEs and the long pieces that will
become ailerons. This includes end-to-end
slot fit, tip-shaping, and overall surface
sanding.
6) Tape the ailerons in place. Working
from the bottom, mark the location of the
outer 90° bend in the aileron torque-rod
linkage. Remove the ailerons and make a
groove, with a medium round file, that is
slightly larger than is needed for the wire
alone.
7) Fit short brass tubes, with inside
diameters just large enough to allow the wire
to slide freely. The tube provides long-term
wear resistance and allows the aileron to
move without binding or straining the aileroncontrol
torque rod. For ailerons hinged at the
top, the rod will slide substantially within the
tube.
8) Tape ailerons in their final installed
location, with the control torque rod fitted,
and place the wing halves inverted on the
workbench. With a bit of tape sealing the TE
of the brass tube to keep epoxy out, mount the
tubes with a minimal amount of epoxy. I like
to let the assemblies cure overnight at this
point.
9) The next day check the ailerons for free
movement and clean up excess epoxy. With
the ailerons separated from the wing halves,
fill any gaps with epoxy and apply a piece of
fiberglass cloth to strengthen and stiffen the
inside end of the aileron and give a smooth
surface for the iron-on covering. When cured,
trim excess fiberglass cloth and sand the
parts.
10) Install the aileron servo and wire
control links according to the kit
manufacturer’s instructions and/or your
preference for hardware. I like hinging the
ailerons with the covering film or fabric
because it produces a highly flexible hinge
with a long service life, and it stops air from
circulating through the hinge line. I hinge
scale airplanes on the top to produce a lessvisible
hinge line.
Using an Airtronics 94358 high-torque
servo to swing the big ailerons, I hauled my
new Kingcobra to Wilson Lake, Kansas, for
sport-flying and to run in the 2005 Midwest
Slope Challenge Foamie Warbird Racing
class.
We had excellent winds and good lift in
the days before the 2005 event, and the big
Kingcobra’s flight performance exceeded my
expectations. Getting bolder with each
passing hour, my model’s climbs got higher
and its dives got faster and longer.
Then Gadzooks! Aileron flutter! My heart
sank.
Flutter is rapid and energetic oscillation of
a control surface in the airstream. Once
control-surface flutter starts, it tends to
increase in severity, sometimes to the point
where the aileron or elevator is ripped from
the airframe. Suppressing control-surface
flutter is a design consideration in models and
in full-scale aircraft, and there are design
techniques to reduce the chance that flutter
will occur.
Once flutter is spotted (and sometimes it
can be heard), it’s important to reduce
airspeed quickly, generally by pulling up into
a climb, to stop the flutter and reduce the
chances of airframe damage. If you’re lucky
and the model is still controllable, bring it in
for a landing. Then search for the cause of the
flutter and devise a strategy to eliminate it.
I asked the designer—Jack Cooper—
to look at my aileron setup and see how it
could be improved. He found two
possible contributing factors and fixed
them both.
There was a tiny bit of excessive
clearance between the nylon threaded fittings
on the torque rods and their mating clevises.
That might be enough to contribute to flutter
starting, but Jack looked further and decided
that the wire control links between the servo
arms and the torque rods were not stiff
enough to handle the speeds at which I had
been flying.
Jack stiffened the 1/16-inch-diameter wire
control links by gluing carbon-fiber tubes in
place with plastic-tube spacers between the
carbon-fiber tubes and the wires. Good news:
problem solved. Flying the ’cobra five more
days, including one day with steady 28 mph
winds gusting to 40, posed no more flutter
problems.
Another way to stiffen the linkage using
fewer parts might be to install heavier and
stiffer wire for the control linkages. Rather
than the 1/16-inch-diameter variety with 2-56
threads, use the next size heavier, with 4-40
threads.
Spending time at the Leading Edge Gliders
shop during the Midwest Slope Challenge,
there was a parade of Slope glider designers,
builders, photographers, and first-rate fliers.
One night or another during the annual spring
event we enjoyed the assistance, advice, and
company of people such as hardworking
sailplane action photographer Alex Paul of
Nassau, Bahamas; Andreas Mergner of Plane
Insane Models (www.planeinsane
models.com) in Albany, New York; and Ed
Berris of Sky King RC Products (www.sky
kingrcproducts.com) in Minneapolis,
Minnesota.
Also Erik Eaton, master builder and finder
of new slopes in central Kansas; Greg Smith,
ace photographer, writer, and Web publisher
(www.slopeflyer.com) of Milwaukee,
Wisconsin; and TufFlight (www.tufflight.
com) co-owner Joe Chovan of Syracuse, New
York.
In attendance as well were Leading Edge
Gliders (www.leadingedgegliders.com)
honcho Jack Cooper of Lucas, Kansas; Edge
RC (www.edgerc.com) owner Justin Ammon
of Lucas, Kansas; and designer and maker at
Midwest Slope Models (www.midwest
slope.com) of Maize, Kansas, and Kansas
slope-event promoter Mike Bailey.
I love traveling to fly slope. MA
Edition: Model Aviation - 2006/02
Page Numbers: 137,138
Edition: Model Aviation - 2006/02
Page Numbers: 137,138
“IT’S WHAT YOU learn after you know it all that really counts.” I
wish I could remember who taught me that. It may be from the writings
of Dave Thornburg or perhaps spoken by one of the philosopher fliers
I’ve had the good fortune to fly with and learn from.
I had intended to write this column detailing my method of
installing aileron control linkages, thinking that since I had done it 70
or more times I had the routine down and would able to bestow my
wisdom on the readership—especially those with less time at the
building bench.
But, alas and alack, my 71st aileron installation proved to have a
crucial flaw. Following is the story of how the linkage was built and
how the flaw was discovered and rectified.
First I’ll cover how I’ve been happily installing single-servo aileron
control linkages throughout the years. The Power Scale Soaring Slope
sailplane under construction is the Leading Edge Gliders 60-inch-span
P-63 Kingcobra.
This installation uses one servo to control two ailerons via torque
rods and wire control linkages—a common geometry in sailplanes with
wingspans of 50 inches or less: low- and high-wing mounts. The goal
is to have a tight, strong, accurate linkage that will last for the life of
the airframe.
I find it easier and more convenient to
install the pair of linkages before the wing
halves are joined. In this case the spars have
been set into the EPP-foam wing halves, the
spruce sub-TE sticks installed and sanded.
I dug into the scrap box to find hard-balsa
aileron stock for the short centerline TE
pieces; they will receive quite a bit of
handling, and the harder material resists nicks
and dings better than the light balsa I prefer for
the rest of the aileron.
Following are the steps I used to fit these
aileron control linkages.
1) Cut the pair of centerpieces of aileron
stock to length. They need to be sized to fit
from the wing centerline out to the end of the
tubes holding the torque rods. The kit maker
may specify this length in the instructions.
Plane and sand these pieces to the correct
thickness.
2) Draw centerlines on all four parts: the
two short pieces of aileron stock and the sub-
Leading Edge Gliders’ P-63 Kingcobra in “Pinball Squadron” aerial
gunnery training target scheme. Photo by Alex Paul.
The underside of one aileron linkage on the Kingcobra.
[[email protected]]
Radio Control Slope Soaring Dave Garwood
Installing aileron control linkages
Aileron-linkage mounting components on the Kingcobra, ready for
installation. The text details this process.
Luminaries at the Leading Edge Gliders shop (L-R): Joe Chovan, Alex Paul, Ed Berris,
Mike Bailey, Pat McCleave, Jack Cooper.
February 2006 137
TE stock where the torque tubes will be
located. These serve as guides to carve halfround
slots in the sub-TE and in the TE stock
to enclose the torque-rod holder tubes.
3) Carve the half-round slots with a hobby
knife or a roto-tool. Work slowly and
carefully. If you use a knife, remember that a
sharp blade is safer than a dull one; less
pressure is needed to make the cut, reducing
the hazard if the knife slips. Be sure to hold
the part and the knife so that the knife will not
cause injury if it does slip.
4) Finish shaping the slots with a small
round file, trial-fitting the parts often to see
when the slots are just deep enough to fit in
place with the torque-rod tubes inside.
5) Final-shape and sand all four of the
wing TE pieces: the short pieces to be
mounted as TEs and the long pieces that will
become ailerons. This includes end-to-end
slot fit, tip-shaping, and overall surface
sanding.
6) Tape the ailerons in place. Working
from the bottom, mark the location of the
outer 90° bend in the aileron torque-rod
linkage. Remove the ailerons and make a
groove, with a medium round file, that is
slightly larger than is needed for the wire
alone.
7) Fit short brass tubes, with inside
diameters just large enough to allow the wire
to slide freely. The tube provides long-term
wear resistance and allows the aileron to
move without binding or straining the aileroncontrol
torque rod. For ailerons hinged at the
top, the rod will slide substantially within the
tube.
8) Tape ailerons in their final installed
location, with the control torque rod fitted,
and place the wing halves inverted on the
workbench. With a bit of tape sealing the TE
of the brass tube to keep epoxy out, mount the
tubes with a minimal amount of epoxy. I like
to let the assemblies cure overnight at this
point.
9) The next day check the ailerons for free
movement and clean up excess epoxy. With
the ailerons separated from the wing halves,
fill any gaps with epoxy and apply a piece of
fiberglass cloth to strengthen and stiffen the
inside end of the aileron and give a smooth
surface for the iron-on covering. When cured,
trim excess fiberglass cloth and sand the
parts.
10) Install the aileron servo and wire
control links according to the kit
manufacturer’s instructions and/or your
preference for hardware. I like hinging the
ailerons with the covering film or fabric
because it produces a highly flexible hinge
with a long service life, and it stops air from
circulating through the hinge line. I hinge
scale airplanes on the top to produce a lessvisible
hinge line.
Using an Airtronics 94358 high-torque
servo to swing the big ailerons, I hauled my
new Kingcobra to Wilson Lake, Kansas, for
sport-flying and to run in the 2005 Midwest
Slope Challenge Foamie Warbird Racing
class.
We had excellent winds and good lift in
the days before the 2005 event, and the big
Kingcobra’s flight performance exceeded my
expectations. Getting bolder with each
passing hour, my model’s climbs got higher
and its dives got faster and longer.
Then Gadzooks! Aileron flutter! My heart
sank.
Flutter is rapid and energetic oscillation of
a control surface in the airstream. Once
control-surface flutter starts, it tends to
increase in severity, sometimes to the point
where the aileron or elevator is ripped from
the airframe. Suppressing control-surface
flutter is a design consideration in models and
in full-scale aircraft, and there are design
techniques to reduce the chance that flutter
will occur.
Once flutter is spotted (and sometimes it
can be heard), it’s important to reduce
airspeed quickly, generally by pulling up into
a climb, to stop the flutter and reduce the
chances of airframe damage. If you’re lucky
and the model is still controllable, bring it in
for a landing. Then search for the cause of the
flutter and devise a strategy to eliminate it.
I asked the designer—Jack Cooper—
to look at my aileron setup and see how it
could be improved. He found two
possible contributing factors and fixed
them both.
There was a tiny bit of excessive
clearance between the nylon threaded fittings
on the torque rods and their mating clevises.
That might be enough to contribute to flutter
starting, but Jack looked further and decided
that the wire control links between the servo
arms and the torque rods were not stiff
enough to handle the speeds at which I had
been flying.
Jack stiffened the 1/16-inch-diameter wire
control links by gluing carbon-fiber tubes in
place with plastic-tube spacers between the
carbon-fiber tubes and the wires. Good news:
problem solved. Flying the ’cobra five more
days, including one day with steady 28 mph
winds gusting to 40, posed no more flutter
problems.
Another way to stiffen the linkage using
fewer parts might be to install heavier and
stiffer wire for the control linkages. Rather
than the 1/16-inch-diameter variety with 2-56
threads, use the next size heavier, with 4-40
threads.
Spending time at the Leading Edge Gliders
shop during the Midwest Slope Challenge,
there was a parade of Slope glider designers,
builders, photographers, and first-rate fliers.
One night or another during the annual spring
event we enjoyed the assistance, advice, and
company of people such as hardworking
sailplane action photographer Alex Paul of
Nassau, Bahamas; Andreas Mergner of Plane
Insane Models (www.planeinsane
models.com) in Albany, New York; and Ed
Berris of Sky King RC Products (www.sky
kingrcproducts.com) in Minneapolis,
Minnesota.
Also Erik Eaton, master builder and finder
of new slopes in central Kansas; Greg Smith,
ace photographer, writer, and Web publisher
(www.slopeflyer.com) of Milwaukee,
Wisconsin; and TufFlight (www.tufflight.
com) co-owner Joe Chovan of Syracuse, New
York.
In attendance as well were Leading Edge
Gliders (www.leadingedgegliders.com)
honcho Jack Cooper of Lucas, Kansas; Edge
RC (www.edgerc.com) owner Justin Ammon
of Lucas, Kansas; and designer and maker at
Midwest Slope Models (www.midwest
slope.com) of Maize, Kansas, and Kansas
slope-event promoter Mike Bailey.
I love traveling to fly slope. MA