Project Extra Volume III: Trammeling and Incidence

60 MODEL AVIATION
■ Mike Hurley
CRITICAL SETUP adjustments are an integral step to building
any aircraft that is expected to fly well, but they are especially
important when seeking precision flight characteristics. As with all
of the chapters in “Project Extra,” it is hoped that you can use these
steps and ideas on any aircraft that you are building. To that end,
I’ve gone into considerable detail so that you might transfer these
instructions to your own projects.
On the most basic level there are three critical horizontal
adjustments to be concerned with—the engine thrustline, the wing
incidence, and the horizontal stabilizer incidence. Our Extra 300LX
is designed around one horizontal line: the thrustline. All of the
design measurements are taken from this reference line. This
airplane was designed to have an alignment of 0-0-0—engine
mounted along the thrustline, 0° wing and 0° stabilizer incidence.
The top longeron follows parallel to the thrustline just 115⁄16 inches
above the thrustline, and the engine’s crankshaft is centered on the
thrustline.
All three of these adjustments work together to give you an
aircraft that flies at a level attitude while holding altitude at differing
throttle settings. This is especially important in precision aerobatics
flying. The wing incidence will affect the airplane’s attitude. A
positive incidence will give your model a nose-high/tail-low
attitude, and a negative adjustment will raise the tail.
Incorrect alignment of the engine with the thrustline or incorrect
stabilizer incidence may cause the aircraft to change altitude with
varying throttle settings. This becomes evident on vertical lines
where you have full power for an up line or power off for a down
line. Don’t worry about perfect elevator to stabilizer trim; it means
very little if you have a slight amount of trim on the elevators as
long as the airplane can cope with all attitudes of flight.
For exacting results, the following adjustments are made before
the control surfaces are cut from the wings or stabilizers. Follow the
same procedure for the wing and stabilizer. The stabilizer alignment
is referenced from the centerline of F3.
Fitting the Tube Socket: Project Extra uses a phenolic wing tube
socket glued into the fuselage, so the first order of business is to set
that socket into the fuselage and get it aligned perpendicularly and
Trammeling
and Incidence
Volume III:
03sig2.QXD 12.19.02 3:00 pm Page 60
horizontally. We cut the socket to approximately 101⁄8 inches and fit
it into the fuselage, sanding it flush to the sides (but don’t glue it in
at this time).
To fit the tube horizontally, the best method is to flip the fuselage
on its back using a perfectly flat table, and take measurements from
the tabletop to the wingtips. We didn’t have a perfect table, so Erik
Richards used a spare wing tube clamped to the top of the fuselage
and took measurements at the tips. Then the wings were placed on
the tube, and an 8-foot piece of angle aluminum was used to
measure the wings.
We made tiny adjustments by sanding the fuselage slightly to
adjust the socket then remeasuring until the horizontal angle was
perfect. You can use a small wedge or a toothpick to hold the
adjustments until you are ready to glue.
Wing Alignment (Trammeling): Next we checked the fore and aft
alignment of the wings to ensure that they are square to the fuselage
centerline. To do that, Erik made a nice little device from a steel
cable. A piece of string is largely inaccurate at the distance we have
with a model this size because it will stretch.
On one end there is a loop for pinning to the fuselage, and on the
cable he used a piece of fuel line and an Allen wrench for a pointer.
Pin the loop of the cable to the rear former centerline on the top of
the fuselage, then slide the pointer to the trailing-edge tip of the
wing. Walk to the other side of the airplane and check the other
wing. Again, adjust the fuselage tube socket until the trammel (wing
alignment) is perfect.
From 1⁄8 light plywood, make a pair of 3-inch square tube socket
doublers with a 1.610-inch-diameter hole at the center. It may help
to make the hole slightly undersized and sand it until you get a snug
fit on the phenolic; the doublers need to have a good, tight fit. Box
in the area where the doubler fits to the fuselage with two pieces of
3⁄8 square balsa.
Fit the socket into the fuselage with the doublers in place, then
square the tube to alignment using any wedges you may have made
to keep the socket in place. Do a final check to see that the socket is
where you want it, then tack-glue it to the fuselage with
cyanoacrylate (CyA). Once you’re satisfied with the socket’s
placement, you can final-glue the socket to the fuselage sides and
slide the doublers over, and glue them in place to the 3⁄8-inch balsa
framework and the socket.
After the tube socket is finished, you can add the last diagonal
brace into the fuselage.
Follow the same procedure with the stabilizer tube socket, except
it does not utilize an inside doubler. However, a circular doubler
may be used glued directly to the inside of the fuselage sides if a
large adjustment is necessary to bring the tube into alignment. Make
Erik checks alignment of tube to fuselage with dial caliper. He
and author also measure with wings attached using 8-foot-long
aluminum angle to check wing level.
To check fore and aft alignment on a model this size, steel cable
is superior to string because of string’s stretching factor.
Attached to the cable, Mike and Erik use a sharpened Allen
wrench and a piece of fuel tubing as a pointer.
When wings and stabilizers are aligned and level, centerline of
stabilizers should be parallel to top line of wing.
March 2003 61
Flight photo by Michael Ramsey Construction photos by Mike Hurley Graphic Design by Carla Kunz
03sig2.QXD 12.19.02 3:01 pm Page 61
To hold their incidence position they glued in a small piece of balsa block
while they drilled for the dowels.
A critical step in drilling dowel holes is aligning dowels
with wing tube. Drilling hole into wing root from opposite
side of fuselage ensures properly positioned dowel hole.
62 MODEL AVIATION
For setting incidence Mike
and Erik use Robart
incidence meter with
optional long bar and
homemade platform for
SmartTool digital meter.
Accuracy is to 1⁄10 degree.
sure that the horizontal alignment of the
stabilizer is adjusted to the top line of the
wing or the wing tube, even if it is slightly
askew from the fuselage. The head-on photo
shows the relationship of the stabilizer to the
wing. Since the stabilizer has no dihedral,
the centerline of the leading edge should be
on the same plane as the top line of the
wing.
Setting Incidence: The wings and
stabilizers are square and level to the
fuselage (trammeled), and the tube sockets
are set, glued, and trimmed, so now it’s time
to set incidence. We put a block under the
rear of the fuselage and set the top line to
level using a SmartTool digital meter. The
SmartTool is accurate to one-tenth of a
degree, and when building a competition
aircraft, we insist that all our final settings
are within that tolerance. Incidence was
measured with a Robart tool using the
optional long bar and modified with a
piece of 1-inch aluminum angle as a
platform for the digital meter.
As a starting point, use a short piece of
1⁄4 square balsa glued to the outside of the
fuselage as an alignment guide. Set the
incidence for each panel to zero, then CyA
the block to the fuselage side. We will
remove the blocks after the dowels are in
and the incidences are set.
Trace the outline of each wing panel to
the fuselage side, then mark your dowel
points as indicated on the plans, making
sure to center the points vertically using the
outline. With a 12-inch length of sharpened
5⁄16-inch brass tubing, drill the alignment pin
holes in the fuselage sides. Be sure to back
up the inside of the fuselage with a scrap
piece of plywood so the tubing doesn’t
shred the grain as it bores through the wood.
Install one wing panel at a time, and,
using the fuselage holes as a guide, drill the
alignment pin holes into the wing from the
opposite side of the fuselage. After the first
hole is done, insert a dowel to hold the
alignment before you drill the second hole.
Cut six (two for each wing panel and one
for each stabilizer half) 3-inch sections of
5⁄16-inch hardwood dowel to use as
alignment pins. Sharpen one end of each
dowel, and lightly bevel the edges of the
other. Epoxy the dowels into the root,
leaving approximately 5⁄8 inch extended
from the root. The sharpened end of the
dowel should slide right into the foam,
giving a nice, snug fit.
The plan incorrectly shows the dowel
pins at 90° to the root of the wing.
Remember that you should orient the pins so
that they are parallel to the wing tube, thus
they slide into the fuselage locations at the
correct angle with no binding. If you drilled
your dowel pins like we show here, the pilot
hole should already have the correct
orientation.
Once the pins are glued in place it’s time
to do the final incidence adjustment. Just as
before, make sure the fuselage is zeroed
(level), then fit the wings in place with the
dowels inserted into the holes and the root
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03sig2.QXD 12.19.02 3:01 pm Page 62
The cockpit is sheeted, the instrument panel is installed, and the
tabs have been glued in place.
Once the hatch is finished, you can glue on the turtledeck using
the hatch as a guide for its placement.
The finished tab has been doubled to the
inside with the blind nut installed.
March 2003 63
The hatch is generally assembled using fuselage as fixture so
everything fits perfectly when finished. Base of hatch is aligned,
trimmed, sanded to fit perfectly onto fuselage.
Hatch is glued to hatch base while on fuselage. Piece of waxed
paper is used as glue barrier, and temporary balsa blocks are
used to keep everything in alignment.
Mike and Erik used the fuselage as a fixture when gluing the hatch hold-down tabs in
place. Clamp everything together while the glue dries.
03sig2.QXD 12.19.02 3:01 pm Page 63
Using foam core from turtledeck, cut and fit an extension to
turtledeck that will be used as rudder fillets later.
With incidences set and fuselage alignment done, cut control
surfaces from wings and stabilizers. Be sure to use foam-core
shucks as base to keep cutting lines aligned.
Elevator surface cut away from stabilizer and section of material
removed that will become leading and trailing edges for hinge lines.
Use 1⁄16 balsa for all the end caps except the tips. Mike and Eric
used 1⁄8 balsa for tips of wings and rudders for durability.
64 MODEL AVIATION
flush against the fuselage side. With a file or sandpaper, adjust the
holes to obtain a zero reading on the SmartTool on both wings and
the stabilizers. It’s okay to open up the holes quite a bit if
necessary, but try to keep the fit so that you can hold the wing
tight against one stop up or down with the meter at zero.
Cut four 11⁄2-inch-diameter light plywood “doughnuts” with a
5⁄16-inch center hole that fits the dowels snugly to use as the final
alignment setting. We used scrap left over from cutting the
fuselage lightening holes for our doughnuts. With the wing held at
“zero,” glue the doughnuts in place inside the fuselage over the
pins, being careful not to get any glue on the dowels. Do the same
for the stabilizer pins, but the doughnuts can be smaller, at
roughly 1 inch in diameter.
Hatch and Turtledeck: Before we separate the control surfaces
from the wings and stabilizers, we’ll finish the foam hatch and
turtledeck. If you haven’t already sheeted the hatch and
turtledeck, now is the time to get that done. Our cores took a bit of
sanding to get the shape just right to fit the front of the fuselage
before we did the sheeting. Fit them carefully here so there will be
less work later.
The foam for the hatch is cored out for weight savings. Put a
front end cap of 1⁄8 balsa on the turtledeck. We use only 1⁄16 balsa
for the base of the hatch. To make the base, lay 4-inch sheeting
sections across the fuselage to former station F6 (approximately
341⁄4 inches), and mark the outline with a pencil. Remove them
from the fuselage, and cut and glue them together. We pinned the
sheet to the fuselage and sanded the sides flush to obtain a perfect
fit.
Remove the pins and fit the hatch. Remember to use a piece of
1⁄8 light plywood at the front edge to get the proper spacing for the
front hatch end cap. Use some waxed paper under the hatch base,
and glue the hatch onto the base using the fuselage as a fixture. To
keep everything aligned, we used short sections of 1⁄4 balsa glued
to the fuselage sides, then we held it all together with masking
tape while the epoxy dried.
Using the plan as a guide, cut the opening for the cockpit. Erik
used a large level as a cutting guide and angled it out slightly at
the bottom to give the cockpit sides a tapered look.
Sheet the inside of the cockpit and build the center instrument
panel with 1⁄16 balsa. The template on the plan for the instrument
panel is a guideline. You’ll need to fit it to your specific cockpit.
Use two identical pieces for the front and back, placed roughly an
inch apart, and sheet over the top. No strength is required for this
piece.
For the hatch retaining bolts we inserted four small tabs that fit
just inside the fuselage along the top longerons. In the photos you
can see that Erik added small doublers to the longerons, but
03sig2.QXD 12.19.02 3:01 pm Page 64
March 2003 65
The final rudder fillet has been installed and shaped.
Before hinges are beveled, mark and drill hinge pin holes. Mike
and Erik used a Robart tool for aligning the bit and a piece of
sharpened copper tubing to clean-cut holes.
they’re unnecessary. See the plans for locations. Tape the hatch
in place ensuring the proper location (use a dummy sheet of 1⁄8
light plywood at the front for spacing), and, with an ink pad, use
one of the tabs for a stamp marking the location for each of the
four tabs.
Cut the balsa away for the tab locations and slice the foam,
but don’t remove any foam. Sharpen one end of the tab so that it
can fit snugly into the slit you made in the foam. With the hatch
taped in place, epoxy the tabs into the hatch. Be sure to protect
the fuselage from excess glue with waxed paper, and clamp
each tab while the epoxy dries to be sure of a snug fit.
When the tabs are in and the epoxy has set, double the tab to
the inside with some scrap 1⁄8 light plywood. Re-place the hatch
onto the fuselage, and drill through the fuselage and the hatch
hold-down tabs. Install a 4-40 blind nut in each tab.
To cut the front end cap and the rear canopy former, trace
the outline from the front of the hatch and the front of the
turtledeck onto 1⁄8 light plywood. We opened up our canopy
former for weight savings, leaving 11⁄8 inches spacing around
the top and 13⁄4 inches at the bottom. You can put some
conservative lightening holes in the front end cap, but we left
ours solid. When you glue, use the turtledeck as a guide to get
the canopy former angle just right. From the front side of F1
drill the 5⁄16-inch dowel holes into the hatch. See the plan’s page
3, former F1A for location. Again align the dowels while gluing
with the hatch in place.
With the hatch in place and protected by a separator of
waxed paper, glue the sheeted turtledeck to the fuselage. Tape
the turtledeck down, and use clamps or balsa tabs to maintain
alignment while the glue dries. After the glue has set, clean up
the seam by block-sanding it smooth with a large “T” bar. We
used the inner core scrap from the turtledeck to make a rudder
fillet. Cut and sand it to follow the contour of the turtledeck,
then sheet with leftover 1⁄16 balsa. For this piece we used sprayon
contact cement. Set it aside for later.
With the airframe squared up and the incidences set, it’s time
to cut out the control surfaces for hinging and final preparation.
Mark the lines you’ll use from the plan or from your original
template that you made when setting up the foam cores. Tape
the control surface into the foam shuck to keep it level; this
ensures that all of the cuts are made on a vertical plane. A good
band saw is the best tool. (When cutting foam, remember to turn
the saw off if you have to back the blade out of a slot.) You will
remove a center section from each core for the trailing and
leading edges of the hinge lines. Refer to the plans.
(Hint: when cutting the ailerons from
the wings, set one wing half into the
bottom shuck so that the band saw fence
follows the cut, then you must set the
other wing in the top shuck with the
opposite side up.)
From sheet stock, cut and epoxy-glue
hinge-line sections of trailing and leading
edges. The wings and vertical stabilizer
are 1/2-inch thick, and the horizontal
stabilizer uses 3⁄8-inch stock. (If you want
more than 45° of elevator throw, you can
use 1/2-inch stock for the elevators too.)
After the glue has set, finish-sand the
hinge-line stock to fit flush to the flying
surfaces. Don’t bevel anything yet; we’ll
drill and do a trial installation of the
hinges before we bevel.
End Caps: After all of the hinge stock is
in place and sanded, it’s time to install
end caps for all of the open foam areas.
For wing and stabilizer tips, we used 1⁄8
balsa. You can get away with 1⁄16 for
further weight savings, but the pieces
become a little more susceptible to hangar The assembled Extra 300LX airframe is ready for fitting hardware.
03sig3.QXD 12.20.02 8:13 am Page 65
rash. If you are careful when you handle
your airplane, it should not be a problem.
Cut 3⁄16 inch off the inside of each aileron
to create space for two end caps and a 1⁄16-
inch gap. Don’t install the tip cap until
the hinging is done. That way, if the
aileron is not perfectly aligned you can
block-sand it flush before you install the
end cap.
Mark out the hinge positions
according to the plans. We used large
Robart hinge points and the Robart
alignment tool for making hinge holes
that are centered and straight. Find the
appropriate size of copper tubing, and
sharpen the inside with an X-Acto knife
for making the hinge holes. The tubing
will cut the hole without ripping and
make for a better fit and glue adhesion.
Mark the tubing with a piece of tape to
indicate the proper drilling depth.
Once all the hinge points are done, it’s
time to bevel the hinge gaps. Mark the
centerline and the bevel point on each
side of the hinge wood. It’s okay to bring
the bevel right down to the edge of the
wood. To keep the lines straight, use
masking tape to ensure that the final
sanding point is correct. Erik used a
Master Airscrew razor plane to get close
to the final shape, then he finished up
with a sanding block.
66 MODEL AVIATION
Double-bevel all the hinge-line stock
so that you can get enough controlsurface
deflection for 3-D maneuvers—
45° or more for rudder and elevator, and
25°+ for ailerons. Remember that the
trailing edge for the rudder follows the
fuselage all the way to the bottom, and it
is glued to the rear of the fuselage. We
didn’t bevel it until the rudder was glued
to the fuselage. After the hinge locations
are marked and drilled, you can fit the
rudder and glue it in place.
We placed the stabilizers on the
airplane and aligned the rudder by
measuring the top center point of the
rudder to the tip of each stabilizer. The
distance should be exactly the same. Note
that the rear of the turtledeck does not
have an end cap; TD2 shown on the plan
is not needed. The rudder hinge line will
be beveled after it is glued in place and
the fillets are installed.
To make the fillets, use the
fin/fuselage template on sheet 1 of the
plans. Tape the template to the centerline
of the fillet core that you made earlier and
cut it out while flat on the band saw. You
do not get the required taper that way, so
it will take a bit of sanding to fit the
fillets for a clean appearance. Erik stuck a
piece of sandpaper to a plastic bottle for a
nice, round contour. Epoxy the fillets in
place, then you can finish the bevel on the
rear of the rudder.
Next Month … At this point you should
have a nearly completed airframe ready
for fitting your servos and electronics.
The photo shows the gear cuffs and wheel
pants in place, but the canopy has yet to
be trimmed.
Next month we’ll cover those steps
and build and install all of the control
hardware, finish the wing and stabilizer
fasteners, build the firewall, and mount
the engine. The following segment may
seem like a process you’ve gone through
many times in the past, but these steps
can be critical for an airplane this size.
The processes we’ll outline will help to
ensure precision flying and enable your
airplane to last for many trouble-free
years. MA
Mike Hurley
11542 Decatur Ct.
Westminster CO 80234
[email protected]
03sig3.QXD 12.20.02 8:13 am Page 66

60 MODEL AVIATION
■ Mike Hurley
CRITICAL SETUP adjustments are an integral step to building
any aircraft that is expected to fly well, but they are especially
important when seeking precision flight characteristics. As with all
of the chapters in “Project Extra,” it is hoped that you can use these
steps and ideas on any aircraft that you are building. To that end,
I’ve gone into considerable detail so that you might transfer these
instructions to your own projects.
On the most basic level there are three critical horizontal
adjustments to be concerned with—the engine thrustline, the wing
incidence, and the horizontal stabilizer incidence. Our Extra 300LX
is designed around one horizontal line: the thrustline. All of the
design measurements are taken from this reference line. This
airplane was designed to have an alignment of 0-0-0—engine
mounted along the thrustline, 0° wing and 0° stabilizer incidence.
The top longeron follows parallel to the thrustline just 115⁄16 inches
above the thrustline, and the engine’s crankshaft is centered on the
thrustline.
All three of these adjustments work together to give you an
aircraft that flies at a level attitude while holding altitude at differing
throttle settings. This is especially important in precision aerobatics
flying. The wing incidence will affect the airplane’s attitude. A
positive incidence will give your model a nose-high/tail-low
attitude, and a negative adjustment will raise the tail.
Incorrect alignment of the engine with the thrustline or incorrect
stabilizer incidence may cause the aircraft to change altitude with
varying throttle settings. This becomes evident on vertical lines
where you have full power for an up line or power off for a down
line. Don’t worry about perfect elevator to stabilizer trim; it means
very little if you have a slight amount of trim on the elevators as
long as the airplane can cope with all attitudes of flight.
For exacting results, the following adjustments are made before
the control surfaces are cut from the wings or stabilizers. Follow the
same procedure for the wing and stabilizer. The stabilizer alignment
is referenced from the centerline of F3.
Fitting the Tube Socket: Project Extra uses a phenolic wing tube
socket glued into the fuselage, so the first order of business is to set
that socket into the fuselage and get it aligned perpendicularly and
Trammeling
and Incidence
Volume III:
03sig2.QXD 12.19.02 3:00 pm Page 60
horizontally. We cut the socket to approximately 101⁄8 inches and fit
it into the fuselage, sanding it flush to the sides (but don’t glue it in
at this time).
To fit the tube horizontally, the best method is to flip the fuselage
on its back using a perfectly flat table, and take measurements from
the tabletop to the wingtips. We didn’t have a perfect table, so Erik
Richards used a spare wing tube clamped to the top of the fuselage
and took measurements at the tips. Then the wings were placed on
the tube, and an 8-foot piece of angle aluminum was used to
measure the wings.
We made tiny adjustments by sanding the fuselage slightly to
adjust the socket then remeasuring until the horizontal angle was
perfect. You can use a small wedge or a toothpick to hold the
adjustments until you are ready to glue.
Wing Alignment (Trammeling): Next we checked the fore and aft
alignment of the wings to ensure that they are square to the fuselage
centerline. To do that, Erik made a nice little device from a steel
cable. A piece of string is largely inaccurate at the distance we have
with a model this size because it will stretch.
On one end there is a loop for pinning to the fuselage, and on the
cable he used a piece of fuel line and an Allen wrench for a pointer.
Pin the loop of the cable to the rear former centerline on the top of
the fuselage, then slide the pointer to the trailing-edge tip of the
wing. Walk to the other side of the airplane and check the other
wing. Again, adjust the fuselage tube socket until the trammel (wing
alignment) is perfect.
From 1⁄8 light plywood, make a pair of 3-inch square tube socket
doublers with a 1.610-inch-diameter hole at the center. It may help
to make the hole slightly undersized and sand it until you get a snug
fit on the phenolic; the doublers need to have a good, tight fit. Box
in the area where the doubler fits to the fuselage with two pieces of
3⁄8 square balsa.
Fit the socket into the fuselage with the doublers in place, then
square the tube to alignment using any wedges you may have made
to keep the socket in place. Do a final check to see that the socket is
where you want it, then tack-glue it to the fuselage with
cyanoacrylate (CyA). Once you’re satisfied with the socket’s
placement, you can final-glue the socket to the fuselage sides and
slide the doublers over, and glue them in place to the 3⁄8-inch balsa
framework and the socket.
After the tube socket is finished, you can add the last diagonal
brace into the fuselage.
Follow the same procedure with the stabilizer tube socket, except
it does not utilize an inside doubler. However, a circular doubler
may be used glued directly to the inside of the fuselage sides if a
large adjustment is necessary to bring the tube into alignment. Make
Erik checks alignment of tube to fuselage with dial caliper. He
and author also measure with wings attached using 8-foot-long
aluminum angle to check wing level.
To check fore and aft alignment on a model this size, steel cable
is superior to string because of string’s stretching factor.
Attached to the cable, Mike and Erik use a sharpened Allen
wrench and a piece of fuel tubing as a pointer.
When wings and stabilizers are aligned and level, centerline of
stabilizers should be parallel to top line of wing.
March 2003 61
Flight photo by Michael Ramsey Construction photos by Mike Hurley Graphic Design by Carla Kunz
03sig2.QXD 12.19.02 3:01 pm Page 61
To hold their incidence position they glued in a small piece of balsa block
while they drilled for the dowels.
A critical step in drilling dowel holes is aligning dowels
with wing tube. Drilling hole into wing root from opposite
side of fuselage ensures properly positioned dowel hole.
62 MODEL AVIATION
For setting incidence Mike
and Erik use Robart
incidence meter with
optional long bar and
homemade platform for
SmartTool digital meter.
Accuracy is to 1⁄10 degree.
sure that the horizontal alignment of the
stabilizer is adjusted to the top line of the
wing or the wing tube, even if it is slightly
askew from the fuselage. The head-on photo
shows the relationship of the stabilizer to the
wing. Since the stabilizer has no dihedral,
the centerline of the leading edge should be
on the same plane as the top line of the
wing.
Setting Incidence: The wings and
stabilizers are square and level to the
fuselage (trammeled), and the tube sockets
are set, glued, and trimmed, so now it’s time
to set incidence. We put a block under the
rear of the fuselage and set the top line to
level using a SmartTool digital meter. The
SmartTool is accurate to one-tenth of a
degree, and when building a competition
aircraft, we insist that all our final settings
are within that tolerance. Incidence was
measured with a Robart tool using the
optional long bar and modified with a
piece of 1-inch aluminum angle as a
platform for the digital meter.
As a starting point, use a short piece of
1⁄4 square balsa glued to the outside of the
fuselage as an alignment guide. Set the
incidence for each panel to zero, then CyA
the block to the fuselage side. We will
remove the blocks after the dowels are in
and the incidences are set.
Trace the outline of each wing panel to
the fuselage side, then mark your dowel
points as indicated on the plans, making
sure to center the points vertically using the
outline. With a 12-inch length of sharpened
5⁄16-inch brass tubing, drill the alignment pin
holes in the fuselage sides. Be sure to back
up the inside of the fuselage with a scrap
piece of plywood so the tubing doesn’t
shred the grain as it bores through the wood.
Install one wing panel at a time, and,
using the fuselage holes as a guide, drill the
alignment pin holes into the wing from the
opposite side of the fuselage. After the first
hole is done, insert a dowel to hold the
alignment before you drill the second hole.
Cut six (two for each wing panel and one
for each stabilizer half) 3-inch sections of
5⁄16-inch hardwood dowel to use as
alignment pins. Sharpen one end of each
dowel, and lightly bevel the edges of the
other. Epoxy the dowels into the root,
leaving approximately 5⁄8 inch extended
from the root. The sharpened end of the
dowel should slide right into the foam,
giving a nice, snug fit.
The plan incorrectly shows the dowel
pins at 90° to the root of the wing.
Remember that you should orient the pins so
that they are parallel to the wing tube, thus
they slide into the fuselage locations at the
correct angle with no binding. If you drilled
your dowel pins like we show here, the pilot
hole should already have the correct
orientation.
Once the pins are glued in place it’s time
to do the final incidence adjustment. Just as
before, make sure the fuselage is zeroed
(level), then fit the wings in place with the
dowels inserted into the holes and the root
For Web-only
content, go to
www.modelaircraft.
org/mag/index.htm.
There you will find
online supplements to
this groundbreaking
MA series.
03sig2.QXD 12.19.02 3:01 pm Page 62
The cockpit is sheeted, the instrument panel is installed, and the
tabs have been glued in place.
Once the hatch is finished, you can glue on the turtledeck using
the hatch as a guide for its placement.
The finished tab has been doubled to the
inside with the blind nut installed.
March 2003 63
The hatch is generally assembled using fuselage as fixture so
everything fits perfectly when finished. Base of hatch is aligned,
trimmed, sanded to fit perfectly onto fuselage.
Hatch is glued to hatch base while on fuselage. Piece of waxed
paper is used as glue barrier, and temporary balsa blocks are
used to keep everything in alignment.
Mike and Erik used the fuselage as a fixture when gluing the hatch hold-down tabs in
place. Clamp everything together while the glue dries.
03sig2.QXD 12.19.02 3:01 pm Page 63
Using foam core from turtledeck, cut and fit an extension to
turtledeck that will be used as rudder fillets later.
With incidences set and fuselage alignment done, cut control
surfaces from wings and stabilizers. Be sure to use foam-core
shucks as base to keep cutting lines aligned.
Elevator surface cut away from stabilizer and section of material
removed that will become leading and trailing edges for hinge lines.
Use 1⁄16 balsa for all the end caps except the tips. Mike and Eric
used 1⁄8 balsa for tips of wings and rudders for durability.
64 MODEL AVIATION
flush against the fuselage side. With a file or sandpaper, adjust the
holes to obtain a zero reading on the SmartTool on both wings and
the stabilizers. It’s okay to open up the holes quite a bit if
necessary, but try to keep the fit so that you can hold the wing
tight against one stop up or down with the meter at zero.
Cut four 11⁄2-inch-diameter light plywood “doughnuts” with a
5⁄16-inch center hole that fits the dowels snugly to use as the final
alignment setting. We used scrap left over from cutting the
fuselage lightening holes for our doughnuts. With the wing held at
“zero,” glue the doughnuts in place inside the fuselage over the
pins, being careful not to get any glue on the dowels. Do the same
for the stabilizer pins, but the doughnuts can be smaller, at
roughly 1 inch in diameter.
Hatch and Turtledeck: Before we separate the control surfaces
from the wings and stabilizers, we’ll finish the foam hatch and
turtledeck. If you haven’t already sheeted the hatch and
turtledeck, now is the time to get that done. Our cores took a bit of
sanding to get the shape just right to fit the front of the fuselage
before we did the sheeting. Fit them carefully here so there will be
less work later.
The foam for the hatch is cored out for weight savings. Put a
front end cap of 1⁄8 balsa on the turtledeck. We use only 1⁄16 balsa
for the base of the hatch. To make the base, lay 4-inch sheeting
sections across the fuselage to former station F6 (approximately
341⁄4 inches), and mark the outline with a pencil. Remove them
from the fuselage, and cut and glue them together. We pinned the
sheet to the fuselage and sanded the sides flush to obtain a perfect
fit.
Remove the pins and fit the hatch. Remember to use a piece of
1⁄8 light plywood at the front edge to get the proper spacing for the
front hatch end cap. Use some waxed paper under the hatch base,
and glue the hatch onto the base using the fuselage as a fixture. To
keep everything aligned, we used short sections of 1⁄4 balsa glued
to the fuselage sides, then we held it all together with masking
tape while the epoxy dried.
Using the plan as a guide, cut the opening for the cockpit. Erik
used a large level as a cutting guide and angled it out slightly at
the bottom to give the cockpit sides a tapered look.
Sheet the inside of the cockpit and build the center instrument
panel with 1⁄16 balsa. The template on the plan for the instrument
panel is a guideline. You’ll need to fit it to your specific cockpit.
Use two identical pieces for the front and back, placed roughly an
inch apart, and sheet over the top. No strength is required for this
piece.
For the hatch retaining bolts we inserted four small tabs that fit
just inside the fuselage along the top longerons. In the photos you
can see that Erik added small doublers to the longerons, but
03sig2.QXD 12.19.02 3:01 pm Page 64
March 2003 65
The final rudder fillet has been installed and shaped.
Before hinges are beveled, mark and drill hinge pin holes. Mike
and Erik used a Robart tool for aligning the bit and a piece of
sharpened copper tubing to clean-cut holes.
they’re unnecessary. See the plans for locations. Tape the hatch
in place ensuring the proper location (use a dummy sheet of 1⁄8
light plywood at the front for spacing), and, with an ink pad, use
one of the tabs for a stamp marking the location for each of the
four tabs.
Cut the balsa away for the tab locations and slice the foam,
but don’t remove any foam. Sharpen one end of the tab so that it
can fit snugly into the slit you made in the foam. With the hatch
taped in place, epoxy the tabs into the hatch. Be sure to protect
the fuselage from excess glue with waxed paper, and clamp
each tab while the epoxy dries to be sure of a snug fit.
When the tabs are in and the epoxy has set, double the tab to
the inside with some scrap 1⁄8 light plywood. Re-place the hatch
onto the fuselage, and drill through the fuselage and the hatch
hold-down tabs. Install a 4-40 blind nut in each tab.
To cut the front end cap and the rear canopy former, trace
the outline from the front of the hatch and the front of the
turtledeck onto 1⁄8 light plywood. We opened up our canopy
former for weight savings, leaving 11⁄8 inches spacing around
the top and 13⁄4 inches at the bottom. You can put some
conservative lightening holes in the front end cap, but we left
ours solid. When you glue, use the turtledeck as a guide to get
the canopy former angle just right. From the front side of F1
drill the 5⁄16-inch dowel holes into the hatch. See the plan’s page
3, former F1A for location. Again align the dowels while gluing
with the hatch in place.
With the hatch in place and protected by a separator of
waxed paper, glue the sheeted turtledeck to the fuselage. Tape
the turtledeck down, and use clamps or balsa tabs to maintain
alignment while the glue dries. After the glue has set, clean up
the seam by block-sanding it smooth with a large “T” bar. We
used the inner core scrap from the turtledeck to make a rudder
fillet. Cut and sand it to follow the contour of the turtledeck,
then sheet with leftover 1⁄16 balsa. For this piece we used sprayon
contact cement. Set it aside for later.
With the airframe squared up and the incidences set, it’s time
to cut out the control surfaces for hinging and final preparation.
Mark the lines you’ll use from the plan or from your original
template that you made when setting up the foam cores. Tape
the control surface into the foam shuck to keep it level; this
ensures that all of the cuts are made on a vertical plane. A good
band saw is the best tool. (When cutting foam, remember to turn
the saw off if you have to back the blade out of a slot.) You will
remove a center section from each core for the trailing and
leading edges of the hinge lines. Refer to the plans.
(Hint: when cutting the ailerons from
the wings, set one wing half into the
bottom shuck so that the band saw fence
follows the cut, then you must set the
other wing in the top shuck with the
opposite side up.)
From sheet stock, cut and epoxy-glue
hinge-line sections of trailing and leading
edges. The wings and vertical stabilizer
are 1/2-inch thick, and the horizontal
stabilizer uses 3⁄8-inch stock. (If you want
more than 45° of elevator throw, you can
use 1/2-inch stock for the elevators too.)
After the glue has set, finish-sand the
hinge-line stock to fit flush to the flying
surfaces. Don’t bevel anything yet; we’ll
drill and do a trial installation of the
hinges before we bevel.
End Caps: After all of the hinge stock is
in place and sanded, it’s time to install
end caps for all of the open foam areas.
For wing and stabilizer tips, we used 1⁄8
balsa. You can get away with 1⁄16 for
further weight savings, but the pieces
become a little more susceptible to hangar The assembled Extra 300LX airframe is ready for fitting hardware.
03sig3.QXD 12.20.02 8:13 am Page 65
rash. If you are careful when you handle
your airplane, it should not be a problem.
Cut 3⁄16 inch off the inside of each aileron
to create space for two end caps and a 1⁄16-
inch gap. Don’t install the tip cap until
the hinging is done. That way, if the
aileron is not perfectly aligned you can
block-sand it flush before you install the
end cap.
Mark out the hinge positions
according to the plans. We used large
Robart hinge points and the Robart
alignment tool for making hinge holes
that are centered and straight. Find the
appropriate size of copper tubing, and
sharpen the inside with an X-Acto knife
for making the hinge holes. The tubing
will cut the hole without ripping and
make for a better fit and glue adhesion.
Mark the tubing with a piece of tape to
indicate the proper drilling depth.
Once all the hinge points are done, it’s
time to bevel the hinge gaps. Mark the
centerline and the bevel point on each
side of the hinge wood. It’s okay to bring
the bevel right down to the edge of the
wood. To keep the lines straight, use
masking tape to ensure that the final
sanding point is correct. Erik used a
Master Airscrew razor plane to get close
to the final shape, then he finished up
with a sanding block.
66 MODEL AVIATION
Double-bevel all the hinge-line stock
so that you can get enough controlsurface
deflection for 3-D maneuvers—
45° or more for rudder and elevator, and
25°+ for ailerons. Remember that the
trailing edge for the rudder follows the
fuselage all the way to the bottom, and it
is glued to the rear of the fuselage. We
didn’t bevel it until the rudder was glued
to the fuselage. After the hinge locations
are marked and drilled, you can fit the
rudder and glue it in place.
We placed the stabilizers on the
airplane and aligned the rudder by
measuring the top center point of the
rudder to the tip of each stabilizer. The
distance should be exactly the same. Note
that the rear of the turtledeck does not
have an end cap; TD2 shown on the plan
is not needed. The rudder hinge line will
be beveled after it is glued in place and
the fillets are installed.
To make the fillets, use the
fin/fuselage template on sheet 1 of the
plans. Tape the template to the centerline
of the fillet core that you made earlier and
cut it out while flat on the band saw. You
do not get the required taper that way, so
it will take a bit of sanding to fit the
fillets for a clean appearance. Erik stuck a
piece of sandpaper to a plastic bottle for a
nice, round contour. Epoxy the fillets in
place, then you can finish the bevel on the
rear of the rudder.
Next Month … At this point you should
have a nearly completed airframe ready
for fitting your servos and electronics.
The photo shows the gear cuffs and wheel
pants in place, but the canopy has yet to
be trimmed.
Next month we’ll cover those steps
and build and install all of the control
hardware, finish the wing and stabilizer
fasteners, build the firewall, and mount
the engine. The following segment may
seem like a process you’ve gone through
many times in the past, but these steps
can be critical for an airplane this size.
The processes we’ll outline will help to
ensure precision flying and enable your
airplane to last for many trouble-free
years. MA
Mike Hurley
11542 Decatur Ct.
Westminster CO 80234
[email protected]
03sig3.QXD 12.20.02 8:13 am Page 66

60 MODEL AVIATION
■ Mike Hurley
CRITICAL SETUP adjustments are an integral step to building
any aircraft that is expected to fly well, but they are especially
important when seeking precision flight characteristics. As with all
of the chapters in “Project Extra,” it is hoped that you can use these
steps and ideas on any aircraft that you are building. To that end,
I’ve gone into considerable detail so that you might transfer these
instructions to your own projects.
On the most basic level there are three critical horizontal
adjustments to be concerned with—the engine thrustline, the wing
incidence, and the horizontal stabilizer incidence. Our Extra 300LX
is designed around one horizontal line: the thrustline. All of the
design measurements are taken from this reference line. This
airplane was designed to have an alignment of 0-0-0—engine
mounted along the thrustline, 0° wing and 0° stabilizer incidence.
The top longeron follows parallel to the thrustline just 115⁄16 inches
above the thrustline, and the engine’s crankshaft is centered on the
thrustline.
All three of these adjustments work together to give you an
aircraft that flies at a level attitude while holding altitude at differing
throttle settings. This is especially important in precision aerobatics
flying. The wing incidence will affect the airplane’s attitude. A
positive incidence will give your model a nose-high/tail-low
attitude, and a negative adjustment will raise the tail.
Incorrect alignment of the engine with the thrustline or incorrect
stabilizer incidence may cause the aircraft to change altitude with
varying throttle settings. This becomes evident on vertical lines
where you have full power for an up line or power off for a down
line. Don’t worry about perfect elevator to stabilizer trim; it means
very little if you have a slight amount of trim on the elevators as
long as the airplane can cope with all attitudes of flight.
For exacting results, the following adjustments are made before
the control surfaces are cut from the wings or stabilizers. Follow the
same procedure for the wing and stabilizer. The stabilizer alignment
is referenced from the centerline of F3.
Fitting the Tube Socket: Project Extra uses a phenolic wing tube
socket glued into the fuselage, so the first order of business is to set
that socket into the fuselage and get it aligned perpendicularly and
Trammeling
and Incidence
Volume III:
03sig2.QXD 12.19.02 3:00 pm Page 60
horizontally. We cut the socket to approximately 101⁄8 inches and fit
it into the fuselage, sanding it flush to the sides (but don’t glue it in
at this time).
To fit the tube horizontally, the best method is to flip the fuselage
on its back using a perfectly flat table, and take measurements from
the tabletop to the wingtips. We didn’t have a perfect table, so Erik
Richards used a spare wing tube clamped to the top of the fuselage
and took measurements at the tips. Then the wings were placed on
the tube, and an 8-foot piece of angle aluminum was used to
measure the wings.
We made tiny adjustments by sanding the fuselage slightly to
adjust the socket then remeasuring until the horizontal angle was
perfect. You can use a small wedge or a toothpick to hold the
adjustments until you are ready to glue.
Wing Alignment (Trammeling): Next we checked the fore and aft
alignment of the wings to ensure that they are square to the fuselage
centerline. To do that, Erik made a nice little device from a steel
cable. A piece of string is largely inaccurate at the distance we have
with a model this size because it will stretch.
On one end there is a loop for pinning to the fuselage, and on the
cable he used a piece of fuel line and an Allen wrench for a pointer.
Pin the loop of the cable to the rear former centerline on the top of
the fuselage, then slide the pointer to the trailing-edge tip of the
wing. Walk to the other side of the airplane and check the other
wing. Again, adjust the fuselage tube socket until the trammel (wing
alignment) is perfect.
From 1⁄8 light plywood, make a pair of 3-inch square tube socket
doublers with a 1.610-inch-diameter hole at the center. It may help
to make the hole slightly undersized and sand it until you get a snug
fit on the phenolic; the doublers need to have a good, tight fit. Box
in the area where the doubler fits to the fuselage with two pieces of
3⁄8 square balsa.
Fit the socket into the fuselage with the doublers in place, then
square the tube to alignment using any wedges you may have made
to keep the socket in place. Do a final check to see that the socket is
where you want it, then tack-glue it to the fuselage with
cyanoacrylate (CyA). Once you’re satisfied with the socket’s
placement, you can final-glue the socket to the fuselage sides and
slide the doublers over, and glue them in place to the 3⁄8-inch balsa
framework and the socket.
After the tube socket is finished, you can add the last diagonal
brace into the fuselage.
Follow the same procedure with the stabilizer tube socket, except
it does not utilize an inside doubler. However, a circular doubler
may be used glued directly to the inside of the fuselage sides if a
large adjustment is necessary to bring the tube into alignment. Make
Erik checks alignment of tube to fuselage with dial caliper. He
and author also measure with wings attached using 8-foot-long
aluminum angle to check wing level.
To check fore and aft alignment on a model this size, steel cable
is superior to string because of string’s stretching factor.
Attached to the cable, Mike and Erik use a sharpened Allen
wrench and a piece of fuel tubing as a pointer.
When wings and stabilizers are aligned and level, centerline of
stabilizers should be parallel to top line of wing.
March 2003 61
Flight photo by Michael Ramsey Construction photos by Mike Hurley Graphic Design by Carla Kunz
03sig2.QXD 12.19.02 3:01 pm Page 61
To hold their incidence position they glued in a small piece of balsa block
while they drilled for the dowels.
A critical step in drilling dowel holes is aligning dowels
with wing tube. Drilling hole into wing root from opposite
side of fuselage ensures properly positioned dowel hole.
62 MODEL AVIATION
For setting incidence Mike
and Erik use Robart
incidence meter with
optional long bar and
homemade platform for
SmartTool digital meter.
Accuracy is to 1⁄10 degree.
sure that the horizontal alignment of the
stabilizer is adjusted to the top line of the
wing or the wing tube, even if it is slightly
askew from the fuselage. The head-on photo
shows the relationship of the stabilizer to the
wing. Since the stabilizer has no dihedral,
the centerline of the leading edge should be
on the same plane as the top line of the
wing.
Setting Incidence: The wings and
stabilizers are square and level to the
fuselage (trammeled), and the tube sockets
are set, glued, and trimmed, so now it’s time
to set incidence. We put a block under the
rear of the fuselage and set the top line to
level using a SmartTool digital meter. The
SmartTool is accurate to one-tenth of a
degree, and when building a competition
aircraft, we insist that all our final settings
are within that tolerance. Incidence was
measured with a Robart tool using the
optional long bar and modified with a
piece of 1-inch aluminum angle as a
platform for the digital meter.
As a starting point, use a short piece of
1⁄4 square balsa glued to the outside of the
fuselage as an alignment guide. Set the
incidence for each panel to zero, then CyA
the block to the fuselage side. We will
remove the blocks after the dowels are in
and the incidences are set.
Trace the outline of each wing panel to
the fuselage side, then mark your dowel
points as indicated on the plans, making
sure to center the points vertically using the
outline. With a 12-inch length of sharpened
5⁄16-inch brass tubing, drill the alignment pin
holes in the fuselage sides. Be sure to back
up the inside of the fuselage with a scrap
piece of plywood so the tubing doesn’t
shred the grain as it bores through the wood.
Install one wing panel at a time, and,
using the fuselage holes as a guide, drill the
alignment pin holes into the wing from the
opposite side of the fuselage. After the first
hole is done, insert a dowel to hold the
alignment before you drill the second hole.
Cut six (two for each wing panel and one
for each stabilizer half) 3-inch sections of
5⁄16-inch hardwood dowel to use as
alignment pins. Sharpen one end of each
dowel, and lightly bevel the edges of the
other. Epoxy the dowels into the root,
leaving approximately 5⁄8 inch extended
from the root. The sharpened end of the
dowel should slide right into the foam,
giving a nice, snug fit.
The plan incorrectly shows the dowel
pins at 90° to the root of the wing.
Remember that you should orient the pins so
that they are parallel to the wing tube, thus
they slide into the fuselage locations at the
correct angle with no binding. If you drilled
your dowel pins like we show here, the pilot
hole should already have the correct
orientation.
Once the pins are glued in place it’s time
to do the final incidence adjustment. Just as
before, make sure the fuselage is zeroed
(level), then fit the wings in place with the
dowels inserted into the holes and the root
For Web-only
content, go to
www.modelaircraft.
org/mag/index.htm.
There you will find
online supplements to
this groundbreaking
MA series.
03sig2.QXD 12.19.02 3:01 pm Page 62
The cockpit is sheeted, the instrument panel is installed, and the
tabs have been glued in place.
Once the hatch is finished, you can glue on the turtledeck using
the hatch as a guide for its placement.
The finished tab has been doubled to the
inside with the blind nut installed.
March 2003 63
The hatch is generally assembled using fuselage as fixture so
everything fits perfectly when finished. Base of hatch is aligned,
trimmed, sanded to fit perfectly onto fuselage.
Hatch is glued to hatch base while on fuselage. Piece of waxed
paper is used as glue barrier, and temporary balsa blocks are
used to keep everything in alignment.
Mike and Erik used the fuselage as a fixture when gluing the hatch hold-down tabs in
place. Clamp everything together while the glue dries.
03sig2.QXD 12.19.02 3:01 pm Page 63
Using foam core from turtledeck, cut and fit an extension to
turtledeck that will be used as rudder fillets later.
With incidences set and fuselage alignment done, cut control
surfaces from wings and stabilizers. Be sure to use foam-core
shucks as base to keep cutting lines aligned.
Elevator surface cut away from stabilizer and section of material
removed that will become leading and trailing edges for hinge lines.
Use 1⁄16 balsa for all the end caps except the tips. Mike and Eric
used 1⁄8 balsa for tips of wings and rudders for durability.
64 MODEL AVIATION
flush against the fuselage side. With a file or sandpaper, adjust the
holes to obtain a zero reading on the SmartTool on both wings and
the stabilizers. It’s okay to open up the holes quite a bit if
necessary, but try to keep the fit so that you can hold the wing
tight against one stop up or down with the meter at zero.
Cut four 11⁄2-inch-diameter light plywood “doughnuts” with a
5⁄16-inch center hole that fits the dowels snugly to use as the final
alignment setting. We used scrap left over from cutting the
fuselage lightening holes for our doughnuts. With the wing held at
“zero,” glue the doughnuts in place inside the fuselage over the
pins, being careful not to get any glue on the dowels. Do the same
for the stabilizer pins, but the doughnuts can be smaller, at
roughly 1 inch in diameter.
Hatch and Turtledeck: Before we separate the control surfaces
from the wings and stabilizers, we’ll finish the foam hatch and
turtledeck. If you haven’t already sheeted the hatch and
turtledeck, now is the time to get that done. Our cores took a bit of
sanding to get the shape just right to fit the front of the fuselage
before we did the sheeting. Fit them carefully here so there will be
less work later.
The foam for the hatch is cored out for weight savings. Put a
front end cap of 1⁄8 balsa on the turtledeck. We use only 1⁄16 balsa
for the base of the hatch. To make the base, lay 4-inch sheeting
sections across the fuselage to former station F6 (approximately
341⁄4 inches), and mark the outline with a pencil. Remove them
from the fuselage, and cut and glue them together. We pinned the
sheet to the fuselage and sanded the sides flush to obtain a perfect
fit.
Remove the pins and fit the hatch. Remember to use a piece of
1⁄8 light plywood at the front edge to get the proper spacing for the
front hatch end cap. Use some waxed paper under the hatch base,
and glue the hatch onto the base using the fuselage as a fixture. To
keep everything aligned, we used short sections of 1⁄4 balsa glued
to the fuselage sides, then we held it all together with masking
tape while the epoxy dried.
Using the plan as a guide, cut the opening for the cockpit. Erik
used a large level as a cutting guide and angled it out slightly at
the bottom to give the cockpit sides a tapered look.
Sheet the inside of the cockpit and build the center instrument
panel with 1⁄16 balsa. The template on the plan for the instrument
panel is a guideline. You’ll need to fit it to your specific cockpit.
Use two identical pieces for the front and back, placed roughly an
inch apart, and sheet over the top. No strength is required for this
piece.
For the hatch retaining bolts we inserted four small tabs that fit
just inside the fuselage along the top longerons. In the photos you
can see that Erik added small doublers to the longerons, but
03sig2.QXD 12.19.02 3:01 pm Page 64
March 2003 65
The final rudder fillet has been installed and shaped.
Before hinges are beveled, mark and drill hinge pin holes. Mike
and Erik used a Robart tool for aligning the bit and a piece of
sharpened copper tubing to clean-cut holes.
they’re unnecessary. See the plans for locations. Tape the hatch
in place ensuring the proper location (use a dummy sheet of 1⁄8
light plywood at the front for spacing), and, with an ink pad, use
one of the tabs for a stamp marking the location for each of the
four tabs.
Cut the balsa away for the tab locations and slice the foam,
but don’t remove any foam. Sharpen one end of the tab so that it
can fit snugly into the slit you made in the foam. With the hatch
taped in place, epoxy the tabs into the hatch. Be sure to protect
the fuselage from excess glue with waxed paper, and clamp
each tab while the epoxy dries to be sure of a snug fit.
When the tabs are in and the epoxy has set, double the tab to
the inside with some scrap 1⁄8 light plywood. Re-place the hatch
onto the fuselage, and drill through the fuselage and the hatch
hold-down tabs. Install a 4-40 blind nut in each tab.
To cut the front end cap and the rear canopy former, trace
the outline from the front of the hatch and the front of the
turtledeck onto 1⁄8 light plywood. We opened up our canopy
former for weight savings, leaving 11⁄8 inches spacing around
the top and 13⁄4 inches at the bottom. You can put some
conservative lightening holes in the front end cap, but we left
ours solid. When you glue, use the turtledeck as a guide to get
the canopy former angle just right. From the front side of F1
drill the 5⁄16-inch dowel holes into the hatch. See the plan’s page
3, former F1A for location. Again align the dowels while gluing
with the hatch in place.
With the hatch in place and protected by a separator of
waxed paper, glue the sheeted turtledeck to the fuselage. Tape
the turtledeck down, and use clamps or balsa tabs to maintain
alignment while the glue dries. After the glue has set, clean up
the seam by block-sanding it smooth with a large “T” bar. We
used the inner core scrap from the turtledeck to make a rudder
fillet. Cut and sand it to follow the contour of the turtledeck,
then sheet with leftover 1⁄16 balsa. For this piece we used sprayon
contact cement. Set it aside for later.
With the airframe squared up and the incidences set, it’s time
to cut out the control surfaces for hinging and final preparation.
Mark the lines you’ll use from the plan or from your original
template that you made when setting up the foam cores. Tape
the control surface into the foam shuck to keep it level; this
ensures that all of the cuts are made on a vertical plane. A good
band saw is the best tool. (When cutting foam, remember to turn
the saw off if you have to back the blade out of a slot.) You will
remove a center section from each core for the trailing and
leading edges of the hinge lines. Refer to the plans.
(Hint: when cutting the ailerons from
the wings, set one wing half into the
bottom shuck so that the band saw fence
follows the cut, then you must set the
other wing in the top shuck with the
opposite side up.)
From sheet stock, cut and epoxy-glue
hinge-line sections of trailing and leading
edges. The wings and vertical stabilizer
are 1/2-inch thick, and the horizontal
stabilizer uses 3⁄8-inch stock. (If you want
more than 45° of elevator throw, you can
use 1/2-inch stock for the elevators too.)
After the glue has set, finish-sand the
hinge-line stock to fit flush to the flying
surfaces. Don’t bevel anything yet; we’ll
drill and do a trial installation of the
hinges before we bevel.
End Caps: After all of the hinge stock is
in place and sanded, it’s time to install
end caps for all of the open foam areas.
For wing and stabilizer tips, we used 1⁄8
balsa. You can get away with 1⁄16 for
further weight savings, but the pieces
become a little more susceptible to hangar The assembled Extra 300LX airframe is ready for fitting hardware.
03sig3.QXD 12.20.02 8:13 am Page 65
rash. If you are careful when you handle
your airplane, it should not be a problem.
Cut 3⁄16 inch off the inside of each aileron
to create space for two end caps and a 1⁄16-
inch gap. Don’t install the tip cap until
the hinging is done. That way, if the
aileron is not perfectly aligned you can
block-sand it flush before you install the
end cap.
Mark out the hinge positions
according to the plans. We used large
Robart hinge points and the Robart
alignment tool for making hinge holes
that are centered and straight. Find the
appropriate size of copper tubing, and
sharpen the inside with an X-Acto knife
for making the hinge holes. The tubing
will cut the hole without ripping and
make for a better fit and glue adhesion.
Mark the tubing with a piece of tape to
indicate the proper drilling depth.
Once all the hinge points are done, it’s
time to bevel the hinge gaps. Mark the
centerline and the bevel point on each
side of the hinge wood. It’s okay to bring
the bevel right down to the edge of the
wood. To keep the lines straight, use
masking tape to ensure that the final
sanding point is correct. Erik used a
Master Airscrew razor plane to get close
to the final shape, then he finished up
with a sanding block.
66 MODEL AVIATION
Double-bevel all the hinge-line stock
so that you can get enough controlsurface
deflection for 3-D maneuvers—
45° or more for rudder and elevator, and
25°+ for ailerons. Remember that the
trailing edge for the rudder follows the
fuselage all the way to the bottom, and it
is glued to the rear of the fuselage. We
didn’t bevel it until the rudder was glued
to the fuselage. After the hinge locations
are marked and drilled, you can fit the
rudder and glue it in place.
We placed the stabilizers on the
airplane and aligned the rudder by
measuring the top center point of the
rudder to the tip of each stabilizer. The
distance should be exactly the same. Note
that the rear of the turtledeck does not
have an end cap; TD2 shown on the plan
is not needed. The rudder hinge line will
be beveled after it is glued in place and
the fillets are installed.
To make the fillets, use the
fin/fuselage template on sheet 1 of the
plans. Tape the template to the centerline
of the fillet core that you made earlier and
cut it out while flat on the band saw. You
do not get the required taper that way, so
it will take a bit of sanding to fit the
fillets for a clean appearance. Erik stuck a
piece of sandpaper to a plastic bottle for a
nice, round contour. Epoxy the fillets in
place, then you can finish the bevel on the
rear of the rudder.
Next Month … At this point you should
have a nearly completed airframe ready
for fitting your servos and electronics.
The photo shows the gear cuffs and wheel
pants in place, but the canopy has yet to
be trimmed.
Next month we’ll cover those steps
and build and install all of the control
hardware, finish the wing and stabilizer
fasteners, build the firewall, and mount
the engine. The following segment may
seem like a process you’ve gone through
many times in the past, but these steps
can be critical for an airplane this size.
The processes we’ll outline will help to
ensure precision flying and enable your
airplane to last for many trouble-free
years. MA
Mike Hurley
11542 Decatur Ct.
Westminster CO 80234
[email protected]
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