RADIO CONTROL SLOPE SOARING 2003/06

June 2003 113
THE LAST TWO Slope Soaring
columns covered fiberglass models; this
month I turn to foam sailplanes. The
wonder material of expanded
polypropylene (EPP) foam has enabled
designers to give us “bounceable”
sailplanes. The EPP-foam model kits
I’ve seen have excellent building
instructions, so there is no need to cover
basic techniques. I have 27 advanced
tips and tricks for building stronger,
better-performing, and longer-lasting
foam sailplanes.
1: Exercise your best craftsmanship
when installing control systems; they
can be difficult to reach for repair in a
foam model. Make sure servos are firmly
mounted, pushrods are solidly supported,
and links are as strong and slop-free as
you can make them.
I put a small piece of waxed paper
over the servo arms and linkages to
make certain I don’t get a blob of Goop
adhesive on these parts when attaching
the wing to the fuselage or when gluing
small pieces of EPP foam to close the
cavities.
2: Be sure to cover the hollowed-out
cavities for the battery, receiver, and
elevator servo with EPP foam to protect
the equipment and to stiffen the
fuselage.
When shaping this part, it’s not easy
to get the correct thickness. I carve a
larger-than-necessary foam block to fit
the cavity, glue it in place, and, after the
Goop has cured, trim it flush with the
fuselage using a knife and sanding block.
Dave Garwood, 5 Birch Ln., Scotia NY 12302; E-mail: [email protected]
RADIO CONTROL SLOPE SOARING
Jim Harrigan’s beaten, battered, and taped-up Dave’s Aircraft Works Kawafoamie Ki61
flies at Wilson Lake. There’s no shame in wearing out an airframe.
Battery, receiver, elevator servo, Sullivan 517 pushrod in foamie
fuselage. ElectroDynamics charge switch is above fuselage in
original form.
EPP fuselage with oversized EPP blocks glued in place with
Goop. When glue cures, trim excess foam and sand flush.
Make paper pattern to cut Coroplast “Hard Sides” armor. Drawing on wing saddle helps
to know where to carve fuselage cavity in fuselage to clear aileron servo.
114 MODEL AVIATION
3: Consider substituting tougher parts,
such as the heavy-duty Sullivan No. 517
pushrod for elevator control. I’ve had
foamie combat models take a hit to the
fuselage that kinked the inner control
snake, yet no damage was evident upon
external examination. We didn’t know
why the elevator linkage had developed
more friction until the pushrod was
withdrawn for inspection.
4: Do you find mounting the receiver
on/off switch and the battery-charging
connector troublesome? Try using a
“charge switch.” The ElectroDynamics
Heavy Duty Ultra Switch is well worth
its $16 price. It’s available from
www.electrodynam.com or (734) 422-
5420.
5: Have you been flying foam long
enough to learn that the fuselage wears
out before the wing? Even on a “Nerf
airplane” every hit takes a little toll on
fuselage stiffness and integrity, and
eventually the nose becomes a squishy,
floppy mess.
One solution is to order a new
fuselage part from the maker, excavate
the salvageable radio gear from the
worn fuselage, and build a new one.
Order new vertical and horizontal
stabilizer parts at the same time. It’s
quicker to replace a fuselage and tail
parts than it is to build a whole new
model, and there’s no shame in wearing
out an airframe.
6: Painted parts withstand wear better
than covered parts. We want most of our
foamie to be covered, not painted, so we
can smooth out wrinkles with a covering
iron, but we can paint the horizontal and
vertical stabilizers. I tape the edges with
masking tape and apply Testors enamel
with an airbrush or the Testors threeounce
spray cans.
7: Terry Dwyer of Syracuse, New York,
taught me his “Hard Sides” method of
stiffening a fuselage by gluing lengths
of Coroplast along both sides before
final-taping. Coroplast is the corrugated
material many foamie-warbird tail parts
are made from, and you can get it at sign
shops or from your kit maker.
Terry has applied 5-millimeter (mm)
material, and I’ve done it with 3mm
stock; either will stiffen the fuselage and
armor the internal components against
external damage. This modification adds
weight to the model, but you’re happy to
have the weight on heavy-wind flying
days.
Following are foamie building, repair,
and setup tips contributed by five
experienced designers, manufacturers,
and builders. You’ll find additional
information on each of their Web sites.
Trim the paper pattern for cutting Coroplast “Hard Sides” armor so that it clears edges
of fuselage where you will carve and sand rounded corners.
Completed EPP-foam fuselage with “Hard Sides” installation, ready to tape and cover.
This is a Dave’s Aircraft Works Kawafoamie Ki61. Tail parts are painted.
Mike Bailey
([email protected],
www.midwestslope.com):
8: When building any Slope airplane, put
some thought into what type of flying
your model is intended for. The
manufacturer takes care to provide the
information to get the airplane flying
well, but there is still room for tweaking.
If you expect to fly the model in combat
or over rough terrain, extra tape on the
nose and underside will help protect the
foam. Control surfaces can take a great
deal of abuse.
Many manufacturers use Coroplast for
best durability. Other kits are supplied
with balsa for more accurate and lighter
surfaces. If you decide to replace a balsa
tail with Coroplast, remember that more
nose weight will be necessary, resulting
in a heavier airplane. With balsa, strength
can be increased by adding a light layer
of fiberglass, although this will also add
weight.
9: Even though we are flying flexible and
“squishy” airplanes, we need to take care
that we build them as accurately as
possible. When taping a wing, it can be
easy to introduce a twist. This is the most
important time to go slow and keep
checking your work.
Many times the foam beds that the
wing cores come with can be used to help
keep the wing straight while covering. If
you need to sand the wing, be careful not
to change the airfoil. On the fuselage,
rounding the corners results in better
aerodynamics and better looks.
Tom Henscheid (Mountain Toys at
www.mtntoys.com):
10: I like to add torsional stiffness by
taping an X pattern on the wing. I use four
Xs of tape on each wing, top and bottom.
This method combined with tape over the
spars and on the leading edges ties all of
the tape together, forming a matrix. This
will help prevent the wing from twisting
and deforming.
11: To strengthen the fuselage, spiralwrap
it with four pieces of tape starting at
the tail. One piece starts on the right side
and wraps up, one starts on the left side
and wraps up, one starts on the right side
and wraps down, and the last one starts on
the left side and wraps down. Then use
two pieces of tape on either side, adhering
them longitudinally along the fuselage
from back to front.
Be sure to wrap the wing saddle well.
Make sure that the wing-saddle tape pieces
are long enough so that they tie into the
spiral wrapping. This will tie everything
together and make a stiffer fuselage.
Steve Greenfield (Sailplanesteve@
aol.com, www.californiasailplanes.com):
12: We’ve learned that sign vinyl
(available from a sign shop) makes a
great covering for EPP. Just spray the
finished model with a light dusting of 3M
77 and apply the sign vinyl. It is durable,
and the color selection is amazing.
13: I made a bad mistake by packing
some heavy items in my van behind my
Canterbury F-20 Tigershark. When I
stopped abruptly, the items slid forward
and bent my fuselage at a 45° angle. I
straightened the fuselage by hand then
added a strip of carbon fiber to each side.
It’s as good as new, with little added
weight.
14—Bungee Launch: We hate those
windless days at the slope. It is easy to
make a fast and high launch using a
bungee cord. For details, see
www.californiasailplanes.com/f20
bungee.wmv. For the first attempts, make
sure your model is well trimmed and
flying straight and level. Modestly pull
back the bungee the first time. Have fun
and be careful!
15—Hinge Tape: I’ve tried many tapes,
but the only reliable kind so far has been
Scotch bidirectional strapping tape. Since
it is 2 inches wide, you need to lay a strip
long enough for your hinge on waxed
paper and cut it lengthwise with a razor
knife. It works very well.
16: Use heavy-duty Du-Bro servo horns
on your servos. Hopefully you are using
metal-gear servos. If not, they are worth
the money for foamies. Remember how
deep that servo installed and how hard it
will be to get at if there is a problem.
17: You can learn how to build plug-in
charging jacks to replace your on/off
switch at www.californiasailplanes.com/
Powerjack.html.
Mark Mech ([email protected],
www.aerofoam.com):
18: I don’t glue in radio components or
foam. I trace the part to be installed and
cut on the inside of the lines to make a
tight fit. I use a permanent marker to
mark the depth of the cut on the blade.
The servo will push snugly into the foam
cavity. If it doesn’t sit flush, pop out a
few more beads of foam.
19: I make a simple slice in the foam to
route wires. They can be pushed into a 1⁄4-
inch-deep slot, and they disappear. The
small cable-type pushrods can also be
installed this way.
20: For combat foamies I recommend
“servo savers.” They will prevent servogear
damage, so you won’t need to dig
out servos for repairs.
Charles Varvaro (lasierraslopesoarers@
hotmail.com):
21: Rather than bury the aileron servos in
the fuselage, if the wings are thick
enough I like to put one microservo in
each wing half. Access to the servos is
easier, and you get more positive control
from shorter, stiffer linkages.
22: A terrific alternative material for
covering foamies is thin vinyl sign tape.
Our club obtains scrap in 3-inch x 10-
foot rolls at no charge from a local sign
shop. The tape comes in rolls that are too
wide for the shop’s cutting machines, and
they just throw out the 3-inch trimmings.
Advantages of vinyl sign tape are that
it is easy to apply because it has peel-off
backing; it adds only slightly more
weight to an average model than color
tape, but it makes the aircraft far more
rigid (rigid models fly faster and more
precisely); and it seems to stay on better
than color tape.
23: A simple way to stiffen the fuselage
without adding much weight is to run a
1⁄4-inch hardwood dowel dipped in
silicone glue through it, front to back.
24: The area directly in front of the wing
saddle takes lots of stress during hard
landings. Be sure to reinforce it with two
or three layers of strapping tape. Even if
the instructions don’t call for doing so,
June 2003 115
reinforce the wing leading edge with one
layer of strapping tape. It may save your
wing in a head-on midair hit.
25: EPP-foam models cannot be cut as
precisely as balsa models; that’s why it is
important to check the incidence of the
horizontal stabilizer to make sure it is the
same as the wing. After the wrong center
of gravity (CG), an out-of-incidence
horizontal stabilizer is probably the main
reason why a foamie won’t fly well.
26: Rather than put dead weight in a
foamie’s nose to balance the model, install
a higher-capacity battery. That way you
116 MODEL AVIATION
will balance the model and have longer
flight times. A fifth cell can also be used
to add nose weight. Flight times will be
slightly shorter, but servo responses will
be faster.
27: How well an EPP-foam combat wing
recovers from a hit can make the
difference between winning or placing in
a contest. A slightly forward CG and only
enough ballast necessary to penetrate the
wind will make recoveries faster. MA
Online Resources:
Charles Varvaro is a prolific builder and
Slope flier. See many more of his
building tips, and ratings of 53 kits by La
Sierra Slope Soarers, at www.lsss.
homestead.com.
More foamie-building information is
available at
www.davesaircraftworks.com and
www.magnum-models.com.
Got your race models and combat
aircraft ready for the Midwest Slope
Challenge (MWSC) in May? Get more
information at www.alltel.net/~mwsc.
Read R/C Soaring Digest’s report on
MWSC 2002 at
www.b2streamlines.com/
RCSD.html.
I hope to see you western-branch Homo
Slopiens at the Southern California PSS
Festival in May. Information is available
at http://ourworld.compuserve.com/
homepages/ISR.
Read R/C Soaring Digest’s report on
Cajon 2002 at www.b2streamlines.com/
RCSD.html.
See if you recognize yourself or any of
your flying buddies in the “Slope Pilot
Identification Guide” at
www.slopeflyer.
com/artman/publish/article_185.shtml.
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