Radio Control Slope Soaring - 2010/04

106 MODEL AVIATION
TAKING STOCK during the first week of
the new year, I found that I have four kits I’d
like to get built this winter. They are a Marty
Hill Curtiss P-40 Warhawk moldie that spans
48 inches, a Jack Cooper Lockheed P-80
Shooting Star foamie that spans 60 inches, an
Erik Eaton Duster One Design Racer that
spans 60 inches, and a Ray Hayes Olympic III
thermal sailplane, built from traditional balsa
and plywood, that spans 132 inches.
I can’t be certain that I’ll complete all of
them by the time the snow clears here in the
Great Northeast, but right now I’m moving
and grooving on the Marty Hill Warhawk. It’s
a priority, because five guys and I plan to fly
ours in Kansas in May, near the time of the
Midwest Slope Challenge.
That contest will take place May 13-16. The
February 2010 column contains contact
information for this and other slope events that
will be held this year. Be sure to check with
the sponsoring club to confirm event dates.
Yes, five New York Slope Dogs and one
Cape Cod Beach Bum are building Warhawks,
likely to be painted identical as squadron mates, and flown together at
Wilson Lake. It will be grand. Marty has shipped six kits to the group,
and he can mold and send more if other fliers are interested. See the
“Sources” list for his contact information.
The Warhawk comes in what we call a “short kit.” Designed for
experienced builders, a short kit for a molded warbird design provides
the two most difficult parts for a modeler to make: a molded fiberglass
fuselage and hot-wire-cut foam wing cores. A clear molded canopy
might be included, depending on the design.
The short kit will probably include a page or two of building hints
and specifications, such as balance point, decalage angle, and control
throws, but no detailed building instructions. It may come with
drawings that show the layout of radio gear and routing of control
rods, or it might contain, at a minimum, outline drawings of the
vertical and horizontal stabilizers: the parts to be cut from balsa sheet
that the builder supplies.
[[email protected]]
Radio Control Slope Soaring Dave Garwood
Overview of fiberglass-fuselage short kit construction
Dave’s Su-25 Frogfoot, at the 2007 Southern CA Power Scale Soaring (PSS) Festival,
built from a Carl Maas short kit. It represents one of the reasons we build short kits; it’s
often the only way to get a kit of a less common model.
An old flying buddy, Rick Schwemmer, prepares to launch Dave’s
model to fly for the judged competition at Cajon Summit in the
San Bernardino National Forest during the 2007 PSS Festival.
Dave’s Su-25 and other modelers’ F-86s in the judging area at the
2007 PSS Festival. These models were built from short kits, which
are great for modelers who expect to finish an aircraft in a
distinctive and personalized paint scheme.
The F-86 Sabre was the Inland Slope Rebels’ 2007 club project. At
least seven were built, and they were flown at the PSS Festival.
These Sabres can be purchased from the club’s molding man, Dan
Sampson.
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In the Internet age, information for
builders can often be found on a Web site or a
“building thread” on one of the messageposting
pages. For the Warhawk kit, you can
find Marty Hill’s building thread on
RCGroups; the address is in the source list.
A short kit rarely includes wood or
hardware; those decisions and acquisitions are
left up to the builder. What do you get for
your trouble? A tested sailplane design—
perhaps a rare or unusual one that is not
generally available from other sources or
attained by any other method.
If you have enough building experience to
sheet your own foam-core wings, sand and
finish fiberglass parts, design your own radio
installations, and research your own paint
schemes, short kits are for you. I’ve built
eight and have four on the shelf ready to
build. I love them.
Following is an overview of fiberglass-fuselage short kit
construction, but first I’ll tick off the advantages and disadvantages of
composite molded construction compared with wood or EPP foam. (I
discussed these in more detail in the August 2009 Slope Soaring
column.)
Advantages of fiberglass construction:
1) Shape:Molding is probably the best way to get beautiful rounded
and curved shapes.
2) Stiffness: The rigidity of the composite materials allows lighter
airframe construction.
3) Easier construction: Radio installation is easy in a hollow
fuselage. Parts can be glued on with epoxy.
4) Takes paint well: For camouflage markings, paint is the answer—
and fiberglass was made to be painted.
5) Reparability:With molded fiberglass, you can get back to the
original shape, strength, and appearance after a crash.
6) Flies better:Molded sailplanes with sheeted wings penetrate
headwinds better. Molded gliders accelerate quicker, have higher top
speeds, and fly better in off-direction lift. The real deal, go-fast
sailplanes are molded. Fly a fiberglass Slope Soarer after flying a
foamie, and you’re in for a pleasant surprise.
Disadvantages of fiberglass construction:
1) Higher cost: Composite model parts might be more expensive
than an equivalent-size wood or foam construction design. Building
time will likely be longer with composites, which, in effect, adds to the
price.
2) Learning curve: The techniques used to build and finish molded
fiberglass might be new to some builders, depending on their previous
experience. But hey, foamie construction was new at one time too.
3) Fear of breaking the model: This is possibly the largest fear that
keeps pilots from trying fiberglass. Yes, these aircraft can be broken,
but they can be repaired to 100% in strength and appearance—and
that’s not always possible with foam construction.
Are you ready to review the steps to build a fiberglass short kit? Let’s
get started.
1) Open the box and inventory the parts. It’s a thrill to pull the
pieces out of a new kit box and examine them. It’s at this point that I
begin to imagine the sailplane built, painted, and flying.
Check the molded fuselage, examine the wing cores, and review the
information that comes with the kit. Perhaps begin making a list of tools
and materials you’ll need for construction.
If that info is not in the kit or part of your previous building
experience, check for an online building log, search the MA or RC
Soaring Digest online archives for a building how-to article, or get
advice from more-experienced builders.
2) Sheet the wing. A foam-core, wood-sheeted wing offers many
benefits for slope sailplanes. It produces stiff and light wings, which
April 2010 107
Typical for a short kit, the Su-25 included a molded-fiberglass
fuselage, hot-wire-cut foam cores for sheeted wings, and a molded
clear canopy. Also included were drawings for tail parts. If there is
sufficient reader interest, Dave will write more about short kit
building skills.
Short kit builders at the 2007 PSS Festival (L-R): Brian Koester (F-86 “Sky Blazers”), Ian
Gittins (F-86 “ANG”), Russ Thompson (Focke-Wulf P-1), Dave Garwood (“Su-25”), and
Jeff Fukushima (F-86 “Sky Blazers”).
can be repaired with a reasonable amount of effort.
To sheet wings, prepare “skins” by joining 1/16 balsa sheeting or
similar wood veneer material, such as obechi or 1/64 plywood. Sand the
skins, sand the cores, and cut pieces slightly larger than the cores—
roughly 1/4 inch all around works well.
Adhesives that work for attaching the skins include double-stick
tape, brush-on contact cement, spray-on contact cement, and epoxy.
After you have sheeted the cores, trim them flush and sand them
square. Add the recommended LE sticks (often hard balsa or
basswood) and the balsa sub-TE sticks, and shape to the specified
airfoil shape.
3) Cut the balsa parts using balsa stock that you provide. Some of
the components include wingtip blocks, vertical and horizontal
stabilizers, and elevators. The short kit instructions often include
cutting templates and specify the thickness of the balsa stock. If they
don’t, check with the designer or the research methods I mentioned for
getting how-to info.
4) Construct the wing and fit and shape the tips. Fit the aileron
torque-rod assemblies. Shape the ailerons, and install them using the
hinge method you like best. Join the wing halves, remembering to set
the dihedral to specification. Add layers of fiberglass cloth and epoxy
resin, to strengthen the wing center joint.
5) Prepare the fuselage.Wet-sand the fuselage to remove the moldrelease
agent and break the glaze on the fiberglass, to allow it to take
paint well. Apply primer paint, fill holes with common auto-body
repair materials (Bondo is a favorite brand), and wet-sand again.
Repeat as necessary to get a smooth finish that is ready to take the final
color coat.
6) Mount the wing and tail parts. You may be deciding whether to
build a removable wing for easier storage and transportation or a fixed
wing for a stronger airframe. One thing to keep in mind is that the joint
between the wing and fuselage can be faired with Bondo more
smoothly with a one-piece airframe.
7) Install radio components and control linkages.Most slope
warbirds with spans as large as 50 inches are controlled by two
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channels—aileron and elevator—so the radio
installation consists of five components: two
servos, receiver, battery pack, and switch.
During installation, try to get the heavier
components as far forward as possible, to
reduce the nose weight that you must add to
balance the model.
8) Cover, paint, and apply markings.
Apply your selected covering material.
Solartex iron-on fabric is a favorite for slope
warbirds because of its toughness. It might be
too heavy for a longer-wing slope sailplane
such as a racer.
Another reason why I like Solartex is that
it takes paint well. And the fiberglass fuselage
and covered wing and tail parts can be
matched in color, with airbrush or rattle-can
painting.
Apply markings—either national insignia
or canopy markings for a warbird or slope jet
or bold and distinctive markings for a racer.
Take a moment to admire your work; this is
quite an accomplishment. No one else has a
model that looks exactly like yours.
9) Check balance and correct-direction
control throws before test-flying. A noseheavy
aircraft maneuvers sluggishly and can
be corrected on the second flight, while a tailheavy
model might be so uncontrollable that
there is no second flight.
Triple-check control-surface movements
for correct and free operation. On a new
airframe, I have another pilot triple-check the
control-surface movements; that might
preclude a preventable crash.
Using the methods I’ve summarized, I can
get an airframe ready to fly in 26-30 shop
hours. I can paint and detail the sailplane in
another six to 12 shop hours.
I’ve built eight models this way, and I
have four short kits in stock for future
building. If there is enough reader interest,
I’ll be happy to write in more detail about the
construction methods: wing sheeting,
fiberglass finishing, and airbrush painting. MA
Sources:
RCGroups
www.rcgroups.com
Marty Hill
[email protected]
Marty Hill P-40 short kit description
www.rcgroups.com/forums/showthread.php?
t=992094
Marty Hill P-40 build thread:
www.rcgroups.com/forums/showthread.php?
t=738935
Dan Sampson (molds Inland Slope Rebels
club-project short kits):
[email protected]
MA online archives:
http://modelaircraft.org/mag
RC Soaring Digest online archives:
www.rcsoaringdigest.com
www.rcsoaringdigest.com/pdfs