Free Flight Duration - 2010/11

As seen at the AMA Nats
[[email protected]]
Free Flight Duration Louis Joyner
Also included in this
column:
• New rules, new
propellers
• Recycling makes new
ideas possible
• Critics’ choice field box
• Great hooks
• Angles of a straight
wing
• Wiggle wings explained
Bill Shailor has gone back to carving propeller blades for his F1B
Wakefield Rubber models. The do-it-yourself approach allows him to
try blade shapes and airfoils that are not commercially available.
Bill carves each blade from a thick sheet of balsa and then covers
it with light fiberglass cloth and epoxy. The tapered basswood root
reinforcement is drilled to accept an aluminum fitting for
attachment to the Andriukov variable-pitch hub.
Dick Mathis put the tip panels from a crashed F1C Power model
to use for a tip-launch glider. The new wing features a carbon-fiber
D-box, carbon TE, and carbon-capped balsa ribs.
Doug Petty converted an inexpensive artist’s box into a field box.
Added compartments organize flying and repair equipment; the
lid holds tools, a stopwatch, and sectional stuffing stick.
ONE OF THE most enjoyable, and purposeful, reasons for going to a
contest is meeting other aeromodelers and seeing what new ideas they
have. Following are some innovative tips seen at the 2010 Nats.
F1B Propellers: Bill Shailor likes to carve propellers for his F1B
Wakefield Rubber models. As do many other F1B fliers, he had been
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using the excellent carved-balsa Andriukov blades. But last year he
switched to fashion his own.
“The Andriukov blades were designed for 40-gram motors,” said
Bill. Rules changes have reduced the allowable motor weight to 30
grams, or approximately an ounce.
“My new blades are narrower and thinner, at least a third thinner,
maybe more,” he said.
Bill has also reduced blade undercamber and slimmed the blade
near the root. In addition, he has increased tip washout and increased
pitch.
“I’m up to 26 to 27 inches at rest,” he said.
As do most F1B fliers, Bill uses a torque-actuated, variable-pitch
hub that decreases pitch during the flight to roughly match the
decreasing torque of the rubber motor. “At rest” refers to the lower
pitch setting.
He carves the blades from thick sheet balsa rather than from a block.
For each blade he cuts a rectangular blank that is 0.60 inch thick from
balsa that weighs 8.25 pounds per cubic foot. The blank is slightly
wider and longer than the size of the finished blade.
Then Bill adds a tapered basswood hub reinforcement. To get a
good fit, he drills a slightly undersized hole in the blade blank at the
point where the basswood will stop.
Two cuts with a band saw create a
shallow “V.” The he uses a tapered
sanding block to shape the V to match
the precut basswood reinforcement.
After that is glued in place, Bill drills
the root end of the reinforcement to fit
the aluminum hub fitting. Then he cuts
the block to outline shape and edges it
with 1/32 basswood. Templates made
from 1/64 plywood are pinned to the
curved sides of the blade blank, and the
exact position of the LE and TE of the
block are traced onto the blank. Now for
the fun part.
“I put on Pink Floyd and start
carving,” said Bill.
After creating a pile of shavings, he
carefully sands in undercamber,
checking with templates as he goes.
Then he carves and sands the top surface
to the desired airfoil and thickness, again
checking with templates.
At this point Bill covers each blade
with 1.4-ounce-per-square-yard fiberglass
cloth set at 45°, using Pro-Set epoxy.
Then he vacuum-bags the covered blade
on a form that matches the underside of
Based on his son’s suggestion, Jim Jennings uses dress hooks from
a fabric store on his Rubber-model propeller. A light rubber band
on blades aids folding; a hook on the nose block helps hold it in
place during flight.
David Mills packs turns into his Moffett
Rubber model. Wing construction is the
popular Union Jack, with both straight and
diagonal ribs.
David has developed a quicker method of
assembly for the wing, using two half-depth
spars to create a full-depth main spar without
the need for webbing.
Simple wire and tubing wing wiggler on this F1G Coupe allows the
left wing to change incidence in flight. At launch the TE is raised
slightly to give a left roll that counteracts torque; after a few
seconds it moves down to glide position, shown.
Removing the left wing of the Coupe shows setting for launch. A
rubber band runs from the wire arm forward to a timer. When
that band is released, a second rubber band pulls the wire back,
lowering the wing TE.
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the blade. Teflon-coated bleeder felt is used to
absorb excess epoxy resin.
Bill sands the blade with progressively
finer sandpaper, ending with 2,000 grit. A
final polishing completes the process.
In the last year or so, Bill has made 13
pairs of blades. See the February 2010
Duration column for more about carving
blades.
Recycling: A half-century ago it was
common practice for an aeromodeler to raid
his or her supply of leftover components to
make a “new” airplane. My older brother
fitted a Fubar wing and stabilizer to a simple
stick fuselage to make a quick Rubber model.
I even flew a Wakefield with a T-Bird wing at
the 1960 Nats.
But this early form of recycling seems to
have fallen out of favor. Gas models, the
source of those wings and stabilizers from the
past, now last much longer. In the days before
epoxy and better fuel-proofing, high-nitro
fuels took their toll on Gas-model fuselages,
leaving orphaned wings and stabilizers.
However, Dick Mathis has revived the
practice. His tip-launch glider uses the tips
from an F1C Power model. A crash, rather
than fuel-soaked old age, made the carbon Dbox
tips from a six-panel wing available.
“It’s called repurposing,” he said.
Unlike most sheet-balsa Catapult Glider
wings, the wing is undercambered, not flatbottomed.
“It’s way undercambered,” said Dick. “It
gets higher than my conventional ones; it’s
faster.”
The wing is attached to the fuselage with
screws, allowing removal for transportation.
A carbon peg running through the left tip
provides finger grips for tip launch.
As do more and more FF models, the
glider uses RDT (remote DT) to allow flight
termination at will. This makes test-flying
more convenient by allowing the flier to
terminate the flight if an adjustment is needed
and, more important, permits test-flying on a
small field with minimum risk of going offfield
or into a tree.
Artful Field Box: Keeping the tools and other
odds and ends we need at the flightline is an
age-old problem. Doug Petty’s solution is a
custom-fitted box that holds only what he
needs—nothing more and nothing less.
“I was using a big box and I had to dig to
find anything,” he said. “I made this new box
to organize myself. I’ve got everything I need
in that box.”
Doug actually has a series of boxes, each
fitted out for a particular type of model. The
one shown is his Rubber airplane field box.
He purchased the box itself for roughly
$10 at a Hobby Lobby craft store. It is
intended for carrying paint, brushes, and other
artist’s tools out into the field.
Doug relocated the handle to the top of the
box. Then he added various compartments
and racks to hold the desired accessories, as
well as a small first-aid kit.
Hooking Up:Most FF models use a variety
of hooks for various small rubber bands that
hold the aircraft together. As an alternative to
the usual bent-wire hooks, Jim Jennings found
a more fashionable solution at a local fabric
store. Sew-on dress hooks are compact, have
more gluing surface, and offer no sharp points
to puncture covering.
On his Mulvihill Rubber model, Jim used
the hooks as attachment points for the bladefold
rubber band. Two other hooks on the top
and bottom of the nose block, combined with
hooks on either side of the motor tube,
provide four-point anchorage for the rubber
band that holds the nose block in place.
Each hook is attached to the model with
epoxy and then reinforced with a small patch
of thin fiberglass cloth. To assure a good
bond, Jim makes a series of pinholes in the
balsa before attaching the hook. This allows
the epoxy to penetrate into the wood.
As with any epoxied metal joint, it is a
good idea to roughen the surface of the metal
with fine sandpaper first; degreasing with
acetone also helps. For an even stronger joint,
you could use the hooks as intended, sewing
them in place with thread through the balsa.
Spars Times Two: Union Jack wing
construction has been around since the 1950s.
It basically consists of straight (fore and aft)
ribs combined with diagonal ribs. The result
resembles the flag of Great Britain, where the
construction method originated. The wings
are a bit more trouble to build because of the
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Viewfinder
Lost in Muncie
I was at the FAC (Flying Aces
Club) Outdoor Champs at AMA
Headquarters in early September,
flying hard, and was exhausted after
spending time in the soybean fields to
the south along the runway.
Fortunately one of my lost models
was found by a groundskeeper at the
airport and was returned to the AMA
offices. I was so impressed by the field,
the AMA staff, and the museum, which
is a jewel. I could spend days there
taking it all in.
What happens if a lost model is
brought to the AMA by a local
resident? I lost my 36-inch Glenny
Henderson Gadfly in a massive thermal
that took her well off the field to the
west, perhaps 1-2 miles away. I
searched as best I could but to no avail.
My name and phone are on the
model, so chances are if she’s found at
least there’s a contact. I had flown this
model for 18 years so she is certainly
something special in my fleet. MA
—Tom Hallman
[email protected]
E-mail your high-resolution
“Viewfinder” photo and a short note
telling the airplane or helicopter story
to [email protected].
11sig5.QXD_00MSTRPG.QXD 9/23/10 10:22 AM Page 138
diagonal ribs, but the increased torsional
strength makes it worthwhile.
David Mills has added a few twists on his
Moffett model, based on a Joe Williams
design that Lee Campbell kitted.
A Union Jack wing is traditionally built by
installing the diagonal ribs and then adding
the straight ribs. Top and bottom spars run
along the intersection of the straight and
diagonal ribs, with vertical-grain sheet-balsa
webbing between the top and bottom spars, to
create an I-beam. Installing the webbing takes
time and, unless the fit is perfect, offers little
extra strength.
David uses a full-depth spar done in two
pieces. This eliminates the webbing and
speeds construction.
He glues the un-notched straight ribs to the
LE and TE. Then he sands a notch halfway
through the wing where the diagonal ribs will
cross. David adds a 1/16-inch-thick spar half
the depth of the wing. Then he turns the wing
panel over and sands a corresponding slot on
the bottom.
A second 1/16 balsa spar is added, creating
a full-depth spar without the need for
webbing. Then he adds the diagonal ribs from
LE to the spar and from TE to the spar.
“This is fast,” said David. “It gives you a
great glue surface compared to an I-beam.”
As with any type of structure with
diagonal ribs, it is important to build in
desired washin or washout when you add the
diagonals. After the wing is sanded, David
adds a glue fillet—using diluted Ambroid—
to every joint.
Wiggling Wings: A wing wiggler is a device
that changes the angle of attack on half of a
two-piece wing. Operated by a timer, a wing
wiggler acts like an aileron to introduce roll
during a certain phase of flight.
On a Rubber model a wing wiggler that
reduces incidence on the left wing could be
used to counteract the right-roll tendency of
the model during the first portion of the flight.
In the Free Flight Quarterly Coupe Book,
British Rubber flier Dave Hipperson
suggested using a wing wiggler as the only
auto surface on an F1G model. He suggested
using a lot of wiggler for a short period of
time, say 5 to 6 seconds. (F1B models
typically use a tiny amount of wiggler, but it
is left in for most of the motor run.)
I tried Dave’s suggestion on a new Coupe
and it worked well. It allowed a straight and
steep initial climb, transitioning to a spiral
climb without the bother and rear-end weight
of an auto stabilizer or rudder.
In an old Aeromodeller I found an article,
also by Dave Hipperson, detailing an easy
way to make the wiggler using brass tubing
and wire. The model in the article used a timer
mounted on top of the pylon in front of the
wing.
Because I wanted to use a timer mounted
on the left side of the pylon under the wing, I
had to basically turn Dave’s design upside
down, but it took only a few minutes to make.
I used 1/16-inch-OD brass tubing and
music wire that fit inside with no slop but
with the ability to rotate freely inside the
tube. I made a 450° bend in the wire so it
would fit tightly over the brass tube. Then I
soldered the wire in place and trimmed the
tubing to approximately 1/4 inch in length.
One end of the wire was bent in a right
angle, to go into the left wing; the other end
has a small loop on the end as well as a
slight dogleg, to allow it to go down 1/2 inch
or so and then exit the left side of the pylon.
Two short pieces of brass tubing are
attached to pylon sides with the tube/wire
piece in between, pivoting on a second
piece of wire. A rubber band runs from the
loop in the wire forward to the timer. A
second band runs to the rear to pull the
wing panel up for glide. I used small
hardwood stop blocks to limit burst and
glide movement of the wing.
None of the dimensions is critical;
simply make sure that the wing panel can
rotate freely on the main wing wire and that
there is no binding in the system. It is much
easier to install the wiggler in the pylon and
then use it to mark the exact location of the
hole in the left root for the wire.
A bonus of any type of wing wiggler is the
ability to adjust the differential washin or
washout between the left and right wing
halves during the cruise and glide. MA
Sources:
2010 Nats official scores:
http://bit.ly/b3a1ZP
National Free Flight Society
http://freeflight.org
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