86 MODEL AVIATION
How to build a wing with curved dihedral
Micro-Flying Dave Robelen | [email protected]
Also included in this column:
• A Canadian micro
• Stefan Gasparin offers a new
line of magnetic servos
• Dave shares a building tip
Above: John Krouse’s wing sections were
bonded with Elmer’s White Glue to
produce a midchord span of 16.5 inches.
The author’s 13-inch-wingspan, three-channel S.E.5a winter project is constructed
from balsa, music wire, and thin carbon fiber, and it weighs 30 grams.
John Krouse’s completed indoor RC micro electric model has a curved dihedral that
produces docile and stable flight characteristics.
Phil Alvarez’s ultra-light indoor model
has Plantraco equipment, a 12-inch
wingspan, and weighs 4.6 grams.
GREETINGS, micro fans. I am writing
this during the coldest spell in February,
but chances are that by the time it reaches
many of you, the weather will have
warmed enough to get out and do some
flying.
I have several topics this time. The
first material comes from one of my
regular contributors: John Krouse, 1124
Pipestem Pl., Rockville MD 20854. I will
let John describe his newest project.
“This indoor RC micro electric model
airplane represents an attempt to build a
wing incorporating a conventional airfoil
profile (as opposed to a single-cambered
surface) and curved dihedral and LE
sweep (my own personal preference).
“I started with a pair of Gary Jones
EPP blue foam preformed blanks with a
4-inch chord, and proceeded to divide
each one into five equal ‘slices.’ I cut a
narrow wedge—1/8 inch at the TE—from
each panel, sanded the edges for 3/16-inch
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May 2007 87
Floor takeoffs are easy with the author’s little S.E.5a, and the model has lively flight
performance and good climb at full throttle.
This close-up shows the 4 x 4 GWS
propeller that provides the right amount
of thrust for the S.E.5a.
The top and wings of the S.E.5a were constructed from 1/32 balsa
molded over a foam form.
dihedral, and bonded them together with Elmer’s White Glue. The
result was a wing that has an overall midchord span of 16.5
inches, a nearly circular arc dihedral, and an LE sweep of 2.25
inches and 1.5 inches respectively.
“The electronic components, available from BSDMicro
RC.com and AirMidiMicros.com, consist of the following: 6mm
x 12mm 4.5-ohm (green) pager motor, Gasparin 4:1 reduction
stainless-steel gearbox, MCF 3222 carbon-fiber propeller,
MicroInvent Minor receiver, MCS2 .75-gram actuator, and a
single 90 mAh Li-Poly battery.
“With two-channel control (throttle and rudder) and a wing
loading of 1.7 ounces per square foot, the flying qualities of this
model can best be described as docile and stable.”
Thanks, John, for sharing the information about this
interesting project.
Paul Bradley, a champion of tiny RC models, provided the
information about this next project. It comes from Phil Alvarez in
Canada and following is his description.
“Enclosed is a picture of my micro RC based on a concept by
Rob Romash. When I attended the Indoor Nats at Johnson City
last year, I watched Rob flying his two micro RC models: a
monoplane and a biplane. I knew I had to design one that size.
“It’s some sort of blown up Mini-Stick (12-inch wingspan),
with Plantraco’s Butterfly gear. The components weigh 2.6
grams. They include a .38-gram receiver, a .23-gram actuator, a
.9-gram 30 mAh cell, a .86-gram geared motor, a .2-gram
propeller, and some nano connectors. The airframe is 2.0 grams
for a total weight of 4.6 grams.
“The wing and tail are built from 3/64 x 1/16 balsa, the fuselage
structure is 1/16-inch-square balsa, and .6mm (.024 inch) carbonfiber
rods form the wing support and landing gear. The wheels are
cut from picnic dish foam and the covering is Hyperlite Mylar.
“I flew it for the first time at the Heritage in Detroit,
Michigan, and the guys went crazy about it. Everyone had to fly it
and the most enthusiastic was Stu Weckerly. He kept asking
questions and making notes from the instruction sheet that
fortunately I brought with me.
The flight started with my releasing it on the floor from my
chair by the wall and watching it take off. The flight is absolutely
unbelievable—so slow and relaxed.
“Perhaps you’ll find it interesting enough for your readers to
see. It’s a new dimension in modeling. I have flown indoor
rubber-powered airplanes for many years and there is nothing like
that, but this is a new way that lets you control it. That’s the big
difference. There is room for both. It’s a new category in
modeling that is so much fun!”
Thanks, Phil. I am glad you are enjoying this new dimension
of our hobby.
I received a nice letter from Doug Dahlke, 1393 BLK, Wolf
Ave., Oshkosh WI 54902. He wants to remind us that the Jim
Walker-designed 74 glider (now produced by Frank Macy in
Oregon) would be an excellent candidate for light RC conversion.
It has been a long time since I tossed a 74 glider, but I have to
agree that it would bear a close look. The Frank Macy replicas
are made from some of the finest wood I have seen, and they
faithfully follow the Jim Walker originals.
So many ways to have fun with the new gear are available!
Who will be the first to try this concept and send me a picture for
the column?
A nice E-mail came in from Stefan Gasparin describing a new
line of magnetic servos that he has developed. The pictures were
too small to reproduce here, but there is plenty of information on
the Web site, www.microinvent.com.
It appears that the servo is a coil mounted on a section of
printed circuit board (along with some electronics), with a
magnet mounted so that it can rotate within the coil, and an
output arm is attached to the magnet.
There is an extensive line of these servos in different sizes and
configurations, and the quality of Stefan’s work is well known.
He sent some pictures of models the company sells as ARFs. The
tiny scale airplanes have wingspans between 8 and 13 inches.
Along with the servos and models, MicroInvent.com has a
nice line of electronics and drive units. I suggest that you check
them out.
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This is the building season and I have
been at it myself. Three of the pictures
show my micro S.E.5a with a 13-inch
wingspan. The construction is almost all
1/32 sheet balsa with a couple of small
blocks, a little music wire, and some thin
carbon fiber. The 30-gram weight
produces a lively flight performance.
The equipment includes a JMP combo
receiver, two 1-gram BSD actuators, a
GWJ 4:1 ball-bearing drive with a 7mm
Super Slick motor (blue end), and a 170
mAh Li-Poly cell. A 4 x 4 GWS propeller
provides the S.E.5a with the right amount
of thrust.
I have Scott Christensen to thank for
some of the features in this little airplane.
The primer under the color is Delta
Stencil Magic Top Coat Satin Spray that
works beautifully, and the rigging is
0.3mm carbon-fiber rod. Scott introduced
both of these products on his gorgeous
little biplanes and they are ideal for the
job.
The little S.E.5a is a sweet flier. Floor
takeoffs are easy and it has a nice climb
performance at full throttle. The only
deviation from true scale is a slight
increase in the dihedral to enhance the
rudder turns. This is one of those “natural”
scale designs that tends to fly well when
built with a modest wing loading and no
extensive changes to the geometry.
One of the pictures shows the top of
the S.E.5a being molded from 1/32 balsa
over a foam form. This method of
producing sections of a model shell can
produce nice, uniform parts that fit in
place with a minimum support structure
and hold their shape well. The wings were
formed to the airfoil shape using the same
method, and it only took a couple ribs to
stiffen things up nicely.
Why not try it? A variety of subjects
could benefit from formed-shell
construction.
You have read my modeling tip for the
month. Please share your methods of
producing model parts. We all have much
to learn.
I enjoy information about those
finished models, so keep in touch. MA
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