Bob Aberle

The new JR synthesized RF module

THIS IS THE 38th monthly column in which
I try to give you the best possible answers to
questions you have written or E-mailed to me.
Each new inquiry is given a sequential
number for future reference.

May 2007 79
Left: Underside of the wing Bob designed
for his Lil’ Eaglet II. It is a variation of the
once-popular Jedelsky section.
Right: Bob Selman Designs sells this 2-
ounce plastic dispenser bottle for
cyanoacrylate accelerator fluid.
Below: FMA Direct’s upgrade for the
Cellpro 4S allows you to charge A123 and
Li-Poly batteries. On the right is an A123
three-cell pack.
JR Indoor Electric Festival Event Director Terry Nitsch erected this 60 x 15-foot water
tank so model aircraft with floats could take off and land.
Some of many cements that are classified
as “foam friendly.” They won’t melt foam
material during your models’ assembly.
fun-fly) was a 15-ounce foamie on conventional twin floats: the Super
Zoom sold by Hobby Lobby (www.hobby-lobby.com/super
zoom.htm). The ARF and the twin floats are available!
The water tank at the event created a great deal of fun and added
another dimension to indoor RC flying. Terry expects to repeat this
feature at the 2007 JR Indoor Electric Festival, which will be held
November 3-4. You can find the details at www.jriefestival.com.
Q291: “It is my understanding that certain cements will cause foam
material to melt. Since so many aircraft are now constructed from
various foam materials, what cements do you recommend? In other
words, what cements are foam friendly?”
A291: The “friendliest” cements for foam have generally been the fiveminute
epoxy, the 30-minute epoxy, and the white water-based glues,
similar to Elmer’s. The epoxy can become brittle and it is heavy, but
assembly can go quickly because of the short curing time. The waterbased
cements can often loosen (get soft) when water gets into the
joints.
Various cyanoacrylate (instant glue) distributors have recently
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80 MODEL AVIATION
come out with “foam-safe” cements. I have
successfully assembled models made from
“C” foam board and Depron sheeting using
the NHP Flash brand of cyanoacrylates
from BP Hobbies—specifically the NHP
411 Flash Thin Foam Safe and NHP 421
Flash Medium Foam Safe products.
Both adhesives are odorless and will
bond in three to 15 seconds. Also available
is the NHP 228 Foam-Plastic Friendly CA
Accelerator. The foam will not melt if you
use this brand of cyanoacrylate cements.
On several modeling forums I’ve read
about a Loctite product called “Sumo
Glue” (www.sumoglue.com). It is reported
to be “friendly” with many materials
including foam, wood, metal, ceramic, and
fiberglass. It is also 100% waterproof.
I’ve tried this glue, and it definitely
does not attack foam. But it takes at least
30 minutes to set up, and even when fully
cured it is slightly pliable. That may have
advantages because you don’t want cement
to become brittle.
I also noticed that this glue tends to
foam up when curing. Sumo Glue is worth
trying, but you will have to develop your
own techniques when using it.
There are certain foam materials that
will accept almost any kind of
cyanoacrylate and accelerator. The
Multiplex EasyStar RC electric-powered
trainer is made entirely from a molded
polystyrene foam called “Elapor.” I’ve
used regular, thin, medium, and thick
cyanoacrylate on that aircraft without
anything melting.
To give equal time, similar
cyanoacrylate products are available in the
ZAP product line from Pacer Technology
(http://zap.supergluecorp.com).
In the future more and more airplanes
are going to be constructed from foam, so
you better learn the cementing techniques
now.
Q292: “Several of my fellow club
members have talked about an all-balsa
wing section called the ‘Jedelsky’ that was
popular with FF and Towline Glider
enthusiasts years ago. Since I don’t like
covering aircraft but don’t mind spray
painting, I was wondering if this airfoil
section might be logical for me to use.”
A292: You can obtain lots of technical data
on the Jedelsky wing section by using one
of the popular Internet search engines such
as Google, Yahoo, or Ask!.
There were various ways to construct a
wing with this type of airfoil, but the most
popular involved two thin sheets of balsa
along with wide-spaced ribs. I tried a
design recently using flat 3/16 sheet balsa
for the wing with no real airfoil, and the
airplane did not fly!
While pondering this design problem I
thought about the Jedelsky-type wing
section and realized that this would be a
quick way to get some airfoil shape into my
all-balsa wing. I call the resulting design
the Lil’ Eaglet II. It was featured in the
January 2007 RC Micro World Webzine
and comes with downloadable plans.
I constructed the model’s wing from
two sheets of 1/8 medium balsa. A seam
line was placed at 25% back from the LE.
Does Your Club
Have a Flying Site
Success Story?
If so, MA wants to hear about it!
Finding and keeping flying sites
is a paramount issue facing the
Academy and its members. Just as
there are stories about clubs losing
flying sites or being unable to find
flying fields, success stories abound
as well. It is vital that these success
stories be shared so that others may
learn and apply sound methods for
finding and keeping flying sites.
Your club can assist others in
similar situations by submitting an
article to MA that meets the
following guidelines and includes
the following information.
• Text—not to exceed 1,500
words—should include the name and
location of the club, the chronology
of events leading up to obtaining or
retaining the site, the names of club
members who were responsible for
the success story, and the members’
opinions about what their most
important action was that ultimately
resulted in the venture’s success.
Note which government agencies
were contacted and the process
involved.
Electronic text should be
submitted in Microsoft Word on a
CD or via E-mail.
• Photos and diagrams of the field
should be included. Pictures should
number no more than a dozen and
must complement and illustrate what
is in the text.
Glossy 35mm prints and digital
photos on CD will be accepted. MA
will not accept E-mailed photos or
ink-jet printouts of digital
photographs. Please include captions
on a separate page.
• Send your article to MA
Aeromodeling Editor Bob Hunt at
Box 68, Stockertown PA 18083.
All submissions are subject to
review prior to acceptance. Payment
is made upon acceptance. Article
submissions will only be returned if
an SASE is included.
For more information, contact
Aeromodeling Editor Bob Hunt at
(610) 614-1747 or [email protected]
Ribs were fashioned from 3/16 balsa; notice
that there is no curvature to the ribs. The
sheet balsa goes straight up to the seam
point (the highest point on the rib) and then
trails down toward the TE. A 1/8-inch
hardwood dowel is used at the LE for added
strength.
Most Jedelsky sections (the thickness of
the airfoil) were 6%-10% of the wing chord.
The ribs were spaced wide and with straight
lines, and they were easy to cut. No spars
were necessary.
I hope the photo included with this
column will tell the story. If it doesn’t, see
the published plans.
This wing section is worth looking into
for smaller models because of its basic
simplicity. By the way, not all Jedelsky
airfoils have that abrupt peak! Some have a
more rounded (carved to shape) section. But
Jedelsky wings are typically all balsa, and
the ribs are left exposed, without the need
for bottom covering.
Q293: “I find when using a cyanoacrylate
accelerator spray that it tends to go all over
the place. All I want to do is cure a small
joint but end up wiping off the excess spray
from half of my aircraft. What do you do for
this problem?”
A293: This is more of a problem than you
might believe. Some cyanoacrylate
accelerators have been known to attack the
plastic portion of electrical connectors, such
as the Sermos/APP variety, causing the
plastic to literally crumble.
Recently I happened upon a plastic
dispenser bottle with a fine steel tip or nozzle.
You can fill the bottom (2-ounce capacity)
with cyanoacrylate accelerator. A protective
plastic tip covers the needle.
Turn the bottle upside down and only a
few drops will flow onto the exact spot you
need. Not only is this neater and safer to
work with, but you don’t waste accelerator.
These dispensers will soon be showing up
in our hobby market. I received my sample
from Gary Jones of Bob Selman Designs
(www.bsdmicrorc.com). They will cost
approximately $5 plus shipping and handling.
Q294: “I just bought a new battery pack
made up of A123 System M1 Lithium-Ion
cells. This pack has wiring for a balanced
charger, but I have yet to find one. What
should I do?”
A294: In December I learned that FMA
Direct has developed a modification for its
Cellpro 4S balanced charger that will
enable it to balance-charge Li-Poly
batteries and the new A123 batteries. If
you already own a 4S charger, the factory
upgrade will cost you $12. For $64.95 you
can buy a new unit that will include the
A123 modification.
You can find more information about
this new Cellpro 4S charger at www.fma
direct.com/support_docs/item_1223.pdf.
Red Scholefield also mentions it in this
month’s “The Battery Clinic” column. MA
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