Frequently Asked Questions-2007/12

THIS IS the 45th
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
question is given a
sequential number
for future
reference.
A good many
questions and
answers have been
posted on the AMA
Web site.
Unfortunately that
posting stopped in
August 2005 and
will not continue until that entire section of the Web site is
revamped. In the meantime, if you can’t find the subject matter
you are interested in, drop me an E-mail or letter and I will try to
assist you.
Q324: “I’m brand new at this model aircraft hobby and have a
fuel tank that someone passed on to me that has three exiting
tubes. I know this must be easy for you, but please be patient and
explain the function of each tube. Thank you!”
A324: Don’t ever be embarrassed about asking any question, no
matter how basic it might be. That is the primary purpose of this
column. Had you purchased the fuel tank yourself, it probably
would have come unassembled but with detailed instructions
Fuel tanks and tubing connections explained
December 2007 91
? Frequently Asked Questions Bob Aberle | [email protected]
Also included in this column:
• Tubing bender
• Digital scale batteries
• Magnetic coil servos
• AMA Insider
• Follow-up on FMA Direct
Li-Poly batteries
• Follow-up on 1/2A engine
mounts
A typical Du-Bro 10-ounce fuel tank. Tanks in general must be
assembled by the modeler. Exiting the stopper are two or three
tubes, as explained in text.
How a three-tube fuel tank would be assembled. Vent line is at top;
fill line is at bottom. The third tube, the fuel pickup, is flexible inside
the tank. Metal tubing inside the tank must be bent properly.
Du-Bro’s tubing bender can handle copper, brass, or aluminum.
This tool prevents “kinks” in your tubing bends, which might
restrict fuel flow.
about how to install the tubes and explaining their functions.
Today all model-aircraft fuel tanks have an opening on one end
and come with a rubber plug and a cap. The plug fits into that hole
in the tank. The tubing you asked about passes through that plug
(or stopper).
Two or three lengths of aluminum, brass, or copper tubing
(with an outside diameter of approximately 1/8 inch) are usually
provided with the tank. These pieces are inserted in holes that are
molded into the rubber stopper.
One tube will go to the carburetor on the engine, providing a
flow of fuel from the tank. Inside the tank that tube is connected
to a flexible piece of silicone tubing with a weight attached to the
The tiny 1.1-gram Micro Invent magnetic coil servo is kind of a
“hybrid” of a conventional servo and a magnetic actuator.
FMA Direct’s new line of Li-Poly batteries, the Revolution series,
continues to use the FMA balanced charge node connectors.
The mounting ring (the one with many holes!) sold by Texas Timers.
Hank Nystrom also makes a special needle-valve assembly (left) for
Cox Tee Dee .049/.051 engines.
Check or verify the calibration of your scales with a known
measured weight. Erroneous weight readings can be obtained
when the battery gets low in voltage.
end. The weight keeps the tubing at the bottom of the tank,
regardless of the aircraft attitude. The other two tubes are for fill
and vent purposes.
When using a three-tube tank, all the tubes can remain
connected. You hook your fuel-pump line (from the fuel can or
bottle) to the fill tube. Begin pumping the fuel. When the tank is
almost full, a small amount of fuel will spill out of the vent tube.
That’s the function of the three fuel-tank tubes.
Some fuel tanks have only two tubes exiting it, one of which
goes to the engine. The other (which is like a vent tube) goes up
to a pressure fitting located on the engine muffler. At that
location a small amount of positive pressure is generated.
That pressure aids in getting the fuel up to the engine’s
carburetor; it “pushes” the fuel from the tank to the engine. This
is especially helpful when the tank must be located a distance
from the engine.
When using a two-tube fuel tank, you must disconnect both
fuel lines to be able to fill the tank. Once disconnected, pump the
fuel into the line that goes to the engine. When the fuel spills out
the other tube, the tank is full. Then reconnect both lines and
you’re set. I’d say that most modelers today use the two-tube
tank with pressure.
Photos show a typical Du-Bro fuel tank and its fittings. Their
assembly instructions are quite good.
If you would like even more details, the instructional Airfield
Models Web site has a section titled “How to Assemble a Fuel
Tank.” You should browse around the site; it contains many
subjects that would interest a hobby beginner.
Q325: “I’m having a hard time bending soft copper and
aluminum tubing without getting kinks. Is there any tool
available that can simplify this job?”
A325: What perfect timing! I just answered the question about
fuel-tank assembly, and bending tubing is a necessary part of that
assembly.
Since Du-Bro sells fuel tanks, I checked the Web site to see if
the company sells a tool that would bend tubing. It wasn’t a
surprise to find two benders: one for 1/8-inch-diameter tubing (the
more common) and one for 5/32-inch-diameter tubing.
The bender shown is Du-Bro catalog number 785, for 1/8-inchdiameter
brass, copper, or aluminum tubing. You have to try this
tool to see how easy it is to make a perfect bend, at almost any
angle, without any kink forming in the
tube. This is especially important for fueltank
fittings since a kink can easily reduce
the fuel flow.
I’ve included a diagram of the bender
to give you an idea of how it works.
Q326: “I own a small digital scale, which
I have used for several years. Recently I
started getting some inconsistent weight
readings and decided to try a new battery
in my digital scale. That immediately
helped the situation.
“Have you ever experienced such a
thing? Should these batteries be replaced
at routine intervals?”
A326: This is a case in which a reader
question actually helped me.
I have two digital scales (large and
small capacity). I coincidentally noticed
some unusual weight differences on one of
them while constructing a new parking lot
flyer. My partial weight analysis indicated
that I was heading for a 20-ounce weight,
but it totaled only 18 ounces finished and
ready to fly.
I weighed a piece of lead weight on my
other scales. Then I put it on the scales in
question, and it was off several ounces. I
replaced the battery in the scales and then
obtained the same weight reading on both
sets. Now I keep a small sheet of lead with
the exact weight written on it. It is my
weight calibrator.
Based on this experience I placed a
piece of tape on the bottom of each set of
scales and indicated the last time the
battery was replaced. From now on I will
calibrate the scales regularly and replace
the batteries, say once a year, to be on the
safe side. Erroneous weight readings,
especially in the smaller models, can
prove to be extremely important.
Q327: “I’ve seen sub-micro proportional
servos weighing as little as 2.5 grams, like
the little Blue Arrow job. I’ve also seen
the Falcon 1.6 gram digital proportional
feedback servos. But I’d still like to see
something smaller, but don’t want to go
through the tedious process of using
magnetic actuators. Is there an
alternative?”
A327: Micro Invent, a European
manufacturer, has a new series of what it
calls magnetic coil servos. They are kind
of a hybrid between a conventional servo
and a magnetic actuator. Two of the four
types offered weigh only 1.1 gram, operate
on 2.7-5.5 volts, and sell in the US for
roughly $34.
These servos are capable of controlling
aircraft that weigh as much as 50 grams
(1.75 ounces). The nice part is that they
have regular output arms and are far easier
to install than magnetic actuators. The
only problem to date is the type of
connector offered. Right now Micro
Invent supplies these servos with
connectors that mate only to its own
receiver.
With the prospect of the new Horizon
Hobby/Spektrum 2-gram, 2.4 GHz spread
spectrum submicroreceiver, it would be
nice if you could use these Micro Invent
servos with a mating connector. Then you
would have regular “plug-and-play,” as
you do with any RC system. Adapter
cables might be offered.
These Micro Invent micro coil servos
are available in the USA from Air Midi
Micros and Bob Selman Designs.
Q328: “A hobby friend of mine asked me
recently if I had read The AMA Insider. I
didn’t know what he was talking about but
tried looking it up on the AMA website. I
couldn’t find any reference to it. What is
The AMA Insider?”
A328: The AMA Insider is a bimonthly
publication that is available only on the
AMA Web site. It hasn’t been that well
advertised, which may be why you have
missed it until now.
On the left side of The AMA Insider
current-edition home page you can click
on “Subscribe” and provide your
information to sign up for the newsletter.
You will be alerted via E-mail when each
new edition is available for your viewing.
The AMA Insider uses articles gleaned
from the best national model-aircraft-club
newsletters. The recent July 2007 issue
had a great deal of excellent info for the
hobby beginner. It is definitely a mustread.
Follow-Up: Every once in awhile a reader
will respond to a question-and-answer with
some new information to add. In some cases
it is even about a comparable product I
missed that still deserves your attention. I
will add this extra feature when I feel it is
necessary.
In my answer to question 301 (July 2007
MA) I mentioned that FMA Direct went out
of the battery business. At the time the
company did! Keep in mind that there is a
several-month lead-time for my column.
Several months later FMA Direct found
a new source for excellent-quality Li-Poly
batteries and is now selling the Cellpro
Revolution Series. They all come with the
FMA Direct balanced charge node
connectors that will mate with the popular
Cellpro 4sA charger.
In answer 303 (July 2007 MA) I provided
several references to 1/2A engine mounts. I
left off by accident a very important source:
Hank Nystrom of Texas Timers.
On the Web site you will find his 1/2A
engine aluminum mounting ring that can
accommodate several types of .049-.061
glow-fueled engines. Hank makes an entire
line of accessories for the FFer, so it is
worth your time to look through his entire
Web site. MA
Sources:
Air Midi-Micro (Micro Invent micro coil
servos)
(775) 783-8545
www.airmidimicros.com/MIServos.htm
Airfield Models: “How to Assemble a Fuel
Tank”
www.airfieldmodels.com/information_sour
ce/model_aircraft_engines/assemble_a_fue
l_tank.htm
Bob Selman Designs (Micro Invent micro
coil servos)
(417) 358-9521
www.bsdmicrorc.com/productDetails.cfm?
ProdID=10501&catID=10004
Du-Bro
(800) 848-9411
www.dubro.com
MA’s “Frequently Asked Questions”
www.modelaircraft.org/mag/faq/index.asp
Texas Timers
(423) 282-6423
http://texastimers.com/accessories/engine
mounts.htm
The AMA Insider
www.modelaircraft.org/insider/index.html