The Engine Shop-2007/12

Highlighting the SuperTigre G-34
Also included in this column:
• PSP engine test-mount
improvement
• 1960-era Fox .049s still
available
• GloBee’s new IntelliTach
• Why we should use fuel
filters
December 2007 85
The Engine Shop Joe Wagner | [email protected]
Filing away the front corner of the case’s bottom fin permits angling
the needle valve back. Notice the fuel filter; we should all use these!
SUPERTIGRE’S LINE of model-airplane
engines covers an extremely wide scope.
From the smallest—the G-34—to the huge
G-3250, all the SuperTigres provide
extremely well-built, low-cost glow power.
I’ve owned some of the larger
SuperTigres for a while, and I like them a
lot. I recently acquired one of the G-34s to
see how it compared with them, and I’m
quite impressed!
The G-34 is a ringed-piston, double-ballbearing,
Schnuerle-ported two-stroker. It
arrived with its carburetor assembly, twopiece
muffler, glow plug, and all the
“associated hardware” separately packaged
in the box.
That is doubtless one reason for the
SuperTigres’ low price. Partial assembly
saves considerable time at the factory—
and assembly labor is responsible for much
of any model engine’s manufacturing cost.
When I began trial-fitting the G-34’s
components, their unusually close fits led
me to do something I’ve never done before
while assembling a new-out-of-the-box
model engine. I preoiled everything before
installing it—even the glow plug! That
precluded any chance of bare-metal parts
scraping particles from each other as I put
them together. Everything fit snugly—even
the propeller washer and the carburetor
retaining bolt!
A 32-page, well-illustrated instruction
booklet comes with each SuperTigre. (It’s
the same booklet for all the engines, from
the G-34 to the G-2300, since they all share
the same basic design.) Even though I’ve
put together many hundreds of model
engines, I carefully read all the way through
the instructions before I began assembling
the G-34.
Okay, I admit that I didn’t follow those
instructions in every detail. For instance, the
booklet shows the muffler retaining screws
being installed from the muffler side. I
found that it was easier to do that the other
way around, which makes the nuts far more
accessible for tightening.
You can see a close family resemblance between the SuperTigre .75 and .34. Notice
the extra-deep head fins and large, quiet mufflers.
SuperTigre .34 running in a PSP test mount. The author’s modified
tank holder allows height adjustment to fit nearly any size engine.
Another change I made was one I
make whenever possible on a front-rotary
RC engine. I twisted the carburetor 10°-
15° away from straight-ahead alignment.
Doing that moves the needle back, away
from the propeller disk, which makes
needle adjustment safer. It also causes
the throttle arm to work at a slight angle,
but that doesn’t affect its operation in
any way.
Repositioning the needle back away
from the propeller is easy on the larger
SuperTigres, but on the G-34 I had to file
off much of the front corner of the
bottom fin on the engine’s case. Doing
that provided clearance for the fuel line.
The G-34 hand-started easily on my
test mount. As do most of the ring-type
engines I’ve run, the G-34 likes to be
“wet” for starting—hot or cold. I used
10%-nitro fuel with extra castor oil for
the break-in runs.
Especially with ringed engines I want
ample lubrication for the initial runs. The
idea is for the moving parts to burnish
one another into proper fits rather than
wearing them down during the break-in
process.
The SuperTigre’s instruction booklet
calls for leaving the glow lighter
connected 15-20 seconds after the engine
starts. I’ve found that to be necessary!
Probably because of the extra cooling
effect of the tall, closely spaced head fins
it takes a SuperTigre a bit longer to reach
its full operating temperature than it does
most glow two-strokers.
I keep my model-engine break-in runs
brief. Two or three minutes at a time is
plenty to allow all the engine’s parts to
reach their normal operating
temperature. Then I stop the engine (by
pinching its fuel line) and let everything
cool all the way to “ambient temperature.”
I follow that with another two- to
three-minute run. I repeat the brief run
and the cool-down four times and then
my break-in procedure is complete.
I always break in my engines on a
test stand. That way everything is out in
the open, for maximum cooling and
minimum “plumbing problems.”
To test-run most of my engines larger
than .20 I prefer the PSP all-metal test
mount. However, because model engines
vary so enormously in dimensions and
needle-valve locations I found it
necessary to modify my PSP unit’s fueltank
holder.
I screwed a 3/4-inch-thick aluminum
block (approximately 1 x 2 inches) to
one side of the PSP’s tank holder. This
block has a tapped hole through it, to fit
a 6-inch length of 1/4-20 “all-thread”
steel rod. I filed down the threads at one
end of this rod so it can rotate freely—
but snugly—in the existing threaded
hole where the PSP’s stock tank-holder
retaining screw fit. (That way I can
return to the stock tank-holder
arrangement if I want.)
Adding a plastic knob to the top end
of my “all-thread” rod gave me a neat
and easily adjustable way to set the tank
These Fox .049s, hand-fitted by Douglas Martin, are made from 1960-era factory parts.
All are Nostalgia-eligible and run well.
GloBee’s new IntelliTach has an extralarge,
adjustable-angle readout and
“memories” to save rpm readings from
one test to the next.
height. It even works while the test
engine is running.
(I had hoped that the fuel and vent
tubing from the tank would provide
enough “twisting resistance” to keep the
tank position stable; not so. I had to add a
vertical “tank alignment guide,” which I
made from hardwood, alongside the new
assembly. Now everything works fine.)
In the October column I mentioned the
disappearance of all the many Americanmade
1/2A engine manufacturers of
yesteryear. Yet some US-made .049s are
still being put together.
Doug Martin has acquired a
considerable quantity of original 1960-
era Fox .049 parts. From those
components he has been customassembling
three Fox 1/2A engines and
making them available to fliers in
Nostalgia FF and CL events.
Two of those .049s have single
bypasses. They were originally intended
for ready-to-fly plastic CL airplanes. The
third Fox .049 is the twin-bypass “FAI
Special.” The name comes from Duke
Fox’s expectation (in 1963 when he
decided to produce this engine) that the
FAI would make .049 the upper limit for
1/2A competition events.
Alas, Duke guessed wrong. The FAI
set .061 (1cc) as the limiting size for
“1/2A.” That made the Fox FAI Special an
orphan—and it’s the reason why ample
stocks of its parts survive today.
Doug Martin custom-fits each Fox
88 MODEL AVIATION
.049 he sells and he does something no
other American 1/2A engine maker ever
did. He test-runs each engine before
sending it to its buyer. That way he can be
certain that he’s delivering a fineperforming
product.
I waited for months for GloBee’s new
digital tachometer—the IntelliTach—to
become available. I have one now, and it’s
well worth the delay.
For one thing the device’s red case
makes it easy for me to find after setting it
down somewhere in the midst of an
engine-testing session. But that’s only a
minor virtue. Another of this new
tachometer’s features is its positionable
readout screen. The half-inch-tall LCD
numerals are easy to read, even at an
angle.
On the topic of angles, the IntelliTach’s
screen can be snapped into any of five
angular positions, from flat to 45°. I found
this feature to be helpful when taking rpm
readings from behind the engine, as the
16-page “Owner’s Manual” recommends.
With the screen raised it’s shielded from
any “back splatter” of raw fuel and oil in
the engine’s slipstream during rich
running.
Other features of the IntelliTach are
presettable propeller-blade selection—for
two-, three-, and four-blade varieties—and
three “memory functions.” Those can
retain rpm readings from one test session,
or flying event, to the next. I can see how
that would also be useful in setting up a
twin’s engines for close-to-identical
performance.
One More Handy Hint: In-line fuel filters,
such as Du-Bro’s, can save a power flier
considerable troubleshooting time! It’s
amazing how easily tiny “foreign particles”
in fuel can mess up a needle setting or the
ability to idle reliably.
In fact, I believe that the biggest reason
for recapping a fuel jug promptly after
drawing fuel from it is to block the entry of
airborne “crud.” Especially at the flying
field, dust particles and shredded grass
blades abound. They’re too small to be
easily visible—but not too small to give
you plenty of trouble if they get into your
model’s carburetor.
Fuel filters prevent that problem. Not
only that, but as my late, great friend
George Aldrich pointed out to me once,
fuel filters block air bubbles in the fuel
line. With a filter installed up close to the
needle valve, any fuel foaming in the
model’s tank becomes inconsequential. MA
Sources:
GloBee IntelliTach
www.bestrc.com/globee
Doug Martin
(719) 269-3274
PSP Manufacturing
(219) 622-6566
www.pspmfg.com