The Engine Shop 2003/05

May 2003 77
BILL BROWN died on January 8, 2003. I’m not going to write an
obituary for him here. However, I do want to point out that Bill Brown
accomplished the same thing for model-airplane engines—not once,
but twice—that Thomas Edison did for electric light. Although neither
man made the original inventions, each of these creative geniuses was
the first to come up with practical-for-production versions that anyone
could use.
Bill Brown developed his famous Brown Junior two-stroke modelairplane
engine 70 years ago, while he was still in high school! A
dozen years later he originated the CO2-powered model motor design
that has become the basis for all other CO2 motors made since then.
Consider the many OK, Campus, Buzz, Telco, Modela, G-Mot, and
Gasparin CO2 motors; every one uses the same fundamental principles
and basic design that Bill Brown worked out in the 1940s.
Two topics provide the subject material for most of the readers’ mail I
get in response to this column. One of those (of course!) is more power
from model engines. Free Flighters are forever seeking faster climb;
Radio Control (RC) fliers want “unlimited vertical” performance. But
many attempts to extract increased power from model engines turn out
to be quite disappointing. Then readers write to me about them to see if
I can provide a solution.
The growing popularity of Nostalgia Free Flight competition has
led many participants to use “high-nitro” fuel. This has far greater
nitromethane content than the “Nostalgia-eligible” engines (pre-1960
types such as K&B Greenheads, reed-valve Coxes, Holland Hornets,
early O.S.s, and Enyas) were designed to use. Even though their major
components—cylinders, pistons, shafts, and rods—can usually take the
increased power loads from being run with 35%-plus nitro fuel, other
equally vital parts often can’t.
Head gaskets blow, glow plugs fail, and ball-and-socket piston/rod
connections disintegrate. The usual reason for these problems is
excessive combustion-chamber pressure. That is caused by the fuel-air
mixture firing too soon: while the piston is still on its way upward.
Instead of the burning fuel transferring most of its expansive energy
to the rotating crankshaft via the piston, wristpin, and connecting rod,
the far-higher-than-normal combustion-chamber pressure blasts a
passageway through the head gasket, or detonation (I think of that as
“instantaneous combustion”) bursts the plug seal or shocks its glow
element loose.
The usual “cures” I suggest for these problems are using “colder”
glow plugs, reducing the nitromethane percentage, and adding extra
castor oil to the fuel. All of these “fixes” will delay the combustion
point—and a performance gain normally results from that.
RC fliers usually choose a different path to maximum power—
selecting the most potent engine available in the size their model calls
for—and I get inquiries from readers about how best to do that.
In a recent E-mail query from a college engineering student in
China (Model Aviation is read around the world, it seems), Guan Lei
asked, “Why don’t the model magazines publish horsepower and
torque performance curves for engines any more?” Guan went on to
request advice about designing and building a dynamometer for model
engines.
Since I’ve done that (while I was chief engineer at Veco 50 years
ago), I was able to describe a simple, accurate minidynamometer of the
“torque reaction” type. However, I cautioned Guan that “The
dynamometer I built worked just fine. But the only useful thing we
ever learned from it was the benefit of a long, slow engine break-in
process.”
That’s because “brake horsepower” numbers bear no necessary
relation to what happens in flight. (You could measure model-engine
horsepower precisely with a length of yardstick on the shaft instead of
a propeller!)
I believe my late English friend Peter G.F. Chinn was among the
Joe Wagner
T h e E n g i n e S h o p
212 S. Pine Ave., Ozark AL 36360
1951 K&B Torpedo .29s like this one are back in action, powering
Nostalgia Free Flights and Old-Time Control Line Stunters.
1950s Hornet .049 some called the “Holland Hand Grenade” can’t
stand up to high-nitro fuels some Nostalgia competitors use.
Engine-performance data from dynamometer testing was often
published but had little value for optimizing model performance.
first to accurately analyze model-airplane
engine performance. Month after month in the
1950s he published detailed results of his
engine tests in Model Airplane News and the
British Model Aircraft magazine.
Pete’s meticulous work and thorough
reporting greatly impressed most of us modelengine
enthusiasts at the time. Yet as accurate
as it was, Pete’s information didn’t really help
us model fliers much.
As I told Guan, “One of the engines that
Peter Chinn tested was among my favorites
for flying. I built and flew Free Flight,
Control Line, and RC airplanes powered with
these. Yet not one of those models performed
at all well with the propellers that Pete got his
best dynamometer readings from!”
We model fliers are primarily concerned
with what our power plants do for us in flight.
What happens on a test-bench dynamometer
is largely irrelevant to us. That’s no doubt the
reason why not much “dyno data” is
published in the model press anymore.
The second popular topic I find in my
readers’ mail is engine-cleaning methods.
There are two distinct problems involved
here, and one is baked-on sludge from long
periods of flying between cleanups.
As I’ve stated in earlier columns, the best
cleaning solvent I’ve found for externally
cruddy model engines is Dave Gierke’s
Demon-Clean. In response to the evaporationfrom-
a-closed-can problem with Demon-
Clean that I mentioned here a few months
ago, Dave recently improved the sealing
gasket in his containers and added a warning
note to keep the can out of direct sunlight.
As superb as Demon-Clean’s performance
is on the exterior of model engines, it’s of
little help with the other common type of
“contaminated engine”: the kind that has been
stored away for a long time and is jammed up
internally.
Before going any further with this topic,
I’ve got to warn you to never try forcing an
engine that won’t turn over with normal
“hand effort.” Something hard to replace will
surely bend or break!
I’ve disassembled and manually cleaned
many “frozen” model engines. To do that,
I’ve used tricks such as removing the plug
from an engine which had a piston jammed
partway up the bore, filling the cylinder with
ice-cold Liquid Wrench solvent, then
installing a spark plug (its seal is strong!) and
heating the whole assembly slowly with a
hot-air gun.
Now a somewhat simpler and exceedingly
effective way of freeing up a stuck-piston
model engine has come along, and it cleans the
outside of the engine at the same time it
unsticks the interior. This method uses an
electric “slow cooker” pot (available at thrift
shops for $5 or less) and automotive antifreeze.
Dave Gierke’s Demon-Clean’s new container seal and
recommended storage precautions provide a long shelf life.
A $5 “slow cooker” pot and automotive antifreeze provide still
another way of cleaning fouled model engines.
78 MODEL AVIATION
The technique is new and untried for me—
especially since I own no stuck-up engines on
which to practice. However, I’ve received
reports from several “reliable sources” who
swear that this is the way to clean a hopelessly
sludged (inside or out) model engine.
Put your problem engine in the pot, pour in
enough antifreeze to cover it, plug in and turn
on the pot, then let it simmer as long as it takes
to free everything up—even if that takes three
days. The solvent action of the ethylene glycol
in the antifreeze cuts through sludge and
carbon deposits, the rust-inhibiting/
neutralizing chemicals dispose of surface
corrosion, and the heat accelerates penetration
and the chemical activity.
There are a few drawbacks involved in this
method. Car antifreeze can act as a potent paint
remover, so if you subject your K&B
Greenhead or McCoy Redhead to this
treatment, you’ll need to repaint the previously
colored parts. (Use auto-engine enamel; it’s
available in spray cans in a fair range of colors.)
Antifreeze also attacks some plastics. It
partly dissolves a few and embrittles others.
How can you tell which is which? I don’t
know! The safest thing to do is remove all
plastic parts before trying the antifreeze-in-apot
method.
Antifreeze is toxic. That calls for taking
several precautions. One is to plainly label
your “engine-cleaning slow cooker”; use it for
this purpose and no other! Don’t dump the
used solvent down the drain or even on the
ground outside. (It can contaminate the
underground water supply.) Instead, pour the
used antifreeze into a plastic jug with a tightsealing
cap. Label the jug clearly, and dispose
of it at a gas station.
Last, you’ll need to wash out, dry, and
relubricate all of your engine’s internal
components before you run it. That usually
means taking it all apart and reassembling it.
I’m not wildly enthusiastic about the “slow
cooker” engine-cleaning technique for the
preceding reasons. I can see myself using it to
free up a long-stored-away, valuable antique
model engine (e.g. a Forster .99 or an OK
Twin), but that’s about all. My “usual
methods” work most of the time, and they
don’t require much in the way of toxic
chemicals. MA