would run the engine, blew out the center of the
plug at full throttle. The plugs that had a more
durable constriction would not run the engine. I am
sure the right head volume coupled with a plug that
has a ceramic center would work. We were not
particularly interested in this combination so we
went back to the spark ignition head button.
The engine ran fine on 15% nitro fuel. We then
tried 40% nitro and promptly blew the plug
electrodes out the exhaust. The sleeve and the piston
were dinged so that ended that experiment.
Again, the proper compression and a more
durable plug would probably work, but we were
interested in developing a gasoline fueled engine.
The next set of experiments were done on an
M&D engine. We wanted to see if any of a variety
of fuels and oils would develop more power. We
ran the engine on mixtures of nitromethane in both
regular gasoline with out ethanol and premium
gasoline that contained around 8% ethanol. The
ethanol was a mutual solvent so the nitro mixed
easily in the premium gasoline. We got a 5% nitro
mix with the regular and 15% with the premium.
We could easily have mixed in more with the
premium gasoline. We also mixed nitro with a fuel
advertised as E10 (actually 32% alcohol) for a 10%
nitro fuel. Surprisingly, there was no significant
power gain with any of these fuels. We limited
ourselves to only adjusting the standard Walboro
carb’s mixture for best performance.
PROPWASH
12
April 2014
In Memory of Bud Vanderbush
Glow vs Spark Ignition
By Lohring Miller
NAMBA Safety Chairman
Recently there has been discussion about running spark ignition engines
in the traditional glow ignition classes. When model internal combustion
engines were first developed, they all ran spark ignition systems and used
gasoline for the fuel. Shortly after World War II, tether car and control line
speed racers started to play with fuels other than gasoline. They still ran
spark ignition. The development of the glow plug was regarded as a great
advancement that freed modelers from the batteries, points, and coils
ignition systems needed.
Now fast forward to the twenty first century. Compact magneto based
solid state ignition systems were developed for small industrial engines and
battery operated CD ignitions are widely available along with miniature
spark plugs. IMPBA forgot that a glow only ignition rule was passed for
what I call the open fuel classes, and NAMBA has always had that rule.
With the development of the gas classes, racers wondered why their spark
ignition engines could not run with similar sized nitro engines.
Mike Bontoft and I have done some testing of various fuels in standard
gasoline engines. Along the way we also tested glow ignition with glow
fuels in an engine designed for spark ignition and gasoline. Our experiences
with the early versions of the CMB 35 could be considered testing an engine
with glow ignition construction that runs on gasoline. These are the
conclusions from these tests.
We ran a 26 cc Quickdraw with a glow plug head button on some
standard boat fuels. Except for a modification of the WYK carb that
removed the pump and pressure regulator, the engine was unchanged from
the gas version. We had numerous problems with glow plugs. The ones that
Bud Vanderbush was a Scale Unlimited Hydroplane racer and member of the
Southern California Scale Thunderboat Association in District 19 in the 70’s
and 80’s. Pictured above, left to right are Bud Vanderbush, Larry Knudsen,
Joe Monohan, Jack Bishop, Red Blackford, Ralph Henry, and Leonard
Feeback. Photo courtesy of Joe Monohan (707 Specialties)