BY CLARENCE LEE
resonic timing (later changed to “tuning”
when the engine was replicated 40 years
later), which guarantees a continual flow
of power through the speed range. The
engine also featured a Centriflow bypass
diffuser, which imparts a swirling action to
the gasses as they are transferred from the
crankcase to the cylinder, thereby accelerating atomization of the fuel. I cannot find
any explanation of what these features
actually are or how they work. Can you
shed any light on this?
Fixes and Facts
Here’s a little engine history and a look at
Saito’s latest gasoline engine. It was back in
1934 that Bill Brown introduced the world’s
first mass produced “gas model” engine—
the .60-cubic-inch displacement Brown Jr.
The engine featured a one-inch bore and
stroke and developed 1/5 horsepower. The
engine utilized a spark ignition system
composed of a point ignition assembly and
a spark coil and condenser operated by a
3-volt battery. The fuel mixture consisted
of three parts white gas and one part SAE 70
motor oil. Other model engine manufacturers such as Ohlsson, Bunch, and Denny-mite, to name a few, were quick to follow.
Then in 1947, Ray Arden introduced the
glow plug, which dominated for years. In
the 1950s, the swing to larger aircraft began
with many fellows realizing that the larger
aircraft flew and handled windy conditions
better. With nothing available in the way of
power, leaf blower, weed wacker, and other
utility-type engines were modified, which
started the trend of using gasoline again.
Some of the model engine manufacturers
took note and began marketing larger displacement size gasoline-powered engines.
Some of the more popular gas engines are
now being produced by Saito, O.S., Desert
Aircraft, and 3W.
As regular readers of the column will
know, we occasionally do a bit on an old-time engine, which is usually inspired by
one of our readers. These articles always
bring in quite a bit of positive response.
Our first letter this month is typical of
many letters received that ask questions
related to old-time engines.
U I am interested in the development of
the model airplane engine, and I’m trying
to obtain information about two features of the EDCO Sky Devil . 65 designed
by Ira J. Hassad. The Sky Devil featured
Here is the 1947 Hassad Sky
Devil, which was produced in
.60-displacement size for
aircraft (shown here), and in
.65-displacement size for
tether cars. It ran well, but was
never competitive with other
racing engines in its class such as
McCoy and later the Dooling .61s.
Ray, I have quite a bit of information on
the 1947 Hassad Sky Devil including original operating instructions, various engine
reviews, etc., and cannot find any reference
to “resonic tuning” or “Centriflow bypass
diffuser.” This must have been some magazine advertising hype. I have had quite
a few Sky Devils pass through my hands
over the years, as well as having one in my
engine collection, and am pretty familiar
with the engine.
The engine is of pretty conventional
design other than the fuel mixture intake.
With a cross-flow front intake design
2-stroke, the fuel mixture normally enters
the crankshaft into the crankcase, up a
side bypass channel and port, and into
the combustion chamber where combustion occurs. Then the spent gasses exit a
side exhaust. The Sky Devil differs in this
respect in that the fuel mixture enters the
combustion chamber through a rear bypass
channel and port, and exits through two
exhaust ports on the front of the engine. I
can’t see where this would have anything
to do with “resonic tuning.” The engine
uses a high dome piston with a short
baffle extending out either side. This is a
common design utilized by many racing
engines of that era: McCoy, Hornet, Dooling, etc. This is possibly where the term
“Centriflow bypass diffuser” came about.
For those not familiar with the Sky
Devil, it was the production version of Ira’s
1941/46 Hassad Custom actually designed
by a gentleman named Bill Batzloff and
manufactured in limited numbers by Ira
Hassad. The Sky Devil was produced in
both a .60-displacement size for aircraft use