The Engine Shop - 2010/12

December 2010 97
required by other 1/2As. Third, they use
standard glow plugs.
And the Mark I .049 and .061 come with
mufflers. The main benefit of those is to
attenuate the annoying high-frequency note
from small-model engine exhaust. The
Brodak Mk I .049 complete with its muffler
weighs a mere 1/10 ounce more than a Cox
Killer Bee—and puts out the same power.
Moving upward in the series, the new .15
(soon to be released
in an RC version)
appears to be scaled
down from the older
and popular Brodak
.25. I haven’t flown
my .15 yet, but I
have no doubt that it
will make an ideal
power plant for a
Squaw (one of the
well-known CL
Precision
Aerobatics, or
Stunt, models I
designed for Veco
in the early 1950s).
The Squaw kit
called for a .19
engine. However,
Brodak’s new .15
puts out nearly as
much power as the
For two decades Brodak
Manufacturing has been the mainspring of
US CL model building and flying activity.
The company started out in 1991 with
aircraft kits and supplies, and in recent years
it has begun carrying engines for CL use.
This line of power plants includes 19
types, five for RC, with even more to come.
Seven engines bear the Brodak name; they
range in size from .049 through .40—and
one of the .049s is an RC version, with a
precision barrel-type carburetor.
Brodak’s 1/2A engines differ from those
of earlier manufacturers—e.g., Cox and
Wasp—in several important ways. First,
they are more ruggedly constructed, to
better withstand “unplanned landings.”
Second, they are designed to run well on
lower-nitro fuel than the 25% and more
1951 K&B .19 in my original design
prototype—and I considered that model to
be somewhat overpowered.
This brings up a related point. One of
the key criteria for CL Stunt maneuvering
is to keep as close to a constant flying
speed as possible. We want just enough
flight velocity to keep the lines taut at all
times, even when flying in the wind. That’s
because too high of a flying speed
translates to excessive Gs in loops and pullups.
That can cause stalling and erratic
maneuvers.
Maintaining a near-constant flight speed
calls for large-diameter, low-pitch
propellers. We Stunt fliers never tune our
engines for maximum shriek! We set our
needles rich, and our models leave a smoke
trail behind them as they pirouette through
the sky.
Back to the Brodaks. The .40 is the
largest of the lot (so far). Mine has always
been a highly reliable performer.
It’s in a 600-square-inch flapped Profile
Stunt model that I designed. Although I’ve
made a few changes in that airplane
throughout the years to check their effects
on maneuvering, one thing I’ve never
needed to alter has been the engine.
A noticeable feature of the .15 through
.40 Brodak power plants is their tall
intakes. These provide two advantages:
improved power output and increased fuel
suction at the spraybar.
This results from the momentum of the
moving column of intake air. That
compensates somewhat for the pulsating
flow into the engine caused by the intake
port’s continual opening and closing.
I’ve been adding intake extensions to
my earlier CL engines for years. I’m happy
that with Brodak’s engines I don’t need to
Joe Wagner The Engine Shop | [email protected]
Also included in this column:
• Two-stroke vs. four-stroke
• Castor oil: facts and fiction
Brodak’s lineup of model engines
Brodak Manufacturing has been adding RC
engines to its lineup. As does the earlier
unthrottled version, the potent new .049
Mark II RC (L) uses a standard glow plug.
Brodak also markets the Aviastar line of
ABC-type CL power plants. Their tall
intake stacks increase both fuel suction
and power output.
Two superb performers for CL are the Brodak .25 (L) and .15. The large-diameter, lowpitch
propellers that they turn deliver maximum thrust at moderate rpm.
12sig4x_00MSTRPG.QXD 10/22/10 8:43 AM Page 97
98 MODEL AVIATION
go to that trouble
anymore—
particularly with the
Aviastar engines
that the company
markets.
Available in .46,
.53, and .61
displacements,
Chinese-made
Aviastars have the
tallest intakes of any
CL engines on
today’s market.
They are ABC
(aluminum-brasschrome)
designs,
with the typical
“TDC [Top Dead
Center] pinch” when
new.
But after breakin
my Aviastars
turned out to be easy to hand-start. And their massive
mufflers—straight-through-flow types—do an excellent job of
decreasing the exhaust sound output.
Brodak also carries eight of Saito’s four-strokes, which have
displacements of .40, .56, .62, and .72. Half of the eight are CL
power plants without throttles; the other four are RC types.
Several months ago I tested the three largest Saito CL fourstrokes,
to find out what advantages (if any) would come from
using a heavier, more expensive, and more complex power
plant in my models. After all, until recently CL airplanes have
invariably been powered by two-strokes. Why change?
In-flight comparisons between two similar CL Stunters
showed little difference in performance between my Brodak
.40-powered Shrike and my much-modified ARF Brodak
Cardinal with a Saito .56 in its nose. The Cardinal weighs 5
ounces more than the Shrike. Yet flown on the same lines,
alternately on the same day, the models performed almost
identically.
A slight difference in maneuverability I noticed was
possibly caused by the control setup. The ARF Cardinal has its
leadouts reversed from my usual practice of having the “up”
line at the rear. I have to admit that the Saito-powered Cardinal
flew a tad better.
Spectators did notice one significant difference between my
two-stroke-powered Shrike and Cardinal: the sound. The fourstroke
was both significantly quieter in flight and lower in tone.
Since the two airplanes had essentially the same lap times,
I’d say that the Saito .56 had a little more power than the
Brodak. That’s because the Cardinal weighs 11% more than the
Shrike.
Both models have the same wing area and general
configuration. Therefore, the Saito produced more power in
flight at the same speed as its lighter companion.
I continue to receive readers’ inquiries about model engine
fuels. One topic that comes up repeatedly is castor oil.
Although it has been used in high-performance internalcombustion
engines for almost a century, many modelers
seem to think that it’s obsolete now, having been surpassed by
modern synthetic lubricants.
Not so! It’s true that synthetics produce a less messy exhaust,
and they won’t congeal inside an engine that hasn’t been used for a
while. However, the virtues of castor oil make up for its two lessthan-
ideal characteristics.
Castor is uncannily adherent to metal surfaces, even at
high temperatures. Its high film strength doesn’t decline as
it gets hot. It doesn’t burn; in fact, it absorbs heat in the
combustion chamber, thus it acts somewhat similar to how
Left: Brodak’s earlier 1/2A CL engines: the
.049 (blue fin) and .061 (red fin). Their
mufflers muted the usual 1/2A high-frequency
screech, and they used a standard glow plug.
Below: Brodak now carries Saito four-strokes
for RC and CL. The .72 CL is ideal for Old
Time Stunt models designed for .60-size
spark-ignition engines.
A Brodak .40 and a Saito .56 are installed in similar models,
providing direct in-flight comparisons between two- and four-stroke
performance. The text reveals which one nudged ahead.
12sig4x_00MSTRPG.QXD 10/22/10 8:44 AM Page 98
“water injection” did in World War II fighter
aircraft engines. And castor oil prevents rust.
The “gumminess” in an engine that has
been flown with castor-lubed fuel and then
left unused for a while is not caused by
“gum.” Gum comes from trees, and there’s
none of it in the beans from which castor oil
is cold-pressed.
“Degummed” castor oil is merely an
advertising slogan. It’s as factually
meaningless as “decaffeinated bananas.”
What causes the stickiness is oxidation.
Castor oil is akin to linseed oil, in that
exposure to heat and air slowly causes it to
oxidize and thicken. Both will eventually
form a solid film—a well-known property of
linseed oil that is responsible for its use in oil
paints for centuries.
To avoid that kind of effect in model
engines—other than diesels—we merely
need to copiously inject after-run oil (ARO)
into our engines if we don’t expect to use
them again soon.
ARO in diesels will prevent them from
running! But model diesel fuel is a good
solvent for congealed castor oil, and I’ve
never had difficulty loosening a stuck diesel
by using its fuel and a hot-air gun to free its
moving parts.
Castor oil has a long and honorable
history of use in high-performance
internal-combustion engines. It was the
only lubricant that worked in the rotary
radials that powered World War I fighters
such as the Sopwith Camel, the French
Nieuport biplanes, and the Fokker
triplane.
Their engines produced more power for
their weight than in-line water-cooled
types, but they ran hotter and needed the
utmost lubrication. Castor oil provided
just that. It was also the lubricant of
choice in the famous Offenhauserpowered
racecars of the 1930s and ’40s.
However, after the races mechanics
quickly drained the oil from the engines and
rinsed them internally with solvents. That
prevented valve stickiness and other problems
from castor’s tendency to congeal. Yet for the
next day’s race the mechanics filled the
Offenhauser’s oil sumps with castor oil again.
You can’t surpass castor oil’s lubricating
qualities. MA
Sources:
Brodak Manufacturing
(724) 966-2726
www.brodak.com
Saito Engines
(800) 338-4639
www.saitoengines.com
Model Engine Collectors Association
www.modelenginecollectors.org