there hAs been a great deal of
discussion about bringing new fliers into the
fold. In this day and age of computers and
Ready-to-Fly (RTF) models, we have much
competition for drawing people into “easier”
activities.
Bringing the builder-of-the-model rule
back to Speed flying has been discussed. We
will be shooting ourselves in the foot if we
don’t make models easier to obtain, and
come up with kits that are easy to assemble
or RTF models.
I strongly urge all Speed fliers to pass
your old equipment on to modelers who
have an interest in Speed flying, and help
them learn to fly it.
I also urge you to build a trainer that
you can make available to interested fliers,
and show them that the pylon isn’t such a
terrible obstacle to flying.
At the end of the column, I have listed
a few Web sites for engines. When I was
compiling the information, I noticed that
the companies’ main business is car
engines. The availability of ready-to-run
cars and kits that are easy to assemble has
made them very attractive. I hope we can
learn to apply their examples to our
favorite hobby.
engine Cooling: In 1995, I went to England
to learn about engine-building from Sergei
Kostin. Sergei looked at the cooling on my
model and said, “Hmmm, I’ve never seen
anybody who did it right before; where did
you learn to do that?”
I learned a great deal during five years in
Boeing’s wind-tunnel model shop. I’ve also
done considerable computational fluid
dynamics (CFD) testing on the computer.
All my cowlings have exhaust-cooling
vents that go to the front of the cowl. On the
F2A models, the top of the engine is cowled,
except for glow-plug access.
Current F2A airplanes are considered the
epitome of Speed models, but a couple
things in them make it difficult to get
maximum horsepower from the engines.
The side vents on the cowls of current
F2A models suck air out of the cowl—not
ram it in, as fliers want them to do. Many of
the models have carefully configured air to
the front of the engines, but they don’t direct
that air around the back of the engine.
My F2A models have the side-exhaust
cooling channels that go to the front of the
cowl, so they are in positive-pressure areas
of the cowl. I cowl the backside of the
engine just as carefully, so the cooling air is
forced around the cooling fins on the hottest
side of the engine.
I’m convinced that Carl Dodge’s
homemade engines and Sergei Kostin’s Zalp
engines would go several miles per hour
faster with reconfigured cooling. Of course,
they could say to me, “so go out and beat
me or shut up.” I’m working on that.
Several years ago, we experimented with
Nelson 40s for Formula I Pylon models. We
built a shroud around the engine to direct
cooling air around the back of the engine.
We learned that dropping the head clearance
.004- to .008-inch increased horsepower and
improved plug life.
I cowl so tightly around the fins on my
engines, that grooves are worn in the cowl
from the fins rubbing against it when the
engine runs. I’ve been told that if the cowl
contacts the engine in any way, it gives up
horsepower; that is not true.
I also cowl the top of the engine, so there
is only access to the glow plug.
Something else frequently done wrong is
having the exit vents larger than the inlet
vents.
By having the outlet vents with 5-10%
less area, you increase the pressure of the
cooling air and tremendously increase its
cooling ability by increasing its density. I
learned about that from Formula I car racers.
The current trend in F2A is to have a
tightly cowled engine with additional air
introduced at the back of the engine onto the
exhaust stub, in addition to the air forced
through the cooling fins. I use this method
on all my models.
The only real exception to this is the
Zalp setup, which I think is in error. The
Zalp setup has a bifurcated (aerodynamic
term for splitting the air into two paths)
inlet.
It splits the cooling air so it hits the
engine at 2 o’clock and 10 o’clock, if you’re
looking at the engine with the exhaust at 6
o’clock.
There are no baffles to force the air
around the backside of the engine.
In addition, there are two NACA ducts at
the widest point of the cowl in the lowest
pressure area, to add air near the exhaust stub,
but there are no baffles to direct this air around
the exhaust stub’s fins. The CFD work I’ve
done says it’s pulling air out, not introducing it.
The Zalp engine is the most powerful
one out there for F2A, but the cooling is
holding it back and making the engine much
more difficult to run.
The Russians purposely tilt the cylinder
bore in the case, because they know it’s still
hotter on the exhaust side of the engine.
They work hard to thermally isolate the
exhaust stub from the rest of the engine by
cutting a groove in the case above the
exhaust port before the first cylinder cooling
fin, and they cut notches in the fins on the
exhaust stub to prevent the heat from
traveling up the fins to the rest of the
crankcase.
Jim Clary’s comments on the Coanda
effect are interesting. The work I’ve done on
this indicates that you need air dams that
stick out quite a way, to get past the
boundary layer and into a usable air stream.
I’ve experimented with (but haven’t
gotten repeatable results with) trying to keep
the heat in the exhaust, i.e., polished
combustion chamber, polished chrome in
the liners, and polished piston tops.
The theory is to keep the heat in the
gases, and not into the metal of the engine.
Then you would get more expansion in the
combustible gasses while in the cylinder,
which should convert to more horsepower.
I haven’t been able to measure more
horsepower, but I have noticed that I can
drop the head .001- to .002-inch without
damaging plugs. Carbon and soot buildup
on the piston and head make this difficult.
When you build cooling ducts, the
leading edge of the vent should have a
radius that is as big as you are comfortable
making it to the outside of the cowl. Make
one centered exhaust side vent 1⁄4-inch wide,
and slowly taper it (roughly 2°) to its exit
point in the cowl.
If you can vent the cowl at the top of the
fuselage where it’s at its largest crosssection,
this will help draw out the hot air.
You can also split the inlet air, so you’re not
putting cold air directly on the front of the
engine; this is the coolest part of the
cylinder.
I spoke with my old friend Alberto Dona in
Southern California, who owns Hobby Club
(a hobby distributor). Alberto carries a large
CONTROL LINE SPEED
Scott Newkirk, 4840 N. Glendale, Bel Aire KS 67220
… pass your old
equipment on
to modelers who have
an interest in
Speed flying, and
help them learn to fly it.
January 2001 153
number of great engines, and his business
has been unknown to the Control Line
community.
Engines Alberto is importing to the
US include the Cipolla (a couple of the
.21s look interesting for sport .21, and
there are two interesting-looking .15s);
CS (including the GZ .049); HPI;
MVVS; OPS; Picco; Profi (he has the
good F2A, F2C, and F2D engines);
PUMA; and Rossi.
Alberto is sending me samples of several
of these “unknown” engines for my
inspection, and I will report on them in the
next issue. MA
sources:
Hobby Club
Box 6004
San Clemente CA 92674
(949) 240-4626
Fax: (949) 240-5931
www.hobbyclub.com
Cesare Rossi’s NovaRossi engines:
www.novarossi.it
Ugo Rossi’s .21 engine with ceramic piston:
www.rossimotors.it/english/rossien.htm
Ron Paris’s Picco and NovaRossi site:
www.parisracing.com/
Steve O’Donnell:
www.odonnellracing.com
