MIke Fredricks on the RC Combat Association Forum about 1/2A Combat I have decided to give it
a try.
I have been building and flying model airplanes for almost fifty years but cannot claim to be an
expert on any part of the hobby. I have been able to gain some ability with certain engines and
type of planes through dogged determination. When considering Half A engines I turned to the
experts for their advice, so that I could avoid the mistakes they had already made and do what
made them successful.
Thanks to my Dad, Charlie Melancon who is one of the most knowledgeable engine/fuel people I
know. Through him and letters he had exchanged with Jim Ong I was able to gain some insights
into fuel content for half A engines. Also thanks to Dale Kirn, 1/2A world record holder in CL
Speed for his advice to Jim regarding oil content.
Thank you to Larry Driskill, many time US National 1/2A Control Line Combat champion and
proprietor of "Kittingittogether". Larry's advice on breakin, props, fuels, and handling of the 1/2A
engines plus his ability to supply the many special items needed to run them has been
invaluable in getting me going. I urge you to visit his web site for information and products.
I purchased two Norvel .061 engines. One is a CL version, and has no throttle. The second is
the RC version and has a carburetor. Both engines are the "AME" models. Norvel also offers the
"Big Mig" version in .061 displacement. For more information click on their logo above.
The next decision was the type of fuel and its content. Most experts I spoke to or communicated
with advised that 1/2A engines need more oil content and more nitro content than larger engines.
The higher nitro content is necessary because the cooling surface area of the fins on a 1/2A are
much greater than those of a larger displacement engine, and therefore they run cooler. Dave
Gierke in his engine column notes that 1/2A engine manufacturers could leave the fins off entirely
and not adversely affect the engines performance.
Also the oil in a 1/2A engine is more critical because the engines turn at higher revolutions. Dale
Kirn, a designer of 1/2A engines at Cox felt that 20% oil was required in the Cox engines and that
at least half of that oil be high quality castor oil.
The fuel I selected to use for break in and testing is SIG Champion 25% nitro, 20% oil. The oil is
50% Baker AA Castor, and 50% Klotz Synthetic Racing oil.
During breakin I wanted to measure engine performance. Shown below from left to right are
some of tools on hand for testing: 1)Temperature/Humidy gauge from Radio Shack;
2)Tachometer from Tower Hobbies; 3)Ofna infra-red temperature gauge 4)Glow driver with
Sullivan plastic clothes pin type clamp that plugs into glow starter.
board) with 4/40 bolts and lockwashers holding the engine in
place. The fuel tank is a two ounce DuBro. The fuel tubing and
lines inside of the tank are made with Aerotrend "small"
neoprene tubing. The supplied tubing with the Sullivan tank is
too stiff and will not allow the clunk to move freely.
Speaking of the clunk, it will bounce all over the place, and
suck in air if you do not cushion the tank on the test stand. I did
not cushion it and the vibration of smaller props shakes the
fuel up a lot. The clunk was jumping up and down and getting
lots of bubbles in it.
Notice that the Norvel Glo-Head has been replaced with a
Galbreath conversion and Nelson STD glow plug
The Norvel CL .061 was broken in first. When cold the piston to cylinder fit was so tight that the
engine could not be turned over by hand. The Glo-Head was removed and the cylinder filled with
Marvel Mystery oil and allowed to sit for a couple of days. The porous Norvel Cylinder wicks up oil
during breakin. When it is saturated Norvel pistons and cylinders have a liquid to liquid fit. After
two days I flipped the engine over smartly by hand and determined that it could be hand started. I
did not use a starter until the engine had some running time on it. I was afraid of bending the
connecting rod because the fit was initially so tight.
Break In Process:
Norvel engines have tapered cylinders. They are narrower at the top than the bottom. This is the
same as with ABC engines. The idea is that the top of the cylinder will get hot from combustion
and expand. When it expands the piston will move freely through top dead center. To break in a
Norvel (or any ABC) you run it at high operating temperatures so it will expand. If you run it cold, by
setting it rich, the cylinder will not expand and the piston and sleeve will grind away on each other
leading to a poor running engine.
Set the throttle completely open (do not use the throttle till the engine is broken in) and open the
needle valve 3 turns. It took me ten flips to get the engine running. After five flips I added two
drops of fuel to the venturi and the engine then "popped" on the next flip. I flipped it with authority
till it started. Once running I adjusted the needle valve so that the engine went from its 4 cycling
sound to 2 cycle. You can definitely hear the change in pitch of the engine. Break in was done
with a Graupner 5X2 propeller. This prop is below the recommended diameter range which
allows the engine to turn it fast without a lot of effort. Upon later measurement it was determined
that the Graupner prop labeled as a 5" diameter is actually about 4.75 inches.
respect the needle settings and seemed to run rich and lean at its
own whim. I then realized that the muffler had come apart, causing
me to lose pressure to the tank. The photo on the left shows the
muffler opening. A second muffler was tried with the same result.
The muffler was taken off and all break in was done without the
muffler. The mufflers will be reassembled with JB Weld.
Started by hand, ten flips to start. Needle valve sensitive. Would not
hold 2-Cycle setting. Either too fast or too slow. Ran 30 seconds
then shut off and allowed to cool. Without glo-driver attached engine
would quit. Surprisingly easy to hand start.
Run for 30 seconds, again erratic. Realized muffler coming apart was causing the erratic running
condition. Shut off engine and removed muffler. Also noticed hard mounted tank was
experiencing fuel foaming. Filled tank to top on each subsequent run to keep clunk in pure fuel
and not bouncing out into air.
Run #3
Without muffler. Good run. Beginning to hold settings. Checked RPM on Graupner 5X2, 22,500.
Shut off after 30 second.
Run #4
Noticed some head leakage at either head adapter or plug. Still not smooth, settings again
becoming erratic. Will now run without glow plug clip. Notice the venturi is loose. Remove venturi
and reinstall. Erratic running may be due to air leaking at venturi. In the future the venturi should
be sealed with red RTV and tightened with thread locking compound
Run #5
Started this time with Sullivan electric starter. Had to tap venturi with finger to draw fuel. I had
been told these engines flood easily. I found just the opposite to be true. It needed to be primed
with finger over the venturi on each run after this one. This run total 90 seconds.
Run #6
I am surprised at how quickly the engine cools down. After a minute it is only slightly warmer than
air temperature. Run 5 rpm check showed 25,000 on Graupner 5X2. After running for 3 minutes
rpm reading showed 26,500 peaking to 27,000. After rpm check ran for another minute on lean
side of 4-2 break for one minute then shut off.
Run #7
Run two ounces through engine. Set RPM to just over 4-2 break, 26,100 steady running. It is
coming up in rpms each run. With the heat gun at 8 inches from the plug the CHT drifts from
250-300 degrees. After this run we begin propeller testing.
was done with Sig 25%nitro, 20% oil fuel.
