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Fuel Commentary
by Anonymous
Have any of your club members tried some of the formulations on the mixing your own fuel page? Clubs can frequently have fuel made up by
various companies for about $6-$8 per gallon, in drums. Problem is it is very difficult to get folks in your club to agree on what that fuel
mixture will be. There are 2-strokes, 4-strokes and helicopters to consider. I have found that several clubs were getting fuels with just
16% total lubrication, and that is not enough for most ABC, ABN and AAC engines. Okay for 4-strokes, even high oil for several. Some just
order FAI fuel and let people add a little nitromethane. That would be 20% castor and 80% methanol. I have tried many different kinds of oil,
including Klotz KL-200, RM62 oil, Mobil Jet II (turbine oil!), various castors, synthetics, etc. Most commercial fuels do NOT have enough oil
in them and I see many a good engine bite the dust because of the fuel chosen being run through them.
We find that the Enya #3 plug, the OS #8 run about the best in our RC engines here. Even the cheapo $2 (AMA price) plugs from Tower Hobbies work okay, the new ones WITHOUT the idle bar. I broke in six of the new K & B .48 engines last October and they were
tough. First of all, to break them in correctly, you need to "run the hell out of them", a quote from K & B and they were right on the money
there. I broke them all in with an APC 11 x 6 prop, using 20% total oil fuel, ran them full lean after about a 15-20 second rich run to lube
both ends of the connecting rod, then back off just 2-4 clicks of the needle. Only ONE engine of the six sagged a LOT, started to really slow
down a LOT, I just opened the needle about 15-20 seconds to cool the cylinder, and took it back to full lean and off 4 clicks rich of that.
All the engines took 1-2 quarts, most took about 1.5 quarts or so and I did NOT break them in on the plane. They ALL sounded terrible, very
tight at ATDC, noisy FRONT ball bearing set, like the balls were running outside the ball bearing race, and the connecting rod clicked badly on
most of them just past top dead center. This is all NORMAL for this engine, unless the sucker catches on fire, keep running it and IGNORE
all these terrible sounds. The throttle transition is very crisp and the idle will continue to get smoother and lower with time on the
engine. This engine DOES put out about 2 HP at 15,000 rpm. :-) I prefer to run half castor and half synthetic through most of my
engines. The Mobil Jet II is the only oil I can remember that will actually run Nelson and other speed engines (Jett, etc.) with 5% Mobil
Jet II as the ONLY lubrication, then high nitromethane and the rest methanol. This oil boils off around 550 degrees F or so, even higher
than good Bakers AA castor oil. Klotz is not the very best oil, but the best oils, especially synthetics, were generally found too expensive for
routine model fuel use and Klotz works fine with castor present. There are three excellent castors still available, two in the U.S., Bakers AA
castor oil, Klotz Benol (racing castor) and in Europe and Australia, Castrol M (only, Castrol R is NOT an equivalent oil, and not miscible
with methanol). There are many suitable synthetics, Klotz is just relatively inexpensive and works fine with castor oil. Earlier attempts
(late 1950s) with Klotz ALONE as the only oil with speed, rat racing and combat were NOT very satisfactory, burned the suckers up (one good
Dooling .29, McCoy racing .29, etc.). We had to use castor based fuels, or mixtures of synthetics and castor. Pattern flyers today use a lot of
straight, high quality synthetic oil, but that is one of the few exceptions to all synthetics, also, you cannot get much more than about
30-35% nitro in castor oil based fuels, you have to go to a synthetic to reliably hold 35%+ nitromethane in solution. Most high nitro boat fuels
are totally synthetic, they often use 30-45% nitromethane. Mixed up some fuel the other day for a guy with a Cox .049 TD engine, they take
castor based fuels only, due to the design of the ball and socket arrangement of the connecting rod to piston fit. They run great on
25-30% nitromethane, at least 20% castor oil (20-25%) and the rest clean dry methanol. His hobby shop had sold him a gallon of 10% nitro fuel to use in this engine. Arghh!
Thanks for listening. As always, I am glad to hear from other modelers and to answer questions about fuels.
Happy flying. Terry Joe
Terry Joe Sprinkle
The old fuel mixing dinosaur
sprinkle@np2.mcg.edu
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