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RPM REAL PERFORMANCE MEASUREMENT
by Dave Gieike
It's time again to answer your engine questions. We have a
variety of situations this month, from an engine that isn't getting
enough fuel to flying with antique powerplants to mixing
your own fuel. Keep those letters coming; if you have a question
you'd like to see answered here, please write to me c/o Model
Airplane News, 100 East Ridge, Ridgefield, CT 06877-4606 USA, or
email me at man@airage.com.
MIXING FUEL
Gerald Weiss of Menomonee Falls, WI, writes: "I am a 65-year-old
model builder and flier. I have several old model engines from my
childhood, including a K&B, GHQ, McCoy, Pacemaker .59 and
O&R. The smallest engine is a .19, and all are in good running
condition. 1 would like to use them, but where can I obtain—or
how do I mix—new fuel for these engines? I can only get 5- or 10percent-nitro
fuel here. Should I add castor oil to these fuels?"
The author mixes his own fuel. The 5-gallon can on the left is methanol;
the graduated cylinder holds 1,000ml; the plastic 5-gallon can (third from
the left) contains nitromethane; the short gallon jug contains castor oil;
the standard gallon container (far right) contains Klotz KL-200 synthetic
oil. All fuel ingredients are available from Klotz. Many specialty fuel companies
will custom mix fuel to your specifications; others already have
the desired blend as part of their standard products.
Gerald, I wish that you had included the individual displacements
for each of your engines. Some manufacturers such as
McCoy used both lapped steel and ringed aluminum-alloy pistons
with meehanite (fine-grain cast iron) cylinders. Others such as
O&R produced only lapped-steel piston and cylinder units. Early
K&Bs had lapped iron pistons and a steel cylinder. Both versions
of the Pacemaker .59 were outfitted with a lapped-steel piston and
meehanite cylinder. As for the GHQ (in my opinion, the worst
American engine ever produced!), sell it to an engine collector;
they have been paying up to about $125 for one of these lemons.
All of these early engines required extensive break-in with relatively
high percentages of castor-oil-based fuel. Except for very
early spark-ignition examples, K&B engines were all glow. McCoy
started out with ignition but had mostly switched to the glow
112 MODEL AIRPLANE NEWS
Engine advice
plug by the early '50s. The Pacemaker .59s were both spark ignition.
The Ohlsson & Rice engines were originally spark ignition
but finished their production run with glow plugs. If your
Pacemaker, O&R and McCoy engines are still fitted with their
ignition timer and breaker points, I suggest running them on
spark ignition with gasoline/oil fuel. Here's a good mix: three
parts (by volume) of regular-grade pump gasoline and one part
SAE-70 oil.
Unfortunately, SAE-70 mineral oil is almost impossible to find
today, but Klotz BeanOil castor oil (available at motorcycle shops)
is a substitute that will not contaminate your engine's combustion
chamber with carbon deposits. It's an excellent lubricant.
For glow O&R, K&B and McCoy engines, use 5- to 10-percent
nitromethane, 25- to 30-percent Klotz BeanOil castor oil and 65to
70-percent methanol. Several companies, including Wildcat
Fuels, will mix this blend to your specifications. Don't attempt to
use RC fuel in these old engines; 100-percent synthetic lube won't
adequately protect lapped pistons and cylinders, and the percentage
of lubricant is usually too low. If you know the oil content of
the RC fuel, however, here's a useful formula for determining how
much castor oil to add to bring it up to acceptable specifications:
(F -1) x A
100-F
= oz. of castor oil to add
Where:
F = final percentage of oil desired;
I = initial percentage of oil already in the fuel;
A = ounces of fuel you are treating.
Example: if you have a gallon (128 ounces) of 18-percent synthetic
oil fuel, and you want to add castor oil to bring it up to 28 percent
(not a bad idea with all that synthetic), find the following:
(10)x 128
100-28
= 17.8 oz.
Therefore, add 17.8 ounces of Klotz BeanOil to the gallon of 18percent
synthetic-oil fuel. Of course, you will need another empty
gallon jug to help mix all of this together, since the original container
is now too small. Also, the actual percentage of
nitromethane and methanol will decrease slightly but not enough
to affect engine performance.
FUEL-STARVED POWERPLANT
Tom Schumacher sent this email. "I hope you can help me with a
problem I'm having with my MDS 1.48. The engine is mounted
inverted and powers a Hangar 9 1/4-scale Cub. I originally used the
remote needle-valve setup with very poor results. It seemed that
no matter how much the engine was turned to the rich side, I
could never get it to 'four-cycle.' At first I thought that I might
have an air leak somewhere in the fuel system, so I replaced the
[fuel] lines and used wire-ties to cinch down every connection—
no luck. I've now eliminated the remote needle valve all together.