MegaTech R/C Real World Helicopter Series Manuale Utente Scaricare il pdf (Pagina 67)

RPM REAL PERFORMANCE MEASUREMENT

by Dave Gieike

Engine advice

t's time again to answer your engine questions. We have a

variety of situations this month, from an engine that isn't get-

ting 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 [email protected].

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 10-

percent-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 com-

panies 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 displace-

ments 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 rela-

tively 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

plug by the early '50s. The Pacemaker .59s were both spark igni-

tion. 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 combus-

tion 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 65-

to 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 percent-

age 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:

-1) x

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 per-

cent (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 18-

percent synthetic-oil fuel. Of course, you will need another empty

gallon jug to help mix all of this together, since the original con-

tainer 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.

112 MODEL AIRPLANE NEWS

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MegaTech R/C Real World Helicopter Series Manuale Utente Pagina 67

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