Glow to gasoline conversion

REAL PERFORMANCE MEASUREMENT

Walt Wladyka of Shelton, CT, writes, "I would like to convert an O.S. BGX-1-3500 from glow to gas, primarily for economy of operation. Would you recommend this conversion?"

Walt, converting the BGX-1 to gasoline is a pretty straightforward procedure, provided you are prepared to invest in a spark-ignition system and, possibly, a new carburetor. One ignition unit that I'm familiar with is produced by CH Ignitions of Riverton, WY. This company markets a capacitive discharge ignition system with Syncro-Spark timing control, which is widely used throughout the modeling community. The Syncro-Spark feature automatically retards the ignition timing when you hand start (no kickbacks here) and during idle. For relatively large engines such as the BGX-1, CH offers a Syncro-Spark unit that completes its spark advance curve by about 4,000rpm, and this ensures that lowrpm torque and horsepower performance aren't compromised.

A second consideration involves the carburetor. Although the glow carburetor supplied by O.S. will function satisfactorily on gasoline, there are advantages to using an aftermarket unit that both pumps and regulates fuel to the engine. Walbro, a Japanese company, is one of several manufacturers that provides diaphragm-type carburetors intended for small engines that power weed-whackers, chain saws, leaf blowers and other equipment. Over the years, these carburetors have been successfully adapted to many miniature aircraft engines such as the BGX-1.

Fuel-tank positioning (vertical and horizontal) within the airframe is critical for proper engine operation with the O.S.supplied throttle-barrel carburetor that uses muffler pressure. With a Walbro-- equipped engine, the tank can be placed anywhere within the model without affecting the air/fuel mixture. This means that you can place the tank at the model's balance point, if you wish. The standard O.S. carburetor can be made to work more reliably by adding a Cline regulator, which has a diaphragm-type pressure regulator and is driven by timed engine crankcase pressure to pressurize the fuel tank. CH offers a gasoline conversion kit for the BGX-1; it includes a Walbro carb, a carb adapter, bolts, a gasket, an O-ring and a pressure fitting.

You can't run lean gas/oil mixtures (50:1, for example) with this engine because it isn't fitted with needle-bearing-- type connecting-rod bearings. Its plain-- bearing bushings require about 10 percent lubricating oil in the fuel (9:1). CH suggests using Klotz KL-100 (half synthetic and half castor oil) for this application.

If you have never used gasoline fuel in one of your miniature engines, there are several things to remember. Safety is the first consideration. When using gasoline fuel, I always carry a fire extinguisher to the flightline because the chance of fire is much greater than with glow fuel. Transporting gasoline in an approved container vented to the outside of your vehicle is another important safety and health consideration.

Relative to glow fuels, gasoline engines run at higher temperatures, so it's important to provide good ducting through engine cowls-especially to the cylinder and head fins. Don't worry about cooling the crankcase; it operates at a reduced temperature because of the fuel vaporization (a physical change during which heat is absorbed) happening there. Although gasoline removes less heat than methanol-- dominated glow fuel, it's still enough to keep the crankcase cool without external airflow considerations.

As always, avoid setting the needle valve right at its peak rpm; instead, back it off a few hundred rpm (rich). You won't notice an appreciable reduction in performance, and besides, you can't afford a damaging hot, lean run. Remember that gasoline doesn't have the power potential of glow fuel, so the engine will produce a few hundred less rpm on any propeller size.

Requiring only about half the tank size for an equivalent run time-depending on how rich or lean you set the needle valve-the gasoline mix is much less expensive (even at $1.75 per gallon) than glow fuel, and it promises improved idle and throttling with less oil residue deposited on your model. Are the benefits worth the additional costs and concerns? Many believe they are.

TIGHT ABC PISTON

Hal deBolt of Sun City, FL, writes, "A while back, K&B sent me one of its new .48s ... a pretty engine. I attempted to use it, but It was so tight I couldn't get it to turn over-no way! So, I set it aside.

"Recently, I needed an engine, so I loosened the K&B piston by hand lapping it to the cylinder; now it starts normally and runs fine.

"Anyhow, I wondered if you have had a chance to play with this one? From what I see, it seems to be very, very potent. For my flying, I used a 12x8 Master Airscrew that tached 11,500rpm (like most .60s). I have it in a Jenny which would tear up most pylon courses-too fast for me these days!"

Author's note: with more than 60 years of experience working with miniature aircraft engines, Hal "Pappy" deBolt has done it all, from control-line speed to RC Pattern to pylon racing. He certainly doesn't need advice from me concerning the K&B engine and its operation! Living in western New York all of my life afforded me the opportunity to become his friend, work at his factory (Demeco Models) during college summer vacations and fly against him in competition. Our many conversations at his shop, home, contests and conferences were always inspiring. Hal always looked for ways to improve the hobby-which he did with his many designs, innovations and products. He's doing the same today-at the age of 82-with autogyro experiments.

Copyright Air Age Publishing Sep 2001
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