The Engine Shop
927 Pine Ave., Ozark AL 36360 E‑Mail: engineshop1@juno.com
Book recommendation: 2-Stroke Glow Engines For R/C Aircraft
In a recent column I wrote, "Few reference books devoted to model airplane engines are available nowadays." In response, Dave Gierke mailed me a copy of his book, 2-Stroke Glow Engines For R/C Aircraft. This is a truly comprehensive, exceptionally well-written, and thoroughly illustrated work that covers considerably more territory than its title suggests.
The first dozen chapters cover the general theory, design, and development of model airplane engines, including material on early spark-ignition types — and even Free Flight and Control Line power plants. The latter half of the book is devoted to "operational topics," and I can't think of any significant area that Dave has missed.
There are five chapters on "Running It Right" that provide the most thorough explanation of the model engine procedure I've read. From choosing a propeller for the first "break-in" runs to throttle adjustment for flight, Dave covers the art of two-stroke model airplane engine operation in minute detail without becoming bogged down in boring minor technicalities.
Though I've had no previous contact with Dave Gierke, his recommendations on running and maintaining glow engines are almost identical to mine. On the topic of mixture setting, Dave writes:
"The mixture should be set slightly rich for maximum power. Many modelers insist upon leaning the mixture in an attempt to squeeze out the highest possible engine speed ... this is asking for trouble. Piston and ring damage are possible, with varnish deposits a certainty (if castor oil lubricant is used in the fuel) because of the increased temperatures encountered. The truth is: engines can be operated noticeably rich and still produce power near the maximum without fear of damage."
Dave also recommends breaking in new model engines on a test stand instead of in an airplane, a minimum of 20% oil in the fuel (including some castor), and a cleaning and devarnishing procedure identical to the one I've developed over the last third of a century for my own use.
I highly recommend Dave's book. You can buy it for $17.95 (postpaid) direct from:
- Dave Gierke Flying Models, Box 83, Bowmansville NY 14026.
A copy of Dave's book — plus one of Eric Clutton's classic Dr. Diesel's Diary — will tell you almost everything you'll ever need to know about two-stroke model airplane engine operation.
On customization — Bill Dahlgren
Longtime engine experimenter Bill Dahlgren (Glenview IL) dislikes the concept of model engine "customization" — largely because much of it has been done thoughtlessly. Bill writes:
"I've gotten downright annoyed at the 'doofs' who seem compelled to do such things as sawing off an O&R exhaust stack in the name of 'streamlining,' thereby messing up a perfectly good engine for no good reason. On the other hand, when one has acquired such a butchered engine, one can feel free to do some real improving ...
"Someone had hacksawed the exhaust stacks from an E.D.2.46 Racer, and destroyed the cylinder seating area in the process. Some machine work on the top of the crankcase and a turned-up adapter ring restored the cylinder seating — and since the backplate assembly had also disappeared, an adapter was made to accept a reed-valve backplate from a Cox Sportsman .15. Success!"
Bill is certainly right about model engine butchery. In my engine-collecting days I encountered botched attempts at customization that provided some educational experience for the perpetrator — teaching what not to do in the future.
Favorite model engines
In recent remarks in this column about the impossibility of answering the question "What's the best engine?" I got a few responses from readers. When asked "What's your favorite model engine?" I'll have to equivocate. I've had enjoyable experiences with many model power plants over the past six decades — Free Flight, Control Line, Radio Control airplanes, for example.
I fondly recall the Arden .099 in the immediate postwar years; it was beautifully designed, made highly reliable runners and pioneered development of the glow plug. Yet I can't truly place Ardens among my favorites because they were too fragile — they couldn't stand up to the day-in, day-out punishment of sport flying.
Taking everything into account, I'll have to vote the Ohlsson .23 and the OK Cub .049 as my all-time favorite model power plants. I've received flying pleasure and fewer pesky problems from these two engine types than others, though some have come mighty close.
In terms of worldwide popularity, no model engine compares with the Mills .75 (.047 cu. in.) diesel. Introduced more than 50 years ago, the little Mills has long gone out of production by its original manufacturer. Yet its persistent popularity has inspired "replication" of the Mills .75 all over the world — in China, India, Australia, and Brazil. Replica Mills .75 diesels, made in India from the original British tooling, are presently available in the U.S. from:
- Carlson Engine Imports, 814 East Marconi Ave., Phoenix, AZ 85022.
With the proper fuel, Mills .75s start and run just as well today as ever. Their antiquish sideport long-stroke design has never been surpassed for friendliness and reliability. Those qualities, and not record-breaking power output, are what appeal most to sport-type model airplane fliers — who have always far outnumbered the competition-minded set.
Those same qualities are what made the Ohlsson .23 and the OK Cub .049 so immensely popular in their day. Their low rpm (less than 10,000) made it possible for millions of youngsters to fly their engine-powered (but mufflerless!) model airplanes in schoolyards and neighborhood ballfields all over America without seriously annoying nearby residents.
Millions of active model airplane fliers meant millions of engine sales. Ohlsson and OK enjoyed a total sales volume measured in seven figures for their most popular engines. The .23 was made from 1939 to 1949, with an almost four-year interruption during World War II. The Cub .049 was on the market continuously from 1949 through the mid-1960s, with most direct sales to modelers occurring in the first seven or eight years. During their heyday, those two model engines sold at an annual rate more than ten times as high as anything on today's model engine market.
Tachometers and the Sensi-Tach
Almost from the beginning, model engine enthusiasts have been curious and concerned about performance. The criterion has always been rpm. Yet few ways to accurately measure rpm have been readily available to modelers. Early attempts at rpm measurement via vibrating wires were inaccurate, and precision instruments cost far too much for hobbyists to afford.
With the advent of inexpensive phototransistors (circa 1965), electronic tachometers appeared on the hobby market. These analog-type tachometers indicate rpm on a dial like that of a voltmeter. They're handy and useful tools but are imprecise and require occasional recalibration.
When digital tachometers appeared, with direct readouts, they at first looked like a major improvement. Yet those devices too had weaknesses (one that annoyed me was the incessant "chattering" of the last two digits in the readout).
Now Tony Criscimagna of TNC Electronics (2 White's Lane, Woodstock, NY 12498) has made a breakthrough with his new digital/optical "Sensi-Tach." This high-precision unit uses a crystal oscillator circuit instead of the earlier (and less expensive) time-base modules of prior digital/optical tachometers. Thus the Sensi-Tach never needs calibration, and its readout design, which displays rpm to the nearest hundred, eliminates the confusing "digital jitter" of less-expensive units.
Some modelers seem to use their tachometers mainly to provide bragging data: "My Webra turns up 2,200 rpm more than your Super Tigre!" or "Bob's O.S. idles way lower than your Enya."
But a tach can be of real help throughout the life of a model engine. During break-in, an accurate tach allows you to monitor progress so you can tell when you've reached your goal. (Some engines in a given production batch require more break-in time than others.)
After your engine has run in, a record of its normal rpm range, made with a precision tach, can act as a standard to compare future performance. If you find that your top rpm with a given propeller and fuel is consistently down a few hundred (and changing the glow plug doesn't help), that's an indication that internal friction has increased and your engine probably needs to be cleaned and devarnished. See Dave Gierke's book for how to accomplish that.
Transcribed from original scans by AI. Minor OCR errors may remain.
