Letters to the Editor
Send your Letters to the Editor to: Model Aviation 5151 East Memorial Drive Muncie, IN 47302
Engines
I am not in the habit of writing to magazine editors. As an ASE Certified Master Automobile Technician with more than twenty years of experience working with engines — including model glow engines, two-stroke go-karts, motorcycles, and automobile passenger car and racing engines — I am compelled to comment on the August and September issues.
The article by Joe Bunn in the August issue contained several misleading or inaccurate statements that could cause an inexperienced modeler to have problems. He advises heating the aluminum cylinder with a propane torch, placing a steel tube over the sleeve, and rapping on it with a hammer. I'm not sure what he's rapping on, but this advice could easily lead an inexperienced modeler toward disaster. In the bearing removal instruction, he advises tapping the front bearing out with a 1/4-inch socket extension. Running a steel socket extension through your aluminum-alloy front housing, heating it, and tapping with a hammer puts the crankshaft bore at risk of serious damage. He then says to reverse the procedure to remove the rear bearing. This is physically impossible. The rear bearing inner diameter matches the crankshaft bore. Any tool that can fit through the bore will pass through the center of the bearing.
In the September issue, Joe Wagner wrote a column titled "The Engine Shop." By his own statements, he apparently sends his engines to someone else's shop for repairs. This is probably a wise move for someone advocating the use of Vise-Grips to "flatten the threads" on a glow head to create a "force fit." He may have years of experience "playing with model engines," but he apparently has little or no knowledge of internal-combustion theory. He begins the section on four-stroke model engines by stating "don't fly with four strokes yet..." then goes on to tell us the rest of the world doesn't know how to calculate two-stroke engine displacement. His theory of standard displacement calculation being correct for four-strokes but not for two-strokes is way off the mark and damages the credibility of your magazine. He would have us believe that once the two-stroke piston reaches the exhaust port it is "coasting" and "not displacing anything." The rest of the world recognizes geometric compression and effective compression ratios for two-strokes. It has nothing to do with displacement. Displacement calculates the volume of the cylinder which can be filled with fuel mixture prior to compression. Four-stroke engines also have a geometric compression vs. effective compression discrepancy. This is due to valve timing — the exhaust valve actually opens before bottom dead center (this would be Wagner's "coasting" period) and the intake valve stays open past BDC, while there is also an overlap period around top dead center when both valves are open. Wagner's self-proclaimed "engineering analysis" is flawed and illustrates his lack of technical knowledge of internal-combustion engines.
Many newcomers to the hobby are eager to learn. Rather than learning the hard way through trial and error or by listening to the often-conflicting advice heard at the field, I believe modelers would be better served by learning the fundamental theory of internal combustion and its application to model engines. Once the basic operating principles are understood, the operator can make informed decisions regarding the correct operation and adjustment of the engine.
It is not my intention to make this opinion a personal attack on Mr. Wagner or Mr. Bunn. I do feel that a magazine devoted to the members of the AMA, and one that is dedicated to furthering the growth of our hobby, should be careful in the selection of writers and only hire those that have real expertise in their respective fields. Of course, experience is a great teacher, but unfortunately it can also lead us down the wrong path. After all, the world was considered flat for centuries!
Michael J. Kuper Darrington, Washington
I want to comment on how much I enjoyed the first appearance of Joe Wagner's new column, The Engine Shop. Joe is a great choice to write this column with his years of experience. I found his writing style to be very clear and to the point. This column should be very useful.
George Abbott Raleigh, North Carolina
Thank you for an excellent magazine. I would like to point out that amateur aerial photography is neither difficult nor expensive. I have many good shots taken by an aging House of Balsa 2x6 glider with a Kmart single-use 35mm camera rubber-banded against the fuselage under one wing. The shutter is tripped by a third servo via a short pushrod guided through a hole in the side.
Yes, you have to land to advance the film, and it takes a long time to take 27 pictures.
My glider uses a Cox Tee Dee .049 pod-mounted above the wing. For best results, trip the shutter while gliding into the wind after the engine quits.
The same photo is of the Checkerboard R/C flying field in Maywood, Illinois.
Gene Zendek Woodridge, Illinois
One Design
Enclosed is a photo of my new scratch-built One Design. Ron Kaul (right), founder of Ron's RC Model Building in Brookville, Ohio, framed the 38-1/2% aerobatic model. I covered it with UltraCote, and Kirby's Kustom Vinyl Graphics provided the cosmetic finishing touches. The 90-inch wing was custom-designed by Ron with the high point moved forward, creating a flatter leading edge (similar to the 300S), and the ailerons were extended out to the wingtips.
The rolls and snaps are very crisp, with no wobbling in finding center when you get off the sticks. Knife-edge performance and maneuverability are any pilot's dream — if you have the courage. Landings are slow and predictable; no "funny stuff."
With the Spear 4-6 twin and a 22 x 10 prop, the vertical is unlimited, even though the airplane came out at just over 23 pounds (a little heavier than normal for Ron).
This week I logged flight number 31 and I enjoyed flying this big bird immensely.
Rick Arrowood Troy, Ohio
Transcribed from original scans by AI. Minor OCR errors may remain.
