Letters to the Editor
Program Suggestion
Like many AMA members, I am concerned about the future of our hobby. I agree with the AMA's philosophy of introducing model aviation to young people through education, and I have a suggestion for another program that the AMA might pursue.
Every spring, middle schools and high schools around the country sponsor science fairs. Winners go on to compete at the regional, state, national, and international levels. Local businesses and major corporations alike sponsor awards in a variety of categories. As an Army recruiter, I judge a number of these fairs. I have always found a number of projects at each one that use model aviation to investigate aeronautical principles.
My suggestion is this: promote model aviation by recognizing the outstanding achievements of students who use model aviation in their science fair projects. Give an award that recognizes the "Best Use of Model Aviation" or the equivalent. The prize could be an AMA youth membership, a subscription to Model Aviation, or perhaps an opportunity to learn to fly with a local club.
I see this as primarily a local effort promoted by AMA clubs who volunteer to judge their local science fair and present the award. The AMA could assist by promoting the program so that local clubs are aware it exists. The AMA could also create a certificate or medal and create a prepaid membership that the club could buy in advance. I also see the AMA providing and promoting this sort of award at the state and national level.
I am sure that finding local AMA volunteers to participate in this program would not be difficult if the AMA promoted it. With our decision to significantly lower the cost of youth membership, the cost of the program could remain minimal. The potential gain in exposure for our hobby would be worth this cost.
Glenn Dean Frederick, Maryland
The Engine Shop: Two Views
In Joe Wagner's May column he is struggling to explain why a two-stroke engine doesn't make twice the power of a four-stroke. He mentions two "dissenting letters" and states that neither came from a model engine manufacturer or a renowned expert.
I am not a renowned expert nor am I a manufacturer. I am certified by the National Institute for Automotive Service Excellence as a Master Automobile Technician, a member of the Society of Automotive Engineers, and have been employed by an automobile manufacturer in the Technical Service Department for 20 years.
Our disagreement began with Mr. Wagner telling the readership that two-stroke displacement is incorrectly calculated. I wrote a letter explaining the flaws in Mr. Wagner's argument. He now tries to defend his position with the preposterous notion of grinding an exhaust port one-quarter inch higher and comparing power output.
I don't know how his theory has taken this turn, but this idea demonstrates a lack of understanding with regard to the timing events of a two-stroke engine. Raising the exhaust port much will, of course, destroy the engine. The fuel charge would be expelled out of the exhaust port instead of remaining in the combustion chamber during compression. However, I have seen many engines respond favorably to exhaust timing changes where the port was raised up to 0.025 inch. How does this square with Mr. Wagner's explanation?
Mr. Wagner now goes on to tell us another reason why a four-stroke can make essentially the same power as a two-stroke. He says some two-strokes' gross energy output has been expended compressing the fuel mixture in the crankcase. This is true and is usually referred to as "pumping loss." I would like to point out that pumping losses also occur in four-stroke engines; additionally, four-strokes have higher internal mechanical friction losses because of valve-train requirements.
The real answer that has escaped Mr. Wagner and led his readers down a path of misinformation is gas exchange. The output of an internal combustion engine is governed by the density of the fuel mixture in the combustion chamber. After firing, the spent gases must be cleared from the cylinder before a fresh charge is introduced. With a four-stroke engine, a complete stroke of the piston is devoted to clearing the exhaust gases and another stroke to introduce a fresh charge. In a two-stroke engine, these events occur in fewer strokes, which affects scavenging, charging, and overall power output.
Transcribed from original scans by AI. Minor OCR errors may remain.
