CL Aerobatics
Frank McMillan, 12106 Gunter Grv., San Antonio TX 78231
Introduction
By the time this column is printed, the competition season will be fast approaching an end. However, several months of excellent flying weather are begging to be utilized.
Many times during the years, I've been burned out from the Nationals and I took the rest of the year off. In retrospect, this was a waste of some great opportunities!
If you want to improve your capabilities, now is the time to test and evaluate your equipment and techniques.
That "motherhood and apple pie" statement demands a plan that lays out the tests you want to run, and has some general goals to be achieved. At this stage, what I'm dealing with may seem like a great deal of trouble—to achieve what? That's what I'm going to get at, just to give you an idea.
Look at the variables
Too many times, I've rushed completion of that "super" airplane, only to learn that I didn't have time to make it fly well before the Nationals (Nats). That usually means the fine points of trim, propeller, and engine were not optimized. Sometimes I went with it anyway and suffered the consequences.
Did that affect how the model flew? Sure, because I naturally got it to work better after the Nats. If that hasn't happened to you, you probably haven't been in the game very long.
Make a few flights to get the feel for how your setup is working. This is your baseline to evaluate your development program.
Now look at retiming; vary the tip weight—many times we have a tendency to carry a bit too much. Observe how the wing behaves at the top of the hourglass and in vertical flight.
You may have to reduce the tip weight until the wing flies cleanly. Sometimes you're looking at a gram or less to find an optimum point. Now is the time to do this, because you're not in a hurry.
Look at the leadout location. Shift the setting ahead 1/16-inch at a time, just to see what happens. Remember that the weight, leadout locations, and center of gravity (CG) are interrelated. Moving the CG back is like moving the leadouts forward.
Why? The key is the relationship of those two factors—not the actual position of the leadouts. The tip weight also bears on the leadout location. Less tip weight has the effect of a more-forward location.
That's why you have to try a variety of combinations. The problem is quantifying what you are looking for in setting up an airplane.
Line tension
One key point that is surprising to me is that line tension needs to be reduced to a minimum. That goes against what I had thought for many years.
If you think about it, line tension equates to physical stress on the pilot. He or she not only has to hang on, but also has to apply the correct control input time after time. It is logical that the heavier the airplane flies, the more stress there is on the handle. Couple that with the force on the controls, and you have major factors determining how well you can fly your model.
This really struck home with a new Caudron; it had a new configuration that initially had exceptionally heavy line tension. That really opened my eyes. I couldn't make more than a few flights before my arm hurt so much that I had to stop!
The ultimate goal is to achieve sufficient line tension to keep the model on the end of the lines at all points in the patterns. This also implies that the tension will allow the pilot to apply the proper amount of control, to maneuver the model precisely.
We "fall down" because this goal is difficult to achieve uniformly. The ST .60-type airplane had large amounts of line tension at 45° and below. The tension dissipated rapidly above 45°. We typically lived with this, but you can anticipate the difficulty of flying accurate patterns with the varied line tension.
The closer you can get your model to consistent light-to-moderate line tension throughout the pattern, the more accurately and consistently you will fly.
The three factors—CG, tip weight, and line setting—have a great deal to do with this goal. Use flights to vary the settings to improve your trim before going on. Assume the model wasn't properly set up to begin with—no setting is sacred.
Adjust one parameter at a time. I suggest tip weight first, then CG, followed by line adjustment.
Line length and trim
Another trim element is line length, which is a comfort-zone factor.
Typically, the better the airplane, the more line it will carry. You gain time in the maneuvers, and your model can carry more rpm for the same lap time.
A change of approximately one foot in line length equals a tenth of a second in lap time for the same engine speed/propeller.
At this time of the season, you can afford to experiment with lines you have been using. They will have to be replaced for next season anyway.
One symptom of too-short lines is that the airplane will give the impression of being pushed or crowded—especially when the wind is up. For lines that are too long, the model will float away into the pattern, turn slowly at the top of the loop, or be caught high in the outside turn. The remedy is obvious—more or less line, lighter or heavier tip weight, or change the CG. The only way to find the best combination is to experiment.
Propeller
We now come to propellers, the most critical single component in determining the power and speed of your model. There are a few factors and relationships to keep in mind as you explore the potential of new props.
Perhaps the best place to start is with a discussion of the materials. There were basically two propeller choices for many years: wood, and later, the Grish plastics.
There were modifications to the wood types, with the Tornado pressed wood—a hot-resin-impregnated light product. Top Flite® experimented with another resin-impregnated wood, but no prototypes were developed because the molds were ruined!
The next generation saw the development of fiberglass-and-carbon epoxy-molded props, which really matured for Stunt during a 10-year period. Various resin materials and techniques evolved, and the fliers developed their expertise and learned how to use the new props.
The APC molded propellers provided another option.
The real question is, are certain props the choice? Maybe, and the "next" one yet to be developed.
Wood props do work as well as the carbon props. However, the factors that govern how well the prop works are the engine and the airplane. The airplane "wants" to fly at certain speeds; the engine "likes" a certain load, and works best at a certain rpm range.
Conclusion
Next time I'll look at how to approach putting this all together, to get your best combination. But remember, it takes personal preference and your hard work to find that flying goal. MA
Transcribed from original scans by AI. Minor OCR errors may remain.
