CONTROL LINE AEROBATICS
Frank McMillan 12106 Gunter Grove, San Antonio, TX 78231
Recently, I've read some excellent articles on competition. In particular, Ted Fancher's outstanding series in recent PAMPA (Precision Aerobatic Model Pilots Association) newsletters has exceptional insight into what it takes to progress and win. I encourage everyone with an interest in precision aerobatics to read and reread this series because the many points that Ted makes are subtle, but truly significant. Contact PAMPA at 327 Pueblo, Anniston, AL 36206.
One absolutely key point of Ted's is a properly built and trimmed airplane. There are excellent articles from PAMPA and Windy Urtnowski, but I recommend Paul Walker's piece in the May 1991 issue of Flying Models as a can't-miss.
After his win at the 1990 Nationals, Paul wrote a comprehensive article showing the evolution of his Impact design, the powerplant package he evolved, construction and alignment procedures, and the area I want to highlight — trimming the airplane.
Paul included a set procedure, like a software program, to be followed from start to finish. Paul also dealt with the subtle adjustments that make all the difference in flight quality. One point he discusses was the options in trimming the tracking of the plane by adjusting the handle — all of which are, in most cases, based on individual preference. However, if you are not aware of what various adjustments do, you can't try them.
For example, everyone's wrist is different; his setup may have a different neutral point, different up-and-down movement from neutral, and probably different rate of movement. Many fliers will set neutral on their handle and then fly, living with that initial setting or only making a slight adjustment. However, with that setting, even after you have tried to trim the inside and outside turns, you may not get it just right.
Paul points out that the neutral position of the handle can be altered slightly by pulling the up or down line and fixing it in the new position. This changes the handle position at neutral elevation to a more angled or more vertical position. Although a slight adjustment, this can be a major improvement in the way a model flies. Jim Casale flies with a noticeable handle-down position at neutral; I use an almost-vertical position. The adjustment on the line length could be as little as a sixteenth of an inch.
What might prompt you to explore this particular adjustment is if you find that you have to consciously fly level at an altitude other than where the plane wants to be. If your model tends to be low, pull up the top line; if high, pull the down line slightly. You will notice a subtle change that will put you nearer to where you want to be. Remember that the changes you make are interrelated, and most are compromises, so act accordingly.
Do yourself a great favor and order a copy of the May 1991 issue of Flying Models at Flying Models, P.O. Box 700, Newton, New Jersey 07860 ($2.50).
Resources
- PAMPA (Precision Aerobatic Model Pilots Association): 327 Pueblo, Anniston, AL 36206
- Flying Models: P.O. Box 700, Newton, NJ 07860 (May 1991 issue)
CL Aerobatics / McMillan
Tech Tips
Last year I discussed how sealing control-surface hinge lines is an extremely effective trimming tool. Because the chances are good that it will help, there is no question that you should try this on new planes. Although it doesn't help all planes, you won't know until you give it a go. The benefit is the prevention of the "funnies," as Windy Urtnowski calls them. The outboard wing of my rebuilt Caudron popped up at the top of the inside and outside rounds. First, I sealed the space between the hinges, but the wing still behaved the same. In desperation, I ran a continuous strip from root to tip. The funny was gone. The best I could figure out was that the hinge cutouts at the tip were bleeding air. The small things can be real killers.
The main reason I bring this up was to pass on information I found in a most unlikely place. I had been using 3M's plastic tape, which had been satisfactory. The adhesive was effective because it was low tack; however, since the tape was a bit thick, the controls were somewhat stiff. This led to a search for something better.
Fas-Cal had gained some acceptance because it was thin, but the adhesive tends to pull the paint when you have to replace it. To make a long story short, I began using the Walgreens replacement, all-purpose tape.
This 1/2-inch, thin, plastic, low-stick adhesive tape resembles the Scotch brand, but it is pliable. When applied, it becomes almost invisible and does not affect control movement. There was no catalog number on the tape — only a blue card with the Walgreens logo. At four for $1, the price was incredible. This stuff really worked well.
For those of us who fight the pipe wars, the props are the real weapon and the road to better performance. The two APC props in stock form are viable:
- 11.5 x 4
- 12.25 x 3.75
But tweaking the glass and carbon props is a way of life.
Before we continue, let me make clear that you modify props at your own risk! You must be careful about the integrity of the blades and the balance. I'm certain that if you modify the props, the manufacturers are relieved of responsibility.
Many of you already know that the molded props can be adjusted by heating until the blade becomes pliable. The repitching process is sometimes an art. While it is still pliable, you have to grip the blade and twist it to the chosen angle. This is easy to say, but much more difficult to do. Bill Werwage says to always do it when you are fresh; if you are fatigued you will get frustrated.
I have tried hot air and hot water to heat the props. It's difficult to really control the temperature and direction of hot air (usually a hair dryer or heat gun). My recommended method of boiling water provides consistent temperature and allows you to dip the blade where you want.
Gripping the hot blade was the chief problem. Holding the hub with the pitch-gauge block was easy, but grasping the other end was inconvenient. The wide-jaw pliers messed up the soft blade. A rag worked, but slowed down the positioning of the blade, which cooled off rapidly. Using my bare hand had the same results because I had to wait until I could hold the blade.
The best and quickest method arose out of frustration: right by the stove were some kitchen oven gloves, so I tried one and it worked superbly! I could twist and hold the blade right out of the water. I'm not sure if it was coincidence, but that repitching session went extremely fast, so give this a try.
Transcribed from original scans by AI. Minor OCR errors may remain.
