CL Aerobatics
Frank McMillan, 12106 Gunter Grv., San Antonio TX 78231
I RECOMMEND a book to you that has relevance across a variety of subjects: Who Moved My Cheese? by Spencer Johnson. The focus is how to deal with change, using mice as characters in a very simple story. They have different "traits" that contribute to the insight provided by the book.
You might ask how this applies to Control Line Aerobatics.
We all have our "comfort zones"—routines we have established, favorite foods we like on certain days, or particular combinations of trim we love on our favorite models.
Take the case of a trip to a contest at an unfamiliar site. The chances are excellent that you will face changes in trim and engine settings. Someone has moved your "cheese"! What will you do?
Not too many years ago, I would have lived with the status quo and done the best I could.
There was a character in the book faced with the same situation, who also did nothing to change the situation. Not surprisingly, the circumstances did not improve.
It took me a long time to focus myself to analyze the situation and change the model. Once I broke the mind-set, everything improved. It really evolved into part of the enjoyment of the sport, making the package work well.
But for many, change is difficult to accept; it imposes stress and inhibits optimum performance. Do yourself a favor and check out the book.
While on the subject of trimming, I want to mention a general trait we have. When I classify it as "general," I mean that it applies to all types of trim devices.
But a particular device is not the trap; the trap is the assumption that at any one point in time you have a trimming parameter locked in, such as tip weight. Or you think you're making a change, which then becomes the new false baseline.
Some years ago, I was practicing for the Nationals and observed the wingtip throwing. I removed some tip weight and went to the Nats. I assumed that the change I made was correct.
Flying all through the event, I knew something was not quite right, but I couldn't put my finger on it. The model wanted to jump off the ground on takeoff, and it seemed light on the transition in the eights.
As it turned out, I had removed approximately a quarter-ounce. However, the conditions at the site required an additional quarter-ounce, leaving me roughly a half-ounce short.
As so often happens, I solved the problem after the Nats when Bob Hunt observed that the inboard wing was flying low. This accounted for the problems observed at that point.
You may wonder why I didn't pick up on this. Remember the assumption trap; I had convinced myself that the tip weight change had made things better. And until observed evidence contradicted my assumption, I didn't look again.
A way to avoid such traps is to measure and record conditions and changes. Keep a log of models, trim, tank position, engine settings and weather conditions. That way, when you travel to a new site, you have a baseline and can see what adjustments you need to make.
Also, resist the temptation to make many changes at once. Change only one variable at a time so you know which had what effect. Little by little you'll learn to adapt.
I took the appropriate step to fix the throwing problem, so that was okay. The problem was right in front of me, but I couldn't get it to come into focus.
A similar problem was the misalignment of tank height. This is a critical adjustment for piped engines; they are very sensitive to the proper height.
For some reason last spring, I looked at adjusting the tank. The tank was approximately 1/8 in. higher than I had been using. The lap times upright and inverted were within hundredths of a second. I was right on!
At roughly this time, I noticed that the engine was running nicely in good weather. As the wind started to blow, the engine ran hard in certain spots. I was mystified as to the cause. After all, I had just set the run precisely!
This erroneous assumption of a good tank setting caused me to go to extremes to try to adjust the engine from hitting hard in certain maneuvers. I shimmed the head, lengthened the pipe, and lowered the propeller pitch and diameter.
All of this helped but did not clear the problem—only the symptoms.
When I returned from the Nats, I had time to reflect, and I moved the tank down to where I had it and, just to be really "smart," I moved it 20 thousandths more.
Then the symptoms of hitting hard were in different spots in the pattern, but at least I had some limits. By this point I was really frustrated.
I finally went back to my original setting, and everything settled down immediately.
The engine was much more docile with no hard breaks in the maneuvers. It cycled predictably and controllably from four- to two-cycle and back in just the correct places.
It was surprising to me how small the "sweet spot" was—approximately plus or minus .010 inch for me, with my metal tank setup. The top of the feed line to the surface the engine was mounted on is .5 inch. That is not equal to the old, accepted half inch and is measured with a dial micrometer. A ruler is not accurate enough.
By sweeping a setting, as correct, finding the proper trim and proper length, with many false tries.
Stop and analyze the situation before changing, etc. Determine what could have caused the problem. But, equally important, when did the problem show up? Did it materialize after something changed?
Fuel problems are a potential source of difficulty to solve, probably because sometimes they take a few flights to manifest. Please remember to keep everything on the table when evaluating problems. Everything is interrelated.
New items: I just watched one of Windy Urtnowski's videos about how he constructs carbon composite fuel tanks. The tanks are constructed on a custom base using precisely machined molds.
The design of the mold is the key to controlling the thickness of the tank wall and resin, which equates to weight.
The video details how the tanks are constructed and assembled. At the outset, Windy discusses the value of the exceptionally light tanks. He states that they typically save an ounce compared to conventional metal tanks.
The tanks use aluminum tubes to save weight compared to copper.
Windy also says that the decision to use tanks should be considered carefully. They are not cheap!
However, after watching the video, I realized that there is a lot of work involved in producing one of these tanks, so the price seems fair—if not a bargain.
It's an interesting video, and you should see it if you're considering purchasing a composite tank.
Contact Windy at 93 Elliott Rd., Rutherford, NJ 07070; Tel/Fax: (201) 896-8740.
He has many other videos about specific topics, such as the Pullwalker B-17 at the 2001 Nats, the 2001 Team Trial, and many technical building features.
New flying lines are available from Tom Morris at Tom's Building Service, 327 Pueblo Pass, Anniston AL 36206. These 19- and gable lines have the smoothest, slinkiest feel. I have a few in the .015 size and really like them!
The lines performed without a hitch while soaked in water. They are really good, so give them a try if you use cables. Because of a wire crimped ends, use carefully wrapped ends as per the AMA rule book.
Tom also has many of the hardware pieces everyone needs. Check out his new catalog.
Transcribed from original scans by AI. Minor OCR errors may remain.
