CONTROL LINE AEROBATICS
Frank McMillan, 12106 Gunter Grove, San Antonio, TX 78231
One of the most difficult and most rewarding challenges in Stunt is to work with another flier's airplane and get it to fly to its potential.
Much has been written about trimming, but it is surprising how much is ignored or misunderstood. I wish there was a magic wand you could wave that would make every airplane fly at Nationals level, but there isn't. There are so many areas to adjust that many fliers start without a plan or orderly approach; having a plan is the best way to do it.
The best method for systematically trimming an airplane is Paul Walker's article on his Impact published in Flying Models. Reprints are available through PAMPA (Precision Aerobatic Model Pilots Association), Box 2026, Loomis, CA 95650-2026.
Trimming approach and common problems
In the last few years I've been flying other people's airplanes. A common theme with many of them is the handle neutral setting, or rather the lack of a good neutral setting. This may seem to be a small issue; after all, everyone is different, and this is the politically correct era.
Some time ago Bill Werwage was flying one of my Classic models and remarked that of all the airplanes he flies, there seem to be two basic settings: angled setting (much as a pistol grip) and vertical grip. You might ask, "what's the big deal?" Many fliers have chosen to hold their hands as they naturally chose—still politically correct.
The problem that can arise with a misaligned handle is that the setting, by itself, can cause the misinterpretation of the trim of the airplane. By biasing the neutral, you set up a mechanical advantage, which causes the control to be more sensitive/quicker in one direction. Usually this is the up control because the handle is most often canted forward or the top pushed forward.
Consider that when you were constructing your model, you spent considerable time and effort to get the controls neutral. The surfaces were set neutral with the controls. The controls had the latest tricks and alignments to ensure that the surfaces faithfully followed the inputs. However, after all of that work to make the controls linear, the handle setting can destroy the linearity.
I've finally gotten to the real deal—the system linearity. If you don't follow through on every aspect, you can expect problems.
Handle position
Back to the handle: the models that I get to try usually have the handle set forward. I have flown several in which the handle was so rotated that the airplanes were extremely difficult to fly level, let alone put through the pattern safely.
My observation was, admittedly, the result of being used to a vertical setting. However, there was no question that up was very sensitive and down almost required pulling the handle to get a safe outside corner.
All of this may sound as if I'm exaggerating, but I'm not; this situation really does prevent you from flying the airplane well.
I prefer a vertical setting for my handle, and I've mentioned several times during the last few years that what you are shooting for in a handle setting is equal pressure (the control force/feel to apply) for up and down. My assumption—and I realize that this is not always so—is that a vertical setting brings equal turn.
To practice good patterns, you need to strive for the honest, equal turn; you cannot fly uniform maneuvers if the airplane is not set up to turn the same each way.
Setting the handle in a vertical position sounds very simple, and it is, but you may have noticed that when adjusting a new set of lines, minute variations with the neutral tend to be compensated for subconsciously. Indeed, on one model I specifically had to set the handle in what looked to be an awkward up position so that when the airplane was in flight, the handle was properly set. That particular airplane/handle always took several flights to work back into because of the handle position.
You might have to work with your particular setting to get the best feel, but strive for a position that is very close to vertical. This will give you the optimum position to base your trim on, much the same as leveling the wings. If you start eliminating the variations now, that can affect your trimming program; you can guarantee that as you go through the trim process, you will have the most honest trim possible.
Thus far this discussion has focused strictly on the physical position of the handle. To comply with the suggestions that I’ve made, you can simply adjust the length of either line. Every basic handle has this feature. After you’ve flown with your setting for a few flights, you will naturally become accustomed to the way it feels, and start to become aware of certain characteristics of your model.
Fine adjustments: inverted flight and thumb wheels
Your airplane might tend to fly inverted lower than the four-foot limit. Why not fly it a bit higher? After all, do it upright! You can, but the issue is the slight compensations that you—the flier—make. The adjustment that you’re after is very small, and is one of those experienced/feel things that once you do, you will understand the why.
The adjustment to take care of this situation is a slight pull of the down line; shorten it, by, say, 1/32 inch. Fly and try; see what the effect is. If you are in the ballpark, the model should settle to a slightly higher inverted flight. Remember, this is a very fine adjustment.
While I’m into fine adjustments, there are other capabilities that exist in some handles. Thumb wheels give the ability to make extremely fine adjustments while in flight; this can be valuable in that now you can look at the next level—the pressure required at the handle to turn the airplane. This can be the last step to extracting the best trim.
Before you even look at acquiring a handle with this capability, you should feel comfortable with the basic handle; but having flown the basic handle, you will probably want to step up to the next level.
One source is Brodak’s Distributing Company, 100 Park Ave., Carmichaels, PA 15320; Tel: (412) 966-2726. The handles come in Standard, Expert, and XPA Expert series. The quality is excellent.
When using the thumb wheels, understand that they are a very fine adjustment. For this discussion, I’m going to exclude post lengths and overhang, which are also adjustable with the thumb wheels. I’m after equalizing pressure on the controls to effect movement.
It will take less than a turn to experience a change; rotate the appropriate wheel, and see how it affects the feel of the controls. If it’s the first time, try each wheel in each direction. There is no magic in this, but you can do the same thing with the thumb wheels as you can with the cable length adjustment. However, they are not interchangeable because too much thumb wheel can angle the bar in front of the handle, causing an unequal post length, which changes the linearity of the control input. It’s best to use the fine adjustment only, and keep the bar at the same angle as the basic handle—vertical.
This discussion should give you some insight into making your airplane work up to its potential. Don’t be reluctant to work with these adjustments; you can do it if you try. The fun is in exploring.
New items
As he has done many times before, Randy Smith of Aero Products has introduced an item to help the competitor in the quest for perfection. This time the focus is on the wonderful precision CNC spinners. For years, he has had several kinds available; they were two-inch types, profiled in Classic and Old Vee Needle Nose, available in aluminum or magnesium. The magnesium was special purpose, very light, and expensive.
Randy’s revised item combines a thinner aluminum shell and a magnesium backplate/nose cone. This re-engineering provides equivalent weight to the all-magnesium version, with better strength and handling.
To try these quality products, contact Randy at Aero Products, 1880 Scenic Hwy., Snellville, GA 30278; Tel: (770) 979-2035.
Till next time. Send pictures. If there’s a topic you’d like to see discussed here, let me know.
Transcribed from original scans by AI. Minor OCR errors may remain.
