Control Line: Scale
Mike Gretz
It seems that the February ’79 column on the basics of 3-line throttle control systems has unearthed a slightly tongue-in-cheek debate about the proper direction for high and low throttle movement. Should the throttle lever at the handle be moved forward or back to yield high throttle? Two expert CL Carrier fliers wrote pointing out that most 3-line fliers in their event prefer the directions opposite to those I had diagramed as correct for Scale flying. I prefer, and steadfastly recommend for Scale, that high throttle be forward at the control handle, while these Carrier fliers claim that back for high throttle is better for their event.
Who is right? Undoubtedly both are correct for our respective events. The exacting demands of both these competitive challenges produce slightly different equipment requirements for each. Although this column concerns itself with the Scale event, I’d like to share some of the recent correspondence because there is intriguing food for thought in the reasoning behind the preferred set-ups for both.
In his letter, George Lieb said in part:
"I read your article in the February Model Aviation about throttle controls, and would like to comment on it. First, most carrier people hook up their throttle so that pulling the trigger gives high throttle. This seems to me a more natural movement than the way you show it. Just like a chain saw, drill, saber saw, soldering gun, etc. You can mount any of the Roberts or G-S bellcranks either upright or inverted. The reason for having two different types is so you can accommodate engine throttles that move in either direction. My planes have inverted-style bellcranks mounted upright so that the engine will be at high throttle with the trigger pulled. If the throttle on the engine moved the other way, I could use an upright bellcrank mounted upright to have high speed with the trigger pulled. You could also use a bellcrank throttle reverser lever to change the throttle movement within the plane."
I replied that throttle direction at the handle was simply a small point of personal preference. In fact, a person could become just as proficient in either mode of operation if he learned either one equally well. I do have some specific reasons for preferring Scale high throttle forward at the control handle.
When I set up the first 3-line system years ago, it became obvious that when you mounted an inverted bellcrank the engine would almost always be at high throttle with the trigger pulled. The same holds true when mounting an upright bellcrank upright. Throttle-equipped engines I know require the throttle pushrod to move forward to open the carburetor (except Fox engines, which often have levers that move both directions). In other words, if the modeler uses the stock equipment mounts the manufacturer intended, he would, in almost all cases, get high throttle by moving the control handle forward.
I noticed Scale fliers at the Nationals doing things the other way. To make the system work that way one must reverse directions somewhere along the linkage. You can do this by:
- incorporating a straight reversing bellcrank arm between the engine and the 3-line bellcrank;
- mounting an inverted-style bellcrank upright, or an upright-style bellcrank inverted (although some control-rod hookup problems can result); or
- loosening the throttle arm on the engine and rotating it 180 degrees.
I couldn’t see any possible advantage for Scale flying in doing things differently; the arrangements mentioned seemed unnatural for our needs.
You mentioned that it seemed more natural to you to pull back on the handle’s trigger to get fast throttle. To me, it seems more natural for fast throttle to be forward as it is in a full-size airplane or an automobile.
"I use my left hand to operate the lever on top of the handle and thus always fly with both hands. Perhaps this is the real heart of our personal preferences in this matter. I’m wondering if you, and other Carrier fliers, normally fly with only one hand, using your index finger to operate the trigger? I feel that, my way, I can operate the throttle more precisely through all stages of the scale flight. In competition Scale flying a good share of our point-getting maneuvers are done at or very near low throttle—like the initial takeoff, landing, touch-and-go, and taxi. During these maneuvers, where precise coordinated elevator and throttle use is most important, I prefer the trigger to be back in what you seem to agree is a more comfortable position."
The day after I mailed that reply a letter arrived from MA’s own Carrier expert and my respected friend, Dick Perry. He very knowledgeably shed some light on why the Carrier fliers prefer their control set-up opposite of what is normal for Scale. Dick said:
"It looks like we disagree a little on which way is appropriate direction for open throttle on a 3-line system. It’s certainly not a big thing! Carrier requirements are just a little different from Scale. Your way—forward is open—is the way the real airplane builders do it, and it works great for two-handed flying—the way most Scale fliers I’ve seen do it.
"Carrier fliers are a little different. We are generally one-handed with a few exceptions (you can fly a bigger circle on low speed with one hand). We use two hands on high speed, but the left hand is there for support only—the right index finger still operates the throttle; and with 50–75 lbs. pull a pull-to-open throttle is much easier to keep open than a push-to-open rig. With one-hand operation, low-speed throttle action is also more natural when back pressure opens the throttle as up is applied. Also, if properly rigged, an up-elevator condition (against the stop or with lines really loose) will automatically open the throttle. Not a bad situation when the total airplane pull is about two pounds!"
So there you have it: two different methods for two unique events. We could go on and on with a meaningless debate about the merits of this or that method, but let’s just conclude that a devoted pilot can get satisfactory results either way. For years RC has had its Mode I (throttle on the right stick) and Mode II (throttle on the left stick) fliers and their tongue-in-cheek word-war about which is best. Perhaps we should divide up into the "two-fisted lever pilots" and the "one-handed trigger pilots." Are we that crazy?
Mike Gretz Box 162, Montezuma, IA 50171
Transcribed from original scans by AI. Minor OCR errors may remain.
