adjustable leadouts

I tend to agree with you. I have had individual sliders, and have fiddled with independent movement to try to trim outside vs. inboard roll/yaw charactertics. But I always wound up putting them right next to each other, as close as possible without chanceing interference. This was even when running as big a prop as possible, and forward CG, both of which make the differential potentially more useful.

With aft CG's and large bellcranks, the control loads and mechanical advantage are such that the line tension differential is pretty darn small in any case, which means the adjustment has relatively small effect, even it you want some.

I now use a single slider, with a spacing of 3/4". That's as close as I have the guts for. My cohorts run them even closer. The interference problem can be solved with different leadout lengths, although I don't do it myself because I don't want to add the complication of having lines incompatible with my flying buddies.

So you use the leadouts to trim for line tension. What is the goal? A lot of tension? Just enough? How do you know? As an old combat flier, my prejudice is that it is difficult to have too much tension. I liked to fly looking at the opponent's plane, and "feeling" mine. That is probably more tension than needed for competitive stunt. But it is a prejudice hard to shake. Does flying with a lot of tension hurt anything?

I put leadouts close together,a hangover from the racing days, I suppose. Out one hole sometimes. Of course I use unequal length leadouts. I would do that even if they were separated. I've had equal length handle cables foul, so it is ok with me for them to be unequal also.

If the leadouts are too far back, the airplane will get light in the upper part of the circle because it will yaw when you give it control. I suspect any of the Old Time airplanes would benefit from closely spaced adjustable leadouts.

On the other hand, I built an old Bear Viper kit with a ST G21-35 to sport fly and put in adjustable leadouts. It's a 100 mph airplane and the leadouts are as far back as I can get them. I thought you combat guys were nuts for having them so far back, but that is where they go. I do not understand it.

Matt and I like to fly with a lot of line tension. Others prefer less tension, feeling that it gives them greater feel for the controls. Under ideal conditions, flying light on the lines is fine. If you get up wind and hit a gust, however, having more "pull" on the lines can keep the plane from going slack and losing control. Some of the top flyers know how to compensate and even when to anticipate--and having flown hundreds of flights on their plane, they, also, know its (and their) limitations. I think this was demonstrated on Friday's flights at last year's Nats when a number of top 20 qualifiers elected not to fly their second flight even though the two flights were added together for their final score. Bringing the plane back alive was more important than moving up a notch or five in the final scoring.

Still, trimming and proper leadout location is more than getting maximum tension. The leadout location is going to be affected by tip weight, and changing tip weight can affect leadout location. (Moving the leadouts forward can add to the outer tip dropping in a sharp maneuver as can adding too much tip weight.) Leadout location is, also, affected by center of gravity location, line size, line length, air speed, tip weight (already mentioned), engine and/or rudder offset...a lot of factors.

Essentially, after all other factors have been accounted for in the trimming process (wings level upright and inverted, good tracking, no excessive yaw, no tip "banging" in the sharp corners) we are trimming to find the optimum location that will equalize tension all over. Since gravity is fighting you up above, we will sacrifice a little tension while flying level to add a little more tension overhead.

The above is an oversimplification of the process, but leadout location is merely one of the adjustments that are made to find the proper trim that you are seeking. But, yes, it can affect the amount of overall tension that you have, and for some, that becomes personal preference. Some top flyers fly with very little, some fly with a lot. And we will always get a lot of argument on that subject, I suppose. Sort of like dredging up the "pipe wars" again. I, personally, feel that the beginning pilot is better served with more tension as he is learning to fly, and then, as he becomes comfortable with his ability to fly and his plane's chraracteristics, he can keep the tension, or decrease it to his liking.

>You guys are all dancing around
>a major issue for us
>novices without directly addressing it.
>LINE TENSION. At the top
>levels of competition, are line
>tensions just enough to "keep
>it from coming atcha" or
>"dig in your heels and
>hang on"?

The line tension, "lots" vs. "just enough", has been a point of some contention. I trim and fiddle the engine to optimize other parameters. I then set the lap time to get adequate line tension. I don't like compromising the control feel I like to get more tension than necessary. But that's just me.

The line tension for most of us is set primarily by speed and line length, and secondarily by power. While it's possible to fiddle the trim for more line tension, you certainly give something up in other ways.

To me, the goal/definition of "trim" is not a way to maximize line tension, it's a way to get an ideal control response in pitch and minimize unexpected roll and yaw. Line tension is set by other parameters. If you trim the model well enough and have adequate power, the line tension will take care of itself. This is particularly true these days with tremendous overkill power available.

But line tension is not directly relevant to leadout position, the way I trim. I use the rudder to control the yaw angle as an independent variable. The leadout position I end up with is then adjusted for minimum yaw transient. If I see the airplane yawed outboard, for instance, I would not move the leadouts forward to fix it. I would instead move the rudder a little bit to straighten it out, then adjust the leadouts to minimize the yaw jerks that will probably result. The goal is to have the leadouts to never supply any torque. If it was perfect, the leadouts would just float right in the middle of the holes in the guide, never touching. Of course that never happens, but the idea is useful

The method I use to find the correct yaw angle was described in the "Roll Trim Problem" thread on RCO.

Speed of course matters in the leadout position. The drag on the lines makes them drag behind the model, and more speed usually straightens it out, meaning the leadouts would need to go forward. But I just make a speed change, then look at the model reaction to see if the leadouts need to move.

To sum up, for me, the leadout position is the tail end of the train. I like to use the aerodynamics and tip weight to set the roll/yaw trim, and then set the leadouts to match up with it. I try to avoid using the leadouts to force the model to a particular angle.

We would, however, bring the leadouts into play sooner in the equation than what you described, trying to get them to the expected location with each trim change. (We try to do one thing at a time, however, unless things are drastically out of line. Add tip weight, for instance. Then next flight adjust leadouts if needed. Remove nose weight. Then next flight adjust leadouts if needed. I am talking here the minor trim changes needed to get it to the desired trim. This may go on, periodically, for 400 flights, or maybe even 1000. The trimming process is never really done.)

Every change in trim can result in another needed (although minor) change in leadout position. We work these together, where I take it from your response that you try to get everything else pretty close before doing a lot of adjusting on the leadout position. You are absolutely correct, however, that one should never attempt to use the leadouts to force a certain attitude. They should, instead, be adjusted to follow the natural arc that the lines will assume while in flight with whatever amount of trim you have dialed into the plane.

I actually think we may be in near agreement for once. I think based on previous discussion that we are setting the tension primarily with power/prop/speed and trimming very similarly, for negligible reaction.

>Every change in trim can result
>in another needed (although minor)
>change in leadout position.
>We work these together, where
>I take it from your
>response that you try to
>get everything else pretty close
>before doing a lot of
>adjusting on the leadout position.

That's not exactly what I meant to imply. I don't wait till the end. It's just that it follows any other adjustment. So if I don't like the yaw angle, and fiddle with the rudder to fix it, I'll set the leadouts to match. As opposed to setting the leadouts and then trimming other parameters. Think dependent variable - the other adjustments are attempts to change the characteristics of flight, and the leadouts are set to minimize the raction yaw.

Is there a better solution?

You can also move the slider frame as far out to the tip as you can, rather than putting it in the tip rib. I havn't thought that necessary.

Hi Larry,

I just finished a plane with the leadouts you first described. I glued the slider to the outboard rib and made the tips out of 3 pieces sandwiched so I could easily leave a cut out for the leadouts to exit... It works great as long as you don't have to wide of a tip. But thinking about it... Even with fairly wide tips, a control line airplane would have to do one mean roll in order to get the leadouts rubbing on the wing tip. If this should happen you would probably have a much more serious problem at hand.... works great go ahead and try it.

Bob

PS: independantly adjustable 3/4" line spacing...

One warning with any adjustable guide: put in a little longer socket head bolt, and then mash the threads on the end after the bolt is inserted. That way, even if the bolt should ever come lose (yes, some day it will come lose) you won't lose the bolt. And, in case you are interested, we found out this trick the hard way. The slider went half way up the wing and we had to kind of work it down through the ribs and then fiddle around trying to get a new bolt in it. All planes since then have had that mashed bolt and we have had no worries about losing a bolt since.

OK, I know the next question. The plane still flies, even when that bolt comes out and the slider goes up the wing. Just a little less responsive. I guess if the plane is in pretty good trim the leadouts become sort of self centering. Still, it is not a good idea to lose the bolt or to even have it come lose. Just check it periodically and all should be well. (Murphy, did you hear that? All should be well.)

Thanks, Leonard!

Leonard, Jim, and Bob --

Thanks. My big, strong, handsome wife is happier now. She was pretty sure my idea was not quite enough. You guys confirmed "no problem". Thanks.

Larry F.

Can I refer you to the tip design that Tom Morris devised for his Cavalier kits. It was shown in Stunt News late in 1999 if I remember correctly. I think it has all the answers.

Check with Tom Morris on how he is now doing his adjustable leadouts on his Cavalier models - he is using some slotted hardwood in the inboard wing tip with the slider on the inside of the wingtip itself and the hold down bolt anchoring straight to the outside portion of the slotted hardwood section imbedded into the tip. This puts the pivoting on hardwood and at the very tip. Seems to be working pretty well so far.

I then applied CA glue to all holes that were drilled, and then had to drill through them a second time. The CA hardens the balsa so it doesn't crumble later on.

The key here, for those who may not be aware of this style of adjustable leadout, is that you use a 1/8 inch eyelet over the leadout wire as your guide and simply slide this into one of the selected holes. The leadouts would string through the eyelets and be finished off as normal. To adjust the leadout, you would simply pull the eyelet back, then slide the wire through the slot (.031 solid wire = 1/32" so it will just slide through) and then reinsert the eyelet in the next hole to fix it into place.

We used Scotch Tape to hold them in place while finding the correct location. Without something, they do tend to come out again. This is one problem with this style of adjustable leadout. The other is that you can only adjust every 3/32 of an inch. There is no fine adjustment, so it can get you into the "ball park", but not always (not usually) perfect. For those who don't know the difference (or care) this is a simple, inexpensive, and definitely light solution. Bob Gieseke used it for a while I know.

Still, the Brodak slider weighs only 4 grams complete (although it is best to add a longer bolt and mash the end to keep it from falling out if it comes loose) which must be offset by additional tip weight. So the total weight penalty is 8 grams (10 with a longer bolt?) or a bit over 1/3 of an ounce. Everything extracts a weight penalty, and we must individually determine to what lengths we are willing to go to achieve the necessary function, while still striving for acceptably light weight. (If a certain prop weighs more, does it provide a sufficient additional benefit? If a certain spinner weighs more, is it worth the additional benefit? Are larger wheels worth the additional weight? If I go to higher nitro and use more fuel, is it worth the additional weight? Everything is a compromise.)

What are your thoughts?