Leadout Adjustment Strategy

[Larry Fulwider]

A “local expert” once advised a flyer experiencing poor 45 degree line tension to move the leadouts rearward, which didn’t help, of course. More experienced experts often advise the opposite – move leadouts forward to increase line tension up high. To me, that doesn’t make sense either.
   My reasoning is, in situations with poor line tension, the least important adjustment one can make is leadout position. My thinking is, there are a lot of forces affecting the actual flight path, and if you think of those as “levers”, the leadout position “lever” is mounted firmly in Jell-o when line tension is minimal. Why talk about leadout position at all in situations of poor line tension?

Starting from scratch, here is what I know: Hundreds of folks are quick to give advice on leadout postioning; Seven guys really understand it; I am not one of those seven.

How about this approach? Set the leadouts where Line III says as a starting point. Try moving them a tad forward (is an 1/8” at a time a reasonable amount for one move?) until the level flight line tension doesn’t feel “overly multiplied”. My thinking is that with a lot of line tension in level flight, the lines are pulled real tight, and a leadout position too far aft will show up as a dramatic increase in line tension in level flight.
   That is, think of a “too far aft” leadout position as an engine governor hooked up backwards. It increases line tension when we least need it, and doesn’t help when we do need it. More forward postioning can mildly reduce line tension when it is excessive, and not get in the way when line tension is low? How to know they are far enough (or a tad too far) forward? Beats me! (One piece of advice I read said engine out glide was a clue)
   Once the “not too far aft” leadout position is found, leave the leadouts alone, and proceed with trimming however you choose.

The advice I am discarding as irrelevant, is logic centered around a too far aft leadout position causes excessive yaw overhead, slowing the plane, and thereby reducing line tension. A too far aft (or too far forward) leadout position simply has less of a positive (or negative) effect as line tension decreases.

OK, straighten me out. I’m listening. The flaws in my thinking, I suspect, are due to thinking in terms of steady state, not transient, situations; transient conditions are a lot harder to picture. All of us would like to reach a point where we can "reason" about leadout position, not just follow canned advice, wouldn't we?

Larry Fulwider

[Alan Hahn]

Larry,
I am not one of the 7 either!

However my understanding of the leadout position issue, with respect to overhead stuff, is that the relevance is due to what is happening when you pull up from level flight. The outward yaw deprives the plane of thrust which is fighting gravity, so the airplane begins to slow down--more than it would if the leadouts were positioned "correctly". This is all happening before you get up to 45 degrees or higher. So now you are up high at a low airspeed and of course the tension is down the tubes. Yes the leadout position doesn't matter at that exact instant--but you have already in deep s*it at that point.

So that, for better or worse is my understanding. Now lets hear from the Magnificent Seven (dum dum dee dum...dum dee dum dee dum.....   theme song from movie---or the Marlboro Man tune!)

[Leo Mehl]

I have leadout adjuster in new Grinder. I decided to move leadouts back and the airplane then slowed down in manouvers and also had a terible yaw because of it. I then moved them forward and the line tension went up and the yaw disapeared and this is the purpose of the adjuster in the wing so you can make these adjustments as part of the trim process. In the old days we either had the leadouts in the right position or not. Same with our building strait. either it was straight or not. we didnt have insterments to build things strait in those days. Not only that we didn't know how to keep things strat so the model either flew good or not.

[EddyR]

I fly with Larry a lot so I don't know If I am one of the guys mentioned or not. Now that that Is out of the way let me say I never have the problem of my planes getting loose at 45 degrees. All my stunt planes seem to pull the same all over the circle. I think it is the designs and the set up before I ever get to the field. Also having motors that pull hard all the time. I see many modern pipe planes that have poor pull above 45 degrees and I am dumbfounded to see this with all the power that they have.I started using zero offset in the motor and rudder about 20 years ago in a Cobra and have built all my planes that way ever since. When I fly I can't see the outboard wheel  so the plane must be flying with no offset at all. My last plane I finished the Tempest has never had a adjustment made at the field except the small tab on the outboard tip to get the wings level. The planes pulls hard in the wingover even in a four cycle. I think it comes down to a good design and preflight trim. My adjustable leadout is set before I ever fly by holding the plane by the leadouts and getting the plane to hang level. One thing I have noticed also is many motors pull hard on the ground but don't do well in the air when they get in the corners. Many people are using low pitched props at to low of a RPM and the don't pull well through the corners.
Ed

[Larry Fulwider]

I fly with Larry a lot so I don't know If I am one of the guys mentioned or not.  . . .

Ed

Well, not the "local expert" giving faulty advice, for sure! Good point about the hanging from the leadouts, I think. Too far aft would show up for sure, wouldn't you think? Sometimes I get too "calculation centered".
     When the weather clears, let's go fly and do some live testing, OK? It's too crummy today to even make a set of lines.

Larry Fulwider

[Charlie Pate]

Some say move the leadouts forward if tension is light on the overheads.
Some say move the leadouts back if the tension is light on the overheads.
  Both can be right .! Howszatt!?
Build a new plane ,move the leadouts as far forward as possible. fly the plane,. lousy.
 Move the leadouts backward ,  flys better.!
 Move the leadouts as far back  as possible  . Flys lousy
 Move the leadouts forward flys better!
What i think Im trying to say is it depends on where the leadouts are placed to begin with
in relation to the c.g.And where you have the cg to begin with.
This can be confusing to beginners(not to mention old folks (looking in the mirror).
I  check plan cg first .Plane drawing)
Then hang plane by leadouts (flexible) .
note body angle pointing . Down (outside circle ,move leadouts forward) up(inside circle) move leadouts backward.
 Nose should be down (outward) just a tick, for starters.
As one guy said " I know you know" Now you explain it to me so i,ll know"
This method was and the explanation was passed on to me years ago by Tom Dixon  and I have not found reason to dissagree with it.

[Brett Buck]

Some say move the leadouts forward if tension is light on the overheads.
Some say move the leadouts back if the tension is light on the overheads.
  Both can be right .! Howszatt!?
Build a new plane ,move the leadouts as far forward as possible. fly the plane,. lousy.
 Move the leadouts backward ,  flys better.!
 Move the leadouts as far back  as possible  . Flys lousy
 Move the leadouts forward flys better!
What i think Im trying to say is it depends on where the leadouts are placed to begin with
in relation to the c.g.And where you have the cg to begin with.

      Of course, the initial relationship to the CG is everything, and of course, too far forward is not going to work at all.

      I continue to suggest starting where "LineII" says, and adjusting the rudder  to minimize the yaw reaction in the corners. If everything else is straight, this will be so close to the right value that most people will not ever improve on it.

    Some of the other methods will work after a fashion and you can more-or-less eyeball it if you are very careful to observe the results and correct accordingly. And for the average 60-oz 40-60-sized TP airplane, it's around 1" behind the CG. But given that you can get it within probably 1/8" or so of perfect by spending 30 seconds running a computer program there's not much justification for guessing.

      Brett

[Charlie Pate]

I tried to get the line two program a good while back and couldn,t get it.
I have since changed servers and would like to try again.
Any suggestions for the computer illiterate would be appreciated .

[Bob Reeves]

"Line III" is "Line II" with a much friendlier user interface, a save that actually works and uses US measurements most of us can easily understand. I believe It can be downloaded off this site in the download section. Also available here...  http://www.tulsacl.com/Linelll.html

I always set the leadouts during the bench trim process using "LineIII" and have seldom needed to change it. I personally don't believe in force correcting a yaw issue with leadout position.. Rudder adjustments and tip weight are much better options.

[Charlie Pate]

Thanks Bob! I will try to get line II tomorrow;as its now midnite and I just got  inzzzzzzzzzzzzzzz 

[Larrys4227]

Well, this may be a dumb question ...... after calculating in LINEIII, it gives the position of the leadouts from the CG. Is this measured from the center of the 2 leadouts?, the rear leadout?, the front leadout? This may be obvious to the seasoned veteran, but I'm new at this intricate stuff and simply dont know.

Thanks for the patience .....

FlySafe!  Larry (Larrys4227)

[Terry Bolin]

   LOTS of good information posted here but let me throw a wrench in the fan toooo. Play with props: I greatly improved the over head on two planes last year by switching to a different prop than what was on the plane to start with. I tried 5 different brands on the Cheif and one prop really performed better than the others. Try what you have available, maybe borrow a few. Best results for me so far were the APC Sport and the By&O Props from Brodak.
 Moving lines forward has worked for two of us here.... good luck!
Terry

[Serge_Krauss]

Larry-

It's the point midway between the two leadouts.

I agree that using LineII or LineIII is the way to go. These place the leadouts relative to the c.g. so that tension and line drag cause them to exit without binding or causing a further yaw from ideal in this regard. Having chosen this leadout exit position (fine tuning to achieve that goal), you should fine tune further with other adjustments. The rudder keeps the fuselage close to tangent to the circle at the c.g., but is not itself tangent to the circle. So it gives a slight outward yawing moment and can be adjusted to choose the yaw you might want, although no yaw seems ideal.

BTW, the c.g. position should be chosen with regard to pitch considerations; you want the c.g. set in relation to the quarter-chord MAC position for desired pitch sensitivity. IMO, the c.g. should not be moved for yaw considerations, and the leadout position should not be used to create outward yaw. I think that the leadouts should only be moved from the calculated position to achieve the original purpose of Line II-III. Like others, I have found that moving them forward from  the point where they create outward yaw has improved tension higher up. 'hope I said that right - and understandably.

SK

[Larrys4227]

Thanks Serge!  Makes sense on paper, but alot of what your talking about will have to be experimented with by me, and on the plane. I'm using the LINEIII for the first time on a plane that will maiden in a couple weeks. Trying to eliminate some guessing that I've done with other planes, which result in .... lets say .... a butt-squishing flight. 

Thanks!  FlySafe!  Larry (Larrys4227)

[Serge_Krauss]

One thing I forgot to mention: from my more limited experience and postings from several others over the last few years, it seems that thrust and perhaps rudder offset are more needed in smaller, lighter models, the extremes being ultra light indoor CL models. I have offset thrust and airfoiled my vertical stab on my .25 and even .40-powered planes. BUT I agree that centrifugal/centripetal force is THE force that determines line tension, far overshadowing adjustments that may lead to other problems. There is a lot of discussion on this in the SSWF archives and perhaps some here too by now

SK

[Charlie Pate]

Thanks Bob! I will try to get line II tomorrow;as its now midnite and I just got  inzzzzzzzzzzzzzzz 

Bob
With my ever increasing kompueter skills , i was able to load up line III.
Thanks!
I am anxious to check my current /////cra-- er crop of planes and see how close I am   

[Joe Yau]

I personally don't believe in force correcting a yaw issue with leadout position.. Rudder adjustments and tip weight are much better options.

so, what's the usual rudder/wing tip weight adjustments for controlling the yaw in corners?    (add approx __ oz in tip weight and __  degree right rudder offset) Thanks

[Jim Thomerson]

First, I think the leadouts should be as close together as you are comfortable with.  On a 1/2A airplane I put them out through the same hole.  Secondly, make adjustments maybe 1/8 in at a time. On a 40 size airplane, I have seen a difference from a 1/16 move.  The advice on experimenting with props is sound. 

[Brett Buck]

so, what's the usual rudder/wing tip weight adjustments for controlling the yaw in corners?    (add approx __ oz in tip weight and __  degree right rudder offset) Thanks

    Tip weight doesn't really effect the yaw. Yawing effects the tip weight because yawing make it seem like you need a different amount of tip weight in corners than you do in level flight. I have beaten this to death over the years on SSW, just check the archives, but set the leadouts where LINE II says, set fin/rudder dead ahead, adjust tip weight to get the minimal roll in hard corners, adjust the rudder offset for minimal yaw motion in hard corners, while futzing with the tip weight to keep the wings level in hard corners. If everything is straight and you have minimum yaw motion, the only remaining adjustment would be to adjust the tab/flap differential to get the roll minimized. Rolling usually won't create a yaw motion, but a yaw motion is very likely to mess up roll.  Details/explanation on SSW.

     Brett