Hi All,

After seeing a few other posts I have a question:

Just how effective is having "both" lead outs adjustable, separately from each other?  I have used both but can't come to a conclusion myself.

Thoughts and ideas please!
Bill

Maybe I'm missing something, but I would think that the best lead spacing is to get them as close as possible without danger of the line clips binding.

If you look at Jim Walker's patent, one of his claims is about having well-spaced lines with one line specifically in front of the other, arranged so that if the plane yaws in it'll automatically pitch up or down (I can't remember which).  There's a long bit of razz-matazz about how this would self correct for line tension (so I assume that if it pitched in it'd get down elevator, go faster, and get more tense).

But as far as I can see, whatever benefit you may gain in positive-G flight from the lines being separated and arranged in a certain way (up in front vs. down in front), will turn into an equal and opposite liability as soon as you do negative-G maneuver  -- so it would seem to my over-analytical and under-experienced brain that the best thing to do is to negate any coupling between yaw and pitch commands as much as possible (by spacing your lines closely together), and get whatever effects you want in a direction-neutral way.

Maybe I'm missing something, but I would think that the best lead spacing is to get them as close as possible without danger of the line clips binding.

If you look at Jim Walker's patent, one of his claims is about having well-spaced lines with one line specifically in front of the other, arranged so that if the plane yaws in it'll automatically pitch up or down (I can't remember which).  There's a long bit of razz-matazz about how this would self correct for line tension (so I assume that if it pitched in it'd get down elevator, go faster, and get more tense).

But as far as I can see, whatever benefit you may gain in positive-G flight from the lines being separated and arranged in a certain way (up in front vs. down in front), will turn into an equal and opposite liability as soon as you do negative-G maneuver  -- so it would seem to my over-analytical and under-experienced brain that the best thing to do is to negate any coupling between yaw and pitch commands as much as possible (by spacing your lines closely together), and get whatever effects you want in a direction-neutral way.

HI Tim,

Commercial lead out guides come with both holes in one slider, or two separate sliders.  I have used both, and when using the two line adj. I still keep them very close together.  I am wondering if guys like Howard, Ted, Brett, Dave, Derek, etc., etc., find a definitive reason to use separate adj. lead outs.

BIG Bear
RNMM/AMM

Mightn't having lines separated by a larger distance (say >2") have some potential for imparting yaw to the model, particularly in a very rapid control application, like a 120 degree turn? A single slider is simpler, however dual sliders can be oriented to allow narrow line spacing, so you have more options.

A popular feature is the Rabe-style "backwards" bellcrank orientation, which sets the front line as UP. I always assumed this in the interest of orienting any yaw induced by the lines in a specific direction {say to yaw outward during an outside maneuver?}. In other words, it would seem to indicate we feel that line induced yaw exists. If this is not the case, please explain the thinking which prefers the front line as UP..

A few ships have oriented their line guides vertically, again making me assume someone intended to minimize line induced yaw.

I'm not referring to historical arguments about bellcrank fore/aft positioning inside the wing. {Ignoring leadout guide friction and altered bellcrank to flap horn geometry effects, bellcrank position does not matter.}

So. Does a significant force couple really exist?

L.

"Right now I'm having amnesia and deja vu at the same time. I think I've forgotten this before." -Steven Wright

OK,  the front line is "UP" control.  I am needing some tension over 45*.  I move my unified line slider 1/8" forward and test.

Same scenario but I have separate sliders.  Do I move both, equally 1/8" forward?  or just the front line?  Just the rear line? 

I have never really heard what the procedure is for trimming using two sliders.

   To start, put them as close together as you dare, and them move them together. IF and only if you have some untrimmable yaw in the square 8, move them apart to try to control it. You may find that you want the rear line up if you have it the other way, putting them right next to each other is the best you can do.

    Brett

Reply to #6, Larry Cunningham's...

35 or so years ago, I worked up coarse estimates of several basic things:

...the leverage train from handle to bellcrank to horn(s)...

... using the fore-aft CG as the entire model, reduced to a hypothetical single point, to study forces acting on, through or near it...

... estimating the g-loads IF the model actually flew 5' or 10' radius turns, and in 45° loops, both low and high...

... using the g-loads, model weight, airspeed (from laptime on the flight radius, and approx time to complete a 90° turn or a 45° loop) to swag the lift required, and the lift coefficients needed to get the lift...

Various model publications printed ways to estimate the shape of the lines due to their drag, and to estimate the gyroscopic moments of props (by RPM, diameter and mass <weight>). The line curvature equation was by Pete Soule' in an Aeromodeller Annual (?1970-71?) and the gyro by J. van Hattum, a Dutch flier, in another AM Annual. (Pete Soule's article apparently led eventually to the highly refined LINE... programs.)

Coarse, crude but worked pretty well for me at my ever modest skill level.

Relevant conclusions:

Prop Gyro precession effects are - or can be - quite signicifant.

Leadout position can reduce unwanted yaw.

"Line rake" can be estimated. ...meaning, the angle the lines make as they reach the inboard tip/leadouts, so that the pull force aims through the CG. Flying lines can't push sideways, but the leadouts aim Pull through the leadouts along the "rake angle" direction.

Simple centrifugal force "Pull" (accepted term, let's ignore the precise definition for now?) can be estimated. Half the Pull is on each line when the model is ideally trimmed and flying low and level. The mid-point between leadouts is the effective "aiming point" at the CG.

Lines apply differing force to the bellcrank for maneuvering. The UP line, say, needs more force to force the flaps and elevators out into the airflow to execute inside maneuvers, and vice versa.
With the crude estimates of forces on the control surfaces, and knowing the linkage train, the difference between loaded and unloaded line force requirements can also be swagged.

As the gyro precession torques also can be estimated for severe maneuvers, these ideas can be combined to offset, or cancel out!, each other. Placing the leadouts to straddle the level flight pull direction by the distance which should counter the gyro yaw tendency should help...


Gross presumptions: to perform minimum radius corners, ALL line pull acts on the loaded line, none on the other. Where Pull aims - through the leadouts - shifts from centered on the CG toward the leadout on the loaded arm of the bellcrank.

"Natural" gyro reaction on a standard model (CCW engine, CCW flight) is "out on UP" and "in on DOWN" inputs. If the pull shifts forward of the CG on an inside maneuver, that forms a torque tending to pull the nose in, i.e., opposing the nose-out gyro yaw.

Using this loose chain of estimated forces, I guesstimated how wide the leadout spacing should be. The idea is to aim the pull through the loaded line far enough ahead of the CG (on insides) to at least partly counter the nose-out gyro yaw, and, vice versa, far enough aft of CG to partly counter the nose-in yaw on outsides.

All this for worst case conditions. Lesser cases were presumed to be covered when the worst cases were dealt with.

Of course, it is easier to estimate things for steady, low level flight. We fly an almost symmetrical pattern, in terms of the directions, locations and violence of rapid g-load changes.

"Hinging" seems to be a result of incorrect trim failing to counter the gyro yaw swing on hard corners:

 The advancing wing goes faster, lifts more;  retreating wing slower, lifts less -> roll;

 The higher lifting wing produces more induced drag, and vice versa -> yaw opposite to the roll's bank angle.

Again, all this is IMHO, but apparently did work to a useful degree for several years.

Dang, Lou, I clean forgot and ignored gyro precession effects.. There's our justification for front line UP, right?

One thing you mentioned estimating 5' or 10' radius loops - I'd suggest 15' is closer to worst (best?) case. I believe I calculated ~17' by watching videos of seemingly very good pattern flights: stepping frame by frame, assuming line length at the 70' maximum + 3' arm length, timing laps to guess average speeds, and counting video frames from level to vertical or vice versa as a "quarter loop period" {I know - that is crude 1/30 second = 33.3 ms resolution}. And there's a time lapse photo which I believe shows a similar result.

I'm confident you did a rigorous analysis, but did I miss it? Did you mention what you finally chose for your leadout spacing, in a typical case? Tell us! Hahah

The discussion of your analysis reminds us again how complex the real world is, and renews my own respect for serious analysis and simulation (particularly real time) work. It's obvious than cubic megaflops of computing power are needed for the real time stuff. And it again triggers me to renew my poo-pooing of fears of (digital) microprocessors pulling auto-pilot duties on CL Stunt models.

I remain very interested in logging acceleration, RPM, temperature, control deflections, voltage and current, etc. relevant data for trend and other fuzzy post flight analysis. Maybe we can come up with some workable control laws for modulating motor RPM, or "families" of swags for setup of various common competitive stunter control configuration. Satisfaction of interest alone justifies it for me.

Good input, Lou, as always.

Best,

L.

"We especially need imagination in science. It is not all mathematics, nor all logic, but it is somewhat beauty and poetry." -Maria Mitchell

Howard : If you want to get REALLY accurate.

This is how I did it..

We installed a very tiny camera onto the wing facing toward the fuselage rear . On the fuse where the Flap meets the root, we had a small ( looked like a protractor ) and we could see the control deflection in flight.

You would be amazed at how LITTLE we actually and for very minute time frames. I never saw anymore than 5 degree's of inflight deflection. - I was astounded....

Charles,
one of the most basic presumptions of CL stunt is that you are constantly trimming, adjusting, to improve your planes performance. In the lifespan of my Avenger ( aproaching 100 flights or more at this point) I have adjusted my leadouts probably a dozen times as I fidget with other trim items. they all interact. If I am experimenting, I may move them 1/4" , but If I am trying to hone in on something, I have moved them less than 1/8".
I cannot always tell definitevly that I have affected what I wanted. Typically I will move a large amount to see the change ( 3/16" ) and then back off the change if needed. The leadouts typically move any time you adjust the CG for one example.
Brett Buck is one of the masters at trimming and he has a far better method than I do. In fact a search on here should net his "trim chart" which is a flow chart that outlines the process for trimming, and a very logical progression. I dont know the full history, I think perhaps that Brett and Paul Walker collaborated, or modified each others aproach? it was before my time,,,,,

To : Howard's #12 and Larry's #13 -

Thanks for adding things learned since!

I may have to dig back into the relevant threads to get a clearer view of the sideslip action...
 
Please keep in mind I first played with these things in the mid-1970's, when few people applied the full-scale aerodynamic,  and even space-age, technologies as we do today for our toy airplanes. I just used the theoretical g that would be needed IF we flew a 5' radius. Bill Netzeband eventually wound up agreeing with the 17 to 20 g some have observed. He admitted he wasted a lot of effort trying to achieve that 5' radius...

The formulas I used were very basic - Lift, Induced Drag, CF, etc., etc. And, no, Larry there is no universal magic number for line rake or leadout separation... I suspect you knew that  

Each model's dimensions, including CG location, were used. I even came up with a solution for the theoretical panel length difference. Approached this way:

All forces applied to the model in flight have lines of action. If a force's line of action does not pass through that hypothetical point, the CG, it forms a torque tending to rotate the model until the force does pass through the CG.

The aerodynamic performance across the wingspan is affected by the gradually increasing velocity from the inboard tip to the outboard tip. Lift, in other words, is not centered at the physical mid-point of the span.

The CG is usually within the fuselage, spanwise, or very nearly so when the model is neither connected to the lines nor moving in its basic circular orbit at flight speed. Differing lift between the physical half-spans means that its theoretical center point is somewhat outboard.

That's where it seems sensible to hang the fuselage, AT the dynamic mid-point of the wing's lift in flight. The weight of the fuselage, engine and empennage, ahem... would not be off center, causing a torque trying (unsuccessfully) to roll the model until it lines up.

This involves the shift of lift AND tip weight... Simplest starting point to find the needed tipweight is to balance half the weight of the flying lines. Trim to perfection from there; you'll have enough for a safe first flight. The idea is that in the neutral condition, low, level, steady flight, the flier carries half the lines' weight and the model carries the other half.

The shift of lift, in a simplified reduction, should be close to the (ready?) cube root of the average of the cubes of the dynamic radii. Lift's dynamic radius? The actual radius to the point lift is equal to  the inside and to the outside as the model flies in that neutral condition. It includes some of the length of the flier's arm, of the line connector overhang, the eye-to-eye line length, the distance from the connectors at the inboard wingtip and the span to the outboard tip.

Would an example help?

Arm: 24" from center of rotation to handle
Handle Overhang: from 2" to however long the cable is to the flying line connectors. We'll use 6".
Flying lines: 60' (720")
Wing leadouts to "last airfoiled rib": say another 6"
Span: 48"

So, we have the inboard tip term: (24+6+720+6) and outboard tip term(24+6+720+6+48).

Cube each and average them.

Find the cube root of the average.

Subtract that from the outboard tip term to get the dynamic spanwise lift center location measured from that tip, or subtract the inboard tip term from the dynamic spanwise lift center. Either way finds the intended location.  

So, these two factors try to reduce a 'mass' imbalance due to tip weight, and to try to place the fuselage and assorted bits ON the center of the wing's lift in flight.

Line pull is one of the major forces on the model, and it provides a large stabilizing factor. Somewhere in the neighborhood of 3g is a generally acceptable SWAG. For a 4 lb model, that's 12 lbs. The various shifts from perfectly aligned trim due to maneuvering are immediately countered by the way they tend to aim pull force away from the CG. ...creates a restoring torque  ...trim is quickly restored. Is even takeoff thrust as much as 12 lbs?

Now, let's see what word was posted while I was typing...

I hadn't thought of that.  I was stuck on having to attach something to the bellcrank or flap control horn.  Thanks, Tim.

No fair coming up with some clever means of using an inexpensive RC item in the service of CL Stunt.. ;->

There may be only 3 or 4 blood vessels to my brain which are not blocked by bacon grease.

L.

"Procrastination is the art of keeping up with yesterday." -Don Marquis

Wow............. now I am going to have to do some serious reading and study to catch up in this conversation I started...........

BIG Bear
RNMM/AMM

I also like the nylon coated fishing leader. It was my belief that .027" was the diameter of {uncoated} braided wire leadouts.

Some swear by solid leadouts, but I've never liked them. They rattle, and they're a pain to terminate. One sharp bend and they're ruined. I see no significant benefit to them (feel free to englighten me).

Just sayin'.. ;->

L.

"Ability is a poor man's wealth." -M. Wren

Howard that's why my leadout guides have both ends flared..

(I experienced the same problem once - and uncoated braided wire can also catch. I suppose this is one obvious advantage to using solid leadout wires, isn't it?)

L.

PS - A small round punch can be used to flare brass tubing.

"You are the weakest link. Goodbye." -Anne Robinson

.. and I forgot to mention, the solid leadouts lack coolness ;->

L.

"If life was fair, Elvis would be alive and all the impersonators would be dead." -Johnny Carson

Just extending on the use of wire in models, it seems that years ago the humble piece of wire was an incredibly useful piece of material to have for model aircraft.

One could fashion undercarriages, push rods, lead outs AND their guides, bell crank pivots, tail wheel skids and their stooge attachment points, and flap horns in any form dreamt possible.

But these days just about all of the above can be substituted for a more fashionable and less labour intensive item.

But does the more modern equivalent work any better? Probably ...... but not by much though.

I had a solid leadout break about 20 years ago . I had solids in a 46 powered stunt plane and one got damages at the leadout and I didn't trust it so I changed it. A week later at a contest at Atlanta that leadout broke 12" from the bellcrank. I found that the wire was made with a defect. It was very thin at the spot were it broke. I check all solid wire now before using it. I still use solids on a few planes.
Here is the plane the leadout broke in,I called Nostromo. It had Flap Fences and they helped in the wind.Nostromo was the space ship in the movie Alian. Everone said this plane looked a little strange
Ed

The flap fences are intriguing to me. What do they do to improve flying in the wind? Do they turbulate?

They LOOK cool. ;->

L.

"Injustice is relatively easy to bear; what stings is Justice." -H. L. Mencken

Chris  
 The wire was the same music wire that I used for years. The problem was not unique at that time. I believe Windy had it happen also. Windy was at that contest and he let me use one of his backup planes.

Ed

Hi Ed,
          would that brand of wire by any chance be K+S?
Talk to any supplier of real music wire for pianos they will soon tell you that there is an absolute world of difference between real music wire and hobby store spring steel.

Pages from site says it all -

http://books.google.com.au/books?id=7dODrrDI1kEC&pg=PA122&lpg=PA122&dq=piano+wire+inclusions&source=bl&ots=5Ll4rV9Itv&sig=JpdLYAwus5wV14hgjubm64cVuYQ&hl=en&sa=X&ei=rTlET_v7M4-YiAe819yyAw&ved=0CD0Q6AEwAg#v=onepage&q=piano%20wire%20inclusions&f=false

Is 'turbulate' even a real word?

Spell check pings it, as does Google.

Fence technology on wings attempts to arrest span wise airflow much the same as a baffle on a piston top tries to arrest flow across it.

Chris     The plane was built over 25 years ago so I have no clue what type of wire was used. I had two piano tuner friends who gave me wire but more than likely it was hobby store wire.
Ed

Sounds like the people who installed the fences gave them the wrong instructions.  I think the airflow would resist arrest, but may take a tumble.

Straight from Wikipedia -
"They obstruct span-wise airflow along the wing, and prevent the entire wing from stalling at once."

And they are commonly called 'stall fences' in the trade.

Of course the flow is going to resist that arrest so where are the 'wrong instructions?'

I am perplexed.

So I guess my question would be, "Has anyone ever placed leadouts ahead of the CG?

Thanks,

I think that racing and speed models may do this, as well as slight in thrust but flying at the speed of death requires very little help with line tension.

On my Humongous, built from Ted Snow's quarter scale pencil drawings, had some rudder offset, enough that the leadouts ended up slightly ahead of the CG.  In a high wind, coming around into the wind, the line drag would be enough that it yawed in and had very little tension. I thought it kind of interesting.

Well the technical info quickly flew over my head, but I am still wondering what, if any advantage the split LO guide would offer.  Having the LO's close together is already something I do.......

BIG Bear
RNMM/AMM

Hi Bill,
        two things come quickly to mind mate, one, if the locking bolt mechanism is outboard of the individual guides then you could narrow the gap between them to almost whatever you like, and two, perhaps one bolt per guide is a bit of a fail safe.

One could let go and allow slippage whilst the other is still holding tight, that sounds 50% better than the whole guide system sliding to and fro in the advent of failure!

Well the technical info quickly flew over my head, but I am still wondering what, if any advantage the split LO guide would offer.  Having the LO's close together is already something I do.......

I think you can ignore all of the technical stuff above and not miss anything helpful for this question.  Brett posted something useful, and I was hoping that Randy Powell or Paul Walker would write in.  They were fiddling with leadout spacing to fix a problem Randy had.  I forget what it was.

I remember Randy talking about moving one leadout to address a specific issue on one manuever, perhaps the hourglass? but that's about what I recall, not much help,,

HEY RANDY

..much longer than you'll ever need 

L.

"2 is not equal to 3 - not even for very large values of 2." -Grabel's Law

Charles, how do you propose to adjust it? I dont think you can get a ball driver through that slot to make any adjustments. Mine are usually closer to 1/8" wide. ( vertically) and depending upon how far back into the tip the adjustor is, you may end up wearing the sides of a narrow slot with the leadouts.

Larry,

Thanks for the reply.

OK, that's good news.

What measurement will I need? Forward of the CG and aft? Half inch forward and an inch back?

Charles

HI Charles,

Since we do not really have a clue yet as to where you will be starting out with the LOs, it's hard to say how much is a minimal distance to add to both sides. 

How do they adjust?  I cannot see a way to get a tool of any source in there to adjust the guide.  A general guideline is 1/8" to 3/16" opening for the slot.  Always remember the KISS principle especially for things that are simple.

BIG Bear
RNMM/AMM

Mark, Bill,

That "slit" is all I need! I'll probably line each side with thin brass or aluminum sheet. Keep the lines a bit snug plus to keep the lines from wearing down the balsa.

I'm not using the traditional adjustable leadout device which is available, as I mentioned above. I said I may not use it.

I've designed a different one, as I mentioned in a Thread, way back, when I first saw what was available.

I'll have to see if it works correctly once installed.

Charles

Charles, remember every gram is significant, 1/32 ply is a lot lighter than aluminum or brass, and it will not fray the leadouts either. You do not want the leadouts to touch the sides of the slot. it will cause problems with in flight control. remember, there is no self centering servo on this, its only line tension and  your deft touch that centers the controls. I typically encourage innovation, but there is also a time to look at what has been done and think about WHY its done the way it is now. often times there is a very good reason.. but then who knows you may come up with the next great mousetrap...

Howard, as you no doubt know but are chosing to ignore, many of the more advanced religions on this planet recognize the living status of ALL things, even those you think of as simple material bits. This is why if you curse a stunter, it will typically respond by being a worthless POC. Meanwhile, a beloved model, even if it has a canted stab/elevator, and other aerodynamics which are crookeder than the proverbial dog's leg, it often returns the affection, making itself a beloved creature.

I want you to back down off all this negative crap, my friend. Model airplanes are PEOPLE TOO!

L.

'I had an uncle who was a leper - he only did the  "pull my finger - fart joke" 10 times' -Steven Wright