LAST EDITED ON Nov-27-04 AT 06:01 AM (CST)
 
Apologies to Jim not trying to hijack his thread, but it's taking way too long to load. (and I have a cable modem) No Tricks and no text required.

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OK I lied.. I want to say that I observed something that was interesting. In the conventional position the plane was relatively stable, didn't swing forward or back. In the rear position it was unstable and when I would upset it with a light bump on the nose, it would oscilate around the CG. The nose would yaw in and out for some period of time. Would highly recommend not moving the bellcrank too far from the CG if possible.

We are going to out do the President's message in number of posts. This will demonstrate our greater interest in arcane model airplane stuff as compared to politics. Good for us!

>>OK I lied.. I want to say that I observed something that was
>interesting. In the conventional position the plane was
>relatively stable, didn't swing forward or back. In the rear
>position it was unstable and when I would upset it with a
>light bump on the nose, it would oscilate for and aft for
>some period of time. Would highly recommend not moving the
>bellcrank too far from the CG if possible.

I stand under.. You are now onto what I was trying to get at. If you move the BC to far aft from my experiences IMO the plane feels tail heavy. Too far forward it will feel nose heavy.

Now this all can be corrected with trim (weight) and lead out location. But by adding weight doesn't the model fly differently?

Hey! Put a 15 on that thing and fly it.

Actually it is the size of a Sterling 1/2A mustang. That's what I used to take measurements so I had something that was dimensional similar to some real world model. The two 1/2" nuts taped up front to get a proper CG probably weigh more than a Baby Bee.

Replying to my own post... Geez!

A question for Jim Ivey.

...In the conventional position the plane was relatively stable, didn't swing forward or back. In the rear position it was unstable and when I would upset it with a light bump on the nose, it would oscilate for and aft for some period of time.

In your initial post when you were talking about the plane walking when the bellcrank was moved back, was it like the plane was shaking it nose back and forth slowly in sort of a swimming motion?

What I saw above may be the contributing factor. The plane sort of hinging back and forth everytime it's disturbed by wind, etc.

dick
What I was referring to is that fishtail motion you get when u crank hard on the controls, as in a square loop or any hard corners. Airplanes with extra long inboard wings seem to be among the worst offenders. I think theres probably a lot of factors involved. I was just trying to get that bellcrank question out of the way. To me hunting is an uncontrolable up and down motion in level flight. But i think a larger bell crank might solve that. i dont like adding weight to an airplane.
jim

LAST EDITED ON Nov-27-04 AT 07:04 AM (CST)
 
>dick
>What I was referring to is that fishtail motion you get when
>u crank hard on the controls, as in a square loop or any
>hard corners. Airplanes with extra long inboard wings seem
>to be among the worst offenders. I think theres probably a
>lot of factors involved. I was just trying to get that
>bellcrank question out of the way. To me hunting is an
>uncontrolable up and down motion in level flight. But i
>think a larger bell crank might solve that. i dont like
>adding weight to an airplane.
>jim

That makes sense to me. The period or rate of this fishtailing (oscilation) is a function of the distance from the CG to the leadout eyelet. Also the amount of deflection (how far the nose swings back and forth) depends on this distance among other things. The longer the length the slower it fishtails but the larger distance the nose wanders around center. So your comment about longer wings makes perfect sense to me.

Leadout spacing would also affect this. You are shifting that side load on the eyelets from front to back depending control direction. All of the tension is taken up by one line and its' eyelet. Think of a little triangle formed by the leadout eyelets and the CG. If you load up one eyelet, the plane wants to rotate until the eyelet lines up with the CG. So give it hard control and the load bounces back and forth between the eyelets which is like grabbing the wing tip and moving it back and forth. The less the side loading of the eyelets (get the bellcrank close to the CG). The less critical line spacing would be.

OK JIm, I have to ask another question.....what is your opinion on bellcrank location?

awwww dick....do i hafta answer that...im still bruised,bloody and sore from yesterday!!!
jim

>OK I lied.. I want to say that I observed something that was
>interesting. In the conventional position the plane was
>relatively stable, didn't swing forward or back. In the rear
>position it was unstable and when I would upset it with a
>light bump on the nose, it would oscilate for and aft for
>some period of time. Would highly recommend not moving the
>bellcrank too far from the CG if possible.

Let me take a guess at this one. The belcrank is loose with no pushrod attached. In the extreme position the leadouts are bent at a rather sharp angle (certainly excessive over a real world situation.) Is it possible that your oscilation was from leadout guide drag as the belcrank moved slightly? What happens when you hang it by one line only? Is it stable in all positions then? Or if you fix the belcrank so that it cannot move? I am guessing either would stop the problem.

So, to keep drag down we want to keep things as straight as possible. But being an inch or two off is certainly not going to be a problem. So, we are back to placing the belcrank at the high point or on the spar, and from there, who cares?

LAST EDITED ON Nov-27-04 AT 06:03 AM (CST)
 
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I think this is what's going on and I'll try not to use any math for the explaination.

The blue line is a "torque arm" from the pivot point of the bellcrank to the CG.

The red arrow at the CG is the weight of the plane and it always is acting down in this case.

The other red arrow at the top is a resultant force that is being generated by the plane attempting to rotate down but being restrained by the eyelet. Because it's in equilibrium the guide is "pushing back with a force equal in magnitude and oposite in direction to the leadout. The size of this force is a function of the length of the torque arm (blue line) and the weight of the plane

The green line is the leadout and the tension is equal in all parts of the leadout. This tension is equal to the weight of the plane.

When the bellcrank is moved back the force at the eyelet increases (the length of that top red arrow). Any upset in the fore and aft direction is magnified because of this force that is already present. The motion is more of an oscilation around the CG with the leadout eyelet sort of wiggling back and forth. The eyelet bumps against the leadout kind of like a trampoline and springs back. The tighter the line the more rebound energy is transmitted back.

If you look the first picture with the bellcrank in the normal position. The pivot point for the pendulum is a long way away at the handle so the period is much much larger.

Harmonic motion isn't my strong suit but that's my two cents.

Hey Brett... you can jump in anytime.

>[photo not recovered: 41a7fafb3643b7c7.jpg]
>
>I think this is what's going on and I'll try not to use any
>math for the explaination.
>
>The blue line is a "torque arm" from the pivot point of the
>bellcrank to the CG.
>
>The red arrow at the CG is the weight of the plane and it
>always is acting down in this case.
>
>The other red arrow at the top is a resultant force that is
>being generated by the plane attempting to rotate down but
>being restrained by the eyelet. Because it's in equilibrium
>the guide is "pushing back with a force equal in magnitude
>and oposite in direction to the leadout. The size of this
>force is a function of the length of the torque arm (blue
>line) and the weight of the plane

All correct. Case closed, except for the 75 posts to follow...

>The green line is the leadout and the tension is equal in
>all parts of the leadout.
>
>When the bellcrank is moved back the force at the eyelet
>increases (the length of that top red arrow). Any upset in
>the fore and aft direction is magnified because of this
>force that is already present. The motion is more of an
>oscilation around the CG with the leadout eyelet sort of
>wiggling back and forth. The eyelet bumps against the
>leadout kind of like a trampoline and springs back. The
>tighter the line the more rebound energy is transmitted
>back.
>
>If you look the first picture with the bellcrank in the
>normal position. The pivot point for the pendulum is a long
>way away at the handle so the period is much much larger.
>
>Harmonic motion isn't my strong suit but that's my two
>cents.
>
>Hey Brett... you can jump in anytime.

I don't think it makes any difference in the dynamics, either. Dynamic forces and torques just add and subtract, but the variation is the same.

With the exception of the "springiness" of the leadouts, of course. If you are using solid leadouts, the bend required at the leadout guide applies a non-trivial torque, and in the case in the picture, would result in the nose being torqued inboard more than you would think.

Brett

Since the beginning of control-line models, back in the 40’s, the design phase, viewed from published information, has been a “black art” relying on phases of the moon, superstition, etc. “Designers” appeared to ignore, or misunderstand, the unique effects of flying in circles tied to a pilot in the center. We were told to balance the model on front lead-out; or balance it on the bellcrank pivot; or to balance one thumb-print forward of the main spar, or any other such nonsense that popped into a designer’s head. All we really knew was that his model balanced there and he liked it! Always they were half right and half wrong. Actually, we lived by the “Flea Fright” practice of adjusting each ship to tailor out the kinks, if it survived the first flight! Ultimately, we were subjected to a lot of marginal designs (mine, too) flown by talented pilots who took it upon themselves to explain phenomena they didn’t understand. Luckily, we do not wipe out pilots during crashes. - Bill Netzeband, "Control-Line Aerodynamics Made Painless"

LAST EDITED ON Nov-27-04 AT 07:41 AM (CST)
 
Here's one of the 75:

You are conceding that the leadout guide must apply a reactive force to maintain equilibrium, and that torque is not insignificant with solid leadouts.

The leadout guides were never designed to act as pulleys, or as point loads. Solid leadouts should be an option, not a contributor to a problem that doesn't have to exist.

Analytically, it may be proven with a force diagram and the assumption of point loads, yet that has undesireable results in the real application.

As a matter of fact, the force diagram proves that as the bellcrank is moved further back, the leadout guides must assume more and more of the total load on the bellcrank pivot to maintain equilibrium. No one applies the kind of structural integrity to the guides as they do to the bellcrank pivot.

>(snip) As a matter of fact, the force diagram proves that as
>the bellcrank is moved further back, the leadout guides must
>assume more and more of the total load on the bellcrank pivot
>to maintain equilibrium. No one applies the kind of structural >integrity to the guides as they do to the bellcrank pivot.

Although this is true, the pictured location on the bottom is an extreme that nobody designs to. I have been a long time advocate of solid lines (flexibles work, too. I am just saying I use solids) and have never seen a leadout guide wear out on one of my planes (some dating back to the earlyh 50s) or one of Matt's which were also made with solid leadouts. But the belcrank was situated at the high point or spar location of the wing. You adjust the leadout guide fore and back to get proper trim, but it is never at any extreme. Twice Matt has lost the bolt that holds the leadout guide in the wing tip during flight. Once, as I recall, "it felt a little strange", but he completed the pattern. The other time it was just in practice and he pulled out and flew it level. The belcrank location was close enough, and the airplane was flying (not a rock on a string) so that full control was maintinained throughout the flight even with the leadout guide fully floating. On one of these occasions (It was at the Nats, first day of qualifying) the guide had lost its bolt and centrifrugal force had let it slide about half way up the wing to where the webbing started between the spars. Matt had to shake it down and then cut into the tip to get a new bolt in.

All I am saying is, although the belcrank can be located most anywhere, for practical purposes on our airplanes, we locate the belcrank very near the cg meaning the guide isn't that far off.

(And for the record, standard procedure these days is to replace the bolt in the leadout guide with one that is longer and smash the threads on the inside so that if it ever comes loose, the bolt cannot fall out. Good priactice for anyone I would think.)

>
>>(snip) As a matter of fact, the force diagram proves that as
>>the bellcrank is moved further back, the leadout guides must
>>assume more and more of the total load on the bellcrank pivot
>>to maintain equilibrium. No one applies the kind of structural >integrity to the guides as they do to the bellcrank pivot.
>
>
>Although this is true, the pictured location on the bottom
>is an extreme that nobody designs to. I have been a long
>time advocate of solid lines (flexibles work, too. I am
>just saying I use solids) and have never seen a leadout
>guide wear out on one of my planes (some dating back to the
>earlyh 50s) or one of Matt's which were also made with solid
>leadouts. But the belcrank was situated at the high point
>or spar location of the wing. You adjust the leadout guide
>fore and back to get proper trim, but it is never at any
>extreme. Twice Matt has lost the bolt that holds the
>leadout guide in the wing tip during flight. Once, as I
>recall, "it felt a little strange", but he completed the
>pattern. The other time it was just in practice and he
>pulled out and flew it level. The belcrank location was
>close enough, and the airplane was flying (not a rock on a
>string) so that full control was maintinained throughout the
>flight even with the leadout guide fully floating. On one
>of these occasions (It was at the Nats, first day of
>qualifying) the guide had lost its bolt and centrifrugal
>force had let it slide about half way up the wing to where
>the webbing started between the spars. Matt had to shake it
>down and then cut into the tip to get a new bolt in.
>
>All I am saying is, although the belcrank can be located
>most anywhere, for practical purposes on our airplanes, we
>locate the belcrank very near the cg meaning the guide isn't
>that far off.
>
>(And for the record, standard procedure these days is to
>replace the bolt in the leadout guide with one that is
>longer and smash the threads on the inside so that if it
>ever comes loose, the bolt cannot fall out. Good priactice
>for anyone I would think.)

Leonard: I have started using nuts with the nylon insert in them. I thin think they are called locking nuts. -DOC Holliday

I certainly agree with you. In my post #119 in the intial thread I wrote "So I'll try to line up CG - bellcrank - leadouts to minumize velocity induced yaw and keep control loads down."

Add to that narrow line spacing.

Lots of things will work but somethings work better than others.

LAST EDITED ON Nov-27-04 AT 10:54 AM (CST)
 
4 of 75

There's something else going on here than what may be solved through a force diagram. So far, we have three photographed experiments:

1. Howard's example shows the cables without bends, and the bellcrank is rotating.
2. Igor's example does not use a bellcrank - only a pin point, and the strings bend at the leadouts.
3. Dick's example uses strings as well, and they also bend, and the bellcrank does not appear to rotate.

In Howard's, the bellcrank rotates to alter the geometry of the plane and it's CG to maintain the much greater forces along the cables. The cables remain straight. It may be that with real world forces, the friction in the leadouts (interesting that he used only eyelets with trivial length) is never enough to overcome the overwhelming tension forces in the cable.

The other two cases may involve examples where the forces are much more equivalent to the tension forces in the strings. In Dick's case, the bellcrank does not even appear to rotate. It may be that frictional forces allow a precarious balance. As Dick states, the equilibrium is easy to upset.

The force diagrams, and making assumptions, may have the effect of misleading the importance of some of the component forces. The other component forces are there, but they may be so insignificant relative to the tension force in the cables that they have no bearing. One has to assume that a friction force in a leadout guide is sufficient to bend the lines in the face of overwhelming tension. That is probably not possible - at least not for very long.

Some of my models are heavy enough that if the leadouts did not line up with the bellcrank, they would eventually rip the leadout guides right out of the tip.

Given that proposition, the resulting geometry from an usually located bellcrank (without leadouts lined up) will result in yaw. This is because the aerodynamic forces would try to act in line with the plane's geometry, but the tension forces on the lines would be fighting that.

Quote:
SNIP

"The other two cases may involve examples where the forces are much more equivalent to the tension forces in the strings. In Dick's case, the bellcrank does not even appear to rotate. It may be that frictional forces allow a precarious balance. As Dick states, the equilibrium is easy to upset."

The reason that it doesn't appear to rotate is that I adjusted the leadout lengths so the bellcrank would be in the same orientation for both positions. I wanted all things to appear the same to avoid confusion. I did play around working the leadouts and rotating the bellcrank. It did not affect the position of the plane at all. So this is independent of the bellcrank's rotational position. The forces on the bellcrank are applied to the plane at the pivot point only. The plane and even the pivot point of the bellcrank have no idea what we're doing to the bellcrank regarding rotation.

"The force diagrams, and making assumptions, may have the effect of misleading the importance of some of the component forces. The other component forces are there, but they may be so insignificant relative to the tension force in the cables that they have no bearing. One has to assume that a friction force in a leadout guide is sufficient to bend the lines in the face of overwhelming tension. That is probably not possible - at least not for very long."

Beside friction, what other component forces are you thinking about?
The friction forces on the line are acting along the axis of the line so they can't produce any bending. The line bend is cause by the plane trying to reach equilibrium by rotating nose down until the CG is below the bellcrank. At that time the leadouts,bellcrank and CG are all nicely lined up vertically. The only thing preventing this are the leadout eyelets and the force they see is because they are being pushed into the leadouts by this attempt to rotate.

No doubt about, if the bellcrank was placed that far back the leadout eyelets wouldn't last long at all.

I selected this extreme position for the pictures to show that even this condition wouldn't cause the pane to hang any different.

This experiment is flawed. You didn't tape batteries to the far side of the tail so the CG would lie on the line from the leadout guide to the bellcrank (and onward to the center of the earth).

Yep - had to figure Howard's clown suit was coming out.

OK. I AM WRONG. BRETT IS RIGHT.

Dick:

Beautiful! Thank you!

Put both leadouts through thr same leadout guide and you see no differance. I had some 1/2A combat plane that Dave Hinderson from Denver designed and the bell crank was on the tail and with the leadouts going out the same hole and they worked the same as when I put the bell crank at the CG and the leadouts at the same hole and also had the CG the same on both planes. On my airplanes I have the leadouts as close as I can get them.

Hi Carl,

You said that you place your leadouts as close together as possible. Do you stagger the length of the leadouts?

The first sliding block adjustable leadouts.

American Aircraft Modeler, March 1970, Bearcat article

LAST EDITED ON Nov-28-04 AT 07:11 AM (CST)
 
>
>The reason that it doesn't appear to rotate is that I
>adjusted the leadout lengths so the bellcrank would be in
>the same orientation for both positions. I wanted all things
>to appear the same to avoid confusion. I did play around
>working the leadouts and rotating the bellcrank. It did not
>affect the position of the plane at all. So this is
>independent of the bellcrank's rotational position. The
>forces on the bellcrank are applied to the plane at the
>pivot point only. The plane and even the pivot point of the
>bellcrank have no idea what we're doing to the bellcrank
>regarding rotation.
>

Agreed. Since you say you worked the leadouts back and forth, you have proven that to be true.

>
>Beside friction, what other component forces are you
>thinking about?

The plane has a CG, but it is not a point load - neither are the leadouts. This causes moment arms to change when the pivot point changes. Everyone is also assuming that the friction load at the leadouts is worthy of consideration. Just because we can draw it, it may not be. The plane is also not fixed, it will rotate to find equilibrium with tension force (or weight). As you have stated in earler posts, aerodynamic forces in flight will also induce a rotation (if all the forces are not lined up).

>The friction forces on the line are acting along the axis of
>the line so they can't produce any bending. The line bend is
>cause by the plane trying to reach equilibrium by rotating
>nose down until the CG is below the bellcrank. At that time
>the leadouts,bellcrank and CG are all nicely lined up
>vertically. The only thing preventing this are the leadout
>eyelets and the force they see is because they are being
>pushed into the leadouts by this attempt to rotate.

Friction force is actually causing the bending. The reactive force only exists because the airplane wants to turn - similar to the rock that pushes back if you appy force. However, the friction is not directly perpendicular to the leadout guides - everything happens at the edges. Friction is not a constant force, either - it only exists in the moment - as long as the forces do not exceed the strength of the surface coefficients.

>
>No doubt about, if the bellcrank was placed that far back
>the leadout eyelets wouldn't last long at all.
>

Exactly. The real world case is an extreme that no one wants to perpetuate. The leadout guides are the constraint that helps determine the orientation of the plane, but only to the extent that two of the arms of this 4-link mechanism can rotate at the bellcrank arm connection. Flexible leadouts are fooling us in this discussion. They are possible because those two arms of the linkage are always under tension, and they are a convenient answer to hangar rash. However, it doesn't mean that we can apply them to bend in an attempt to change the system.

The leadout guides are not designed to be pulleys, either. If they were, they would become additional pivot points, and exert reactive force as you have drawn. We do not want to design-in controls that bind, though. Instead, they probably should rotate to relieve the stress, or be lengthless exit points, as in Howard's example.

We've forgotten how we build something as simple as non-adjustable leadout tubes. We orient the plane's rotation as needed to give us the leadout rake we want, then we glue tubing (sometimes 2 or 3 inches long!) in the position that causes no binding (friction!). How do we do this? I always pulled on the leadouts to get it right. Simple, but it also assumes that the bellcrank is somewhat close to the CG, and that yanking on the leadouts is a reasonable approximation of the tension in flight. Picking up the plane will demonstrate this, and moving the lines back and forth will cause no rotation of the plane.

It still sounds like we are agreeing, and the rest may be semantics. Moving the bellcrank may cause undo friction and stress at the leadout guides, and the plane will attempt to rotate to relieve that stress. If that rotation is different than the thrust line (assuming some aerodynamic differences), then yaw will occur in flight. Line rake does the same thing, as everyone will agree. The key is that both are altering the centerline of the mechanism with respect to the orientation of the plane.

>I selected this extreme position for the pictures to show
>that even this condition wouldn't cause the pane to hang any
>different.

Yep, but the friction and low tension forces may have caused the result. It is a very commendable job, and it shed a lot more light on the discussion. On the other hand, everything I said may end up BS when Howard puts on his clown suit.

Update: Looks like Jim's pictures prove this, too.

I still say you should get it off the wall and fly it.

LAST EDITED ON Nov-28-04 AT 06:30 AM (CST)
 
Just th facts man. No hidden weights, no hi-jinx of no kind, plain and simple truth. pics 1&2=0", 3&4=3 3/4", 5&6=6 3/4, 7&8=10" The wing is 33". The marks are a 1/4 inch apart. Looks like bellcrank position might make a difference.
jim

LAST EDITED ON Nov-28-04 AT 06:20 AM (CST)
 
Good Morning Jim... been busy. Obviously you are getting different results, so here goes the first of I'm sure many questions.

[photo not recovered: 41a9c9312891a6d0.jpg]

I'm interested as to what's happening at the yellow arrow.

1. Do the leadouts thread thru a set of leadout guides and are they free to slid without binding in the guides if they are threaded thru?

2. Is the model suspended by the leadouts and not to a hook at the wingtip?

3. Is the bellcrank attached to a hook at the wingtip?

th cam moved on two pics i fixed one ...still workin on it

no need to cheat of course they are free

Do us a favor..while you still have it hanging (sounds personal). With the bellcrank in one of the rear locations, grab the model and rotate it back to the level position and then take to a nose up position.

Does the model return to the original position or does it stop somewhere in between?

LAST EDITED ON Nov-28-04 AT 07:02 AM (CST)
 
here ya go ill take pics of it occilating...gimme a bit ok?

1 an eyelet made from a "t" pin
2 yes
3 no
This was a lot of work I took th picks with a web cam. About thirty of em darn thing turning. this is about the best i can do. I need sleeeeeep! jim

Thanks. I didn't ask what you are using for leadout lines.

I think your results are affected by the friction of the leadout in the guide. If you do what I suggested in the above post and rotate the plane and it always returns to the exact same condition then my theory is out the window.

Another thing that affects this experiment is the weight of our experimental model planes. The heavier the plane the greater the side load in the leadout guide and the bigger the bind. The bigger the bind the harder it is for the system to reach equilibrium.

Also, you did see the nose shaking oscillation as you moved the bellcrank back. Farther back you go the longer and larger the shakes.

Get some sleep.

1st pic not very restrictive is it?
2nd pic lots of room to move around huh?
i think i covered allll th bases but, maybe not...im sure ill hear did u do this? WELL!!! how about THAT!!! n ill say yep ha ha ha ha ha ha yall have a good day....nite all
jim
ps ya think it would be worth changin to a 3" bellcrank?

Me thinks me sees the problem mate. How stiff is that"leadout". Looks like nyrod from RC is it?

come on dick...its nylon box cord...cant u see how limp it is?

LAST EDITED ON Nov-28-04 AT 08:07 AM (CST)
 
Try it with 4 to 6 lb monofilament line. We know your not cheating so we will believe the results.

I still think it's stiff enough to cause the old whip antenna effect. Hence the oscilation you are seeing.

I gotta get to church and save my sorry soul...later guys.

Edited - I'll say a prayer for all those poor people that don't have model planes to keep the juices flowing.

Can I get an Amen?

>I think your results are affected by the friction of the
>leadout in the guide. If you do what I suggested in the
>above post and rotate the plane and it always returns to the
>exact same condition then my theory is out the window.

Hi,

Dick - I think the bellcrank used in the test is just too heavy (against the model weight). And moving the belcrank causes the CG of the model is moving too. The result is whole model is rotating the tail down...

Regards

Dalibor Toman

It may be another case where the plane is not heavy enough to completely overcome the friction at the leadouts. It still shows the tendency, though.

Good job, Jim.

Thanx Tom
That almost model,is absolutely free to go where it wants, no restrictions, and dicks plumb line on c/l from the opposite tip like that, shows just what happens when u move th bell crank around. i used 12lb monofiliment line before but u couldnt see it. So i swiched to the yellow nylon. I wanted everyone to see i didn't cheat

The other thing that comes to mind with a front or rear placement of the belcrank location is that you will get uneven amounts of travel pull between the front and rear leadouts. If the Belcrank is moved toward the rear, you have a lot of travel with the rear leadout, and if the belcrank is moved forward the front leadout would have a lot of travel. Obviously, you have even travel with 90 degree belcrank only when the leads are perpendicular to the belcrank leadout arms.

You will also have some effect on the travel of the pushrod arm. The solution is a belcrank with the leadout arms perpindicular to the leadouts, and a push rod arm that is perpindicular to the direction of the pushrod. This is similar problem that you have with the flap horn that is resolved with the bent horn. The Brodak pathfinder plans show a horn to solve this, and Tom Morris sells his "True 90 Horns".

The net effect being uneven amounts of travel for either up or down depending on how the controls are configured. The solution would be a custom non-90 belcrank or a round belcrank with an offset hole for the pushrod.

Regards,
Jim Amos

LAST EDITED ON Nov-28-04 AT 11:51 AM (CST)
 
Jim,

A lot of work that you are to be commended.

Now let me make a suggestion that might, or should, account for the change in the "bob" weight position that you have taken pictures to show that the airplane is changing its orientation.

Mark the CG of the airplane for each position that you have the bellcrank. Make sure that you include the weight of the leadout material that you are using. As you move the bellcrank rearward, your CG is also moving rearward. It does not look like this is a very big airframe and it does not weigh very much. The location of the bellcrank will have an affect of the CG. If your set up is accurate enough, can you show how far the CG moves with respect to the leadouts in your photographs. I think the intuition that you and Tom Blanchard and your anomynous famous personalities that agree with your concept will dictate that that CG is not lining up with the leadouts in any of your photographs.

You have devised a very clever way to accurately show that the airplane changed in yaw as you moved the bellcrank rearward. What you have not shown is where the CG is relative to the leadouts. If you can accurately show this as you have accurately shown the yaw angle, I think you will be somewhat amazed at the results. Before you blow this off, please at least try to determine this.

Also, I do not think that the flexibility of the leadout material you are using is a question as long as it reasonably represents the flexibility of leadouts usually used on our models whether they be solids or cables.

It is interesting to me that after seeing the various sets of "photographic proof" of what happens as the bellcrank position changes. For some reason, the "fixture" that Dick Fowler used is flawed as determined by some who are posting here. For some other reason, the photos by Howard Rush appear to support those who have been preaching that the bellcrank position does affect yaw. So now, there is to be no question that the intuitive thought of the non-half fast thinkers is irrefutability correct. There are evidently several forms of gravity warps going on here. In the case of Jim Ivey's photos, it appears that the airplane is yawing outboard, albeit slightly, as the bellcrank has been moved rearward. (My contention here is that the actual CG is still lined up with the leadouts.) Then, in the case of Howard's photos, the model yaws extremely inboard as the bellcrank moves rearward. This represents entirely different results for the same repositioning of the bellcrank. Can somebody please explain this unless there truly is a different set of physics going on?

Please do not misunderstand what I am saying. Under static conditions, the model will orient itself with the CG directly in line with the leadouts. Yaw angle will change due to other factors, like rudder offset, engine offset, flap and wing assymetry and aerodynamic loading, tip weight and perhaps many other more subtle factors. It is desirable to place the bellcrank as close to the CG as possible to reduce friction and wear at the leadouts. But until there is a large displacement of the bellcrank from the CG, there should be little concern on the part of the designer of builder where the bellcrank is, and this concern is only for wear and unwanted friction at the leadouts.

I have had some experience with a rearward position of a bellcrank on a scale model with a lot of wing sweep (like 40-degrees). In order to keep the bellcrank hidden, it was necessary to bury it in the wing center section a good 3 or 4 inches infront of the CG. (This was a small 1/2 A scale model with a 38 inch wing span.) The leadouts came out of the wing leading edges, slightly staggered behind the CG per Bill Netzeband's nomographs through pulleys inside the wing. There has been absolutely no control problems with this configuration.

By the way, under static conditions, the CG of an aircraft can be considered a point mass. Weight distribution is of no consequence under static conditions. Now, in a dynamic situation, weight distribution does make a difference.

The writings of Bill Netzeband still stands where he wrote that those who believe that the bellcrank position makes a difference for the yaw angle of our models know not what they speak.

Jim,

Just a suggestion if it is difficult to show how the CG position changes with respect to the leadouts in your setup in the photograps.

I think there is a simple demonstration with your setup that will either show you are absolutely correct or indeed, the CG will always line up with the leadouts (under static conditions).

First, with the bellcrank in the forward position. Mark where the CG is. Then your first photograph will be duplicated. Then, with the next bellcrank position, determine the new CG, but add ballast (it will not take much) to move the CG to its original position. Then take a picture of your plumb line to see if the yaw angle changed. Then repeat the process for the rearward position that you show, again adding ballast to maintain the original CG postion. Then take your picture and show us the results. It will be interesting to everybody regardless of which side of the fence they are on on this seemingly never ending debate. (It has been going on for years and now, you have the tools in your hand to show, maybe irrefutably, one or the other is correct.)

Again, please do not blow this off until you have tried this. Also, please do it with an open mind so as to not bias the experiment, either intentionally or unintentionally. I know you are not trying to skew any of the results. But the CG on that small light airframe is an important factor on what is going on here, and the CG positions must be determined as accurately as your plumb bob has shown the difference in yaw as you moved the bellcrank rearward.

Thanks in advance for doing this.

LAST EDITED ON Nov-28-04 AT 05:19 PM (CST)
 
The very first picture shows that. I went from there, just changin the bellcrank positions.
jim

LAST EDITED ON Nov-28-04 AT 04:20 PM (CST)
 
ok

lets see him (Bill) refute my hard evidence with hard facts! ...or anyone...i'll listen....jim

>lets see him (Bill) refute my hard evidence with hard facts!
>...or anyone...i'll listen....jim

Jim,

OK, you said you will listen. Please go back to my posts in #39 and 41. To make it easier for you, I will repeat part of my post #41:

"First, with the bellcrank in the forward position. Mark where the CG is. Then your first photograph will be duplicated. Then, with the next bellcrank position, determine the new CG, but add ballast (it will not take much) to move the CG to its original position. Then take a picture of your plumb line to see if the yaw angle changed. Then repeat the process for the rearward position that you show, again adding ballast to maintain the original CG postion. Then take your picture and show us the results. It will be interesting to everybody regardless of which side of the fence they are on on this seemingly never ending debate. (It has been going on for years and now, you have the tools in your hand to show, maybe irrefutably, one or the other is correct.)

"Again, please do not blow this off until you have tried this. Also, please do it with an open mind so as to not bias the experiment, either intentionally or unintentionally. I know you are not trying to skew any of the results. But the CG on that small light airframe is an important factor on what is going on here, and the CG positions must be determined as accurately as your plumb bob has shown the difference in yaw as you moved the bellcrank rearward."

I will try to explain it another way. It appears that the CG has moved when you moved the bellcrank rearward. This might account accounts for the change in the yaw angle that you show. The only way that you can really proove that the CG does not line up with the leadouts, you must show where the CG is for each of the three bellcrank locations you show, and then show its position relative to the leadouts as accurately as you have shown how the yaw angle changes. Or you can negate the problem of changing CG positions more simply by making sure the CG is in exactly the same position for each of the three locations you show. The CG is not in the same position in the photos you show because the weight of the bellcrank has moved rearward. I maintain that with your small and light airframe that you show in your photos is very sensitive to CG change as you have moved the bellcrank rearward. Add ballast as sugested above to keep the CG in exactly the same location for each of the bellcrank positions and repeat the photos. If you can attest that CG is exactly the same location for each bellcrank position when you take the photos, and the yaw angle still changes as you have originally shown with your pictures, then you are in a similar gravity warp but in a different direction that Howard Rush experienced.

Again, please give it a serious attempt before you blow me and Bill Netzeband off again. I am trying to be polite about this. Please note that I have not described your hypothesis as "half fast" thinking which was a serious putdown and was totally uncalled for.

At the same time, maybe you and the several that seem to agree with your intuitive thinking, it would be interesting to hear why your nose point slightly more outboard as the bellcrank moves rearward and Howard's test shows a severe inboard yaw as the bellcrank moves rearward.

>Just th facts man. No hidden weights, no hi-jinx of no kind,
>plain and simple truth. pics 1&2=0", 3&4=3 3/4", 5&6=6 3/4,
>7&8=10" The wing is 33". The marks are a 1/4 inch apart.
>Looks like bellcrank position might make a difference.
>jim

I guess to put this to the real test some one will have to build two full size PA planes. One with the BC in the right location and one with it as far back as possible. It won't be me as I have done this in the past with unfavorable results.

It caused a hinging effect or the plane felt tail heavy. So I think I will continue to put the BC in the place I normally do.

For anyone who try's this experiment in real life situation good luck and let me know how it goes.

Post #83 in the first thread shows a bellcrank mounted three inches behind the spar.The plans show the bellcrank mounted in the spar center.I have been flying in contests for 24 years, what more do you need?I am not saying to do this but I have done it both ways on Cobra's and it doesn't have any effect on the plane.
Ed

>Post #83 in the first thread shows a bellcrank mounted three
>inches behind the spar.The plans show the bellcrank mounted
>in the spar center.I have been flying in contests for 24
>years, what more do you need?I am not saying to do this but
>I have done it both ways on Cobra's and it doesn't have any
>effect on the plane.
>Ed

I went back and studied. Yours was the probably the best post - simple, unpretentious, with pictures representing years of evidence. In effect, you just said, "Here it is - it works - been doing it for years." Should've studied it more - my bad.

What's the crossbracing in the Cobra ribs? Are those the same as the rib strips, or just square sticks? Did it add much weight?

LAST EDITED ON Nov-28-04 AT 03:37 PM (CST)
 
[photo not recovered: 41aa30fb17004db8.jpg]

OK ...If I'm pulling back there at the bellcrank in the direction of the arrow why doesn't the nose rotate down like the front arrow. Howard (who I hope gets his just rewards ) and Jim are getting rotation in the other direction the nose is going the wrong way....hhhhmmmmmmm.

PS. Brett and Keith you are excused from this one. (for Now)

Edit - This is an exercise to see if intuitive thinking will get us to the other conclusion. The one that says as the bell crank moves back the plane hangs different. Remember.. intuition tells me the sun revolves around the earth.

>>>the sun revolves around the earth<<<

NO, wrong, I am telling you it is gravity what makes sense. That your question is very static. Look to Jim’s pictures. Earth rotates 15 deg per hour. As you can see on his pictures that nice gauge clearly shows speed of photo shooting. He did a picture every ~10 minutes.

If I see your original message in this thread, I see that when you moved the bellcrank for that second shot, it is clear that you have much smaller angle than Jim. The second shot shows only ~1 deg yaw in comparison to first. It is well visible on LE of model to edges of door. I think it looks for 5 minutes? You are probably much quicker then Jim. I see it is easier to move bellcrank on cardboard model.

What bothers me is that Jim has opposite yaw in time that you got. Aren’t you form Australia? That could explain all.

Geez... I forgot about that gravity thing again, just like in your experiment. "Southern Hemisphere" gravity rule doesn't apply I'm in the USA. Maybe we should get one of our friends from down under to run this same experiment.

No chance. They are sleeping now. And tomorrow is too late. If minutes make such a difference, who know what will happen after a day, could be it will not hang anymore. ... it can stand on lines or what ...

... no wait a moment, they are down the head, it can work, what is standing here that is hanging there ... so - guys, who is from Australia? NZ is OK also

Hey Igor... interestingly enough if you wait long enough the nose points up like everyone else. I guess I caught the gravity shift at the wrong time. But now its' OK. It must reset itself but I'm not sure of the cycle time.

Seriously though, I retried the experiment cause my "force diagrams" didn't predict that nose down thing. Now its' nose up like I thought.
Science triumphs all is right with the world.

I'm tired and will post pics tomorrow.

I.ve noticed nobody answering my quiz.

LAST EDITED ON Nov-28-04 AT 05:52 PM (CST)
 
Bless ya, Igor
I thought I was the only one that noticed that,or cared. Hey, I'm sorry about the "rube goldberg" remark ok?. You do very nice work. Now just for you, I'm going to do this. Im going to hang the aiplane and reposition belcrank "Exact"(=/-.015") distances from th orginal center of balance c/g, zero zero ok? I'll use lighter leadout line. The yellow cord was so it could be easily seen. I live in a trailer(wouldnt ya know it) and every time the heater comes on it twirls th airplane. Real results take a while, so please be patient. It sounds to me like you may be able to come up with an equation that would make sense.
jim

Thanx Jim, but I afraid the only one who recognized what is REALLY happening on your pictures was Keith

>>>Hey, I'm sorry about the "rube goldberg" remark ok?<<<
I have no problem with humor. I enjoy such pictures. It opens mind.

You are going to get into big trouble marking on the wallpaper.

Ok, just to really twist the tails out there, let's throw this into the mix...what about the Focault Pendulum? Bwaaahhaahaaaaahaaaaa...
http://www.fi.edu/time/journey/Pendulum/

For more info, my cousin did some interesting work on this, actually building his own Focault Pendulum in a suitcase, so to speak, and did a presentation for those ivey leagers... The trick is keeping the pendulum stationary to record the earths rotation... but I digress from the far out excuses and such things...

I've seen the ships that Eddy R has posted pics of fly for over 25 years from construction phase to flying, to retirement. None had premature control failure from a rearward belcrank position, and none had any "REAL WORLD" issues with control functions. As a matter of fact, next time you see Gene Martine, ask him what he thought of Eddy's 1980's Juno after Eddy let him fly it & Gene will tell you it was the best flying and trimmed plane he'd ever had his hand's on.

Now, we're not talking putting the belcrank in the tail for crying out loud, just moving it maybe back as far as the trailing edge of the wing, or whatever is needed to get decent structure of your stunt ship right? I say fire for effect, and let the rest sort itself out. The effect would seem to be in the white noise, and other building imperfections and factors will probably out weigh this in the final evealuation of a stunt ships performance.

Eric V.

This is to Jim Ivey:

Reference your posts #44 and #48.

In case you have not noticed, there have been a few converts in the last day or so to the fact that the CG will line up with the leadouts, regardless of the bellcrank position. Actually, if you will check what Howard Rush did, you will find that in his photographs, the above fact was again demonstrated. Bill Netzeband and Brett Buck and others that subscribe to that fact are correct.

I think you will do yourself a great favor if you will properly account for the CG in your test set up. I know you have not had much time to redo the work that you have done, but it will be interesting if you do it and share what you find. Until your tests account for the slight shift in CG that occurs when you have moved your bellcrank rearward, the results of your tests as shown in your photographs are flawed.

As before, I qualify this that we are talking about static conditions here. Yaw with our control line airplanes is dependent on a number of factors, but none of them have anything to do with bellcrank location.

Just curious - how heavy IS that bellcrank?

:-) ... well ... enough to say that if you move it, it will change yaw

... it is well documented in two seriouse experiments by Dick and Jim ... you move bellcrank, you change the yaw

LAST EDITED ON Nov-29-04 AT 10:44 AM (CST)
 
OK. This started as a personal experiment to see why I got results which were not consistent with my hypothesis. My Premise was that the nose shouldn't drop by moving the bellcrank (BC) back. The force diagrams, which some consider to be BS, predict a rotation upward not down as the BC is moved aft. The cause of this rotation is related to the BC location and as Keith indicated, is a simple shift in CG dependent on the BC weight and location.

Brett also stated that the properties of the leadout will influence the results and that's exactly what tilted the results (so to speak) in my first experiment.

[photo not recovered: 41ab1ce37a677981.jpg]

This is the starting point with the BC located at or very close to the CG. The same location as the original experiment.

[photo not recovered: 41ab1f5f0b9a95f8.jpg]

This shows a repeat of the first experiment with different results but now consistent with predicted results (that force diagram thing again). The nose has rotated up.

The reason for the apparent contradictory results was the little unaccounted for forces at the eyelet and leadout interface. Tom B alluded to these in some of his posts. This is what happened.

1. Hung the plane to rerun the experiment and the nose went down. Lots of head scratching.

2. Went upstairs for coffee and more scratching of other body parts. Returned two hours later and now the model was hanging as in the picture slightly nose up.

3. I used sewing thread for leadouts and 1/8” SIG eyelets. When I first hang the model, the thread is relaxed. As it hangs with weight on it, the thread stretches growing thinner and more rigid. At first the eyelet will bend the thread causing a drop in the nose. Eventually, all the “stretch” is removed and the eyelet no longer deflects the thread and the nose is up as predicted. (answer to my previous quiz)

[photo not recovered: 41ab25af307cca88.jpg]

If the diagrams all work (and I never thought they wouldn’t) , I should be able to add weight equal to the BC and equal in distance forward of the CG which would balance the load (torques) and return to the vertical position . I moved the BC to a new position 3 ½” aft of the CG. The BC assy weighs just 2.17 grams. It now hangs slightly nose up. I could have increased the effect by increaseing the weight of the BC assy but skeptics would say I changed the experiment.

[photo not recovered: 41ab29fe4c71a0ca.jpg]

This shows the results. I added a bolt weighing 2.21 grams located at the yellow arrow. Now the model is hanging close to vertical. It’s actually hanging a touch nose down again and probably due to the 2.17g vs 2.21g difference in weight, small errors in location of the CG and the string needing to “stretch” some more.

I drew a little balance (teeter-totter) to show the forces (there goes that diagram thing again) to show what’s happening. If the bolt isn’t there then the little blue arrow which represents the weight of the bolt is gone. So the expected result would be that the little balance would rotate down in the direction of the arrow at the BC and the nose lifts.

The thing to remember is that the amount of tilt (rotation) is a function of the weight of the BC and the distance that it is from the current CG. The total weight of the model does not affect this. (I may regret saying that). Theoretically, a fly landing on the end (actually any place other than the pivot point) of a perfectly balanced 20 ft long 2000lb steel beam will cause the beam to rotate under its’ weight. (assuming no friction, I’ve learned that minutia will be considered and argued ad nauseam.).

So it first seemed we got different results and all of them prove the original hypothesis wrong. It would be easy to conclude that the theory was wrong and quickly argue that “science sucks” and doesn’t really predict what’s happening, which some have done. Just because it’s counter intuitive doesn’t mean it’s wrong. Some concepts are harder to understand than others but please don’t demean the messenger simply because you don’t understand the message. I’m off the box now.

IMHO I conclude:

That other than moving the CG (which becomes fixed after installation), the position of the BC doesn’t affect how the plane hangs. The plane will always align itself to the leadouts (past the guides) and the CG. (Jim proved that)

Radical locations of the bellcrank (far from the CG) presents issue of wear on the guides, added loads on the control and in my opinion a somewhat less stable system in yaw.

The space/time rift has repaired itself and things are behaving themselves again.

I’m going to go downstairs and cover myself in balsa dust .. a much more productive activity.

Besides that.. I’m kind of bellcranky

Mr Buck - only 13 to go

Nice scientific work Dick!!!

But let me ask one stupid intuitive question. The BC is hinging on lines, so how it can change the CG position and force the nose rotate up? How can even its pivot force down and against what to make that moment?

>>>I may regret saying that<<<
sorry if already

psst.... Igor ur I think your intuition is correct. The heavier part, AKA the nose should go down. But maybe gravity isnt as strong where he lives.

give him little bit time, he is now trying to separate ying and yang

Jim,

If you are admitting that you understand and agree with Dick Fowler's work and explanation, you owe Bill Netzeband and others you accused having "falf fast" ideas a big apology.

Kieth
In dicks first illustration the airplane at this point is balanced on th bellcrank, leadouts don't come into play here, ok, you got that much? Then when he moved the bellcrank aft, it shifted th balance point to the leadouts essentially making it "tail heavy". Did that lightbulb go on yet? He proved it does make a difference where u place the bellcrank. No apoligies from this side of th fence are necessary.
jim

>Kieth
> In dicks first illustration the airplane at this point
>is balanced on th bellcrank, leadouts don't come into play
>here, ok, you got that much? Then when he moved the
>bellcrank aft, it shifted th balance point to the leadouts
>essentially making it "tail heavy". Did that lightbulb go on
>yet? He proved it does make a difference where u place the
>bellcrank. No apoligies from this side of th fence are
>necessary.
>jim
"be" smart .... dont just "act" smart

>>Kieth
>> In dicks first illustration the airplane at this point
>>is balanced on th bellcrank, leadouts don't come into play
>>here, ok, you got that much? Then when he moved the
>>bellcrank aft, it shifted th balance point to the leadouts
>>essentially making it "tail heavy". Did that lightbulb go on
>>yet? He proved it does make a difference where u place the
>>bellcrank. No apoligies from this side of th fence are
>>necessary.
>>jim
>"be" smart .... dont just "act" smart

I have tried to be nice about this.

I will suggest you go back to any one of my posts in 44, 48 or 59 and explain what happens when you change the CG when you have changed the position of the bellcrank in the airframe you use for your demonstration of how the yaw angle. If you can show that the yaw angle does change when you hang the plumb bob even after you have made sure the CG of that airframe is exactly the same with each of the three bellcrank positions, then I think you might have proved something.

Until you account for, accurately, the shift in CG in your demonstration and photographs, you have not yet proved anything other than I think on careful examination of your existing photographs, the CG is still alining with the leadouts. Because the CG changes with the changed bellcrank position, there will be a change in the yaw angle.

Several other of those who were in your side of the fence have seen the light in the last several days. Or have you missed their revelations in several other threads that are on-going at this time? The CG lines up with the leadouts, regardless of the bellcrank position. You have changed the bellcrank position. Yes, the yaw angle changed, but the yaw changed because the CG has moved and is still lined up with the leadouts.

Thanks for the advice, but I am not trying to "act" smart. I still maintain you owe Bill Netzeband a big apology unless you prove otherwise. Your test and photographs do not prove your position. Your test and photographs will not prove your position until you fully account for the location of the CG in each of the configurations you show.

LAST EDITED ON Dec-01-04 AT 03:47 AM (CST)
 
kieth
I think I've pretty well proved my point that th bellcrank position does matter! Dicks illustrations showed it. mine showed it, what more proof do you need! By your own admission moving it affects th yaw and c/g you say...Looks like I'm the one due an apoligy.
jim
this is my last post on this...ill read but i wont answer..no point

>kieth
>I think I've pretty well proved my point that th bellcrank
>position does matter! Dicks illustrations showed it. mine
>showed it, what more proof do you need! By your own
>admission moving it affects th yaw and c/g you say...Looks
>like I'm the one due an apoligy.
>jim
>this is my last post on this...ill read but i wont
>answer..no point

As you say, there was this:

"Because the CG changes with the changed bellcrank position, there will be a change in the yaw angle."

If A does B, and B causes C, then A results in C.

It's called Engineering semantics. However, no one will let us go back and attempt to re-define our intent at this point. Part of arguing a point is understanding the cultural language. As was also said early on, none of this may be valid with the many forces in play during actual flight.

I chose to "cry uncle," and will save it for the next issue.

>>>If A does B, and B causes C, then A results in C.<<<
And no one beleived me that rotation of earth can cause independent angle does matter where I put leadouts. ... and I did so nice pictures

>>>>If A does B, and B causes C, then A results in C.<<<
>And no one beleived me that rotation of earth can cause
>independent angle does matter where I put leadouts. ...
>and I did so nice pictures

... and there are other language differences as well. If you add humor, that makes it even more difficult.

I keep trying to understand, Igor. I think you mean that the earth's precession also causes variations in the solar gravity pull, as the distance and angle to the Northern hemisphere changes. Don't you think the moon causes more of an immediate effect? Look at the tides - that's not exclusively rotation of the earth.

We also had a lunar eclipse recently. That probably altered this entire thread.

dont forget th hemorrhoid factor....

LAST EDITED ON Dec-01-04 AT 07:10 AM (CST)
 
Are you choosing to ignore what happened when I compensated for the CG movement by adding weight back on the nose?

I can return it to original condition (nose straight) by this weight addition. Isn't that about where the plane would fly? So can I assume that even with the bellcrank in that stupid position, I can make adjustments so that from outside the airplane you don't know where I put the bellcrank. Geez.. even the plane doesn't know!

By the way Igor.... I took it down before it hit the wall!

Short answer to your "trick question" in the other post. Sum of torques. The wing is now participating in producing a tension component. Hanging straight down only the lines working away. Did all the forces and torques around CG, BC, guides. Haven't done this stuff since 1964 (Akron University - Home of the ZIPS!)

It doesn't matter anymore. I really think Jim is a "Master Baiter" and I'm tired of playing. Tom B...... leave me alone on this one and I'm with you. It doesn't matter anymore.

In the words of the immmortal Rowan and Martin - Say goodnight Dick....GOODNIGHT DICK

To Brett - You are soooo smart! You said 75 responses and here we are at 74. Any guesses as to who wants the last word?

LAST EDITED ON Dec-01-04 AT 05:02 PM (CST)
 
ok ill move th leadouts and throw some chunks of lead on it...jim

OK, Brett-

Here is the 75th: "Jim, you just HAVE TO to be kidding."

SK

LAST EDITED ON Dec-01-04 AT 05:04 PM (CST)
 
never mind, sorry i asked such a stupid question...jim

LAST EDITED ON Dec-01-04 AT 11:37 PM (CST)
 
>kieth
>I think I've pretty well proved my point that th bellcrank
>position does matter! Dicks illustrations showed it. mine
>showed it, what more proof do you need! By your own
>admission moving it affects th yaw and c/g you say...Looks
>like I'm the one due an apoligy.
>jim
>this is my last post on this...ill read but i wont
>answer..no point

You flat missed the point.

Yes, I recognize that the yaw angle changed. There is a reason that it did, but not for the reason you preaching.

One more time and I will try to speak very slowly and distinctly.

You moved the bellcrank.

The CG changed.

The yaw angle changed because the CG changed.

The airplane in your photos actually show that the CG in each case is lined up with the leadouts.

The yaw angle changes because the CG is in different positions and the CG in each case is still lined up with the leadouts.

Until you fully account for the shift in CG in you test rig, you have not proven anything more than the CG will always line up with the leadouts, REGARLESS of the bellcrank potition.

The fact still remains that the CG will always line up with the leadouts, REGARDLESS of the bellcrank position.

Go back and read the following posts in this thread.

#10
#45
#57
#52
And pay particular attention to #62. Dick's test orriginally showed the same results as your test. Then, all of a sudden, he accounted for the CG shift as I have been trying to explain to you and voila, the CG lines up with the leadouts.

I think this all started with your question on where to put the bellcrank. The answer is that it makes no difference where the bellcrank is placed, except for unwanted wear and some unwanted drag at the leadouts if the bellcrank is a noticable distance from the CG. The reason is that the CG always lines up with the leadouts REGARDLESS of where the bellcrank is placed as shown in your test set up.

Kieth
"I think what we have here is a failure to communicate."...the question was "what was the best position to put the bellcrank pivot point in relatioship to the center of balance,the c/g and peak of the airfoil"....and u among others said it dont matter where u put the bellcrank...now your backpedaling and sayin "u gotta rebalance the airplane and move th leadouts"...that sounds like it mattters to me.. also when brett cited th now famous "cardboad airplane experiment" of bill netzban...nothing was mentioned about moving the leadouts and rebalancing...that would "prove" that when u moved the bellcrank that it "DID" matter...as Igor would say "do you still not get it!"....had i known i was going to be attacked, ridculed for my grammer, typing style and have my question misrepresented like it was....i wouldnt have bothered asking...oh...and for the record...i put my leadouts at the proper angle to th bellcrank...that way i have no wear or friction problems...jim

>Kieth
> "I think what we have here is a failure to
>communicate."...the question was "what was the best position
>to put the bellcrank pivot point in relatioship to the
>center of balance,the c/g and peak of the airfoil"....and u
>among others said it dont matter where u put the
>bellcrank...now your backpedaling and sayin "u gotta
>rebalance the airplane and move th leadouts"...that sounds
>like it mattters to me.. also when brett cited th now famous
>"cardboad airplane experiment" of bill netzban...nothing was
>mentioned about moving the leadouts and rebalancing...that
>would "prove" that when u moved the bellcrank that it "DID"
>matter...as Igor would say "do you still not get it!"....had
>i known i was going to be attacked, ridculed for my grammer,
>typing style and have my question misrepresented like it
>was....i wouldnt have bothered asking...oh...and for the
>record...i put my leadouts at the proper angle to th
>bellcrank...that way i have no wear or friction
>problems...jim

OK, I am about ready to give up. I guess I do not communicate very well.

First, I have not said anything about how you write, or made any comments about your grammer or spelling.

Second, I am not backpedalling.

Third, I am not saying that you have to move the leadouts. I am saying that the CG determines were the leadouts are to be located.

Fourth, I have not meant to misrepresent your question. This question comes up on a fairly regular basis, and there seems to be a handfull of people who choose not to understand the physics involved and press forward with preconceived ideas of what happens when the bellcrank is moved.

Now again, for the record, and for some reason, my explanation is just not comming through to you. You have twisted things around. First, I think it is safe to state that for a given design, there is a single desirable CG location. Once that balance point is determined, there is an optimum location for the leadout position. And I mentioned in my ealier posts on this thread as well as what was said in posts that were referenced in the thread that you started this topic that the CG will align itself with the leadout position under static conditions. (Other factors in the dynamics of flight and maneuvering will affect the yaw of the model, but that is not the question here.) The whole point here is that with a FIXED CENTER OF GRAVITY, the position of the bellcrank will have NO EFFECT on the yaw angle of the model.

I evidently should have explained it to you more clearly before, but your test fixture does not have a FIXED CENTER OF GRAVITY as you moved the bellcrank rearward. You have a small and light airframe in your test. The bellcrank location affects the CG. You have very cleverly and accurately shown that the yaw angle changed as you moved the bellcrank rearward. (This is a compliment for your work.) But if you were to fly that airplane, you would want to have a CG fixed for best flying characteristics. If you move the bellcrank rearward, it would require a slight addition of weight to the nose (or conversely, remove weight from the tail) to keep the CG in the original position. As soon as you balance your model to the original CG, there will be NO change to the yaw angle due to the relocated bellcrank.

It is probably most desirable to place the bellcrank at or very close to the CG of the model, again, to minimize wear and friction at the leadouts.

For the record, the proper location for the leadouts is determined by the CG, not by the bellcrank location. You can put the bellcrank wherever you choose depending on various constraints due to structure, airplane configuration, engine/tank/muffler combinations, or whatever. I do not think anybody has said that it is not best to place the bellcrank at or near the CG. It is just not necessary to do so as the bellcrank location will have no affect on the flying characteristics of the model.

The cardboard airplane experiment you mention is supposedly something that Bill Netzeband did. Fine. The several articles he wrote, photographs of a test fixture he made (which has been described on this forum several times), the test flights that Williamson did years ago where the bellcrank was placed in 9 different positions from a location beneath the tank to a location just in front of the horizontal tail, the test that Dick Fowler did on this thread (which by the way is almost identical to what you did, only a cardboard representation of a model was used), and his discovery as well as the revelation of at least one other naysayer who have opened their mind to understand of what has been written and demonstrated during the last several weeks on this forum, and the test that you did all show the same thing. The CG lines up with the leadouts regardless of where the bellcrank is located.

That is all the issue is here. The CG lines up with the leadouts, regardless of where the bellcrank is located.

The recommendation to a less experienced modeler should be to locate the leadouts according to where the CG is. It makes now difference where the bellcrank is located.

On several occassions, I have asked you to adjust for the change in CG before you blow me off. But you still choose not to even try to comprehend what has been explained and proven over and over. Either you do not understand what I have tried to explain or you have chosen not to adjust your test procedure to maintain a constant CG because you are uncomfortable with what the results might be. The results will be that Netzeband and Williamson (from years ago), and the recent postings by Buck, Walker, Fancher, Rush and others are correct. These people are not prone to "half fast" ideas as you have stated which is a monumental put down far beyond what has been written about you. You can have your own ideas, but that does not mean these people or the facts are wrong.

Give it a try and then come back and explain what you have found. I would again ask that you carefully measure and maintain the CG on that fixture as accurately as you have shown the yaw angle change in your original setup.

LAST EDITED ON Dec-02-04 AT 11:50 AM (CST)
 
EDIT * I changed some words and adjectives that were too strong - am not trying to start anything, I just have a personal weakness with hyperbola (not as in a catenary function), and can get carried away in writing *

>
>That is all the issue is here. The CG lines up with the
>leadouts, regardless of where the bellcrank is located.
>
>The recommendation to a less experienced modeler should be
>to locate the leadouts according to where the CG is. It
>makes now difference where the bellcrank is located.
>
Wow - a lot here. I have read every post in these threads (although my eyes did glaze over when the force diagrams came up) and I would beg to differ on a number of points.

1. "First, I have not said anything about how you write, or made any comments about your grammer or spelling."
No, but a lot of people did say that about Jim, and he didn't directly accuse you of doing it, anyway.

2. "I am saying that the CG determines were the leadouts are to be located."
Agreed, and that is why many of us have admitted being wrong. However, that statement gets a little tweaked as you go on.

3. "... the CG will align itself with the leadout position under static conditions. (Other factors in the dynamics of flight and maneuvering will affect the yaw of the model, but that is not the question here.)"
The question was always about the dynamics of flight. The discussion became deflected as blanket statements were made, then attempts to bring up the complicated forces in play during flight were ridiculed, and made to seem trivial. Jim's question always centered around the bellcrank, and therefore leadout location, with respect to his observation of "walking" and "the hula" during flight.

As the discussion continued, several attempts at static experiments were conducted. By my count, at least 4 of these experiments were tried. Out of the four, the first was an outright visual trick (Howard's), Igor's didn't even include bellcrank, separate leadouts, an engine or tail on the plane, and Dick's and Jim's were admittedly skewed because of light weight (cardboard, 1/2A scaling). Three of four of those experiments appeared to initially support the argument that bellcrank location made a difference.

To fuel the discussion further, the outright visual trick example was the only one that appeared to use a legitimate plane with realistic features and weight.

So the discussion grew among those who have never been privy to the mulititude of previous articles, the other experiments you cite, and most importantly, the cultural understanding. At least for myself, all of this reflected badly on the newbies and others returning to the sport, who thought we at least had a handle on fundamentals.

4. "If you move the bellcrank rearward, it would require a slight addition of weight to the nose (or conversely, remove weight from the tail) to keep the CG in the original position. As soon as you balance your model to the original CG, there will be NO change to the yaw angle due to the relocated bellcrank."
Your statements above are the first time I've seen anyone try to clearly state, "The weight of the bellcrank will affect the CG of the very light airplane when moved." Even then, it was not very clear. If we keep saying that moving the bellcrank will affect the CG, that does not necessarily mean that the bellcrank location has no effect.

Without making too fine a point of it, if the bellcrank location results in altering the leadout position with respect to CG, then the bellcrank location will have an effect. If we're discussing the absolutes of analysis, that could be viewed as a ridiculous statement, but in the practical sense it is not. Most kits, plans, and designs base the leadout position based in some respect to the bellcrank location.

5. "The recommendation to a less experienced modeler should be to locate the leadouts according to where the CG is. It makes no difference where the bellcrank is located."
I disagree. It seems that the entire discussion has arrived at the conclusion that the bellcrank should be located at the CG - at least as close as structure will reasonably allow - not the leadouts. Look at any older plan that does not have adjustable leadouts. The leadouts do not line up with the CG. They line up in a perpendicular opposition to the line of thrust, with some "guessed" amount of rake to account for line tension, drag, and other aerodynamic forces. That's why the more experienced modeler came up with adjustable leadouts in the first place.

More often than not, in the typical stunt design, the rear line of the bellcrank is perfectly perpendicular to the plane's thrust line. The front line of the bellcrank is then swept back with respect to the rear line. Altering the bellcrank location significantly will demand a conscious decision by the builder about where to locate the leadouts. Whether the leadouts go back, forward, or straight from that point will matter greatly, and it no longer becomes "intuitively" obvious to the less experienced modeler.

my apoligies to everyone....please!....im not trying to win converts or make enemies...though it seems i have....the arguement over bellcrank placement and that ##### cardboard wing is "personal" to me....i didnt know that was in the mags....i guess thats a good thing....i would have been demanding a rematch...lol...Hi aint here to argue with anymore....i knew moving that bellcrank would change things and he would argue that it didnt....by having to balance and place the leadouts according to the location of th bellcrank does seem to me like it makes a difference....i just take it one step farther than balance....i think its important to the center of lift....this is how i set up...balance the airplane on the peak of the airfoil...like you would a glider...there i put the bellcrank pivot...then i tape both leadouts togeather in level position and hang the airplane vertically i make a line across the wing tip where the leadouts cross it...i recheck it a couple of times to make sure it stays the same...then i drill the holes according to those lines...i hadnt done that with this little airplane....i musta just said to myself "oh...that looks about right"...that front leadout was way to far forward and th rear wasnt close either... i hope that fixes it...if not you may see that "cute lil airplane" hangin on the wall @t&a hobby lobby in burbank as a conversation piece...again apologies to all...jim

LAST EDITED ON Dec-03-04 AT 09:01 PM (CST)
 
Tom,

Maybe we are finally making some progress here. You have taken a few statements of mine and commented, now I will return the favor.

>Wow - a lot here. I have read every post in these threads
>(although my eyes did glaze over when the force diagrams
>came up) and I would beg to differ on a number of points.
>
>1. "First, I have not said anything about how you write,
>or made any comments about your grammer or spelling."
>No, but a lot of people did say that about Jim, and he
>didn't directly accuse you of doing it, anyway.

Granted, he did not directly accuse me of so doing. However, he did post the comment in reply to my post. And he has also previously told me to "think smart, not act smart", which I took as a big put down. And he also included me with several other names including Bill Netzeband as having "half fast" ideas regarding various concepts and technical matters with these toy airplanes of ours and I consider that a complete, inappropriate and monumental put down of Bill Netzeband which is totally uncalled for.

>2. "I am saying that the CG determines were the leadouts
>are to be located."
>Agreed, and that is why many of us have admitted being
>wrong. However, that statement gets a little tweaked as you
>go on.
>
>3. "... the CG will align itself with the leadout
>position under static conditions. (Other factors in the
>dynamics of flight and maneuvering will affect the yaw of
>the model, but that is not the question here.)"
>The question was always about the dynamics of flight. The
>discussion became deflected as blanket statements were made,
>then attempts to bring up the complicated forces in play
>during flight were ridiculed, and made to seem trivial.
>Jim's question always centered around the bellcrank, and
>therefore leadout location, with respect to his observation
>of "walking" and "the hula" during flight.

Perhaps you believe that the question has always been "about the dynamics of flight". However, in the comments that I have made, I have tried to qualify what I was saying by explaining that the CG will line up with the leadouts, regardless of bellcrank position was always with respect to static conditions. As soon as you introduce the dynamics of flight, including rudder and engine offset, fuselage design, assymetric loading which is always present on the wing and flaps in our circular flight, line drag, and the variables of maneuvers in different planes on the surface of our himisphere will all have some affect on the actual yaw angle of the aircraft in flight. It is still usefull to understand that the position of the bellcrank has no affect on the yaw angle that the aircraft takes while in flight assuming that the CG is fixed to the desired trim position.
>
>As the discussion continued, several attempts at
>static experiments were conducted. By my count, at
>least 4 of these experiments were tried. Out of the four,
>the first was an outright visual trick (Howard's), Igor's
>didn't even include bellcrank, separate leadouts, an engine
>or tail on the plane, and Dick's and Jim's were admittedly
>skewed because of light weight (cardboard, 1/2A scaling).
>Three of four of those experiments appeared to initially
>support the argument that bellcrank location made a
>difference.
>
>To fuel the discussion further, the outright visual trick
>example was the only one that appeared to use a
>legitimate plane with realistic features and weight.
>

Actually, a "legitimate plane" is not required to demonstrate the static conditions to show that the CG will always line up with the leadouts. The concept can be demonstrated with a device that includes an item that represents a "leadout guide, a mass that represents a physical body with a center of gravity that can be located, and an attachment point somewhere on that mass with a tether that goes throught the "leadout guide" that can suspend the entire fixture. Change the attachment point and the CG will still align with the leadouts. Change the CG location, and the device will shift to align the CG with the leadouts. Change the leadout position and the device will again shift to align the CG with the leadouts. That is all that I have been trying to explain as has been explained for the last 40 years.

>So the discussion grew among those who have never been privy
>to the mulititude of previous articles, the other
>experiments you cite, and most importantly, the cultural
>understanding. At least for myself, all of this reflected
>badly on the newbies and others returning to the sport, who
>thought we at least had a handle on fundamentals.
>

Thanks for showing you have an open mind.

>4. "If you move the bellcrank rearward, it would require
>a slight addition of weight to the nose (or conversely,
>remove weight from the tail) to keep the CG in the original
>position. As soon as you balance your model to the original
>CG, there will be NO change to the yaw angle due to the
>relocated bellcrank."
>Your statements above are the first time I've seen anyone
>try to clearly state, "The weight of the bellcrank will
>affect the CG of the very light airplane when moved." Even
>then, it was not very clear. If we keep saying that moving
>the bellcrank will affect the CG, that does not necessarily
>mean that the bellcrank location has no effect.
>

The very light models and the very light cardboard representation are very sensitive to shifts in CG by moving the bellcrank hardware including the weight of the leadout material. Indeed, in the photographs that have been posted, the yaw angle shifted. But the shift was due to the repositioning of the CG. If the CG was maintained by rebalancing the model to its original location with the changed bellcrank position, the yaw angle would not change, thus the statement still holds that the CG lines up with the leadouts, independent of the bellcrank position.

>Without making too fine a point of it, if the bellcrank
>location results in altering the leadout position with
>respect to CG, then the bellcrank location will have an
>effect. If we're discussing the absolutes of analysis, that
>could be viewed as a ridiculous statement, but in the
>practical sense it is not.

See my comment above.

>Most kits, plans, and designs
>base the leadout position based in some respect to the
>bellcrank location.

Here, I will beg to differ. The plans for a well designed stunt ship that has been properly trimmed will show the leadouts to be placed with respect to the CG determined for that design to work best. (This assumes of course that the plans actually represent the the optimum location of the leadouts as determined by flight test.) If you want to make a general statement, it would be revealing to first examine a number of proven designs by the top designers (again, assuming they are sharing their experience in trimming the model including the position of the optimum CG for that design). I think you will find that the leadouts are positioned very close to a location suggested by the equations and nomographs generated by Bill Netzeband in the 1970's after he took a lot of work by Pete Soule who quantified a lot of information regarding line drag and the shape of the lines during flight (a cantenary curve). From all of that work, it is fairly easy to establish, within a very small tolerance, the line rake, or postion of the leadouts with respect to the CG. It matters not where the bellcrank is in any of these calculations. If you understand this, you are starting to understand what several people have been trying to explain for the past 40 years on this subject.

>5. "The recommendation to a less experienced modeler
>should be to locate the leadouts according to where the CG
>is. It makes no difference where the bellcrank is
>located."
>I disagree. It seems that the entire discussion has arrived
>at the conclusion that the bellcrank should be
>located at the CG - at least as close as structure will
>reasonably allow - not the leadouts. Look at any older plan
>that does not have adjustable leadouts. The leadouts do not
>line up with the CG. They line up in a perpendicular
>opposition to the line of thrust, with some "guessed" amount
>of rake to account for line tension, drag, and other
>aerodynamic forces. That's why the more experienced modeler
>came up with adjustable leadouts in the first place.
>

Here is where the difference comes in when we start talking about the static situation of the CG wanting to align with the leadouts. When we talk about the the optimum leadout position while flying through our pattern, a whole different set of factors are introduced. An initial adjustment for the "design location" of the leadouts for the stunt model that is to be flown can be made by calculations developed by Soule and Netzeband based on model weight, speed, line length, and line diameter. The desired line rake angle can be fairly well calculated and has resulted in being able to generate some general "rules of thumb" based on type and size of model. But again, that location of the leadouts for dynami flight is determined by a whole list of factors, not one of which is bellcrank location.

>More often than not, in the typical stunt design, the rear
>line of the bellcrank is perfectly perpendicular to the
>plane's thrust line. The front line of the bellcrank is
>then swept back with respect to the rear line. Altering the
>bellcrank location significantly will demand a conscious
>decision by the builder about where to locate the leadouts.

Not so.

>Whether the leadouts go back, forward, or straight from that
>point will matter greatly, and it no longer becomes
>"intuitively" obvious to the less experienced modeler.

I think you have almost grasped the idea. I am not sure what you are trying to say with the above statement. Except for the wear on the leadout guides and almost negligible drag/friction of the lines at the leadouts when the bellcrank is located a "significant distance" from the CG, it makes no difference and it does not "matter greatly" if the leadouts wires go back, forward or straight from the leadout guide to the bellcrank.

It all boils down to what most have already said: It still makes sense to place the bellcrank at or reasonably close the the desired CG of the model. But not doing so will NOT affect how the model flies regarding the yaw angle the model assumes while in flight.

(Now, I can throw in a whole new bucket of worms that has not been mentioned in any of these threads. Moving the bellcrank any significant distance from the CG will result in a change in the geometry of the control system and there will be a change in the way the bellcrank imparts the up and down movement to the control surfaces based on input from the pilot's hand and handle. I do not know what extremes must be reached before this difference is noticable, even with the most experienced flyer, but there will be a point when this can and will happen. I would guess that the several "golden arms" in this event will feel this difference on a "finely tuned competitive model" if the bellcrank pivot location starts to approach a position near or in front of the leading edge or near to slightly ahead of the trailing edge (of a conventionally configured model). I cannot post a diagram of what I am trying to explain. Rather than me trying to generate a word picture, simply draw a diagram of a bellcrank in each of these locations and see what happens to the way the bellcrank rotates for a given input from the control lines. In this context, it makes sense to mount the bellcrank at or near the CG. But the fact that the yaw angle of the model does not change, for a given CG location, regardless of the position of the bellcrank.)

(Edited for correcting a type where a significant word ("NOT") was left out of a sentence above.)

>>More often than not, in the typical stunt design, the rear
>>line of the bellcrank is perfectly perpendicular to the
>>plane's thrust line. The front line of the bellcrank is
>>then swept back with respect to the rear line. Altering the
>>bellcrank location significantly will demand a conscious
>>decision by the builder about where to locate the leadouts.
>
>Not so.
>

Yes, it is - unless you want to argue that my layman's description of "thrust line" doesn't account for engine right thrust. I am merely referring to the geometry of the plane. We can take a survey of old time and classic stunt planes, and just see how many have a rear leadout line perpendicular to bellcrank neutral.

>Except for the wear on the leadout guides and almost negligible
>drag/friction of the lines at the leadouts when the bellcrank is
>located a "significant distance" from the CG, it makes no difference
>and it does not "matter greatly" if the leadouts wires go back,
>forward or straight from the leadout guide to the bellcrank.

There's another perfect example of these "absolutes" brought up in a technical discussion that cause argument. First, you're making an assumption that drag/friction at the leadouts is "almost negligible." Those assumptions include how far off the leadout guides really are, and whether you have equal tension (or any tension) during all attitudes of flight. It also assumes that you have no binding, or even intermittent binding.

Then you state that the position of the leadout wires does not matter greatly??!! Are you now stating that leadout rake has no affect on yaw, and that adjustable leadouts were never necessary?

>
>It all boils down to what most have already said: It still
>makes sense to place the bellcrank at or reasonably close
>the the desired CG of the model. But not doing so will
>affect how the model flies regarding the yaw angle the model
>assumes while in flight.
>

Exactly what I have been saying (along with others) and another case of semantics. Refer back to your post just before this one. The entire theme was that the leadout guides must be aligned with the CG. Now you've just stated that the bellcrank should be, and that not doing so will affect yaw. Surely that's a typo.

Dazed and confused, but not knocked out,

Mr. Blanchard,

When I designed and built a semi-scale F-104 Starfighter, see previous SSW threads about the N-104 Red Baron by Grzly23, I put significant anhedral into the wing just a Vic Macalusco did with his early 70s F-8 Crusader. I made sure the ship would fly level even with the leadouts kinked at the leadout guide by balancing the vertical CG of the Starfighter to make sure it projected through the leadout guide of the inboard wing tip. Most said the ship would fly with a bank outboard in upright flight and a bank inboard in inverted flight because the leadouts would force themselves into straight alignment from the handle to the leadout guide to the bellcrank. Guess what? They were wrong. The ship flies perfectly level with kinked leadouts even though the bellcrank is 1 inch removed vertically from the vertical CG. This condition is exactly the same as your discussion with Keith Trostle only instead of it being in the horizontal, my example is in the vertical.

The bottom-line is that the vertical and horizontal CGs are the detemining factor with regards to the position of the leadouts on the wingtip. The bellcrank position, if you keep the vertical and horizontal CGs exactly where they belong, means nothing. Only the position of the leadout guide on the wingtip is of concern. It must compensate for air drag on the lines and project dynamically from the handle to the CG. Nothing else matters. And leadout friction in the leadout guide is negligible. My Starfighter with approximately 8 degrees of line kink proves this. I have experienced no difference in the performance of my flight controls from those of a flat no dihedral or anhedral wing.

You would do well do learn from the hard work of Mr. Netzeband and Mr. Trostle. They are only trying to be of help and keep you from reinventing the wheel.

Tom... not to be a nitpicker but it's probably important to amplify a point. The verticle and horizontal CG is really the same point and in the same place. It's a matter of a from where (your reference )you are starting from.

Just trying to avoid confusion.

Actually,

The vertical and horizontal CGs can be different. It is best if they coincide, but you can create a ship that the two are removed from each other. For example, it is possible to have the horizontal, pitch, CG correct, but have the vertical, roll, CG too high or low and have a condition where the ship will fly in a bank, but turn well. It is essential to make sure both are exactly where they need to be. A great set of articles was written by Chris Lella in Model Aviation back in the late 70s about balancing a precision stunt ship in roll, pitch and yaw.

LAST EDITED ON Dec-03-04 AT 12:20 PM (CST)
 
>
>You would do well do learn from the hard work of Mr.
>Netzeband and Mr. Trostle. They are only trying to be of
>help and keep you from reinventing the wheel.

* DELETED *

Keith made some suggestions about the "less-experienced" modeler - I guess that's me - and the placement of leadouts and bellcrank. As a matter of fact, just as he allowed that my mind was open, so was his. He understood that proving a point with force digrams might not be as important as what advice should be given.

So, I responded.

Just be sure you guys don't leave out Bill's article on high aspect ratios and turning capability. It just happens to be about a combat plane, so prejudices against it may win out. However, it has always made me respect his analysis as much as you guys.

>> But not doing so will affect how the model flies regarding the yaw angle the model assumes
>>while in flight.

>Surely that's a typo.

Yes, it's a typo. "...not doing so will NOT affect..."

SK

LAST EDITED ON Dec-03-04 AT 03:00 PM (CST)
 
Im tired of this...no use trying to convince you guys that you ARE adjusting the leadouts and balancing due to the posistion of the bellcrank...you just keep on with those end around examples...well it dont matter where ya put th bellcrank long as you move th leadouts around and throw some chunks of lead on it to rebalance it...is that what i can't git?...that would make you right i suppose....sure you can put the bellcrank anywhere you want...but that dont mean it dont make any difference.....jim

LAST EDITED ON Dec-03-04 AT 11:53 AM (CST)
 
Jim What they are trying to tell you is in your's and the other test that some have run is you are using a very light model,maybe 3-4 ounces with a 1/2 ounce bellcrank. Moving a 1/2 ounce bellcrank 4 inches in a 4 ounce model is going to move the cg a lot.Now take a 60 ounce plane and move the 1/2 ounce bellcrank four inches and the CG is not going to move very much and the plane does not tilt. Yes the CG will move a very tiny amount. So the test is only valid when the Cg is maintained as it would be in a trimmed stunter.The test is only valid when the CG is maintained as it would be in a properly set up stunt plane. On the classic Mr Wizard tv program of the 50-60's he did a neat test that shows this relation of angles and CG. Maybe I can explain it. He had a pencil standing on it's point on his finger. At the top of the pencil he had a wire connected at a 90 degree angle,this wire went out for about 6 inches and then was bent down 90 degrees for 9-12 inches and then crosses under his finger and does another 12 inches. He had a small weight on the end and the pencil would stay on his finger as he moved his hand back and forth.This was all very amazing to a young person. I do this all the time at my wifes day care and the kids think it great.They just can't grasp why the pencil will not fall off of my finger.The bell crank and the CG are the same as the CG and the pencil.Try it.
Ed

Jim-

I am sorry if this tries your patience, but you just need to understand the necessarily accepted method of aircraft design - model or full scale aircraft. If you question this, then you are challenging the designers of successful full sized aircraft - military or civil and mechanically actuated or "fly by wire". Models follow the same rules, albeit at lower Reynolds Numbes.

The C.G. position is determined by the aerodynamic center of the aircraft (choice of 'static margin') and flap induced moments. This is necessary for the plane to fly right and optimally. Thus the C.G., as determined by aircraft aerodynamic configuration, is the determining factor for the leadout position. The C.G. range is a constant for aircraft of a particular configuration to fly right and is determined by aerodynamic configuration and BEFORE the rest of the design. This applies to CL models as well. It is a constant. THEN and ONLY THEN are lead outs positioned at the wing tips. The leadout positions are not influenced by bellcrank position for this constant and predetermined C.G. position. If you adjust C.G. to leadout position or allow it to vary according to anything besides A.C., then you have the tail wagging the dog and can only hit the optimal trim by pure luck. Even then, the bellcrank position will not change anything for a given C.G. Changing the C.G. from its optimal position is UNdesigning the airplane.

Only if - and this has been pointed out since before my first post - ONLY IF the bellcrank is positioned extremely, in an extremely light model, will its position have any effect, and this will concern FRICTION or bending forces of the lines only. Only if you fly a relatively massless plane - paper airframe, engine, and hardware? - with stiff leadouts, then the yaw might change due to wire stiffness. Otherwise, tests have proved out this "theory", which is akin to the "theory" that the Earth rotates. It's a done deal.

You just have to understand and accept what is the independent variable here. In all of professional aviation design, the C.G. and A.C. are coordinated; THEN the rest follows. In CL models, for a given desired and optimal C.G., the bellcrank position is irrelevant to all but wear phenomina and control freeness; you just don't want to bend the wires more than you have to. As far as yaw is concerned, the bellcrank position is irrelevant. Yaw depends on the relationship between C.G. and leadout position.

Sorry, but even if I wanted to do so, I cannot repeal the laws of physics for anyone. Now I am really DONE with this; I don't have to defend the great designers of history; their work and "theory" in the textbooks that reflect it speak for themselves.

SK

Tom,

I had planned on not continuing with this discussion. However, you have taken some of my statments out of context. This is probably because I did not express myself very clearly. I will try to explain.

>>>Altering the
>>>bellcrank location significantly will demand a conscious
>>>decision by the builder about where to locate the leadouts.
>>
>>Not so.

>Yes, it is - unless you want to argue that my layman's
>description of "thrust line" doesn't account for engine
>right thrust. I am merely referring to the geometry of the
>plane. We can take a survey of old time and classic stunt
>planes, and just see how many have a rear leadout line
>perpendicular to bellcrank neutral.
>

My response "Not so" response above was in regard to your statement

"Altering the bellcrank location significantly will demand a conscious decision by the builder about where to locate the leadouts." It was not in regard to where many designs show the leadouts. The "Not so" goes to the whole issue that has been on these threads. The bellcrank position does not dictate where to put the leadouts. The CG dictates the basic position for the leadouts and then adjustments are made in flight test to trim the model for more desirable flight characteristics.

>>Except for the wear on the leadout guides and almost negligible
>>drag/friction of the lines at the leadouts when the bellcrank is
>>located a "significant distance" from the CG, it makes no >>difference and it does not "matter greatly" if the leadouts wires >>go back, forward or straight from the leadout guide to the >>bellcrank.

>There's another perfect example of these "absolutes" brought
>up in a technical discussion that cause argument. First,
>you're making an assumption that drag/friction at the
>leadouts is "almost negligible." Those assumptions include
>how far off the leadout guides really are, and whether you
>have equal tension (or any tension) during all attitudes of
>flight. It also assumes that you have no binding, or even
>intermittent binding.
>
>Then you state that the position of the leadout wires does
>not matter greatly??!! Are you now stating that
>leadout rake has no affect on yaw, and that adjustable
>leadouts were never necessary?
>

My statement "it does not 'matter greatly' if the leadouts wires go back, forward or straight from the leadout guide to the bellcrank."
was making reference to the amount of line drag or friction at the leadouts even if the lines make a noticeable angle from the leadout guides to the bellcrank. I can understand the confusion my statement above could have made since I assumed it would have been understood the leadout postion is critical to the design and trim of the model and what I have been saying, the bellcrank position is not.

>>It all boils down to what most have already said: It still
>>makes sense to place the bellcrank at or reasonably close
>>the the desired CG of the model. But not doing so will
>>affect how the model flies regarding the yaw angle the model
>>assumes while in flight.
>>
>

This was a monumental typo -- the last sentence should have read "But not doing so will NOT affect how the model flies regarding the yaw angle the model assumes while in flight."

>Exactly what I have been saying (along with others) and
>another case of semantics. Refer back to your post just
>before this one. The entire theme was that the leadout
>guides must be aligned with the CG. Now you've just
>stated that the bellcrank should be, and that not
>doing so will affect yaw. Surely that's a typo.

YES IT WAS and thank you for recognizing it as such.

Keith,
Please accept my apology if I took some of your statements out of context.

well yall may be right...thanx for ur patience...please excuse my ignorance and rude remarks...jim

Ron B.
F4Fguy

Keith:

Cut your losses,there are none so blind as those who will not see, nor none so deaf as those who will not hear.You've been far too patient.