bellcrank position

what i wanted to know about is the pivot point of th bellcrank and its relationship to the balance point,center of gravity and peak of the airfoil...i have a scratch built(its 1/2a stunter)...and i reasoned all three should be th same in order to prevent walking or th "hula" what ever its called these days..ive noticed th farther back th bellcrank pivot is the worse they seem to walk...so i reasoned on center it shouldnt walk like that...however it was awfully sensitive like that....now ive moved the foward leadout back from where i had it to th balance point/peak/cg...do you think that will fix it or am i going to have to move th bellcrank back also...is there something im misssing...heeelllllpp...jim

Jim:

Unless you're way out of line and generating friction in the system, the location of the bellcranck pivot bolt doesn't matter. Leadout position, CG, yaw angle and mysterious forces only understood by "D-Dan" are meaningful, but not that.

Try this: Take a piece of cardboard and punch a hole mid point along the top big enough for thread to freely go through. Feed some thread though it and tape it to one bottom corner. Look at the hanging angle. Now move the thread to the opposite corner. See: it hang's the same.

I know this logically but still just did it myself to avoid "hoof in mouth" disease.

Friction at the leadout exit is a factor so don't get too carried away, but your problem is not with the pivot bolt location.

LAST EDITED ON Nov-23-04 AT 07:15 PM (CST)
 
Bellcrank mount is typically very close to max wing thickness, because that is probably where the spars are, or should be, giving you something strong to fasten to. The CG will be a little ahead of max thickness for a flapped model, a bit more forward yet, for a non-flapped model. One of the things you'll find most different is that now most models are built with adjustable leadout guides, tipweight boxes, tailweight boxes, rudder trim, and maybe a wing tab. Some guys have mechanically adjustable flap horns, so flap adjustments are not so risky. Stunt News has the details, or check the Brodak, RSM or Tom Morris websites. If you only have one bookmark/favorite for CL, let this be the one: http://home.att.net/~philbrown36641s5/clhomepage.html Steve

Or, maybe this one, 'cause Phil's is on the top of our links page: http://www.nwskyraiders.com/index.html

LAST EDITED ON Nov-23-04 AT 08:46 PM (CST)
 
thanks jeff...however...now dont get me wrong and im not trying to be contentious and i appreciate ur thoughtful answer...however if u took that cardboard bell crank and put its pivot point on the balance point(C/G) of a cardboard airplane and then repositioned the pivot point farther back toward th tail or closer toward th nose i believe you would find it would make a difference in th "yaw"...hanging as u say...hi said that the pivot point s/b app 2/3 th distance between th front leadout and th pivot point...behind th c/g...say app 3/4" with a 2 1/2" bellcrank...however ALL his designs were walkers th panther and cougar being th worst...on leadout position we once ran both leadouts out th same hole on th b/p c/g....it still walked and seemed even worse...i later moved th rear one back about 1" and just let it go...later he tryed to see if he could determine th angle of sway in the lines and maybe at least eliminate that as a reason for walking... but never came up with anything concrete that i can recall...i think we tryed just about everything reguarding leadouts...pivot point was another matter...he just never thought that was particularly important beyond his 2/3 rule...i still think it is...jim

Jim,
If you had no leadout guides, you would be exactly correct--the pivot point of the bellcrank would be the pivot point of the model. But leadout guides placed in or near the wingtip become the new pivot point(s). Other than the aforementioned friction potential, bellcrank location then becomes of no consequence. I know it's counterintuitive, but it's true. the CG relative to the leadout guides determines the yaw (if any) of the plane. That's why that yaw can be changed without moving the bellcrank...adding nose or tail weight will change it; moving the leadout guides will change it; moving the bellcrank alone will have absolutely no effect on it. Strange but true...
--Ray

Jim:

There was a test performed by Walter Williamson in the 60's. The plane tested two items location of the bellcrank and leadout guides. He built the plane so he could move the bellcrank almost from the front to the back of the fuselage and the leadouts from leading to trailing edge. After a series of tests his findings were that the bellcrank position wasn't very important the leadout placement is the governing factor.

The findings were published in American Modeler.

ok...ill give you guys this....movement of th front leadout can redetermine th center of balance...maybe moving that front leadout back to th c/g is all ill have to do...and ive done that...ill leave th rear one where it is....we'll soon see...if i ever get th dogggone thing finished(a couple of weeks i hope) its a 1/2a with a 200sq"wing it "flew" really well...just real "tricky" i may have fixed that though....made th flap horn longer and swapped th rods around...couldn't do anything for th elevator horn ...im maxed out for room

LAST EDITED ON Nov-23-04 AT 09:32 PM (CST)
 

Jim:

I understand your response, but that's why I gave you the way to test. Just make your own mock up as I described and move the bellcrank pivot (the taped bottom end). You'll find the mock up hangs the same regardless of position. Looks wrong but it isn't. I have no problem with your questioning the answer, but do try the test.

As a matter of fact on my new Klapinski Tempest (RSM kit), I went from the 3" bellcrank used in the kit and on the original, to a 4" which would have gone through the spar. I this case I just moved it back 1/2" rather than weaken the spar.

Good luck!

Jeff

Additional edit: I think what you are calling "walking" is what I call hunting, or the inability of the model to "groove" in level flight. If that's the case, look at control system friction with none being the standard, look at CG being too far rearward, check for up or down thrust and finally, check for negative incidence in the stab. The stab leading edge can be slightly above the stab trailing edge and the model will fly fine but if it is even a little bit lower (negative incidence), the model will not groove at all. This is due to the airflow from the prop not going staight back at the stab but going slightly back and down on midwing or low wing airplanes due to flow over the top of the wing. The opposite is true for high wings. This can be really dramatic and way too exciting when it's wrong.

If hunting is not what's happening, disregard that paragraph.

To convince yourself on the pivot, make the mock up the size of your wing (cardboard is just fine). Punch a 1/4" hole at the center of your leadout spot, then move the attachment around on the other end.
It will hang the same.

Good luck again....
Jeff

LAST EDITED ON Nov-23-04 AT 10:22 PM (CST)
 
nope wrong!!!! jeff do your own experiment ok...like this....two feet of string put a 2"loop in one end of it ...take a piece of cardboard say 2 feet long x 6"-8" wide put a hole in th left side of th wing in th center close as u can to one end...then 12 inches(the aproximate center of the 2 feet) from the first hole put a second hole off center of th cord width say 1 inch....now thread that string,the tag end, not th loop, thru th hole on th end of th wing...then thread the tag end through that off center hole(the second one) and secure it...now stick one finger through that loop in th string and let that wing hang on that finger...then tell me that th pivot point doesnt make a difference...try it...put several center holes if u like everytime u move that string in th center th angle will change...hey dont blame me if you got bit by ur own dog...lol...jim

LAST EDITED ON Nov-24-04 AT 00:39 AM (CST)
 
Jim:

It's an old argument. That's why we don't mount bellcranks on the glow plug or the trailing edge. Weight or centrifigal force will try to straighten the line out if it has a substantial bend, not to mention the increased friction at the exits. No one's questioning that.

If that were the dominant factor, then verical lead outs would be more prone to yawing than horizontal because under load, as in a square, you are essentially flying on one line, and since that line would always be halfway between the location on horizontal leadouts, the angle and yaw should be increased. Since horizontal leadouts are 1 to 2" apart and vertical leadouts Zero apart (fore and aft), under heavy load they would have from 1/2 to 1" more arc/angle as the line passes the leadout guide and should increase the yaw. This is simply not the case, as the Klapinski Tempest with its vertical leadouts proves. I can't prove that they reduce yaw because I haven't flow that plane with horizontal lead outs, but I can tell you that my old Tempest (crashed at VSC) had less yaw than any other stunter I've owned. MY new one also has the Vertical Leadouts. The main reason the never got popular is that adjustables became popular and it's a whole lot easier to do that with horizontals.

It's fun to argue the theory, but I doubt that you'll cure your problem by moving the bellcrank.

Jeff

Added note: I just did it exactly your way and dimensions. ON a 24", 8" wide piece of cardboard with the bellcrank equivilant holes at center, + 4" and -4", the difference in vertical hanging angle from + to -4" over the 24" length was 3/16". With the weight doubled, the difference increases slightly to just over 1/4". Again, undoubtedly due to the weight trying to straighten the string. An engineer could give you a formula for that.

The point is that the item balances on the entry/exit point or leadout guide, not the bellcrank pivot. The slight angle change is due to the mechanical forces trying to straighten out the line.

By the way, I had this arguement with an engineer/modeler about 20 years ago----and lost. He even projected the yaw change from line straightening on paper then proved it with the mock up. He still is trying to collect the cup of coffee I owe him!

the airplane balances th yaw on th pivot of th bell crank....i was right about th experiment wasnt i? u did it...jim

Point of teather is in the center of bellcrank regaurdless of where the leadouts are. And what anyone might think IT DOES MAKE A DIFFRENCE!

THANK YOU SPARKY...I knew someone would know....and it doesnt surprise me its you...id shake ur hand if i could reach ya....jim

LAST EDITED ON Nov-23-04 AT 09:47 PM (CST)
 
>what i wanted to know about is the pivot point of th
>bellcrank and its relationship to the balance point,center
>of gravity and peak of the airfoil...i have a scratch
>built(its 1/2a stunter)...and i reasoned all three should be
>th same in order to prevent walking or th "hula" what ever
>its called these days..ive noticed th farther back th
>bellcrank pivot is the worse they seem to walk...so i
>reasoned on center it shouldnt walk like that...however it
>was awfully sensitive like that....now ive moved the foward
>leadout back from where i had it to th balance
>point/peak/cg...do you think that will fix it or am i going
>to have to move th bellcrank back also...is there something
>im misssing...heeelllllpp...jim

Do yourself a favor and put the bell crank around 30% of wing cord less flaps. EDIT: (back for LE) Just my well thought out guess.

LAST EDITED ON Nov-23-04 AT 10:31 PM (CST)
 
hey ..i really wanted to hear from you....maaaaan u do beautiful work....you and godzilla...i was hopin for a better answer though darn it...thats just about on th center of th cord c/g and b/p...where i have it...i did move th leadout back though...it was to far forward before...jim

LAST EDITED ON Nov-23-04 AT 11:25 PM (CST)
 
>hey ..i really wanted to hear from you....maaaaan u do
>beautiful work....you and godzilla...i was hopin for a
>better answer though darn it...thats just about on th center
>of th cord c/g and b/p...where i have it...i did move th
>leadout back though...it was to far forward before...jim

Think of it this way draw a line from aprox lead out postion to Wing tip weight box. Put the bell crank pivot in that aprox line . So when it's flying centrifugal force will try to line things up.

MAKE SENSE?

LAST EDITED ON Nov-24-04 AT 00:15 AM (CST)
 
yep

yes that would put it on theoretical c/g....and that sir is a good answer...i do realize some airplanes dont fly well un less they are nose heavy...u take for instance a flite streak...put ur fingers on th c/g thats on th plans and see if it balances....that nose will drop like that 'devinin-rod" in gods little acre....jim

ive got a feeling were all gonna learn something here...a hard fact...no guessing....jim

LAST EDITED ON Nov-24-04 AT 00:54 AM (CST)
 
Jim:

On my first reply I should have said hangs VIRTUALLY the same. That was a shorter mock up and you couldn't measure the change from line straightening.

No doubt also that having everything in as straight a line as possible is a no lose situation.

In any case, good luck curing your problem.

ha ha ha ha ha...thanx jeff

>what i wanted to know about is the pivot point of th
>bellcrank and its relationship to the balance point,center
>of gravity and peak of the airfoil...i have a scratch
>built(its 1/2a stunter)...and i reasoned all three should be
>th same in order to prevent walking or th "hula" what ever
>its called these days..ive noticed th farther back th
>bellcrank pivot is the worse they seem to walk...so i
>reasoned on center it shouldnt walk like that...however it
>was awfully sensitive like that....now ive moved the foward
>leadout back from where i had it to th balance
>point/peak/cg...do you think that will fix it or am i going
>to have to move th bellcrank back also...is there something
>im misssing...heeelllllpp...jim

To cut to the chase, the location of the bellcrank in the wing MAKES NO DIFFERENCE in the yaw angle (or more accurately, the yaw *torque*). See many previous threads on this topic. Like this one:

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=1804&forum=DCForumID1#73

brett...what?...cut to th tail chase?...that guy spells worse than i do...and how is a bridge truss stress formula gonna solve this?...this is a tough problem...and its over that guys head!
always question authority....jim

>brett...what?...cut to th tail chase?...that guy spells
>worse than i do..and how is a bridge truss stress formula
>gonna solve this?...this is a tough problem...and its over
>that guys head!

Huh? It's over Paul Walker's head? Or Al's? Or mine? The principles of static mechanics are not uniquely applicable to bridges, and this is not a tough problem.

I have no idea what you are saying here. And I think I spelled everything correctly. So you got me flummoxed.

> So you got me flummoxed.
>
> Brett

Young man, are you sure you should use that type of language around here? Go to the Principal's office right now!
Bill <><
(That's a new one on me! LOL!!)

im sorry brett..now im th one confused...what does th theorhetical center of the mass have to do with it...explane that so we can ALL understand it please....jim

I think that jim's reference to tail chase could mean that he is in doubt of something a combat flyer told him. This sounds like healthy skepticism to me.

> To cut to the chase, the location of the bellcrank in the
>wing MAKES NO DIFFERENCE in the yaw angle (or more
>accurately, the yaw *torque*). See many previous threads on
>this topic. Like this one:
>
>http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=1804&forum=DCForumID1#73
>
>
> Brett

I'll probably regret weighing in on this. Generally, I agree with Al Rabe's response in the thread you reference - put the bellcrank at the spars and forget about it!

Unfortunately, I wonder if the statics analysis may be flawed. A flying control line plane is not static - it's dynamic. P. Walker admits in that post (#73) that re-positioning the bellcrank does put "... considerable force on the guide and it's associated wear and drag on the control system ..."

Isn't it possible that much force on the tip guides results in yaw when subjected to other forces? I wonder if it would be something like the "barbell effect" in the horizontal plane. Maximum tension on both lines would result in no change from the static analysis. However, the imperceptible differences in line tension when exposed to different forces from wind and maneuvering might cause Jim's "walking." This would occur as the tension on each line (or both) changed, while the bellcrank was exerting a huge constant force to compensate for a position other than ideal.

Maybe my intuition is off, too. Yet, I get irritated at supposedly enlightening factoids that may themselves be flawed (down wing flaps cause a pitch down?). Could it be kind've like an urban legend for stunt?

>> To cut to the chase, the location of the bellcrank in the
>>wing MAKES NO DIFFERENCE in the yaw angle (or more
>>accurately, the yaw *torque*). See many previous threads on
>>this topic. Like this one:
>>
>>http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=1804&forum=DCForumID1#73
>>
>>
>> Brett
>
>I'll probably regret weighing in on this. Generally, I
>agree with Al Rabe's response in the thread you reference -
>put the bellcrank at the spars and forget about it!
>
>Unfortunately, I wonder if the statics analysis may be
>flawed. A flying control line plane is not static - it's
>dynamic. P. Walker admits in that post (#73) that
>re-positioning the bellcrank does put "... considerable
>force on the guide and it's associated wear and drag on the
>control system ..."
>
>Isn't it possible that much force on the tip guides results
>in yaw when subjected to other forces? I wonder if it would
>be something like the "barbell effect" in the horizontal
>plane. Maximum tension on both lines would result in no
>change from the static analysis. However, the imperceptible
>differences in line tension when exposed to different forces
>from wind and maneuvering might cause Jim's "walking." This
>would occur as the tension on each line (or both) changed,
>while the bellcrank was exerting a huge constant force to
>compensate for a position other than ideal.

No, I don't think so. Of course, the differential in line tension in maneuvers does create yaw torque related to the distance between the line guide holes. That's the theory behind the "front line up" bellcrank - because it creates a yaw torque in the opposite direction to the precession. I think there are problems with that because of dynamic effects, but it's sound from the static soundpoint. There are of course a myriad of other effects that effect the yaw angle. But not this one. And moving the bellcrank doesn't really help anything in that regard. It might have a lot of force on the guide, but the differential force isn't any different no matter where you put it.

Paul (being a senior fellow in structures as Boeing) is of course correct in that if you have it way off, it wears the guide. I think it *does* matter where it is from *other effects*. If it was possible to put the bellcrank right on the CG, that would probably be good from a control friction standpoint, since there would be negligible force (just the "convergence angle" trying to spread itself out) onthe guide and therefore the drag in the controls would be less. But in most case, the structure and bellcrank size don't permit it to be far enough forward. I usually put it as close as I can without cutting into the LE wood, and then design it so the suspension point hangs off the spar.

>
>Maybe my intuition is off, too. Yet, I get irritated at
>supposedly enlightening factoids that may themselves be
>flawed (down wing flaps cause a pitch down?). Could it be
>kind've like an urban legend for stunt?

There are plenty of these sorts of "urban legends"/"fencepost wisdom" that's just dead wrong - or more often, an overgeneralization ("I tried a Rev-up 10-6EW on my All-American, and it had a lot more like tension, so now I use EWs on all my airplanes", etc.). But this one is pretty unassailable, and it gets hashed out every year or so. Since 1948...

LAST EDITED ON Nov-24-04 AT 09:47 AM (CST)
 
> Paul (being a senior fellow in structures as Boeing) is
>of course correct in that if you have it way off, it wears
>the guide. I think it *does* matter where it is from *other
>effects*. If it was possible to put the bellcrank right on
>the CG, that would probably be good from a control friction
>standpoint, since there would be negligible force (just the
>"convergence angle" trying to spread itself out) onthe guide
>and therefore the drag in the controls would be less. But in
>most case, the structure and bellcrank size don't permit it
>to be far enough forward. I usually put it as close as I can
>without cutting into the LE wood, and then design it so the
>suspension point hangs off the spar.
>

I think the point with good design, is that you want to minimize potential of forces that you cannot control or calculate. In that regard, placing the bellcrank closest to the CG is the best choice, and maybe flatly stating that it makes no difference is not.

>> Paul (being a senior fellow in structures as Boeing) is
>>of course correct in that if you have it way off, it wears
>>the guide. I think it *does* matter where it is from *other
>>effects*. If it was possible to put the bellcrank right on
>>the CG, that would probably be good from a control friction
>>standpoint, since there would be negligible force (just the
>>"convergence angle" trying to spread itself out) onthe guide
>>and therefore the drag in the controls would be less. But in
>>most case, the structure and bellcrank size don't permit it
>>to be far enough forward. I usually put it as close as I can
>>without cutting into the LE wood, and then design it so the
>>suspension point hangs off the spar.
>>
>
>I think the point with good design, is that you want to
>minimize potential of forces that you cannot control or
>calculate. In that regard, placing the bellcrank closest to
>the CG is the best choice, and maybe flatly stating that it
>makes no difference is not.

I said it makes no difference in terms of the yaw angle, which was the gist of the original question. It quite obviously does matter from other aspects.

But I'm not sure why you think these other effects are not calculatable. I am not aware of any effect in model airplanes that is not well within the bound of classical dynamics, or aerodynamic principles well-understood in the 30's. We don't have a lot of the numbers, just because we don't have sufficient raw data, but the principles are not at all difficult. There's a lot of it, but there's nothing involving quantum mechanics or set theory.

Just because people tend to (and seem to prefer to) treat the topic like it involves metaphysical principles, and like to argue "by authority", doesn't mean that's what it's really all about.

>
> Just because people tend to (and seem to prefer to) treat
>the topic like it involves metaphysical principles, and like
>to argue "by authority", doesn't mean that's what it's
>really all about.
>
> Brett

I think the Navier-Stokes equations are complicated enough, and I know my limitations.

What's your favorite CFD software?

thank you tom...some in here seem to get this wrong...im not trying to proove im right in my asumption...only"if"i'm right and why...then if im not why...i'm simple uneducated guy....as ricky ricardo would say"splain it to me lucy" so i can go "ooooooh now i unnerstan"...jim

Brett, Tom, why you think that placing the bellcrank pivot at CG makes smallest friction at leadouts. I think smallest friction is if lines goes straight. And since typical stunt fuseage has permanent yaw moment out of the circle, lines must act against that yaw and thus they can not be straight. The optimal placement will be FRONT of CG - just to replace that yawing moment by centrifugal moment from CG to pivot.

Am I right?

LAST EDITED ON Nov-24-04 AT 12:16 PM (CST)
 
>Brett, Tom, why you think that placing the bellcrank pivot
>at CG makes smallest friction at leadouts. I think smallest
>friction is if lines goes straight. And since typical stunt
>fuseage has permanent yaw moment out of the circle, lines
>must act against that yaw and thus they can not be straight.
>The optimal placement will be FRONT of CG - just to replace
>that yawing moment by centrifugal moment from CG to pivot.
>
>Am I right?

I'm in over my head again but I think the key phrase is "... if lines goes straight." I guess the assumption is that the CG will dictate the center of centripetal force, but my intuition says NO as soon as I typed it.

It always seemed to me that control line flight is a balance between the aircraft constantly crabbing in level flight (trying to go forward) and the cables. In this regard, wherever the bellcrank is attached should dictate where the center of centripital force is located. The trim then becomes an effort to balance the aerodynamic forces so that they contribute to the centripetal force, or at least, they don't fight it. That's how you end up with a tail wiggling back and forth behind the belcrank. All of this static force analysis and experiments with dead weights don't count the fact of the rudder and prop applying a moment arm due to air.

A reasonable analogy is a kite - the bridle position (aka, bellcrank) is critical to the stability of the kite. It's also important where the bridle is attached to the structure of the kite. The attachment point absolutely determines how much lifting area is fore and aft, and that ratio varies with wind speed and even turbulence. In model airplanes, the wing structure pretty much dictates the location of the bellcrank, so trimming becomes a function of changing everything else.

All of this thread is saying that those "intuitions" are all wrong, so I'm very confused.

igor...thats th conclusion i came to....with bellcrank pivot on th cg and before i'd covered th wing or added th leadout guides....i balanced the airplane on th theoretical c/g.....then with both leadouts(long leadouts)held between my thumb and forefinger of my left hand i allowed th airplane to hang on its own weight....i let the leadouts find their own position on th wingtip...then with my right hand i took a pencil and lightly drew a line along side each leadout on both sides of them...then i said ooops what about line sway?....i erased th 1st lines and moved them back towards th rear about like i thought the lines would sway i put new lines on and drilled the holes then i hung it it again after th holes were in and it hung straight...but i figured in th air..line sway would straighten out th leadouts....hows that for physically establishing alignment ?...think it might be right?...it seems like it would to me...im a darn "nit-picker" i know...it comes from having to be exactly like th print says...not just pretty close ....right paul?...jim

i agree with u 100% on that brett...i didnt see "that" explanation of paul walkers u just mentioned...or i would have backed off...maybe i should have read farther...ooops he was also right about centripetal...my apoligys paul if ur readin this...u too brett...time to get out th towel again to wipe th egg off...jim

>i agree with u 100% on that brett...i didnt see "that"
>explanation of paul walkers u just mentioned...or i would
>have backed off...maybe i should have read farther...ooops
>he was also right about centripetal...my apoligys paul if ur
>readin this...u too brett...time to get out th towel again
>to wipe th egg off...jim

No big deal, and no need to apologize! That particular thread was rather fubar'ed. But it got the right answer eventually.

I just had a little trouble understanding what you were saying.

Geez...

All this time I thought Brett was well versed in static and dynamic analysis..and general physics as well.

So here we have a new product oportunity...a sliding bell crank mountng system. Of course it will include sliding adjustable flap rod attachment points and be made from new massless material so its position will not otherwise effect the CG of the plane.

Perhaps we can incorporate some of the Z tron technology to adjust it from the handle in flight!

With TPFIC,

>Geez...
>
>All this time I thought Brett was well versed in static and
>dynamic analysis..and general physics as well.
>

>With TPFIC,
>
>Curt

Well yes, although the analysis was in the referenced thread, not Brett's post. I also did NO analysis, just posed the questions, instead. Sometimes there are reasons for a practice that get lost in the passage of time, sometimes not.

One might say, though, that general physics looks at the possible and impossible as a specific exercise, while engineering tries to get it close enough to work anyway. I always thought Physics majors were another name for Liberal Arts majors.

With TalsoPFIC,

aww come on curt....u want another spankin?...jim

Engineers design it and mechanics fix it so it will work.

LAST EDITED ON Nov-24-04 AT 01:13 AM (CST)
 
sparky u are definately right about that...i was a machinist....and not a great one at that...well i was paid pretty well...so maybe i was pretty good...not great just pretty good and fast...jim

This is getting silly. I just have one observation (question--rhetorical?): If the bellcrank position (pivot) is the governing factor, why don't we use adjustable bellcranks rather than adjustable leadouts? Answer: We adjust that which changes the model's attachment point (point of pivot), and moving the bellcrank will not do it. I saw a plane fly once that had no bellcrank at all--the lines ran through tubes curved in a large radius toward the back, and attached directly to the elevator horns (top and bottom). Jim, according to your theory, wouldn't that put the pivot point at the elevator? Yet this airplane flew perfectly well, balancing around the exit point of the lines at the wingtip.
--Ray

LAST EDITED ON Nov-24-04 AT 08:53 AM (CST)
 
To show my age, if I remember right, back in the sixties the was a gentleman in Colorado who did experiments with the bellcrank location. The same airplane, but, the bellcrank on one was on the leading edge, then the trailing edge and finally on the center of gravity. The leadout wound up being at about the same location at the wing tip. His conclusion was the leadout location at the tip was more important then the bellcrank location if kept reasonable. I have moved belcranks back in a wing to make room for fuels tanks. Later, DOC-

PS:Just remembered, his name Walt Williamson.

Of course...

Except for the friction and wear issue at the tip, and the actual slight change in CG location that moving of the BC weight creates, there is no difference based upon pivot position.

The controlling effect is the vertical and horizontal seperation of the CG location and the leadout exit position at the guide--wherever that might be (wingtip usually)

It would be a different story if the leadouts went to the BC without an intermediate guide point--then the pivot location WOULD matter.

I usually place the BC axle just slightly aft of the spar so I can use the tapered tension/compression strut glued to the aft edge of the spar.

FWIW

>I usually place the BC axle just slightly aft of the spar so
>I can use the tapered tension/compression strut glued to the
>aft edge of the spar.

>Curt

Ahhhhhhhh....... the old "tapered tension/compression strut glued to the aft edge of the spar" ploy!

Quick, Kato! The Green Hornet!!

Bill <><

And "generous helpings of Secret Sauce Please, Mom" the boy said with dreams of summer wins in mind.

The "boy" still dreams.............
Bill <><

LAST EDITED ON Nov-24-04 AT 11:32 AM (CST)
 
that was th way vic stanzel set up his super"V"shark in th40s...it seems i remember something about the bellcrank as an alternative set up ...or maybe the other way around...not sure on that...i had one of those kits in th early fifties....and ur th one being silly...its th pivot point and in ur illustration that would be th elbow tubes...which if my bad old memory serves me well ...were well behind th c/g....jim

hmmmmm...jim

LAST EDITED ON Nov-24-04 AT 10:46 AM (CST)
 
Well, I just lost my entire post after retrieving the Pete Soule "LineII" URL. So I'll try again...

Brett and Jeff are absolutely correct. Bellcrank position has absolutely no relevance to yaw of CL models. It only affects friction, wear, and structural strength. This is not a matter of opinion - just cold, hard fact. The theory is not difficult to fathom, and simple experimental results easily bear this out. Published experiments with the bellcrank mounted everywhere from ahead of the wing to the tail have demonstrated this (e.g. Williamson; "Case of the Wandering Bellcrank"; American Modeler; 7-8/66; p.26). As Brett has demonstrated, you can find more information using the SSW search function.

This post also includes such an experiment and explanation:

http://www.clstunt.com/cgi-bin/dcforum/dcboard.cgi?az=read_count&om=1804&forum=DCForumID1#43

Sometimes strongly intuitive solutions are just wrong, if part of the whole picture is missing. Look for the "walking" problem elsewhere in trim.

To trim for zero yaw, position the bellcrank where there is room, a strong mount that does not induce unnecessary torques on the inner structure, and minimal bend in leadouts at correctly positioned tip leadout guides. As Jeff implied, first establish the c.g. correctly relative to the center of lift. The c.g. position will be at 15%-16%+ of the MAC (mean aerodynamic chord) for flapless wings and up to 25% of the MAC for flapped wings. Then set the leadout position to account for c.g. position and line rake. Brett has posted many times how to determine the leadout position relative to the C.G. He cites Pete Soule's "LineII" freeware, downloadable at Pete's site. I'll insert that URL here with an edit after posting this:

http://www.geocities.com/AMA271/Aeronotes/lines.htm

Bill Netzeband also set up nomographs based on theory and tests by Roger Wildman: Netzeband; "Control-Line Aerodynamics Made Painless"; American Modeler; 7-8/66; pp.22-25, 48-9, 52.

Line rake at the tip will amount to about 1 1/4" - 1 1/2" behind the c.g. for most medium-sized CL stunt models. It works, and it has ABSOLUTELY NOTHING to do with bellcrank position. Just position the bellcrank to avoid unnecessary friction and anchor it well. C.G. and leadout position are then the whole game, unless you employ rudder offset or get yaw from a coupling with unwanted roll or wind/circular-air-flow effects on lateral area.

SK

LAST EDITED ON Nov-24-04 AT 11:37 AM (CST)
 
>Sometimes strongly intuitive solutions are just wrong, if part of
>the whole picture is missing. Look for the "walking" problem elsewhere in trim.

>then the whole game, unless you employ rudder offset or get
>yaw from a coupling with unwanted roll or
>wind/circular-air-flow effects on lateral area.
>
>SK

Take that! You despicable intuition!

OK, so you and Brett killed that one dead. The download program is apparently lost in the Ether of the Inter NET. How about someone posting it on the PAMPA site?

In following this thread, I have come to the conclusion that Jim I really had decided for himself what the answer was and was just looking for someone to agree with him (right or wrong).

His own emperical data lead him to that conclusion (right or wrong).

I suspect what he may have felt was (for a normal full size stunt plane) a secondary effect (and small at that) which was the drag force on the leadout guide on the leadouts creating this "walking". A 1/2 A has significantly less line tension, but the friction forces may be porportionally higher due to a higher coefficient of dynamic friction. This could be a result of the relative stiffeness of the leadout cable to leadout guide. If the coefficient of friction is the same as a FSSP (fullsizestuntplane), then there would be no difference. But with 1/2 A's, the leadout sizes and materials are not porportional to a FSSP, they are over size, and this could lead to the increased friction. Since the LO position is usually aft of the CG, this friction force on the lines would then produce a YAW.

I'm sure Jim will not be convinced (nor Robert S), but I can't help that. I know that machinists have all the correct answers!

LAST EDITED ON Nov-24-04 AT 03:20 PM (CST)
 
paul
i really wish i could agree with you...im trying to be agreeable but it is hard to do when u stray off th point like that.

you assumed i was having a walking problem...i wasnt...and i didnt want to create one...thats why i didnt want to move th bellcrank...i know moving the bellcrank farther in back of th c/g may create a walking problem...i also know it will increase stability...probabaly because it changes the center of "balance"...i suspect because this makes it in "effect" nose heavier.

i have no friction or stiffness and being a machinist u "know"theres no alignment problems with my control set-up...u can move th controls up and down with ONE flex leadout either one...would that be stiff in ur opinion?

come on uve read my posts..."hunting"(flying up&down uncontrollably) and "walking"(yawing in&out) are/were 2 different conditions.

i think al rabe may be on to something with that rudder...i saw that and went....hmmmm...interesting i may try that on a larger airplane...a 1/2a is light enough on th lines already.

jim

well sparky they are all right...the earth is flat...why cant we see it?...at least we'll be in good company when they burn us at the stake for heresy!!...jim

>ive got a feeling were all gonna learn something here...a hard
>fact...no guessing....jim

>well sparky they are all right...the earth is flat...
>why cant we see it?...

It takes 50 posts to debate what is not only a well-established
fact but simple geometry???

The location of the bellcrank is IRRELEVANT. Full stop.
The leadout exit point is all that matters.

Also, correct spelling, punctuation, and grammer go a long
way towards enhancing one's credibility.

LAST EDITED ON Nov-24-04 AT 03:58 PM (CST)
 
>>ive got a feeling were all gonna learn something here...a hard
>>fact...no guessing....jim
>
>>well sparky they are all right...the earth is flat...
>>why cant we see it?...
>
>
>It takes 50 posts to debate what is not only a
>well-established
>fact but simple geometry???
>
>The location of the bellcrank is IRRELEVANT. Full
>stop.
>The leadout exit point is all that matters.
>
>Also, correct spelling, punctuation, and grammer go a long
>way towards enhancing one's credibility.

EDIT: I would also be lighter as a shorter push rod would be used. Why didn't I think of that.

HUMM?? I wounder why no one puts the bellcrank by the trailing edge?
It would allow more room for the pipe tunnel.

LAST EDITED ON Nov-24-04 AT 04:07 PM (CST)
 
>HUMM?? I wounder why no one puts the bellcrank by the trailing edge?
>It would allow more room for the pipe tunnel.

As pointed out elsewhere, friction of the leadouts against
the guides when there is a sharp angle there.

However, as a thought experiment, if the leadouts
were routed through, say, ball-bearing rollers at the wingtip,
then a bellcrank location like you describe would
pose no difficulty, other than a tight fit.

I have put the bellcrank behind the spar on all my Ibeams so that the front leadout would not need to go through the spar.This creates a new problem that the pushrod to the flaps is at a steep angle. I also corrected that problem by running the pushrod from the bellcrank to the elevator not to the flap horn. I then ran the flap horn pushrod back to join the elevator pushrod about six inches behind the trailing edge.In the 50's they ran the flap pushrod from the elevator horn.I have done this for over 25 years and I use no engine or rudder offset and these planes always pull hard and they never hunt. Also I use no slop in the control system. In the old Ibeams you end up with a control set up that all lines up in a straight line.There is no angles up and down of the pushrods as in a regular hookup. The bushings in the horns seem to last longer also.Also a adjustment of the pushrods can be made through the bottom of the plane if you get a plane that turns tighter one way I put a hatch in two plane but never used it.I built my USA-1 this way.If you don't understand the set up I can find a picture of a old plane or ever draw it and then scan it and post it hear.
Ed

>EDIT: I would also be lighter as a shorter push rod would be
>used. Why didn't I think of that.

It would be lighter - but it would also greatly exacerbate the pushrod geometry problem. That's a lot more important than saving a gram or so.

>
>>EDIT: I would also be lighter as a shorter push rod would be
>>used. Why didn't I think of that.
>
>
> It would be lighter - but it would also greatly
>exacerbate the pushrod geometry problem. That's a lot more
>important than saving a gram or so.
>
> Brett

Brett It was meant as a joke. I am not trying to tell anyone where to put there bell crank. Makes no difference to me. Just tried to tell the man my experience. Now when I first got here you didn't think I could build. How about now? I have build a few hundred of these planes. So I think I am entitled to my opinion and you to yours..

>>
>>>EDIT: I would also be lighter as a shorter push rod would be
>>>used. Why didn't I think of that.
>>
>>
>> It would be lighter - but it would also greatly
>>exacerbate the pushrod geometry problem. That's a lot more
>>important than saving a gram or so.
>>
>> Brett
>
>Brett It was meant as a joke. I am not trying to tell anyone
>where to put there bell crank. Makes no difference to me.
>Just tried to tell the man my experience. Now when I first
>got here you didn't think I could build. How about now? I
>have build a few hundred of these planes. So I think I am
>entitled to my opinion and you to yours..

Uh, OK - and when did I say you couldn't build?

>>Brett It was meant as a joke. I am not trying to tell anyone
>>where to put there bell crank. Makes no difference to me.
>>Just tried to tell the man my experience. Now when I first
>>got here you didn't think I could build. How about now? I
>>have build a few hundred of these planes. So I think I am
>>entitled to my opinion and you to yours..
>
> Uh, OK - and when did I say you couldn't build?
>
> Brett

When I first started here we got into a big discussion over my ideas of weight. Which by the way are not my ideas at all. But people with like minds like Billy Werwage,Bob Hunt,Bob Gieske to name a few I can think of off the top of my head. You tried to ramrod me into a corner. While no one can take away from you your accomplishments. Just be aware there are a few people out there besides your self that might know something about model airplanes.
When I say I have built hundreds of plane I do mean it as when I was a kid my parents owned a hobby shop in West Covina CA. I had at one time or another tried every combination you can think of. I know what works for me. How I try to set things up is to get a edge by not having to work at flying the plane so hard. Let me explain. When I fly a heavy airplane I have to run it tail heavy to get it to corner like I want. So in level flight you have to be a computer to get it to groove. On the other hand with a light airplane I can run the CG forward and still have the turn. I tried tapered trailing edges to manipulate the CG but to no avail. A reasonably light straight aircraft works best for me.
Communication is hard over the internet for me to express my thoughts I am sure that when we meet we will have much in common.

I am not sure if I can convey this right but the people who read this will understand. Some people have extended the olive branch out in peace.

Yours in stunt Bob

>>>Brett It was meant as a joke. I am not trying to tell anyone
>>>where to put there bell crank. Makes no difference to me.
>>>Just tried to tell the man my experience. Now when I first
>>>got here you didn't think I could build. How about now? I
>>>have build a few hundred of these planes. So I think I am
>>>entitled to my opinion and you to yours..
>>
>> Uh, OK - and when did I say you couldn't build?
>>
>> Brett
>
>When I first started here we got into a big discussion over
>my ideas of weight. Which by the way are not my ideas at
>all. But people with like minds like Billy Werwage,Bob
>Hunt,Bob Gieske to name a few I can think of off the top of
>my head. You tried to ramrod me into a corner.

How so? I've had precisely the same argument with Bob Hunt, and indirectly with Billy. We all got along throughout. Nothing at all has changed to make me think otherwise.

It's not a matter of who "believes" and who doesn't. It's a matter of engineering and experience. The contest record* certainly doesn't support your ideas, that's for sure.

I went back and reviewed previous threads on the topic. And in no case did I ever suggest you couldn't build. I have no idea either way, having never seen one your airplanes fly. Having built a 55 oz Thunderbolt tells me nothing about anything we had previously discussed, and you can't tell how well an airplane is built or will fly by weighing it. Positive or negative.

Sorry that you think we are having some sort of conflict. I wasn't aware of any intent on my side.

Brett

*Nats winning wing loading:

2004 58 oz/650 sq inches
2003 58/650
2002 ~65/680
2001 63/650
2000 63/650
1999 63/650
1998 62/700
1997 63/650
1996 72+/750
1995 68/650
1994 64/700
1993 64/700
1992 64/700
1991 64/700
1990 64/700
1989 ?
1988 64/700
1987 ?
1986 62/660
1985 ?
1984 62/700?

As Brett has mentioned several times in this thread, this gets hashed over about every year or so on some of these forums. Brett also referenced the SSWF from some time ago when FUBAR was a regular on this forum and he was also trying to prove his mistaken theory that bellcrank position makes a difference. Paul Walker provided a very precise description and mathematical solution to the force diagram that represents our configuration where our lines go through a guide (normally at the wing tip) to a bellcrank that is attached to a pivot somewhere on the model. In addition, I provided the following that has been published over the years, some of which has already been mentioned on this thread.

From the previous FUBAR thread:

QUOTE FROM MY POST:

Bill Netzeband wrote in his Control Line Capers column, American Modeler, October 1962:

"Misconception Blasted. Pictures illustrate that the bellcrank has NO effect on locating the CG. Rather, the bellcrank should be ON the CG to prevent binding (Pic #2). CG will always fall in line with the center of line lead-out spacing (1, 2, & 3) during flight. Locate your leadouts relative to the CG to produce desired yaw angle for proper tug. ... Next time a guy tells you to locate your CG forward of the BC or in front of the lead out, shun him. He don't know the facts. The CG comes first, all else is related to it."

There are three pictures in this column that show his test rig that represents a wing tip holding the leadout position relative to a fuselage where the bellcrank can be located in different locations. This test rig was suspended by the leadouts. Regardless where the bellcrank was located, the CG of the structure lined up with the leadout position at the tip.

There is another article in American Modeler, JulyAugust 1966, by Walter Williamson. Photographs show an all wood model that appears to have about a 40 to 50 inch span with a 35 size motor. The fuselage looks like a horizontal flat plate based on a crutch assembly to hold the upright engine. The bellcrank was externally mounted on the bottom of the fuselage and could be located in various positions along the length of the fuselage. Williamson ran flight tests with the bellcrank mounted in nine different locations from six inches in front of the CG to ten inches behind the CG. His conclusion was that "It makes no difference where the bellcrank is located. What matters is where the leadouts exit through the guide plate."

In the first installment of Bill Netzeband's series of articles titled Control-Line Aerodynamics Made Painless, American Modeler, July/August 1966, he talks in great detail about leadout position, line rake and bellcrank positions. This installment provides the nomographs to determine the line rake relative to the CG of any control line model based on line diameter and length, model weight and model speed. Bill makes an interesting comment that "If it were possible to mount the bellcrank pivot exactly on the cg and the load of each line didn't change (it does) we could fly without a line guide." Bill also writes of an experiment similar to what he showed in his October 1962 column regarding bellcrank position and representative of the actual dynamics of what goes on when we hook lines onto a model. Bill's results are significantly different than what Fubar described above in a different procedure. I am not sure if I completely understand the procedure that Fubar described, but it reads like whatever he is pulling on or whatever else he is doing, it does not represent the forces actually experienced by our control line models. The following is from Netzeband's 1966 article:

"For years we were fooled into believing that the position of the bellcrank in the airplane controlled its attitude. Not so. The bellcrank can be almost anywhere in the airplane.

"A simple cardboard outline of an airplane will show this relation. Place an eye (U-shaped bent pin) in one wing tip and tie a pin on the end of a thread. Run the thread through the eye and stick a pin anywhere in the cardboard. Observe how the thing hangs and then move the pin (string end) to some other location. Right! Anywhere you stick that pin, the airplane hangs the same. Now move the eye (line-guide). The airplane assumes some new position. The CG of the airplane will line up with the line-guide. (Note: It would be nice to mount the bellcrank on a line between the CG and the line-guide, because the control lines could lead straight through the line-guide, therefore operating with the least stiffness.)"

Given all of the above, I do not intend to get into any long discussion about what others might think, either correctly or incorrectly. I think it all boils down to what Al Rabe just said. Mount the bellcrank at the spar. It is desirable to put the bellcrank at or near the CG. This will reduce the rubbing by the leadouts at the tip guides.

Another subject but related: It is really not necessary to use the wing spars to anchor the bellcrank. I much prefer to run the bellcrank post through the wing and tie it to the fuselage doublers. So basically, none of the loads imposed on the bellcrank are carried to the wing structure. The fuselage has to carry this load anyway so all of the structure that would otherwise be needed to hold the bellcrank inside the wing can be eliminated. The pull test is simply accomplished by applying the force at the point where the bellcrank structurally ties in to the fuselage. The wing structure does not have to carry any of this load.

END OF QUOTE

In a later post in that same thread, I responded to FUBAR who was convinced that his pre-conceived idead that bellcrank position did change the yaw angle of a model, I challenged him to do the following test:

QUOTE FROM THAT THREAD:

I challenge you to do the simple demonstration described by Bill Netzeband in his 1966 article referenced in the #18 post of this thread. You could make the airplane he talks about out of cardboard or from a bar of lead (which would represent more G's or a greater centrifical force which results from a heavier airplane or a faster airplane flying in a circular path or a combination of both). Suspend the thing from the wire or string that passes through the wing tip guide. No matter where the bellcrank is positioned, the cg of the unit will always line up with the tip line guide.

Your test subject does not have to be an airplane. You can glue two sticks together to make a "T". Put an eyelet at the end of the one stick that represents the inboard wing of a model airplane. Run a cable or string trough the eyelet and anchor it anywhere on the cross piece that represents the fuselage. Suspend this by the cable running through the eyelet. Notice that the attitude of the assembly when suspended does not change, no matter where the cable is attached on the cross piece (fuselage). Now put a one-pound lead weight or five pound anything or whatever (It could be 100 pounds) and attach it to the "T" assembly at the intersection of the two sticks. (This represents either a heavier airplane or a faster airplane or both, it is more G's or more centrifical force which puts more tension on the line.) Again move the anchor point anywhere on the cross piece (the fuselage). Behold! Nothing changes. The CG will always line up with the tip line guide.

Please try this and tell us what happens.

END OF QUOTE

It was sometime after that thread that FUBAR picked up his marbles and deleted all of his posts. I would suggest that those who still feel that the bellcrank position does make a difference to try the simple experiment above. It only takes a few minuntes to set up. If the results are different than that suggested by the published magazine articles and the physical force diagram that Paul Walker described, then we have entered into a new universe where different laws of physics apply.

This all boils down to the fact that the CG always lines up with the tip line guide, regardless where the bellcrank is.

>It was sometime after that thread that FUBAR picked up his
>marbles and deleted all of his posts. I would suggest that
>those who still feel that the bellcrank position does make a
>difference to try the simple experiment above.

While I am not trying to argue the point of bell crank location I am simply stating that this is how I do it and have done it for 35-40 years now. Furthermore if it works for you another way it works for me.

I have no formal degree in engineering or any thing like that. I have just built hundreds of model airplanes . While building these planes I have found that bell crank location does make the planes act differently. So as far as ever backing down well if I see I'm wrong guess I will. But if not?

LAST EDITED ON Nov-24-04 AT 05:20 PM (CST)
 
Keith, Paul, Brett, Serge, Ray, et al:

THANK YOU! By late last night I was beginning to feel like I was sitting on a horse with a noose around my neck.

Jeff W

PS: I was about to file for a recount!

>From the previous FUBAR thread:
>
>QUOTE FROM MY POST:
>
>Bill Netzeband wrote in his Control Line Capers column,
>American Modeler, October 1962:

I might also note that there was an episode of the TV program "Mr. Wizard" in about 1966 that described the essential elements of the theory, with typical demonstrations.

bill netzban was (if my bad memory is correct)responsible for th "half fast II" one of th crappiest flying airplanes ever...yeah listen to him...i knew him...nuff said...jim

>bill netzban was (if my bad memory is correct)responsible
>for th "half fast II" one of th crappiest flying airplanes
>ever...yeah listen to him...i knew him...nuff said...jim

I know him, too - not as well as I would like to, but well enough. Bill Netzeband is the elder statesmen of stunt engineering analysis and has forgotten more about the technical end of this hobby than most of us will ever know. His body of work should be required reading, as he more-or-less addresses every topic you need to know at one time or another. It took 30 or 40 years before the rest of us understood it.

If Bill tells you something, you should indeed listen to him. Quietly, with rapt attention. You'll learn something.

AMEN on that Brett.

Bigiron

Be still, my heart! We ARE in a strange universe! Marvin has agreed with Buck on something! Way to go, guys! I am one happy camper. Y'all have made a good day great. Thanks, dg

>Be still, my heart! We ARE in a strange universe! Marvin has
>agreed with Buck on something! Way to go, guys! I am one
>happy camper. Y'all have made a good day great.

Glad to be of assistance!

Seriously, it should be remembered that we ALL have far, far more in common than we do in opposition. We generally only discuss the things that we disagree on, because if we agree and/or all accept the same points, there's nothing to talk about. I (obviously) have no problem arguing with most people, because I know that we are all in such close agreement the vast majority of the time. There are only a few people - very few - that I think are posting with malice aforethought.

>Be still, my heart! We ARE in a strange universe! Marvin has
>agreed with Buck on something! Way to go, guys! I am one
>happy camper. Y'all have made a good day great.
Glad to be of assistance!

Seriously, it should be remembered that we ALL have far, far more in common than we do in opposition. We generally only discuss the things that we disagree on, because if we agree and/or all accept the same points, there's nothing to talk about. I (obviously) have no problem arguing with most people, because I know that we are all in such close agreement the vast majority of the time. There are only a few people - very few - that I think are posting with malice aforethought.

Brett

like pogo said"we has met th enemy and he is us"
jim

>>>the fact that the CG always lines up with the tip line guide<<<

I wrote it already abowe - that is true only if you have no aerodynamic forces, but as we fly on circular path (permanently left) we have permanet righ yaw force (moment), the CG does not line up with leadouts, it is always behind. (it must balance that yaw moment). It is ~1.5 deg depending on fuselage length and circle radius.

You can see it on flying model on hingeline or wheels - fuselage is never perfectly tangent, it always points little out ... unless extremely forward adjusted leadouts.

There was another you-can-put-the-bellcrank-anywhere article in Aeromodeller not too long ago. I think it is a good idea to put it where the leadouts don't have to bend and flex too much at the leadout guide, particularly with solid leadouts.

LAST EDITED ON Nov-24-04 AT 06:49 PM (CST)
 
No offense to all of the effort of repeating the former articles, studies, etc., but they all talk about dead weights on a string.

How is that a valid comparison to the complicated (yes - I said complicated) forces at play with a flying airplane?. Yes, all things will equalize toward some center of gravity, but at what yaw angle, and is it the CG we measure at rest?

Are we saying that control line flight is a simple dead weight equation for centripetal force? That the rudder has no force effect on turning the fuselage? That the prop and engine imparts no torque? That the wetted side area has no effect? If we are saying that, then I guess the dead weight test is valid.

I keep going back to a kite, sorry - but the kite can impart line tension without any motion of revolution - because of the aerodynamic force of the wind. Yet, we keep trying to explain our airplanes with dead weights and forces that only result from speed and gravity (weight).

A kite's bridle location (bellcrank?) is critical. It means the difference between stable successful flight and failure. Yet, anyone can grab a kite line at some distance away from either the kite or anchor point, and completely change the direction of the line. While holding it at that intermediate position, your hand becomes a leadout guide, but there is no effect on the kite. However, relocate the anchor point of the bridle, and the kite may become unflyable. Moreover, you can hang a kite from your fingers in dead air, and it will balance on it's CG, but it has no bearing on the attitude it assumes in flight.

>No offense to all of the effort of repeating the former
>articles, studies, etc., but they all talk about dead
>weights on a string.
>
>How is that a valid comparison to the complicated (yes - I
>said complicated) forces at play with a flying airplane?.
>Yes, all things will equalize toward some center of gravity,
>but at what yaw angle, and is it the CG we measure at rest?
>
>Are we saying that control line flight is a simple dead
>weight equation for centripetal force? That the rudder has
>no force effect on turning the fuselage? That the prop and
>engine imparts no torque? That the wetted side area has no
>effect? If not, then the dead weight test is valid.

You are all over the place here. Of course there are forces in addition to line tension and torques in addition to those applied as the result of the leadouts. Most of the above only addresses the bellcrank position. It's only one answer to one question - not the only question that matters.

The rest of the dynamics have occupied many people for many years, so I won't attempt to address the analysis state of the art for all of them. Many previous threads have addressed most of these questions at one time or another, but discussing the entire system would take several books.

I would note that while you can have aerodynamic and engine effects adding to the line tension, it's my considered opinion that the very best you could do it to have ONLY centrifugal force, and nothing else. Mostly because almost everything you do to increase line tension to get more also makes it more variable.

>
> You are all over the place here. Of course there are
>forces in addition to line tension and torques in addition
>to those applied as the result of the leadouts. Most of the
>above only addresses the bellcrank position. It's only one
>answer to one question - not the only question that matters.
>
> The rest of the dynamics have occupied many people for
>many years, so I won't attempt to address the analysis state
>of the art for all of them. Many previous threads have
>addressed most of these questions at one time or another,
>but discussing the entire system would take several books.
>
> I would note that while you can have aerodynamic and
>engine effects adding to the line tension, it's my
>considered opinion that the very best you could do it to
>have ONLY centrifugal force, and nothing else. Mostly
>because almost everything you do to increase line tension to
>get more also makes it more variable.
>
> Brett

Well, I'm not sure I would categorize my attempt to discuss as "all over the place."

In your post #36, you wanted to minimize the issues. I'll do you the courtesy of not singling out individual quotes, but now you're saying including these other issues would take several books.

Is it possible that the recognition of stress on the leadout guides is itself a symptom of deliterious affects of bellcrank location, and that is because the airplane is trying NOT to yaw?

As far as striving toward the goal of achieving only centrifugal force, I think the opposite is true. Seems like we really don't want the dead weight on a string (yo-yo's are a lot more fun in that regime). We really want the airplane to always fly in a perfect circle, without centrifugal force. The difference is that the slightest failure to achieve that lofty goal results in catastrophe. So, we opt for methods to ensure line tension.

Anyway, it's certainly an interesting discussion.

>In your post #36, you wanted to minimize the issues. I'll
>do you the courtesy of not singling out individual quotes,
>but now you're saying including these other issues would
>take several books.
>
>Is it possible that the recognition of stress on the leadout
>guides is itself a symptom of deliterious affects of
>bellcrank location, and that is because the airplane is
>trying NOT to yaw?

I really don't see what you are getting at. Of course it's a bad idea to put the bellcrank at the TE of the wing, no one ever said it wasn't a bad idea. All everyone is saying is that it doesn't effect the yaw angle. That's because the torque from force on the bellcrank being applied behind the CG is being offset by a torque applied by the leadouts. Of course, that torque imposes a force on the leadout guide, and this is what makes it want to saw through the guide

>As far as striving toward the goal of achieving only
>centrifugal force, I think the opposite is true. Seems like
>we really don't want the dead weight on a string (yo-yo's
>are a lot more fun in that regime). We really want the
>airplane to always fly in a perfect circle, without
>centrifugal force. The difference is that the slightest
>failure to achieve that lofty goal results in catastrophe.
>So, we opt for methods to ensure line tension.
>

I can absolutely, positively, guarantee that the ideal trim is not when the aerodynamics of the airplane cause it to fly in a left-hand flat turn of 68 foot radius! Because there's no way to ensure you are going to always be in the center, and it's going to be awfully difficult to do maneuvers with 0 line tension.

There a big, big difference between relying on centrifugal force, and putting in a bunch of rudder offset, leadout sweep, engine offset to "get more line tension".

The reason I say that centrifugal force is the best you can do is because everything you do to "get more line tension" aside from centrifugal force also creates other issues. Rudder offset, excess leadout sweep, excess tip weight, engine offset can only be balanced *at one set of conditions* - like level flight, or a constant inside loop, or a constant outside loop, etc. Once you start maneuvering, they are no longer in balance, and the airplane starts moving in roll and yaw, in addition to pitch. As far as I am concerned, most of the challenge in trimming the airplane is to prevent this from happening.

I get the impression you want to challenge me somehow, and I really don't understand why. I'm happy to explain what I say, but I really don't think it helps to be confrontational about it.

>
> I can absolutely, positively, guarantee that the ideal
>trim is not when the aerodynamics of the airplane cause it
>to fly in a left-hand flat turn of 68 foot radius! Because
>there's no way to ensure you are going to always be in the
>center, and it's going to be awfully difficult to do
>maneuvers with 0 line tension.

That's about as strange as saying that all you want to achieve is pure centrifugal force. I qualified it anyway - by saying that less than a perfect achievement would result in catastrophe.

>
> There a big, big difference between relying on
>centrifugal force, and putting in a bunch of rudder offset,
>leadout sweep, engine offset to "get more line tension".
>
> The reason I say that centrifugal force is the best you
>can do is because everything you do to "get more line
>tension" aside from centrifugal force also creates other
>issues. Rudder offset, excess leadout sweep, excess tip
>weight, engine offset can only be balanced *at one set of
>conditions* - like level flight, or a constant inside loop,
>or a constant outside loop, etc. Once you start maneuvering,
>they are no longer in balance, and the airplane starts
>moving in roll and yaw, in addition to pitch. As far as I am
>concerned, most of the challenge in trimming the airplane is
>to prevent this from happening.

Well, that certainly fits in with your philosophy of power and prop is everything. I would suggest that a combat plane, with no fuselage, and very little side area, may be the epitome of using centrifugal force to an advantage. I don't think a stunt plane would benefit from the high speed, though. This is really digressing from the bellcrank issue, but is there no knife edge flight component allowed in your design philosophy? Are you really saying that overheads are simply due to speed and centrifugal force?

>
> I get the impression you want to challenge me somehow, and
>I really don't understand why. I'm happy to explain what I
>say, but I really don't think it helps to be confrontational
>about it.
>
> Brett
>

Now you're taking it personally. Perhaps I used too many question marks in this discussion. That can often seem challenging, rather than conveying the humble admission that I don't know the answer. Please accept my apology.

LAST EDITED ON Nov-25-04 AT 08:16 AM (CST)
 
Tom, The idea of having 0 centifugal force present a real problem at anything other than level flight. In addition to having nothing to use for the added tension of a handle movement (no reaction force), whenever the plane starts to climb there exists a weight component that points toward the handle. This will promptly put you into a negative line tension situation (that's poetic license). Not a good thing as we all know.

>>
>> I can absolutely, positively, guarantee that the ideal
>>trim is not when the aerodynamics of the airplane cause it
>>to fly in a left-hand flat turn of 68 foot radius! Because
>>there's no way to ensure you are going to always be in the
>>center, and it's going to be awfully difficult to do
>>maneuvers with 0 line tension.
>
>That's about as strange as saying that all you want to
>achieve is pure centrifugal force. I qualified it anyway -
>by saying that less than a perfect achievement would result
>in catastrophe.

You generally want to create as much line tension as you can get, as long as you don't create other problems in the process. I contend that those things (like crabbing sideways to get some "outward" lift from the fuselage) cause problems that are worse than any small increase in line tension you might get from doing it.

Think about this. The centrifugal force from a 4 lb stunt plane flying level at 5.3 second laps on 65 foot lines is about 11 lbs. Overhead, it would be about 7 lbs. I contend that if you could get between 7 and 11 lbs of steady line tension through all the maneuvers you would be one happy camper. 7 lbs is A LOT of tension, plenty enough to move the controls far enough any time you need to .

Therefore, you don't need to try to "manufacture" more, and also therefore you don't have to compromise the steadiness of the tension.

Hey, trim your airplane any way you want, no skin off my nose. But I have been moderatly successful doing it my way.

>
>Well, that certainly fits in with your philosophy of power
>and prop is everything. I would suggest that a combat
>plane, with no fuselage, and very little side area, may be
>the epitome of using centrifugal force to an advantage. I
>don't think a stunt plane would benefit from the high speed,
>though. This is really digressing from the bellcrank issue,
>but is there no knife edge flight component allowed in your
>design philosophy? Are you really saying that overheads are
>simply due to speed and centrifugal force?
>

That's certainly what I am shooting for. Of course, it's actually mv^2/r - mg when it's directly overhead. But that's more than enough assuming it's going close to the same speed overhead that it is in level flight - hence the importance of engine/prop response.

Brett,

Go eat your turkey.

Having gone through a kite building and flying frenzy many years ago, I think your analogy is a little off. Where you attach the line to the bridle is like the leadout guide in some respects, don't you think? And, yes, there are aerodynamic forces involved, and they may well rotate the airplane one way or another around the leadout guide position.

There was a post on SSW a couple of years back by a flier, one of his leadouts had sawed through the leadout guide, and he was asking how to make a new leadout guide around the leadout. I suggested threading a small spring onto the leadout and gluing it into the wing tip as a guide, moved to keep the leadout from sawing through again. Sounds to me like a leadout being bent at the leadout guide because of bellcrank placement, or whatever.

>There was a post on SSW a couple of years back by a flier,
>one of his leadouts had sawed through the leadout guide, and
>he was asking how to make a new leadout guide around the
>leadout. I suggested threading a small spring onto the
>leadout and gluing it into the wing tip as a guide, moved to
>keep the leadout from sawing through again. Sounds to me
>like a leadout being bent at the leadout guide because of
>bellcrank placement, or whatever.

Of course, of the leadout guide is in the wrong position, it puts force on it too. And no matter what, the "convergence angle" causes the leadouts to try to spread apart, unless your leadout separation is 4" - in which case you have a lot bigger problems than wearing out the guide!

>Having gone through a kite building and flying frenzy many
>years ago, I think your analogy is a little off. Where you
>attach the line to the bridle is like the leadout guide in
>some respects, don't you think? And, yes, there are
>aerodynamic forces involved, and they may well rotate the
>airplane one way or another around the leadout guide
>position.
>
>There was a post on SSW a couple of years back by a flier,
>one of his leadouts had sawed through the leadout guide, and
>he was asking how to make a new leadout guide around the
>leadout. I suggested threading a small spring onto the
>leadout and gluing it into the wing tip as a guide, moved to
>keep the leadout from sawing through again. Sounds to me
>like a leadout being bent at the leadout guide because of
>bellcrank placement, or whatever.
>
>Jim

The analogy to the leadout guide was the example of grabbing a kite string at some midpoint along it's length. The line is constrained from the kite to the hand, and then to the anchor point (someone else's hand), just as leadouts are constrained from the bellcrank to the guides. Regardless, the bridle itself is analagous to the bellcrank arm, and its location on the kite is critical.

Take a stunt kite, for instance, would you suggest that the location of the two pivot points make no difference whatsoever? What if both were located on the same side of the kite?

What happens to the horizontal center of lift (the yaw axis) if the bellcrank is located near the tail or near the nose? I agree that the leadouts will attempt to compensate, but at a very great price.

>What happens to the horizontal center of lift (the yaw axis)
>if the bellcrank is located near the tail or near the nose?
>I agree that the leadouts will attempt to compensate, but at
>a very great price.

It shouldn't be affected - horizontal center of lift would simply be a function of the distribution of side area of the plane. It might also depend on how much the airplane is already yawed (analogous to the center of pressure of a wing shifting according to angle of attack).

I think what you're getting at is the sum of all yawing moments. "Horizontal center of lift" will account for some, things like thrustline and rudder offset will account for some, leadout position will account for some. Bellcrank position won't, though it will affect the free movement of your controls.

There was a CL Combat plane design published, once, that had the bellcrank in the tailboom. It was a plug-in-wing foamy 1/2-A.

i think that would be considered th x axis x=left/right y=in/out z=up/down...who knows maybe thats changed too....jim

well i tried that experiment like this...i have a 48"x2"wide aluminum straight edge rule and it is straight..it has a 1/2"hole 1" from one end...so i took some strong nylon thread(carpet thread)and strung it through that hole down to the 25" mark all the way over to th edge of the rule and taped it on that 25"inch line....i then took the other end of the thread and about 18" up wound it around a "T"pin and tied it...1"over to the right i put another pin wound that same thread around that pin....then i played out enough thread to reach beyond the far end of the scale and tied a weight to the end...i bet that thread split that line easily within .010"-.015 i said oh oh...darn they were right!!...then i looked at th other end that thread was at least 3/32" from the edge...i turned it over...then the bottom edge went over thread aproximately 3/32" i rechecked thread at hole end and made certain they were as close to 1" as i could get them...they were.

page 2...then i went one step farther/further...i put a piece of 3/8" X 2" x 36" balsa on it to represent th fuselage....sorta like a cross centered to balance on the centerline@24"...i let it hang free as before....now theres over a 1/4" difference...try it yourself.

now u know the rest of th story...good day

thought i'd add a little levity...jim

LAST EDITED ON Nov-24-04 AT 11:58 PM (CST)
 
>Are we saying that control line flight is a simple dead weight equation for centripetal force? That
>the rudder has no force effect on turning the fuselage? That the prop and engine imparts no
>torque? That the wetted side area has no effect? If we are saying that, then I guess the dead
>weight test is valid

No, these things weren't being said.

I mentioned these aerodynamic forces in my earlier post, and if you do a search for posts by Brett, you will find some of the best trimming advice anywhere, often addressing these same aerodynamic forces and more. The point though is that changing the bellcrank position will not effect the model's reaction to aero forces or engine/prop related torques. As noted from time to time, only if leadout friction is a large percent of forces acting on a plane (tiny, light plane?) with widely spaced leadouts, then the amount of bend at the leadout guide could have a yaw effect. Both Bill Netzeband's analysis and Pete Soule's "LineII" program do take into account aerodynamic drag on the lines as it varies outward toward the plane, to cause line rake. Also, unlike the kite, leadout guides constrain the lines vertically and horizontally in their accelerated reference frame.

It is a good idea to trim the model in such a way as to minimize reliance on aerodynamically induced line tension, because it varies as the square of the speed. This would tend to aggravate variation of tension with speed and to give the model a one-speed trimmed setting, the trim being upset as speed varies through maneuvers. It is fairly well accepted that drag from such aerodynamic "solutions" as excessive rudder offset actually slows the model enough to diminish overhead line tension. I have noted this on my smallish Fox-.35 powered SkyRay too; moving the leadouts forward a bit and reducing right rudder actually increased overhead tension. The centripetal acceleration of a model doing 5-second laps on 60-ft lines is about 3 g's in level flight (so 2 g's remain, directly overhead). This can cause a lot of line tension for a heavy model. So the "rock on a string" part of line tension is important, and the largest contributer, unless the model is trimmed to yaw. Because of the plane's circular path, there is already inherent out-thrust and "right" rudder, because of the positions of prop and V-stab ahead of and behind the plane's point of tangency to the circle. FWIW.

Yes, the control line model operated in a hemisphere, with relative wind and gravitational acceleration constantly varying along its route, is a complex system - deceptively so. But it can be handled.

SK

P.S. My modem is misbehaving to the point that I have to fool with it and re-establish internet connections after reading each post or two. So, IF I can get reconnected and post this, I'll probably be off-line for the count.

LAST EDITED ON Nov-25-04 AT 02:57 PM (CST)
 
>>>Because of the plane's circular path, there is already inherent out-thrust and "right" rudder<<<

That is one of, but not the only unanswered questions which I noted above.

But I think I rather start new thread "Leadouts position", because this is out of topic here.

look again i just did it...it does change...th stuff i used probably only weighed...what 6-8 ozs...and i got that difference...on a 2 1/2 to 3 1/2 pound airplane it would be a lot more noticeable...it did show a difference and i didnt skew the results...jim

It is a little hard to see but the bellcrank is mounted about 3 inches behind the spar. It is what is sometimes called a floating bellcrank as it's mounted between two pieces of plywood and the body carries the load. This is a very easy set up to build.
Ed

That's a beatiful job, regardless of bellcrank discussions. The webbing in the fuselage behind the wing is interesting. Is that standard procedure these days?

Happy Thanksgiving!

Tom The plane is a USA/1 and it is a very large plane,760 sq inches. The body is also long and to keep it from twisting when mounting the stab I use the cross pieces. When the top and bottom is on they are not needed but I leave them in as they add no weight.I put them in the top and bottom
Ed

LAST EDITED ON Nov-25-04 AT 09:25 AM (CST)
 
Jim-

Edit: See post script.

Any deviations from my own, Bill's, or Keith's results are probably due to using a light "airplane" in which frictional and/or line bending forces are significant compared to the mass of the model, and center of mass varies with attachment points ('bellcrank' position). Such effects should be diminished to insignificance, rather than increased, for a larger, more massive model. With free controls and constantly maintained c.g. position, the bellcrank position has no effect. My low friction experiment using popsicle sticks, copper eyelet guides and fine thread, with a penny for increased weight at the intersection of the sticks and pins for the bellcrank attach points, worked just as physics analysis predicts, in complete agreement with Bill and Keith's results.

SK

Edit: I just re-read your two posts. The weight does not seem to be an issue, although I'm still trying to visualize your balsa and straight-edge setup. If I have time between modem breakdowns and requests for hauling Thanksgiving things, I'll give it further thought.

Jim,
Your experiment with your 48" x 2" wide alum. rule is flawed by the hole diameter, which you state is 1/2". This allows the thread to move from one side of the hole to the other as the taped end is moved from one side of the rule to the other. What you're seeing as a change is really the "slop" of the thread moving in the oversize hole. Leadout guides (hopefully) don't have anything like that much slop. The results don't translate. CA a piece of 1/16" tubing on the end of your rule, run the thread through that and try again. I believe you'll see different results. Just a suggestion.
--Ray

I am getting ready to start on one called "JUMBO". Has a hugh wing. Bellcrank in normal location, but, leadouts come out at the trailing edge of the wingtip. Needless to say I am going to put a line slider in, as that is why I think he had line tesion problems while flying it. --DOC Holliday

LAST EDITED ON Nov-25-04 AT 10:41 PM (CST)
 
is that a J.R. HUGH WING?

LAST EDITED ON Nov-25-04 AT 04:19 PM (CST)
 
Jim,
Your experiment with your 48" x 2" wide alum. rule is flawed by the hole diameter, which you state is 1/2". This allows the thread to move from one side of the hole to the other as the taped end is moved from one side of the rule to the other. What you're seeing as a change is really the "slop" of the thread moving in the oversize hole. Leadout guides (hopefully) don't have anything like that much slop. The results don't translate. CA a piece of 1/16" tubing on the end of your rule, run the thread through that and try again. I believe you'll see different results. Just a suggestion.
--Ray

ray...
a 1/16" .0625" 1.59mm dia tube wouldnt be quite as accurate it would allow .015"max off center im closer than that unobstructed...remember it can't touch the wall...if u are gonna try and poo-poo this...be sure u read it all...i said the thread was EXACTLY in th middle within.010/.015 of an inch...thats aproximately 1/64"...line width...ok!!!...and the second thread(the plumb line)was exactly 1" inch over from the leadout line(the center thread)at the tip...i have no need to cheat!...that would tell me nothing!!...i dont know how i could have made this any simpler...oh and another thing....that rule is only 48 inches long if it were 60 it would be out aproximately another 1/32" then it would be darn near 3/16 out of square@60"...with the balsa fuse it would be out about3/8"...with an airplane it would probably be three quarters to one inch out...y'all are makin this an "us" against "them" thing...do the experiment right...u'll see bill was "WRONG"...the way i did it was much more accurate than bills...ask paul!!!...i know i have a bad temper and sometimes berate people when i shouldn't...but it allways irritates me when someone implys or says im stupid and they cant even understand simple things...but dont let that sway "your" common sense... i liked"wild bill"almost everybody i knew did...but bill wanted his results to proove him right...i just wanted to know...didnt care if if i was right...jim
ps ive gotten emails from some very well known flyers that said ur right jim ..weve known this for years we just dont bother arguing with these guys.
ps:
ray ill do as u suggest it takes awhile for it to settle so ull have to wait a bit for results

>ps ive gotten emails from some very well known flyers that
>said ur right jim ..weve known this for years we just dont
>bother arguing with these guys

Oh! The old "lurkers support me in email" gambit! I love the classics!

Name one.

LAST EDITED ON Nov-25-04 AT 03:37 PM (CST)
 
Besides, "proof by authority" is no real proof.

Brett, I think should should let this one go.
I think it's clear he won't change his mind (perhaps about anything, ever),
and besides, how would the world be improved if he did?

Besides, it's Thangsgiving and we all know how to deal with turkeys.

ughhhhh ..... nope they didnt want to get into this...or they would have

>ughhhhh ..... nope they didnt want to get into this...or
>they would have

Riiight......

Just a gentle reminder - most of us know each other, and referring to people you might make your argument for you can easily be verified.

As Preston correctly notes, this is definitely a dead end.

I look forward to your article on the adjustable bellcrank pivot. Maybe cut a chordwise slot in the wing sheeting right at the center joint, top and bottom, maybe 8" long, and use a jackscrew and.........

>ps ive gotten emails from some very well known flyers that
>said ur right jim ..weve known this for years we just dont
>bother arguing with these guys
Oh! The old "lurkers support me in email" gambit! I love the classics!

Name one.

Brett

brett
no....its not my place to do that...besides u guys really did answer my question...i dont need to change its location...its ok on th c/g like i have it...thank you...happy tg(Thanks Giving)...(stop stop stop)jim
ps: i gotta break that habit!(stop)

Guys, I can't believe that you dignified this asinine post by making 100 replies. It was obvious in the first couple replies that no one is going to change preconceived ideas. Its a simple case of "Don't bother me with facts. My mind is made up".

Al

LAST EDITED ON Nov-25-04 AT 11:38 PM (CST)
 
Guys, I can't believe that you dignified this asinine post by making 100 replies. It was obvious in the first couple replies that no one is going to change preconceived ideas. Its a simple case of "Don't bother me with facts. My mind is made up".
Al

et tu brute' ?
and here i stuck up for ur rudder idea.
jim

Jim:

Since I wrote reply #1 which started the example of "ultimate in epitamy", let me write what I hope will be the finishing comment:
(bet you can't leave it un answered.....)

MERRY CHRISTMAS TOO ALL AND TO ALL A GOOD NIGHT!

Well....

After all of this discussion, I think that I'll continue to place my Bellcrank either where the plan says to put it or, if that won't work, wherever it'll fit within the wing.

Being an artist, I don't know much math but I DO know how to do what works.

Amazingly enough, whatever Bill Netzband has advised us has ALLWAYS proved out in my planes so I'll keep listening to what he says.

BIGS

PS: I think that Bretts pretty smart too (When he's talking down far enough for me to understand what hes talking about anyway!)!

" What constitutes the dignity of a craft is that it creates a fellowship, that it binds men together and fashions for them a common language. For there is but one problem - the problem of human relations."

ur right on both counts bigs,make it like th drawing and Brett's real smart man
jim

How about posting some pictures of the rule and balsa plank experiments? I can't visualize what you did, from the descriptions.

Incidentally, I think if there is yawing due to leadout guides being spaced far apart, it is because there is assymetrical loading on the leadouts during turns. And this happens due to aerodynamic forces on the flaps and elevators resisting movement away from neutral - if there weren't any, the tension on each leadout would be equal no matter what the bellcrank deflection, and the plane would "hang" from the center point between the leadout guides.

OK, I did an experiment to settle this. I used a slow combat plane that Max Boyd gave me. The airplane has an internal bellcrank, but for the purpose of this experiment I added a makeshift leadout guide typical of external-bellcrank combat planes (first picture). I mounted a Sig 3" bellcrank at three different locations and hung the model by the .023" cable leadouts. The second picture shows the leadouts hanging from a clamp. The internal leadouts are not attached to anything, and are not under tension. It was a little difficult to take the pictures, because the airplane tended to rotate slowly. When I got to the tripod, it had often rotated with the nose or tail toward the camera, so I'd have to go back to nudge it into position. The third, fourth, and fifth pictures show the airplane hanging with the different bellcrank positions.

Hmmmmm, he said scratching his head. We may need to start thread #2 so it doesn't take so long to load.

Howard am I right.... it looks as if the yaw angle is changing with bellcrank location and a fixed leadout position. I don't think the mass of the bellcrank is causing this.

Control Line 101
Lab report Number 1

Assignment:
To determine the veracity of the "Ivey Hypothesis" perform the "Rush Experiment" also known as "Hanging the Slow".

Be sure to consider the possibility that clamping the two leadouts together might cause an error in the experiment. Possible alternatives would be to hang it alternately from each leadout, or provide a pivot at the attachment point.

For Bonus marks, provide a free body diagram explaining the results, which seem to defy widely held beliefs, my own included!

LAST EDITED ON Nov-26-04 AT 09:10 AM (CST)
 
>
>Be sure to consider the possibility that clamping the two
>leadouts together might cause an error in the experiment.
>Possible alternatives would be to hang it alternately from
>each leadout, or provide a pivot at the attachment point.
>

The relative position of the elevator and bellcrank rotation would change, but not the hang. That' why the bellcrank rotates, so that the pivot point may remain the same.

no pat...i call it the "half fast" experiment.
jim

LAST EDITED ON Nov-26-04 AT 05:30 AM (CST)
 
Howard, that could be with combat, but stunters fly always tangent ... does not matter where you put leadouts ... look pics

Igor, Howard moved the bellcrank. You moved the leadout guide. I'm goin' downstairs and hang somethin'.

LAST EDITED ON Nov-26-04 AT 05:48 AM (CST)
 
I must, because we have little bit differnt gravity here - you know we ar 1/4 of globe shifted ... o go and try to hang something , but when you see the reslt, do not hang yourself .. otherwise we will miss you result

LAST EDITED ON Nov-26-04 AT 07:28 AM (CST)
 
>I must, because we have little bit differnt gravity here -
>you know we ar 1/4 of globe shifted ... o go and try to hang
>something , but when you see the reslt, do not hang yourself
> .. otherwise we will miss you result

Gee..... I forgot to take that gravity thing into account! Was it the gravitational attraction of my part of the world that caused the nose to shift forward?

Seriously, there is an obvious difference between static and dynamic results in what you and others have done. Introduce angular momentum into the mix and the plane will yaw nose out trying to align the CG with the leadouts. So my conclusion is that we can't really demonstrate the effects of CG vs bellcrank location vs leadout location with static models.

Edit two - Actually we might be able to simulate the effects of adding angular momentum (flying in a circle) by hanging weights equivalent to about twice the static weight at the CG. This gives about 3 G's which is a good approximation of flying loads. But alas, somebody will argue that I'm ignoring trim , engine thrust etc.. So I'll try to line up CG - bellcrank - leadouts to minumize velocity induced yaw and keep control loads down.

LAST EDITED ON Nov-26-04 AT 07:22 AM (CST)
 
>So my
>conclusion is that we can't really demonstrate the effects
>of CG vs bellcrank location vs leadout location with static
>models.
>

I tried to say that almost a week ago (whenever this all started) and got vociferously attacked, and then eventually had to explain why it wasn't a personal challenge?!

The one thing that's certain is that the multiple force effects of flight will make a change. The chances of all those forces combining to minimize the location effect may be reasonable, given the small (aerodynamic-wise) differences in most stunt models, and the universal goal of trim.

Howard's photos appear sufficient to allow dissent from the "group theory."

LAST EDITED ON Nov-26-04 AT 12:28 PM (CST)
 
>Igor, Howard moved the bellcrank. You moved the leadout
>guide. I'm goin' downstairs and hang somethin'.

Igor's pictures prove adjustable leadouts make no difference.

igor
thats a really "half fast" experiment...it prooves nothing...sorta like hi johnson with the cardboad hanging on the drafting table with it set in the vertical position...drawing lines madder than a hornet and saying "see jimmy it dont make any G.D.difference!!!" didnt believe it in "62"...and i dont believe it now! Howard has shown you all that it clearly does make a difference...i already knew this...if you read my original post i was inquiring about the "position" in relation to th c/g...not if it mattered, i knew that it did!!...Howard has prooved it...jim

Well done, Igor.

DUH!

Howard, you are still my hero.

LAST EDITED ON Nov-26-04 AT 08:23 AM (CST)
 
>OK, I did an experiment to settle this. I used a slow
>combat plane that Max Boyd gave me. The airplane has an
>internal bellcrank, but for the purpose of this experiment I
>added a makeshift leadout guide typical of
>external-bellcrank combat planes (first picture). I mounted
>a Sig 3" bellcrank at three different locations and hung the
>model by the .023" cable leadouts. The second picture shows
>the leadouts hanging from a clamp. The internal leadouts
>are not attached to anything, and are not under tension. It
>was a little difficult to take the pictures, because the
>airplane tended to rotate slowly. When I got to the tripod,
>it had often rotated with the nose or tail toward the
>camera, so I'd have to go back to nudge it into position.
>The third, fourth, and fifth pictures show the airplane
>hanging with the different bellcrank positions.

Thank You....Now fly it and see how it feels. I have done all this stuff.

Hi, Howard-

My preliminary thought is that by clamping the wires together, you have made a triangle of the two wires and bellcrank length. The leadout guide will need to push the wires further apart against the inward component of the supporting line tension in order for the plane's center of mass to again center itself directly below your suspension point. That and friction are probably the culprits, since I'm sure moving your bellcrank didn't move the c.g. far enough aft to make the plane hang tail down. Otherwise, we'll have to assume that the magnitude of your efforts redirected the graviational vector so that your plane hangs toward a new Earth center. 'you got special friends in high or low places?? My little experimental plane doesn't hang like yours. Ha!

Serge

P.S. I'm leaving for Indiana in a few minutes. I look forward to whatever has come of this when I return after the weekend.

LAST EDITED ON Nov-26-04 AT 10:44 AM (CST)
 
Boy, I know I'm going to regret getting back into this.

I agree with your observation that without leadout guides, the weight of the plane cannot make the tail hang down with a further aft bellcrank.

However, isn't the friction and constrained location of the leadouts a valid factor? Since the leadouts and their position are very real requirements - naturally assumed by anyone interested in CL flight - then the bellcrank location has a very real effect, regardless of analytical proofs. Adjustable leadouts allow us to optimize for those small differences in bellcrank location (and additional, difficult to calculate, flight forces).

After all, no one would seriously consider running the leadouts directly to the aft fuselage. Yet, if a pulley is placed in the wing center to route the lines to an aft-mounted bellcrank, I would guess that the pulley axle then becomes a pivot point, and the plane may yaw around that, instead.

The analysis may be correct in the absolute sense, but there's no point if it ignores real world effects. The fact that the world is really round has nothing to do with whether I have to cut my grass flat or on a slope.

I have no doubt everyone is correct in the calculations - too many people have looked at it. If we perhaps recognize that the leadout position is a constraint, and it must be somewhere along the axis of the wing, then the bellcrank location has an effect. It doesn't have to mean anyone is wrong.

Just a thought - I'll duck for the incoming.

LAST EDITED ON Nov-26-04 AT 02:34 PM (CST)
 
serge..Its gravitating towards me........Like my egghead friend said,the reason the magnetic compass was pointing a different direction for north than he thought it should be. Was because of the nonferrous metal in my artificial hip!!!!ha ha ha ha ha ...jim

WAY TO GO HOWARD...HA HA HA HA HA...THANK YOU...i dont have a digital camera, so i couldnt take pics to show i disproved bills "so called" findings with his own experiment...i was gonna do a two line experiment next because i thought that the yaw would be even more pronounced but u saved me the trouble... again THANK YOU...looks like all th nay sayers are gonna hafta eat "crow"...jim

>WAY TO GO HOWARD...HA HA HA HA HA...THANK YOU...i dont have
>a digital camera, so i couldnt take pics to show i disproved
>bills "so called" findings with his own experiment...i was
>gonna do a two line experiment next because i thought that
>the yaw would be even more pronounced but u saved me the
>trouble... again THANK YOU...looks like all th nay sayers
>are gonna hafta eat "crow"...jim

GUESS THE WORLD IS NOT FLAT.

howard saved us from being burned at th stake,ha ha ha ha ha.
jim

Jim, What you fail to see is the 4 0z. sticky weight Howard cleverly hid behind the stab in an masterful plan to drive Brett to the point of no return. Some guys will resort to drastic measures to eliminate the competition.

thats great,i bet he did. sneaky guy

Hey guys!

If you go back to what I said in the first reply you'll see that I said there were other forces including CG, Friction, etc in addition to the bellcrank location in play in this problem. What's so mysterious about the fact that if you pull on a bent string it either straightens out or exerts force trying to do so?

The flaw in the hanging model is that it brings all the factors in at once, plus severl new ones we hadn't even thought of, so you can't isolate which one causes what. That explains why it actually seems to hang counter intuitively to what you'd expect if Bellcrank location was the sole cause.

I've never seen so much baloney so well tenderized!

Howard,

This is strange. When I set up a fixture with a bellcrank to test the same thing you did, the test always showed that the CG of the fixture always lined up with the position of the leadouts. This was the result, no matter where the bellcrank was with relation to the CG and did not change if the weight I used on the fixture to represent the mass of the model was one pound or five pounds.

If I had the ability, I would post the several tests that have been published over the years that show photographs to show the same results.

I too wonder if the clamp on the leadouts somehow makes a difference in the results. In your photographs, the angle of the bellcrank relative to the leadouts does not appear to change, which shows that down elevator is increasing as the bellcrank is moved back. This indicates that the leadouts were clamped in the same position throughout the series of photos. What I do not understand is why it would make a difference unless we are talking about solid leadouts. This situation was discussed years ago by Netzeband in one of his articles on this subject that rigid/stiff leadouts will make a difference in the position of the bellcrank with respect to the leadout position. However, with the flexibility of solid lines (being similar to cables) over the length of our lines, the affect of solid leadouts would have little affect which is not the case in the set up you show.

Let me ask if it is possible to free up the ends of the leadouts as if they were attached to a handle and see if the same results. Maybe there is a different set of physical laws in your shop than in mine.

I have tried to visualize Jim I's test set up, but cannot yet figure out what he has described and claims to have shown.

I want to make clear that all that I have tried to explain, and I think that what has been published over the years in the explanations that the CG of the model will line up with the leadouts is that this is under static conditions. Indeed, there are many other factors that will affect yaw, but the position of the bellcrank is not one of those factors that affect yaw.

Your suggestion of solid leadouts is interesting. I wonder why flexible cables would change the force relationships as opposed to solids. I believe it's because the leadout guides cannot be removed from the equation. Since they must go through the wing and tip (to meet the symmetry of the planform), the location of the bellcrank makes a difference.

Since it's Howard, though, there's probably a punchline coming.

LAST EDITED ON Nov-26-04 AT 03:45 PM (CST)
 
Howard you are an evil man !!
LOL

Randy

PS were you wearing the clown suit when you did this experiment?

LAST EDITED ON Nov-26-04 AT 04:46 AM (CST)
 
Brett:

With the line going through the leadout hole,(rays 1/16"x1/8" long brass tube, ca'd on the center of the tip) directly to pivot point...it was over 5/16" out of plumb in 48 inches...So I mounted a 3" bellcrank...The pivot point is 1"aft of c/l...I hooked the line in the forward leadout hole in the bellcrank...That hole is actually 1/2"forward of the c/l...Its still out of plumb about 3/16" in 48inches...The plumb line is exactly on the center of the leading edge, at the tip, on the leadout side...This whole mess is hanging freely about 1"out from the wall...You can't skew the results of a plumb line, gravity takes over.

"Visualize"!!! "whirled peas"...jim

I'll have to confess, I didn't follow through this whole thread, because I didn't want to get flummoxed.
But Jim, aren't you the 1950's Jr stunt champ from California. If you are, you can get another chance to fly with Dennis Alford. Wasn't he your rival. He's flying again too. Rematch!
I fly at Whittier Narrows in South El Monte, CA. If you are still nearby, come out and fly with us. I'm heading out there right now(11am Friday) with my faithful control line dog, Buster, to fly with Jim Armour and Joel Chesler. Wherever you are, welcome back.
Happy Landings

You guys all talk about it but I have put the bellcrank as far back as the trailing edge in my Jet which has been seen here plenty of times. I built it in 1964 and it has sweptback wings but none of the odd flying problems that many sweptback wings had in the 50-60's. When I hold up my I beam planes by the leadouts they hang straight.The planes that had the bellcrank behind the spar all pulled better above 45 degrees than my other planes.I think the main point is that these planes don't hunt.Also note my leadouts come out straight of the wing as the spar is very far forward on Ibeams at the wing tip.My leadouts do not sweep forward in the wing.Also most of the old designs have leadouts farther back than many do today.I think Billy has his pivot point well behind the spar in his Ares built with four inch bellcranks.
Ed

Hey John
I saw dennis a few weeks ago at the Hi Johnson meet...I was really glad to see him. It had been over 40 years since I last saw him. We were always really good friends. I live in Ione now,outside Sacramento.I was thinkig about flying again,but just sport flying. I get dizzy easy,also i have health issues,maybe next year.
jim

LAST EDITED ON Nov-26-04 AT 01:22 PM (CST)
 
OK.. I went and hung something.

[photo not recovered: 41a7812009594870.jpg]

A Brodak ARF Cardinal suspended from the ceiling with a single wire threaded thru both of the leadout eyelets. A simple plumb made for a string and nut. The top of the plumb line is attached in the center of the leadouts. The piece of tape on the fuselage was marked with a marker where it intesects the plumb line. Interestingly enough, the line falls on the CG as measured by several other methods.

[photo not recovered: 41a782dd145625bb.jpg]

First test was to use both leadouts. Although it appears that the string is not centered between the leadouts it is.It's a camera angle problem. Same problem Howard had with rotation.

[photo not recovered: 41a783b8172bacda.jpg]

The results

[photo not recovered: 41a784011aa34a0f.jpg]

It's now hanging by one leadout but string remains in original position.

[photo not recovered: 41a784671bb05b1e.jpg]

The nose has tilted down and the line has now moved forward. Did the CG shift?

[photo not recovered: 41a7850d210c28a2.jpg]

I then moved the plumb line back to the center of the supporting leadout. Any guesses as to the results?

[photo not recovered: 41a7895a37d517e9.jpg]

It returned to it's original position. So in all cases, the CG is lining up with the leadout that is supporting the model.

Case of the wandering CG solved. As others posted, Howard's results were probably influenced by the clamping of the leadouts.

It feel that this also makes an arguement for narrow leadout spacing.

No offense, but if you hang it from the tail, the nose will point down, and if you hang it from the nose, the tail will point down. I'm not sure what your demonstration proves about moving the bellcrank relative to the leadout guides on the wing tip.

Tom... the basic premise early on was that the CG always aligns with the leadouts. Others are saying "no sir" it lines up with the bellcrank. I think I demonstrated that the CG always aligns with the leadout or leadouts that are supporting it.

I don't have a "real" plane to show the bellcrank effects but on a balsa mockup, it didn't make a rodent's rectum of difference where I put the bellcrank. The leadouts tether point is the key.

LAST EDITED ON Nov-26-04 AT 02:54 PM (CST)
 
this has now fallen to the level of "flapdoodle" im out of here...I thank you howard...but th "donkey quire" will never forgive ya...jim

LAST EDITED ON Nov-26-04 AT 02:53 PM (CST)
 
>Tom... the basic premise early on was that the CG always
>aligns with the leadouts. Others are saying "no sir" it
>lines up with the bellcrank. I think I demonstrated that the
>CG always aligns with the leadout or leadouts that are
>supporting it.
>
>I don't have a "real" plane to show the bellcrank effects
>but on a balsa mockup, it didn't make a rodent's rectum of
>difference where I put the bellcrank. The leadouts tether
>point is the key.

And yet, unless Howard has that tailweight punchline coming, his photos dispute that. Igor's pictures never moved the "bellcrank" attachment point, just the leadouts. His plane never rotated, which is what I would expect if he found the exact CG line in the plane's horizontal axis. Yours moves because the bellcrank (or the end of its arm) is not at the exact CG.

I don't want to argue about what we're suppsed to be arguing about, but CG was only one of several things Jim was asking, all having to do with his moving the bellcrank.

I liked your post about the difference of studying this in flight. The only thing this determines is the static relationship in the horizontal axis of the plane. It doesn't test for anything else.

LAST EDITED ON Nov-26-04 AT 03:12 PM (CST)
 
Thanx Tom:
It seems everyone else wanted to say it makes no difference.I was sure it did. I wanted to know if th c/g was th best place to put it and if not,why? I hope it flys better next time. If it does, I'll build a big one just like it.
repectfully yours....jim

LAST EDITED ON Nov-26-04 AT 07:06 PM (CST)
 
Reference post 153. Apology accepted and I apologize for being overly sensitive. We will make up... but I won't kiss you!

LAST EDITED ON Nov-26-04 AT 03:45 PM (CST)
 
>You want to know something Jim? You posed a question to this
>group and asked for our help. As soon as the responses
>started you began to respond with personal attacks on the
>person posting. You have attacked some of the brightest
>people in our hobby, made crude, belittling remarks and
>ridiculed everyone who doesn't share you opinions.
>
>I've not seen any pictures or drawings from you explaining
>your experiment that demonstrates your premise. Just
>cryptically written descriptions that defy understanding.
>
>I try very hard to not launch personal attacks on someone
>but you strain me to the limits. I will never post to one of
>your threads again, and I hope others do the same. You've
>earned it!
>
>P.S. Barnes and Noble sells dictionaries and keyboards
>contain vowels! (No smilies intended)

I've followed every word on this thread, and I don't see it that way. Unless Howard is putting one over on all of us (he may be), Jim has every right to be excited that he may be correct. After all, some of the first responses told him he was all wrong to be asking the question anyway. I saw his response just given to you as strong, but not personal.

On the other hand, criticizing language and keyboard technique could be viewed as personal. We all have our own talent level.

It definitely re-opened the discussion for me. I will be interested to see what Howard may add after sitting back and observing the comments.

Howard HAS been known to wear a clown suit on occasion.

Bigiron

Dick,

Should've added - it was great that you conducted your own experiment, made gauge marks, then took all the pictures and uploaded them with a description. That was a lot of work. It's much more than I've done sitting at this keyboard!

LAST EDITED ON Nov-26-04 AT 08:32 PM (CST)
 
Dick
Im sorry i guess that was a bad attempt at being humorous, but you did not move th position of th bellcrank. Afterall that was what my question was about. Most of the load is going to be on the bellcrank pivot when you are airborn, not the leadout guides. The bell crank pivot point "IS" the balance point of the "X" axis of the aiplane from the control lines. The leadouts do have an effect on that certainly, but they are not the entire governing factor as some would have you believe. I dont know how to make that any simpler. Also I stated I have no digital camera. If I did, I would have posted pictures. But what good would that do. Some in here still wouldnt believe the results. Just as some are skeptical of Howard and accuse him of hi-jinx. I think howard himself was surprised by his results. He probaly said to himself "doggone i guess location does make a difference". I liked your idea and the location of your plumb line. Kudos for that one!! I'm going to use it on what i hope to be my last experiment with this.
Yours respectfully,
jim
ps. I know someone with a cam maybe i can use his.
pps. I cant find that other post. I must have already deleted it.
ppps. as Martin Mull might say "If we cant kid eachother, then who can we kid?"

Jim, still did not get it? If you have pivot directly at CG then everything falls to one line right? If you move pivot back, then you say it makes some yawing moment yes? Look to pictures. You say that if you have pivot out of CG it makes a moment. The first picture shows it. You have lines to handle, leadouts position, CG and pivot. The line tension is force F. You say that pivot shifted back will make yaw. Yes you are right. If the distance between CG and pivot is “A” the moment will be F1xA. F1 is perpendicular component of line tension to arm A – what is actually distance between pivot and CG. Agree? You see that the size of force F1 is in that picture equivalent with distance B. OK? So the resulting moment is BxA.

Now look to second picture. I say that there is another moment, coming from overhanged lines in leadouts. Perpendicular force of that moment is F2 and it is on arm B. But as you see the force F2 is equivalent to “A”. The moment is opposite to that moment above. That moment above is of size BxA this opposite is of size AxB = BxA. So they are equivalent but opposite – they cancel each other. And that means if you move pivot, you do not get any new moment in system … or … CG must be alighned with lines out of leadouts. And it also means it does not matter where the pivot is (in this static example).

dont tryit!!!lol jim

Here is a picture of my 38 year old Jet hanging from the ceiling. The rear bellcrank leadout is in the trailing edge planking. The leadouts come straight out, no sweep forward or backwards as in most swept wings planes. The 12 year old cobra has the bellcrank behind the spar but notice how far back the leadouts are. This is the spot shown on the plans.The leadouts are adjustable by plugging them in different holes in the wingtip.One thing I have noticed is when the bellcrank is moved back the leadouts can also go back with no bad effect.One thing I can tell you for sure is that moving the bellcrank will not make the plane hunt.By putting the bellcrank behind the spar I have only mover it 1.5 inches back. In the Jet is is the same if you figure in the swept wing ratio. Even though the Jet looks very different it has the same moments as a Nobler if you figure in the swept wing ratio.
Ed

I've been a little busy lately, haven't had much time to check in and straighten y'all out.

But I just went through this whole thread, and it is amazing the trouble some of you guys got yourselves in while I was gone. Sparky, I always thought we had your number; now we know it. Jim Ivey...well, Jim's just havin' a good ol' time, isn't he? The fall is bound to be brutal, but he's on top of the world right now.

As for one of my very favorite local jesters, and long-time friend, you have just recently used up all of your get-out-of-jail-free cards. And no matter how merciless I may be in the future when it comes to thrashing someone on this forum, you can not, indeed will not be allowed, to criticize me in even the most wildly oblique terms for, say, the next two years.

I must admit, it is a great trick, and those who lay their private parts out on the floor deserve to get 'em stepped on once in awhile. But this is far more brutal than anything I've ever done! Well, at least on SSW...

So how is it I'm the Bad Boy, you're the soft-spoken, erudite gentleman engineer??!!

LAST EDITED ON Nov-28-04 AT 09:08 PM (CST)
 

Aaah Come on Dan. It's time for you to take off the hex you put on Jim Ivey.
When he wakes's up he'll think it was all just one of those bad dreams where you get caught where you shouldn't be, doin' something you shouldn't be doin'!