Author Topic: self centering bellcrankes (Read 5160 times)

Jim Morris · « **on:** February 01, 2007, 09:33:16 AM »

Just curious, has anybody tried a self centering bellcrank? If so what do you think?

Bob Reeves · « **Reply #1 on:** February 01, 2007, 10:02:18 AM »

Never tried one but would think you can get the same effect by using the CA hinges that come with some of the ARF's. I would give it a thumbs down as not something you would want.

Bootlegger · « **Reply #2 on:** February 01, 2007, 10:24:23 AM »

If you are refering to the Sig bellcrank as self centering then yes I use them a lot. I make the front line the up line and they work well.
This is NOT to discredit Bob Reeves post at all, but I like them and use them a lot.. Hope that this helps.....

Bill Gruby · « **Reply #3 on:** February 01, 2007, 11:45:17 AM »

SELF-CENTERING----The ability to return to a center position without any outside help. My definition.

I have never seen a C/L Bellcrank with the ability to do this? Is there such a thing? Maybe they have this type of thing in R/C I don't go there so I can't say. I know that I have been out of touch with new products, how much catching up do I have to go?

I see lots of people looking, can anyone answer my question?

??

Bill Gruby

Randy Powell · « **Reply #4 on:** February 01, 2007, 02:33:06 PM »

I assume you are referring to the type that has the arms of the bellcrank set up forward so the connections to the leadouts are ahead of the center pivot. This make the bellcrank tend to return to center easily when neutralized. Dennis Adamisin was, I think, the first to use this. It shows up on his plans anyway.

L0U CRANE · « **Reply #5 on:** February 01, 2007, 08:18:38 PM »

There's another side to the idea of a self-centering bellcrank...

Draw it out on some graph paper for yourself, and you'll see it. The arm taking the extra pull to make the control surfaces move is shorter than the distance from the bellcrank pivot to the leadout, to begin with. (Think of 'arm' as the distance from the line of pull force to the bellcrank pivot.) As this line is pulled, that gets worse.

The term 'mechanical advantage' comes in, here. A lever 4 whatevers long to the handgrip, and one whatever long from the fulcrum to the load has a 4 to 1 mechanical advantage, get the idea? Because of the trig involved, the pulled line has less mechanical advantage the further it moves from neutral.

Which should mean it takes more force to get the control surfaces as far out from neutral as we need, to make the turn, or radius. On the other side, when we relax pulling the controlling line, the far side has MORE leverage to resume neutral.

In short, a 'drooped' bellcrank works the reverse of what we want: it takes more motion and more force to get the job done. By comparison, a 'square' bellcrank - with pivot and both leadouts on the same line - has the same mechanical advantage at all positions. The trig affects the leadouts and the pushrod hole the same way, and to the same extent, both ways from neutral.

Yes, a 'drooped' bellcrank layout restores neutral a tad more positively than a 'square' bellcrank, but the feel varies in unexpected ways. That would put me off.

Since Archie Adamisin tried it, we have gone to very large stabs and elevators, which give the strong neutral restoring effect, without making the handle response change as much as a drooped bellcrank.

Steve Helmick · « **Reply #6 on:** February 01, 2007, 10:49:07 PM »

I happened to have the Primary Force plans handy, and a SIG 4" bellcrank, so took a picture of both, since apparently Mike Pratt designed both (he discussed this feature on another forum, awhile ago). What Lou said is correct, installed as shown. However, if you install it opposite (pushrod outboard), the "self-centering" becomes "self-uncentering" (I think). As Lou explains, it would make the tensioned leg get longer as the 'crank rotates. The 'pushed' leg of the crank gets shorter, but so what...the longer leg gives more leverage. Anybody tried that? Any speculation as to what would happen? I'm thinking that I probably couldn't tell the difference, unless the Glad Bag is too small.

Steve

Keith Spriggs · « **Reply #7 on:** February 01, 2007, 11:54:15 PM »

Somewhere I saw a circular bellcrank. I assume it had a groove around the edge. Has anyone ever tried one of those?

Greg L Bahrman · « **Reply #8 on:** February 02, 2007, 12:02:40 AM »

<Somewhere I saw a circular bellcrank. I assume it had a groove around the edge. Has anyone ever tried one of those?>

I used one and really liked it. As Lou was explaining the force or should I say mechanical advantage remains the same on this one because the leadout lines are always tangent to the circular bellcrank. The pulling point does not change as it does with a standard bellcrank. I used one in this plane for 8 years.

Bill Gruby · « **Reply #9 on:** February 02, 2007, 06:12:24 AM »

Thank-you everybody especially you Lou---Looks like I've got some catching up to do?

Bill Gruby

George · « **Reply #10 on:** February 02, 2007, 08:58:13 AM »

Then came the EXPOCRANK!

George

Randy Powell · « **Reply #11 on:** February 02, 2007, 10:04:50 AM »

I've used a circular bellcrank a couple of times. Makes for a smooth feel, but I've never been convinced that it provided any significant advantage. Ted Fancher used one of these in a early 'tation. Don't know what he thought about it.

L0U CRANE · « **Reply #12 on:** February 02, 2007, 11:54:36 AM »

Bill G,

Thanks for the kind words...

Circular bellcranks: The pull applied for control keeps its 'arm' length, and gains in leverage as the controls move off neutral. The pushrod hole movesfore or aft less per degree of travel since it is "riding down the rim of a circle." This usually doesn't become very noticeable untill the bellcrank has turned 45° from neutral or more.

If, instead, we had another grooved drum or pulley mounted to the bellcrank, and to the flaps, possibly also the elevators, the angle response would be linear. The leverage would be constant at full radius. Anyone want to set up a higly strung harp inside your stunter?

With the standard lever-type bellcranks the leverage ratio stays the same, but the actual arm radius from the pivot, at right angles to the pull and pushrod loads, gets smaller. We'd need more effort at the handle even if the airloads were constant. They aren't, so we get more "feel" of the airloads as we turn the surfaces further from neutral - and the airloads increase.

Again, we usually stay under 45° rotation from neutral; none of this should become critical.

Bill Little · « **Reply #13 on:** February 02, 2007, 12:06:09 PM »

Quote from: Greg L Bahrman on February 02, 2007, 12:02:40 AM

<Somewhere I saw a circular bellcrank. I assume it had a groove around the edge. Has anyone ever tried one of those?>

I used one and really liked it. As Lou was explaining the force or should I say mechanical advantage remains the same on this one because the leadout lines are always tangent to the circle. The pulling point does not change as it does with a standard bellcrank.

One of those is going into my (Imi)'tation! Gonna build it pretty much like the original with some consideration given to the "tail wiggles".

Lookng forward to seeing just how this set up "feels".

Bill <><

Jim Thomerson · « **Reply #14 on:** February 02, 2007, 08:00:40 PM »

I did not understand about the Sig self-centering bellcranks, and have installed several backwards. Because I expected them to work fine, they did.

Randy Powell · « **Reply #15 on:** February 02, 2007, 09:54:45 PM »

Lou,

I actually built a couple of planes with a linear and semi-linear motion control system. Two pulleys that the leadouts went around with two more connected to a slider that a pushrod attached to. Made for a pushrod with zero inboard to outboard motion, though the flaps and elevators were standard horns. Worked very well, though not enough to convince me that the additional complexity was worth it. Even worse in that way was a cable control system I tried. Circular horns on flaps and elevator with the same, basic pulley system for a "bellcrank". Very smooth motion and absolutely linear response. But it was quite complex and I don't know how it would have worked over time. I was concerned with wear issues. The plane only got about 50 flights on it, but it worked pretty well over that time.

Keith Spriggs · « **Reply #16 on:** February 02, 2007, 10:18:34 PM »

I would think the simplest set up for linear motion would be a circular bell crank attached to a rack and pinion gear. The pinion wouldn't have to be a complete circle. To change the sensitivity just change the size of the pinion gear. With additional rack and pinions attached you could also have complete control of the flaps together or separately. No need for me to worry about it as the simplest set up will work better than I will ever be able to fly.

W.D. Roland · « **Reply #17 on:** February 03, 2007, 12:25:02 AM »

my 2 $ worth
i cant see where self centering effect would be high enough to make any diffrence around the nutral range as i dont think our hands would miss nutral enough for the geomtry to make it work noticeably.
also if we missed in the linkage set up and the self centering had enough effect to make a diffrence then we might have an airplane with a slightly up or down biased pull?
just my early thought on this

circular bellcranks--i was always worried that lead out cables could come out of pully grove(bellcrank)unless tension on cable was never lost.i hate cutting into airplanes to fix leadouts/bellcranks/ect

i have a new(verry old--hi johnson?)circlar bellcrank--i think it was intended for speed

David

Randy Powell · « **Reply #18 on:** February 03, 2007, 12:33:17 AM »

The circular bellbranks usually have some sort of retainer for the leadouts. I used a simple clip that kept the line for jumping.

Bill Gruby · « **Reply #19 on:** February 03, 2007, 06:28:33 AM »

OK everyone I understand the self-centering concept just fine now. Looks to me like a good thing to have?
I will certainly look into it on my next build.

Now one step further I guess, I can't even imagine what George Bain is talking about when he threw in the term EXPOCRANK?

Bill Gruby

George · « **Reply #20 on:** February 03, 2007, 12:37:41 PM »

Quote from: Bill Gruby on February 03, 2007, 06:28:33 AM

...Now one step further I guess, I can't even imagine what George Bain is talking about when he threw in the term EXPOCRANK?

Bill Gruby

Bill,

The Expocrank was a concept to provide a more linear motion. It was published several years ago in Stunt News. Since it never caught on, I would guess the gain was not worth the effort to produce it. Never tried it myself.

Charlie Pate · « **Reply #21 on:** February 03, 2007, 06:09:56 PM »

As to the circular bellcrank:
Ted Fancher used to use them.
When asked if he still used them, he allowed as how they were replaced by the four inch bellcrank on his
parts list as the four inch accomplished the same thing for him. (Ted Fancher/to/ Charlie Pate).

Bill Little · « **Reply #22 on:** February 03, 2007, 07:36:12 PM »

Quote from: George Bain on February 03, 2007, 12:37:41 PM

Bill,

The Expocrank was a concept to provide a more linear motion. It was published several years ago in Stunt News. Since it never caught on, I would guess the gain was not worth the effort to produce it. Never tried it myself.

I did a write up on the Expocrank in Stunt News when I wrote the Products Column. Mr Fred Bachl designed it and I have a mocked up example of it. I am pretty sure Larry Cunningham and a few others have used one. So far, I have not, but it begs to be put in an I-beamer due to the way it mounts.

Bill <><

Will Hinton · « **Reply #23 on:** February 09, 2007, 05:26:15 PM »

Here goes - I used the circular bellcranks for several years, but when I saw the Sig "self centering", I went to it. My circulars were three times the weight, for one thing, but I find I DO feel a difference at nuetral. The one place I notice this the most is out of the second loop of the clover and when I go to nuetral I can actually "feel" the straight up position of the ship as though it "clicked" into place. I'll probably never use anything else although I plan to mold my own from carbon fiber in the future as a weight savings. (Ya, I know, I know, the Sig isn't that heavy, but I have to have SOME excuse for experimenting!)
Blessings,
Will

Dennis Adamisin · « **Reply #24 on:** April 05, 2007, 10:41:21 PM »

Jeesz, felt my ears burning, found this thread and joined the forum so I could reply!

Yes I used self-neutralizing inverted "Y" bellcranks exclusively - except for my Jetco Dolphin in 1966! Yes I like how they FELT. The analogies to the stiff CA hinges and oversize elevators are inaccurate. The feedback is not stiff controls, rather the bellcrank LOCKS IN the neutral, and requires the utility to center control surfaces based on flight tests to make sure the neutral IS neutral. It does require a model that is aerodynamically responsive: nose-heavy trucks with oversize flippers need not apply. Done well it results in a model that is paradoxically is easy to fly and which can be flown aggressively. if done badly.... sigh.

But rather than take my word for it, TRY one, then comment.

If I ever make my oft-postponed comeback I would want to try a circular bellcrank (for steady mechanical advantage) with a Fred Bachl expo system (for soft neutral and aggressive throws) - but then again i would probably just take the lazy way out and use a Sig 'crank...!

Dennis A

Howard Rush · « **Reply #25 on:** April 06, 2007, 12:37:14 AM »

I'm with Lou and Steve. I put doodads on my flaps to lighten the control loads, but a Sig bellcrank installed backward might be an easier way to do it. It's a wee bit difficult to change if it comes out wrong, so I'll probably stick to the good ole straight bellcrank.

Didn't Igor Burger make a reverse expocrank for the same reason?

minnesotamodeler · « **Reply #26 on:** April 06, 2007, 01:43:11 AM »

How about this for self-centering? If you're wondering, it flies very well.

MikeyPratt · « **Reply #27 on:** April 07, 2007, 08:42:19 AM »

Well guy’s I have to chime in on this.

The self-centering B/C does work and was tested with different amounts of forward sweep in the arms ranging from 5° to 25°. I settled on 10° of sweep for the best all-around feel. What Lou is talking about has very little effect on what is really happening when flying the model. Bigger models with larger control surfaces don’t make it any harder at all. The G-Force is big at 720 squares with a 25% tail and turns as well if not better than many of the designs out there. The self centering aspect of this type of B/C is slight to begin with it but can be felt when properly set up. The B/C must be centered when the controls are in the neutral position.

I’ve tried all kinds of B/C and control systems including the expo crank (and no B/C at all) and found that all of them have some kind of disadvantage that you have to put up with.

Mikey

MikeyPratt · « **Reply #28 on:** April 07, 2007, 09:54:55 AM »

After looking up my notes on S/C crank, I thought that this would be helpful to some of you to better understand how this bell-crank works. I don’t take credit for this idea, that goes to Big Art and sons. But I wanted to validate the concept through flight testing and analysis before I would commit to using this bell-crank on a big time PA model.

The testing was done on an old, slow combat model with an exposed control system so the bell-cranks could be quickly changed. I made five different cranks from circuit board with different amounts of forward sweep in the arms starting at 5°, 10°, 15°, 20°, and 25°. As per my notes, there was little to no difference from a standard Sig 3” crank and the 5° crank. The 10° showed there was a marked improvement over the Sig 3” with the model grooving better and flatter bottoms in the squares. The 15° crank also worked pretty well. There seemed to be a slower start to the turns, but the bottoms were really flat and the groove was great (almost too good). The 20° and the 25° cranks were sluggish at best in the turns, and to be honest, they were better suited for C/L racing planes.

I went back to the 10° and the 15° cranks and moved the CG rearward slightly which made things really start to come alive. After flying each of the cranks about 20 times, I decided that the 10° provided the best feel and control response. How many of you remember the Silver Magnum? That was the first big model that the crank was used in and I was not disappointed in the performance at all. The next model to use this crank was the Force, Magnum Force, Super Dave, G-Force, and many others, including classic and old time.

What I have learned over the years is that the bell-crank must be centered with the controls in neutral position to take full advantage of the bell-crank. Many other factors come into play here as well to make this system work properly. CG and handle spacing have a huge part in the overall performance, which really isn’t any different than any other PA model.

Bottom line, try using it on a simple sport model and see for yourselves if it works or not.

Later,
Mikey

RandySmith · « **Reply #29 on:** April 07, 2007, 03:01:16 PM »

Quote from: Dennis Adamisin on April 05, 2007, 10:41:21 PM

Jeesz, felt my ears burning, found this thread and joined the forum so I could reply!

Yes I used self-neutralizing inverted "Y" bellcranks exclusively - except for my Jetco Dolphin in 1966! Yes I like how they FELT. The analogies to the stiff CA hinges and oversize elevators are inaccurate. The feedback is not stiff controls, rather the bellcrank LOCKS IN the neutral, and requires the utility to center control surfaces based on flight tests to make sure the neutral IS neutral. It does require a model that is aerodynamically responsive: nose-heavy trucks with oversize flippers need not apply. Done well it results in a model that is paradoxically is easy to fly and which can be flown aggressively. if done badly.... sigh.

But rather than take my word for it, TRY one, then comment.

If I ever make my oft-postponed comeback I would want to try a circular bellcrank (for steady mechanical advantage) with a Fred Bachl expo system (for soft neutral and aggressive throws) - but then again i would probably just take the lazy way out and use a Sig 'crank...!

Dennis A

I have used most all of the differant bellcranks, and at the small amount of movement I use , I have not really found much differance, biggest differance I have found is in the 4 and 4.5 ich bellcranks going to them from the 3 inch

and Dennis welcome to Stunt Hangar It is great to see you here, please say hello to Art and the whole family when you see them next

Randy Smith

Dennis Adamisin · « **Reply #30 on:** April 07, 2007, 04:45:29 PM »

Randy:
Thanks for the welcome. I'll be seeing BigArt in a couple weeks for his 80th (!!!) Bday Party. I concur that the first BIG improvement is going from 3" to 4" (or more) crank.

"Mikey"
I like your approach to finding the best 'crank angle. I also like the way you went back to retrim the bird to exploit the newfound self-neutralizing capability. I was flying with a 30 deg offset and a little voice in the back of my head was saying maybe that was too much. I was also flying with AFT CG that probably let me get away with an overcranked crank!

Igor Burger · « **Reply #31 on:** April 07, 2007, 05:05:47 PM »

Quote from: Howard Rush on April 06, 2007, 12:37:14 AM

Didn't Igor Burger make a reverse expocrank for the same reason?

Primary I wanted logarithmic response, unloading flaps in corners was another advantage. It allowed to flight with CG at 15% MAC.

http://www.netax.sk/hexoft/stunt/the_max_ii.htm