Round bell crank, Yes, you heard me right!

[Avaiojet]

Modelers have used circular/round bell cranks. A fact.

Their purpose is to allow for only two small openings in the side of the fuselage for the control lines, instead of elongated slots.

Obviously I'll be needing one for my scale Gee Bee Z.

My quest is to "NOT" re-invent the wheel by designing and making one myself, although I'll have absolutely no issues with doing this.

But possibly, possibly a generous modeler may already have suitable "drawings" or even one hanging around? One never knows.

I'm hoping I'll get lucky. Even though I'm never lucky.

Charles

P.S.

If I do have to design one from scratch, are there any scale modelers who may want or need an item like this, now or in the future?

 "Cheaper by the dozen."

[Brett Buck]

Modelers have used circular/round bell cranks. A fact.

Their purpose is to allow for only two small openings in the side of the fuselage for the control lines, instead of elongated slots.

  Look at the Imitation plans. In that case, it was NOT to permit two small holes, it was to maintain the mechanical advantage over the entire range of travel.

   Brett

[Avaiojet]

 Look at the Imitation plans. In that case, it was NOT to permit two small holes, it was to maintain the mechanical advantage over the entire range of travel.

   Brett

Brett,

 

I just got it! "Imitation" is the name of a CL model. Bingo! Great! OK, then someone designed a round bell crank.

However, In my case, my only concern are the "two small holes" for line exit. This will allow for a nice clean look. I really don't care if there's a mechanical advantage or not?

Based on what you're saying, that "mechanical advantage" that is, then why hasn't it cought on? Why aren't they more common?
 
Charles

[Will Hinton]

I flew them for three years in my original Ephesian, found no advantage to them, and even the designer stopped using them as I understand it.  However, for the scale application, I can see a definite advantage as far as the exit points.

[Dennis Leonhardi]

Old stuff, Charles ...

[Avaiojet]

Old stuff, Charles ...

Yes, I know it's old stuff. It's been brought up before, possibly by me, but I don't remember.

Thanks for that sheet. It will be useful. You know I appreciate it.


Charles

[FLOYD CARTER]

My own Gee Bee has leadouts through the wing.  Therefore, no slots in the fuselage.  With wing dihedral, the leadout exit is (almost) in line with fuselage vertical CG.

The circular bellcrank is interesting.  I see they use some copper wire "keepers" to keep the leadout wire in the bellcrank groove.  But, there is still some unsupported part of the groove where the leadouts could slip out whenever there is no line tension (as in "most of the time")  I wonder how they prevent that.
F.C.

[RandySmith]

LOTs and LOTs of problems  with Round  bellcranks !  and  to top it off, in order to make it work like some proposed you will "HAVE"  to use a  "round"  handle at the other end for best results.


I will be looking forward  to seeing  your  round design.

PS I do have a round crank and round handle here  

Randy

[Avaiojet]

My own Gee Bee has leadouts through the wing.  Therefore, no slots in the fuselage.  With wing dihedral, the leadout exit is (almost) in line with fuselage vertical CG.

The circular bellcrank is interesting.  I see they use some copper wire "keepers" to keep the leadout wire in the bellcrank groove.  But, there is still some unsupported part of the groove where the leadouts could slip out whenever there is no line tension (as in "most of the time")  I wonder how they prevent that.
F.C.

Floyd,

That's a good observation.

I have a different idea in mind for what I would design. And yes, what you mentioned, I've considered. And I believe have that worked out.

Here's my Gee Bee Z. As you can see, it's scale and the lines would have to exit the fuselage. I think? Not sure about that yet?

Charles

[Avaiojet]

LOTs and LOTs of problems  with Round  bellcranks !  and  to top it off, in order to make it work like some proposed you will "HAVE"  to use a  "round"  handle at the other end for best results.


I will be looking forward  to seeing  your  round design.

PS I do have a round crank and round handle here  

Randy

Randy,

Thanks for the reply.

Got a photo?

Charles


I don't need a round handle for what I have in mind?

[Paul Smith]

The round bellcrank is based on a grooved pulley.  The key element is that it needs to be tightly constrained so the leadout cable cannot get off the pulley.

Advantages,

1. Equal full mechanical advantage throughout the swing (turn) of the bellcrank.
2. The leadouts do not travel back-and-forth within the wing. 
3. No splicing of the single leadout cable.

Disadvantages.

1. Make, not buy.
2. Containment of the cable on the pulley.

[Tim Wescott]

At the expense of some friction you could just put guides in the fuselage and use a regular bellcrank.  Particularly given that it's for scale I don't think you'd lose much performance until the leadouts wore into the guides.

[Tim Wescott]

But, there is still some unsupported part of the groove where the leadouts could slip out whenever there is no line tension (as in "most of the time")  I wonder how they prevent that.

Floyd, that's only a problem if you insist on using flexible leadouts.  With solids, it's just not an issue.

(My mind conjured up an image of a pair of tubes acting as guides for the leadouts right up to the bellcrank.  That, a nice deep slot in the bellcrank, and the keepers on the bellcrank, wouldn't give the leadouts much opportunity to go astray, even if you did insist on using cable.)

[Mark Scarborough]

Tim, unless you have some really flexible rigid solid leadouts, not sure how you would get them to work while they wrap around the round bellcrank as it travels,,

real aviation uses turnaround pulleys quite a bit, however most of them have preload on the cable as well as rather significant "cages" to contain the cable on the pulley,, same theory, different application

[Avaiojet]

The round bellcrank is based on a grooved pulley.  The key element is that it needs to be tightly constrained so the leadout cable cannot get off the pulley.

Advantages,

1. Equal full mechanical advantage throughout the swing (turn) of the bellcrank.
2. The leadouts do not travel back-and-forth within the wing. 
3. No splicing of the single leadout cable.

Disadvantages.

1. Make, not buy.
2. Containment of the cable on the pulley.

Paul,

Thanks for that!

The containment of the cable is easy, just have a really deep recess or grove. Extra material, possibly, but holes can bedrilled in the aluminum to remove weight if necessary.

I know a guy that knows a guy, not kidding here, that said his guy could get it done from my drawings. AND possibly improve it.

I really don't want to cut groves in the side of the fuselage.

Charles

[Avaiojet]

Floyd, that's only a problem if you insist on using flexible leadouts.  With solids, it's just not an issue.

(My mind conjured up an image of a pair of tubes acting as guides for the leadouts right up to the bellcrank.  That, a nice deep slot in the bellcrank, and the keepers on the bellcrank, wouldn't give the leadouts much opportunity to go astray, even if you did insist on using cable.)

Tim,

Interesting, your method, we think alike.

Also, I don't think I would use solid wire. Tom Morris has some stuff, I think 24 or 27 strand cable?

Keep im mind, the cables are always in the same place, they don't travel as with a standard bell crank.

Sorry if this "traveling thing" is obvious.

Charles

[Brad LaPointe]

Maybe try a pull-pull system . No bellcrank just an upper and lower control horn . I've seen them used in combat planes before .Very light .The ones I saw had bent tubing for guides .

Brad LaPointe

[Tim Wescott]

Tim, unless you have some really flexible rigid solid leadouts, not sure how you would get them to work while they wrap around the round bellcrank as it travels,,

Oh dangit.  There's just a new problem that comes up with every solution, isn't there.

[Mark Scarborough]

The containment of the cable is easy, just have a really deep recess or grove. Extra material, possibly, but holes can bedrilled in the aluminum to remove weight if necessary.


Charles

a deep groove is not enough,, when the airplane is sitting idle,, with no line tension on it, the cable can and likely will fall out of the groove,,
some sort of "finger" to retain it would be good, or perhaps a tight fitted cage which is stationary

[Mark Scarborough]

Oh dangit.  There's just a new problem that comes up with every solution, isn't there.

  n~engineers,, creating new ways to solve problems that did not exist until they solved the previous problem,,

[John Stiles]

Very lightly spring loaded leadouts might keep the soft type from jumping out of the "grooves"....might work fine on a heavy plane.

[Avaiojet]

a deep groove is not enough,, when the airplane is sitting idle,, with no line tension on it, the cable can and likely will fall out of the groove,,
some sort of "finger" to retain it would be good, or perhaps a tight fitted cage which is stationary

Mark,

Good point, point well made.

Let me think.

Both of those ideas could solve that issue.

Charles

[qaz049]

Circular bellcranks are commonly used in modern team racers, F2C and F2F classes especially.

The cable passes around the central "Pulley" one and a half times and is then crimped.

There's quite a few variations in design but the general ideas are shown in the diagram below.

Ray

[Dennis Saydak]

Here's a picture ......

[L0U CRANE]

It's interesting to see the instructions for the Dynamic circular bellcrank again...

And, thanks Ray F (edit to add, also to Dennis Saydak, who posted while I was writing this)  for the illustration! Makes it easier to visualize the following. Picture lines from the pivot, to the right, at 30° and 45° above and below the line from the pivot through the pushrod output hole, at neutral.

I seem to remember that they recommended a copper wire tie about 30° to 45° each side of neutral. You won't likely use more than that bellcrank rotation: total of 60° or 90° (-30° to 0° to +30°, or -45° to 0° to +45°.) The  leadouts' "pulley departure angle" remains tangent over either range.

Note the additional drilled holes through the 3-piece pulley sandwich at about similar positions... Just a turn or two of fine copper wire through an appropriate hole, ends twisted down and nipped short...

With the solid, soldered join at the (neutral) 0° outboard position, such ties allegedly kept the leadouts in the groove, which was a few diameters of the leadout wire deep. There would be much less likelihood for the leadouts to be able to expand enough to "fall off."

[Dan Bregar]

Yeah, we used them in the mid 70's in T/R airplanes.  Can't remember who made them back then though.  

[L0U CRANE]

Right, Dan!

And I'm pretty sure they were the commercial Dynamic Models article, unless you needed a smaller overall diameter (or did Dynamic also offer one with something like a 2" overall diameter?)  The main advantage was that the leadouts could be passed through a a single tube, or groove, each. That made for a stronger wing for a racer or speed model - no great holes hogged out for leadout chordwise 'travel' on the bellcrank/leadout side.

Let's remember - the mechanical advantage (ratio) of the standard T-shaped bellcrank remains constant over the bellcrank's range of rotation. The Sine and Cosine effects apply to both the leadout radii and the pushrod output radius. What happens at flap and/or elevator horn radii is a different caLculation.

The circular bellcrank's "advantage" here is that the leadout "arm" applying force to the system stays constant, where the trig of the traditional T-form loses force as it rotates around the pivot. But, is it an advantage? If so, is it important enough to use for 'Stunt' (CLPA, please!) Some of our top level stunt fliers named Ted Fancher say it isn't, or enough to be worth it. I'll go with Ted's remarks, he sure is qualified to comment... 

We have way over half a century of experience with the 'feel' of the traditional T-form. Any significant change in that might or might not 'feel' right. Ted said it isn't significant enough. I accept that. We (in CLPA) can stay with Jim Walker's ingenious initial solution, as developed over, what?, 70+ years?

[Dan Bregar]

Yes Lou, they may have been Dynamic Models brand.  I don't think the ones I used were any more than a 2" round.  Maybe even 1.75 or so.  And what you said about helping maintain the strength of a racer wing is certainly correct. Sounds like you been there and done that ! 

[Steve Helmick]

Monoline would be the ideal solution.  Steve

[Mark Scarborough]

Monoline would be the ideal solution.  Steve

[Avaiojet]

Monoline.

From a chair "outside" the circle, using 2.4. There could be an event!

Round bell crank.

I think I have all bases covered with this round bell crank issue. I don't think I can explain it well.

I can't even draw it well, and I can draw!

Balsa wood mock-up probably.

OK! I'll try to explain it.

Three layers. Only the center layer is round.

Added material on the top layer and bottom, projecting outwards on the 45 degrees at the half way point of the center round layer. A triangle.

Both these top and bottom layers turn upwards with a slight radius to the 45 degree position. A miniture slide, if you will. Tension on the cable allows for centering on the center layer circle. If the cables are slacked, when tension is applied will allows them to follow that "slide" they are in and will stop at the center layer. which is round.

This takes care of what Mark mentioned about the cable falling out when idle. Top of the two layers that make up the slide, or turned up ends could be sealed. A benifit if the model was to be rotated up side down.

The wing is removable for access anyway.

So, it would look like an elongated triangle, with the circular/round bell crank layered between both top and bottom layers.

Would resemble a triangle flying wing with the sides turned up.

I think I have it!

Charles

[Mark Scarborough]

I would be VERY leary about a removable wing ala Radio control standards, its unlikely that it will withstand the stress of control line,,

[Howard Rush]

Let's remember - the mechanical advantage (ratio) of the standard T-shaped bellcrank remains constant over the bellcrank's range of rotation. The Sine and Cosine effects apply to both the leadout radii and the pushrod output radius.

You can manipulate the mechanical advantage by rotating the bellcrank output hole position relative to the input.  Did you try my program?

...where the trig of the traditional T-form loses force as it rotates around the pivot.

The trig loses force?  For a given input force, the moment on the bellcrank reduces as travel increases. 

We have way over half a century of experience with the 'feel' of the traditional T-form. Any significant change in that might or might not 'feel' right. Ted said it isn't significant enough. I accept that. We (in CLPA) can stay with Jim Walker's ingenious initial solution, as developed over, what?, 70+ years?

I guess we'll have to stay with it if we don't go to the bother of figuring how to improve it.  I think that Igor has shown us that improvements can be made.

[Douglas Ames]

Round bellcranks don't necessarily have to be "round"...

[Avaiojet]

I would be VERY leary about a removable wing ala Radio control standards, its unlikely that it will withstand the stress of control line,,

Mark,

That Gee Bee Z would be scale, no stunts. The wing is held on with four aluminum 1/4 x 20 bolts, plus, if I had to, I could add double dowels in the LE. It'll be fine. Bell crank will be in the fuselage. I believe that idea I have for the bell crank will cover all bases. Reliable.

I've heald off on this model because I'm thinking electric. That's the future!

It's a cute little, 55" in span, scale model. It's probably 98% scale outlines. Gotta be 15 years old or more. I think it's more? Built it when Adrian Paige came out with his semi-scale Gee Bee Z. The basis of this model was his kit. Didn't use much of it, but what I did is in there.

I love the 30's Racers, built a few of them. Including those I never finished.   

Sold the 1/3 scale Gee Bee Z. Sold the 1/4 scale Williams Racer. Sold the 1/4 scale Hostetler Gee Bee Z. I have one left partically framed and have someone interested.

I'm keeping the first R/C Gee Bee Racer I ever built. Built this in the 80's, the "Gee Bee E." It needs a re-paint, a bit heavy from repairs, but still a nice model to fly and look at. 72" on this one. I had a 90 4 stroke in it.

Charles

[Thomas L Tilley]

Hi Charles  I have used round bellcranks for a lot of years in speed and Fai team race. Go to almost any european c l web site and check it out . 1 advantage is no lead lag between control movements.   

[Larry Renger]

Don't need no stinkin' round bellcrank if you have a hard-point exponential handle!  

With this handle, your line spacing increases with handle deflection instead of decreasing like a standard handle.  Smooth at neutral, all the kick you want for squares.  You adjust the amount of exponential by varying the length of the arms.  More is more, in this case. 

Flying with this style handle does require a bit of getting used to it.  The model seems dead or noseheavy at neutral and it takes a bit of nerve to find out that it does respond to your needs as you crank on the handle.

The finalized kit is available from RSM.

[Randy Powell]

Ted used a round bellcrank so I, of course, tried it. I've tried all kinds of non-standard control systems over the years. It worked find, I guess. Gave the plane an odd feel.

[Don Hutchinson AMA5402]

I use a round bellcrank in the Stearman models just for the purpose of avoiding the slots in the side of the fuselage. I can't tell any difference in the flying from a normal bellcrank. One can see how I kept the wire in the bellcrank slot and the mechanical stops. What is not seen is the section at the top of the bellcrank where I wrapped the leadout wire to the crank with heavy thread. The center bearing is a nice little flanged ball bearing.

[Avaiojet]

I use a round bellcrank in the Stearman models just for the purpose of avoiding the slots in the side of the fuselage. I can't tell any difference in the flying from a normal bellcrank. One can see how I kept the wire in the bellcrank slot and the mechanical stops. What is not seen is the section at the top of the bellcrank where I wrapped the leadout wire to the crank with heavy thread. The center bearing is a nice little flanged ball bearing.

Don,

I was looking for that photo. Nice installation.

Got a drawing?

Charles

EDIT: Spelling error.

[George Mitchell]

I used one years ago in a Imitation I liked it. It came with full
instructions but this is all I could find. I think my friend has one
if your interested I will ask him.

George

[Avaiojet]

I used one years ago in a Imitation I liked it. It came with full
instructions but this is all I could find. I think my friend has one
if your interested I will ask him.

George

George,

Thanks for the reply.

Sure! I'd like to see what he has?

I downloaded your PDF file and it opened up "blank.?'

Charles

[Don Hutchinson AMA5402]

I do not have a drawing of the bellcrank, that model was built about 14 years ago. I worked out the amount of travel I needed and positioned the two "spokes" where they needed to be, then I simply I sawed it out of 1/8th aluminum with a jewelers saw. I turned the outside round and cut the groove using a watchmakers lathe.

Don

[George Mitchell]

Charles,

It is  3 1/2 " full circular  designed by Ted Fancher. it has 2 or 3
holes in the back to lace the wire through to keep the wire from
slipping and has 2 wire keepers to keep the wire in the groove.
The wire keepers were wrapping wire. I forget if we used coated
wire or not to help in not slipping. Also it was aluminum manufac-
tured by John schwickrath.

George

[Avaiojet]

Charles,

It is  3 1/2 " full circular  designed by Ted Fancher. it has 2 or 3
holes in the back to lace the wire through to keep the wire from
slipping and has 2 wire keepers to keep the wire in the groove.
The wire keepers were wrapping wire. I forget if we used coated
wire or not to help in not slipping. Also it was aluminum manufac-
tured by John schwickrath.

George

George,

Thanks for the reply.

The bell crank you are referring to, will it meet my purpose, that is, allow for the cables exiting a fuselage with only a small hole for each?

I'm not sure if this is clearly understood?

My apologies if it is.

Charles

[Howard Rush]

Very cool, Don.

[Larry Renger]

Sorry to get off topic. I misunderstood the intent of using a circular bell rank in this installation.

[Tim Wescott]

The tubes in Don Hutchinson's picture are what I was babbling about in my post, as a way to keep the cables on the bellcrank.

[Randy Powell]

I used a fairly thick bellcrank and "V" shaped tracks. Pinned the cables and the end of the travel. I didn't have any problems with the cable skipping the track.

[Don Hutchinson AMA5402]

Thanks Howard. Another great Boeing airplane! Have you seen this?