Lateral positioning of bellcranks.

[Curare]

Guys, I know there's been a lot of talk about longitudinal positioning of bellcranks, but I'm struggling to to find any details of lateral positioning.

My thoughts are that the lateral positioning of the bellcrank should be such that the pushrod is more or less aligned with the horn, so for a central horn I'd want the pushrod to be along the centreline at say half the travel of the bellcrank and then the pivot point would be determined for that, irrespective of whether is a normal bellcrank or reversed. Is this correct?

[Howard Rush]

You gotta look at the 3D geometry to get the control response you want, but I think you're on the right track.  In my latest dog I located the bellcrank sideways so the pushrod wouldn't hit the other claptrap, then fiddled with other parameters to linearize the response. 

[Garf]

After crashing a NoblARF, I turned it into a profile. Proper placement of the fuselage would have put it right where the pushrod was. I put it where I thought it would work. NO. I ended using a massive amount of INBOARD tip weight. It's still not right. Back to the drawing board. I believe I should have moved the bellcrank inboard.

[Curare]

Most of my planes use a reverse crank, and fitting the bellcrank in or about the centre of the wing allows for an inboard pushrod, and offset horn.

But in the case of full fuse model, I would have thought that having a central flap horn and reverse crank would mean that I would need to have the bellcrank pivot outboard, to get the pushrod centred, yeah?

[RC Storick]

After crashing a NoblARF, I turned it into a profile. Proper placement of the fuselage would have put it right where the pushrod was. I put it where I thought it would work. NO. I ended using a massive amount of INBOARD tip weight. It's still not right. Back to the drawing board. I believe I should have moved the bellcrank inboard.

Ask anyone it don't matter where you put it..

[Brett Buck]

After crashing a NoblARF, I turned it into a profile. Proper placement of the fuselage would have put it right where the pushrod was. I put it where I thought it would work. NO. I ended using a massive amount of INBOARD tip weight. It's still not right. Back to the drawing board. I believe I should have moved the bellcrank inboard.

    Of course it's not the lateral position of the bellcrank, it's that you had to offset the wing and thus increased the asymmetry (which was already excessive).

    Brett

[Serge_Krauss]

As I posted on the Design Board recently, my spreadsheet indicated that lateral movement of the bellcrank can be compensated for by changing the tilt of the flap or elevator horn. I naturally didn't try all of those infinite possibilities, but a few lateral moves of the bellcrank arm were satisfactorily compensated by changing the horn angle. FWIW.

SK

[Randy Cuberly]

You gotta look at the 3D geometry to get the control response you want, but I think you're on the right track.  In my latest dog I located the bellcrank sideways so the pushrod wouldn't hit the other claptrap, then fiddled with other parameters to linearize the response. 

UUHhhhhhhh...Other Claptrap...gee Howard, is that an advanced engineering term or what.
Must be at least two of them because you referred to it as "the other..."  I'm really interested in learning how to linearize a "claptrap".   
I obviously don't know as much about engineering as I thought!

Randy Cuberly

[Howard Rush]

I'll send you the lowdown.  Blame Igor for the claptrap.

[john e. holliday]

I  remember Tom Morris did a write up of this control geometry for control line planes quite a few years ago.   He also has a display demonstrating how the geometry of the system works.  Contact him and see if he still has copies of his book on building and setting up model control  line planes.  I have a copy in my stash, if only I could remember where in the stash.