belcrank location?

oldguy Fri Jan 15, 2016 11:58 am

I have thought of this probably everytime I have scratched built a control line plane.But have never pursued to find the answer.On any given c/l plane is there an equation to properly figure out where the bellcrank should be located?Or does it matter where it is located?
Jim

fredvon4 Fri Jan 15, 2016 12:12 pm

The bell crank can be anywhere in or on the plane.... generally we locate it so the lead out lines don't rub on stuff and have a more or less straight shot from the Lead out guide to the Bell crank...But you could put pulleys and rout the lead out wires in , back, forward, up or down and the only issues is freedom of travel and stiction causing a loss of good feel at the handle and other issues

Most of the time we prefer it to be near the vertical CG while fore and aft location is usually considered more for good route to the lead out guides

The lead out guide will determine how the plane tracks around the circle (yaw in or Yaw out) and is much more important than the location of the Bell crank

A lot of us try to set CG to the plans and then "bench top" trim the plane buy hanging it by the lead-outs and seeing if the nose is down slightly by 3 to 5 degrees and hopefully the stab and wings (if no diheadral) are near vertical

Mark Boesen Fri Jan 15, 2016 12:19 pm

It's lead out location and of course CG (appx. 25-30% back of leading edge ) that's important. U/C ships usually have bellcrank platform tied into main spar area for strength and proximity to CG.

An easy way to check proper lead out position is to hang plane by leadouts, you want plane to be level or slightly nose down.

Mark Boesen Fri Jan 15, 2016 12:23 pm

opps! what Fred said! i started typing...but didn't post until after Fred already did.

getback Fri Jan 15, 2016 12:26 pm

There probably is some kind of math that goes into it . but from what I gather it don't matter according to this https://www.coxengineforum.com/t8828-reed-speed-2016-qualifying-photos Jim's Reed Speed entrée