vmsguy

I need a little help.

I need to mount some bell cranks. I'm just not sure how. The crank comes with a machine screw, an interior bushing, and washer and nut for the other end.

I've got a couple ideas floating around in my head.. just not settled on anything yet...

I'm just not sure of how to build the structure around it. Do I put balsa above and below? Do I harden the balsa? what?

A couple pictures would be wonderful.....

Thanks in advance...

Lyndon

feihu

Lyndon:

Here is my installation on a park flyer - and I've used this same installation on 40 and 60 size airplanes.
The 1/16 ply base is epoxied between ribs and a drop of glue is put on the nut of the belcrank pivot screw.
The attachment is self-explanatory

feihu

MinnFlyer

My Feedback: (4)

Yep, all you need is a plywood plate to bolt it to. The bushing is slightly longer than the bell crank, so once it is tightened down, the bell crank can still swing freely

bluestratos

ON a smaller or low performance craft, the bolt can just pass through a piece of light ply or hardened balsa. This is ok but there will be a bit of slop due to the bolt flexing. To really get it firm, I make a top and bottom plate that the bell crank will just side between. I even thread the holes so the bolt has zero slop. Make sure the connectors are on the tight side when installed to avoid slop at these points. The problem with bellcranks for control surfaces is that there are too many places for slop to built up = at the servo arm, at the bellcrank bolt, at both holes of the bellcrank and at the control horn. The best connectors are the bolt on ball mounts, if all four points use these there will be almost no slop. If the you use care to mount the bellcrank you eliminate even more. For the ultimate control horn, I fab my own and install small bearings at the top and bottom.

Slop (play) can lead to very poor flight characteristics and worse, flutter.

Best regards,
Randy