Untwisting F-631A Tip up

[Michael Burbidge]

I adjusted the outer flange of F-631A. After doing so it has a wicked twist. Both inside ends have twisted up about 1/2 inch when the part is laid flat on a table. The outside edge is close to flat its entire length. I've puzzled over this for some time and cannot envision where to flute to remove the twist while still maintaining a flat outside edge.

How did you go about fluting this? Where did you flute? e.g inside-middle, outside-end, etc.

Here's a couple of pictures.

Thanks for the help,
Michael-

 

[bruceh]

These canopy ribs are evil. I did everything and nothing seemed to work better than just twisting them back in the other direction. You need to get the angle correct on the outer side to match the canopy bubble, but the inner side shouldn't be fluted unless you really want this to do an even more ugly twist.

Just make sure when you fit everything together to make the roll bar that it is clamped down flat. Once you match drill and rivet it will stay flat.

 

[Rivethead]

I agree those are evil. In fact that whole roll bar is evil. I think I struggled with it probably more than any other part. If I was to do it over again I think I'd make it out of wood.

 

[Michael Burbidge]

Twist first then flute

After stewing on this for awhile I decided that no amount of fluting would fix the twist. So I clamped the middle of the rib to the bench and twisted each end the other way until both laid flat on the bench. After this procedure, it then became a simple matter of fluting where the inner and outer edges were high. The fluting did not change the twist.

Tip: Untwist then flute.

Michael-

 

[Rupester]

Canopy frame rib ...

FWIW ... I approached the fab of that assembly with great fear having read the problems of so many others, but when the time came, I had no problem. When done my canopy fit the frame like the door on a bank vault.
For the canopy frame, I marked out Vans precise dimensions for height and width onto my work table, then clamped (because of the twist) the first two pieces to same. Immediately found the canopy "ribs" were too long in both dimensions, so I ground them down to Vans numbers. Then reclamped and proceeded with drilling and riveting while affixed to the Vans dimensions on the table. Never had a problem after that. I believe that's the reason the canopy fits so well at the aft end.