Friday, October 26, 2012

Fin Tubes Fitted Up

 I've finally had a little time to fit up the tubes for the fin.  The plan is to tack weld it together then fit the tail surfaces to the fuselage, just in case the fin needs to be modified.  There's not much magic to it except the top tube of 1/2" steel.  It's flattened at the aft end and has a pin at the front spar.
 The flat side of the tube is supposed to be all on one side (the top) of the tube.  My first idea for flattening the aft end was to make a 1/2" thick block with a radius on one end.  I assumed I could flatten the tube in the vise.  The vise worked fine and the tube flattened very well.  The problem was the flatten area was near the middle of the tube, not on one side.  It also was not parallel to the top edge. You can see the bend starting to form in this picture.  The good thing was the nice radius the block formed in the tube.
 I realized the tube needed to be clamped against the backing plate to keep it from bending and force the tube to flatten along one side.  I used some pieces of plywood to clamp the tube.  If I were doing it again I'd use some steel pieces.  The wood let the tube move more than I would have liked, but I got there in the end.  I used the same block of steel and pounded it into the tube.  The back side was close to the edge of the tube and tipped up a little.

 Because I pounded on the block instead of squeezing it in the vice, it didn't form the radius as well.  To clean it up I used the side of a ball-peen hammer to improve the radius.  I used the hammer because I could hold the handle and pound on the head at an angle to drive it into the radius.  It worked great.

I then bent the tab down a bit so it would line up with the top of the rear spar tube.

 At the other end of this tube there is a pin which holds the front brace wire bracket.  I used a 5/16" hardware store clevis pin.  You might think a good AN pin might have been a better choice, but I had to weld this in place and didn't want it to accidentally harden while cooling.  Based on the stress analysis the loads in the pin are low enough that mild steel will be fine.  Besides this whole plane was originally made from 1005 steel.

I used a longer pin than needed so I can cut it down to fit.  There is a washer to protect the weld. Next the fitting is .095" steel and then there is a washer under the cotter pin.

Before I can weld the tubes I need to make the upper hinge for the rudder.  It goes at the top of the read spar.

No comments:

Post a Comment