Tuesday, October 30, 2012

Upper Rudder Hinge

These pictures are of the lower hinge.  It is made the same as the upper hinge but it is on the 1 1/4" tail post which the fin rear spar (1 1/8") fits into.  It's made form 16 gauge (.o5o") steel 1" wide.  The 1" wide strap which goes around the rudder spar is made from 18 ga. (.040") steel.  It bolts to the hole through the tail post and hinge.  That hole has a bushing in the tail post.  The bolt hole in the hinge is larger than the bushing O.D. which allows the 3 pieces to be welded together, with the weld below the surface of the hinge.  This lets the strap bolt on nicely.
The ends of the hinge are formed to fit the tail post and welded on all the way around.  The bottom of the hinge socket has a dimple running the full width.  It appears to have 2 advantages.  It provides a nice place to weld the hinge to the post without the weld being in the bearing area.  It also adds some gap between the rudder and fin to allow more room for the fabric covering, surface tapes, and dope.  I've never seen the hinges on a real stabilizer so it makes me wonder if they were really made in the same way.  The WACO TEN hinge drawing doesn't have this feature.

I started with a strip of steel about 7" long.  The first step was to put the dimple into center of the strip.  The vise was adjusted to have about 1/4" gap.  You can't see it here but there is a slight radius filed on the jaws and then steel jaw covers add a little more.  A 3/16" drill was pounded into the strip to form the dimple.  The strip is bent a little but the shape is perfect to start forming the socket shape.  The drill was pounded in to about 3/4 of it's diameter.

To clamp the part for forming and keep the dimple from flattening, I made a support block from a bar of 1/4" steel.  A 1/4" slot was cut 1 1/14" into the steel and the edges rounded to fit the hinge.  With the bar clamped in the vise, the hinge was clamped to it with a 3/4" socket to use as a form tool.  The ends of the hinge were bent around the socket as far as possible making a "U" shaped part.

The hinge with the socket and bar still clamped to it was held in the vise so the ends of the hinge could be bent 90 degrees to the socket.  OK, I was having fun and forgot to take a picture.  With the side "U" bends started it was stood back up in the vise and the sheet metal pliers used to bend the ends 180 degrees.  These bends were tightened a little with a clamp.  With the clamp still in place the ends were bent back to be 1-1/8" apart and close to parallel.  The bends to do this were made about even with the dimple.

To locate the bolt holes the ends of the hinge were squared to the fin in the jig.  The holes were then drilled based on this dimension from the formed ends.  I drilled the holes 7/16" dia. to give clearance for welding.

I used a slightly larger (22mm) socket to hammer the ends to fit around the spar.

The finished part fits great.  Now I just need the remains of hurricane Sandy to pass so I can use my outdoor welding booth.

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.