Saturday, June 16, 2012

Stabilizer Brace Wire Bushings

 The brace wires for the stabilizer attach to fittings which are bolted to the stabilizer with 1/4" bolts.  The bolts go through bushings, short pieces of 3/8" tubing, which are welded to the front and rear spars next to the last full rib at the tip.  I needed some way to hold these in position while I welded them.  It probably isn't critical but I wanted them nicely square to the spars and lined up with each other.  I found a piece of steel channel I salvaged from an old fold up table a few years ago.  You know, one of those things you save because some day you'll have a use for it.  Glory be, I have a use for it!  How cool is that?
I cut 2 lengths long enough to hold the bushings next to the front of each spar.  Next I punched 1/4" holes in one piece and duplicate punched them in the second piece.  That way the bushings would be parallel.
 By grinding nice square ends on the bushings with the belt sander it all clamps together tight and square.  I used Stainless Steel bolts and nuts to hold the bushings tight to the channels.  Stainless doesn't get welded into the bushing so easy if I get it a little to hot.  The little piece of welding rod was used as a spring to center the bottom end.  The whole assembly just hangs from the top bushing.  I tacked each bushing to the spar and the ribs before removing the jig.
Originally it appears the bushings were either a couple inches inboard or not welded to the rib.  The rib on the stabilizer, but not the elevator, was moved outboard about 2 inches.  I think the bushing was originally just welded to the spar and the spar probably cracked so they moved the rib out to help support the bushing better.

I still have two tabs to add for mounting the Fin front spar but I don't want to weld them until I fit everything to the fuselage, so I'm sure the holes all line up.

Thursday, June 7, 2012

Elevator Hinge Straps

 With the hinges welded on the last thing needed to make them work is the strap for the outboard hinge.  The strap is made of .050" steel 3/4" wide.
 The strap holds the elevator spar in the hinge block.  It gets bolted to the stabilizer with a 3/16" bolt.  The center hinge does not get a strap.  The inboard hinge socket we've discussed already.

 I made a pattern from card stock to work out the length of the strap and the made it 1/8" longer.  It's easy to trim off the extra once the straps are done.  I used a piece of 1" tubing clamped in place to locate and start the "U" bend in the strap.  The strap was bolted to the block and the center of the elevator spar marked as a reference for the start of the bend.  To assure the ends of the "U" line up I squared the strap to the spar.

 To hold it in place and keep the strap flat to the start of the bend I clamped it to the hinge block.  I then bent it around the tube until it hit the clamp.  You can see here that it springs back so that it is not close to the tube.  To get the correct 1/2" radius for the bend  I then clamped the strap to an 11/16" deep socket (about 7/8" O.D.).  To finish the bend it's just a matter of making sure the bend starts at the line and the legs end up parallel.

 With the strap in position so there is about 1/64" - 1/32" play in the tube The bottom hole center was marked with a 3/16" duplicating punch.  A little care is needed to make sure the drill locates the punch mark.

I need to trim off the 1/8" excess on the second end.  They came out great.  I can swap them to either elevator and they fit the same.  Very nice.  Now I need to add the bushings for the stabilizer brace wires and the tab for bolting the front of the fin to the front spar of the stab.

Wednesday, June 6, 2012

Stabilizer Attachment Hinges

 The bearing at the inboard end of each elevator also serves as the attachment bracket for the stabilizer to the fuselage.  The bearing is made from a piece of 1 1/8" x .049" tubing 5/8" long.  It is welded to a bracket which is folded from a piece of .050" steel (paper pattern shown).  The bracket is welded to the aft side of the stabilizer rear spar.  The end of the elevator spar fits into the tube and the bracket stops it from moving inboard. The hole in these brackets is for bolting the stabilizer to the tail post of the fuselage (more later).

 This bearing cup is spaced out from the spar so that it is lined up with the 2 outboard bearings.
 The spar on the stabilizer is  made from 1" tubing and the bearing socket is made from 1-1/8" tubing so the bracket tapers from end to end.  The easiest way to get this right is to make a form block to bend the bracket around.  The only scraps I had that could take the pressure of bending .050" was some 1/2" thick aluminum.  The 1/4" bolt hole makes a nice locator for holding the steel in position while bending it.

 To get nice square sides on the bracket the sides of the block need to be ground to more than a 90 degree bend to allow for spring back.  I ground this to 4 degrees past square.  I should have used more like 5 or 6 degrees.  Setting such small angles on the belt sander is easy by using a little trigonometry, the tangent of the angle = the rise over the run.

 Aluminum heats up very quickly so it's easier to hold with some pieces of wood.  I first ground the front to back taper to just touch my scribe line with the table square to the belt.  When I added the spring back angle I carefully ground to just remove the scribe line.
The edges where the bend is formed were then filed to a 1/16" radius.  I like to use the radius gauge to assure I get the radius I intend.

 To make the steel blank I first made a template from some galvanized steel.  I can screw it up several times without wasting expensive 4130 steel.  The bolt hole is then drilled in the steel.  The hole makes a nice a locator for scribing the cut lines.  I use a felt marker before scribing like using die ink but easier.  It realy helps to see the line.
 The blank is then bolted to the form block and clamped in the vise for bending each side.  The bend always comes out better if you hammer on a piece of hardwood rather than directly on the piece you're bending.

 A nicely formed part.

 To position the bearing cup and hold it in position I used a bolt and AN970-4 washer.  The washer is 1-1/8" in diameter so it lines up perfectly with the outside edge of the tubing and clamps it very well.  Where the tube welds to the bracket I left about 1/64" of bracket past the scribe line to make welding easy.  It also leave the scribe line easy to see for aligning the tube.
 I welded the outside edge and about 1/2" of the tube to the middle of the bracket.  The tabs get welded to the tube when everything else is done.

 With the parts welded the cut out for the stabilizer spar could be made.  It made forming and welding easier to to this after welding on the tube.
 A piece of 3/4" tubing, with square ends, was cut 1-9/32" long as a spacer for the brackets.  The tail post on the fuselage is 1-1/4" tubing.  With this assembly bolted together it was clamped to the rear spar.  A straight edge was used to align the Inside Diameter (I.D.) of the beading with the O.D. of the spars

 One clamp at a time was remove to allow the assembly to be tacked to the spar.  The ends of the tabs were then heated and bent to fit the spar.  I don't normally bend 4130 hot but the area gets reheated to weld it.  These parts should have been formed and positioned before assembling the stabilizer.  After welding the brackets and tabs to the spar the bearing ends of the brackets were bent slightly to maintain the gap and square up the bearings before welding the tabs to the bearing tubes.

 The outboard bearings could now be welded in position.  First the ends of the tubes were drilled out to fit some stainless 10-32 screws.  The screw just set there to hold the tube and bearing in position while welding the tube to the bearing.  I should have welded these assemblies before assembling the stab. as well.  Live and learn.  They're turned 90 degrees to their correct position to make it easier welding the small tube to the bearing strap ends.

A piece of 1" tubing is inserted into the bearing cup and clamped with sticks to align it with the spars.  This tube holds the bearings in position while tack welding them to the stab.  Once these were tacked on, it was to dark to finish welding so I'll just have to wait for another calm evening.  The bearings all line up great.  I really need to go fit this to the fuselage.

Saturday, June 2, 2012

Rudder Repair

 I ordered some pieces of tubing I need to finish the stabilizer, so while I wait for them I decided to repair the rudder.  The trailing edge tube has been repaired, badly, a few times and is missing a section.  I bought enough tubing to build a new one but I would like to have as many original parts in the plane as I can.  The first step was to layout the the rudder on the jig I made for the horizontal tail.  The board needed to be a little wider so I added a piece of wood to one edge.  The balance horn part of the rudder is in good shape or I would have needed to build a whole new jig board to get it all to fit.  With the layout complete I formed the new trailing edge from 5/16" tubing using the same methods as the elevator Trailing Edges and Stabilizer Leading Edge.
 With the new trailing edge formed I'm ready to cut off the old one. The top section, the middle section and the bottom section have all been damaged.  The ends of all the ribs are still the factory welding which makes it easy to see how it was all done.
 I used a 3" cut-off wheel to remove the trailing edge.  I left a little of the trailing edge to clean up with better tools.  A 4" grinder, mill file and rat tail file worked great to clean off all the weld and trailing edge tube.

 Everywhere I opened tubing it was in great condition.  To see how the bottom end of the Trailing Edge was attached to the Spar I removed the piece closing the bottom end.  The trailing edge is welded to the back of the spar and passes through to the front but is not welded to the front. The tube is clean and free of rust.
 The spar is clamped in place on the jig.  I started fitting the Trailing Edge at the bottom so splice at the top could be made to fit better.  It's clamped in place as are the ends of the tubes.

 The splice at the top is made at the top of the spar so there is more to weld the ends to than just each other.  I also fit a piece of 1/4" tubing inside.  I'll weld it into the joint.

 The 2 tubes for the top rib had a lot of rust near the rear end so I've cut them off and will splice on some new tubing.  Again a piece of 1/4" tubing is sleeved inside.  To keep it positioned while sliding on the new tubing a small hole was drilled and a piece of weld rod inserted as a temporary stop.  I'll weld up the holes.
 Everything is fitted up ready for welding.

I got it tack welded before I lost the daylight, so I'll finish welding in the morning.  I like it.