Wednesday, April 24, 2013

Fin Forward Brace Wire Fitting

 The brace wires on the stabilizer cross.  The wires at the front of the fin and fuselage go to the rear spar on the stabilizer.  The wires at the rear of the fin and fuselage go to the front spar on the stabilizer.  The fittings for the wires on the lower fuselage longeron are welded to the longeron. The fittings for the stabilizer and rear of the fin are bent tabs bolted to the structure.  We'll get to them in another posting. The fitting at the top front of the fin sets on the top tube and is held in place by the clevis pin welded into the front spar.  The brace wire angles back 15 degrees and down 23 degrees.  I used the string to double check my math for the angles.

 The fitting is made from .095" steel.  It can't just be bent in place because bending it would damage the tubes.  Instead I bent it around a 3/8" pipe nipple.  I used the nipple because I'm going to use a piece of it for a spacer under the fitting.  The spacer is needed because of the weld bead where the pin stick through the top tube.

The fitting was bent cold with a hammer until it matched the paper gauge I made to check the angles.

 The ends of the nipple were cut of and the cuts cleaned up on the belt sander.  The tube was split by slipping it over a piece of dowel to make it easier to hold.  Again the cut surfaces were cleaned up on the belt sander.
A 5/16" hole was drilled to fit the pin and the underside was ground out to provide clearance for the weld.

 The spacer fits nicely over the tube providing a nice mount for the without grinding out the fitting to fit over the weld.

The pin was left long so it could be cut to fit all of this.  A new cotter pin hole was drilled and the end of the pin cut off to a nice length.

I need to make up all the brace wires.

Tuesday, April 23, 2013

Tail Surface Welding is Finished

 The last parts to weld to the stabilizer are the fittings which hold the front spar of the fin to the front spar (or as WACO called it, the Front Beam) of the stabilizer.  The rear spar goes into the tail post of the fuselage.  The bolt which holds that together also holds the rear of the stabilizer.  When it's done there is no adjustment to the fin for rudder trim or to the stabilizer for elevator trim.  They solved those short comings on the Model TEN (GXE).
A fitting is welded to the stabilizer spar 7/8" apart  on each side of the fin and a bolt passes though it all to hold it together.  The fittings are 3/4" wide made from .0125" steel.  The 1/4" bolt hole is 15/16" above the top of the stabilizer spar.  It's taken some research and the help of Frank and Rich to find all these dimensions since most are missing from the factory drawing of the tail surfaces.
 To carry the loads better and to prevent distortion to the fin front spar I welded a piece of 5/16" x .028" tube into the bolt hole.  The rear spar mounts in a way that a bushing would not help and welding it in would just cause more problems than it's worth.
The rear bolt was installed and some string used to hold the fin in positions to tack weld the fittings.  I tacked them at each end, and in the middle.  With the fittings tacked I bolted a 7/8" spacer tube between them to help assure the spacing didn't change during welding.  It worked great.

 Welding was easier with the stabilizer tipped by setting it on some bricks.  Welding these on warped the spar a little.  It shrunk on the fitting side.  The trick of heating the back side of the spar and letting it cool took out the warp.
It all fits perfect.  With the bolts in the fin is square to the stabilizer.

My first tail surface is sand blasted, ready for priming.  This is so cool to finally have the tail surfaces made.

I've go some modifications to make to my blast cabinet to do the other parts and the prime them.

Tuesday, April 16, 2013

Wing Strut Attachment Fittings Finished

 When I made the fittings I used 3/16" pilot holes for the 5/16" bolt holes at the ends where the wing flying and landing wires attach, as well as for the 3/8" spar bolt holes at the other ends.  I didn't drill them to finished size at that point because I didn't want to buy large bolts to ruin during welding and I wanted to use small cheap pieces of tubing for the spacers.  The drilling was no more difficult after welding then before.  I drilled them out with center drills because the steep angle on the cutting edge helps them center better on the pilot hole.  The 3/8" hole was then drilled slightly (.002") larger with a letter V drill.

 I've decided to go back to using Zinc Chromate for primer except where I need to protect the finish for applying fabric.  There are wood blocks around these fittings for attaching the fabric so they're well protected.  The epoxy primer is much more easily scratched than Zinc Chromate.

I finished them with Black enamel, for the same reason, and then baked them in the sun.  I still need to paint all the small fittings and form the drag and  anti-drag wires.