Monday, May 28, 2012

Elevator Hinge Bearings

The elevators are attached to the stabilizer with a socket at the inboard end (my next task). in the middle and at the outboard end there is a little bearing block formed from a strip of 1/2" wide .050" steel.  You can see the middle one in this picture just outboard of the control horn.  The outboard hinge has a 3/4" wide strap of .050" steel which holds the elevator spar into the bearing.  The middle bearing is just pulled snug by the control cables.  The 2 elevators operate independently.

To form the bearing strap I started with a 6" strip of steel with bend lines marked 17/32" either side of center.  As with the hinge block clips I'm forming the bends with my sheet metal pliers with a radius filed on the edges.The bends are made to form a triangle.

The formed strip is slipped over one side of the sheet metal pliers with the jaws open.  The pliers are setting in the vise to provide something to pound against.
The plan is to use my 5/8" deep socket as a form tool to pound the curved bearing surface into the strip.  I found that after just starting the bend I needed to clamp the sides tightly to keep the sides spaced correctly and parallel.  Once it's done you have a nice bearing.

I did find I needed to twist the legs slightly to square them up to the bearing surface.  I clamped each part to a piece of 1" tubing and the adjusted the legs to square.
I made this little fixture from a piece of aluminum angle.  There is a 3/16" bolt which goes through the strip in front of the stabilizer rear spar.  A small piece tubing gets welded to front of the spar for this bolt. The purpose of the fixture is to punch the bolt holes in the legs of the bearing strips.

The tab bent over on the fixture is a stop to locate the bearing relative to the hole so the 2 holes are on a line perpendicular to the legs.
With the holes punched the legs can be trimmed  to length and the bearings are ready to weld to the stabilizer.  I believe the factory probably welded the small tube and bearing together as an assembly and slipped them over the spar during assembly into the stabilizer jig.  It would make welding much easier.  I've got the stabilizer assembled so I'll just need to be careful welding all this in place.

Sunday, May 27, 2012

Welding Horizontal Tail

 I decided after all these years to take a weekend off and just work on airplanes, no embroidery.  The weather was forecast to be hot and fairly calm so a good weekend for welding.  Because I'm using 4130 steel I still needed a place where I could work without any drafts.  I set up one of the 10'x10' tents I use for selling embroidery at shows as a temporary welding booth.  The side flaps zip completely shut. If you open some gaps at the top of the sides you get ventilation without the breeze.  The side are so light the slightest breeze will move them.  Early mornings and evenings were breeze free all weekend.

 A variety of saw horses, clamps and hooks made of welding rod made positioning the parts fairly easy. There is a lot written about welding fuselages to prevent warping but I found nothing specifically on welding long flat tail surfaces.  Fortunately the general principals apply.  The best way to weld the stabilizer seemed to be to start welding in at the center rib and work outward 1 rib at a time on each side.  The other thing is to weld the rib to both side of the spar before moving to the next joint.  Luckily if you forget or the spars warp a little because they will, you can fix it fairly easy by heating the tube.  You do this on the high (convex) side of the tube where you want to straighten it.  In my case I heated the spar from the weld out about 3"-4" beside the rib.  I heated it to a dull to bright cherry red along the to 1/3 of the spar and then let it cool.  As it cools it pulls the spar back to straight.  It was very cool to see it happen.

 At each hinge strap there is a block of wood for attaching the fabric.  To hold the blocks in place there are some clips (straps) which are held secure with a screw and nut.  The clips are welded to the back of the spar.
 Making the Hinge Block Clips (P/N 188) was easy.  They're made from 1/2" strips of .050" steel 2" long.  The first step was to punch a 3/16" hole for the screw.  The hole was punched in the first part and then duplicated on the other parts.

 I filed a radius on the inside edges of my sheet metal pliers for bending such parts. The bend was started 1 33/64" from the weld end.  The square makes a nice gauge for setting the distance and getting the strip positioned square to the edge of the pliers.  By holding the strip snug against a hard surface while forming the bend you get a nice tight bend.

 I used a piece of scrap to make a little fixture to hold the spacing and clamp to the to control the location, centered 9" from the tip.

Welded on ready to be formed around the wood block.  At this point I've spent about 16 hours welding the elevators and stabilizer after tack welding them.  I've also use 16 lengths of welding rod.  They probably wouldn't hire me at WACO but it was good fun and worth every minute spent in the tent in 80-90 degree weather.  I'm just delighted.

Friday, May 25, 2012

Tack Welding Second Half of Stabilizer

You may have noticed all the holes and removable panels in my jig for the tail surfaces.  The idea was to be able to stand the jig up on edge to tack the bottom tubes.  The c-clamp keeps it from falling over.
The stabilizer is completely tacked, ready for welding.
There are 2 bushings in the front spar for the bolts which hold the front spar to the fuselage.  These bolts don't line up with the fuselage longerons.  The stabilizer front spar sets on top of the longerons and a block of wood is bolted to the stabilizer clamping it to the longerons.  The center on the top of the spar was marked like when I flattened the ends.  By using the same piece of paper wrapped around the spar, the center line was drawn around the spar to locate the bottom hole. I get more accurate holes by drilling from both sides than drilling all the way through. The Port-Align is clamped to some pieces of angle to hold the drill perpendicular to the spars.  The holes are drilled with a center drill to control the drill better.
The bushings, ready to weld, have been left a little long so they are easier to weld.  I'll grind them to length after welding.

Thursday, May 24, 2012

Tack Welding First Side of Stabilizer

 The first side is now tack welded. I didn't weld the front spar to the ribs at this point or the spars and leading edge at the end without the ribs.  I also shouldn't have trimmed leading edge tube at the far end until I flipped it in the jig.  It turned out it was the right length, but again I think it was more dumb luck.
 One thing I noticed when I flipped the Stabilizer in the jig was that by sliding the front spar along the blocks it put a bend in the rear spar.  To make sure the rear spar was straight I clamped it first and then clamped the front spar so that the rear spar was straight.
 Everything is clamped ready to fit the ribs.
 When forming the bend at the front of the ribs I held a piece of 1" tubing in the formed end at the rear so I could see that the bend would be made in the plane of the rib.  Otherwise the bend will wander to the left or right.
 Shims under the bottom rib tubes hold them tight to the spars and leading edge.  The pieces of tape are there to hold the top rib tubes in place while I carry the jig outside for welding.
I'm on a temporary hold on welding.  When I was shutting down the tanks after tack welding the first half I noticed the oxygen line was loosing pressure before I bled it off.  The problem was a scratch in the seat of the tank valve.  I forgot to leak check the tank when we got it replaced last fall with a fresh tank.  I've lost half the oxygen while I've been welding.  I probably won't make that mistake again.

Wednesday, May 23, 2012

Stabilizer Spars & Ribs

The same flattening operation is used on the second end of the spars.  The only difference is that the blocks need to be clamped to the tubes so they touch just at the center line.  This way the 2 flattened ends come parallel.
 To assure everything fits when the stabilizer is flipped in the jig some sticks were used with shims to hold the tubes up straight.  Another stick was used to control the spacing between the spars.  I should have also used one to space the rear spar with the leading edge.  It all worked out without it but that was mostly dumb luck.  The length of the flattened front spar was filed until the spacer just fit with the spar and leading edge fit snugly.

 The 5/16" tubes for the leading edge were cut to length leaving about 3/4" extra.
 The ends at the rear spar were flattened as was done for the elevators.
The leading edge of the ribs were bent using the same bender I made for the elevator trailing edges. Once the bend was made the end was cut of at about a 45 degree angle starting a the top of the leading edge.  The cut side was then ground to a good fit with a 1/2" grinding wheel in the Dremel tool.

Tuesday, May 22, 2012

Stabilizer Spars

 With the leading edge formed the, 1" diameter, spar ends need to be flattened to fit to the, 1/2" diameter, leading edge tube.  These tubes are .035" thick so they're relatively easy to flatten.  I could have hammered the ends flat, as I did for the elevators, .065" thick.  I thought it could be done better with a vise with angled jaws.  Some c-clamps and blocks of 3/4" plywood worked fine.
 You need a clamp at the wide end of the taper to hold the blocks from opening.  Three clamps are needed at the flattened end, one on the tube and one on each side of it.  The clamps on each side keep the 2 blocks parallel.  As each clamp is tightened the other 2 get loose so you have to make 1/4 turns on each as you work the tube flat.  There is some spring back so you have to squeeze well beyond 1/2".
 I started with the front spar because I had a little extra length in the tube, in case I screwed up.  Also I needed to figure out how much the tube widened out forming it.  It was about 1-3/8" wide once it fit the 1/2" tube.
 On the front spar the widening can be even on both sides, but on the rear spar the aft edge must end up in a straight line.  By knowing how wide the tube was flattened, I was able to use the conduit bender to offset the ends of the rear spar about 3/16" to allow for the widening.
 Once flattened the rear edge is straight.  The fit came out very good.

 OK, the first end is easy.  The second end must be parallel to the first end or it won't fit the leading edge properly.  Because the spars are the same diameter I use them to find the top center.  First mark the top with a permanent marker.  Then I use a piece of aluminum angle to rub along the tubes leaving a nice center line mark without scratching the tubes.

 For the rear spar I need a line 90 degrees from the top to use when bending the end forward 3/16".  First wrap a piece of paper around the tube and mark the overlap point. Divide that length into quarters, in this case every 25/32". Then just mark the tube at the 1/4 mark.