Friday, February 1, 2013

Ready to Weld Wing Fittings

Now that all the holes are in the fittings and the drag wire tabs have been bent, the strut attachment clips need to be welded to the fittings.  The clips are 3/16" thick steel vs the .095" steel fittings.  Spacing the fittings is easy with some pieces of 5/16" x .028" tubing, with the length cut to the width of the spar.

The ends of each spacer are ground square on the belt sander by holding the tube against the miter with a finger while sliding the miter across the belt.  By rolling the tube as you slide the miter and giving the tube a slight pressure against the belt you get a very square end as well as good control to create spacers all within .001" - .002" in length.  Whenever I cut off a piece of tubing I square the end of the remaining tubing right then because it's easier to do it with a longer piece than to do both ends of the short spacer.  With square ends on the spacers and a snug fit of the screws in the fitting holes, the fittings line up very well.  Check them with a square just to make sure.  You can adjust them slightly as you tighten the nuts on the screws.

With the fittings aligned, the the next problem was how to align the clip.  On the NINE it's perpendicular to the 2 lower bolts along the center line of the spar.  It also has to be a certain distance up to clear the spar and correctly positioned between the bolts.

To do all this I made some pieces of steel which locate off the 2 lower bolt bushings and then have a slot to hold the clip in the correct position. The locator piece is more or less centered between the fittings holding the clip ready to weld.

The parts are fairly simple. The bolt holes were punched from the fitting template and then drilled to fit the spacers using a center drill.  The slot was bandsawed and then filed to a snug fit on the clip.

The locator for the rear spar fittings needed a relief cut to clear the spacer part way up the arm.  I could have used less screws but it seems better to hold the fitting as securely as possible while welding.

There are 4 rear spar fittings and 4 front spar fittings so I made 2 each of the locators and spacers.  Clearly I could have done all this with 1 set of each.  Now I need the wind to die down so I can weld these.  It would be nice to have a shop where I could weld inside.

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