Wing Assembly Jig

You can , of course, assemble the wing on saw horses. However there are two major problems with the saw horse method: (1) a horizontal wing takes up a lot of floor space, 5X16=80 square feet.  Plus room to walk around all sides, doesn't leave much room in a small shop for other important things like the fuselage and tools. And (2) you can't reach both sides of the wing unless you're willing to turn it over very often.

I use saw horses to begin the assembly:  attach wing spars to the compression struts, thread in the drag wires and trammel the assembly. I modify the saw horses by adding 6 inch "lifts" to them to bring their tops up to a more comfortable, work bench like, height.  Photo 1.

But for the remainder of the assembly, nose ribs, trailing ribs, leading edge, etc., it's much easier to use a vertical jig.  I can get at all sides of the wing easily, and the whole thing takes up less than 20 square feet.  I use a couple C clamps to secure the wing to the vertical jig.  Photo 2.

I made my jig out of 2X4's bolted to the rafters and standing on the cement floor.  Another 4 foot long 2X4 is bolted to the upright member and to the wall of the shop.  This gives me a 4 foot space to work behind the wing and makes the jig nicely rigid.  Photo 3 is a drawing of the jig.

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Wing 10: Trammel

Trammel the wing to ensure compression struts are perfectly perpendicular to the spars.  Trammelling means that you measure the diagonals that the drag wires form in each wing bay.   In other words, you'll measure the "X" s made by the drag wires and adjust the wires until both arms of the "X" are the same.

The wires in each bay are adjusted to the same length.  But then the trammel bar is reset for the next bay and the wires in that bay are adjusted independently.  One bay at a time.

Before you start, while the wires are loose, wrap each wire with about 1 inch of vinyl electrical tape where the wires cross.  This will reduce the chafeing of the wires and cut any noise they would produce rubbing together.  Don"t tape the wires together as you want them independently able to move when you rig in the wing wash out later.  Photo 1.

I suppose you could trammel the wings with a tape measure, but the actual length of the drag wires is unimportant...what you want is just for the lengths to be the same.  A trammel bar a quick, handy way to do it.  If you can, barrow one for a few hours.  Otherwise, it's easy to make your own out of scrap steel and a bolt.  Mine is a 6 foot length of 3/8 steel rod, with a one inch length of  3/8 ID tube slipped over and a AN3 bolt and nut make the adjuster.  I used some scrap 1/8 inch rod to make the pointers and welded it together. Photo 3.

Start at the root end of the wing and work toward the wingtip.  Adjust the wires in one bay until the trammel bar says they are identical length, then move on to the next bay and do the same.  After you've trammelled the entire wing, go back and double check...you'll probably have to do some minor adjustment.  Photo 2

When you get done the wires should all have approximately the same tension and give a nice TWANG when you pluck them.  Use a very short wrench to keep from getting the wires too tight.  I made my own out of a 1/2 by 1/8 by 3 inch long piece of steel.  I simply hack sawed a slot in the end.  Photo 4

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Wing 9: Drag wires

Drag wires (and anti-drag wires) hold the compression struts in the interior of the wing.  They form an "X" between compression struts and resist fore and aft motion of the wing.  In other words, drag wires resist the force that drag produces on the wing, the force that would make the wing fold up against the side of the fuselage.

Drag wires look like giant bicycle wheel spokes, they are more like thin steel rods with threads on their ends.  The threads screw into drag wire fittings in the end of the compression struts.  See photo 1.  The fitting opposite the camera has a drag wire screwed into it, the one closest to the camera is ready to receive it's anti-drag wire.  Be sure to secure the drag wire fittings with little pieces of black tape, as shown here.  Don't remove the tape until you're ready to screw in a wire, otherwise the fitting can fall back into the compression strut end and it'll make your curse when you have to take it apart to get the fitting back out.

Screw one end of the drag wire into a fitting until it meets the lock nut.  Photo 2.

Put a drop of Marvel Mystery Oil (MMO) onto each wire end thread before attaching it to the fitting.  Photo 3. hold a paper towel under so you don't drip oil on the floor or your beautiful, restored wing.

To get the other end of the drag wire into its fitting you'll have to bend a modest arc in the wire.  Don't worry, it'll pop right back straight.  Photo 4.

Very important.  Install the drag wires on top of the anti-drag wires.  The drag wires resist the motion of the wing toward the tail of the airplane, anti-drag wires resist wing motion toward the nose.  Drag wires have to be on top so that later when you rig your aircraft you can rig wash out into the wing.

Go to Wing 10:Trammel

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Wood

I wanted to recycle the old wing spars...lots of great old spruce in them.  I decided to use them to make new cabin door frameing.  The problem is that the old spars are 3/4 and 5/8 thickness...and the cabin frameing is 1/2. 

I set up my band saw to re-saw the old spars down to 1/2 thick.  I used a 1/2 inch, 6 tooth per inch blade and a home-made fence.  And a slow, slow feed.  Checking the resulting boards with a dial caliper I found the blade wandered about .030 (the boards were about .530 to .560 thick).  Photo 1.

I used a hand plane to remove the high spots and then I went to work with a belt sander.  I used an old Sears belt sander mounted upside down on a plywood base.  Photo 2.  After planeing and sanding my boards were nice and smooth and  running .510 to .530 thick...close enough.

Tom Baker was kind enough to lend me his old door frame boards (original!) to use as patterns.  So I just traced around Tom's frames and then back to the band saw to cut them out.  Photo 3.

The cabin wood frameing turned out beautiful.  It all looks like new, but with that mellow 60 year old patina.  Photo 4.  I set the wood pieces aside for varnish and fitting with the stringers later.  AND I still have plenty of old spruce left in those old spars!

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