WingSpars

WingSpars

August 9, 2002 - Leonard is advising new builders to fabricate front and back wing spars with web lightening holes in the last two out-board wing bays ONLY... Wing spar web lightening holes may be omitted entirely for construction simplicity...

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I learned that my woodworking and gluing skills were not what they needed to be on the spars... The spars were the first woodworking I had done on the project as Stan had been making ribs while I did the empennage and fuselage... My woodworking skills come from the construction world and an early life on a farm... I have a California General Contractors B license which gives me the credentials to criticize and manage wood based commercial building... The credentials do not translate to craftsmanship as we shall see... Craftsmanship comes from doing, failing, learning, correcting and succeeding...

After reading Leonard's wing building script numerous times I finally understood what he was saying about the spar jigging process - it's simple and beautiful... My building table has swales on the top and sides because I built it with wet lumber and didn't put supporting cross pieces in on 16" centers... Therefore putting Leonard's backstop jig on the table was not an option... If your jig is crooked the spar will be crooked and YOU DON'T WANT A CROOKED SPAR... Stan built a spar jigging assembly to put on top of my uneven table seen in the next photo...

You will also note that I'm not using the intended backstop to hold the spar against... There was an ever so small wiggle in the backstop between the vertical pieces in the spar... I said that won't matter, "It'll spring right back when it comes out of the jig"... Guess what, it sure didn't... The final spar jig was the jig assembly leveled up with no swales on the flat and a snapped line with the 3/4 x 3/4 x 4" oak blocks centered on every vertical leaving enough space between to use the wood wedges against the spar cap...

The spar building stages...

1) Figure out your spar jig and make the wedges - I used shim stock...

2) Layout the vertical and doubler locations on the flat and top of the jig...

One layout makes all 4 spars -

[EXCEPT FOR THE ROOT BRACING/DOUBLING]-The left and right of it!... Don't forget those verticals for the close set ribs at each end - let the dimension be a challenge to you...

3) Look at the wood grain in your spar caps, mark which side is up in the jig and cut to length...

4) Put a backstop in your cutoff saw and cut all the verticals after you have made sure caps plus first cut vertical equal spar slot on the ribs... On the cap doubled areas trim the vertical to fit from standard cut pieces as you build...

5) Do a trial fit with the wedges in place... If your on the second spar be sure you have the left and right of it by putting the root of the first spar next to the root of the second spar as it would be in the airplane...Pencil mark where the glue joints are for a location to put glue on both mating pieces... IS THE ASSEMBLY FLAT AND STRAIGHT?

6) Put down handy wrap in the jig bottom and up the stops...

7) Find top markings and put caps in jig...

8) Put all verticals and braces near location outside the jig...

9) Put glue on [both] mating surfaces and assemble starting at the root and (lightly) wedging... Look back as you go to see that the overall alignment is being maintained - no cap or brace drift...

10) No more parts to glue? Top marked vertical locations all filled? NOW, from the center of the spar working in both directions check vertical and doubler location and tighten the wedges... REMEMBER, don't squeeze out a T88 joint - light contact is the objective!

11) Stay with the assembly until the glue is stiff in the mixing cup...

12) Rip out the 1/8 plywood webs leaving long enough to run wild at the root and wing tip... We put the splice out at the 3/4 vertical near the 8' mark from the root...

13) 2 of the cap and vertical assemblies can be left in the jig for the web to be glued on... I snug the spar with the wedges for the web gluing...Be sure to put glue on [both] surfaces and work from the middle in both directions of each piece... I got in a hurry in the middle of the night and created the need for the double root bracing on our right wing seen elsewhere on the site - a close look shows the word -O O P S- marked on the braces for extended right turning inverted flight...

14) These 2 cap and vertical assemblies need to be turned over in the jig to put the spar web on...

15) The water is gone now as the shop reached 111 F at times when I was in there...Even weights have a shelf life...

Final note:

One of our spars took a heavy cord wise curve... We put blocks under the spar ends and weighted down the middle past level... It took several weeks for the spar to take heed... We keep the spars stacked on the floor with wood spacers in several places under them... The spars need to be straight when the wing is assembled or the alignment steps will be ugly sessions...