Chapter 21: Mounting the Center Section Spar


This is supposed to be Chapter 14 stuff, but I put off mounting the center section spar for as long as possible to maximize my time at home in the garage before committing to moving everything to the airport.  Instead of just mounting the spar by itself into the fuselage, I went the full route and mounted the wings to the spar first, set up the wing planform,  then jigged the fuselage onto the spar.  In my opinion, the extra work is worth it to ensure all wings, canard, and fuselage are all aligned properly.

  1. I removed the main landing gear and set the fuselage on the floor to make the jigging easier, and to provide better access to the strakes during the build process.  It will also allow the plane to be flipped easier in a later step.

  2. I approached building the strakes the same way as I approached drilling the main spar.  I used the #4 wing jigs to make two wing cradles to support the wings near the ends of the spar.  These two cradles have lag screws in their footpads.  By turning the lag screws in or out, I could adjust the cradles as needed to level the wings tip-to-tip and to ensure the incidences were at zero.  I attached the wings to the spar and carefully set the entire wing planform onto the wing cradles.  I set up the same water levels from Chapter 14 and adjusted the wing cradles until the wings were at zero incidence with the wing tips at the same height.

  1. I also made two beam cradles to fit under the fuselage so I could independently adjust the fuselage fore and aft, side to side, and more importantly ensure the canard was level with a zero incidence.  I used blocks and adjusted the heights of the cradles so that the fuselage could easily slide onto the main spar WITHOUT disrupting the wing planform.   I set up another water level on the canard and adjusted the beam jigs until I got the canard wing tips to the same height with the incidence angle at zero.

  2. When I had everything in the ballpark, I slid the fuselage onto the main spar for a fit-check.  I must have measured and tweaked everything a hundred times.  Once I was comfortable (Comfortable?  Heck, it was 116 degrees in the hangar!), I slid the fuselage off the spar, installed the EM2 engine mounts, buttered up the spar cutout area, and slid the fuselage back into place.  I spent the next two hours measuring everything a hundred MORE times, tweaking the jigs here and there until all incidences, water heights, and sweep dimensions were dead on the money.  Well actually, because of the heat, things pretty much became rock steady and immovable after 1 hour :-)

  3. I tied up the imaginary dog, locked the hangar doors, went home and conked out big time!  Had NO trouble falling asleep that night.


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