Monday, January 11, 2021

December 23, 2020 - January 11, 2021:

It's been 3 weeks in the making, but I've finally finished the leading edge of this first, left wing! Southern winter outside air temps in the 30's and 40's, with an occassional 50's or 60's, hampers progress (no kerosine heater to keep the garage warm for the adheasives to properly cure).

So, here's the progression of cutting, bending, and gluing 3/32" aircraft-grade plywood to the leading edge, replacing the less than spectacular original foam block and vinyl roof flashing design.



First carefully measure the four critical dimensions of the four wing rib bays to be covered with plywood. Then draw them out, making triple sure the angle of the trapezoid is correct...



... and cut the panel out with a box-cutter razor knife.


Dry fitting the panel. Yep! Cuts were perfect. Now on the soaking the panel in initially hot water in my bath tub over night (12 hrs or so).


 


Let's bend the nose to fit the curve of the LE spar tube by using these items: clamps (can never have enough clamps), 1" steel angle, and a tube form that's a smaller diameter than the LE spar, so that after drying, the spring back is a near-perfect fit.


Sandwich the leading edge of the soaked panel between the steel angle and the form tube, secure with clamps.


Like so.


Using a steamer, spend 5 minutes blasting the leading edge, back and forth, with non-stop steam.


Repeat for the opposite side.


Slowly roll the assembly 90 degrees while sweeping back and forth with steam. Add weight to the assembly to hold it in place. Continue steaming the flat section ahead of the form tube.


Continue slowly rolling another 45 degrees or so (optional -- I did this on panel #3 and it was too much bend).


After allowing to cool for a few hours, remove the clamps and free the bent plywood panel from the form. It will spring back quite a bit, thus the reason for over bending. Let the panel dry overnight. The bend will relax even more.


Apply glue to BOTH the panel and the ribs and LE spar. Shown is the first inboard panel. I used 3M 30NF contact cement for the forward edge, but was not convinced the bond was strong. So, for the remaining three panels, I used the white polyurethane sealant/adheasive.


Use spring clamps along the aft edge and ratchet tie-down straps to secure the panel.


I didn't think to use the C-clamps to press the forward edge of the these first two panels tightly against the LE spar tube, but did for the last two.


Interior view of a rib bay. I tooled (smoothed) the excess Tightbond III with my finger.


TA DA!


Repeat for #2.


Nicely done.


#3 with the added C-clamps.


And lastly, #4.


The finished leading edge "D-cell." 

Not shown is sanding the butt joints smooth, beveling the forward and aft edges, filling the gaps with polyurethane, and creating a "ramp" of polyurethane along the forward edge to smooth even further the stepped edge transition of the panel to the LE spar.


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