The wings of the Bearhawk are completely fabricated and covered with 2024-T3 aluminum with the exception of the flight controls which covered with fabric. The actuation mechanism for these flight controls is fabricated from 4130 chromoly steel. As I am familiar with sheet metal work, I started with the wing construction first and I will only use Alclad aluminum for the additional corrosion protection it provides.
Following the advice given in the various web sites and in the Beartrack Newsletters, I first obtained a sheet of 3/4" MDF from the local Home Depot store to use while creating the various form blocks. To make these form blocks, I carefully trimmed out the full-size template provided with the plans (sheet 7) and glued it to the MDF board with spray-on adhesive. After some thought, I decided to make separate form blocks for each sets of ribs (i.e. nose ribs, center ribs, etc). I reasoned that it would be much easier to work with the smaller form blocks than with a single, large form block. I carefully located and drilled the jig holes in each set of form blocks and then placed steel inserts in these holes for accurate drilling. I had already made these jig holes at a 1/4" when I realized the plans specified 3/16" holes. Since my hole cutter was set up to use a 1/4" drill bit, I opted to continue as is.
When I started to form the trailing edge ribs, I quickly found that the MDF backing boards did not hold up too well down at the trailing edge areas. For these pieces, I ended up making the backing boards from oak.
At this point I have almost completed forming the wing ribs and wanted to pass on a couple of additional tips/lesson's learned during this journey:
Save yourself the trouble and expense of making separate form blocks for each set of ribs. It is very feasible to make a single, full-size form block and use it for all your ribs.
In addition, when creating the form block/s, I recommend that you take into account the thickness of the sheet metal that will be formed in that block. I subtracted .030" (a rough average thickness between the .025" and the .032" sheet metal) from each side of the form blocks to account for this. The result is a rib that exactly matches the size and shape of the scaled drawing in Sheet 7. 3)
When it's time to flange the lightning holes in the larger ribs (center ribs and wing tip ribs), I fabricated a "jig" by taking a flat piece of stock and cutting a hole in it that was slightly larger than the biggest lightning hole in the ribs. I then attached some legs to the jig to elevate the jig from the work surface. The rib was laid onto the jig and clamped into place with the lightning hole centered over the hole in the jig. By clamping the rib onto the jig, I prevented the rib from twisting while I flanged the lightning holes. Occasionally I had to do some minor tweaking of the ribs using the methods described in the BearTrack newsletters.