Phase-one of bearhawk construction: the wing. The wing design
is similar to RV- wings, I'm told. Aluminum 'C' channels for
main and rear spars. Formed Al ribs, and skinned with Al. The
wing control surfaces -- ailerons and flaps -- are fabric
This page updated 25feb01. The thumbnail pictures link through to larger copies of the images. Just click for a closer look.
Description: Laminating the formblock blank. Most people make their formblocks from either a Oak or Maple plank, or MDF (particle board). The MDF didn't appeal to me, and I was interested in trying something a little different. Mine is made up from a piece of 3/4" CDX plywood about 6'x10". Laminated to both sides with "Liquid Nails - Subfloors and Decks - Exterior and Interior" are 4 rows of *unfinished* Oak floorboards. The hope is that I'll get the look of hardwood -- important for the future time the form will hang in my office, with dimensional stability of the underlying plywood.
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Rib Formblock - closeup
Description: Lacking adequate clamps, I brought a box of small nails from the store. (All materials for the formblock came from HomeDepot, which didn't carry an alternate Oak plank.) When putting the thing together, I realized the nails weren't going to be able to generate the needed clamping pressure, so I drilled and screwed it together while the glue dried. In transfering the rib shape to the block, I avoided most of the holes. The edge where the metal is bent over is the critical aspect of the form.
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Description: These are a double layer of pasteboard (cereal box), cut to shape and laminated with packing tape. I've got an adjustable angle transfer tool, but find having a couple of these fixed, cheap throw-away-when-they-become-worn ones very handy. The inside and outside 30-deg cards are for gauging the rib lightning hole flanges.
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Description: Not a highly 'machined' tool, but basically per Bob's description in Beartracks: drill out w/ 1/4", braze in a piece of 3/16" rod. Total cost: ~ $2.50, unless you want to count the full cost of the 3' of rod -- then its around $5. I figured if it didn't pan out, I wasn't out too much, but it seems to work OK.
Bob said apply heat to ease drilling out. I think what made the difference for me was not starting with too small of a bit. I first tried about a 3/32" but couldn't get it to bite in, and finally just hogged it out at close to the full 1/4"; it chewed its way through, just fine.
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Nose rib template
Description: The standard procedure has one trace around the formblock with a pen offset with a spacer. (The flange is 9/16" wider around the block.) Instead, I'm using a template cut from cereal-box pasteboard. On it, I've included tick-cutouts to carry forward the rivet postitions, so I'll know where *not* to flute.
An alternate mechanism to cut the rib blanks is to make a suitable template, then cut a stack at a time with a router.
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Flanging the Lightening Hole
Description: A hardwood stick with a slot cut in one end -- dubbed the 'Bob-stick' -- is used to form the lightening hole flange to a 30-deg angle. Just run around the hole about three times, lifting gently.
Many people reported trouble with their sticks splitting, so I added a couple wraps of iron wire around the business end. Worked fine -- no trouble with splitting at all. I tried it later w/o the wire wrap, when I cut off the end to make a fresh slot. Without the wire, it split on the first hole. This stick made from a piece of the Oak floorboard.
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Description: Using the formblock and a dead-blow hammer the edge flange is bent down about 60-deg, and fluted to accomplish the required 'shrinking'. Then a fly-cutter is used to cut lightening holes, which are also flanged 3/8" deep to 30-deg.
I made one right-wing rib, then one for the left wing, using the other side of the formblock to confirm that the ribs would come out symmetrical from either side of the form block. #1 and #2 were shockingly different, varying in height about 3/32" at the main-spar position. #3 was for the right side again, and much more closely matched #2 for height, confirming that the change between #1 and #2 was due more to evolving technique than a material difference in the two sides of the formblock.
I'd be in the home-stretch for nose ribs, but for rejecting my first dozen ribs (I'm now in my third dozen). I hadn't realized how highly polished the fluting pliers needed to be, and didn't realized until late in the processing that the nicks mine were leaving were unacceptable.
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Send questions, suggestions, or other remarks to me (firstname.lastname@example.org).
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