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A different way to build a wing

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rtfm

Well-Known Member
Joined
Jan 3, 2008
Messages
3,900
Location
Brisbane, Australia
Hi,
There are many ways to build a wing: here's a somewhat novel way which is both quick, simple and strong.
I must begin by saying that this is a thought experiment, and that I don't (at the moment) actually plan to build this wing. Perhaps further down the track I might give it a try, but not till I've built a scale version and tested it.

  1. Make your ribs. I would cut them from foam, since (1) it is WAY quicker and (2) significantly stronger than the traditional method of building ribs from spruce sticks. You could cut all your ribs using a simple template and a hot wire. Those who have a CNC router could use that. Either way, they are very simple and quick to cut. Importantly, both the LE and TE of the ribs are truncated (about 100mm (4 inches) from the nose, and at the aileron line.
  2. Mount the ribs on a cradle in order to get them all perfectly aligned. I'd use something like Fritz' "Rib-o-Matic" - which is essentially a rigid box on which are mounted multiple "arms" to which the ribs are affixed. This ensures that every rib is perfectly aligned. I'd build a 2400mm rib-o-matic box, because the wing will be made in three sections, each of which is 2.4m long.
    71507-aae2995ac6de89cddc78f139d2974fdf.jpg

  3. However, I'd double up on the "arms" - ie four per rib. The reason is that we are going to cut the ribs vertically at their thickest point, and remove 5mm. Why? Because we are going to bond a 5mm shear web (not a spar) to join the two halves. Each rib half needs to be supported at two places to ensure the shape remains perfectly aligned.
  4. Close off the LE and TE with 5mm AC grade plywood also.
  5. The questions are probably bubbling up thick and fast at the moment. But stick with it. I'll get there...
  6. OK, so we now have our foam ribs held in place on the rib-o-matic "arms", with a 5mm plywood shear web running down the length of the ribs, and 5mm ply both at the D-tube position and at the aileron hinge position.
  7. Importantly, the 5mm thick plywood will be (1) way over-built strength wise and (2) way too heavy. A full sheet of Gaboon ply weighs 7.6kg. A 200mm wide strip weighs 1.26kg. Removing 75% of its volume results in a shear web of 316g (about 11 oz). The D-Tube and Aileron close-offs will be less than 200mm deep, but at the thickest part of the airfoil, will be deeper. As a rough estimate, let's assume 3x 200mm deep close-off pieces. Total weight = just shy of a kilogram. This is why we remove about 75% of its volume by simply drilling multiple holes with a hole saw before bonding it to the ribs. Do not remove any surface area where the shear web bonds to the ribs. We're all familiar with lightning holes in ribs. So this is what we now do to the excessively thick shear web. If you have access to a CNC router, you can cut the plywood into fancy diagonals. But multiple circles should be just fine.
  8. Why use 5mm thick plywood when 1mm ply would have sufficed for a shear web? Simple - we need at least 5mm width in order to bond it to the wing skin.
  9. The skin consists of 1mm AC grade plywood. Birch is best, but Gaboon is cheaper. though a bit heavier. But even Gaboon ply weighs only 2.3kg per 2400 x 1200 sheet (8x4).
  10. As we all know, a wing needs a spar, but all we have is a shear web, with no spar caps. Ah, but we do.
  11. Before bonding the 1mm plywood skin to the ribs, first bond carbon fibre rods down the length of the 2400mm plywood sheet exactly where the shear web is. When flipped over, the plywood skin now has the spar cap bonded directly to it, which aligns with the shear web. The top skin bonds to the D-tube close-out, the shear web and the TE close out. Three strong bonds.
  12. Flip the wing, and repeat.
  13. Material used for each section: 8 foam ribs, 3 plywood shear webs, 1 full sheet of ply for the skin. Estimated weight of each 2.4m section: under 4kg. 3x sections: under 12kg
And there you have it. One day to cut the ribs. One day to bond the main shear web. One day to bond the D-tube and one for the aileron close-outs. One day to bond the carbon fibre caps to the skins. 2 days to bond the skins to the ribs.

Of course, there are other things to do. This wing envisages a folding hinge-mechanism, where the outer panels fold upwards (from the Flying Flea designs). A simple hinge, but with inner reinforcements to anchor it. But not a lot else.

Anyway - that's my idea - so please feel free to comment and offer suggestions.

Regards,
Duncan
 
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