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Author Topic: Building undercambered wings  (Read 219 times)
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PantherM100
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« on: April 20, 2021, 09:58:16 PM »

Hi Guys:
Is there a 21st century for building undercambered
Wings?  Other than blocking up the leading and trailing
Edges to correct angle / height, then blocking up the
bottom spar to its vertical position, and then set the
Ribs in position?
TIA
Jon B. Shereshaw
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flydean1
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« Reply #1 on: April 20, 2021, 11:14:54 PM »

Unless you build an assembly jig that matches the undercamber, shims are the way to go.  Simple and elegant.
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Tapio Linkosalo
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« Reply #2 on: April 21, 2021, 01:30:49 AM »

I laser-cut my ribs with an extra part at the bottom, that raises the rib to proper height and acts as a shim to raise the trailing edge to proper angle. After assembly just cut away those extras, that are only atteached to the ribs by a couple tabs. The bottom part of wing spar also has tabs to raise it to right height.
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Kevin M
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« Reply #3 on: April 21, 2021, 01:40:02 AM »

You could make a simple wing jig like the commercial one in the picture below.
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che
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« Reply #4 on: April 21, 2021, 04:58:39 AM »

Hi Guys:
Is there a 21st century for building undercambered
Wings?  Other than blocking up the leading and trailing
Edges to correct angle / height, then blocking up the
bottom spar to its vertical position, and then set the
Ribs in position?
TIA
Jon B. Shereshaw

Yes, it just depends on how much money you want to spend on it. If you're having the ribs cut on a lazer then you can just include the tabs as Tapio suggests, or else do what I do and have a set of 'riblets' cut that you glue to a baseboard and on to which the ribs sit - you can even make this using a classic 'sandwich method' if you wish, but certainly not very 21st century.

Better still is a board with the correct undercamber and warps built in. This can be wood or foam or even metal if you're really keen. The foam can be cut using simple jigs and a hot-wire bow, but not very 21st century. You could use a flat board with curved rubs (so like the laser option above) which is then covered in thin ply - that works; then again wood or foam can be machined with a 3-axis router.

But if you really want a 21st century method then why not 3D print a undercambered board - now that IS very 21st century. You have a lot of fun laying many cubic metres of concrete on to which you can place a few £10,000s (or $s) worth of machine, which you need to run for many hours to get a finished product.

But before you dismiss any technique not invented in the last 21 years, I'd consider the KISS principle and take a flat stiff board and stick some curved ribs on it, made using the sandwich method. Simple, cheap, reproducible, easy to modify, and which will give an accurate result all with tools you'd likely have around already.

Or maybe I'm just a Luddite - feel free to discuss.

CHE
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Starduster
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« Reply #5 on: April 21, 2021, 07:56:45 PM »

Hi Jon

For me, it comes down to a few questions:

1) Am I planning on building more than one wing?
2) How complex is the wing
3) What kind of tolerance can I accept?

If I'm only gonna build one, and it's a pretty easy wing (i.e. say, a Gollywok, or just about any other old-timer) I won't bother building a assembly jig.

However, if I'm working on a prototype, and I'm pretty sure I'm gonna build a few, then, yes, I'll fabricate a fixture.

The pictures are of a well-loved example of a F1H wing (I'm using the same wing on a F1Q now) I knew that I was going to build a few wings, it is a pretty complicated wing (well, for me anyways...) and I wanted to make each wing as identical to the others as possible.

Picture one is all three fixtures. Notice that there is only one center section fixture. I build both the left and right on the same fixture.

The other pictures show different angles of the fixtures. I basically first cut 3/4 inch ply a little larger (span and chord) as the base. I then cut 1/8 ply end pieces that act as a guide for the hot-wire foam cutter. I use the blue insulation foam from the local home depot. I then glue (just plain old carpenters glue) it all together, use a home-made hot wire bow and cut the camber. I then tack-glue the wing drawing on the foam, then cover with 3 inch clear packing tape. I find these work really well.

For this particular wing, I built in about 3 degrees of wash-out in the outer panels.
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