I am again stuck with my trailing edge 0.4mm thickness problem

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 From:  simba
7445.1 
Hello,

for manufacturing reasons, I need to trim the trailing edge of aerodynamic shapes to a thickness of 0.4mm. It should be a straight champfer/vertical cut along the trailing edge.

Is there a way e.g. to create a constant "thickness line" along the trailing edge?

S.
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 From:  Michael Gibson
7445.2 In reply to 7445.1 
Hi simba, the only way I know of is to use filleting. You will need to prepare your surface before trying to do a surface/surface fillet on it, you'll probably need to divide it in to 2 pieces, cut away some amount so the pieces are not touching along the trailing edge, then use ShrinkTrimmedSrf on them so the actual underlying surfaces are not touching, then select the 2 separate surfaces and run a fillet with the "constant distance" option. It's the same process as the previous time, that previous discussion thread is here:
http://moi3d.com/forum/index.php?webtag=MOI&msg=7023.1

- Michael
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 From:  hairykiwi
7445.3 
Hi Simba,

What airfoil section are you using?

This isn't exactly a straight-forward operation, depending on your final OVERALL accuracy requirements. Apologies if I'm getting you to suck eggs with the following explanation - though maybe it helps someone else understand better also:

For a wing of a given taper ratio, in order not to reduce the chord of the wing tip airfoil proportionally more than that specified by the taper ratio, the wing root airfoil trailing edge (TE) needs to be ever-so-slightly closed up at the TE. Now here's the tricky bit: in order to keep the rate of change of curvature of the wing root airfoil section as similar and as smooth as the 'basic' original airfoil, that change in thickness actually needs to originate from about 5 or 10% chord all the way back to the new, thinner TE.

I had the same issue to overcome in drawing a full size build-able wing for a homebuilt aircraft using the NACA 43012A airfoil. Conveniently, the polynomial curves used to define the basic NACA 4-digit and 5-digit airfoils enable the TE thickness to be modified very easily, by varying the A4 coefficient. Search this forum for 'NACA Airfoil Generator' and have a play to better understand the concept. If your foil is a NACA 6-digit series, I got a long way toward generating those by script, (but nowhere near release) and I can't spend any time on it right now, sorry.

Attached is my NACA 43012A example tapered wing (with washout), made by lofting between root and tip airfoils (of root and chord length specified by the aircraft designer), The root and tip airfoil sections are identical save for chord length and A4 coefficient. Note that the TE thickness is constant along the entire span. I determined the root A4 coefficient (as noted in the object names) simply by trial and error.


Cheers,
Hamish

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