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Jan 14, 2020, 10:31 PM
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ibnjmn's Avatar
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Jan 15, 2020, 07:20 AM
Barney Fife, Vigilante
tom43004's Avatar
Thread OP
Wait... did I already share tail mold files with you? That looks freakishly familiar...

Jeez I'm getting old.
Jan 15, 2020, 08:29 AM
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ibnjmn's Avatar
No, I got impatient! I traced the planform you posted using Fusion 360, then lofted it with Z4D and draped 3d toolpaths all over it. I've been reading your old threads about molding - lots of gold in there!

I realize the outlines you posted were adjusted for flat plate tails, but if flat plates are good enough, then so is a slightly outsized airfoiled tail, and Z4D molds will be good for making spare tails, anyway.
Jan 15, 2020, 09:03 AM
Barney Fife, Vigilante
tom43004's Avatar
Thread OP
Well maybe I can make things easier for you.... not sure I have the foam toolpaths etc but here are the base Rhino files

This one will probably be modified slightly. I was using a one piece fuse originally with elliptical profile. Now I am using a round production boom.
Jan 15, 2020, 09:57 AM
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ibnjmn's Avatar
Wow, thanks! I think tails will keep me busy for a few nights, but I might come back and ask you for more hints if you don't release soon.

For instance, on the wing, how far off would I be if I interpolated the Zone-V2-2P foils to the chords you posted on the wing preview, and applied the same amount of twist that Gerald did in the reference design? I'll still be bagging wings for now - I don't think I could cut and polish molds that big in time for San Felasco, and I think bagged wings are the closest to the spirit of the project, anyway.
Jan 15, 2020, 10:49 AM
Barney Fife, Vigilante
tom43004's Avatar
Thread OP
If you took a ZoneV2 reference wing and reduced the chords to those referenced, you'd be very close. The NXT airfoils are not true ZV2 but they started life there and don't vary by much more than the building error for a bagged wing.

I'll be flying a bagged one at SF.
Jan 21, 2020, 01:38 PM
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ibnjmn's Avatar
Tail mold progress. Not the shiniest mold I've ever seen, but I think it's ready for wax and PVA!

Deep blue epoxy pigment on MDF makes an interesting jade color. I kind of like it!
Jan 29, 2020, 10:14 PM
Registered User
The molds are just epoxy soaked MDF? Interesting, guess I never thought of that.
Jan 30, 2020, 08:30 AM
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ibnjmn's Avatar
Mine are, currently. It's kind of an old-school way of doing it. Lots of information on it here on the groups, including from Tom. I think it's more common to make male masters this way, and take impressions of them with a better tooling material. This is cheap and relatively easy, though, so the mistakes I make while learning are less painful.

I finally managed to cut a decent core last night. Now I can actually put this mold to use!

I'll be ready to cut the fuselage or the h-stab soon. Hint, hint!
Jan 30, 2020, 06:51 PM
Registered User
Quietly following along here

I've been wanting to try some molded tails, and this might be the time.

Ibnjmn,

I don't see it on the pic of the foam core, but I assume there is something to index the blank so it can be flipped over to mill the other side? And then, how support the already milled side when doing the second side?

Brian
Jan 30, 2020, 07:55 PM
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Quote:
Originally Posted by jpbldr
I don't see it on the pic of the foam core, but I assume there is something to index the blank so it can be flipped over to mill the other side? And then, how support the already milled side when doing the second side?
Yes, exactly right. The pink piece of foam is my "fixture." I extruded a rectangular block 10mm from the sides of the fin and cut out the negative shape of the left side of the fin. For each core, the right side of the fin is cut first, flat against the bed, and the model contours out a plate extruded from that same 10mm rectangle outline that matches the fixture. I flip it over, cut out a notch so that I can touch off on the corner of the fixture, and tape it down. You can see the outline and the tape pretty well in the first picture I posted above.

I tried using double-sided tape at first, but my tape is both too thick and too tacky. It would leave bumps in the core, and rip it apart when I tried to take it off. I finally found success with the CA+masking tape trick, and only taping the outline, not on the actual core. Since there's only one pass, and it runs straight from one end to the other, the material is supported for just as long as necessary. Next time, I'm just going to flush up the outline and tape the core to the fixture from the outside.

AND this would be much easier if I would get around to making a vacuum fixture like I found in Tom's old threads... no more tape!

Jump in! Have fun! Don't forget to think it through before you cut!
Jan 30, 2020, 10:02 PM
Registered User
Ok. I envisioned some holes in the blank to locate it with dowels to the table, which I have done on other two sided project.
Jan 31, 2020, 09:11 AM
Build and Fly
ibnjmn's Avatar
That's probably a better way to do it, anyway. No reason not to that I can think of. If you're going to make hard points in the fin, those holes might work for locating the core as well, if you work it out that way.
Jan 31, 2020, 10:11 PM
Registered User
A few more questions...

Regular pink insulation foam? What psi/density?

Also, maybe off topic for this thread, but you mentioned using Fusion for modeling. I'm familiar with Fusion and have used it to model lots of parts, including some 3d. I can't seem to get consistent results when lofting airfoils though. Straight, or plain tapered panels work fine, even a regular elliptical planform. But something with the shape of your fin, I get errors when trying to loft. Any advise?
Feb 01, 2020, 01:51 PM
Build and Fly
ibnjmn's Avatar
For wings, the best I have right now is 25psi green foam. 40 or 60 are preferred. I used 15 psi pink foam for the fixture because I had it and it doesn't have to stand up long term.

For lofting the fin in fusion, the trick is to have a single point at the tip. Project the leading edge point and the trailing edge point from the air foil sketch into your plan form sketch, and use splines to trace from the air foil to the tip points(mirrored). Then you can loft from the single point to the air foil, back to the single point at the other side, using the splines as rails.

I hope this makes sense. I still have to play with it a lot every time I do it to make it work right.


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