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Author Topic: Ellipse 16in.  (Read 363 times)
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Tapio Linkosalo
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« on: July 07, 2019, 11:23:58 AM »

Catapult gliders seem to be really popular in Finland this summer. So obviously I have to participate. And when I bumped into a picture of Tmat's new wing for Minimat, with elliptic outlines on the wing, I decided that that is the way I want to try. So after drawing the outline for a 16 inch wing, it was time to produce some cutting. The elliptic wing gives a natural wash-out for the tips if you cut the wedge shape on the top first before tapering the trailing edge. But I did not want wash-out on the center sections, so I modified the trailing edge to straight between the dihedral breaks.

Tail feathers also repeat that same elliptic shape, and I took the dimensions roughly from Hooosier Kitty (same span and root width for both surfaces).

On to the fuselage. Front-pivoted DT is the way to go. Last winter I had drawn a nose pod to be 3D-printed, but felt that it turned too heavy. I then tried to print a mold so I could make the nose out of carbon, but that turned out to be quite tedious. So for this project I re-drew a slightly more simple nose, which turned out at a bit less than 4 grams. Weighting some plywood suggested, that wooden nose would not be much lighter, so I decided to give the printed version a go. And instead of making the wing hold-down of plywood, I printed that too. All in all it was success. The nose pod weights less than 4 grams, and the wing hold-down less than 2. The nose is really rapid to use, as there is ready hole for the timer, tailboom is easily glued and tied to a groove at the aft. And it turned out that the weight of the pod was just perfect, the model balanced without any extra ballast! The wing holddown needs a bit more work. In principle you can print threads to the parts (in this case 2 M2 threads to attach the wing to the holddown and a third thread for a screw adjusting the decalage). but in practice you need to use a tap to open up the threads. Not a big job after all.

I went to test fly the model this morning. No surprises here. Find the proper setting for rudder (about straight) and reduce decalage until model climbs with minimal spiral, and I was done.

That "tumbling pigeon" is really a curious way to DT!
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Ellipse 16in.
Ellipse 16in.
Ellipse 16in.
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tross
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« Reply #1 on: July 09, 2019, 09:52:22 AM »

Very nice. Smiley
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Instructions: Step One...Assemble the pile of sticks shown in pic "A" to look like the model airplane shown in pic "B"........
OZPAF
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« Reply #2 on: July 09, 2019, 09:26:49 PM »

Neat Tapio - that should make you very competitive.

John
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Tmat
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« Reply #3 on: July 11, 2019, 10:40:54 AM »

Very cool Tapio!
I like the nose. Hope it flies as well as it looks!

Tmat
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F1B guy...
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Tapio Linkosalo
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« Reply #4 on: July 12, 2019, 05:32:54 AM »

I tried another color. This also shows the parts in better detail. The rim to attach the parts to platform while printing needs some cleaning.

I have not made any longer test flights yet, but trimming was straightforward and climb altitude is good, so this should be a performer.
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Re: Ellipse 16in.
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flydean1
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« Reply #5 on: July 12, 2019, 09:24:27 AM »

Looks like something you could sell!!
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Tmat
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« Reply #6 on: July 12, 2019, 02:13:35 PM »

Which material did you use for printing Tapio? Does it sand well?

Tmat
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frash
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« Reply #7 on: July 12, 2019, 03:14:21 PM »

Tapio,

I think that you could sell or post these 3D printer files for your cat glider front hook and wing mount, and there would be customers for such nice work!

No 3D printer at my house, but the local public library prints for only the cost of the filament. Some razor blade miter boxes and E36 motor mounts for me were good. Some props were borderline, but that was only a first try.

Fred Rash
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Tapio Linkosalo
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« Reply #8 on: July 13, 2019, 03:57:16 AM »


The material I have used is PLA, the most common 3D print material. Made of corn starch, biodegradable, is said to be sensitive to UV but I do not plan to store my models outdoors. Probably not as durable as some other forms of printable plastic, but popular as it does not have much of odor when printed. Sands and cuts with blade pretty well. Works OK for items such as this nose. I have also printed molds for indoor model VP hub parts from that same stuff.

In the wing platform I have drawn a couple of M2 threads. For these the printer resolution is not quite sufficient, but the threads need to be tapped to take the bolts. Thus the parts need some finishing before they are ready to use. Therefore I would also need to think if the parts would be ok for selling, or how much finishing would be needed. But I guess I should thoroughly test the nose first!
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