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Author Topic: Squarecoupe Build  (Read 2689 times)
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TimWescott
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« on: March 28, 2011, 05:10:49 PM »

Plans made, wood curved (thanks to all who responded to my "bending wood" queries).

This is intended to be a not-too-competitive indoor. So I'm using 1/20" wood where I can (rather than going out and buying decently light wood), but I'm not going to foam at the mouth if it's ten or even 12 grams. If it's 14, I'll call it 'outdoor'.

Here you see the vertical stabilizers (there's two, there, stacked on one former), and the wingtips. Smarter money may have made the wing edge in one piece, LE, TE and tip all in one. Me, I'm dumb, so I'm doing it piecemeal.
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Pit
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« Reply #1 on: March 29, 2011, 08:24:33 AM »

NICE! I'll be watching this one - I like ERCOUP... er, Squarecoupes (maybe even build one Roll Eyes).
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thymekiller
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« Reply #2 on: March 29, 2011, 10:49:20 AM »

Nice woodwork!!!
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Glenn (gravitywell) Reach
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« Reply #3 on: March 29, 2011, 12:16:22 PM »

That is definitely a cutey. Another fine Boston that needs building. Don't forget to post the plans in the gallery.... it would be a welcome addition.
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Glenn Reach
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Dave Andreski
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« Reply #4 on: March 29, 2011, 12:36:30 PM »

Nice work Tim!
Hope you get some flying in soon.

Dave Andreski
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TimWescott
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« Reply #5 on: March 29, 2011, 09:30:11 PM »

Why I use cyano glues: rudders were Ambroid, wing was cyanoacrylate.

I spent an hour on the wings, spread out over an hour. I spent 1/2 hour on the rudders, spread out over two days. Ambroid is nice, but not when you're in a hurry.

This is kind of an experiment: I know that indoor fliers vastly prefer thinned Duco cement. I'm trying out cyano, applied with a toothpick to keep weights down. The built time is certainly benefiting. Now I need to decide how much dihedral to put in, since I'm about ready to crack the LE and TE, block up the tips, and go. I'm thinking one and a half or even two inches. That's a lot, but this is a low-wing plane. Wish I knew...
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TimWescott
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« Reply #6 on: March 30, 2011, 12:07:48 AM »

The tale 'o the tape, so far:

Wing: 1.1g
rudders: 0.2g
Wing + rudders: 1.4g (obviously there was some rounding going on).

This is looking not-too-bad for keeping things under 14g, although I doubt that I'll make it down to 7.
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Indoorflyer
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« Reply #7 on: March 30, 2011, 09:34:05 PM »

I think 1.5 inches dihedral under each tip will do the trick. The Squarecoupe has a layout/geometry very similar to the Maubosson (spelling?) and they seem to fly pretty well with "reasonable" appearing dihedral. 1.5 inches will put the wingtips close to the longitudinal axis passing through the thrust button...

If it doesn't work, blame Bob Isaacks.
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TimWescott
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« Reply #8 on: March 31, 2011, 01:36:52 AM »

I gave it 1-3/4 inches at the tips, which may be excessive. But it's a new design so if it flies even half way good I'll probably do another revision before I release it into the wild.

I got the horizontal stab done -- we're up to 1.8 grams. I realized that the wings still need some sort of landing gear blocks.

I'm planning on making wheels out of Depron and 1/64" ply. Depending on just how crazy I go, these will either be cut and glued, or I'll make aluminum molds and cook them up in the oven, then paint them black & silver to match the general Ercoupe look.
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dosco
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« Reply #9 on: March 31, 2011, 08:06:27 AM »

... I'll make aluminum molds and cook them up in the oven ...

What do you mean by this? (inquiring minds want to know)
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TimWescott
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« Reply #10 on: March 31, 2011, 12:49:06 PM »

... I'll make aluminum molds and cook them up in the oven ...
What do you mean by this? (inquiring minds want to know)

That I'm either going to make a mess in my oven, or some nifty, really light wheels.

When you heat Depron up to about 150 degrees F, the foam softens and the air in the cells expands. So the foam bloats somewhat, and bends. Folks have used this in the past to mold undercambered wings -- you strap the Depron to a curved form with an ACE bandage, which both holds the curve and contains the expansion. Then you wait until your help meet is out of the house, you sneak into the kitchen, and you bake at 150F for an hour or so.

I'm thinking that if I make some wheel molds that are about the right thickness for a sheet of Depron, that don't crush it too much or leave it too much room to expand into, that I can put disks of foam in the molds, clamp them closed, and heat. Then -- if all goes well -- the foam should expand out to the walls of the mold, and stay there when everything is cooled down. If I glue thin plywood axle bearings to the disk before it goes into the mold, then what comes out should be a light, durable wheel in just about any shape I want. Then I just need to paint it to make it look "real".

I really don't know for sure that this will work, but indications are that it should.
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dosco
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« Reply #11 on: March 31, 2011, 12:59:06 PM »

When you heat Depron up to about 150 degrees F, the foam softens and the air in the cells expands.

I really don't know for sure that this will work, but indications are that it should.

Very cool, didn't know that.
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Glenn (gravitywell) Reach
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« Reply #12 on: March 31, 2011, 02:27:22 PM »

A decent hardwood should work for the molds as well. 150 degrees isn't hot enough to ignite the wood, and the heat should transfer to the depron through the wood. Just a thought for those of us that don't have metal working skills/equipment. Smiley
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dosco
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« Reply #13 on: March 31, 2011, 02:35:28 PM »

A decent hardwood should work for the molds as well. 150 degrees isn't hot enough to ignite the wood, and the heat should transfer to the depron through the wood. Just a thought for those of us that don't have metal working skills/equipment. Smiley

What about casting an impression in a small bit of concrete, then using the impression as a mold?
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TimWescott
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« Reply #14 on: March 31, 2011, 03:50:14 PM »

Aluminum is handy for me, so I'd use it. But yes -- hardwood would work well, as would concrete, plaster, or any other casting material that can stand 150F. 150F is at the top end of "really warm"; just about anything but wax (or the plastic they use for Depron!) should work.
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Olbill
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« Reply #15 on: March 31, 2011, 11:44:34 PM »

When you heat Depron up to about 150 degrees F, the foam softens and the air in the cells expands.

Damn!!!!! ----->(Olbill's mind doing backflips with this new bit of information)
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TimWescott
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« Reply #16 on: April 04, 2011, 08:05:13 PM »

Fuselage progress. Note former drawing started in the background -- my CAD program is giving me fits with ellipses.

This thing is fat.

(Dangit. I just realized I forgot to drill for the rubber peg. Oh well -- it's more fun when you do it "in the air". Right?)
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Indoorflyer
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« Reply #17 on: April 04, 2011, 10:33:49 PM »

I'm following this build with great interest--I think it's a great subject, and has "charisma" (oh wait, that's for embryo...)

I'm curious how the rear canopy will be treated; I guess because of the Bostonian box requirement, it will have "facets" that come to a point on the top of the turtledeck?

I would make the nosebowl a little more "pointy" at the bottom center--the full scale Ercoupe has a characteristic almost-triangular nose bowl.

Nice model.
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TimWescott
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« Reply #18 on: April 04, 2011, 11:27:43 PM »

From the 2011-2012 Competition Regulations:

"22.3. Charisma Judging. A “charisma factor” of 1.00 through 1.20 will be awarded each airplane before flight, based on the purpose stated above. The assignment of charisma factor will be made with all the models grouped together so they can be ranked and compared.

There is no reason to award either a 1.00 or a 1.20 score to any of the models in a particular competition. These numbers represent the limits of the range to be used. The judge is encouraged to assign values with at least two (2) significant numbers to the right of the decimal point to fully use the factor to differentiate among the models being judged. This factor will be awarded with whatever weighting the appointed charisma judge sees fit and is not to be the subject of protest after judging. Argument about charisma scoring will be considered unsportsmanlike conduct with penalties provided in this book."


Now, the one place I have to compete around here doesn't judge for charisma points -- but I'm going for that 1.2 anyway!
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TimWescott
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« Reply #19 on: April 05, 2011, 12:50:23 PM »

I would make the nosebowl a little more "pointy" at the bottom center--the full scale Ercoupe has a characteristic almost-triangular nose bowl.

Dang. You're right.

I've made the change as best as I can with the fuselage sides as they are now -- they really need to be more "pointy" for this to work properly, with less of the front parallel. Not only does it look better even now, but my CAD program has numerous problems with ellipses that all go away when I use multiple circular arcs instead. So it's better looking, and easier to deal with on the Confuser!
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« Reply #20 on: April 05, 2011, 12:56:07 PM »

Just curious... What CAD programme are you using?
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TimWescott
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« Reply #21 on: April 05, 2011, 08:22:51 PM »

QCad, free version. It's mostly a really good 2-D CAD program, except that ellipses are buggy as all get out, and the Beziers don't work right at all.

It's worth way more than what I paid for it, though. All in all it's at least as good as what I'd expect for a "hobbyist" CAD program -- so until I want to spend gazillions on a 3-D program, this will do just fine.

Here's a picture of the fuselage mostly done -- it still needs the bottom stringers in front. Somehow I got it's little nose out of joint -- I stripped all the fuse stringers out of one sheet, and still managed to get one side harder than the other. Oh well -- it's supposed to fly in circles anyway.

3.6gm, and I still don't have landing gear or prop. I'm still not sure how much weight gain to expect before it's ready to fly, but I'm not holding my breath for needing ballast.
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TimWescott
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« Reply #22 on: April 08, 2011, 10:20:35 PM »

Molding Depron wheels in the oven appears to work -- pictures to follow, when I get wheel, mold and camera into the same room.

Given how long it takes an aluminum mold to cool down, I'm not sure how this would work with any material that's a better insulator. Someone would want to experiment. JB Weld is, I believe, metal filled, and may have good thermal conductivity. Epoxy in general seems to have good heat resistance, so maybe it'd work.
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« Reply #23 on: April 08, 2011, 10:38:08 PM »

Given how long it takes an aluminum mold to cool down, I'm not sure how this would work with any material that's a better insulator. Someone would want to experiment. JB Weld is, I believe, metal filled, and may have good thermal conductivity. Epoxy in general seems to have good heat resistance, so maybe it'd work.

Could you drop the aluminum mold (still clamped together) into a bowl of ice water? That'll pull the heat out of the aluminum pretty rapidly, probably faster than any other mold material (given you're unlikely to use pure copper or silver).
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TimWescott
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« Reply #24 on: April 08, 2011, 10:42:57 PM »

Could you drop the aluminum mold (still clamped together) into a bowl of ice water? That'll pull the heat out of the aluminum pretty rapidly, probably faster than any other mold material (given you're unlikely to use pure copper or silver).

If one were going to do this on a production basis it may make sense to do so. Since I'm only doing onesies (well, threesies, since it's a trike) the delay isn't that bad. I'm thinking of making up a gang-mold to make more than one at once.
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