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Author Topic: Squarecoupe Build  (Read 2573 times)
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TimWescott
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« Reply #25 on: April 08, 2011, 11:08:08 PM »

I don't think it expanded as much as it could have -- I was really hoping that it'd grow all the way out to the edges of the mold in the "tire" area. This was baked for 20 minutes -- I think I'm going to try for an hour, see what happens.
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« Reply #26 on: April 08, 2011, 11:56:32 PM »

I would expect to be able to compression mold Depron, but I wasn't aware that you could make it expand very much. Might require some experimentation I suppose.

Tony
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TimWescott
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« Reply #27 on: April 09, 2011, 12:01:35 AM »

I cut some random shapes out of 3mm depron and tossed them into a 150 degree oven. They came out about 5mm thick, and puffy around the edges. So they definitely expand in thickness.

I was assuming that they were also expanding in width, but it could be that the outer 'skin' is shrinking (ala ShrinkyDinks). So far I really don't think I've gotten the foam inside the mold that hot, though.
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TimWescott
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« Reply #28 on: April 09, 2011, 02:33:18 PM »

Wheel, take three. On a scale with a 100mg resolution, the weight shows an 100mg -- so it's presumably somewhere between 50 and 150mg. Not too shabby, I think! Now if I can paint the thing without messing it up, I'll be doing well.

The first try was with 6mm Depron (the wheel in this case is a hair under 5mm thick), with the oven at 150 degrees. I used 150, because that's what I recalled as being called out, and because when I tossed my sample bits into the oven at that temperature they puffed up nicely. I got a wheel that appeared to have taken a set where it was squeezed, but that didn't appear to have puffed up into the mold the way I wanted to.

Second try was with 3mm Depron, in the same oven. Definitely no puffing.

Third try is shown. 6mm Depron, purposely cut to be right up to 3/4" diameter. I glued on 1/64" hubs, because I don't think the foam is going to stand up. Put it in the oven at 150 degrees initially, along with the second try wheel on some tin foil. After thirty minutes the second try wheel hadn't puffed up, so I turned the oven up to 200 degrees, let it go for 20 minutes. When I checked, the 2nd-try wheel had shriveled up to the poor remnant that you see in the picture, so I took everything out. When things were cool enough to touch, the wheel came out as shown.

I think that what happened is that the wheel that was out in the open overheated because of radiant heating from the oven as it was going up to 200 degrees -- I suspect that had I put the thing into an already-warm oven it wouldn't have shriveled up. At any rate, the wheel I made is definitely a keeper, and ready for paint.

It's hard to tell from the pictures, but the wheel looks a lot like the wheels that came in the old Comet kits, except that its weight is consistent with being made out of foam instead of hardwood. So I think I have a process that's a keeper.

The second picture shows the motivation for this whole effort: those are wheels that I made for a "Box Car" Bostonian by gluing a ring of 2mm Depron to a 2mm Depron disk. The plans called out 1" Fulton Hungerford wheels: I neither wanted to spend the money for them, nor wait for them to show up. So I made my own. But I was unhappy with the roundness and overall impression of the wheel -- I wanted something that would look like a covered wire wheel from the 1910's or '20's, such as you might see on a WW I fighter or a civilian aircraft from before the "balloon tire" era. That's when I conceived of this molding idea -- and I can't wait to try it out on such wheels!
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RolandD6
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« Reply #29 on: April 09, 2011, 07:29:27 PM »

...I wanted something that would look like a covered wire wheel from the 1910's or '20's, such as you might see on a WW I fighter or a civilian aircraft from before the "balloon tire" era. That's when I conceived of this molding idea -- and I can't wait to try it out on such wheels!

Very interesting work Tim. I too will be interested in seeing how well the molding process works with covered wire wheels. Wheels with metal disk covers should not be difficult, judging by your results so far; but fabric covers may take a little longer. Undecided

My planned approach to that type of wheel is bamboo hub, silk thread spokes, balsa rim and foam tyre, much more long winded than molded wheels and possibly not any lighter in weight. I have made foam balloon tyre wheels by turning blue foam, and then painting tyres and rims while the wheel was still mounted on the lathe. The hub was represented by a printed disk of paper. The actual wheel bearing was a short piece of plastic tube used to extend the nozzle of an aerosol can.

Provided one has determined standard wheel sizes beforehand (because of the need to make aluminium molds), your method may result in consistent and lighter wheels. I found the wastage rate a bit high when trying to get matching pairs of wheels, even when using a form tool. Foam seems to be less forgiving than wood. A blunt turning tool on wood doesn't do much damage (remembered from my large scale wood turning efforts) whereas a blunt tool can tear chunks out of plastic foam.

Getting back to your aluminium mold, did you hollow out the mold free hand, using a form tool, or by using a radius turning tool?

Looking forward to a successful conclusion to your experiments Cheesy

Paul
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TimWescott
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« Reply #30 on: April 09, 2011, 07:49:02 PM »

Very interesting work Tim. I too will be interested in seeing how well the molding process works with covered wire wheels. Wheels with metal disk covers should not be difficult, judging by your results so far; but fabric covers may take a little longer. Undecided

My planned approach to that type of wheel is bamboo hub, silk thread spokes, balsa rim and foam tyre, much more long winded than molded wheels and possibly not any lighter in weight.

But a lot of work if you're just going to cover up all those nice spokes. Obviously this isn't going to replace hand-laced wheels when you need to have the spokes showing -- but I'm just too lazy to go and make up such an intricate wheel by hand, then cover it.

I hadn't even considered the surface texture; I think I'll leave it to others to figure out how to complete that leap.
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I have made foam balloon tyre wheels by turning blue foam, and then painting tyres and rims while the wheel was still mounted on the lathe. The hub was represented by a printed disk of paper. The actual wheel bearing was a short piece of plastic tube used to extend the nozzle of an aerosol can.

Provided one has determined standard wheel sizes beforehand (because of the need to make aluminium molds), your method may result in consistent and lighter wheels. I found the wastage rate a bit high when trying to get matching pairs of wheels, even when using a form tool. Foam seems to be less forgiving than wood. A blunt turning tool on wood doesn't do much damage (remembered from my large scale wood turning efforts) whereas a blunt tool can tear chunks out of plastic foam.

Getting back to your aluminium mold, did you hollow out the mold free hand, using a form tool, or by using a radius turning tool?

I made a 1/8" radius tool (1/4" diameter) for the tire area, and cut the rest with a facing tool that I relieved a bit extra for clearance going into the conical depression of the hub. I'm thinking that I want to make some form tools for this, as it should be an easier way to make multiple mold cavities, easier to see the profile I'm setting out to make, and easier to get both sides of the wheel identical.
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TimWescott
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« Reply #31 on: April 09, 2011, 11:27:24 PM »

Tale -o- the tape. Three wheels, 0.3 grams on the scale. Now, granted, the scale only resolves 0.1 grams, so I couldn't swear that the wheels are exactly 100mg each. But they're pretty light. For comparison, a pair of wheels from a Sleek-Streak or the Guillow's equivalent (7/8" diameter) weighed in at 1.2 grams, or 600mg each. Unless I get paint with the special depleted uranium pigment, I don't think I'll pork the wheels up that much.
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TimWescott
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« Reply #32 on: April 15, 2011, 04:12:39 PM »

OK, I am going overboard on the machined parts. But it's fun!

Here's the prop and prop bearing. The prop is my best guess at a prop with interchangeable blades -- that's about 9/16" worth of 3/32" ID aluminum tube, with bamboo skewers glued into blades sliced out of a styrofoam coffee cup. I can experiment with different prop blades, which is good since I'm a beginner!

The prop bearing is three pieces: a piece of 3/16" ID phenolic tube, and two end pieces of plastic (I'm not sure what it is -- it's from a retired cutting board). The end pieces are machined into a 'T' cross section to plug into the tubes, and the axle holes are drilled about .05" off center. In the picture, the angle is about the maximum that can be dialed in -- you can get anywhere from no offset to that much, pointed in any direction you want. I've put wrench flats on the end pieces, so I should be able to adjust my thrust angle without upsetting the nose block -- which was what I was trying to achieve. The bearing tube could easily be aluminum; I thought the phenolic would be lighter -- and it smells like old radios when you cut it, so that's cool.
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« Reply #33 on: April 15, 2011, 04:29:11 PM »

Tale -o- the tape. Three wheels, 0.3 grams on the scale. Now, granted, the scale only resolves 0.1 grams, so I couldn't swear that the wheels are exactly 100mg each. But they're pretty light. For comparison, a pair of wheels from a Sleek-Streak or the Guillow's equivalent (7/8" diameter) weighed in at 1.2 grams, or 600mg each. Unless I get paint with the special depleted uranium pigment, I don't think I'll pork the wheels up that much.

How did you make the wheels?
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TimWescott
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« Reply #34 on: April 15, 2011, 05:07:13 PM »

How did you make the wheels?

See replies number 25 and 28, in page 1 of the thread, or get on page 1 and use your browser to search for "wheel" or "depron".

Short story: 6mm Depron, compressed between aluminum mold halves, and heated in the oven until everything is set.
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TimWescott
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« Reply #35 on: April 15, 2011, 05:13:41 PM »

When you read about taking pictures, you are advised that every picture should tell some intended story, or should be "about" something.

This picture was supposed to be about the fact that the Squarecoupe is ready for covering (except that I need to put in the motor peg!!) and that it weighs 7.3 grams so far (except for that motor peg...).

But I think maybe it's really about order rising from chaos, or about how I should be cleaning my bench, or something like that.
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« Reply #36 on: April 15, 2011, 07:15:35 PM »

Hmmm. The only thing I see in that image is the uncovered structure of a cool looking Bostonian...
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« Reply #37 on: April 28, 2011, 04:44:48 PM »

I've been distracted -- something to do with an attempt to fly the control line stunt pattern with a poorly running engine and severe allergies, resulting in an outside loop whose bottom was trying to be six inches below the pavement. But I've gotten some work done.

I'm gonna run out of paper before I run out of plane, I think, but here's my paper, stretched on a frame and shrunk, ready to go.

The yellow square in the background is an experiment that wasted a bunch of paper (probably enough to finish the model). Going by directions I found on the web, I shrunk it by covering it with ink. I think I used the wrong ink -- it was too much like paint, which both doubled the weight of the paper and held wrinkles into it while it dried. Oh well.

I should think about which surfaces would be best covered with Esaki.
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Olbill
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« Reply #38 on: April 29, 2011, 10:53:17 AM »

When you read about taking pictures, you are advised that every picture should tell some intended story, or should be "about" something.

This picture was supposed to be about the fact that the Squarecoupe is ready for covering (except that I need to put in the motor peg!!) and that it weighs 7.3 grams so far (except for that motor peg...).

But I think maybe it's really about order rising from chaos, or about how I should be cleaning my bench, or something like that.

At first I thought you had somehow gotten a picture of my workbench! Mine is so messy that I'm paralyzed at the thought of cleaning it so I can get some building done.
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TimWescott
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« Reply #39 on: April 29, 2011, 12:42:23 PM »

At first I thought you had somehow gotten a picture of my workbench! Mine is so messy that I'm paralyzed at the thought of cleaning it so I can get some building done.

Man, I know how that works. It took coaching my kids in cleaning to figure out the worst-case method: Pick one thing up, at random. Put it away. Repeat. Of course, this is hard when part of the mess is some hobby shop haul that doesn't have an 'away' to be put to yet. It's also hard when you have a big pile of disks and oblongs from lightening holes that are big enough to be useful "somewhere", but plentiful enough that you know if you keep them all they'll be running out of your ears.
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TimWescott
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« Reply #40 on: April 29, 2011, 09:42:50 PM »

8.9gm, with everything covered but no windows, and a representative aluminum tube for the motor peg. That tube weighs 0.5gm!!! I need something lighter -- someone suggested using the tube from a spray bottle; perhaps that'll work, but I'm open to suggestions.

So, if I can't do something about that dang tube, less than 9.5gm all up. Maybe close to 9gm if I can. Given that I started this thinking I'd be quite happy to hit 10gm I guess I'm feeling pretty good.
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« Reply #41 on: April 29, 2011, 10:01:32 PM »

A piece of carbon tube would likely weigh significantly less than the aluminum (especially if you can get the carbon with a thin wall). Costs more, but a 50 cm piece of carbon is still enough for a dozen or more motor pegs.

Of course, if you own a lathe (or have access to one), it's actually possible to drill a hole the long way through a 3/32" dowel or 3 mm bamboo skewer. That'd be lighter than aluminum, maybe even lighter than carbon (which is far stronger than it needs to be). It can even be done with a drill motor, solidly mounted, though it's harder (drill motor chucks aren't very carefully checked for runout).
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« Reply #42 on: April 29, 2011, 10:02:13 PM »

Tim,

I couldn't resist building myself and this looks like a practical way to get an Ercoupe to fly. I've finished the rudders and stab and the two fuselage sides. I made my longerons a bit further apart at the nose for more room. I think I'll make the top canopy round from the front too. That may cut down the box needed for it to be a true Bostonian but I don't care about that.

Yours looks great by the way! I'm flying in the Tustin Blimp Hanger (Southern California) this May 15th so it should be a simple enough build to finish it by then. I'll post some photos when I'm further along.

Thanks for drawing the plans too! How about square versions of other airplanes? A Luscombe Silvare? A nice way to make a complicated airplane simple enough to make a good free flight model.

Tom
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« Reply #43 on: April 29, 2011, 10:16:55 PM »

Tim,
I just weighed 12" lengths of 3/32" and 1/8" aluminum tubing. The 3/32 stuff weighs 1.91g. The 1/8 weighs 2.46g!

What size tubing do you have there as a 'representative' piece? I have plans for 7g bostonians calling for 3/32" tubing for the peg. A 1.5" length of 3/32 tubing will weigh less than a quarter of a gram.

Dave Andreski
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« Reply #44 on: April 29, 2011, 10:50:56 PM »

Tom:

You scare me! Those were untested plans, and not complete, either. Have you gotten to the part where you wish the formers were lofted? If not, let me know and maybe I'll flog the old CAD program and try to get them in there and posted. I'll even do them right, as opposed to what I've done on mine.

And please do post pictures! Not just because it's neat to see my plans being used, but because if you've done a better job at some detail than I have, I'd like to incorporate it into the final version of the plans.

Case in point: I really like the idea of rounding off the canopy. You caused me a "wow" moment -- even with a round canopy, the "Bostonian Box" is still there inside the fuselage. I hadn't realized that until I had written "of course, it won't be legal for Bostonian" -- but it will! It will! I had constructed the thing out of a box 1.5" long, 2.5" wide, and 3" tall, and the corners of that box dictated the square corners of the canopy. But as long as you keep the thing 2.5" wide through the wings, you'll have a box that's 3" long, 2.5" wide, and well over 1.5" tall.

This is actually really cool. It's not too late for me to break the canopy structure off (it's not doing anything) and replace it with like-sized hoops. I think I will -- it'll look a lot better that way, even if I'll have to interrupt the build process to bend up the hoops. By chance, the canopy is exactly 1/2 as tall as it is high, so a 1.25" radius hoop will fit perfectly. I'd suggest putting a single member along the middle top of the canopy, to match the hinge line in the original.

This does, however, leave me with a dilemma: I can't call it the "Squarecoupe" any more. "Bentwood Bostonian" would be more accurate, given that some engineer seemed to specify the stuff with abandon. This is bad, because I really liked the play on the name "Ercoupe". Dang. The worst part is that I'm not terribly good with names, and I've already named an airplane "Fred".

So if anyone's reading, and has a suggestion -- "Squarecoupe" is out (sob!), and "Bentwood Bostonian" is the current strawman name for this critter. Feel free to suggest something you think is better, or even something that has hopes of being so, but is somehow clunky.

Dave:

I've got maybe a 1-1/4" length of 1/8" tube, which doesn't quite work out -- except that my scale's resolution is only 100mg, so it could be less than 0.5gm. It needs a peg longer than 1.5" -- because the thing is wider than your usual Bostonian the fuse at the motor peg (I'm putting the peg about an inch ahead of the stab leading edge) the tube needs to be at least 1.75". That's still only a hair more than 1/4 gm -- but I'm still begrudging about spending 1/4 of a gram on the motor peg!!
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« Reply #45 on: April 30, 2011, 03:15:50 AM »

Tim,

Your plans are fine to build from. You'll probably make changes after flying too. I'll also make all the formers rounded. I should start putting the sides together tomorrow and then laminate the canopy rounds. Cool to know it will still be a Bostonian! I'll have enough for photos in a few days especially when the fuselage is almost done.

How about the "Barecoupe" for simplicity? I think the Squarecoupe is still fine though because most of it is still square.

It looks like yours will be ready to fly soon? I'm thinking washout in both wings 3 degrees of incidence in the stab and the opposite amount of downthrust. I usually take the nose block and prop out and add clay till it glides good then mark the CG and put the nose and prop back on and re balance.

Thanks for starting the fun!

Tom
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« Reply #46 on: April 30, 2011, 06:16:56 AM »

I just weighed a 1.5" alu peg of mine that I use for my Mustang (with two loops of 3/16th) at 0.37 grams (it's 4mm/-5/32nd- with a 0.5mm wall) that I recently swapped out for a 3mm one that  weighs only 0.27 grams.  Both were weighed with the end "keepers".  Try to find the thin wall stuff, as one 3mm tube that was bought for me was heavy-wall - I gave it away.
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« Reply #47 on: April 30, 2011, 11:31:09 AM »

Tim,
How about the "Barecoupe" for simplicity? I think the Squarecoupe is still fine though because most of it is still square.

It looks like yours will be ready to fly soon? I'm thinking washout in both wings 3 degrees of incidence in the stab and the opposite amount of downthrust. I usually take the nose block and prop out and add clay till it glides good then mark the CG and put the nose and prop back on and re balance.

I suppose I could still call it the "Squarecoupe". I'll think about that.

I'm sorta copying moments and incidence angles from the "Box Car" Bostonian, which was 0-0, no washout, but considerable down and right thrust. That's for indoor flying, though -- if you want a "power climb then glide" sort of pattern you may need to get fancier.
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« Reply #48 on: May 02, 2011, 03:07:21 AM »

I just took advantage of a dry night with still air for a test glide. Dang but that thing wants to point the nose down and go fast! And that's with the CG at about 50% of the wing chord.

So a little bit of incidence may be a good thing, after all.
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« Reply #49 on: May 02, 2011, 02:16:37 PM »

Yes! Incidence is always necessary at least in my experience. Great you got the chance to take it out for some tests.

Here's some photos of my fuselage and tails. I have to build the wing then add the nose block, landing gear, wheels, prop etc.

Tom
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