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Author Topic: My Couper "S" traditional/hitech build  (Read 4912 times)
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crashcaley
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« Reply #75 on: February 18, 2011, 06:58:19 PM »

Thanks Derek. 7mm Organza Ribbon from Michaels. Is this something like what the plan called for? I tried Wikipedia to tell me what it was, and originally it was a silk type product, though nowadays mostly make from synthetics.

BTW, how did the weight come out on yours? I figure that the way I build, mine will probably come out at least 10 grams heavier. I never can build light.

Caley
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crashcaley
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« Reply #76 on: February 18, 2011, 07:26:58 PM »

Not sure this is smart, but I'd rather like to make the fuselage just 3/4 square so that I can use the readily available screw post Pegs like I have in my Candy. I think that would allow me to use a winding tray and those hooked bobbins when I can afford those.

 For the nose setup, I guess what is on the plan is ok. For a stop I can do what I've seen others do, by drilling a hole, inserting an aluminum tube there for extra firmness, and then using a wire to keep the prop in place, then remove the wire when ready for launch.

I'm curious about the placement of the tail boom. Is this model designed so that the tail must be located at the bottom of the box fuselage, or could it be place dead center in a tapered setup that can be removed using another of those screw post? The post could just be an aluminum book binding post as you don't need a hole in that.

Caley
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« Reply #77 on: February 18, 2011, 09:51:25 PM »

Here's another thought I've gotten. Mentioned in the thread was doping the inside of the fuselage tube. This is after it has been assembled. Could you not dope the sheeting prior to assembly? Since I've never done this kind of thing, would the dope interfere with the gluing together of the parts? Just thought it would be easier to dope things properly, versus having to reach inside with a brush and possibly miss areas.

Caley
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« Reply #78 on: February 18, 2011, 11:46:38 PM »

Here's another thought I've gotten. Mentioned in the thread was doping the inside of the fuselage tube. This is after it has been assembled. Could you not dope the sheeting prior to assembly? Since I've never done this kind of thing, would the dope interfere with the gluing together of the parts? Just thought it would be easier to dope things properly, versus having to reach inside with a brush and possibly miss areas.

Think of a bottle brush... Now think of making one out of a coat hanger (bent straight) Make a loop on one end to hold a wad of cotton. Put newspaper on the floor. Put a can of dope(open) in the center of the newspaper. Suspend the rolled tube (vertically) above the dope can (centered on the can) Install the home made bottle brush THRU THE ROLLED TUBE WITH THE COTTON WAD HANGING OUT THE BOTTOM. Dip the cotton in the dope and pull the bottle brush thru the tube (one time). Hold the doped tube over the newspaper until the dripping stops.

A shotgun cleaning rod will also work fine..only problem is the cost of one cotton bore cleaner/swab which cannot be used for shotgun cleaning any longer Roll Eyes

Bob
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crashcaley
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« Reply #79 on: February 18, 2011, 11:58:17 PM »

Bob, Thanks, I guess I should have said square fuselage, and not tube. I've given up for now, trying to roll a round tube fuselage, as I couldn't keep the knife from wandering, regardless of how careful I tried to cut along the straight edge. As I learn about Coupes, maybe I'll eventually develop skills for rolled balsa tubes, working with fiberglass and carbon fiber, etc.

Caley
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DerekMc
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« Reply #80 on: February 19, 2011, 12:02:37 AM »

Bob's technique will work great on the Couper S square motortube. Just do it before you install the tailboom.
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Derek
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« Reply #81 on: February 19, 2011, 12:31:00 AM »

Thanks Derek. 7mm Organza Ribbon from Michaels. Is this something like what the plan called for?

Yes, and it does work. I couldn't find the chiffon dressmakers ribbon here in the US. I think I talked with the designer about the properties and found something that would achieve similar results. The ribbon adds significant strength to the motor tube.
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Derek
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« Reply #82 on: February 19, 2011, 12:20:59 PM »

Some thoughts cross my mind.

I do not think that the way of making indoor motor tubes (cutting to width after rolling the tube) is necessarily the way to make outdoor tubes. I am not a great fan of tubes but I did once make a coupe with a motor tube made from 1/64 ply. I cut the rectangular blank to the correct width to form the circumference of the tube I wanted. If you don’t trust your calculation of the circumference you can easily check by rolling a scrap bit of the material you intend to use. The blank was soaked and rolled on a mandrel in the usual way except that I was not too concerned about an exact fit. I cut two squares of 1/16 ply and made a hole in the middle of the same diameter as the outside of the tube. The tube was slid a few inches off the mandrel and the two 1/16 ply pieces were slid over the outside of the tube which maintained the circularity of the tube and pressed the joint edges together ready for gluing. This procedure was repeated until the whole joint was glued.

This tube was 3/4 inch inside diameter and a well wound Coupe motor would jam on the inside – I don’t think that a 3/4 square fuselage has enough cross section for a Coupe.

I am also not a fan of sheet fuselages for rubber models. In general they are either too weak or too heavy. Consider that a conventional Coupe fuselage will have four longerons of 3/32 square. Being generous add another four strips for the spacers. Now the cross section of eight strips of 3/32 square is the same as a sheet of 1/32 that is 2.25 inches wide, barely enough for two fuselage sides. And of course 1/32 sheet is not really good enough but if you go to 1/16 sheet you can only make one fuselage side for the same volume of wood!

John
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crashcaley
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« Reply #83 on: February 19, 2011, 04:38:01 PM »

Hi John, The making of balsa tube fuselages is one of those difficult skills for me. I found it easier to create a fiberglass/epoxy tube a while back. I may try that to see if I can improve on my first attempt. My first attempt was to make a blast tube for my Gollywock, and it has worked well for that purpose.

I decided not to shrink the fuselage size for my Coupers. I am making three. I'll just go with the standard aluminum tube rear motor peg. But I am still going to try, on at least one, to make the tail boom removeable. I may also try to make a two piece wing using CF tubes like I have in my Candy, with metal pins in the rear. Of course that will require four of the ribs to be at least doubled with a sheet of 1/64, probably 1/32 ply.

Caley
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« Reply #84 on: February 20, 2011, 01:02:59 PM »

I just added a possible solution for those with "Wanderlust" cutting problems (Caley Roll Eyes). It's HERE and should be usable for anyone.
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crashcaley
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« Reply #85 on: February 20, 2011, 01:14:40 PM »

Pete, That's something like I was thinking. Your little tutorial definitely will help those of us who don't have rock steady hands and a grip like a vise.

I continue to putter away with the square built up type fuse for my Couper. Almost have the sides done for all three copies.

Caley
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crashcaley
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« Reply #86 on: February 22, 2011, 07:51:33 PM »

On my sixth try, I finally got a semblance of a fuselage. Yup, took me six tries. For some odd reason, it's been a bad month for me when it comes to building, but I struggle on.  Embarrassed I finally gave up on trying to do what Derek did, using 1/16 sheets between the longerons. I went with 3/32 all the way around, and of course, that ballooned the weight. With 1/64 ply on nose and for support on rear motor peg, and with that peg, 8.8 grams. I searched high and low yesterday for that ribbon that Derek mentioned, but my craftshops didn't carry it. Not sure what to use. Guess I could just use 6/10 ounce fiberglass and do the whole outside of the tube. That should make it bulletproof. Guess that is the plan. Then I'll make up the noseblock and tail block. Tail block will hold the carbon fiber tube I'll order next month. In the interim, I'll also start cutting ribs, though they will be of A grain balsa, since that's all I have, though maybe I could substitute 1/32 C grain and just space the central panel ribs closer together.

No pictures from now on. I thought I got pictures at the Ike, but found my camera has given up the ghost.

Caley
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« Reply #87 on: February 22, 2011, 07:58:50 PM »

Why cover the motor tube in anything if it's that solid?

Use some light glass round the nose, and maybe a band of colour to disguise (on the glass), then clear finish the rest of the tube.

Just a thought
John
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DerekMc
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« Reply #88 on: February 22, 2011, 11:42:09 PM »

Caley, bummer that the fuselage is giving you trouble. I used a piece of aluminum angle to keep everything square. I lined it with wax paper then put the 3/32" stringer in the corner. I butted the 1/16" sheet to the stringer and applied glue, one on each face of the angle. You end up with an L shape with the sheet flush with the stringer. Once the glue was dry I removed the half fuselage and placed the next stringer. I glued the previous L shaped part to the stringer and added the next sheet side to the other face of the angle and glued. You end up with a U shape. By placing the stringer in the corner of the angle and gluing the sides to it you end up with everything nice an square and smooth at the the end.

Reply #18 has a picture of the aluminum angle I used to align the stringers and sides. It also shows how I used it to make sure the tailboom was glued on accurately.
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crashcaley
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« Reply #89 on: February 23, 2011, 09:46:08 AM »

Derek, I use a magnetic building board that has 1/4 inch graduations etched on it, so I get things pretty straight. I've just been having problems building the past month or so. It's not just making fuselages. I can't even cover properly right now. I'll just keep plugging away. Maybe the gremlins will go away.

Caley
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crashcaley
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« Reply #90 on: February 24, 2011, 07:43:59 PM »

I didn't find what Derek found when it comes to that super light weight ribbon, but I managed to find 3/4 wide transparent, sheer stuff at Wally World. So it will be wrapped with a bit more material than called for, but probably lighter than if I used fiberglass, and more than likely just as strong.

Caley
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« Reply #91 on: March 03, 2011, 09:08:06 AM »

A note for Coupe builders in the UK the Aviasport Skinny UL tubes will no longer be available from The Highwaymen. He will have stock in about a month of a SkyShark product to replace it but I cannot help in terms of quality. They believe it to be better and about 1 gram heavier. Anyone tried it?

Martin
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« Reply #92 on: June 10, 2019, 08:48:04 PM »

Looks like I'm going to build a Couper "S" soon. A local mentor is trying to give someone and easy way in to a really nice flying model so he made some rib sets and did some other stuff to give the builder a head start. I just need to go pick it up and get to work. Smiley
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