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Old Nov 25, 2008, 09:48 AM
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Bagged Supra, the light way

Decided to start this thread to show what I've done building bagged Supras so far and to start a couple new ones for F3J. Hope to put some effort showing how to build them light following the plans Dr. Drela has posted.

I don't intend to make a super detailed building thread like Nuevo did here great thread, you should read all if you have not done yet, thanks Jon for doing it. Also thanks to Dr. Drela for all the design along Tom Kiesling and Mike Lachowski, great guys always ready to answer our questions.

If you don't know yet I've build two bagged Supras so far. One was just the wing and tail feathers to good friend Tony Estep and you can see it here
The other one is this yellow/blue built following the plans using a Lachowski F3J pod and a Polecat tail boom. Have flown this plane for half season this year in many contests and you may not believe but I do have a serious advantage over any other plane (including moldies) in 10 mph or less wind days. Why? Well, the RTF weight is 51 oz (1,446 grams). Will post latter the detailed weights but you have to fly it to believe what a light plane can do for you. I can tell what it did for me. A win and two second places at my local club contest averaging 12 pilots, two third places, a fourth place and a LSF V win at the OVSS contests and 15th place at the Masters. These were actually all the contests I could fly the 51 oz Supra on every round and no I'm not this good of a pilot, this is a clear case were the plane is making the difference. That is the main reason to build more of them and share with you hoping more people also build their own.

Only shortfall of my current Supra is the ballast system. Can add ballast but wasn't a very detailed system and never spent any time to make it to work better so that is the goal of my new plane, carry weight and stand a hard F3J launch on 10 to 20 mph winds. Over that I'll plain use an F3B plane.

I'm in the process of ordering materials so will post a few pictures of the previous one, aka 51
By the way I've been living in America for many years but English is not my first language (was born in Brazil) so please ask me if you are confused or can't plain understand what I'm trying to say. Will add as many pictures as I can for that reason.
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Old Nov 25, 2008, 09:59 AM
F3X
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Looks like some nice work there!
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Old Nov 25, 2008, 11:37 AM
F3J, F3K and F5J eXtreme
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Very nice, I think I will lurk a lot on this thread.
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Old Nov 25, 2008, 12:08 PM
But I am learning
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Old Nov 25, 2008, 02:47 PM
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Have just ordered a couple of CNC foam cores from compufoamcore.com. I gave up cutting my own cores many years ago after I compared price and mainly quality of Les Horvath CNC cores to my work. Les' cores are a work of art and he is always friendly, good vendor and good way to start a project.

Well, let's talk about the only rule of building light planes with an example. Dr. Drela kindly added to the Supra plans weights for many individual parts. I'm assuming everyone knows how to get the plans from the charlesriverrc.org but if you don't please let me know. You can see the stab has a end grain balsa insert listed as 0.4 grams. Very first one of these inserts I build came to 0.7 after about half hour of work finding a light piece of balsa trimming and sanding it. So, would 0.3 grams make any difference flying the plane? Sure not. Would 10 times that make a difference? No, 3 grams would make no difference but then you add 1 gram here and 1 gram there and when you see you have a whole ounce more. More important yet at least for me is the psychological effect. It is easy to give up on been careful about weight if you get a few things over so watching and trying your best is the answer. I scraped that little balsa insert and started over with a new piece.
Many believe the weights posted by Dr. Drela are impossible to be achieved but that is not true, you just need to be careful. You will see here that you don't need to be obsessive or go to radical solutions, just follow the plans and get a 1/10th gram scale.

While I'm still waiting the parts for the new plane to arrive I'll post some pictures of the 51 construction starting by the stab and fin. I took a bunch of pictures so it is going to be a little more detailed.
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Old Nov 25, 2008, 04:17 PM
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Glauco,

This thread couldn't have come at a better time. I have 2 sets of Supra cores from Les plus two Kennedy Composite fuses and one from Mike L. I have everything needed to build two Supras except the 1.0 Kevlar. I plan on using 1.7 on the first one and 1.0 on the second one. I'm still looking for a good price on the 1.0 Kevlar; if that's possible.

The only thing I haven't worked out is the spar and joiner boxes. I know the build process, I just haven't worked out how I will mold in the dihedral, plus I want to use square wing joiners from the molded Supra so I can change the tip angle.

BTW, I'm using my table saw to square up my foam; I found a 10" metal disk that will accept self-adhessive 10" disk sandpaper. It works just like any other 10" disk sander. You can find them and Sears.

1 question about your full size planes; did you print them in tile or did you have them enlarged by Kinkos?

Thanks for another chance to learn even more about building a bagged Supra.

Jim
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Old Nov 25, 2008, 04:53 PM
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Quote:
Originally Posted by Catch-Air
Glauco,


The only thing I haven't worked out is the spar and joiner boxes. I know the build process, I just haven't worked out how I will mold in the dihedral, plus I want to use square wing joiners from the molded Supra so I can change the tip angle.


1 question about your full size planes; did you print them in tile or did you have them enlarged by Kinkos?

Jim
Hope we can build them together. I also would like to build this new batch with the molded Supra square joiners but I'm a bit afraid of changing the plans. Does anyone know of any problems using the square joiners instead of the 3/8" round ones?
Construction would be much easier without having to build those basswood joiner boxes.

For the stab and fin I just tiled them but for the wings it was enlarged of the supra_wing.pdf file. I work in a construction company and just asked the drafters to plot to full scale. Took them a couple of tries but the result was perfect.
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Old Nov 25, 2008, 06:59 PM
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There should be no problem using the square joiners. You just have to build the joiner box so it accepts the square shape instead of the round one . . .

Tom
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Old Nov 25, 2008, 07:01 PM
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I found a thread which showed an easy way to build the square joiner boxes using the joiner itself as a guide. But now I can't find the link; I'll post it here if I do.

Jim
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Old Nov 25, 2008, 08:17 PM
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Thanks Tom.
With the square joiner there is no basswood at the box. My plan is just wrapping the flat joiner with Kevlar to make a tube just like the round one. Since the molded Supra joiner has either 2.5 or 5 degrees bent on it, all that will be needed is to glue the Kevlar box to both carbon caps.

Also I understand if I build the wing with the proposed spar caps and carbon fabric per plans it should take a good F3J tow. I know from experience the wing will flex a lot with braided line and have launched it with an F3B winch but not pushing too hard. My plane has a carbon sock at the center panel but what would be the next step to cut the flex a bit without adding too much weight. A wider spar or a little more carbon caps top and bottom, say .007 or .014.

Glauco
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Old Nov 25, 2008, 09:00 PM
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Square joiners. "My plan is just wrapping the flat joiner with Kevlar to make a tube just like the round one"

That's what I did the first time I used rectangular joiners in a bagged wing (same as square joiners only different) and I had a tough time getting the Kevlar off of the joiners...I had made bent joiners (4 degrees).

The second time I laid up and flat bagged a few layers of Kevlar and carbon fabric then cut it up to build a joiner box that went between the spar caps, the same joiner box I used in the moulded wing I made. A bit more work for a bagged wing but well worth it in terms of fit, precision and bomb proofness.


T.D.
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Old Nov 25, 2008, 09:59 PM
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Hey Glauco,
I have a couple of rectangular joiners from an Eraser (the only things that survived). You can have them if you want. They don't have a lot of dihedral, and the dimensions wouldn't be exactly right for the Supra, but with a little machining they might work just fine....Let me know if you want them.
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Old Nov 25, 2008, 11:26 PM
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Quote:
Originally Posted by Glauco
My plane has a carbon sock at the center panel but what would be the next step to cut the flex a bit without adding too much weight. A wider spar or a little more carbon caps top and bottom, say .007 or .014.

Glauco
Wider caps would be the most efficient. Thicker works too. You could also go to higher modulus carbon.
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Old Nov 25, 2008, 11:53 PM
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Quote:
Originally Posted by Kiesling
Wider caps would be the most efficient. Thicker works too. You could also go to higher modulus carbon.
Comparison of increased width and increased thickness,

Current sparcap, 0.084 x 0.75
Stiffness = 1.000, Weight = 1.000

1.333 x width, 0.084 x 1.00
Stiffness = 1.333, Weight = 1.333

1.5x thickness, 0.126 x 0.75
Stiffness = 1.325, Weight = 1.500

2.0x thickness, 0.168 x 0.75
Stiffness = 1.556, Weight = 2.000

Increasing width is almost twice the bang for the weight buck (and real buck too, since carbon weight = $).

If you want an F3J-capable spar, I'd go with the 1" wide center spar. The ideal taper wants to be a bit more severe and nonlinear than the linear taper stock from ACP, so you might want to add additional 0.007" or 0.014" plies over the center half or so. That's where you get the most stiffness gain for every gram of carbon.

And of course high-modulus carbon is always theoretically better. But that has "issues" as Berrie discovered.
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Old Nov 26, 2008, 08:37 AM
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Thanks Mark and Tom, will go for a wider center spar. Would you suggest widening the tip spars too?
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