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Old Jun 28, 2014, 02:16 AM
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Åtvidaberg, Sweden
Joined Jul 2008
207 Posts
Build Log
JA 37 Viggen Dual propp

I have a long time thought about making a Viggen. The thing that made me not to is that it has a quite complicated form. But since I saw David on FlightTest make it a got it on my mind again and gave it a go. I am not a fan of ducted fans so has to be a pusher. So after fiddling with AutoCAD and so I began to cut it out. I changed things on the way since I haven't made this type of fuselage before. I also didn't want to make to much changes from the original in terms of wing placement and other stuff.

It is not finished yet and the retractable gear is a bi&"# to get right. I have never used a retract before so that's probably the rote to the problem though.

I used bluecore type of foam but it should be sufficient to use normal white foam, and it is lighter and since it supposed to be covered with fiberglass it will be strong enough. The reason I choose bluecore is that I wanted to check the strength with just that material if not covered. I would say that it is not sufficient because of the sections every 50 mm.
The wing profile is kf4 since the wing is so thin and to cut a wing from a block of foam with delta shape is not a trivial task.

I will use two 3300 kv motors and 6x4 propellers. Optimal would be if one was counter rotating but it will probably not matter much.

Will it fly? Probably but if it flies good or not is the real question...

Finally I got to add the plans for it and they are quite large since the model is large. That's why I opted for Cartesian coordinates for the wing. It is quicker to print out a small copy of the wing and measure plot out those coordinates.
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Last edited by Pukin_Dog; Jul 07, 2014 at 08:06 AM. Reason: Added information.
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Old Jun 28, 2014, 01:28 PM
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Pollock Pines, CA
Joined Aug 2002
1,615 Posts
Nicely done, Pukin Dog.

Dennis
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Old Jul 01, 2014, 08:57 PM
Registered User
Åtvidaberg, Sweden
Joined Jul 2008
207 Posts
I have now more or less finished the build. Have to program the Tx and preferably make sure that the retracts works as supposed.

Due to tests with build material and other changes it got way heavier than it will be normally but then again, it will probably be stable in wind and fly more scale like.
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Old Jul 02, 2014, 09:13 AM
"Experimental"
Scott594's Avatar
United States, NY, Elbridge
Joined Feb 2013
181 Posts
Nice.
Well diciplined, getting the pictures. I always seem to get on a "building roll" and they get forgotten.
They always seem to get heavier as you go. Any ideas you get along the way invariably involve ADDING goodies, not removing them. For me anyway, it's usually about 30% more than all the parts should weigh. Wire, glue and good ideas are heavy. Tape even.

New materials are always a crapshoot. I just got burned by Beacon Foam finish. I'm not sure if it's a bad product, or if I got a jar that was frozen or someting, but it NEVER hardens. At least not enough to sand. Elmers glue consistiency, just rolls off.

Anyway, good job on a complex build. Can't wait to see it finished. The beauty of props over fans is low end grunt, making the weight less critical.

PS - Cats are huge advantage when scratch building, especially when you have a nice crisp sheet of foam bridging something. They always stess test it for you, just to make sure it's a good one. If it's not strong enough for a catwalk, you sure don't want it in a plane.
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Last edited by Scott594; Jul 02, 2014 at 09:23 AM.
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Old Jul 02, 2014, 09:36 AM
Do it Right, the first time!
CoolerByTheLake's Avatar
United States, MN, Hermantown
Joined Dec 2008
5,623 Posts
You can't go wrong with this!
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Old Jul 02, 2014, 09:46 AM
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Åtvidaberg, Sweden
Joined Jul 2008
207 Posts
Yes you're right about adding things. It's so easy to sit at the computer and try to get the stresses that will accour when flying but when the stuff if built and you can feel where it flexes it's a totally different thing. It will then be heavier from adding strength.

Cat's are essential to get a good build. I have one that performs a hardness test on all the Depron sheets, with her claws. So I'm confident that it is good material every single time.
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Old Jul 02, 2014, 09:49 AM
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Åtvidaberg, Sweden
Joined Jul 2008
207 Posts
Quote:
Originally Posted by CoolerByTheLake View Post
You can't go wrong with this!
I assume that is PU glue. I use PU glue to but not for everything. I should have though. Especially if the fuse is not supposed to be covered with fiber glass.
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Old Jul 03, 2014, 09:15 PM
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just got burned by Beacon Foam finish. I'm not sure if it's a bad product, or if I got a jar that was frozen or someting, but it NEVER hardens. At least not enough to sand. Elmers glue consistiency, just rolls off.
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Old Jul 07, 2014, 07:57 AM
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Åtvidaberg, Sweden
Joined Jul 2008
207 Posts
Added drawings.
I tried to compress the parts as much as possible without making it to cluttered.
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