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Old May 03, 2014, 07:41 PM
More coffee, please!
sir_clive's Avatar
Austria, Wien, Vienna
Joined Jul 2011
658 Posts
Build Log
SBach 342 - own plans (call for comments)

Dear friends,

after building 5 planes to the plans (most of them found here on RCGroups), I am about to test what I learned in the process and to produce a set of my own plans.

I chose to build a gorgeous SBach-342, downloaded two silhouettes (as seen from the side and from above) from the vendor's home page, brushed up my "Blender" knowledge and started with design. I am sure the good designers can do without this first step in 3D, but for me, it was a great help for visualizing what I'm actually doing.

Please find attached a few screenshots showing my current progress. Also attached is a 3D Blender model of the plane.

The wing span will be 1m, the motor probably the EMax-2215/09 (70g, 300 Watt) that I already have in my drawer. The power will be supplied by a 2200mAh LIPO @ 3s.

The main wing will be the E168 profile. For the stabilizer (both horizontal and vertical) I aim at NACA0008. I guess a "flat" stabilizer would do just as well, correct? The NACA0008 will look prettier though.

I think the most of the plane can be built from balsa, with some plywood for the motor mount, front-most former, and *maybe* the "cockpit cage" (if that's what the rectangular-shaped box on the front of the plane is called) - I'm not sure however if that couldn't also be built from a harder 3-4mm balsa. I'm not a great fan of plywood.

Currently, I'm thinking of covering the front portion of the fuselage with 1mm balsa and a covering film, the rear portion just with a covering film. Would you say it would be better to also cover the upper portion of the rear part with 1mm balsa before applying the film? I think that might give it more torsional stability and help against deformations due to my sub-perfect applying of the covering film.

I'd be happy to hear your comments! There still are a few things open, but I think I'm pretty much ready to transfer the 3D drawing into 2D cutting plans. I feel like cutting some balsa now, I don't want to spend another month polishing the plans.


Best regards,

Sir Clive.
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Old May 04, 2014, 04:08 AM
More coffee, please!
sir_clive's Avatar
Austria, Wien, Vienna
Joined Jul 2011
658 Posts
Adjusted a few details, added elevator and rudder linkage, servos and a servo mount. It seems I will have to at least partially cover the upper portion of the rear part of the fuselage, so that the linkage has something to hold on when getting out of it.

I guess having the linkage on the outside would have quite a few plus points as far as the build is concerned, but on the inside, it will look nicer.
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Old May 04, 2014, 07:41 PM
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whiskykid's Avatar
United States, WA, Port Angeles
Joined Dec 2009
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yes turtle decks, are generally sheeted!
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Old Jul 27, 2014, 07:45 PM
More coffee, please!
sir_clive's Avatar
Austria, Wien, Vienna
Joined Jul 2011
658 Posts
Finally, I managed to find some time and to continue to work on my SBach 342.

In the meantime, I purchased a copy of DevWing - a very very nice program, although a bit unstable and "quirky" at moments. I'll be posting my wing definitions here as soon as they are finished - for the time being, I concentrate on the fuselage.

What I am pretty unsure about is whether I picked the wood (ply vs. balsa) and thickness correctly. The most will be balsa, at least that's the current plan, and it will be a 2mm balsa of a harder kind. 3 resp. 2mm ply will only be used for the motor mount, firewall and the front part of the fuselage. The turtledeck and the upper area of the fuselage front partition (say, "fore turtledeck" ) will be sheeted with 1 or 1.5mm balsa (please note, that the formers are not yet adjusted for the sheeting thickness!), and the entire fuselage will then be covered with covering film. Thanks for the sheeting tip whiskykid!

I hope to make a depron prototype tomorrow, just the "base" without any sheeting, to see whether all the parts fit correctly. I only have the 3mm depron, but it will be a good approximation for the 2mm parts I guess.

If somebody wants the CAD drawing, I'll be happy to provide it. A "letter / A4 paginated" PDF will be provided with the final plans.
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Old Aug 01, 2014, 01:34 PM
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United States, TX
Joined Jun 2011
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Wow, very nice.
Are you going to also be building a prototype?

1 mm balsa though...wow that's thin!
About the thinnest we yanks can get is 1/32" balsa, and what's that, about 0.80 mm?
Usually, the thinnest we can easily get is 1/16" for stringers, although 1/32" is available in sheet form.
I normally like to use 1/16" sheet for my balsa sheeting, just because it doesn't crack so easily and it's got a little bit more thickness for sanding around edges, etc. That's 1.6 mm thick, so for you, probably 2 mm sheet would work. But that's just a suggestion.

I don't have any way of pulling up the attachments on my computer, but the drawings look almost like foam wings and tail surfaces are used. Is that true? Or are they to be built-up out of balsa?
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Old Aug 03, 2014, 07:22 AM
More coffee, please!
sir_clive's Avatar
Austria, Wien, Vienna
Joined Jul 2011
658 Posts
Hello builderdude,

thank you!

I am planning to build a prototype from Depron but just to see whether all the parts fit together and not as a flying version.

I'll consider taking something thicker than 1mm for sheeting, thank you for pointing it out that it might be too thin. I opted for 1mm because on my Guppy build, 1mm sheets were used for the D-Box and for the tail assembly. I do have some 1.5mm balsa sheets around, that would be pretty much 1/16".

I am planning to do a built-up main wings with D-Box out of balsa, Eppler E168 profile. For the tail, I'd also like to do it "the right way", so no planks, but rather a sheeted NACA0008.

Now, if I could just find some time to continue working on it...
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