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Old May 10, 2013, 09:56 AM
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An Open source 32" Balsa + Foam slowflyer

Hey all, I've been working for about 2 years on an idea for what will one-day be my self-introduction into the world of composites. However, since that's expensive and time-consuming, I'm doing a prototype of the design first.

EVERYTHING from the tools to the plans is completely open-source - I didn't pay a single penny for any of the software, only the time it took to learn how to use it. All my hard work is being shared completely in the open to encourage, use, feedback and community modifications (as long as they're also shared).

Recently the first release of the prototype plans were pulbished plans on my build-log over here. The measurement details and internal components over here.

I thought I'd open up a discussion thread here, since I think it's a more appropriate place for wood-flying-thing discussion and for me to post pictures of my bumbling conversion of perfectly good wood into sawdust "lessons" .

Though I'm reserve the right to delete any naked criticisms (i.e. without "constructive" suggestions). Questions and positive feedback are always welcome!
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Old May 10, 2013, 10:01 AM
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razortoe's Avatar
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Clarification

The fuselage is built-up from wood, the wings and tail surfaces will be foam (for weight reasons). Though I'm sure balsa structures could be used there, I'd like to be able to throw away the wings and try a new set cheaply/quickly. Remember this is a design-prototype.
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Old May 10, 2013, 03:23 PM
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My only query, at this point, is why would you 'design' a model which already exists in umpteen different cosmetic variations? Is there some particular aim behind this, other than to learn to use CAD?

Pete
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Old May 11, 2013, 05:01 AM
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I had a quick look at your blog and it has prompted a couple more queries. What sort of wing loading are you expecting with this model? I see you mention a 17 ounce finished weight, which doesn't seem particularly light for what is supposed to be a slowflyer. I had an ARTF 60" glider (electric powered glider) that was only a little heavier than that. Given its' 480 brushed motor and not particularly small servos, combined with it being an ARTF, that hardly makes for a particularly lightweight model.
Since all this appears to be leading towards a composite model, is it purely an exercise in that, or an attempt to actually produce a workable slowflyer for others to build? Bearing in mind that this forum is really intended for balsa builds, wouldn't a conventionally built slowflyer be more in keeping?
Delete away to your heart's content, but I'm just trying to understand the motivation behind the project. Your mock-up looks more like a funfly style model than a slowflyer - lots of wing and short coupled with fairly large tail surfaces.

It looks an interesting project, but only if it leads to something worthwhile. Currently it isn't any different to many other models in appearance, isn't composite and isn't all balsa/ply. It doesn't seem to fit any particular criteria, in the usual sense.

Pete
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Old May 11, 2013, 06:39 AM
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Excellent questions, with answers, but none i care to type on my phone keyboard You are right in asking them, and i will answer shortly to clarify my goals/intent.
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Old May 11, 2013, 07:51 AM
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Q & a

Quote:
Originally Posted by PETERRAKE View Post
My only query, at this point, is why would you 'design' a model which already exists in umpteen different cosmetic variations?
More of a philosophical question, but I'd point out that most plane's are (more or less) variations of the successful models that came before them I'm not attempting something radical because what came before was successful. So, even if to you this is just a 'cosmetic variation', it's MY cosmetic variation Though I hesitate to say "mine", since so much community input has gone into the design already - hence the open-source bit.

Quote:
Originally Posted by PETERRAKE View Post
I had a quick look at your blog and it has prompted a couple more queries. What sort of wing loading are you expecting with this model?
This is in the details post here. Wing Loading: 20.0 gm/dm² = 6.55oz/ft²

Quote:
Originally Posted by PETERRAKE View Post
I see you mention a 17 ounce finished weight, which doesn't seem particularly light for what is supposed to be a slowflyer.
Call it a "learning" weight target - A realistic goal I can achieve without extraordinary effort, that should fly, and that I refine lighter on successive iterations. Target stall-speed is 20 Mph, if in reality it's lighter and slower, I'm not going to complain

Quote:
Originally Posted by PETERRAKE View Post
Since all this appears to be leading towards a composite model, is it purely an exercise in that, or an attempt to actually produce a workable slowflyer for others to build?
Both! My expectation is the composite version will be lighter than the balsa version, but I'd like both to be adequate for lazy flying in small-ish parks. Composite building is a very time/money intensive effort, so best work from something that already flys "well". It'll also give me something to do while I wait for epoxy to cure

[QUOTE=PETERRAKE;24964072]Bearing in mind that this forum is really intended for balsa builds, wouldn't a conventionally built slowflyer be more in keeping?[QUOTE]

The fuse is balsa and more-or-less will be traditionally build. The reason for the foam wing/tail at this point is to support early-stage experimentation. They'll be committed to wood once their size/shape are more refined.

Quote:
Originally Posted by PETERRAKE View Post
Delete away to your heart's content, but I'm just trying to understand the motivation behind the project. Your mock-up looks more like a funfly style model than a slowflyer - lots of wing and short coupled with fairly large tail surfaces.
Questions are not "Naked criticism", and likely also in the mind of at least one other reader.

Slowflyer, funflyer, parkflyer, meh. TBH, I'm not too hung-up on labels, call it a fun-fly if that term suits it I called it a slow-flyer simply because I want it to fly in parks, slower than a bullet, lazy, and non-aerobatic

Quote:
Originally Posted by PETERRAKE View Post
It looks an interesting project, but only if it leads to something worthwhile. Currently it isn't any different to many other models in appearance, isn't composite and isn't all balsa/ply. It doesn't seem to fit any particular criteria, in the usual sense.
Thanks for your questions and interest. Eventually it will be all wood (see above), which is why I posted here. I've already learned a lot having made it this far. If the remainder winds up being a lesson in what not to do, I'm okay with that. If somebody else learns something from the efforts, I'll be happy. If it flys somewhere near to how I envision, I'll be ecstatic
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Old May 11, 2013, 07:23 PM
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Thanks for the explanation, and the pointer to the specs. Seeing that it's 39" span, rather than 32", makes a lot more sense of your figures. You might find it's strictly a calm weather flyer though at that wing loading. Should certainly be slow enough.

All I meant by my comments about it being not cosmetically different from many other models is that if it's to appeal to others it really needs something to make it stand out from the crowd - apart from being expensive because it's a composite, Stunning looks, or outstanding performance, even just being quirky. If, on the other hand, you just want a model for yourself it doesn't mattter as long as you like it.

Pete
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Old May 12, 2013, 12:16 PM
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Quote:
Originally Posted by PETERRAKE View Post
Thanks for the explanation, and the pointer to the specs. Seeing that it's 39" span, rather than 32", makes a lot more sense of your figures. You might find it's strictly a calm weather flyer though at that wing loading. Should certainly be slow enough.

All I meant by my comments about it being not cosmetically different from many other models is that if it's to appeal to others it really needs something to make it stand out from the crowd - apart from being expensive because it's a composite, Stunning looks, or outstanding performance, even just being quirky. If, on the other hand, you just want a model for yourself it doesn't mattter as long as you like it.
Yep, most likely calm to light breeze, I was counting on as much.

Is it 39 in. ? It's been so long I may have forgotten

Ahh, thanks for the clarification about 'cosmetic', yeah that makes perfect sense. I'd really like to keep this first attempt fairly mundane. However, After having flown it, with a bit more balsa and design experience under my belt, and larger pile of sawdust, there's certainly room for tweaks.

The source plane (my inspiration) was quite a performer, very aerobatic, with a really wide speed-range. Today I cut out all the formers and main fuse stringers. I weighed everything (including very rough attempts at foam wings) and it's a lot lighter then I though.

As spec'd, I'm around 1.5:1 power/weight. However, seeing I may have under-shot the weight by a lot, it *might* wind up being a *wee* bit higher than that (2 or 3 to 1)

Maybe one of the "tweaks" may be to kill the 15° dihedral, beef up the main structure slightly, and toss in a "hot" ESC. That should plump up the aerobatic capability quite a bit, closer to the inspiration.

Heck, maybe It'll have swappable wings (slowflyer and spunky-bullet), then coupled with a nice paint job, maybe the balsa-version will develop some appealing character after-all

Anyway, it's nice to dream, but at this point I'll just be ecstatic to see this get up in the air
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Old May 12, 2013, 12:35 PM
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Build pics

In order to make the formers (The round bits that) identical on both sides, I stuck together two pieces of my 1/8" plywood together with a sheet of tissue-paper in between and a light coat of 50/50 wood-glue and water. Splitting them apart is super easy with a sharp knife, after they're sanded into their final shape.
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Old May 12, 2013, 12:39 PM
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Hmmm, not happy...

The top and bottom main stringers seem aweful flimsy to me, and I haven't even cut out the notches yet I've also found a few "bugs" in my design that need fixing (alignment & notch-size problems). I think I'll switch out the basswood top/bottom stringers for plywood versions. It'll add a smidge more weight, but will help me sleep better at night.
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Old May 21, 2013, 07:03 AM
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More plan refinement

The cycle seems to be, make plans, build, refine plans, build again. Each time I get a bit further along, discovering the next handful of tweaks that are needed. After only two iterations, it feels about 90% "good", and I'm learning a lot working with the materials.

I do have a question for the experts here-

The fuse resists flexing back/forth, up/down fairly well. However, it seems to allow some "twist" along it's length-wise axis. i.e. grabbing from nose and tail and rotating each in opposite direction. Doing this, I can easily rotate the nose or tail about 1/2" with what feels like would be about full motor torque.

I have _not_ glued down the horizontal plate to the formers yet, and I think that will help a tiny little bit. But is there somewhere on the structure I can add re-enforcement to help resist this twisting? Will the iron-on covering (monocoat or similar) help at all

Thanks.
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Old May 23, 2013, 12:28 AM
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Quote:
Originally Posted by razortoe View Post
The fuse resists flexing back/forth, up/down fairly well. However, it seems to allow some "twist" along it's length-wise axis. i.e. grabbing from nose and tail and rotating each in opposite direction. Doing this, I can easily rotate the nose or tail about 1/2" with what feels like would be about full motor torque.

I have _not_ glued down the horizontal plate to the formers yet, and I think that will help a tiny little bit. But is there somewhere on the structure I can add re-enforcement to help resist this twisting? Will the iron-on covering (monocoat or similar) help at all

Thanks.
If you are planning to add any stringers to the fuselage they will help a little, but most of your torsional stiffness will come from whatever you cover your plane in. Open structure wings tend to be the same way, the wingtips will rotate quite a bit relative to the wing root until you cover them.
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Old May 23, 2013, 06:09 AM
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Quote:
Originally Posted by Eclipse_7 View Post
If you are planning to add any stringers to the fuselage they will help a little, but most of your torsional stiffness will come from whatever you cover your plane in. Open structure wings tend to be the same way, the wingtips will rotate quite a bit relative to the wing root until you cover them.
Thanks for the explination. Yes, i plan to add some stringers. I added two as a test, but didn't notice more than a small difference. Aaaaaaaannd then i ran out of CA Might as well pick up a new iron and a roll of whatever heat-shrink plastic sticky stuff they have. Thanks again.
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Old May 23, 2013, 07:31 AM
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Latest iteration of plans

Many tweaks and updates based on completing the previous version. Need to find and mark stringer locations yet, so haven't split this into pages or cutting plan.
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