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Old Nov 29, 2013, 11:46 AM
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Woodstock 1's Avatar
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Question
What's lighter: foam core, or wood built-up wings?

I'm doing a project that needs to have a very low AUW (it's not a thermal glider, but I reckon you guys would have the best idea). The fuse is moulded glass, so the weight of that is a given. So, do I get foam cores cut; or do I ask someone to design me some wood wings and have them laser cut?

Chris
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Old Nov 29, 2013, 12:12 PM
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Depends on what density core you use and what you cover either of them with. In my experience the foam core is fairly light but when I added structure (rod spars or whatever) and glass skins it came out 1 ounce heavier than my built up wing of the same planform. This was on a 90 inch wing with 670 square inches. The glass was a 2oz glass hand layout with no vacuform, low tech.



You can see the carbon fiber rods embedded in the foam for strength. Either wing will support 20 lbs +. If I rebuilt either of these today it would be lighter and stronger.
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Old Nov 29, 2013, 12:29 PM
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Woodstock 1's Avatar
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Quote:
Originally Posted by George Franklin View Post
Depends on what density core you use and what you cover either of them with. In my experience the foam core is fairly light but when I added structure (rod spars or whatever) and glass skins it came out 1 ounce heavier than my built up wing of the same planform. This was on a 90 inch wing with 670 square inches. The glass was a 2oz glass hand layout with no vacuform, low tech.
.........
Thanks George, that's a very good comparison. That would be probably very close to what I would do with foam too...

Chris
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Old Nov 29, 2013, 10:07 PM
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Beautiful work George!
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Old Nov 30, 2013, 02:07 AM
MrE
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I think the weight difference will depend to a large degree on how strong you need the wing to be. Bending and twist are factors.

If its just a very light structure you need and it wont see hi speeds or hi loads, then I think a balsa built up could be done much lighter. They tend to get closer in weight the stronger you make them.
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Old Nov 30, 2013, 05:31 AM
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Woodstock 1's Avatar
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Thanks for your input, MrE! I'm building a (well, two actually, at different sizes) aerobatic slope planes for "low and slow" stuff, so they will not be subject to high speed, high G moves.

My next problem would be who / where I can get someone to design wood wings for me. Any ideas? (I guess a new thread asking that would be needed).

Chris
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Old Nov 30, 2013, 06:01 AM
ahh crap! crunch..
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This old thread again, Chris?

Well, foam, if you are really going to do it right with integrated spars and put a lot of pressure on it, not only launch either- thermalling orientated wings survive a brutal launch a whole lot better than they do high speed dives and aerobatic stuff. Slope is less so, F3J and F3B are heavier than their slope versions, purely on account of winching. Ever been there?


But the most important question is; why in the hell did you post this in the thermal section? did they finally boot you out of slope?

You are sloping. just go the foam.
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Old Nov 30, 2013, 06:13 AM
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Woodstock 1's Avatar
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Originally Posted by atmosteve View Post
This old thread again, Chris?

Well, foam, if you are really going to do it right with integrated spars and put a lot of pressure on it, not only launch either- thermalling orientated wings survive a brutal launch a whole lot better than they do high speed dives and aerobatic stuff. Slope is less so, F3J and F3B are heavier than their slope versions, purely on account of winching. Ever been there?


But the most important question is; why in the hell did you post this in the thermal section? did they finally boot you out of slope?

You are sloping. just go the foam.
Well, my profuse apologies. I didn't know this had been discussed before.

I explained why I posted here in my OP. Truth is, these are not normal slope planes, most there wouldn't understand what I'm trying to do here.

Chris
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Old Nov 30, 2013, 06:37 AM
ahh crap! crunch..
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It's a little bit ambiguous Chris. Wingspan? all that other stuff?

BMI?

I can't help but thinking foam is the way to go. It handles the tumbles and hard knocks so much better than a wood built up wing on the slope. Depending on the slopes you have in mind, no mention of that yet.
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Old Nov 30, 2013, 06:39 AM
ahh crap! crunch..
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I just read the thing under your user name- don't ask you anything..

And with almost 7000 posts here, you should know just about everything, no?
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Old Dec 03, 2013, 11:36 AM
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I can't tell if this is friendly banter or eye-poking.

The plane should be designed for the desired flight characteristics, as OP implied.
It seems the goal is not to be a compromise, but rather a dedicated design for a specific thing...lower weight.
If someone else thinks the design parameters should be different, then they should design their own plane to land or crash a certain way.
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Old Dec 05, 2013, 07:49 AM
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Quote:
Originally Posted by Woodstock 1 View Post
I'm doing a project that needs to have a very low AUW (it's not a thermal glider, but I reckon you guys would have the best idea). The fuse is moulded glass, so the weight of that is a given. So, do I get foam cores cut; or do I ask someone to design me some wood wings and have them laser cut?

Chris
How light do you need it to be?
How strong do you need it to be?
How big do you need it to be?

You said George's comparison was very close to what you want to do. But George's wing has a lot of sheeting and appears to be a D tube type construction. Do you need that much sheeting or can you leave it open and just cover it? If it can be open it can be lighter.

Can an all wood spar meet your needs or will you need to carbon cap it, like a Bubble Dancer? Mark Drela's BD came in at 31 ounces, all up, and can handle a full pedal launch. I don't know anyone who was ever able to build one under 35 ounces, but that is still super light for a 3M thermal glider.

If you are truly a slope pilot you may not know the Mark Drela designs. Take a look at the Alegro Lite, the Bubble Dancer and the Supra for design ideas.
http://www.charlesriverrc.org/articles.htm


So what else would need to be taken into consideration? Or, do you feel you have your answer an this thread is pretty much done?
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Old Dec 05, 2013, 08:11 AM
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Mark Drella may have designed a 31 oz BD but I think it would interesting if anyone has actually built a 31 oz BD.
The AVA pro is a BD knockoff with 6 inches more span and slightly more wing area. The advertised weight of an AVA Pro is 42 oz and the level of technology in an AVA Pro is considerably higher than a BD.
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Old Dec 05, 2013, 09:16 AM
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Originally Posted by George Franklin View Post
Mark Drella may have designed a 31 oz BD but I think it would interesting if anyone has actually built a 31 oz BD.
The AVA pro is a BD knockoff with 6 inches more span and slightly more wing area. The advertised weight of an AVA Pro is 42 oz and the level of technology in an AVA Pro is considerably higher than a BD.
Well, when I was timing for Mark in an Eastern Soaring League contest a few years back, Mark was flying his Bubble Dancer. I asked how he got it down to 35 ounces. He corrected me to say that it was 31 ounces. As I recall, he said that people tended to over build, not following the plans exactly. Then he put it up on a strong winch launch and won the round against the moldies.

So I will take his word for it.

If memory serves, he also said that he tended not to ballast it even in 15 mph winds.
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Old Dec 06, 2013, 03:52 AM
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Woodstock 1's Avatar
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My apologies for not responding to this thread. The unwarranted rudeness early on was for me a tipping point in my overall participation on RCG.

Chris
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