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Old Jun 06, 2010, 09:54 PM
Unrepentant Paragon addict
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United States, OK, Moore
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Quote:
Originally Posted by IHAVAWDY View Post
LV; why are you doubling the wall thickness of .014? there's only one wall thickness of .014 not two.
Woody, (working twice as hard to be half as good)Woody
Because the wall thickness goes all the way around.... not just on one side.... Hopefully my crude diagram will help

OOPS! The bit on the bottom should read Inside Diameter = X-(2Y)
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Old Jun 06, 2010, 09:59 PM
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It must have been crude as the mod wouldn't even publish it?
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Old Jun 06, 2010, 10:13 PM
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Uhhh... huh? You know IHAVA, it's no great feat of skill to confuse me at this late hour!
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Old Jun 06, 2010, 10:25 PM
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...
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Old Jun 07, 2010, 05:46 AM
aejr sucks little black ones
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Hey i got it, and I'm six beers down.. not boasting mind you, more a fact of shame.
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Old Jun 07, 2010, 07:02 AM
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Quote:
Originally Posted by LVsoaring View Post
... I do not want 3 thousandths slop, as this will undoubtedly eventually egg out the tubing over time and cause an even looser fit...
A typical slip fit would be about .001", but that assumes perfectly round and straight parts, etc.. By the time you allow for straightness of the tube and the joiner, out-of-roundness of each, diameter variations along the length of each, temperature effects, a little dust contamination, etc., any closer than .003" is likely to jam, and even that might end up being too tight.

The other thing I'd be concerned with on brass tubing is galvanic corrosion of your joiner rod caused by the copper content of the tube.
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Old Jun 07, 2010, 10:56 AM
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Thanks for the comments Don. The brass tube issue was discussed in this thread, posts 3943-3947. Consensus is, brass is better than aluminum. Do you know of any other materials thin wall tubing is available in besides copper, which is obviously not feasible? Open to all suggestions here!
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Old Jun 07, 2010, 11:14 AM
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On to the next dilemma

Really not a huge issue but here's what I'm mentally grappling with. Spar caps are 3/8 x 1/8 spruce. I want to add .030 CF top and bottom (please, do not go off on a tangent about the top/bottom issue!) and my problem is this: .030 = 1/32 (appx), but I cannot find 3/8 x 3/32 spruce anywhere. I have heard that if adding CF, you can sub balsa for spruce. So, I have 2 options: Add .030 to the stock spruce, and notch the ribs 1/32 deeper to accomodate the added thickness, thus decreasing the height of the shear webs by 1/16, or use 1/16 x 3/8 balsa with .060 CF and preserve the original size of the spar caps. Once again, all comments and suggestions are welcome and eagerly awaited! Need to decide NLT 6/18, as I plan to order from CST sales, and in a roundabout way, support the US F3J team. In case you didn't see it, here's the thread.... CST supports F3J
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Old Jun 07, 2010, 01:12 PM
ein flugel schplinterizer
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Why not make a sanding guide and sand down the spruce by the thickness of the CF?

or: As you mentioned, notch the ribs.

I personally would NOT substitute balsa for the Spruce.
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Old Jun 07, 2010, 05:37 PM
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To be perfectly honest, I am too lazy to sand down spar material. Plus, I have doubts about being able to sand to a uniform thickness along its entire length.

I'm not too crazy about the balsa idea either, just fishing for some input from anyone who might have first hand experience.

My only concern, or question really has to do with shortening the height of the spar webs if I notch the ribs to accommodate the CF. Will that make any difference in the strength of the wing? This is very important to me as I intend to launch this thing relatively aggressively (for a woody)
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Old Jun 07, 2010, 08:11 PM
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Quote:
Originally Posted by LVsoaring View Post
... Consensus is, brass is better than aluminum.
Probably so. The aluminum available in most hobby shops is very soft, and is very vulnerable to galling. Aluminum in general is a terrible bearing material.

Quote:
Do you know of any other materials thin wall tubing is available in besides copper, which is obviously not feasible? Open to all suggestions here!
If you really want to get fanatical about it, I've made my own using metal mandrels, fiberglass or carbon braided sleeve, and epoxy. The tricky part is getting it off the mandrel in one piece.
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Old Jun 07, 2010, 08:32 PM
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I'm a COTS technology kind of guy.... Commercial Off The Shelf
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Old Jun 08, 2010, 09:11 AM
≡LSF8067≡
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Quote:
Originally Posted by LVsoaring View Post
My only concern, or question really has to do with shortening the height of the spar webs if I notch the ribs to accommodate the CF. Will that make any difference in the strength of the wing? This is very important to me as I intend to launch this thing relatively aggressively (for a woody)
LV,

You'll be replacing 60 thou of balsa shear web height and rib notch with, what I gather, 60 thou of pre-impregnated CF strips (30 top and bottom). Dude, it's a lot of work but I think it will be bullet proof....do it!

Don
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Old Jun 08, 2010, 11:04 AM
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United States, TX, Weatherford
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LV... I'm lazy, too... use a jack plane. Properly set up and 3 passes down the spruce and you're done. Beats sanding, any day!
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Old Jun 08, 2010, 01:36 PM
ein flugel schplinterizer
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Quote:
Originally Posted by schrederman View Post
LV... I'm lazy, too... use a jack plane. Properly set up and 3 passes down the spruce and you're done. Beats sanding, any day!
Geeeez, you guys are lazy! Jack, in a few short years you'll just need to do what I do: I'm presently teaching my two grandsons how to build and letting them get plenty of time sanding.......plenty of time.
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