id like to coment phill.....you say the carbon scins are considerably stiffer than the wood.....is wrong untill you get thiker/hevier.the thikness play a bigger role in term of stifness in this particular instance.than does the material used.

kenny just now said..extra scin consederebaly hevier.

the monerai's wing oil can's..i agree with kenny....no problem.

however..caution.......thin carbon laminates are very springy,they are used for reed petals in high performance 2 stroke engines....the thin carbon laminates are fantastic in tension but wood wins in compression for the same weight....this can easily be shown with small test samples.

carbon fiber is not the super hero for this aplication if the aim is to keep this aircraft under 70 kg....becaus of its density of 1800 kgm3...it needs thick ness befor it becomes a super hero in this particular aplication,you need to take a weight penalty to beat or better the wood in compression.

russ.


On Tue, Dec 25, 2012 at 7:12 AM, Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


I'm actually back in the states right now for the Christmas holiday. All the work I had done on the wing is on my computer back in Korea. If there is interest, and it appears that there might be, I'll work on it a bit more. With regard to the foam ribs I think it is important to realize that it doesn't take so much support to act as a panel beaker for the skin since it's stiffness is so low in the first place. Of course the other thing you can do to increase the buckling resistance is to insert additional false ribs.

In any case, the other thing to realize is that a buckle doesn't a failure make! Usually it's a criteria. For example you might not want the webs or skin to buckle at something less than limit load, but at ultimate load you might be willing to live with a redistribution of the bucked load to other stiffeners and adjacent structure.

Also, a web can buckle in shear loading, and continue to carry load beyond the buckled state (as a diagonal tension). Compression buckling however, only carries the load up until it buckles and then carries no more load. Any additional compression buckling load would have to go somewhere else like the spar caps or leading edge.

So as long as there is some place for the buckled load to go, there won't be a failure even though there has been a buckle.

Kenny

--- On Mon, 12/24/12, Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


From: Philip Lardner <This email address is being protected from spambots. You need JavaScript enabled to view it.>

Subject: RE: [Carbondragonbuildersandpilots] ad First Flight, reserve parachute and 3 piece wing

To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Date: Monday, December 24, 2012, 10:40 AM





Hi Kenny,

I don't think I contributed much (anything!) when you were posting about FEM because I have to confess I'm not entirely up to speed on what a FEM analysis could do, or how to exploit it - but I *am* interested!!! Please don't abandon it! A thorough analysis of the wing loads, structure and flight surfaces will be very valuable in designing the Next Generation of CD.

I like your idea for stiffening just the top half (or less?) of the D-section - an extra layer of cloth down the length of the top surface would indeed stiffen that section and minimise the weight gain.

I am curious to discover if the false ribs, made from 5mm paper covered foam board that go between the main load bearing ribs of the D-section, are strictly necessary if we are using moulded carbon fibre D-skins, which should be significantly stiffer than the original 0.8mm ply skins. The original plans call for two foam false D-ribs to be inserted between each pair of plywood ribs from Rib #1 to Rib #4, and a single foam false rib between each pair of plywood ribs from Rib #4 out to the tip. I can't see such thin foam ribs adding much to the strength of the D-section, and I imagine that their primary purpose was in helping to shape the 0.8mm plywood skins when they were being fitted. Would anyone care to comment?

Happy Christmas,

Phil.

---

From: This email address is being protected from spambots. You need JavaScript enabled to view it. [This email address is being protected from spambots. You need JavaScript enabled to view it.] On Behalf Of Kenny Andersen
Sent: 24 December 2012 14:23
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Subject: RE: [Carbondragonbuildersandpilots] ad First Flight, reserve parachute and 3 piece wing



I haven't posted much since I've been super busy and no one seemed particularly interested in the wing FEM, so I quit working on it due to the demands of work and the low apparent interest.


Anyway, one other option would be to bond in a small hat stiffener rather than a whole additional layer of skin, which would add considerable weight. The forward curved portion of the leading edge is quite stiff due to its shape, the low part is in tension so it is stable, you only need more stiffness in the upper surface of the D-tube. So, you could add material there, or add some type of stiffener.
Kenny



Hi Rick,

I'm interested to read about the wing's behaviour when you flew it at 70mph. I'm guessing the 'boink' sound you describe was coming from the upper surface of the leading edge D-section as the compression forces built up with speed.

I am vaguely hoping that I might be able to tow my CD behind the local sailplane club's Super Cub tug plane, which has a Best Rate of Climb Speed (Vy) of around 60mph (though I suspect sailplane tug pilots tend to fly faster on tow - 70-80mph?)

My existing plans are to use just two laminates of CF cloth (in +45deg & -45deg strips) in the leading edges, but I wonder now if I shouldn't take the weight penalty and use three layers for extra stiffness. How many layers of cloth did you use in yours? I've read that Steve Arndt has towed up at speeds in excess of 70mph without wing flutter or any other issues. Do you know how many layers of cloth Steve used?

Happy Christmas,

Phil.