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Re: ad First Flight, reserve parachute and 3 piece wing 29 Nov 2013 15:32 #57
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I alredy tested it and and posted about it here
groups.yahoo.com/group/Carbondragonbuild...ndpilots/message/216 George @ curedcomposites.com/ ==================================== --- In This email address is being protected from spambots. You need JavaScript enabled to view it., "Philip Lardner" > > ..."should be significantly stiffer...", but yes... drat - rumbled for > typing without thinking again! You're quite right - not necessarily stiffer > unless the laminate is a foam core sandwich. I should read my emails before > hitting the send button! I did do a few test laminates - one with just two > lams of CF cloth (very strong and moderately stiff, but still bendable) and > another comprising one layer of cloth laminated either side of a 5mm thick > foam core... which was as stiff as an iron girder! I didn't do any > particularly quantative analysis of the foam core part before I managed to > snap it under extreme load! > > I'm thinking that even a moderately narrow strip of 3mm or 5mm foam board > running the length of the top inside surface of the D-section, laminated in, > would significantly stiffen the structure for minimal weight gain. > > When I did my initial research into materials last year, I came across a > report into the shear strengths and load bearing capacity of plywoods > (including 1/32" 3-ply as used in the original CD.) I'll dig out the paper > in the new year, but if memory serves, 2 layers of 284 Twill carbon cloth > out performed a single layer of 1/32" ply... but don't quote me on that > until I find the paper! > > We're going to have to put this question to rest eventually by generating > sore real test data. If anyone has some off-cuts of 0.8mm ply lying around > they could either post them to me or we could agree a standard test to > compare the two materials. I'd be happy to knock up some carbon strips next > time I'm doing an infusion run. If we had two similarly sized strips, say > 10" x 2" (one of 0.8mm ply and the other of 2-lams of CF cloth) overhanging > the edge of a table we could measure the deflection when we hang a similar > weight off the end of each strip. A simple (and hopefully definitive) test. > For the sake of thoroughness, we'd need to test both the plywood and the CF > cloth laminate with the grain/weive running straight along the strips and > again at 45degrees to the length. The CD plywood D-skins are made up with > the grain running 45degrees to the wing length. Anyone willing to help out > here? > > 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 russell > wilson > Sent: 24 December 2012 21:27 > 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 > > > > > > 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 <kennyrayandersen@...> > 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 <philiplardner@...> wrote: > > > > > From: Philip Lardner <philiplardner@...> > > 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. |
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