>i told you it would have to be 0.3 carbon leading edge skin to be lighter than the wood leading edge scin....i told you this is not as strong as the wood in this aplication.

I hate to burst your bubble me amigo, but as I indicated before without running the numbers it was just a guess. Now, I'm usually pretty good at getting close to the right answer even before I run the numbers, but I will freely admit I have never worked on anything this lightly loaded before (mostly fighters, helicopters and wide-body stuff), so I'm quite sure I will surprise myself a time or two before I finish going through the whole thing. Now, what you said was actually misleading. In fact we often say that buckling doesn't a failure make – especially in regard to local buckling. I have in fact, been told that the plywood buckling has been observed under wing loading. The plywood's main function is to provide torsional stiffness for the D tube, it being part of a closed section. In fact the 2 plies of graphite are stiffer than the 3 plies of plywood in torsion since there are no 45 deg plies in the plywood and the graphite is MUCH stiffer! And the shear-buckling is slightly higher for the 2-ply composite layup despite the fact that it is half the thickness!

Now, it is very slightly heavier out of carbon since we don't have the luxury of using a partial ply i.e. we are probably looking at a 2 ply minimum, so it's going to weigh what it weighs, OK. So why use it? Well, if you will view Steve's video again (I guess you missed it the first time) you'll see that he used the plywood on the horizontal leading edge but that it showed some significant warping, which was clearly visible in the video (despite the lack of resolution). He said if he had the choice to do it again he would have picked the gr/ep for the LE of the horizontal as well. There is more than just weight to consider and more than just the EL skins that are targets for design evaluation and weight-saving. It ain't over till it's over – I haven't even heard the fat lady warming up. If I can't save any weight anywhere else, hey, it ain't no big deal, I concede Jim and Irv did real fine job and move on. If it goes over the 150 Lb mark, as long as it's around the 155 Lb mark I'd be perfectly happy. Additionally, if you add a small turbine as Steve has mentioned, you can get another 100 Lb and still be classified as a UL (maybe it only needs a pint of fuel just to be `legal?!, but I digress).

>you said to me" steady your getting your figures mixed up it will be moor like 0.6 carbon" now your saying it will be 0.4carbon leading edge skin and your still heavier on a standard wing than a wood leading edge scin.

GO back and reread the posts – I believe regardless of me being off by a single ply that there were some unit mix-ups, it happens. I remember something about a mars rover crashing… wouldn't be the first time that happened. AS I said -- it was merely a guess, I never suggested anything else as I said before, I hadn't run the numbers yet.

>your saying that you are going to make a bigger wing and beef up the spar and use modern materials to make this wing lighter...and the weight saving is to offset 20 kg extra body weight ????????

I said I'm going to try. If you look at the Gossamer Albatross, you will find very little wood… why, because good as wood is, if you got lots of money, there is better stuff out there. Also, we are looking at a very specific mission profile here which may dictate some materials… some of those might be wood, and I'm OK with that too, I would just prefer to avoid the whole warping issue if possible. I think this could especially be an issue for someone living in a high-humidity location.


>have you ever seen the movie the castle kenny?..im sure mr carington would tell you yor dremin. you have stated on a number of ocasions that you are a areo stress analus/engineer.

No

>i think it should be made clear to people that are reading this that replacing the leading edge scin with carbon in the manner you are sugesting, is not lighter and stronger at the same time. it can be lighter but not stronger...or....it can be stronger but not lighter.......

I believe I posted the weight as soon as I calculated it (as opposed to just guessing it (and people wonder why stress guys are so non-committal when they drop by to ask they if something is `OK' 10XLOL!)). There has NEVER been a single time there has been ANY effort on my part to hide anything or to deceive. What you said about weight and strength is blatantly not true. There is always some really exotic way of doing it, but I'm at least trying to `keep it real'. I don't know that the 2 plies of carbon aren't significantly stronger than the plywood and frankly 1 lb is pretty small weight difference over 100 square feet , as I stated earlier you'd probably have to run a non-linear FEM (SOL 106) to get an exact comparison and to confirm the actual behavior, and I haven't had time to do that yet. I thought I'd share some thoughts along the way and maybe here some `constructive' criticism. Feel free to share any of that, if you have any…

>remember you said"the right material is the right material"?

well erve culver and jim marpin say ply wood not carbon/graphite and i agree.

There are lots of reasons to decide to use a specific material: cost, weight, manufacturing, labor time, durability etc. I could well see why someone would use wood, and I could well see why someone would choose carbon. I'm not knocking you for using wood, nor am I knocking the couple of guys that have chosen to use carbon.

>however if you use the geodetic construction method as in the wellington bomber,i belive you could beat the ply sheet, but then we could use this method with ply also. but the build time of the dragon is already too long.

I'd have to look into it, but I do know of some boats (row boat, and a canoe) that I believe are built similarly and though they are light, they don't travel well in the water and are quite draggy. Now, it may be that the air doesn't deflect the surface as much as the water does and the effect would be smaller or negligible, I just don't know that much about it, but I think I agree with you that it would likely cost more labor, which wouldn't be a good thing.

>in any case ,in flyte the wings are said to carry them selves....the wings load the air....every thing that hangs from the wings, load the wings.....if you seek a waight saving in order to relive the stress on the wings...you need to unload weight from what ever hangs from them not the wings themselves.

Well, that one is silly as a couple of pounds in the wing one way or another are insignificant compared to the payload weight that has to be carried by the wings, especially at the root. It's more true to say that about a commercial wide-body jet as the wings are full of fuel. Indeed the critical wing loading is when the wings are empty and the fuel isn't counteracting the air loads, but even then, it's just something you analyze for – it's just another flight condition.

>if anyone feels they must use carbon skins in the wings ...im thinking go for a hevier stronger wing not lighter.

In the end you may well be right about that, but if the price to be paid is only a couple of pounds and it could eliminate warping (especially for people in wet locations) it may well be worth it.

>kenny be carefull not to miss lead any one.

I would strongly suggest that I haven't!

Kenny

P.S. you got a spell checker? You are killing me!