hi kenny

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.

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.

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 ????????

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.

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.......

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.

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.

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.

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

kenny be carefull not to miss lead any one.

russ




On Thu, Jul 7, 2011 at 8:37 AM, Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:



Sorry, I got the same age thing going on! I meant carbon rods. I think Marske was a bit optimistic. They ARE incredibly strong, and you don't have to add many to CYA


--- On Wed, 7/6/11, Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


From: Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Subject: Re: [Carbondragonbuildersandpilots] plywood properties
To: "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.>

Date: Wednesday, July 6, 2011, 12:20 PM





Sorry, that's right, you had already told us that. It's that age/memory thing again. I would eventually like to try to make an electric self launch and a few more square feet to handle the extra weight would be nice


I think that when Maupin and Colver were designing the CD 60k PSI was the accepted compressive strength of the carbon tows. When Marske was building his Pioneer he made several samples and when he had them tested he found that the average strength was about 65k and a few were less than that. So if that were the numbers they used for the CD, they had no safety factor or worse, it was slightly under designed. Marske was one of the first to use the carbon rods in wing spars.

---

From: Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.>
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Wednesday, July 6, 2011 10:50 AM
Subject: Re: [Carbondragonbuildersandpilots] plywood properties



I'm a aero-structures stress analyst. I've worked on tilt-rotors, fighters, wide-body commercial jets, and helicopters for 26+ years and also have a fair amount of experience with composites. Additionally I can do finite element modeling etc. so, I think I can take a stab at it.


BTW, my feeling is that Marske was a bit optimistic about how much stress the carbon tows could take -- especially in compression (upper spar cap). A physical test of anything significantly new is ALWAYS a good idea.

--- On Wed, 7/6/11, Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


From: Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Subject: Re: [Carbondragonbuildersandpilots] plywood properties
To: "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.>
Date: Wednesday, July 6, 2011, 8:29 AM



The plans call the entire wings are covered with a lightweight fabric and then painted. I don't see why you couldn't just cover the rear of the wings if you did a carbon leading edge the way Aeros does on their Phantom hang gliders. The carbon would still have to be painted to protect it from UV. By using carbon rods rather than the carbon tows you can get the additional strength to carry more weight. When you talk about making a significant change to the length of the wings though, unless you are an engineer and know how to calculate loads and are aware of everything that is affected, you are really heading into unknown territory. You can't just simply scale a wing up.


What I did on my wing is in the first 8 bays I added one more rib than the plans called for. If it called for 2 I put 3. If it was 1 I put 2. Mick used plywood on his leading edges and gets quite a bit of buckling between the ribs. Plus I wasn't sure how the stiffness of 2 layers of carbon compared to the .8mm plywood. I'll let you know how well it works when I load test it.


Someone posted an article comparing foam and wood ribs to the method used in the plans in the files section here. I would probably use the foam and wood next time.

---

From: Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.>
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Tuesday, July 5, 2011 9:09 PM
Subject: Re: [Carbondragonbuildersandpilots] plywood properties



So, I'm just starting to get down to the nuts and bolts though I've been a CD fan for a long time. I thought that the wings were covered with dacon or something and that the plywood LE (leading edge) was just there for structure (i.e. not the actual aero surface)? If that were the case, you could just cover the carbon with the rest of the wing, and it would be pretty smooth, or maybe fill it with the micro ballon stuff and then cover with the fabric? Does the wing covering fabric only go from the D tube to the TE (trainling edge)?

Molds would be the way to go for sure (but that's a big time investment, no?), but I was thinking of adding a bit more root and tip to increase the payload to around 200 (maybe some extensions?), which would allow me to wear clothes! LOL Actually, I could probably drop to 170, but with clothes and gear, that sill puts me a maybe 180-185 which seems a little heavy for the CD? I was hoping to keep the wing loading somewhere near the original target. I assume you laid the fabric up at 45 degrees?

Adding the extra ribs like you did was exactly the way to go, I was thinking of either changing the spacing from one intemediate rib to 2, or just adding a rib between the the existing ribs based on the LE (leading edge) skin buckling (which would give 3 intermediate ribs). So, did you go to 2 intermediate ribs, or 3? Since they are just there for skin stability they should be fine -- not much load there, and you're right -- not much weight.

Speaking of ribs: has anyone been swaping out foam ribs for the built-up trusses? That seems like another area that might yeild some small weight-savings, or would at least perhaps simplify the construction a bit.

Do you have a blog or anything that shows your build?

Thanks, Kenny

--- On Tue, 7/5/11, Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:

From: Rick Mullins <This email address is being protected from spambots. You need JavaScript enabled to view it.>
Subject: Re: [Carbondragonbuildersandpilots] plywood properties
To: "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.>
Date: Tuesday, July 5, 2011, 11:14 AM



Steve didn't make molds for his leading edges. He made plugs by filling in the spaces between ribs with foam and then laid his leading edges up on them. Because that leaves a rough surface he did two layers of carbon and a lighter fiberglass layer on top that was largely sanded away to make it all smooth.
I have made molds (contact me if you are interested in using them) so I have made my leading edges of just two layers of 284 carbon, and also because of advise from Steve and Mick Roberts, I added and extra foam rib to each of the first 8 bays so there is less unsupported space between them. The ribs are only 1/2 foam with holes cut in them so it didn't add much weight.
From: Kenny Andersen <This email address is being protected from spambots. You need JavaScript enabled to view it.>
To: This email address is being protected from spambots. You need JavaScript enabled to view it.
Sent: Tuesday, July 5, 2011 11:32 AM
Subject: [Carbondragonbuildersandpilots] plywood properties



So, what I've done is taken the properties from birch (assuming it's birch plywood) and made a composite based on 3 layers of birch oriented in the 0, 90, 0 directions (its' the same way (tool) that we use to model composite layups. I had to assume some of the orthotropic properties, since they only publish the axial ones, but it will probably get close. One interesting thing I've figured out so far is that 2 plies of graphite fabric weigh just slightly more than the 1/32 (.8 mm) plywood -- a bit more than a pound per airplane more, but it will be more stable than the plywood.

It makes me wonder how many plies Steve used on his magic dragon leading edge? Interestingly enough, even though the 2-ply composite is 1/2 the thickness, the shear buckling is the same (actually slightly higher)due to being able to orient the composite fabric in the 45 degree direction, and the carbon being much stiffer than the wood. I haven't had a chance to run the in-plane buckling, which I assume the composite will buckle at a lower load for the same reason. However, since the function is to carry primarily shear, it might be OK -- I'll probably have to get around to making a non-linear FE model to smoke that out. I will say 2 plies isn't very thick...