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Re: Carbon Dragon structural limits 10 Dec 2013 22:43 #547

Russ, if you look in the photos section, I have a picture of my load transfer bars. Jim Marske has an excellent book on designing with composites. He shows you how to calculate the loads generated and the amount of carbon needed to prevent tear out. I can't find my calculations at the moment but I needed something like 20 layers of carbon for 9Gs for a 400 pound gross weight. I used 35 layers of carbon because that thickness matched the thickness of the 4 carbon rods I used in my spar so I would get the maximum surface area to glue to.The spar was constructed with a fiberglass layer on the outside, then the rods were put in the corner, another layer of fiberglass to sandwich the rods, then the bars were laid next to the rods, then a third layer of fiberglass over that. That way you have not only the load transferred by the glue shear load, the bars have 12 inches of surface area glued to the rods. but also by the fiberglass encapsulating everything. With the loads we have with the CD, only a single layer of 7725 fiberglass is needed for the web so I have triple strength in the root area. The rods are so strong in fact that I actually only needed 3 but added a 4th because the wing would have bent under load more than I wanted. The rods are so light there was very little weight penalty to do that. The weak point now is probably the .090 aluminum connecting brackets the plans call for. I'm thinking of increasing those.


And Dewey, I got a reply back from Matt Kollman that confirmed that they are only using a single layer of 7725 cloth for the Pioneer ribs. I'll see if I can get the dimensions of the corrugations they are using and maybe Philip can add that to his comparison tests :)



From: russell wilson <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: Sunday, February 5, 2012 7:24 PM
Subject: Re: [Carbondragonbuildersandpilots] Re: Carbon Dragon structural limits




hi kenny
im not knocking the rods or any ones work.....im simply pointing out that no matter what caps or strenth any of us have......the weak point is were the holes are drilled at the root where the highest load is and that any thing stronger/out board of this point is for nort.......actually it becomes a weight penalty......

were the calculations done on one or two pice wings?

russ.


On Sat, Feb 4, 2012 at 10:05 PM, Kenny <This email address is being protected from spambots. You need JavaScript enabled to view it.> wrote:


Russ,
I know you've expressed this a few times, but it just doesn't mater whether it is a one-piece or two piece wing and far as whether the rods will be beneficial or not. They will be! the load from the rods can transfer to the top (or bottom) of a reinforced spar web and then to the opposing wing spar though the wing root fitting. The load doesn't have to go directly through the cap. My buddy has already done this with his two-piece ultralight wing AND proof loaded it to ultimate load, so it's not just some theoretical idea I have!

When you understand the underlying engineering principles you can design around the limitations. I'm not bragging, I'm telling you that this is what I do for a day-job. When in doubt you can test. So what is to fear -- test test test if you can't analyze; I can do both.

Whether the wing is one-piece or two piece the moment at the root is the same i.e. the number of required rods is the same. The only difference is that the two-piece wing cap loads have to transition out of the cap and into the root fittings. That can be done with a local reinforcement of the spar web.

I think the biggest problem is that you are under the impression that there isn't room for improvement when in fact there has been a lot of progress in material and the understanding of how to apply those since Maupan did his work on the CD.

it's not for nort, yer? geez
Kenny


--- In This email address is being protected from spambots. You need JavaScript enabled to view it., russell wilson wrote:
>
> g loading ......wood,carbon tow or carbon rods spar caps...the highest
> loading comes at the root...yer?....how the bolts mate the fittings to
> these spar caps is something that needs to be thaught of carefully.....if
> your weak point is at the root it may be all for nort.
> im yet to be convinced that rods are superior for this aplication...was the
> strenth calculations on the rods done with a two or one pice wing?
> russ.

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