Carbon Fiber Spar

[TES111]

I am strongly considering a retract system from infinity aerospace. I know that phillip Johnson has installed this system in his cozy. My only concern is that (I remember reading somewhere) there was a degreee of roll in the spar on landings. Comments on this issue were "that it was not an issue". I know that was a quote but don't quote me verbatim. My question is.... can you beef up the spar and keep its relative dimensions the same? I know that carbon fiber is stronger and lighter. Therefore a Newbie/wannabe builder would assume that you could use a fair amount of carbon fiber weave to keep the same dimensions of the (plans) spar and infact strengthen it as well. Is this stuff impossible to work with or just very difficult in the home environment? I went to Aircraft spruce and they have it denoted as "difficult". Has anyone used this before? Would it be a stonger spar? Could you simply substitute a layer of glass with carbon?

 

 

Just another wacky idea

 

TES111:confused:

[dust]

Laid up perfectly straight, carbon fiber is about 3 times as strong as e glass, laid up not perfectly straight it is about the SAME as e glass.

 

Adding a layer of carbon fiber to a glass layup results in the carbon fiber, as it is stiffer, taking all of the load.

 

I'm too lazy too look, but, i think that there is no weave in the main spar, just uni and spar filaments.

 

This , in my opinion, is not a place for the uninformed to travel, without ALLOT of study.

[TES111]

Thanks Mike. Still looking for anyone that may have toyed around with this stuff. Any takers?

[dust]

Don't get me wrong, i plan on using it, just not for structure, maybe baggage pods, maybe a cowling.

[John Slade]

Part of the issue here is tht the spar is SUPPOSED to flex and transfer load to the rest of the structure.

 

I'd suggest talking to the Cozy Girrrls, Chrissi & Randi. They're installing infinity gear. You can be sure they will have considered this issue in depth.

[TES111]

Well John How do I get in touch, DOH. How can I contact the Cozy Girls?

 

SUPPOSED to flex and transfer load to the rest of the structure.

 

 

People have built carbon fiber landing gears for fixed gear applications. Even on R/C air planes. I understand that things need to give a little or they eventually develop stress cracks. If you can create enough stress. I just dont want a spar in a plane that wasnt designed to handle the load. I seriously doubt that anyone has hired a structural engy to test this yet, or perhaps aerospace has. Dont know. I would prefer an over built spar that is lighter than a spar that is built to its (possible) limitations. I would hate to think of what may happen if there were an air bubble at the wrong spot or if i had not gotten all the resin out that I could have. I am not nor will I be an experienced composite builder after only doing it once. I guess what I am saying is that an over built part is better. Assuming that it is the same dimensionally and can be made to be lighter than the plans method. I simply dont want to be anyones test bed when the questions is...can the plans spar handel the stress of the retract system?.

 

Back to the question... has anyone worked with this stuff before and how difficult is it to get a proper lay up?

[ekisbey]

I don't think the question is about whether or not the spar is strong enough to handle the loads with retracts. Personally, I'm pretty sure it is. Unfortunately, that's not the question, or perhaps it's improperly phrased. The correct question would be "Is the spar designed to accomodate retractible landing gear?" The answer for that, I believe, is "No," unless I'm way off base with regard to what Nat's been saying for years.

 

It simply wasn't designed for retracts, and it wasn't tested for retracts. So while it may be strong enough to handle the forces that retracts will add to the equation, you're tapping into the safety margin of a structure that's supposed to be doing something else. Remote as the possibility may seem, I wouldn't want to find out the hard way about a problem nobody ever thought of or tested for.

 

On the other hand, they sure are tempting. I mean, it just looks so cool, it's almost worth considering in spite of what I just said! I'd like to see a system where the retracts attach to the same bulkheads as the fixed gear strut. No idea how you'd make that work, but I guess there's a reason why I'm not an engineer.

 

That looks like about two cents, doesn't it? Good, I can shut up now.

[John Slade]

>DUH. How can I contact the Cozy Girls?

Look in the member list under "Chrissi". Duh!

 

 

[HM Andersen]

Sure retract is very tempting.

I to was considering a solution where the retract was fixed like original.Could look a bit like the Velocity.

On the other hand ,using the Infinity system you could redundant the original fix points and save some weight.

As for reinfocrcements would`nt Infinity supply the data needed ?

Regards Helge

[ekisbey]

Is there a Mark IV flying with retracts? Unless there is, I'd say the data was suspect.

[TES111]

Once again has anyone used carbon fiber before. Not on an R/C but on something of this nature and scale. How difficult would it be to make a carbon fiber spar? Or am I simply asking a question that cannot be answered here? I dont want to start a mud slinger about wether retracts are a good idea. It is something that I want on my plane. Aerocad sells an RG model. Are they that different structurally? It seems to me that they are the same airplane. As far as tapping into the saftey margin is concerned thats why I want to build a much stronger spar.

 

 

Oh thanks for the update John. I had not viewed the members tab:rolleyes: DOH;)

 

I agree ekisbey if there is not one flying I dont want to chance weakening the spar w/ an RG system. So in order to remove the guess factor I would like to build a stronger spar if it is infact not to terribly dificult to do. From what I ve read so far you would build a mold fill it with uni carbon strand, wet it out and viola... carbon fiber spar. I just want to know what the process is and perameters for cure. ie special equipment, tension, vacum bagging. in other words what kinda monster am I creating and should I squash the idea now instead of later.

[dust]

OK here is the problem, the spar is not just a spar, it is a load bearing and transfer member.

 

If i were to make a change such as this, i would put the berkut SYSTEM in. The spar/wings and attach parts, they have been tested togthe.

 

Beefing up A part transfers loads diferently than it has been tested for.

 

I don't believe working with carbon fiber is a big deal, except for the fact that you have no tolerance for crooked fibers, BUT, your thinking here is WRONG. you just can't make A part stronger and expect everything else to be OK.

 

Read and consider my post on carbon fiber in the coffee house. All here will help you(well allot anyway) but you need to do a little studying first.

[TES111]

Thanks Dust. I am fearless and will do alot more research. Fourtunatley Ga. Tech is just down the road from my office. I'll go and bug them

[John Slade]

Mike asked me to move this thread to the coffee house. It relates more to retracts and carbon fiber than it does to building the spar. Good and welcome discussion. Just in the wrong place.

[Wayne Hicks]

One thing to keep in mind when working with carbon--> Since it's black, it's hard to tell when the cloth is adequately saturated. It doesn't turn translucent as our normal white-colored cloths do.

 

Technique usually involves putting in more resin than needed to ensure the cloth is wetted out completely. Thus you must also squeegee out the excess prior to cure.

 

.....Wayne Hicks

[TES111]

Sorry John. Thanks Wayne. I am realizing that i'm going to have to do some serious digging to see if its ging to be a huge ordeal. So...off to the pros I gos.

[tonyslongez]

Tes111

 

You are asking for a whole lot of problems if you change your spar to carbon fiber. I wanted to do the same thing to my Long EZ initially when I started building. The big problem that you will soon find out from your friends at Ga Tech is, it's not the carbon fiber that is the problem it's the host of problems it creates. for instance, you are going to change your flutter Coefficient substantially. You will have to do a completely new flutter analysis this is going to take months and your aileron weights and possibly the design will change. you'll need to know what those numbers are going to be and you'll need to know how to interperet them. Carbon fiber is not the end all be all that alot of people think it is, for the Berkut it worked because it was designed that way. Carbon only stretches about 3% where our fiberglass is more of 8-10% you could potentially do some very bad things to your airplane if you don't understand everything that is happening when you mix carbon with fiberglass. Not trying to burst your bubble here but you will need a complete finite analysis and FEA model to compute those flutter issues and you will have flutter issues with out it. if your concerned about strength a better solution may be a well placed bulkhead.

 

Tony

[argoldman]

Tes111

 

You are asking for a whole lot of problems if you change your spar to carbon fiber.

 

Tony

Additionally, when you replace glass with carbon, in a composite setting, you are dealing with problems that need an engeneer with extensive composite experience. Although carbon is better in tensile strength per gram than glass, if mixed with glass, when, and if the glass yields (at its tensile), it will place an explosive load (for want of a better non engeneering word) on the remaining carbon fibers which may cause their rippage before their appearent tensile boundry.

 

This is not to say that carbon/glass/foam composites don't work (the Dragonfly used carbon fiber exclusively for spar caps in wings, canard and vertical stabilizer, it is only to say, that if you are going to consider it, consult with a composite engeneer, for your own safety.

[tonyslongez]

I couldn't agree more.

 

I have seen video of that very same scinario. the glass actually broke the carbons back. The realease of energy was awesome.

[AP3_C]

On the other hand, they sure are tempting. I mean, it just looks so cool, it's almost worth considering in spite of what I just said! I'd like to see a system where the retracts attach to the same bulkheads as the fixed gear strut. No idea how you'd make that work, but I guess there's a reason why I'm not an engineer.

 

You could look at the re-tract system from Shirley Dicky's E-Racer.

Only prob is it will take up rear space.

 

Like you I'm no engineer, no idea if it is possible, also unsure if still available.

 

Jamie

[tonyslongez]

Check out my site go to

 

www.myairplane.com click on construction log then click on tonyslongez I have my own retract design coming back from the machine shop that will surely stand everyone on ear here is a cad drawing

 

Tony

[dpaton]

Looking good Tony. I'm waiting eagerly for the video of your gear legs snapping up into the fuse at the push of a button

 

-dave