Carbon Fiber Wings?

[ultra]

I was just wondering if it was possible to mould carbon fiber over a wing template to create the wings of the XL instead of creating an intricate spruce structure. 

Not that I would replace the current design with it, I always wondered if there was a lighter and stronger alternative as I see a lot of new equipment out there made from thick carbon fiber shells.

[scottiniowa]

I was just wondering if it was possible to mould carbon fiber over a wing template to create the wings of the XL instead of creating an intricate spruce structure.

Not that I would replace the current design with it, I always wondered if there was a lighter and stronger alternative as I see a lot of new equipment out there made from thick carbon fiber shells.

Ultra, as the saying goes, anything is possible... But I would venture to guess that the #1 thing that attracts folks to the XL, is cost to build.  Or at least most of the engineering has been done.  You would lose dearly on both accounts. Mainly because-

• Carbon fiber parts for this are pretty expensive (compared to wood -really expensive)
• Going this route of carbon fiber would be no less shortage of "intricate parts" and most would certainly require testing of your  backyard engineering. And yes, I don't know what else to call it.

So again, not saying it can't be done, just doesn't really make much sense in this case.

[stevejahr]

It might be a shorter jump to a CF fuselage... they build bicycles this way a lot now so there is precedent for lugged CF tube structures.

And you could certainly do a wing in CF... but then it would not be a LE anymore wood it? ;-)  (sorry could not help it)

It would require a lot of study of CF techniques and then using CF approaches to build a plane with the same basic size and shape as a LE.  The size and shape would cover much of the aerodynamic "will this work" unknown.  But you still have the structure unknown, depending on what number and quality of examples you have to pattern after.

Might want to read up/study what Belite has done as they have toyed around with CF wing parts on an UL.

[sideband]

I was wondering the same thing when I first started trying to plan my LE out. I quickly realized how much more complicated the CF was going to be and started looking more to fiberglass. One problem with CF that I didn't even think of is that if it touches aluminum/stainless rivets it will cause them to rust. I will hopefully find a good way to make my ribs and part of my spar out of fiberglass instead of spruce just to avoid any problems with this obnoxious Florida humidity.

[Tom XL-7]

The solution to galvanic corrosion in carbon fiber connections is to use titanium or one of its alloys for your hard points.
Sounds pricey, but probably not worse than the carbon fiber. Your idea of using fiberglass is good. It is the conductivity of carbon that causes the problem.
 Carbon fiber tapes or rods could be laid into the caps of a foam and fiberglass spar giving you the strength without the other.
  I once made a rib out of blue builders foam at an airshow. Someone had a booth for hands on demonstration. Nothing to sell, just introducing people to doing something.  3/4 builders foam cut rapidly on a router table with a template. Using Tite bond, you glued a 3/4 " wide rattan edge band from a big spool of the stuff and it was done.
 I dismissed the idea as not enough rocket science for the jerk that I was ( now a jerk for different reasons, I grew out of that and into something else)
But I still remember how simple, fast and light it was. I should add inexpensive as well.
 The lugs (cluster sockets) would be the game killer in a CF fuselage but titanium can be welded. 
what a sight that would be.
 Tom XL-7
Good luck, more importantly, keep it safe

[scottiniowa]

The solution to galvanic corrosion in carbon fiber connections is to use titanium or one of its alloys for your hard points.
 this generally ends up building a NON-reparable part,  but if the labor saved pays for the part, I am all for it.

 Carbon fiber tapes or rods could be laid into the caps of a foam and fiberglass spar giving you the strength without the other.
I have assisted in the calculations several times on this, and it generally comes out the same- i.e. when calculations for the spar caps come into play, we can easily plug in and come up with the required carbon rod needs.   For example, lets say, we need 4- .125 diam rods for 4 feet, then 3,  2 for another 2 foot, and then 1 for the last.  (all starting at the root)  All easily calculated.  (once you decide which formula is correct)      And you know what weight savings you will have for this “spar cap material” which is generally a great savings.  So then we need to calculate the spar web and or base these rods attach to.   There in lies a major problem, as the rods are so strong for their size, how do we insure the base is strong enough to hold them under extreme load.  Soon a simple formula turns into a massive head scratching event.   I have no doubts that someday this will be all figured out and have great hopes for that..  And folks like J. Marske and others have gone a long ways, but generally come back to full carbon fiber webs and rod cap supports  (i.e. cost)   Certainly a catch 22 

  I once made a rib out of blue builders foam at an airshow. Someone had a booth for hands on demonstration. Nothing to sell, just introducing people to doing something.  3/4 builders foam cut rapidly on a router table with a template. Using Tite bond, you glued a 3/4 " wide rattan edge band from a big spool of the stuff and it was done.
 I dismissed the idea as not enough rocket science for the jerk that I was ( now a jerk for different reasons, I grew out of that and into something else)
I smiled at this Tom,  doing demos and lighting the fires is where/how many great new ideas form.  I suspect what was being shown was how strong the material can be made quickly. Where the problem starts is how this material reacts under the wing load conditions.  Some might call this concern “bond shear”   with one area certainly strong enough, with the other area not strong.  Just a matter of how to make both a combined “strong”  The answer is close…but not sure it is out there for the common builder yet.  Please correct me if I am wrong.

But I still remember how simple, fast and light it was. I should add inexpensive as well.
 
 Tom XL-7
Good luck, more importantly, keep it safe

Just  thoughts above in bold by Scott

[Tom XL-7]

As for the foam rattan rib, I was not suggesting or recommending it as a replacement. Just a story. But you are right it could be a starting point.
There have been aircraft with foam wing ribs, Examples could be found in old drawings. The skypup used them hanging behind a single spar -Dtube I believe.
Somewhere in my mess are drawings for the wing-ding.  What amounts to a biplane go-cart.  I was young and stupid but still smart enough not to build and fly it.
I believe it had foam wing ribs.
 I was lucky enough to attend a seminar on spars by Jim Marske.   Have always been a fan of sailplanes. That was what drew me to aviation. 
Tom XL-7

[stevejahr]

Common practice with CF structures is to line attach points with FG layer.  Very simple and how guys put aluminum bottom bracket into CF bike frames.

As to the "lugs" on a CF fuselage this too is pretty standard practice.  The CF tubes are cut and notched to fit just like metal and then glued together with a fillet (just like a weld filler).  Then wrapping laminations are added around the joint to reinforce it.  Sticky and messy perhaps but not all that hard once you get the technique down (in other words there is a learning curve just like welding and the later joints are going to be a lot prettier/easier than the earlier joints).

The magic of composites is using the best properties of the best material for the problem at hand.  It does not have to be carbon or glass or epoxy to be composite.

[Tom XL-7]

Thanks Steve, It does sound like a messy affair, but doable. 
I was thinking lugs like on an older  steel bicycle
 A cast item that provides sockets that the tubing is brazed into. Kind of like copper plumbing.
Only so many combinations are available and making your own would be a serious effort.
Tom XL-7

[scottiniowa]

I think what Steve was meaning (and certainly a good thing to mention) was all build processes are a matter of getting the process learned.  This would be a layup of carbon and glass,  wood or metal parts. so many different ways.

I would not classify any of the this "hard to learn"  but some of it certainly different than what we were used to even just 10-15 years ago.

When we are glass fairly large parts, and have the gloves on, and things are going quick but to plan- you can think, "boy this could be a mess if we were not ready for action"  but soon the task is done, gloves pulled off and paper/tapes and plastic in the trash.... All good.

cheers
Scott

[okdonn]

The magic of composites is using the best properties of the best material for the problem at hand.  It does not have to be carbon or glass or epoxy to be composite.

Remember, "wood is the original composite" - sorry, I don't remember who said that, but I thought it was good . . .

[Tom XL-7]

any process can be learned and being prepared is the answer. When stuff is all wet with epoxy is not the time to figure out what you need to finish the job.
 Totally agree. 
 So I spend a little time researching CF tube assy.
There are some lugs available in conventional geometries. 
There are inserts and bolted connections
There is the cut, fillet and wrap method as Steve mentioned. That appears most flexible.
 Still, an airframe cluster is so busy compared to the simple connections on a bicycle frame.
Oh, and let's not forget to put it in the oven for the cure as many resins require.
 Scott If I were to tackle a composite legal eagle fuselage. I would go monocoque.
You once made a drawing of a body for the XL. It was green.  That would be a great starting point.
 Then again maybe I will just weld up the steel I have on hand and call it a month.
Tom XL-7

[Tom XL-7]

The original subject of the thread was a concern of a wood wing structure surviving in relentless high humidity.
The gulf coast of Texas where the design originated also has that same issue.   
For those who live there can you seal the wood sufficiently to be comfortable.  I have high humidity in the summer followed by a total lack in the winter.
That can cause a lot of movement in a wood structure as it expands and contracts. Not sure which is worse. I am confident the wood once sealed won't vary in moisture content to a point of concern. 
Tom XL-7

[scottiniowa]

 
 Scott If I were to tackle a composite legal eagle fuselage. I would go monocoque.
You once made a drawing of a body for the XL. It was green.  That would be a great starting point.
 Then again maybe I will just weld up the steel I have on hand and call it a month.
Tom XL-7

Very good memory Tom and yes I did that.  More of a experiment in just how aero dynamic I could make a draggy bird. (and to see if I could blend surface work into a rag/tube aircraft.    This short answer,  yes it can be done and most likely would make a big difference.. But then again, that just wouldn't be a Legal Eagle any more.  And you are very correct- monocoque it would be, for a whole new can of worms...  Ahh, to be 20 years younger and 20 times more funds.
. 
Scott-  PS, it does look like the wings as in the plans will work well for 90-95% of the folks building.

[stevejahr]

Tom/Scott, you guys are picking up all my signals :-)

Indeed one of the challenges in working with resins is racing the cure time once they are mixed.  Just like the T-88 epoxy for wood joints.  Thinking it out, having all the tools present, doing as much preparatory prework done as possible all go a long way towards a quality and maybe even a satisfactory outcome.

Calfee is a recognized leader/expert in building custom composite bike frames, including tandems (one of my other hobbies).  I figure if they can do a hand laid up "lug" on a CF tube joint and have it stand up to the kind of weight and vibration and cyclic loading of a tandem bike... that style of joint must be pretty darn strong.  But if you look at their frames you can see the step for the extra layers of the lug.  Landshark is another custom bike frame builder but on his bikes everything is just so smooth you cannot even tell they are built lug style.

Yes a typical airframe has a few more tubes into some joints than a bike.  So do it 500 lb marshmallow style: one joint or panel of joint at a time.  Or get creative with the layup since nothing requires it to be one piece like a metal gusset. 

In design and engineering we choose materials for optimum trade off.  Cost.  Ease of construction,  Longevity.  Weight.  Etc.  When considering a change in materials one needs to again consider those trade offs.  CF could be a weight saver, but only if done well, but will be much more expensive than CrMo.  I would probably build the LE just like the plans... and fly it... and then take on improving one part at a time.  Maybe a CF rear fuse section keeping the forward CrMo?