Author Topic: Has anyone considered?  (Read 1979 times)

Offline Golden Eagle

Re: Has anyone considered?
« Reply #15 on: March 06, 2018, 03:20:10 PM »
Greetings Steve,

  I’ve pondered the mandrel release process and watched as many videos on the subject that I can find.  There isn’t much out there.  For the big commercial operations it looks like they wax the mandrel well and when it is time to remove it they hook it up to a long pulling device and slide the CF tube off.  I could rig up something similar, but I’d bet if I did that it would be stuck on there for life!!  So I got to thinking about some type of solid coating that covers the mandrel and when the time comes it can be liquified to allow the outer tube to be slid off.  Candle wax came to mind.  The resin wouldn’t stick to the wax layer or the mandrel as a bonus.  If sufficient heat were applied, a moderate pull ought to be able to release the CF tube.

  You are correct.  There is a better way to make the tubing than vacuum bagging it.  You can buy a 2” wide roll of shrink wrap tape.  It comes either perforated or non-perforated.  You can get it with a release coating on it too.  The mandrel should rotate in order for this to be applied neatly.  My mandrel will be motor operated, and with variable speed rotation.

  I think in reality an 18’ tube is unrealistic.  Too long.  12’ Might be more doable.  The process for me would be: 1) coat the mandrel (polished steel tube) with a thick, rubbed-on layer of candle wax.  2) Wrap the candle wax coated tube in a tightly wound 2” wide layer of that non-perforated shrink tape. 3)  Apply all of the wetted layers of appropriately oriented carbon fiber fabrics/strands, etc.  4)  Spirally wrap everything in a tightly wrapped layer of “perforated” 2” wide shrink wrap tape (with release agent).  5)  Use a hair dryer or hot air gun carefully to thoroughly tighten the tape.  Excess resin will ooze out!!!   6)  Let it set up to cure for a day or two.  7)  Do the boiling water routine I previously suggested.  8]  Slide off CF tube.
  Incidentally, I saw a video of this process I just described.  The addition of the outer layer of perforated release tape really squeezes out the excess resin, and the tiny holes allow it to continue oozing for several minutes.  It does a very good job of getting out excess resin and it leaves a very solid product.  Testing would show how solid.

  I have a 3’ Piece of black pipe on hand.  I have epoxy resin, too.  All I need is to buy some carbon fiber material and some of that 2” wide tape I mentioned, both perforated and non-perforated..  One of these days I’ll do a small experiment and make a short tube and see how everything works out.  As a test subject I would do the 8 layer version, one layer of each:  1) plain weave fabric   2) 0 degrees [lengthwise]  3) 90 degrees  4) 45 degrees  5) 45 degrees from the other direction  6) 90 degrees  7)  0 degrees again   8]  plain weave, mostly for appearance.     These eight layers should produce a tube of .09-.12” wall thickness.   If I were to feel the need for an extra strong tube, I would give two additional longitudinal (0 degree) layers.   

  BTW, for joints my thoughts are:  you can buy carbon fiber toray strands.  (Multi lengthwise strands like yarn on a spool). ALL strength is in the direction of the strand.  If I were ever to get so far along as to actually build a CF fuselage, I would build it IDENTICAL in appearance to a CM fuselage.  It would have metered (coped) tightly fitted joints.  3M makes an epoxy that is phenomenally strong.  (#2216, I think). I would put a little dab of epoxy to hold a joint securely.  Then I would use a combination of unilateral CF fabric, twill fabric, and toray strands to build essentially a “PVC style fitting”.  It may sound a bit hokey, but what I have in mind would work out well.
  Added note:  To maintain a consistent and neat appearance for ALL intersecting joints, in preparation of securing a joint I would tape in place some kind of 5” long outer tube, with the end of it roughly 1 1/2” away in all directions from the center of the joint.  Let’s say I use 1/8” walled aluminum tube split lengthwise.  Then, an inch and a half away from the center of the joint I use electrical tape to secure this tightly fitting cut tube.  Let’s say the joint has three adjoining tubes.  There would be therefore 3 split aluminum tubes 5” long, secured 1 1/2” away from the joint.  Next, using various sized and oriented pieces of wetted CF materials, spirally wrap and coat the joint, building up to be even with the aluminum tubes outer surface (1/8”).  Lastly, tightly wrap the entire joint with that 2” wide, release treated, perforated tape, then apply sufficient heat to shrink it.  Repeatedly wipe away excess resin for a few minutes.  After a couple of days, remove the shrink tape, and then remove the aluminum tubes.  Lightly sand the sharp edges of the new “fitting”, and coat with a single brushed on layer of epoxy.

Gotta run.......

Offline stevejahr

Re: Has anyone considered?
« Reply #16 on: March 06, 2018, 06:32:48 PM »
Looking at John Slata's pictures on Landshark bicycles... it appears to me he glues the tubes together, then adds a fillet around the joint, and finishes by wrapping with normal bi-di fabric.  I agree that the strength runs with the fibers so adding CF towe around the joint has it's appeal. But once you get fibers around the joint then you have to keep them attached to the tube lengthwise. And that is where the bi-di cross fibers come into play. I do not expect it would really take much here to get the job done. Likely only 1-2 layers.

The real magic is getting the overlaps right and getting it all to stick down without turning into complete random fiber mat in the process.

If not for the length of mandrel you are talking about I would go for melted wax immersion rather than rubdown. Build up some thickness of wax that way so when melted the tube *definitely* comes off the mandrel.

Offline Golden Eagle

Re: Has anyone considered?
« Reply #17 on: March 06, 2018, 09:09:22 PM »
My thoughts exactly, Steve.

Maybe tomorrow I will steal one of my wife’s candles and see how thick of a wax layer I can get on my iron pipe.  In the meantime, I have come up with another possible way to make a meltable layer on the mandrel.  Sugar.....or salt.  Coat the mandrel in a thin layer of maple syrup, sprinkle on an even layer of sugar.  Wrap it in that 2” non-perforated tape.  Make the CF tube.  Once it is cured nice and hard, hook up my vacuum pump and suck water inside the tube and it will seek to eliminate ALL of the air where the sugar is.  The sugar will melt.  Slide off CF tube.  Probably lots of way to skin a cat (perish the thought since I love cats.)

Offline liteflyt

Re: Has anyone considered?
« Reply #18 on: March 06, 2018, 11:09:12 PM »
There are several sources of ready made Carbon fiber tubes...
One of which is:

Offline Golden Eagle

Re: Has anyone considered?
« Reply #19 on: March 06, 2018, 11:26:37 PM »
Yes, there are a few companies that make carbon fiber tubes, but at their prices it would not be worth the cost.  Much cheaper to make your own.

Offline Vince Carucci

Carbon Fiber Tubes
« Reply #20 on: March 07, 2018, 04:25:15 AM »
Does anyone know:

Is a CF tube strongest in tension or compression?
Or does it not matter?

Offline Golden Eagle

Re: Has anyone considered?
« Reply #21 on: March 07, 2018, 08:04:43 AM »
Hello Vince,

  There is no easy answer to your question because with CF if all depends on how it is made and the quality and orientation of the fibers.  However, assuming the CF tube is designed and built in such a way that it is essentially “as strong as possible”, then it is stronger in both tension and compression when compared to steel.

  In answer to your question, and I am NOT an authority by any stretch of the imagination, I am learning and that is all, but yes, it matters!  There is plenty research material and some tests that easily prove that CF is approximately 3.5 to 5 times stronger in tension when compared to steel.  Steel is isotopic, which means it is exactly the same strength in all directions.  Carbon fiber, on the other hand, is about half as strong in compression as it is in tension.  Therefore, in a properly designed carbon fiber tube it would still be approximately 1.5 to 3 times stronger than steel in compression.  It should be noted at this point that carbon fiber tubing is roughly 1/4th to 1/3rd the weight of steel.

  If you were going to build something out of carbon fiber tubing that was going to undergo severe “denting, scratches, cuts, etc”, then carbon fiber isn’t your best choice.  Or at least you would want to add some layers of Kevlar too, which they certainly do.

  I copied and pasted the following paragraph when I was researching an answer to your question:  (these are not my words below)

“First a disclaimer: most of what I know about carbon fiber fabrication comes from aircraft, not bicycles. Also note that carbon fiber is not the only composite that gets used -- just for one alternative, Kevlar fibers can be useful as well (Kevlar is stronger, but also more flexible than carbon).

Carbon fiber is strong, but does not respond well to point stresses. This is largely because it's basically cloth (woven out of carbon fibers). If you put a lot of stress at a single point, you're putting that stress on only a few of those carbon fibers. While the fibers themselves are extremely strong (for their weight), the bonding holding the individual fibers together is much weaker. For comparison, think of the packing tape that has fiberglass fibers running along its length. The fiberglass itself is really strong, but the strip of plastic and "goo" holding them together is a lot weaker. Although the details differ, the same general idea applies to carbon fiber as well.

The exact strength depends on direction as well. As I said above, carbon fiber starts out as a basically threads that are woven into cloth. The cloth is then impregnated with some sort of epoxy (the exact epoxy used varies with the application), laid up in a mold, vacuum bagged1, then baked to harden the epoxy. You can get the cloth in various different weaves, some with the same amount of carbon fiber running in each direction, other with (say) 80% of the carbon fiber in one direction, and only 20% in the other direction. At a guess, most of the CF used in a bike frame is probably somewhere closer to the latter variety, with most of the threads running along the length of a tube, and considerably less running around the circumference of the tube.

As long as we're at it: carbon is also about twice as strong with respect to being stretched as being compressed. You'll typically have around twice as many plies where it's primarily subjected to a compressive load.”   End of quote.

Offline Bee

Re: Has anyone considered?
« Reply #22 on: March 17, 2018, 12:52:09 PM »
Hey folks,

Some Noob started a thread on printing in carbon fiber over here:

3D printed 1 piece carbon fiber frame - Disrupting the strandards

That Noob would be me.

Thank you


Offline Golden Eagle

Re: Has anyone considered?
« Reply #23 on: April 07, 2018, 11:30:54 AM »
Not happening.

After doing a fair amount of research, and weighing the time, the costs, and other factors, building one LEXL with carbon fiber tubing just isn’t practical.  Could it work?  Yes, I believe so.  But is it worth a ton of hassle?  Not really.  I do believe, however, that a manufacturer that wants to build several CM fuselages could easily make it happen.  Basically he’d save about 20 lbs over using CM tubing.

I bought some CF material to make a few practices tubes, but that is all they’ll be; practice.

So back to Plan A;  Chromoly fuselage.

That is all.


Offline scottiniowa

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Re: Has anyone considered?
« Reply #24 on: April 08, 2018, 07:53:14 AM »
yeah, some of the best answers are ones that we (the question asking person) come up with on our own.

Well done!
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Offline LSaupe

Re: Has anyone considered?
« Reply #25 on: May 05, 2018, 08:01:47 AM »
Here is a nicely executed example

Offline JohnB

Re: Has anyone considered?
« Reply #26 on: May 05, 2018, 04:53:27 PM »
Les, Congratulations !!  your fuselage weighed 4oz less than the last one I welded up.

Scott Bledsoe,  Composite Aero Engineer ( Engineer on Space Ship One) that did the wing engineering on the Double Eagle,  said for about $5K in engineering time he could remove 5# from the L. E fuselage.   After I revived Leonard  with smelling salts  Scott went over areas that he was sure were overbuilt  (don't ask, I don't remember where) and said smaller, lighter tubing could be used in many places.   While lightness is paramount to a good performing airplane so is safety,  it is proven an XL can be built 10# under (at least) weight limit,   it's gonna take qualified engineering to make noticeable
improvement from here , at least on the airframe.  Engine a different kettle of fish. Right huh Frank?
Spencer's weighs 236# last he told me,  Anybody lighter?    John B

Offline Golden Eagle

Re: Has anyone considered?
« Reply #27 on: May 05, 2018, 05:18:41 PM »
The carbon fiber tubing fuselage still seems like a doable project, although I certainly am putting the idea on a back burner at this time.  So, if someone were to actually build a CF fuselage, I think if it were built equally strong compared to a chromoly fuselage, the CF one would come in at around 20 lbs, + or - a pound or two.  Additionally, the more CF you build into the plane, the more weight savings you will see.   But again, this is all back burner speculation stuff.

However, what about the idea of building the fuselage out of .028” chromoly?  Rather than using 5/8” x .035”, is it even worth the consideration of using the next wall thickness tubing down, and the next size tubing up?  In other words, could the fuselage be built sufficiently strong using .028” x 3/4”?  According to my calculations, you’d save just under a pound.  Maybe it’s just a dumb question., but I hear lots of guys say “every ounce counts”.

Offline JohnB

Re: Has anyone considered?
« Reply #28 on: May 05, 2018, 06:00:08 PM »
A Couple things to consider about 028,   it is much more difficult  (at least for me) to weld, especially with a torch in a big cluster.
Engineering wise I have no clue how the Long Column Bending Loads compare between 3/4 .028 vs 5/8 .035      That's what Scott B was gonna charge Leonard $5K to find out. Vibration from our shakers need to be considered as well.    Interesting thread    John B

Offline lowrider

Re: Has anyone considered?
« Reply #29 on: May 17, 2018, 08:27:47 PM »
New here and I'm building a Bearhawk LSA. At one point I did a lot of research on making CF leading edges for my wings. Bottom line was it didn't gain enough weight savings to be worthwhile. Another benefit of CF is it takes bumps (hanger rash) without damage much better than 0.016 Alum. I have alum wings.
I shoot a lot of CF arrows at a variety of targets and they are wonderful, don't break easily or bend like alum arrows...they are either good or broken...there is no in between. Also learned from CF arrows they don't like shear and when they do break wear gloves to fool with them...fibers stuck in your skin is bad.

I have a Cessna 170 and a Long Wing Challenger II which I'd like to replace the Rotax with a 4 stroke...maybe a 4 jug VW. Back in the 70's I used to build fiberglass tub beach buggys and Baja Bugs but it's been a long while since I've played with VW engines and it looks like there are few old engines worth considering for an airplane. Love my Ch II but it needs more power and 4 cycle engine...might even turn it into a single seat tractor "LEXL" like fuselage with clipped Challenger it myself all the time anyway.
Looks like a great little site and look forward to learning a lot from you folks....thanks for having me!
Somewhere along the way I lost the ability to act politically correct. Should you find it please feel free to keep it.