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For this sort of tube one wouldn't need fibers at 45 degrees. The tube is not being used to transmit torsion - it isn't a driveshaft. The loads are axial compression, and bending and ovalization in response to bending. When a long thin tube is bent, it ovalizes - becoming narrower in the direction of applied bending load. This reduction of thickness of the tube reduces the stiffness of the tube against the bending load, and thereby acts as a stress concentrator.

Optimal for this sort of stress will be to have inner and outer layers of the tube using spread tow unicarbon with the fibers perpendicular to the long axis of the tube, with spread tow unicarbon oriented axially between these two layers. The outer layers with that orientation provide the greatest resistance to ovalization. If one were to zoom in to a small section of the tube, ovalization looks like bending a slightly curved plate in the direction perpendicular to the axis of the tube. So orienting the fibers to give maximum resistance to that load is appropriate.

The miniscule difference in radius from the center of the tube for the axial fibers vs outer surface makes almost no difference in the bending stiffness and strength.

Unfortunately having fibers perpendicular to the airflow on the outside might not make for the best failure mode in that regard.

11-24-2013 10-10-38 PM.png
Having fibers at angles not aligned with applied loads essentially wastes the mass of the fibers.

BTW, some posts previously, some mention was made of West Systems epoxy. West Systems has no use for a high performance rocket IMHO. It is the only system available (that I've encountered at least) which has a Tg (glass transition temperature) low enough that a sunny day softens the epoxy, and is also un-responsive to post-cure. It's good for glassing over wooden boats. That's what it's made for. For aerospace work, use an aerospace epoxy.

Gerald
 
I wouldn't really recommend that. I believe when I posted that approach years ago that I also said I wished I had an alternative. One problem with that approach is that the clamping method doesn't provide even pressure, so you actually end up with a fin with varying thickness. That can be an issue if you then try to bevel the fins (several approaches that I use to bevel fins are affected when the fin isn't uniform). Further, C-clamps don't really provide all that much compression.

I've had the best luck laminating fins when I use two flat tiles and then bag the whole thing. I use bagging material that isn't too stretchy because the stretchy stuff gets sucked in between the tiles and messes things up. I also learned that you want tiles that are about the same size as the fin or fins (if you laminate a pair at a time). I tried over-sized tiles once, and the vacuum pressure easily broke them.

I have also tried one-sided bagging (i.e., tile, carbon, fin,bag) using a single tile, and then turning over the fin to laminate the other side. For reasons I don't quite understand, the result of this is usually just a curved fin.

Jim

Thanks Jim for setting me straight on the C clamps. I've read thousands of threads over the last few years that may go back to 2012. I try to follow the guys with high performance in mind such as yourself. I've learned so much from you guys just from reading. I want to thank you personally for sharing your incredible flights with us all!

I have a piece of granite 18x24x3 to within .0001 of being flat. I will use that to layup my homemade dragon plate. No core, just carbon fibre. I don't have a very consistant method for beveling the leading and trailing edges. Can you point me in the direction of your instructions on how to T2T your fins with CF. I don't remember reading them before.
 
I bought a 1" thick 6061 aluminum plate from a junkyard and milled it flat. I layup my fins on it (both sides at once and then vacuum bag the fins to the plate. Fins come out perfect.

Layers go:
-aluminum plate
-layer of Mylar .010 thick
-breather
-perforated film
-peel ply
-fin with carbon
-peel ply
-perforated film
-breather
-vacuum bag

Like Jim I tried doing one side at a time and I got warped fins. Doing both sides at the same time is a must. Composites love symmetry.

Thank you everyone for weighing in on the layup process. Kip, what does the perforated film do between the breather and the peel ply? Three fins, 7 layers each, every layer properly orientated, all the vacuum bag stuff put on correcly. If I pull this off without messing something up, I will be totally amazed! Oh yea, don't forget about the epoxy (4461ss) in between each layer!!!
 
For this sort of tube one wouldn't need fibers at 45 degrees. The tube is not being used to transmit torsion - it isn't a driveshaft. The loads are axial compression, and bending and ovalization in response to bending. When a long thin tube is bent, it ovalizes - becoming narrower in the direction of applied bending load. This reduction of thickness of the tube reduces the stiffness of the tube against the bending load, and thereby acts as a stress concentrator.

Optimal for this sort of stress will be to have inner and outer layers of the tube using spread tow unicarbon with the fibers perpendicular to the long axis of the tube, with spread tow unicarbon oriented axially between these two layers. The outer layers with that orientation provide the greatest resistance to ovalization. If one were to zoom in to a small section of the tube, ovalization looks like bending a slightly curved plate in the direction perpendicular to the axis of the tube. So orienting the fibers to give maximum resistance to that load is appropriate.

The miniscule difference in radius from the center of the tube for the axial fibers vs outer surface makes almost no difference in the bending stiffness and strength.

Unfortunately having fibers perpendicular to the airflow on the outside might not make for the best failure mode in that regard.

View attachment 315415
Having fibers at angles not aligned with applied loads essentially wastes the mass of the fibers.

BTW, some posts previously, some mention was made of West Systems epoxy. West Systems has no use for a high performance rocket IMHO. It is the only system available (that I've encountered at least) which has a Tg (glass transition temperature) low enough that a sunny day softens the epoxy, and is also un-responsive to post-cure. It's good for glassing over wooden boats. That's what it's made for. For aerospace work, use an aerospace epoxy.

Gerald

Gerald,

Some things I can do, and some things I can't, and rolling my own CF airframe is in the can't do area. Can you point me in the right direction of somebody who can using the techniques and high Tg epoxy you described?
 
Gerald,

Some things I can do, and some things I can't, and rolling my own CF airframe is in the can't do area. Can you point me in the right direction of somebody who can using the techniques and high Tg epoxy you described?

Why can't you roll your own tube? The process is well documented. I am not in front of a computer, but in my website www.rocketryfiles.com (username and password guest) I have two really large articles by Jim Jarvis that details this, as well as many of his other techniques.

Frankly, to play in the arena you are talking about rolling your own tubes might be needed.

Also, you are making carbon fiber plate not dragon plate. Dragon is company likely with trademarks and such- just saying.
 
Thank you everyone for weighing in on the layup process. Kip, what does the perforated film do between the breather and the peel ply? Three fins, 7 layers each, every layer properly orientated, all the vacuum bag stuff put on correcly. If I pull this off without messing something up, I will be totally amazed! Oh yea, don't forget about the epoxy (4461ss) in between each layer!!!

Yeah laying up a fin sounds simple but it's quite involved and time consuming once you get to work - a lot of layers. I just did 8 fins this past weekend and it was three days of work. Getting them on the rocket is whole other major process. But it is worth the effort!!

The perforated film meters the epoxy that flows out of the carbon cloth into the breather. Without it you risk a dry layup -> breather sucking too much resin out of the cloth.
 
Why can't you roll your own tube? The process is well documented. I am not in front of a computer, but in my website www.rocketryfiles.com (username and password guest) I have two really large articles by Jim Jarvis that details this, as well as many of his other techniques.

Frankly, to play in the arena you are talking about rolling your own tubes might be needed.

Also, you are making carbon fiber plate not dragon plate. Dragon is company likely with trademarks and such- just saying.

It isn't that I can't roll my own tubes. One of the problems is I don't have any of the equipment needed to do the job correcly. I've read Jim Jarvis technique on how to do it. I would have to make some things myself just to get started. Then there is trial and error time, the first one or two I make might not pass the test, or be of the same quality of somebody who does this for a living. The biggest reason for wanting to farm this out is because I have a job that keeps me busy 8 to 12 hours every day, 6 to 7 days a week. (thats how I finace this stuff) If I overload myself with things to do above and beyond my allready busy life style, than I will lose interest in it because things won't get my 100% effort. When flying rockets ceases to be FUN and becomes a burden, than it will be forgotten. I don't want that to happen, so it is important that I find a happy middle ground. I do agree with you on the arena and will try to scrutinize everything that I buy from somebody else. The biggest and most important thing I have going for me is all of you! All of your experience and knowledge will be the key to my success. I'm counting on you to keep me pointed in the right direction. And that direction is UP!! The faster the better!!

I don't want to get in trouble with Dragon, so from now on it's HYPERPLATE!
 
Ok, that I can relate to in terms of time spent working and how it effect time for the hobby. I have plans for many things, but having the time to do them is largely my issue.
 
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