[RCSE] Dyneema, Spectra
Dyneema is basically equivalent to Spectra fiber, and yes, it has largely been rejected as a material for fabric or linear composite construction due to lousy bonding properties. It can be an amazing fiber when used for rigging (ropes, lines, etc), but even there, it has a couple potential achilles heels: 1)incredibly slippery, making many conventional knots ineffective. 2) very low melting point. If it is used raw (not protected by a much higher melting point braided sheath) then another line (of any kind) dragging across it in one spot can easily produce enough localized heat from friction to simply melt through it. It is no wonder then, that Dyneema and Spectra have probably found their best niche in the low-stretch cores of high performance rigging lines (racing sailboats, etc.) ususally surrounded by braided, friction resistant sheathing, which solves both key problems, protecting from friction burn, and making knots more effective. Exposed braided spectra has found an interesting utility niche as control line for maneuverable multiline sport kites, where it's slippery nature is actually a gift, since these kites need to remain maneuverable even when the lines are twisted around one another from having done one or more 360deg maneuvers with the kite. This particular friction is not a problem for burn-through, because it is spread enough over length not to concentrate the heat in one spot. A sport kite with good quality braided spectra line can easily be turned 10 times in one direction and still be maneuverable. Try that with almost any other fiber Not surprisingly, the ends of the lines that attach to control bars and to the kite are usually sleeved for knotting and anti-chafe. More than you wanted to know, Lift, Scobie in Seattle RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] Dyneema, Spectra
There was a similar fiber available in cloth from a British source, I think it was called Dynel or something similar. The home built boat community liked it for the final layer on the bottom of the boat. It was so abrasion resistant that you could beach the boats with very little wear. This would probably be good on the skid area of slopers.. Mark Mech www.aerofoam.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] Dyneema, Spectra
Mark Mech writes: There was a similar fiber available in cloth from a British source, I think it was called Dynel or something similar. The home built boat community liked it for the final layer on the bottom of the boat. It was so abrasion resistant that you could beach the boats with very little wear. This would probably be good on the skid area of slopers.. Dynel was something else, a form of Dacron if I remember correctly. It was also a bad idea for primary structure in composite construction, but for an entirely different reason. The basic idea in a fiber composite is to have some strong, stiff fibers to carry the loads, and some sort of matrix material to hold the fibers in position. The key is that the fibers must be much stiffer than the matrix material or else the matrix does all the work and the fibers are along for the ride. For example, consider concrete reinforced with steel rods. The concrete holds the rods in position, but the much stiffer steel rods do most of the work of carrying the loads. Now imagine concrete reinforced with rubber rods. Perhaps the rubber rods are indeed capable of carrying quite a bit of load, but by the time you stretch them far enough to start carrying that load, the concrete has long since cracked and crumbled away. The matrix tried to do all the work, the fibers didn't do their job, and the matrix (and therefore the structure) failed. This was the problem with Dynel. It's less stiff than epoxy, so the epoxy tries to do all the work. It would actually be stronger to use just epoxy by itself, at least you'd have a greater amount of epoxy in the same total volume. I remember a seminar by Burt Rutan I attended years ago. Someone asked him his opinion of the Dynel/epoxy used in the KR-2 homebuilt (which fortunately just used the composite for the outer shell for shape, but used wood for the primary load-bearing structure). His comment was that The Dynel is a great way to hold the epoxy in place while it cures. Don Stackhouse @ DJ Aerotech [EMAIL PROTECTED] http://www.djaerotech.com RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
Re: [RCSE] Dyneema, Spectra
Good leading edge material but very hard to cut. Easiest cutting was with a soldering iron. Then in today's thin layers you would probably be left with a bump. After I stopped using it I found I should have been cutting all the fabrics at 45 then I probably would have felt differently about some of the difficult fabrics. Rick Richard Hallett Pittsfield ME USA RCSE-List facilities provided by Model Airplane News. Send subscribe and unsubscribe requests to [EMAIL PROTECTED] Please note that subscribe and unsubscribe messages must be sent in text only format with MIME turned off.
