Looking to buy some carbon

[Warren B. MusselmanModerator]

John, your booster and the spent casing that fell from 23K was maybe 4# or 5# if I recall correctly. My best estimate for weight for this booster is about 25# with the casing. Conways bird (whole bird or just booster with motor case?) was 70#. There is a huge difference in density and weight versus air resistance on these. If Conway’s 70# bird was able to get up and be flown again, I’m in the right ballpark.

Now I’ve never had a fin shred experience except on a cheapy PML Callisto that had previously taken damage but the one thing I most definitely don’t want to see is the 5″ bird I’m working strip a fin right off the pad with an N motor up its butt and start skywriting 30′ above everyone’s heads or ground-sharking around amongst a bunch of spectators. Overkill is good. On this particular project, I’m not cutting it to the bone on weight and I want to see this survive quite a few flights – this bird will be my big sport flyer for 98mm motors. If it comes in without a chute, I’d like to fly it again. All these extra layers are part experiment to develop the layup techniques and part caution and probably add no more than 2# at most to the rocket, maybe less since we’re talking maybe 2 yards of additional material at roughly 6oz a yard plus perhaps an equal amount of resin – so call it 24 oz total added weight on a bird that looks like it’ll have a pad weight of around 35-38#.

My biggest complaint with this project is that each layer on the fin can has required me to build a new vacuum bag around everything – it sure ain’t sparing of the sealer goo and v-bag film. Pre-layup prep for each layer involves carefully cutting out the template, then the actual fabric itself (carbon, Kevlar, glass), then cutting v-bag film, then peel-ply, then breather and finally sealer tape. Then I need to setup the v-bag with sealer along the appropriate edges and get all these layers and material laid out in the order they’re used. Then, once all the materials are organized and laid out ready – I mix epoxy and rapidly apply all three pieces and smooth out any air bubbles, apply peel-ply and again smooth out bubbles, apply breather and tape into place, then construct the v-bag around this whole deal – taking care the whole time to make sure I don’t disturb the laid up glass or carbon or kevlar and finally to pull the vacuum and adjust while things are shrinking down and THEN work my way around all the sealed edges to make sure I have no leaks. So far, every layer has been vacuumed down to about 26″ of Hg – as near perfect as you can get at this altitude.

By the way, there are pictures of all this – or at least of each layer finished – that I’m going to publish sometime today or this week depending on my level of energy.

One final note – satin weave cloth is not nearly as high strength as plain ol’ straight weave. Satin is used for finish layers as it most definitely provides a smoother, more conformal surface that is far easier to drape around corners and over curves but because the roves do not approximate a straight line, the loads are not as efficiently carried. My finish layer will be 2 or 3 oz. Satin weave glass for the sanding veil.

W

Warren

W

[Bruce R. Schaefer]

What I’m getting at is that we seem to be overdoing it, me included.

JW, you may be correct, but are any of us willing to take the chance? I did glass to the G10 motor mount and fins, then tomorrow I’ll layup the CF/Kevlar hybrid to same–which IS a real, uh, pain to cut! Warren, Conway, how do you guys cut that stuff without fraying it? I did it two years ago, but don’t remember the difficulty. I used my wife’s sewing rotating blade cutter, dulled it immediately, then asked her to cut it with scissors, since as a barber/cosmo lady she gets paid to do that, as she pointed out. She didn’t say anything after I embedded Kevlar and CF into her sewing cutting board. I told her that I guess I’d have to buy her a new one. She gave me “the look.” I may or may not put CF over the airframe and fins tip-to-tip, followed by the 8-9 oz. airplane FG, or just use the FG. I’ll make the call after I look it over. My hands have deteriorated so much this past year, honestly, this may be the last big bird I’ll be able to build. Hey, rocket guys don’t go quietly into the night! We light up the sky!
😉

[Warren B. MusselmanModerator]

Kevlar is a total pain in the ass. I have two pairs of supposed “Kevlar shears” I bought at Hobbytown sometime back and even they hack the hell out of it. A clean cut is essentially impossible. No manual rotary cutter is going to do the job. I do know that professional grade shears exist as well as commercial mechanical rotary cutters, but these all start well over $100 and I just don’t do enough Kevlar to justify it. I’d love it if I could send a template to a vendor and have them cut the pieces to order, but that service doesn’t seem to be available.

I used the hybrid carbon/Kevlar stuff on my old 4″ bird and had a helluva time with it. The vinyl flooring in my office has multiple deep cuts in it from trying the rotary cutter and while the carbon cuts very cleanly, the kevlar just pushed down into the cuts in the flooring. Fortunately, my landlord thinks the artist who lived her previously did it somehow.

If someone does know of a decent pair of Kevlar shears for a somewhat reasonable price, let me know – I’d even spend $150 if that’s what it took. I just want a clean, sharp cut like I get with glass and carbon.

W

PS: I’ve moved this entire thread from the Swap Forum to the Composite Construction Forum as suggested.

[Anonymous]

What I’m getting at is that we seem to be overdoing it, me included.

JW, you may be correct, but are any of us willing to take the chance? 😉

I will say that a piston strap broke and a ~30# booster section of Argos fell from a great height, and it totally sprang that heavy-walled Dynacom tubing (5″ diameter, monster thick wall on that stuff).

My fins were fine. They were through the wall – barely… 5″ airframe and 4″ motor mount. The fins had a single layer of 6 oz. glass tip to tip.

I fixed the airframe by jacking it up inside a metal doorway, using a hydraulic jack, and making it all come back together. I then glassed the affected area while it was all under pressure. Worked GREAT! I was proud of my solution. But back to the fins – they were fine.

I’ll soon find out on the overkill thing – I went carbon / carbon / satin weave glass and am headed for m2 using my standard technique (no fin tabs). I think it will be fine…

JW

[Conway StevensParticipant]

What I’m getting at is that we seem to be overdoing it, me included.

JW, you may be correct, but are any of us willing to take the chance? 😉

I will say that a piston strap broke and a ~30# booster section of Argos fell from a great height, and it totally sprang that heavy-walled Dynacom tubing (5″ diameter, monster thick wall on that stuff).

My fins were fine. They were through the wall – barely… 5″ airframe and 4″ motor mount. The fins had a single layer of 6 oz. glass tip to tip.

I fixed the airframe by jacking it up inside a metal doorway, using a hydraulic jack, and making it all come back together. I then glassed the affected area while it was all under pressure. Worked GREAT! I was proud of my solution.
JW

Hmmmm, I think I can remember that. Try #2 maybe when a loop broke? I can also remember that door way opening at your work (if I remember right it was the littler shop building next to the larger facility) even being metal and concreete making some noise as the airframe was jacked into it to straiten it out to fix the spiral fracture/kink. We used the mylar and duct tape compression wrap if I remember right. Turned out quite nice to.

I must admit I do like convolute wound better then Spiral. But would take either over most other materials.

[Bruce R. Schaefer]

You guys are the gurus. Warren, you’ll get a kick out of this, I’ve put the CF/Kevlar hybrid on and will use a Mikita hand disk sander to get rid of the excess and frayed parts tomorrow. Oh, that’ll be fun. 😈 I’ve dulled some scalpels on this stuff immediately–although that may give some hint to its strength. From now on CF and glass. If all goes well tomorrow, then I can epoxy the motor tube and fins in, then just glass or CF and glass after that. This part is the pain, seeing the Crimson Comet fly will be the reward!

[James Russell]

Kevlar is a total pain in the ass. I have two pairs of supposed “Kevlar shears” I bought at Hobbytown sometime back and even they hack the hell out of it. A clean cut is essentially impossible.

if you take a pair of shears and run the blade on a grinder at ~90 deg or so it makes a good cut. I have seen several people have good luck with this. no need to buy expensive ones if you sharpen them your self.

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