John,

As I've told you before - I have plenty and you're welcome to whatever you need.

Warren

Thanks, Warren - I had forgotten who had graciously offered to part with some. I appreciate it - I'll get some more precise measurements, though it looks like about a yard.

My first work with carbon went really well - I found it to be easier to work with than I had anticipated. I'm shocked at how much more rigid it was than glass, too!

Wait until you see the fin can on my L3 bird - You could drive a truck across it and it would probably be fine. I expect the booster section could fall from 10K or better and bounce with no damage except scratched paint.

As for the carbon, it is rough to roll it because it is so stiff and you don't want to fold it as it will break fibers. I don't know how your timing works out, but best would be if you bring your dimensions back to my place when you're here for Mayhem and we'll cut it to order and figure the best way to package it flat for you.

W

Warren, I'll trace out a template of what I need. I'm going to go tip to tip x 2 for my 98mm minimum diameter project. I will fly it at BALLS '09. I figure by doing the layup this summer and letting it sit in my garage, I'll get a really good cure.

The rocket survived well with three layers of glass (each layer "stepped") on an M1939. I've decided to push it now 🙂

Your L3 sounds venerable. I've never gone more than 3 layers of glass, myself. Are your fins through the wall, or is this minimum diameter? I can't remember now...

JW

Through the wall. This is killer bombproof, mainly because I'm building for N motors and also because if the thing comes in on an apogee streamer without the main deploying, I'd rather be able to fly it again rather than pick up the pieces in a bucket. 1/4" G10 core with alternating, stepped layers of Kevlar and glass, each layer larger than the last, laid across the motor mount tube. Then installed in the airframe and 2 layers of carbon (so far - 1 more to go followed by a glass sanding veil) with the inner layers smaller than the outer layers. I figure it will be easier to finish this way and I hope to show some nice carbon weave in the finish after the painting is done. Everything is vacuum-bagged down by the way.

Actually, all this overkill is an experiment in killing fin flutter. I've got this theory I've developed about resonanant vibrations across the span of the fin. By making the root thicker than the tip and by varying the materials in the layers, no resonances should be possible. Fins are 3/8" thick at the root and just a hair over 1/4" thick at the tip. I'm planning something very big as we've discussed in our private emails and I want to build up bolt-on composite fins that won't flutter in the mult-mach regime we've been discussing. I'm thinking aluminum or Nomex honeycomb cores skinned with an alternating mix of carbon, Kevlar, glass. This bird is the first prototype for me of this construction method (except for the bolt-on part). IF I get my L3 cert, I'm going to talk to some of the propellant-heads about making me a big O for a second prototype that will use bolt-on fins in a machined channel.

Which brings to mind a question for the motor-heads out there. What impact would welding aluminum channel axially on an aluminum motor casing have on the burst strength of the casing? (actually combo airframe/motor case) Would it need to be re-heat treated or annealed to restore the full strength of the motor case? This second prototype would be my BALLS project for next year or the year after.

I'm sick as a dog this weekend - picked up a very nasty cold or a mild case of the flu when I flew to Milwaukee last week. (Air travel sucks!) I have no energy whatsoever to do anything except read, watch tv and sleep. Flew right over Ames on my way there by the way - did you see me wave out the window?

W

Warren, you'll do very well. No one doubts that. You are one of our composite gurus. I believe, as you do, that it's better to over-build than under build. I'm using CF/Kevlar hybrid on my motor mount, first layer glass, which I prefer to do over G10 first, then mount the motor mount and fins, then do a layer of CF and a last layer of glass for an easier finish. I owe that to Art. 😯 My L3 G10 core fins were 1/4" as well. I respect your theory on fin flutter, although all those layers of composites will dampen any resonance. What is the resonance of aluminum? And, yes, this probably should be in the construction or composites thread. 😉 Get well, dude! I hope Mike Bennet, JamesR, and Conway see this; they are our "motor-heads." And, be sure to check TRA's use of aluminum (i.e., the amount of metal allowed)... although at Balls no one cares. 🙂

Warren. Your Fin Can sounds like how I did Full Throttles fin can for my L3. The resonance issue is attributed not to just placement but the types of materials used. Two different materials is always better then one similar say CF on a Glass fin and body, Vs. Fiberglass laminate on a fiberglass fin and body. The glass and the CF have 2 different resonance frequencies. Layering them together will aid in canceling out one another. This is a proven fact. In fact its how dampening happens on a lot of things. Now using even one more material like the Kevlar even goes one further. When I did my L3 (BTW Rocketry Planet did an article on it and shows the laminate pictures of the fins and booster) I used Kevlar laminate of 2 layers then, unidirectional CF laminate in 4 layers with opposing direction of placement then layed over with finishing 2oz glass all layed up on a Performance Rocketry 6" Body tube and .093 thick G10 fins. Inside and outside fillets all with chopped CF in them as well as TTW fin construction. I can tell you this. The booster IS bullet proof. Fell from 14,000 feet with only a small drogue chute (70lbs rocket with 24" chute) and it barely scratched the paint.

As far as welding on aluminum of the case. No DO NOT do it. For several reasons. First off welding aluminum is a tricky bit. Not everyone is capable to do it RIGHT. I know guys that can but even they would highly recommend against it. When you weld you take a big chance at taking the annealing out of the aluminum and thus causing a spot where pressure issues can happen and margins of safety for pressure drop. You also can cause distorting of the metal as well. A large failure point on most motors is at an Oring junction. Where the Oring and the closure touch the case. Now in most circumstances the fins are very near and right over that area. Because this is a hot spot and most concentrated pressure heat combo area if you hurt the annealing in that area what once handled say 1500psi may only do 800psi. If you get any kind of spike say on a motor running 5 or 600psi it can go boom very easy. having a safety margin designed into your case is important. The O and P motors that James and I own have been tested to handle at least 1400 to 1500 psi. I run my Loudmouth Blue right at 750 to 800 psi and James runs his red closer to 450 to 550psi. If a small hiccup happens no harm no foul. Without that margin it would be game over. I have been in the works in designing a Min diameter P rocket with a clamp on fin can that rest on a machined lip or even external thrust ring on the case then bolts together to clamp around the case quite tightly. Now this way I still keep my margin. I had also been designing a forward closure for the case that would act as a coupler as well. But thats another story..

Conway

Sounds like we reached the same conclusions Conway. The way I built it up was I took the fin blanks and laid 4 layers of glass from the root out 1/8, 1/6, 1/5, 1/4 on each side and v-bagged that with a food saver. That was just to provide the initial taper. The fins were glued up to the motor mount tube with JB Weld and a small fillet with JB Weld (1/4" radius). After that I ran a layer across the motor tube 1/4 of the way out using 5.7 oz Kevlar. Next layer was 6oz S-glass across the motor tube 1/3 of the way out. Then a layer of 4oz uni-directional Kevlar 1/2 the way out. Then another layer of S-glass 2/3 of the way out. This layer was biased 45 degrees.

At that point I installed the can into the airframe and after doing 1/2" radius fillets inside and out, applied the first layer of carbon across the airframe, again at a 45 degree bias, that went 1/3 way out. Then a layer of S glass 2/3 of the way out. Finally a full coverage layer of carbon at a 0 degree bias all the way out to the tip. I've been thinking of doing yet another layer of carbon that will overlap the fin edges all around and then a final layer of 2 or 3 oz E-glass as a sanding veil. Every layer except the very first Kevlar layer across the motor mount tube was v-bagged - my biggest mistake so far as the layer turned out slightly more than twice as thick as I planned. Oh yeah, and the entire exterior of the motor mount tube (4" PML phenolic) was wrapped with 2 layers of kevlar and one of glass. That wasn't v-bagged, but I used shrink-wrap tape and a heat gun to force it down tight.

This is certainly the nicest job I've done to date in building a fin can and my end result should be bombproof. There is abolutely no give or flex that I can do by hand - even standing my full 198# on the airframe doesn't seem to flex the fins. The bevel edge is razor sharp and I've cut myself on them a couple times and badly enough that I've had to make edge protectors that slip over them. My biggest problem now is I'm falling behind schedule on the rest of the bird due to an emergency trip to Milwaukee for my mother-in-laws funeral and now this nasty case of the flu that hit me Friday morning.

Hopefully I'll have some energy tomorrow and will get another layer v-bagged on - My original plan was that this weekend I would be filling and sanding but that trip to Wisconsin blew that out of the water.

John, where online did you order up that Aeropoxy lite that you've been using for filler? How quick did they deliver?

http://www.wicksaircraft.com/catalog/product_cat.php/subid=489/index.html is a good source of Aeropoxy, though I don't see the "Light" (which is a wonderful filler) there. For that, I went to www.aeropoxy.com

Regarding using kevlar and carbon and mixing and v-bagging, I'll say this... I had a booster fall from 23K that had a spent casing inside. The tube had serious spiral fractures, even with the casing still inside. The fins were three layers of 6 oz. satin weave glass. I didn't pay any attention to orientation, as satin weave all looks the same to me 😯 The layers were stepped, and being a hack I sanded away a LOT of that glass. The fins? They survived teh fall just fine. I cut the rocket back, Warren helped me make a splice onto the airframe, and all is good.

Until this rocket, I've never gone more than 3 layers and they have always been 6 oz. satin weave glass. Never had a problem. Remember Chris LaPanse's I600 rocket wasn't even glassed (it was phenolic) and it had a single layer of 6 oz. glass tip to tip.

What I'm getting at is that we seem to be overdoing it, me included. If the fins stay on my J570 min diameter rockets, then I think we are OK. I did go to carbon on my last rocket as it looks to be well past mach 2. Stay tuned!

HAPPY EASTER ALL!
J

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

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!
😉

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.

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

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.