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CCR

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Hello all, I need some advice on fin attachement on min dia airframes. I am constructing a 54mm min dia rocket that will have surfave mounted 0.140 carbon fins on a phenolic tube with a carbon sleeve. The root is 5 inches and the fins were attached and filleted with JB weld. I have read that the Performances's mongeese (?) have surface mounted 1/8" fins that suvive mach+ flights when attached with the only provided adhesive. My question is should I add another fillet layer with chopped carbon fiber or tip to tip fiberglass or both? Ultimately, I would like to see this bird fly on a full K or smaller L but test flights will be on an H or I and then a J 350 that sims approaching mach 1.

Any advice is appreciated.

Thanks

Craig
 

Terry_TBR

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I cannot answer your question but I am very interested in hearing the answer to it. I am curious to find out if you made the carbon fins or purchased them. Flying on higher J's, K's, and L's is an interest of mine and the next rocket I build I want to ensure will handle this.
 

JimJarvis50

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Hello all, I need some advice on fin attachement on min dia airframes. I am constructing a 54mm min dia rocket that will have surfave mounted 0.140 carbon fins on a phenolic tube with a carbon sleeve. The root is 5 inches and the fins were attached and filleted with JB weld. I have read that the Performances's mongeese (?) have surface mounted 1/8" fins that suvive mach+ flights when attached with the only provided adhesive. My question is should I add another fillet layer with chopped carbon fiber or tip to tip fiberglass or both? Ultimately, I would like to see this bird fly on a full K or smaller L but test flights will be on an H or I and then a J 350 that sims approaching mach 1.

Any advice is appreciated.

Thanks

Craig
I can't tell you the minimum that will work, but I can tell you what I have done. The 2" rocket in the picture has fins with a plywood core and 3 layers of carbon on each side. The fillet (Aeropoxy laminating epoxy with milled glass) was a little on the large side to provide a large radius for one layer of tip to tip carbon. This carbon terminates just above the fins. This 3 lb rocket has flown numerous times on L730's, and several times on L1030's, to just over Mach 2.

Jim

Shocklet Fin Can.jpg
 

CCR

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Terry, I made the fins. 5 layers of Soller Composites 12K fabric were laid up with layers 2 and 4 cut on a bias. Mr. Fiberglass epoxy was used to hold it all together, nylon fabric was used for the peel ply and it was compressed using a bottle jack under a 77 GMC 1/2 ton between two marble floor tiles. Leading and trailing edges were tapered with a router.

Another question comes to mind regarding the layup. I do not remember all the details of the flight profile but I am wondering, if using say a K660, I think the time above mach 1 is over ten seconds (working from memory here, could be way off on the time), will heating due to friction cause delamination in the fin material? Common epoxies I have used in the past degrade at temperatures over about 350 F. We used to bake test fixtures at 400F to make it easier to scrape the hardened epoxy off.
 

CCR

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Thanks Jim, I have seen and admired your work on the composite group. I was hoping to avoid going tip to tip with carbon because I don't have any 3 or 6k material. I would if it seemed to be required. After seeing your work, I may have to paint mine! Beautiful work btw.

Craig
 

JimJarvis50

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will heating due to friction cause delamination in the fin material? Common epoxies I have used in the past degrade at temperatures over about 350 F.
I actually have two of these 2" rockets. The one in the pic has a leading edge of Contronics epoxy. My other one, however, is just "capped" with the Aeropoxy that I used to get the finish on the fins. It has flown at Mach 2 and I have not seen any apparent damage resulting from heat. I was sort of keeping my fingers crossed the first time I did it. This may vary from rocket to rocket depending on fin thickness, ect.etc., but that's one data point for you.

Again, I don't know if the tip-to-tip is really needed, but it's what I do. If you don't use tip-to-tip, keeping the peel ply finish on the root to give the fillet epoxy something to grab on to would probably help.

Jim
 

Rocketjunkie

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I flew this minimum diameter rocket on an O3000 in 1992. The fins were 1/8" G10 surface mounted to the G10 airframe, filleted and then several layers of glass strips were layed in the fillet area. Afterward, everything was sanded smooth. The baggies of sand held the cloth in place as the epoxy cured. I used 5min epoxy to build the rocket and hobby store 20 min finishing epoxy for the cloth reinforcement. The rocket stripped the chute and core sampled. The fins were still on the resulting fence post.
 

jj94

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I can't tell you the minimum that will work, but I can tell you what I have done. The 2" rocket in the picture has fins with a plywood core and 3 layers of carbon on each side. The fillet (Aeropoxy laminating epoxy with milled glass) was a little on the large side to provide a large radius for one layer of tip to tip carbon. This carbon terminates just above the fins. This 3 lb rocket has flown numerous times on L730's, and several times on L1030's, to just over Mach 2.

Jim
Wow! The weave on that carbon looks perfect. You did a great job of laminating the cloth.
 

Handeman

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CCR, not to steal the thread, but if you're going to fly near Mach, I figured you might want to know this too.

Jim, how do you seal the leading edges so they don't split during flight?
 

Diosces

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I flew this minimum diameter rocket on an O3000 in 1992. The fins were 1/8" G10 surface mounted to the G10 airframe, filleted and then several layers of glass strips were layed in the fillet area. Afterward, everything was sanded smooth. The baggies of sand held the cloth in place as the epoxy cured. I used 5min epoxy to build the rocket and hobby store 20 min finishing epoxy for the cloth reinforcement. The rocket stripped the chute and core sampled. The fins were still on the resulting fence post.
Awesome. You should give it another shot;)
 

JimJarvis50

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CCR, not to steal the thread, but if you're going to fly near Mach, I figured you might want to know this too.

Jim, how do you seal the leading edges so they don't split during flight?
Actually, CCR asked that question. Check my second post. In case you're asking for a little more detail, the ttt carbon on each side comes to a point at the leading edge. I do the surface finish on these carbon rockets by painting the carbon with several coats of epoxy and then sanding them flat. In the process, several layers are applied to the leading edges, and I just sand this smooth. These 2" rockets don't spend a lot of time where there is significant heating, so the aeropoxy "cap" appears to be sufficient. On the twin, and on my larger rockets, I paint the leading edges with cotronics.

Jim
 

JimJarvis50

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CCR, not to steal the thread, but if you're going to fly near Mach, I figured you might want to know this too.

Jim, how do you seal the leading edges so they don't split during flight?
And after futher reflection ....

Most of the lessons I have learned in rocketry were just reinforcements of things I already knew in advance. When something bad happens, I typically had some clue about it. So, when the little voice says something, I listen.

After talking about leading edges, I decided that I didn't really like my capped Aeropoxy after all, even though it has worked in the past. I am in the process of coating the leading edge with the cotronics. I sanded down the edges a little in preparation for the contronics, and it appears to me that there could have been some heat damage to the fins (some epoxy that seems more brittle than it should be).

My little voice is happier now.

Jim
 

CCR

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Good to know Jim, thanks for the update.
 

Tominator 2

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Could you use JB weld on the leading edges?Since it has some good heat properties.
 

JimJarvis50

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Could you use JB weld on the leading edges?Since it has some good heat properties.
I haven't used JB weld for that. Might be worth a try. I know for sure that Contronics isn't easy to work with, and coating leading edges with it takes a little care.

My only concern with JB weld might be if it has a higher thermal conductivity than contronics. The Cotronics 4525 isn't all that low, but I would expect it to be lower than JB weld with 10-20% iron in it. The higher thermal conductivity probably would transfer more heat to the epoxy underneath.

Here's some additional related data.

http://www.nakka-rocketry.net/ablatex1.html

Jim
 

init 6

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Here's my fin fixing tale.

Binder design Jaguar with one layer of aerosleeves glass sleeve. Stock fins were replaced with a balsa/fg composite.
1 layer of fg tip-to-tip across the motor tube.

Went up on a K660 to mach 1.6. Separated at apogee and fell > 14k feet.

Front of fincan crushed on contact with ground. Fins cut through the body tube.



Not as pretty as Jims excellent work, but functional.
 

JimJarvis50

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Here's my fin fixing tale.

Binder design Jaguar with one layer of aerosleeves glass sleeve. Stock fins were replaced with a balsa/fg composite.
1 layer of fg tip-to-tip across the motor tube.

Went up on a K660 to mach 1.6. Separated at apogee and fell > 14k feet.

Front of fincan crushed on contact with ground. Fins cut through the body tube.



Not as pretty as Jims excellent work, but functional.
I have a fin can sitting up at Wayside that fell from about 1000 feet. Haven't seen it yet, and I hope it doesn't look like yours!

Jim
 

init 6

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I have a fin can sitting up at Wayside that fell from about 1000 feet. Haven't seen it yet, and I hope it doesn't look like yours!

Jim
To be honest, all it needs is a new airframe tube and a couple of centering rings. The fin/motor mount section is still intact - if a little shorter :)
 

JimJarvis50

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To be honest, all it needs is a new airframe tube and a couple of centering rings. The fin/motor mount section is still intact - if a little shorter :)
Oh, that didn't come out quite right. Yes, repair is good.

When the farmer called me to let me know that my rocket was found, I asked her how it looked. She said it looked fine ... oh, maybe a fin was cracked. Geez. Since they were kind enough to call me, and since the call was on their nickel, I didn't take the time to follow up. So, the condition is still a mystery after several months now. The rocket is all carbon. If the fin is OK it will be flyable. If the fin is cracked, it is toast. That's why I hope it doesn't look like yours - because I won't be able to repair it.

Jim
 

Graham Orr

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My MinDiam method:
1) Tack with cyanoacrylate (superglue)
2) Capillary bond joint with 2 cP (very thin) cyanoacrylate
3) Make ~1/8" radius fillet with JB weld (or use other filler)
4) Use reinforcing cloth (CF) across joint
5) Veil with S-glass micro-weave

The fillet is just there so the fiber doesn't have sharp angle.

Flown to Mach 1.7 but rocket came apart after that... the problem was that we had too many embedded sensors that kept us from getting good bonding between layers...

http://www.thirdcritical.com/RDL/Photos.html#9
 

CCR

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My MinDiam method:
1) Tack with cyanoacrylate (superglue)
2) Capillary bond joint with 2 cP (very thin) cyanoacrylate
3) Make ~1/8" radius fillet with JB weld (or use other filler)
4) Use reinforcing cloth (CF) across joint
5) Veil with S-glass micro-weave

The fillet is just there so the fiber doesn't have sharp angle.

Flown to Mach 1.7 but rocket came apart after that... the problem was that we had too many embedded sensors that kept us from getting good bonding between layers...

http://www.thirdcritical.com/RDL/Photos.html#9

Graham,

Interesting information and pics. I had thoughts of wanting to place strain gauges on fins, joints and airframes but my (very limited) experience is only with PCs to aquire data. Nothing small.

How thick were the fins? Is that a 2" tube?

Can you tell us a bit more about the failure mode? Was the bond to the tube the problem or delamination in the fin?

Thanks

Craig
 

CCR

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The vehicle that prompted this thread made her first test flight yesterday and survived the incredible strain placed on the fins by the mighty G 71R! :D

J 350 at Argonia next weekend if the weather holds then I will have to wait a bit for the K flight while I work on finishing up the L3 bird.
 

Graham Orr

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We delaminated on the reinforcing cloth joint. The problem is that we used kevlar and we didn't bake it out before using it. It would probably had been better to just use CF on it.

The tube and all parts were custom made. The tube is 54mm ID. 25% CF 25% kevlar (100% CF in axial direction, 50% CF in hoop) totaling 0.062" in wall. The tubes were made on an Al mandrel, vacuum bagged, and then painstakingly removed with liquid nitrogen.

The fin material was 50/50 biaxial kevlar-CF with nomex honeycomb core. It was cured via vacuum and extra compression of about 1 psi and cut with a CNC waterjet at about 50 ksi. The leading and trailing edges were 7075 high strength corrosion resistant aircraft aluminum, machined on a mill.

The rocket failed because I did a poor job on the preliminary design of the rocket. The rocket was too long, leading to coning at high velocity. The rocket either snapped in half or came apart and deployed a parachute at Mach 1.7 ... the fins were turned sideways and estimates put the aerodynamic force per fin at 500 lbf... so they just sheared off at the lamination plane described above. This flight was recording the 6-axis IMU and thus we don't have vibration data on fins, unfortunately.

http://www.youtube.com/watch?v=kRdGH11cPEQ&feature=channel

I did do a flight at LDRS with the vib sensors to Mach 1.2 and got some interesting data from the peel-back on one of the fins...

http://www.thirdcritical.com/RDL/Mudd_II_Data,_LDRS.html
 
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gregzo

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I can't tell you the minimum that will work, but I can tell you what I have done. The 2" rocket in the picture has fins with a plywood core and 3 layers of carbon on each side. The fillet (Aeropoxy laminating epoxy with milled glass) was a little on the large side to provide a large radius for one layer of tip to tip carbon. This carbon terminates just above the fins. This 3 lb rocket has flown numerous times on L730's, and several times on L1030's, to just over Mach 2.

Jim

OMG....That is gorgeous!!! Beautiful work!!!
(I'm jealous)
 

JimJarvis50

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Thanks! I've made 8 rockets of this general style and I still have 4 of them. The longevity can be a little short. My best effort (a 3" rocket below) lasted only one flight, but it was a good one.

When I built the replacement of this rocket, I documented the build in sufficient detail so that anyone with a little composites experience and a little patience could build it if they wanted to. I'm hoping to post this in a more convenient location, but for now, it's located in the photos section of the compositerockets yahoo group under the "Jim's TooCarbYen tutorial" folder.

http://groups.yahoo.com/group/CompositeRockets/

Jim

With Cotronics Applied 2.JPG


Finished Fin Can 2.JPG
 
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