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Did my Epoxy Fail?

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Swissyhawk

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I built a Madcow mini-Screech dual deploy in the latter part of 2016. Yesterday it had it's first flight and the results were not good. It weighed in at 2 lbs off the pad. The apogee charged worked well and the rocket separated as expected. I did not use a drogue chute, but I did put an orange 12" chute protector on the harness just to help with visibility. The main was supposed to pop at 300 ft. It came in pretty much right overhead and I could hear and see the main charge go off, but the nose cone didn't separate from the rocket. (That's something I'll need to work on.) However, I wasn't too worried. We were in a farmers field that was pretty soft and wet in some spots. I have a mini-batray that I've flown a bunch of times and it seems pretty indestructible, so I was expecting the same with the mini-Screech. The nose cone buried into about 4 inches of dirt but was otherwise fine. The altimeter was fine, it survived. When I picked up the body tube, the fins looked fine other than having dirt on them. When I got home and started cleaning them, I realized they rocked back and forth. I thought maybe they had broken. I pulled the fins out a bit (see pictures) and realized the fins were fine, but the epoxy had completely cracked. Only the two fins where the impact occurred had failure, the third fin was fine.

Now I'm wondering why the epoxy failed. It was RocketPoxy that I've used on several rockets before and it held up just fine. I did build the rocket and store the epoxy in the garage which I hadn't done before. However, it doesn't seem to get that cold in the garage. I'm starting to think the epoxy got old and turned bad. I bought the stuff in March of 2015. That's not that long ago, but I went to the Glenmarc data sheet on RocketPoxy and it says the shelf life is 1-1/2 years. Maybe it just got too old to use. Any thoughts? Has anyone else had this kind of problem?

IMG_0298.JPGIMG_0299.JPG

Any thoughts on rebuilding this? I have pulled the two fins out. They are fine. I need to figure out how to clean off the old epoxy.
 
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timbucktoo

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Those fillets look pretty small plus the impact in the dirt didn't help. Were all 3 fins cracked or just the 2 in the picture?
 

Steve Shannon

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It looks like the only fillets you had were on the exterior and very small and that your fins weren't epoxied to the motor mount tube.
You don't have to remove the old epoxy. You can clean the surface with alcohol or acetone and put epoxy on the rough edges.
But you should either anchor the root of the fin tab to the motor mount tube or reinforce the fillets greatly.
There's probably nothing wrong with the epoxy. You just expected too much from a small area.
 

The_Lone_Beagle

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I think we may need more info. I'm assuming your mixture was correct (50/50), do you know what the temperature was when you built the rocket & the epoxy cured? You did say you did it in the garage, where do you live & what were the temps like during the time period?

How did you attach the fins to the motor tube? Did you do internal fillets?

Any other details?
 

cavecentral

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Epoxy fillets will crack like that. Too hard of a landing (for the surface - like a rock) or spinning fast as it hits will cause this. I had ever epoxy joint shatter on a Wildman Vindicator - Twice! Chute got stuck in tube once. Drogue never fired and main shredded when it did open. First time with BSI 5min epoxy. Second with US Composites filled with Colloidal silica and Carbon Fiber. I finished 'rekitting' it with a hammer shattering off the rest of the epoxy and rebuilt it each time.
 

Swissyhawk

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The fins were epoxied to the motor mount tube using the "double butter" method. There were no internal fillets due to the tight space.

I doubt it is a mixture problem because I would have mixed 5 different batches to complete those two fins - 1 batch for each fin to MMT and 1 batch for each pair of adjacent fillets. Also, I use scale to weigh out my epoxy each time I mix it.

Only the two fins in the picture cracked. The third fin landed pointing up and was fine.

The fillets are small, but remember, this is a pretty small and light weight rocket.

I live in the DC area and it was a pretty warm fall and early winter. Unfortunately, I'm a pretty slow builder, so I can't say exactly when I did the fins, but its been awhile.
 
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DavidMcCann

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I could hear and see the main charge go off, but the nose cone didn't separate from the rocket. (That's something I'll need to work on.) .
The epoxy is fine and need not be your worry. The above line should be the main concern ;)
 

rocketsam2016

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I also had some rocketpoxy fillets crack this year. Main deployment failed so came down on drogue only and landed on frozen turf. Only one fillet cracked in my case and it is much smaller than yours so I didn't notice for a while. Like yours though the crack was through the middle of the epoxy rather than at the interface between epoxy and fin. I did have internal fillets so I was surprised it cracked like that, though even with the crack the fin is still very firmly on and doesn't wiggle. I'm going to cut into it to see how far the crack goes and make sure the internal fillets are on and then fill it back up.
 

cavecentral

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One of the failures I had with a cato that never got high enough to arm the electronics for deployment, had a G10 fin snap. The very heavy fillets held up, but Replacing the fin was a much more painful experience. Land hard enough something will fail. Finding a balance where you survive all normal flight / landing conditions and don't snap off the fin instead is ideal.
 

crossfire

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Where did my post go???
 

Steve Shannon

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The fins were epoxied to the motor mount tube using the "double butter" method. There were no internal fillets due to the tight space.

I doubt it is a mixture problem because I would have mixed 5 different batches to complete those two fins - 1 batch for each fin to MMT and 1 batch for each pair of adjacent fillets. Also, I use scale to weigh out my epoxy each time I mix it.

Only the two fins in the picture cracked. The third fin landed pointing up and was fine.

The fillets are small, but remember, this is a pretty small and light weight rocket.

I live in the DC area and it was a pretty warm fall and early winter. Unfortunately, I'm a pretty slow builder, so I can't say exactly when I did the fins, but its been awhile.
Larger fillets increase strength exponentially. The centerline of the epoxy experiences the greatest stress. It's obvious that your surface preparation on the exterior at least is good. It may just be that Rocketpoxy isn't great for impact.
I still think you'll be fine putting it together and enlarging and reinforcing the fillets, perhaps even with a strip of fiberglass tape.
 

dixontj93060

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Larger fillets increase strength exponentially. The centerline of the epoxy experiences the greatest stress. It's obvious that your surface preparation on the exterior at least is good. It may just be that Rocketpoxy isn't great for impact.
I still think you'll be fine putting it together and enlarging and reinforcing the fillets, perhaps even with a strip of fiberglass tape.
Hmmm... Interesting. I would agree surface prep was good given where the fracture was exhibited. I would like to hear from Mr. (RocketPoxy) Olevich on this one...
 

DAllen

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I don't have a lot of experience with RocketPoxy but I have used it on several builds and I don't think that's the issue. Probably a surface prep issue and the fillets aren't big enough. Plus, a hard enough landing or the booster section spinning fast enough as it hits there probably aren't any epoxies with that small off a fillet that will hold up to the abuse.
 

The_Lone_Beagle

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One of the failures I had with a cato that never got high enough to arm the electronics for deployment, had a G10 fin snap. The very heavy fillets held up, but Replacing the fin was a much more painful experience. Land hard enough something will fail. Finding a balance where you survive all normal flight / landing conditions and don't snap off the fin instead is ideal.
That was going to be the next thing I was going to bring up...better having it crack at the epoxy joint, than to break fin!
 

michigander

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I have cracked some on construction ,centering rings got bound up in booster tube , I tossed what was left "pint set" I had a fresh quart batch to use

cleaned up with 1/2 " wood chisel

started weighing both 1/2's

Brittle glue.jpg


cleaning glue off.jpg
 

jolevich

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Rocketpoxy should last 1-1/2 years if stored correctly, What this means is to keep it sealed as much as possible ( don’t leave the lids open overnight or for long periods of time), try to keep it stored above 60 Deg. F ( try not to freeze it). Also after such a long time there could be some separation and settling of fillers, So if sitting for a very long time make sure to mix each side independently, that is A side and B side so the epoxy and fillers are fully mixed.

To answer Gregg about his Madcow mini screech failure, there are just so many variables here at work that it may be hard to nail it down. I know it is not the Rocketpoxy if mixed and used correctly. There has been way to much research and way too many high powered rockets using RP over many years ( estimate at least several thousand rockets have been built using Rocketpoxy including many university rocket teams) so Rocketpoxy is probably one of the most used and tested high strength epoxy for building HP rockets.

I have seen some unbelievable crashes where Rocketpoxy has held up where other epoxy would have just completely shattered. I personally had built a 8 inch diameter very heavy all fiberglass Gizmo rocket built like a brick house with Rocketpoxy that I had launched at a previous 2012 Midwest power10 drag race, the rocket came in ballistic from 6,000 feet, it was screamer, lots of high G forces when it hit the ground, I think if you Google this there are still videos floating around showing this, rocket was about 3 to 4 feet into the solid earth ( total core sample) , it was dug out and other than a shattered nose cone the rest of the rocket held together 100%, after replacing the nose cone and electronics, it was launched several more times successfully and I still have it and launch it to this day, in fact thinking about launching it at the next Michiana Rocketry launch at Three Oaks, MI on February 18th. But be realistic if your rocket comes in without a chute or ballistic with high G forces no epoxy manufacturer can guarantee nothing will fail and you shouldn't really expect this either.

But I will take a few guesses at some possible reasons that may have aggravated your situation. Don’t take any of this personally, and yes maybe you did most everything correctly, but I am looking at this forensically from your failure to diagnose this from just what little information I have to go on, and not being personally involved with the build it makes it even more guess work.
General assembly issues:
1) Was the mold release completely cleaned off all the surfaces
2) Did you use a 60 to 80 grit sandpaper to rough up all the bonded surfaces extremely well
3) Your external fillets seem to be extremely small and weak, consider making larger fillets
4) Did you do internal fillets correctly if not this may have helped the fin separation ( I would always recommend doing them on a fiberglass FW rocket), it sounds like you had no internal fillets at all because of the tight space, what I do in extremely tight situations is to mix ( I wait from 15 to 30 minutes after mixed so I have the viscosity I want, thicker for shorter pours or thinner for longer length fin pours), and simply pour the Rocketpoxy from the back open end of the airframe/internal fin area by tilting the rocket airframe/fin assembly nose cone end down so the RP will ooze down inside the joining crack area of the internal fillet, and using a small flashlight I observe where it is and using levels of airframe tilt to get it where I want it to be, then I level out the rocket and fixture in a position where the RP stays in the internal fillet area, and then be patient enough to let it cure before I rotate and do the remaining internal fillets. It really is quite easy and fast when you get the hang of it.
5) Were your fins buttered up with enough epoxy and correctly mounted square against the motor tube, was you motor tube sanded with 60 to 80 grit sandpaper where the fins attach
6) Were you patient when building and made sure RP had cured fully before assembling the next part, for example if you were doing internal fillets and buttering of fins and rotated rocket before it is cured some may have dripped off leaving a thinner weaker bond.
Rocketpoxy issues:
1) Sounds like it was sitting for a long time, you purchased in March 2015, built rocket in latter 2016 you do realize that was almost 1-1/2+ years ago because we probably made it several months earlier from when you received it as it takes time to ship to distributors and them to ship to you. C'mon Rocketpoxy states 1-1/2 years life, this could have been close or even past that limit, If I was building an expensive fiberglass Madcow rocket I would have sprung for a fresh 8 ounce RP kit for $12 just to be sure and not tried to use a 1-1/2 year old material.
2) Was the RP stored above 60 Deg F, it sounds like you had it in a garage maybe some night got very cold in there.
3) Did you thoroughly mix each side of the RP after it was sitting so long, if the fillers settled and/or separated out and wasn't fully mixed this may have caused some issues.
4) Was this the bottom of the RP jar, was the lid left off for extended times on previous builds, how well were the jars lids sealed
5) Of course there could be other issues as well, was it mixed at a 1 to 1 ratio, was it mixed fully, temperature when applied, how cured the epoxy was when applied, etc.

GIZ1.jpg GIZ2.jpg
Photo on left is my 8 inch Gizmo that was built completely using Rocketpoxy right after the ballistic crash from about 6,000 feet, photo on right is after I spent an hour digging it out.

GIZ3.jpg GIZ4.jpg
The next flight of the Gizmo a few months later after digging it out and replacing only the nose cone and electronics, no airframe or fin structure work had to be re-done thanks to the Rocketpoxy.
 
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GRIFFIN

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There were no internal fillets .
The devil is in the detail.

Here is the problem if you are asking for opinions.

If a syringe will fit, there is room for internals. The internal fillet is more important than externals as far as strength.
 

Forever_Metal

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you can use a heat gun on the fillets (FG & CF only, have to be MEGA MEGA careful on ANYTHING else) to make them a little easier to cut off. Once you get to the right temp (warm, not hot), you should be able to almost peel them off.

fm

ps. Remember, MEGA MEGA careful on anything else, don't burn it up or delaminate it
 

Buckeye

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1) Sounds like it was sitting for a long time, you purchased in March 2015, built rocket in latter 2016 you do realize that was almost 1-1/2+ years ago because we probably made it several months earlier from when you received it as it takes time to ship to distributors and them to ship to you. C'mon Rocketpoxy states 1-1/2 years life, this could have been close or even past that limit, If I was building an expensive fiberglass Madcow rocket I would have sprung for a fresh 8 ounce RP kit for $12 just to be sure and not tried to use a 1-1/2 year old material.
That's a bit harsh. Really, after exactly 18 months the stuff goes bad? Storing the epoxy in a garage was probably the biggest offense, not its age.

I have 3 hour Bob Smith epoxy from 2001. It still works.
 

Incongruent

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That's a bit harsh. Really, after exactly 18 months the stuff goes bad? Storing the epoxy in a garage was probably the biggest offense, not its age.
The epoxy actually contains millions of nanobots that, after a predetermined time, release degrading agents into the epoxy which make it stop functioning... mumble... government conspiracy... mumble... commies commieing after us and our epoxy... mumble... tuck that tinfoil in extra tight tonight...
 

blackjack2564

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I would rather have a fin knocked loose and repairable from small fillets, than broken or airframe damage due to large non-flexing fillets.

I see a " spread" hit cracked fillet failure. 2 fins were exposed too force, similar to standing on airframe & flexing fins apart enough to leverage force and crack fillets

These fillets [from what i can see] are pretty much cracked down the middle, no detachment from tube or fin. Glue stuck to both fin & airframe showing good prep.

Seems like a perfect 'play' to me..... everything functioned to limits of design, with the epoxy failing, through NO fault of it's own. All repairable... a win...win situation. Much better than no fillet failure and a broke fin or fin pulled loose with some airframe attached to fillet. Not an easy fix......[many of you know exactly of which I speak!!!LOL]

When stuff comes in ballistic ....somethings gotta give! [most of the time] :wink:


Place fin in vice, carefully placed blows with hammer & chisel, makes very quick removal of fillet.
 
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djs

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I had the exact same thing happen to me this weekend when my rocket (Wildman Interceptor 54) came in from 2100' with no chute (nosecone came out, but not the chute). It landed hard on a frozen pond and bounced a few times. Fins popped loose just like yours. Looks horrible, but like CJ said, it's a fairly easy fix- just takes some time.
 

jolevich

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That's a bit harsh. Really, after exactly 18 months the stuff goes bad? Storing the epoxy in a garage was probably the biggest offense, not its age.

I have 3 hour Bob Smith epoxy from 2001. It still works.
I think you are taking things out of context. No one said that RP epoxy would fail exactly 18 months after it was purchased or that the shelf life was even the only culprit to sissyhawk's failure, I also mentioned many other possibilities (at least 12 + items) that could have had an effect, with probably the number one being the chute didn't open, number two no internal fillets were used, and number 3 small and weak external fillets. The point I was trying to make was if you have some RP sitting around in a garaged for over 18+ months (which is passed the manufacturers recommended shelf life) with unknown storage conditions of temperature, unknown conditions of fillers separating out, and unknown conditions of seal on the jars and are building an expensive fiberglass rocket, maybe spring for a new batch would not be such a bad idea.

We have samples in our lab from 5 years ago, 4 years ago, 3 years ago, etc. That were stored in a known temperature and known sealed container and each side A and B was mixed prior to use that still worked good 3 to 5 years later and retained about 90%+ of its strength but as a manufacturer we need to put some limit on shelf life as we have to take into account the average user will not be storing in optimum conditions and temperature, and seals on jars may leak etc. .

As far as crowing about your Bob Smith epoxy lasting fifteen years, hell it should last for 20+ years. It's basically just an unfilled Bisphenol-A simple resin with a simple Polyamide curing agent for the hardener side. It has no fillers, no complex curing agents or exotic additives that can separate out to give it a reduced shelf life. Not putting it down I'm sure it has its place but you need to be realistic it's definitely not a filled high strength structural adhesive epoxy in the same class as rocketpoxy. It could shatter like glass under high stress especially on a large high power fiberglass or carbon fiber material rocket. Rocketpoxy has several fillers mixed in, each giving it certain physical characteristics such as shatter resistance, higher strength, and bonding properties. Without giving away too much of the formula I can at least tell you that the resin side chemistry of Rocketpoxy is based or a highly modified Phenyl glycidyl ether versus a typical Bisphenol A diglycidyl ether which is what you find in less costly and less complex epoxy systems such as typical off the shelf hardware store epoxies and Bob Smith epoxy. Also the curing agent side chemistry is also quite exotic and based on Tetraethylene Pentamine based chemistry not the typical Polyamide curing agents that are found in off the shelf hardware store epoxies and Bob Smith epoxy. The point is with higher performance epoxy that has fillers, complex curing agents, and exotic additives such as rocketpoxy you probably will have less of a shelf life than a Bob Smith epoxy. It's one of the tradeoffs. I worked in aerospace for many years at the McDonnell Douglas plant which built DC-10, MD-11 and C17 planes which used all sorts of exotic high strength structural epoxies and the typical shelf life was about 6 to 12 months at the most.
 
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GRIFFIN

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I agree with John on this one. My RocketPoxy is over 3 years old and I just finished the tub. I have zero concerns with product if used properly. Internal fillets are a must. RocketPoxy is not some magical product that allows for paper thin application. Build it right, build it strong and it will work.
Again, I also agree with CJ, at least the fin popped off and didn't break off at the body tube. Been there, done that and wished the fun had popped off.
 
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