L1 Build: Wildman Darkstar Jr

[Zeroignite]

Bob Smith also says that you can thin their epoxies with acetone or isopropanol, and similarly claim that it reduces ultimate strength.

Basically in all these cases I'm guessing the thinner just acts a bit of solvent, and boils off easily so most of it comes out as the epoxy cures.

 

[blueapplepaste]

Maybe I'll try emailing glenmark. Question becomes is thinned full fillet with rocketpoxy better than possible shorter fillet with reg rocketpoxy or with generic epoxy?

 

[WoShuGui]

Something else to consider if you thin with IPA is to use a higher concentration, 99% or higher. Off the shelf rubbing alcohol is only 70% or 91% IPA. Balance is water.

 

[G_T]

If you'll notice on the West link, thinning with just 5% denatured alcohol costs almost 50% of the compressive strength. Thinning epoxy is something really to be avoided.

IIRC, if one really wanted to thin epoxy, the correct thinner is usually isobutyl alcohol, which is going to be harder to find and nasty. It is better to just use a thinner epoxy if a thinner epoxy is needed.

Gerald

PS - Rubbing alcohol often contains oil additives to keep it from drying the skin too much. Epoxy does not like oil.

 

[blueapplepaste]

I emailed glenmarc but haven't heard back. I'm thinking I'll probably use my hobby shop stuff (I think it's the bob smith stuff).

 

[michigander]

I did my internals with Rocketpoxy " unthinned" on JR couldn't see how well covered because black rocket , I did a high speed deployed doing mach , rocket fell from 5000 feet with no chutes ,

no loose fins


we land on sod , your results may vary

 

[Dad Man Walking]

Darkstar Junior...great rocket! We got ours when it was just the "Darkstar" and had not been demoted to "Jr." status. Flew it to 2000' on a a mild H motor for our L1, then added electronics and and sorted out dual deployment on H and I motors, and bagged our L2 on a small J with it. And we flew it to over 7000 feet on the biggest motor we could stuff into it at LDRS last July.

Tim's standard build instructions are exactly the same as for his much bigger rockets...internals with flowing epoxy and chopped CF, and externals with thickened epoxy. On the smaller 54mm Darkstar Junior, I doubt you would have a problem if the internals were not perfect because the epoxy didn't flow perfectly. Just shove a bunch in there, finish it off with clean externals, and let it rip. I would choose stiffer epoxy/incomplete coverage over thinned epoxy/uncertain strength. But with a good set of externals, in a L1/small L2 rocket, I would think you will be fine either way.

Darkstars rock.

 

[blackbrandt]

I built mine like an antitank round. The fins are going nowhere. I would have put a J825 in it, but decided against it because I didn't have a tracker (and I probably would have lost Jimzcatz's casing). I used Aeropoxy structural, and probably put 3x as much epoxy as I needed in the tail end of the rocket. The aeropoxy didn't exactly flow (with Chopped carbon in it, it didn't flow very well), and only covers a little bit of the fin joint (maybe 60% of it), but by God, those fins feel like they are attached with unobtanium.


Someday, I will fly it in short mode, and shove a Loki J1000 in it. That is going to freaking teleport into the 10th dimension.

Just a suggestion.

 

[blueapplepaste]

Thanks for all of the replies. Never heard back from Glenmarc, so finally decided I was overthinking it and just went with full-blown normal rocketpoxy. I didn't thin it, and decided it would be better to get a partial fillet with some legit epoxy then a full fillet with some generic stuff that isn't as high quality.

I also used chopped carbon, used less than a dime size as the rocketpoxy is already pretty thick and didn't want it to hairball on me or get too thick. Overall wasn't that bad. Unfortunately because of the black fiberglass no way of knowing how well it flowed along the fin/BT joint.

Here's what I did.

Here are all of the fins attached:

I wasn't worried about it possibly flowing through little cracks and running out the opposite side, but figured better safe than sorry!! So I taped all of the openings and injection holes on other sides:

Here are all of my supplies laid out:

I worked as fast as I could once it was mixed to minimize any thickening. I made up ~20mL of epoxy and injected ~10 mL into each side. Ended up ~5.5-6 mL for the longer forward fin, and ~4-4.5 mL on the shorter rear fin. After injecting I wiped down any drips from the hole with an isopropanol wipe to clean up any epoxy. Waited ~2 hrs for it to set and then did the next one and repeated for the final one.

First forward fin all done and wiped clean:

First rear fin (took pic before wiping down, so there's some epoxy smeared on in the pic):

Also, while all 12 holes are mostly filled, they are definitely not flush with the rocket body. Should I fill these with some more epoxy? Bondo putty? Something else?

Thanks for the continued help and support everyone!! I'm really appreciating it so far. :handshake:

 

[conman13]

any bondo or wood filler will do the job and make a nice smooth surface after lots of sanding of course!!!

 

[Aksrockets]

Thanks for all of the replies. Never heard back from Glenmarc, so finally decided I was overthinking it and just went with full-blown normal rocketpoxy. I didn't thin it, and decided it would be better to get a partial fillet with some legit epoxy then a full fillet with some generic stuff that isn't as high quality.

I'm glad you didn't. I've had my fair share of experience thinning epoxy. Usually in thin coats, the Acetone has time to evaporate before the epoxy reaches the green stage. It's great for thin coating.
Thicker applications are a bit different. Not all the acetone has the chance to leave the epoxy before it solidifies, so it turns into a gel instead of a solid. Over the course of a few days, the acetone leaves the gel and the epoxy turns stiff. With injected fillets, the acetone has nowhere to evaporate to, which I would guess would mean your epoxy would be in a gel state permanently.

Alex

 

[WoShuGui]

Thanks for all of the replies. Never heard back from Glenmarc, so finally decided I was overthinking it and just went with full-blown normal rocketpoxy. I didn't thin it, and decided it would be better to get a partial fillet with some legit epoxy then a full fillet with some generic stuff that isn't as high quality.

I also used chopped carbon, used less than a dime size as the rocketpoxy is already pretty thick and didn't want it to hairball on me or get too thick. Overall wasn't that bad. Unfortunately because of the black fiberglass no way of knowing how well it flowed along the fin/BT joint.

I wasn't worried about it possibly flowing through little cracks and running out the opposite side, but figured better safe than sorry!! So I taped all of the openings and injection holes on other sides:

I worked as fast as I could once it was mixed to minimize any thickening. I made up ~20mL of epoxy and injected ~10 mL into each side. Ended up ~5.5-6 mL for the longer forward fin, and ~4-4.5 mL on the shorter rear fin. After injecting I wiped down any drips from the hole with an isopropanol wipe to clean up any epoxy. Waited ~2 hrs for it to set and then did the next one and repeated for the final one.

Also, while all 12 holes are mostly filled, they are definitely not flush with the rocket body. Should I fill these with some more epoxy? Bondo putty? Something else?

Looking good! I think you made the right call. That fin can should hold up to any commercial motor you can stuff in it. The holes can be filled with the same epoxy you use for the external fillets. The epoxy will sag a little into the holes, so you may want to fill them before doing the fillets to get a perfect finish. Or just do a final fill and sand after doing the fillets. One nice thing about using the rocketpoxy is the black colorant. It can be matched to the FG giving you some no paint options.

 

[blueapplepaste]

I'm glad you didn't. I've had my fair share of experience thinning epoxy. Usually in thin coats, the Acetone has time to evaporate before the epoxy reaches the green stage. It's great for thin coating.
Thicker applications are a bit different. Not all the acetone has the chance to leave the epoxy before it solidifies, so it turns into a gel instead of a solid. Over the course of a few days, the acetone leaves the gel and the epoxy turns stiff. With injected fillets, the acetone has nowhere to evaporate to, which I would guess would mean your epoxy would be in a gel state permanently.

Alex

Hasn't even thought about it not evaporating off. I've only ever thinned before to fiberglass a wing joint on rc plane. Glad I did it full strength.

 

[blueapplepaste]

Looking good! I think you made the right call. That fin can should hold up to any commercial motor you can stuff in it. The holes can be filled with the same epoxy you use for the external fillets. The epoxy will sag a little into the holes, so you may want to fill them before doing the fillets to get a perfect finish. Or just do a final fill and sand after doing the fillets. One nice thing about using the rocketpoxy is the black colorant. It can be matched to the FG giving you some no paint options.

Planning on knocking out the fillets tonight. Where the fins also go into the BT needs to be filled as well - fin slots were quite a big longer than the fins. Think I'll fill it after fillets.

 

[blueapplepaste]

any bondo or wood filler will do the job and make a nice smooth surface after lots of sanding of course!!!

Good deal. Have plenty of the bondo putty so will just use that. Figured it was ok but wanted to make sure if there wasn't something better since it's fiberglass and not normal paper tube.

 

[blueapplepaste]

Got some more done.

When I removed the tape, I was pleasantly surprised to see that some rocketpoxy had flowed all the way down the ends. Glad I used tape after all!! Feeling a lot better about internal fillets since it appeared it flowed pretty well, or well enough:

Next up were the fillets. Got the rocket all taped off:

Then I did the fillets. I let the rocketpoxy set just a little too long as it was a little difficult to work with. But overall, wasn't so bad. I kept the fillets small using a small popsicle stick to pull the epoxy, rather than my finger or PVC tubing. Between the root and internal fillets, I'm not worried about them, so just wanted to keep these small, light, and aerodynamic.

I'm fairly happy with them, good enough for me anyways!

Front fillet:

Rear fillet:

 

[blueapplepaste]

Got some more done. Filled in the injection holes as well as the gaps at front and rear of fins with bondo putty. Sanded it all down. Fiberglass is looking pretty rough from sanding, but it'll be fine after some primer.

Front fin:

Rear fin:

Also drilled out the AV bay ends to start making my sled. I guess on the newer kits (or at least mine) they were one piece aluminum and not 2 pieces of fiberglass that you had to glue together. The metal was pretty soft and super easy to drill out. I'm using 10-24 rod, which is probably a lot of overkill, but I tend to overthink and over worry. So this put my mind at ease.

I also drilled all of the holes and am going to start priming this weekend. My club in Dallas hasn't set any high power launch dates yet, so am in no rush, but I am already thinking of some complex paint designs. But I'm leaning towards keeping it simple, so we'll see.

 

[XJChris]

I'm glad to see that rocketpoxy flowed so well for the internal fillets. I have my fins tacked in with 15min hobby epoxy at the moment and all ready to inject with rocketpoxy. So far I'm really happy with rocketpoxy, used it to make the fillets on my Leviathon to practice before working on my Darkstar Jr.

 

[blueapplepaste]

My advice is to just work pretty quickly and have a game plan when injecting.

And I agree - it's really nice stuff! Especially for fillets - getting that peanut butter consistency is almost cheating.

 

[XJChris]

Did it flow that well with the rocket level, or did you tip it at all?

 

[blueapplepaste]

I didn't tip the rocket. I did sort of change the angle of the syringe as I injected. Doing it that way got at least some to flow to the ends.

I will say that the fins feel beyond rock solid. If they're coming off then something else has gone horrible wrong and I have bigger thugs to worry about at that point.

 

[blueapplepaste]

Got the rocket all painted. I still need to finish the AV bay (have everything I need). I bought a parachute when I ordered it, but can't find it, I think I might have accidentally thrown it away with the box it came in. So I'll need to order another parachute and then do some ground testing for the charges. Found FFFFG bp (the real stuff, not pyrodex, etc) at Bass Pro shop.

I used Rustoleum professional primer to prime it. I hated the stuff. It sprayed a horrible, thick, uneven spray. Took forever to get any semblance of a decent primer base. And in fact, it wasn't even that good, I just got so frustrated with the stuff I moved on to paint. Used duplicolor yellow and purple engine enamel paint. First time I've used the stuff and it was great to use!

I wanted a "different" paint scheme from most of what I've seen. So this is what I ended up with. The trim tape I used was a little thick so at many of the junctions where it overlapped, there is just a tiny amount of purple bleed through. I did throw down a coat of clear coat after I had it taped to seal the edges before spraying the purple, but I think there was still just enough of a gap that a hair of purple got through. Not that big of a deal, I'm going with the TLAR (that looks about right) mantra here. You won't be able to tell when its on the pad anyways!

I only wish I'd had painted the coupler and nosecone yellow and not purple. I thought about sanding off all of the purple on those pieces and completely refinishing them in yellow, but that's a lot of work I don't really want to do. Haven't decided on decals, thinking of some chrome lettering, but may leave it as-is.

No idea when the launch and my L1 attempt will be. My club (DARS in Dallas) hasn't set any HPR launch plans yet. I live so far away from when their meetings are I haven't been able to go and see what the deal is. Hopefully it'll be before it gets too hot here!

(ignore the dog, our greyhound Gordon, he's always curious and getting in on the action)

 

[chadrog]

Yowza!:y: That looks really cool!

 

[blueapplepaste]

Thanks!

 

[blackbrandt]

Wow! Nice!

 

[XJChris]

I haven't had any time lately to finish mine.. I have injected epoxy in 1/3 of the fins and am dying to get back to it.

Great job on the paint!

 

[Jarhead]

Very nice work.
My son is building a wild thing for his L1 which is very similar to yours. He has a question that I can't answer; how best to secure the nose cone to the coupler. He has the bulk plate epoxied (he poured CF fortified West in his coupler).
Did you epoxy the coupler into the NC? Or did you use mechanical fasteners (rivets/pem nuts)?
He is complete minus the nose cone and wants to fly his jr L1 on Saturday at thunderstruck.
He is cutting against the grain and flying naked, I hope this doesn't grow into something with dire consequences for him.
Beautiful work again. Thanks for sharing.

 

[blackbrandt]

The best way to do it (in your situation) is to use 8-32 screws about 3/8" and screw them directly through the nose cone into the coupler. The threads will "tap" themselves. At least, that is what I did. If he never wants to fly with a tracker, then there really is no need for the nose cone. I plan on using trackers soon, so all of my nose cones have space in them for that...

 

[rocketgeek101]

Very nice work.
My son is building a wild thing for his L1 which is very similar to yours. He has a question that I can't answer; how best to secure the nose cone to the coupler. He has the bulk plate epoxied (he poured CF fortified West in his coupler).
Did you epoxy the coupler into the NC? Or did you use mechanical fasteners (rivets/pem nuts)?
He is complete minus the nose cone and wants to fly his jr L1 on Saturday at thunderstruck.
He is cutting against the grain and flying naked, I hope this doesn't grow into something with dire consequences for him.
Beautiful work again. Thanks for sharing.

Or build it like Crazy Jim does: CJ's glueless nosecone (See posts 100, 105, and 109)

 

[Jarhead]

Thanks for the suggestions guys.
I may be hijacking the thread so if I should move this please let me know.
If I use fasteners through the NC into the coupler what is the impact on altimeter venting in future DD situations? Will turbulence from the screw heads cause erratic pressure in the av-bay, possibly giving erroneous altimeter readings? I personally like using Pem-Nuts and button head cap screws because they function well and are aesthetically pleasing. I don't however want to have issues with DD later on because of a poorly planned decision today.
I like the look of Crazy Jim's method. I am presuming the coupler is epoxied to the NC and the rest is secured with the threaded rod. I don't have any eye-nuts, but they should be available.
If the fasteners will not impact the avionics, I will likely have him go that route because I can teach him something I am already comfortable with.
thanks again guys.