The Carbon Kraken

[mperegrinefalcon]

A few months ago I got a Pemberton King Kraken and started work on it as a quick project for mid power flying. I got the fins cut out and set the project aside for a little bit.
Coming back to it, I thought I would try out some lamination with the fiberglass I got from someone cheap and rolled the fins with two layers of 6oz FG. They turned out great, I unfortunately can't find any photos from this stage since I am not in the habit of photographing my builds.
Doing this lamination inspired me. I really enjoyed doing it and it came out really well, so I thought I would take it up another notch. How ridiculous would it be to have a carbon fiber Kraken? I have a large roll of plain weave carbon that came with the fiberglass roll mentioned earlier and I went for it.
I used the only laminating epoxy I have, Duralco 4461. I picked up a gallon kit for some super high speed and high altitude flights and used this as practice for those laminations.

Laminating the main body tube. It got 2 layers of CF. That is perforated peel ply under it and some bagging film.



The ends were trimmed when it was at a leather stage, about 12 hrs. after mixing, and it was taken out of the peel ply after 24hrs.




It absolutely isn't perfect, but it looks good and I am very happy with how it came out.

Now the fins. They only get one layer. I used the same method I used with the fiberglass and just trimmed the excess when it was leather hard.



The ends are rough but can be cleaned up with a belt sander pretty quickly.
I am a total amateur with doing laminations so these aren't perfect but I am satisfied with how they came out.
If I were to do this again I would laminate the tube for the fins before I even cut out the fins, but this worked and looks good.

Next is to attach the fins and rail buttons. I will be putting the rail through one of the fins since that is the only way to use a rail.
More on the way soon.

 

[mperegrinefalcon]

Nosecone fins added. I just slotted along the seam in the plastic and used Rocketpoxy to hold them in place with small fillets. Exterior of the nosecone is still just rough sanded. That will be taken care of later.



The motor mount with shock cord:

All just Rocketpoxy for the centering rings and shock cord. JB Weld for the Aeropack of course.






Fin edges and body tube cleaned up and ready for bonding. All four got the same treatment.



The fins were sanded and cleaned on the area to be bonded. I used Loctite E120HP for attaching them. I am using it because it is the strongest epoxy I have and I like working with it. I would like to fly this rocket on J motors, so I need the fins to be as strong as possible.
I marked lines on the tube using masking tape marked every 1/4 of the circumference using a set of calipers, and drew a line with an angle bar in silver.







I attached these one at a time. Alignment was a much bigger challenge than I anticipated with these. I wasn't able to use any of the methods I have used previously, and the rubber bands I thought would hold the tube stationary just kept rotating them. I ended up just having to let the epoxy cure to a putty like consistency while heating it, then apply it to the rocket and babysit the fin while it was curing.
Overall the result is good enough and you have to look very closely to identify the slight wonkiness in the fin alignment.

I did a test with the spare rail I have at home and it will fit between the tube fins, so I can have my rail buttons on the side of the rocket instead of inside one of the tube fins.
It is all a little rough right now because I lightly sanded the entire body tube.

My finishing plans are to have the carbon areas be clear gloss to see the carbon fiber, then paint the inside of the tube fins and nosecone with a glossy metallic red.
I also have a Kraken paint mask being cut out of vinyl by Mark at Sticker shock that I will have on one side of the rocket.



After filleting I might try a coat of the laminating epoxy over the entire rocket to see if that give it the sheen I am looking for or if I need to go with clear gloss paint. This will me my first time trying to leave a bare carbon look, so any tips are welcome.
Thanks for reading!

 

[ep29030]

I would cover the inside of the tubes with red monokote. Would look great. Here is monokote on the inside tubes of a Fliskits Just Past Due, a MMX size kit. I also used the bright orange monokote on the inside of my Alien Invader and it came out equally good. Monokote beats multiple cycles of fill/finish to get a smooth interior.

 

[DigBaddy]

I would cover the inside of the tubes with red monokote. Would look great. Here is monokote on the inside tubes of a Fliskits Just Past Due, a MMX size kit. I also used the bright orange monokote on the inside of my Alien Invader and it came out equally good. Monokote beats multiple cycles of fill/finish to get a smooth interior.

This is a great idea. I used some chrome vinyl in my scratch 3" mailer Kraken. So much easier than trying to fill and paint.

The carbon is awesome, great build!!!

 

[mtnmanak]

I would cover the inside of the tubes with red monokote. Would look great. Here is monokote on the inside tubes of a Fliskits Just Past Due, a MMX size kit. I also used the bright orange monokote on the inside of my Alien Invader and it came out equally good. Monokote beats multiple cycles of fill/finish to get a smooth interior.

I have never used Monokote before - doesn't it need to be heated with an iron? How do you get it inside the small tubes... or any tube for that matter?

 

[ep29030]

There is the heated version for R/C, but they also sell an adhesive version. That is what I am referring to.

 

[mperegrinefalcon]

This is a great idea. I used some chrome vinyl in my scratch 3" mailer Kraken. So much easier than trying to fill and paint.

The carbon is awesome, great build!!!

View attachment 643543

Thanks, that is absolutely a very shiny Kraken!
The monocote is an interesting Idea. I will have to try it on some low powered kits at some point.
It would not be able to match with the Kraken that will be painted on the side though, so I think I will have to go with paint.
I like painting though and the interior of the tubes are already filled, they just need a little light sanding to remove some epoxy.

 

[mperegrinefalcon]

There is the heated version for R/C, but they also sell an adhesive version. That is what I am referring to.

I was only aware of the heated version for RC. Thanks for the info.

 

[terryg]

The easiest way to finish it is to just clear coat it.

 

[terryg]

The best way to attach and align an odd number of tube fins is to drill a hole in both the tube and the tube fin. Then use a screw to hold it in place while the epoxy cures.

 

[WFWalby]

I was only aware of the heated version for RC. Thanks for the info.

The adhesive version is actually called Trim Monocoat. It used to be available in many colors but the manufacturer has decided that it's only going to produce a few colors like white, black etc. Best bet is to find a LHS that still has NOS sitting around and grab what you can. YMMV

 

[mtnmanak]

The adhesive version is actually called Trim Monocoat. It used to be available in many colors but the manufacturer has decided that it's only going to produce a few colors like white, black etc. Best bet is to find a LHS that still has NOS sitting around and grab what you can. YMMV

Don't want to turn this into a Monokote thread (sorry!), but also don't want to end up on a snipe hunt. Many rumors when you google "monokote" that the entire product line is discontinued. Wikipedia notes "MonoKote was discontinued by Top Flite's subsequent owners, Horizon Hobbies." - https://en.wikipedia.org/wiki/Monokote

I take all Wikipedia articles with a grain of salt, but, considering I never even tried monokote, I am now experiencing FOMO and wondering if I should go buy all of it up that I can find

 

[ep29030]

I have purchased monokote sheets of varying colors whenever I see it in a hobby shop. I now have about a dozen different colors. I find a sheet of it lasts a long time. It’s great stuff for filling tube interiors that show, and it makes great lines on your kits as well. I’ve used the chrome and metallic gold monokote to cover the center portion of fins so they flash in the sun.

 

[JoePfeiffer]

It is my understanding that Monokote (at least the heat-activated) has been discontinued and they are selling old stock now. It is at least true that I was unable to find heat-activated chrome Monokote for the fins on my current build. There is another product called Ultracote that, near as I can tell, is exactly the same stuff under a different name.

A stove griddle works great to heat it for flat fins. Yes, my wife puts up with a lot.

 

[Capt. Eric]

That's a pretty awesome Kraken. I love the way mine came out, but the carbon fiber is really nice. I also had Mark make the graphics (squid-like kraken, and the name stickers on fins).
Too late now, but I decided to airbrush the inside of the fins before attaching to the body. Worked out fine. And yes, a rail fits between the fins, but it's close, so install carefully.
I had to add quite a bit of nose weight. I assume you will too?? Never worked with CF, so I'm not sure how much weight it adds.
I got my L1 with this rocket. Flies great on an H135. I also fly it at my local club's small field on a G77, which is great for lower flights.

 

[mperegrinefalcon]

That's a pretty awesome Kraken. I love the way mine came out, but the carbon fiber is really nice. I also had Mark make the graphics (squid-like kraken, and the name stickers on fins).
Too late now, but I decided to airbrush the inside of the fins before attaching to the body. Worked out fine. And yes, a rail fits between the fins, but it's close, so install carefully.
I had to add quite a bit of nose weight. I assume you will too?? Never worked with CF, so I'm not sure how much weight it adds.
I got my L1 with this rocket. Flies great on an H135. I also fly it at my local club's small field on a G77, which is great for lower flights.

Thanks! I am super happy with how it is coming out. The carbon and all the epoxy has added a lot of weight. The thing weighs 1228 grams without parachute or nose weight. I assume I will have to add nose weight too since it is pretty tail heavy from the tube fins. I haven't looked at the CP on open rocket yet, it struggles with the scalloped tube fins. I got the file from Pemberton though. The CP should be pretty far back with the tubes causing so much drag.
Would you know if rocksim is able to model the fins better?
What CG location have you flown yours with?

 

[Capt. Eric]

Thanks! I am super happy with how it is coming out. The carbon and all the epoxy has added a lot of weight. The thing weighs 1228 grams without parachute or nose weight. I assume I will have to add nose weight too since it is pretty tail heavy from the tube fins. I haven't looked at the CP on open rocket yet, it struggles with the scalloped tube fins. I got the file from Pemberton though. The CP should be pretty far back with the tubes causing so much drag.
Would you know if rocksim is able to model the fins better?
What CG location have you flown yours with?

I don't have Rocksim, so I don't know if it can model the tube fins that are cut on a bias like these. My Openrocket file has them as straight, but I made them about the average length and location, or 7.5" long, set 0.75" from the bottom. The CP is 32.1" per Openrocket.

Mine came out heavy too (thick epoxy fillets). All in but the motor, with a drogue, long shock cord, and JLCR, it's 1338g. Much of that being in the nose. I don't have the CG I've flown with written down, but my OR file shows it at 24.085" with a AT H135, which is what I flew it on first. That should be close, as I checked it and adjusted the sim to reflect real life. I was conservative, with the CP being only a guestimate, and I also wasn't sure what motor I was going to have, so planned for something larger. If anything, it's probably a little over stable at 2-3cal.

Good luck with it. I'm sure it will attract some attention, especially in CF as you have it.

 

[mperegrinefalcon]

I don't have Rocksim, so I don't know if it can model the tube fins that are cut on a bias like these. My Openrocket file has them as straight, but I made them about the average length and location, or 7.5" long, set 0.75" from the bottom. The CP is 32.1" per Openrocket.

Mine came out heavy too (thick epoxy fillets). All in but the motor, with a drogue, long shock cord, and JLCR, it's 1338g. Much of that being in the nose. I don't have the CG I've flown with written down, but my OR file shows it at 24.085" with a AT H135, which is what I flew it on first. That should be close, as I checked it and adjusted the sim to reflect real life. I was conservative, with the CP being only a guestimate, and I also wasn't sure what motor I was going to have, so planned for something larger. If anything, it's probably a little over stable at 2-3cal.

Good luck with it. I'm sure it will attract some attention, especially in CF as you have it.

Thanks for the info. I can verify my numbers against yours that is known to be stable. I plan to be very conservative with my stability margin as well. 2-3 calipers is fine imo for this rocket. I just use Openrocket as well for my sport flyers.

Over stability doesn't seem like it is all that much of an issue from what I have seen. Over stable is much much better than under stable. It is just with extremely long rockets and high winds where issues arise IMO.

 

[Capt. Eric]

Thanks for the info. I can verify my numbers against yours that is known to be stable. I plan to be very conservative with my stability margin as well. 2-3 calipers is fine imo for this rocket. I just use Openrocket as well for my sport flyers.

Over stability doesn't seem like it is all that much of an issue from what I have seen. Over stable is much much better than under stable. It is just with extremely long rockets and high winds where issues arise IMO.

All true. More than once I've brought this rocket to our monthly launch and been surprised by the wind being stronger than predicted. Our field is small, so if it seeks the wind much, it won't get high enough for safe ejection, and/or land in a variety of bad places (we got it all - trees, woods, lakes, houses, parking lot, road). So a couple of times I've had to scratch it from launching. But on a light day... Straight as an arrow!