Pem-Tech Kraken upscale on BT-80

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Tobor

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Hello,

I am interested in upscaling the Pem-Tech Kraken to a BT-80 as I have some of that tubing laying around. But first I'd like to thank Mr. Pemberton for designing such a sexy rocket!

I think I will use this thread as a build-log when the time comes and time permitting.

Now to my only question atm: Which NC was used for the Pem-Tech Kraken? I've DL'd PT's infamous deconstruction manual for it but there is no specific info pertaining to the NC.

The Kraken specs say the model is 22" long. Since it's BT is 18" long, that leaves 4" for the NC. My best guess for the NC, based on the parts photo in the manual, is that it is very close to Semroc's SEM-BNC-60KP 4.4" Elliptical Balsa Nose Cone.

Any thoughts?

snrkl

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How are you simming the fins?

When I did my BT-60 clone, I used 3 fins with the same cross section for each tube fin at a +/- 7° angles.

From sim to flight it was pretty bang on... (within 10% wind adjusted...)

Tobor

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How are you simming the fins?

When I did my BT-60 clone, I used 3 fins with the same cross section for each tube fin at a +/- 7° angles.

From sim to flight it was pretty bang on... (within 10% wind adjusted...)
I used both Freeform Fins (6) and Tube Fins (3). I figured it was the best way to approximate Kraken's Tube Fins. The link above the picture of KK is my .ork file if you are interested in DL'ing it.

Edit:
Here is the rear view for clarification.

snrkl

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I think three fins with the right cross section will calculate it better.

TVM published some guidance on calculating tube fin performance and the sum of it was: a tube fin creates about as much drag as ~3 fins of the same profile.

I think this was the article:
https://www.apogeerockets.com/education/downloads/Newsletter27.pdf

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Tobor

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I Pm'd Mr. Pemberton and he was more then kind enough to respond. The 22" Kraken uses a BMS BNC-60H Ogive NC which is actually 4.5" from shoulder to tip. So, with my upscale ratio = 1.625, that gives me a BT-80 NC = 7.3125" in length. Luckily for me Semroc makes the BNC-80KA Ogive (for std. wall tubing) and the BNC-80HKA (for their thick wall tubing), each of which have a shoulder to tip length of 7.33". How sweet is that!?

Since I have the option of using heavier walled tubing, I'm going with Semroc's HD tubing and use my Estes BT-80s for the fin tubes. Now I can create my parts list and order some stuff...

Tobor

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Well today I pulled the trigger and ordered parts. Had to source from several vendors to get the parts I wanted. I splurged on a few things just because I really like this rocket. Note that this will be my first build using a composite motor. My AeroTech RMS 29/40-120 was initially intended (and still is) for my L1 design that will also serve as a platform for the custom electronics package that I am working on. At some point in the future I will start a blog on the electronics and the rocket.

Anyhoot, I can't wait to get started building this bird.

Btw, for anyone interested, I have a mostly complete B.O.M in G-Docs (Here)

snrkl

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Nice. I await the build thread on this one.

How are you planning on painting it?

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Tobor

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Nice. I await the build thread on this one.

How are you planning on painting it?
Thx, I hope not to disappoint.

For paint I am thinking of using a dark "Sea-ish" green for the airframe and blood red (or as close as I can get to it) for the fin tube interiors. I could not find anything online close to those colors in Metallic and was getting bummed out, when I hit upon a Clear Pearl by Rust-Oleum. So, whichever green and red I choose will be top coated with the pearl.

I am also playing with the Idea of "ghosting" tentacles on the airframe (before the top coat) with a light shot of translucent smoke. The effect, if it works, will have the tentacles only appearing when viewed at certain angles.

snrkl

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Thx, I hope not to disappoint.

For paint I am thinking of using a dark "Sea-ish" green for the airframe and blood red (or as close as I can get to it) for the fin tube interiors. I could not find anything online close to those colors in Metallic and was getting bummed out, when I hit upon a Clear Pearl by Rust-Oleum. So, whichever green and red I choose will be top coated with the pearl.

I am also playing with the Idea of "ghosting" tentacles on the airframe (before the top coat) with a light shot of translucent smoke. The effect, if it works, will have the tentacles only appearing when viewed at certain angles.
Nice one.. I have been playing with the rustoleum colour shift (which is like a dark version of the pearl with blue/green/purple highlights...)

Originally, I had wanted it for my BT60 Kraken Clone, but it didn't arrive in time...

I like the tentacles idea, I was toying with the idea of trying to do a squid tentacle like texture on the lower outside of the rocket in a light colour shift using pantyhose (similar to this technique: [video=youtube;U1eT4Vz6ipg]https://www.youtube.com/watch?v=U1eT4Vz6ipg[/video]) but using something like this:

I might give it a go now that I have flown it a few times and the "it might ruin it" bug has left the building...

Tobor

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Nice one.. I have been playing with the rustoleum colour shift (which is like a dark version of the pearl with blue/green/purple highlights...)

Originally, I had wanted it for my BT60 Kraken Clone, but it didn't arrive in time...

I like the tentacles idea, I was toying with the idea of trying to do a squid tentacle like texture on the lower outside of the rocket in a light colour shift using pantyhose (similar to this technique: https://www.youtube.com/watch?v=U1eT4Vz6ipg but using something like this:

View attachment 325821

I might give it a go now that I have flown it a few times and the "it might ruin it" bug has left the building...
Kool! That looks very interesting. Plz let me know how it turns out. Or better yet, do a thread on it....

snrkl

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Well, I found some stocking like this on eBay for $3 ($6 incl shipping)

They won't be here for a few weeks - once they arrive I'll do a test run and advise.

Tobor

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Sorry for the delay. "The Job" has been kicking my bottom side and my JawStand launch pad project took up a decent portion of what little free time I've had lately.

Anyhoot, on Wednesday I finally started on my Kraken, filling the spirals on the airframe. Then while waiting for the filler to dry I started working on the center rings. The I.D. is actually cut for both BT-50 and BT-52H tubing. When I started removing the smaller BT-50 portion, I realized that the CR's were way too soft for this project. And on test fitting them to the airframe, I discovered the O.D. is too small for the 2.6" AeroTech tubing. So today I ordered CR's from Apogee along with some other supplies I needed. package should arrive on Tuesday.

Tobor

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This build is getting more involved with each passing day. The problem with that is I'd like to have this bird finished and ready to fly for next Sunday, the 17th... :lol:

Last Monday I got the crazy idea to try an adjustable nose weight setup. Not that my Kraken needs it but it is something I will use in my L1 scratch build next year. I felt it was worth the effort to get the bugs out now. So Wednesday evening I used a Ryobi 1-3/8" Forstner bit to bore out the back end of the NC. Bore wound up a tad oblong. Next time I will construct a proper jig to keep things in their places while boring

Today I had the chance to clean up the bore some and added a slightly larger dia. recess for the stepped bulkhead I made today.

I used some scrap plywood I had lying around and turned it in a drill press. Plywood was mounted on a 10-32 x 2" bolt, fixed with washes and nuts.
I forgot to bring along a proper chisel to turn down the bulkhead step so I ended up using a utility knife. Not the recommended way to do things, but it actually finished up really well! :clap:

Back home with my finished pieces.

Close up of my adjustable nose weight idea.

Stepped bulkhead glued up with TiteBond and pressed together using parts of the nose weight assembly. 1/4-20 x 4" eye bolt, 1-1/4" fender washers & 1/4-20 hex nuts.
I also worked on the CRs and MMT. I had planned on using 30 minute epoxy to affix CRs to MMT but discovered the resin had gelled, rendering it useless. Ended up using JB Weld. 1st time I have ever used it in any kind of hobby build. JB Weld is great stuff!

And here is some of the stuff I will use for recovery hardware.

||EOP||

Tobor

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Yep, pieces still on work table. 1st flight will have to wait till Oct.

Monday, Sept. 11: Using 5 minute epoxy, affixed threaded insert Block (Left) into NC (Right). Turned out well.

Tuesday/Wednesday: Finally got up the nerve to cut the fin tubes. I still have all ten digits attached after all that. Then I finished working on the MMT. The tube coupler glued to the aft CR has a small block of spruce glued to the inside. The block is an anchor point for the aft rail button and the coupler sets the position of the anchor point. the coupler also gives the rail button's screw more material to bite into. MMT assembly was epoxied into the airframe using West System G/Flex 650. After everything cured I ran the rail button's screw through the hole I drilled. Then I backed it out and applied some JB Weld into the hole. Next I applied some Fixit putty to the underside of the rail button and then screwed it onto the airframe. I used whatever putty oozed out from under the button as a fillet for the rail button.

Close up showing how I tied off the Kevlar shock cord knot's tail. I used some really thin 100# Kevlar cord I purchased from eRockets awhile back (for use in the Estes builds).

Saturday: After 1st coat of Rust-oleum filler/primer. NC was wet sanded and more cwf applied and sanded again. Airframe and 2 of 4 fin tubes dry sanded. After I get around to sanding the other fin tubes, I will shoot everything with a 2nd coat of filler/primer.

Edit:

Just realized I never posted the layout I came up with for the fin tubes. ooops....

Here ya go!

More to come....

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Tobor

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I have been working on this off and on, as time and patience allows. I must admit that my patience is fraying at the edges. As this is my first non Estes/Centuri sized build ever, I guess I had not fully realized how much more surface area exists on an MPR. I also did not appreciate how errors/mistakes are magnified by the size of the rocket. This is another reason this project is taking so long, as I have made quite a few mistakes. Sigh......

Anyhoot, I am getting close to finishing my Kraken.

1st completed Tube Fin

Although it is not that noticeable in the picture, the Red has significant orange peel. I've never encountered this in any project before, and I've had some fairly large (non model rocket) projects in my life. Lesson learned.

Btw, my Rust-Oleum color choices were Gloss Apple Red, Satin Hunter Green and Clear Frosted Pearl as the top coat.

The Red and Green worked really well as Rust-Oleum colors always do. But, their Clear Frosted Pearl is another story. The main issue is Rust-Oleum's design for the spray cans cap/applicator, it totally sucks. Instead of being the tried and true button style, this Clear Pearl has a tall, hollow cap w/trigger style nozzle. The nozzle just sits on top of the spray can's stem instead of press fitting over it. I presume the design relies on the downward pressure of the trigger to maintain a seal, except it doesn't work. The paint leaks past the stem like a sieve. I ended up using a nozzle from a can of PlastiKote primer my girlfriend had left at my place.

I guess it may be time to invest in a spray gun and compressor. I already own a Paasche Single Action Airbrush I purchased back in the late 70's for my R/C stuff.

Till next time.

snrkl

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TRF Supporter
Did you figure out the cause of the orange peel?

I use rustoleum pretty heavily and it took me a while to figure out the recoat time intervals and the difference is wait times for cardboard tubes and plastics: all done in one hour or wait 24-72hrs depending on surface. Also took me a while to realise I needed to treat glossy cardboard tubes like plastic and leave them 3 days between recoat.

Dupe

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Pem Tech

Well-Known Member
How are you simming the fins?

When I did my BT-60 clone, I used 3 fins with the same cross section for each tube fin at a +/- 7° angles.

From sim to flight it was pretty bang on... (within 10% wind adjusted...)

That is exactly how we simmed the sculpted tube fins. Excellent work! Do you have any pictures?

Pem Tech

Well-Known Member
Nice one.. I have been playing with the rustoleum colour shift (which is like a dark version of the pearl with blue/green/purple highlights...)

Originally, I had wanted it for my BT60 Kraken Clone, but it didn't arrive in time...

I like the tentacles idea, I was toying with the idea of trying to do a squid tentacle like texture on the lower outside of the rocket in a light colour shift using pantyhose (similar to this technique: [video=youtube;U1eT4Vz6ipg]https://www.youtube.com/watch?v=U1eT4Vz6ipg[/video]) but using something like this:
View attachment 325821

I might give it a go now that I have flown it a few times and the "it might ruin it" bug has left the building...
Very nice....
Do you wear these often?

Looking good!

snrkl

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TRF Supporter
That is exactly how we simmed the sculpted tube fins. Excellent work! Do you have any pictures?
You've forgotten - I wrote it up when I did it, and you helped after you declined my offer to send money across the pond for a set of instructions!!

Now I have a JLCR I'm planning on flying it again with much bigger motors that the d12-5s it's flown with to date (the walk to retrieve it on a windy day in the rain/mud was too traumatic for my exercise phobic composition...)

snrkl

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Very nice....
Do you wear these often?
I never fly squids with out them.

I'm feeling like building a larger one now that the trauma of the last one is almost forgotten - it will likely get the stockings spray treatment if I do...

Tobor

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Did you figure out the cause of the orange peel?

I use rustoleum pretty heavily and it took me a while to figure out the recoat time intervals and the difference is wait times for cardboard tubes and plastics: all done in one hour or wait 24-72hrs depending on surface. Also took me a while to realise I needed to treat glossy cardboard tubes like plastic and leave them 3 days between recoat.
That is what I figured.
High gloss = much lighter coats w/30~45 minute intervals between coats. After my last post I also realized that part of the problem was the concave nature (inside curvature) of tube fins, and exasperated by the amount of surface area. Now that I have ventured into larger projects, I need to stop thinking in "LPR" terms.

Looking good!
Thank you.

Btw, I'm sorta mad at myself for not adding the canards. When I began this build, I kept going back and forth with my decision not to use them. But now that the NC is finished, it looks a little lame without the canards. As I really do not want to muck up the NC at this point in the build, I'll probably just order another NC and use 1/8" birch ply for the canards.

Tobor

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I haven't done much on the Kraken since my last post even though it is close to being finished. Got home from work this evening and buttoned up the NC.

And the last thing I need to work on....

Notice the pointed tip of the unpainted stripe. That point was supposed to end up 0.25 inches lower then the tips of the tubes fins. Unfortunately, I forgot to mask it so and instead, I masked the full length of the tube fins. So now I have to decide how to fix this error. I could just correct with the Hunter Green but, I'm thinking of extending the Red from the tube fins in the shape of a spike. I like the spike idea but it will require a lot more work to pull it off well. I will decide later tonight.

Stay tuned...

Tobor

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Finally! Finished, Fini, Finito, Fertig....

Tobor

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Just finished piecing together one little addition to my Kraken...

Made it out of a 1.125" dowel purchased at HD, some scrap 0.20" ply from an open frame PC case I made years ago, and one of the CR's that I decided not to use in the Kraken. Fixed together with cyanoacrylate gel and Titebond II. Went together really fast. I may paint it over the winter.

Tobor

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Well, I finally got to fly Kraken yesterday! Yipeeee. It was beautiful to watch it ascend on a G76. That Mojave Green is killer.

Unfortunately she is now lost in the marshes and reeds South of the launch site. I looked for it for almost 2 hours yesterday, and another 4+ hours today. For some unknown reason I neglected to acquire an audible tracker for my precious Kraken. Hind sight is always 20\20. Though I promise you (and myself), I will never make that mistake again. I won't be able to build another Kraken until after the new year....

:surprised: :hot: :cry: :bang:

On a slightly more positive note, after taking a break half way through my excursion, I remembered I had lost my Estes Sprint XL to power lines back in June/July. So I decided to give it a try and do a search for that rocket.
Well, I found it!!! Err at least most of it.....

I also found someone else's rocket earlier in the day....

I'll post this guy in a separate thread. Hope the owner reads these here forums.