Sharon's 4" Jimbo Jart

Since I want to drag race CJ at Airfest I figured I better get building this rocket.

The first thing was to review his Jimbo Jart Thread and made a series of notes to myself



A sample of these notes are: remember to add bulk plate while fitting coupler to nose cone; read posts 71 and 79 before sticking fins; and be sure and get a skull decal from CJ for my Jimbo Jart. Not sure what that says about my priorities......

Started around 4pm and washed parts, sanded the CNC machine tabs off, smoothed the edges in body and parts. Then sanded and test fit centering rings and fins, numbering the fins and slots:



At this point I am following Post #32

https://www.rocketryforum.com/showthread.php?60755-CJ-s-Black-Sat-quot-JIMBO-quot-Jart-4-in-DD-in-NC-or-any-Jart-build!/page2&highlight=jimbo


Inserting the coupler into the aft portion of the fin can I drew fin line marks for future shear pins and vent placement. Then transferred the marks from the coupler to the vent band. I used a piece of tape to keep the vent band on the coupler while making marks so it wouldn't move while I was handling it.





Putting the bulk plate on the nose side of the coupler I inserted the coupler into the nose cone to a snug but not too tight fit and drew a line with a silver sharpie around the coupler where it met the nose cone. I also marked where the vent band fit the best to the nose cone.




Putting a piece of tape where the silver line was, I added the vent band and marked a silver line around the aft end.

At this point I moved to our Epoxy station (aka laundry room), removed the tape, sanded inside the vent band and sanded on the coupler between the silver lines to "excite the molecules" then wiped with alcohol and then brushed on 30 minute Epoxy and using a twisting motion I put the switch band in place. Clean up was easy with a little alcohol and pulling the tape up after about 15 minutes. Checked it with the nose cone to make sure I got it right, then put the coupler/switchband in the curing oven, aka outside in 107 degree Arizona temperature. At this point it was 5:15pm. I guess I'm not the fastest builder out there....

Wayne got into the act by bringing out his Wildman Extreme to start building and picked up my nose cone instead of his for test fitting. Needless to say: :gavel:

Tomorrow I'll start on #36 of CJ's Thread .....

I'm watching. Miss you guys!

Nice to see you building again !

You always do your research and thoroughly test fit before commiting to epoxy..reminds me to do the same.

My first FG build .. sanded slots til fins would drop through.. then roughed up fins for epoxy .. now they are loose in the slots ..

Will be watching to see how you get the HEDR av bay and electronics to mount up .

Kenny

watheyak said:

I'm watching. Miss you guys!

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You are hard to keep up with. I've been following your Airframe build for the 54/4000 Loki Thread, fascinating.

KenRico said:

Nice to see you building again !

You always do your research and thoroughly test fit before commiting to epoxy..reminds me to do the same.

My first FG build .. sanded slots til fins would drop through.. then roughed up fins for epoxy .. now they are loose in the slots ..

Will be watching to see how you get the HEDR av bay and electronics to mount up .

Kenny

Click to expand...

I'm still thinking about how I'm going to set up the av-bay, pretty sure going with my standard Stratologger but think I'm going to use magnetic switch such as I did on the 3" BlackStar instead of my twist/tie method I used on my Wild Thang.

Looking good Sharon! Your going to love the HED setup, it is easy to prep and the rocket always lands close by. I flew Pegasus using HED two times to 9k and one time 12k ,it landed less than .4 miles away each time. Maybe You, Wayne, and I could have a Jart drag race at Eagle Eye in the winter. Looking forward to seeing the finished product, keep up the good work! :clap:

What's HED?

watheyak said:

What's HED?

Click to expand...

Head End Deployment.

BLKKROW said:

Head End Deployment.

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I still don't get it. I'm slow.

Is this dual deploy from one airframe break and all the electronics in the nose? If so, I am a huge fan.

watheyak said:

I still don't get it. I'm slow.

Is this dual deploy from one airframe break and all the electronics in the nose? If so, I am a huge fan.

Click to expand...

The electronics are inside the nosecone coupler and the parachute is inside the nosecone. You pop the nosecone at apogee and then you pop the nosecone coupler from the nosecone at your desired altitude. I will get you pictures but I can't find my camera right now.

watheyak said:

I still don't get it. I'm slow.

Is this dual deploy from one airframe break and all the electronics in the nose? If so, I am a huge fan.

Click to expand...

This could work on your MD carbon fiber rocket you are making for that Loki 4000 motor. With a 7:1 nosecone, you could put all the avionics in the coupler and still have room for the main in the top of the N/C. CJ does a good job of describing it in his build thread here:
https://www.rocketryforum.com/showt...n-NC-or-any-Jart-build!/page2&highlight=jimbo

That is in fact what I'm doing with that rocket. With a slight twist. I'll check out C'Js thread.

On to item #70 where I start to put the fin can together.

Measured a length of 1/2" flat strap kevlar



Sanded the entire motor mount tube and the centering rings, wiped it all off

EDIT: Next build draw the fin slots on motor mount tube at this point and tape off lines to keep epoxy off

Then laid the kevlar over the forward centering ring and marked the edges



Then filed notches to fit.



put the strap and centering rings on the motor mount tube and marked where the strap. Notice drawing straight lines isn't my forte:



I added the rear centering ring and the aeropack retainer for sizing and fitting and marked their locations accordingly.

Then mixed up 30 grams of Rocket Poxy and encapsultated the kevlar strap and ran a fillet around the top of the forward centering ring and set it out to dry.







and that was it until today.

Nice build thread!
Great looking rocket too!

Couldn't help but notice the pillow in the second picture. Surely it's not what it looks like, or is it?

JP

Okay, now it was time to put on the rear centering ring and start the external fillets.



Measured and taped



mixed 30 grams rocket poxy and had a glass of wine



Tinted the epoxy



sanded, cleaned, poured:



Put out in curing oven:



and sure enough, got bubbles



Oh well.

I see. Dyslexic moment for me, nah, that's not it either.
The more I looked, it appeared to me that it wasn't turned like the dreaded other sign.
My Great Great Grandmother was Half Indian.

Nice work Sharon!

JP

This is an excellent build thread.

When you / Wayne poured in the expanding foam about how high up did it get within the fin can. Is this something you want to have come to the very top and then trim to fit?

JP Morgan said:

I see. Dyslexic moment for me, nah, that's not it either.
The more I looked, it appeared to me that it wasn't turned like the dreaded other sign.
My Great Great Grandmother was Half Indian.

Nice work Sharon!

JP

Click to expand...

Thanks. Appreciate that you are viewing my thread. Posting my builds is good practice for my Level Three write up planned for next year

AfterBurners said:

This is an excellent build thread.

When you / Wayne poured in the expanding foam about how high up did it get within the fin can. Is this something you want to have come to the very top and then trim to fit?

Click to expand...

For this particular build I really was only planning to put in enough to firm up the attachment of the forward centering ring....but got frisky and since I couldn't get the top of Part B off, Wayne cut it off and there was 1/2 oz left after the first pour. So mixed it up and poured it in too. I know it will move the CG back a little but since I didn't do internal fillets I am okay with the weight especially since using the drops of water it lowered the density . Here is how it ended up:

In other builds in which I have foamed the fin can I have made the mistake of filling to the top, then it foamed over and was a complete mess to clean up (hence all the plastic bags taped around the fin can). I now try for multiple small pours (which also helps diffuse the heat) and try to keep away from the area of the rear centering ring.

To answer your questions, no I don't want it to come to the top, but close to the bottom of the rear centering ring and then once I attach it the back is nice and clean. But that is just the way I like to do it.

Nice build.. thanks for sharing !

Damn straight fins !

Kenny

That PayLoadBay is a great site for some tools that help with building and yes I agree with Ken Damn Straight fins!!

This is a very well documented build. I'm enjoying this. What I like most about your build Sharon is how on each phase of the build you have all your supplies and components that you need ready and everything is nicely organized. I feel this helps with a successful build because you're not fumbling around looking for things and it's easier to stay focused on what you are doing. You are also taking your time.

Great work!!

AfterBurners said:

That PayLoadBay is a great site for some tools that help with building and yes I agree with Ken Damn Straight fins!!

This is a very well documented build. I'm enjoying this. What I like most about your build Sharon is how on each phase of the build you have all your supplies and components that you need ready and everything is nicely organized. I feel this helps with a successful build because you're not fumbling around looking for things and it's easier to stay focused on what you are doing. You are also taking your time.

Great work!!

Click to expand...

Thank you for your kind words. Each build I complete I feel I am getting more organized and performing my tasks in a more ergonomic fashion, but I still make mistakes and I am definitely not at Wayne's level at esthetics. I can handle a few bubbles in my fillets whereas he will scoop out his and redo them.


Sent from my iPad using Rocketry Forum

Sharon,

I am enjoying the build. Nice clear pictures and good descriptions.
This will be a good resource for someone else in the future.

I love Rocketpoxy and I rarely get even a bubble in my fillets.
When you mix it install try not to mix in too much air. I use a bamboo skewer to mix it and then to help pour it out of the Dixie cup that I mixed it up in. If you let it sit for 1-2 minutes before pouring it into the fillet it helps some of the air bubbles to raise to the top in the cup and not in the fillet. Then pour into place. You can also use some heat from a heat gun or hair dryer to get some of the bubbles to rise out but I have found that the technique stated above does a good enough job that the heat is not necessary.

Keep up the good work.

Anthony

Just a reminder for next time, the instructions say allow 15 minutes for it to de-gas. Something I've have not noticed, until recently.

By the way did your rocket poxy come in ketchup squirt bottles or did you buy them and put the epoxy in there?


Alexander Solis

Level 1 - Mariah 54 - CTI-I100 Red Lightning Longburn - 6,345 Feet

SinfulDarkLord said:

Just a reminder for next time, the instructions say allow 15 minutes for it to de-gas. Something I've have not noticed, until recently.

By the way did your rocket poxy come in ketchup squirt bottles or did you buy them and put the epoxy in there?


Alexander Solis

Click to expand...

What? There's instructions?

Just kidding......

We bought the ketchup squirt bottles and put the epoxy in them. Once we use them we toss 'em. Locally we have a place called Smart N' Final which carries 6 packs of these cheap.