Humble beginings

I stumbled across some old photos from my very first J-Tube rocket build in 2013
And then Shorty Core 2024...  I have sure come a long way since then!

I came across some pictures of my transition area during a rebuild.

https://permies.com/u/160094/thomas-rubino, I been looking for that cast-cob idea. Looks like a 6", right? How did it work out? How did the 5 gallon bucket work for the feed? I like that you have/had a lid. What other dimenensions did you have? Did you use tapered pieces in front of the reduced air flow into the bottome of the riser? Many questions, I know. Your Shorty Core is beautiful, but I live in a mobile home. Oh well.

Hi Daryl;
That is an 8"
That was my very first rocket build... I did not know shit...
The cast core abraded horribly and ultimately the feed tube was the size of the five-gallon bucket.
That enlarged feed tube made a great alternate riser if the going was tough through the mass pipes...
I learned from my mistakes, although I continued to make more...

What size J-Tube did you want?
8" are 7.5" square in the feed tube, the burn tunnel, and the riser.
6" are 5.5" square in the feed tube, the burn tunnel, and the riser

The roof of the burn tunnel should be 10"-12" long,  any longer and it's a problem

The feed tube should be 16" deep and the riser should be 36-48" tall

Thank you, Thomas. I've been thinking about casting a 6" in a tub (or maybe wood like yours) w/ refractory cement, perlite and sodium silicate (waterglass) for more temperature support. Do you suggest the reduced air flow w/ tapered fronts?

Hi Daryl;
If you are making this for a tiny home then a 6" will be enough.
Anyplace else and I would make an 8" they are so much more user-friendly.
More room for larger wood, longer burn time (45-60 minutes)

I'm not sure what you are referring to about taper.
Nothing should be modified from the specifications, especially not on a first build.
If you build a proven plan, you will get proven results.
Experimental rocket science is fun after you know what results a spec build produces.
Start experimenting on your second or third RMH.

Again, thanks for you time and expertise, Thomas. I need to show you a drawing I guess. How do I go about doing that?

Draw a picture on paper and snap a photo of it.
Add photo as an attachment

Daryl, follow this here link for detailed instructions for adding photos to permies posts.

Thomas Rubino, thanks again for your time. Here's my drawing.

Ok, I see what you are thinking of.
Yes, to the ramp at the back of the riser.
No, to restricting the burn tunnel.

To hot rod a J-Tube rocket, you add a Peter channel at the feed tube to supply cooler air and create turbulence, and then you can add a "trip wire" partway down the burn tunnel in the ceiling.
Before Peter Berg started refining Batchboxes he improved the J-Tube as much as possible.