Question on a square tube rocket stove

Hello everyone, I've started to experiment with rocket stoves, starting with a pile of fire brick, I went from 16 to 20 to 24 and then re arranged them in all different ways. It's been fun and interesting.
I want to try making one from 4 x 4 square tube to be able to transport it for cooking on. I have 4 ideas of how to build but not sure which way would be the best way for ease of operation and usage. in the pic there are no legs but when I make it it will get three legs for stability.
1. Is a typical L with an 18" riser and a 10" feed tube
2 18" riser and a 6 in feed tube
3. 18"riser J tube 5 1/2 "feed tube on top of 45deg angle under the feed tube is a 1 3/4 space that will get a hinged cover to let in additional air under the wood as needed
4 18" riser and 10 in feed tube. Most compact for transport I think this feed tube would get too hot and burn in the feed area

I wish I could build all of these and test them but I dont have enough metal so thats why I ask the experts!
I'm leaning towards number 3 since its gravity fed but I havent had luck making a J tube with the brick setup
Any Ideas and comments are very welcome

Thanks
Rae

As near as I can tell, your heat riser needs to be at least as long as your feed tube and burn tube combined. #3 should work but I would go with #4 if you can. #3 would be easier to clean than #4, but I'm getting the impression that a full J tube is needed to reach the higher temps. I have seen several of these pocket rockets on YouTube and pretty much everyone of them made for an excellent little portable stove, but I saw evidence, or lack of such, that they reach the 1200F needed to burn carbon monoxide. Take this into consideration when you use it.

Thanks for the reply! The riser is 18 inches and the longest feed tube is 10 so I should be good on that part, after reading your post it dawned on me that I could test these somewhat by proping the pieces together with fire brick. I know its not a good test but its cheaper than buying a lot of metal right now . So far I have tried 1 and 3 and neither works as well as a brick rocket setup. I'm not sure I understand why but both seemed pretty finicky and number 3 allowed me to cook on it but after that even tho there was flame in the riser is was lazy and not putting out much if any heat. Hopefully tonight I will try #4 and see how that works. If not maybe back to the drawing board.
Thanks for the input

Rae

Remember that the gases want to travel in a helix. A square tube has a hydraulic cross section that is smaller than the square tube.

That aside, cut your bricks. Diamond blades for miter saws are not as expensive as they used to be. Be sure to get a dry cutting blade though. With a bit of practice you can cut whatever shape you need.

You might consider standing bricks up with the narrow faces cut so you can form a hexagon or even an octagon to better approximate a round tube.