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Those vids look good man, I think it's gonna work fine. There is still quite a bit of stuff in the riser. Once the whole thing is clear and hot I bet it will go smokeless, given dry fuel. Cool spiral in the riser!

Oh I get it now, it's a batch box! I somehow missed that earlier.... I was wondering where the feed tube was!

Really cool, 4 seasons. I really dig the videos too, thanks for posting them. I'll learn how to do that one of these days.

Matt you were right, a couple more burns and fishing out some more of the heat riser mold and this rocket went into orbit. So much power in fact that it tore itself apart. It cracked in several places the last burn and flames came out the sides burning the outer mold.

So I cobbed up the cracks again and lit it off to see just how powerful it could get without the flames shooting out of 4 sides. Here you can see the flames shooting out the top of the heat riser.

Couple move videos, the first one you can see how much clearer the heat riser is now. Pretty cool to see that flame twisting all the way out of the top of the riser.

Then I ran some temperature checks as the burn was slowing down.

Only getting 700F out of the heat riser although it is over 1000 down the tube. The P-channel seems to be heating up over 200F while the sides and top of the firebox are staying under 200. The thinnest part of the heat riser is getting 550F and started eating the plywood that was touching it in that area. The cob patch seems to be holding up though as it was only 150F. With how bad the cracking is I doubt it will hold up much longer. My guess is that the clay/ash/sand mix I used was not a very good ratio, although I am not sure what I should have used more or less off. I also think that the 1 1/2" sides of the firebox are probably about half as thick as they really need to be. My other conclusion is that wood ash is probably not a very good substitute for perlite or vermiculite as I am getting pretty hot in areas where the heat is high and the walls are thin.

Well it died today. I was thinking of building it different anyway as it never seemed to perform the way I was expecting. I am not sure if it was the free materials I used or the ratio I used or if I just built it too thin. Basically it cracked and fell apart.

I have already started on a rebuild but while busting up the clay I missed the clay and hit my thumb with my make-shift hammer and busted my thumb up pretty bad so this project is on hold until I can grow another thumb

Dang it man, sorry to hear about the thumb! The box looks about like most of my found clay experiments. I actually think yours is holding up pretty well, I can still see most of the shape, it's not just powder. That's good. If you did the same thing and packed cob all around it, it might have made it a month or so. One thing about the batch box, they take a much more structural core mix than the J tube. The big roof span there is always a weak spot, even with real castable refractory they are very hard to keep together.

As for performance, I'd say for your next one do it strictly to the numbers, with the port going into the center of the riser for the typical mixing double vortex there. That way at least you will have a baseline for your continued experimenting. It's a pretty finicky thing, and the difference between almost working and then full lift off with a roaring riser is really not subtle but can be brought about(or prevented) by very small changes.

Rhett, in the batch box core there is a "port" instead of a burn tunnel. In Peter's original design the port opens into the center of the riser, and the gasses hit the back wall of the riser and curl in opposing directions in the riser making a "ram's horn" pattern. In 4Season's version here he has the port entering the riser offset to one side, so the gasses swirl in all one direction.

Here's the "ram's horn" pattern....

Oh, by the way 4, I do the same offset riser in my windowed batch boxes, and it works well, so your concept there is sound in my opinion. I'm just saying, give yourself the experience of the tried and true version so you'll know what to look for.

Rhett my offset riser was built under the assumption that the kick tail design of the Dragon Heater would create a superior burn by speeding the exhaust into a cyclone action. While it looked cool and seemed like a good theory it did not perform as well as I had hoped. Upon doing some more reading I found that the J-tube design needs turbulence in the horizontal section to get the most complete burn and then speed the exhaust on the way out to function best. But the batchbox theory seem to lean toward turbulence in the riser to get the best performance. While I would not depend solely on this one experiment to draw that conclusion it would seem that turbulence in the riser of a batch-box gives a better burn although from other experiments with J-tubes seem to need the turbulence in the burn tunnel to maximize performance. In my next build I plan to create a kind of dual heat riser in an attempt to maximize turbulence by crashing two cyclones together in the heat riser. Think of it as a ram-horn design on steroids.

By the way I am in no way saying that Matt's or anyone else approach is wrong to the way to build these stoves. I am only trying to learn as I go and maybe inspire one of the true innovators out there with some small idea that can add to the performance of these already incredible little stoves.