Is it really possible to build an oven, using a rocket-stove J or batch-box design?

Admittedly, my understanding of the various "rocket" technologies is lacking, but it seems to me that each solution (rocket stove and rocket mass heater) is designed for a very specific application, and neither is ideal for use as an oven.

I have build several rocket stoves, of varying effectiveness.  (To my way of thinking) The design and purpose of a rocket stove is to produce a substantial amount of heat in a very small area, specifically for cooking food by frying or boiling.  The temperature tends to be quite a bit higher that what one might use an oven for...at best a rocket stove might be used to simulate the broiler function of an oven?

Rocket mass heaters, from what I have read and seen in videos, are designed to warm a large mass to a safe temperature that is suitable for providing heat and comfort to a living space.  While internal temperatures can get quite warm, the majority of a rocket mass heater does not achieve a high enough temperature, for a long enough period of time, to be suitable for most traditional "oven" functions.

The limiting factor for both rocket stoves and rocket mass heaters is that they create quite high temperatures in a relatively quick burn cycle, not more moderate temperatures for a long period of time.  I'm sure either could be used to function as an oven, by adding fuel over a longer period of time than you normally would, and with the right types of convection or heat regulation.  However, maintaining an even temperature of say, 350 degrees Fahrenheit, for 30, 60, 90 minutes or longer, is not something that seems to be easy to achieve with either of the "rocket" solutions.

Is there something I'm unaware of or are rocket-type stoves/heater simply not well-suited for traditional oven cooking?

I think you might be looking for a rocket oven.

These are not batch box or J tubes, just simple L rockets, but they seem to get the job done:
Jon and Flip Anderson's Rocket stoves and ovens

John and Flip Anderson Rocket Mud Ovens.pdf

WWW.RechoRoket.Com

Yup! Earlier this year Paul came out with a DVD that walks you through the steps to build your own rocket oven - this rocket oven is a white oven. I highly recommend checking it out if you want to learn how to make one.

The DVD literally goes through each step and if you are already familiar with a j-tube you should have no issues building one. There is no welding needed for this build unless you want to use it when building your j-tube.

As a white oven the hot gasses never reach the food which helps address some of your questions. The inside of the oven will heat up and be fairly uniform in temperature with this setup.

The DVD shows how to install a thermometer into the door of the oven. Once you reach the temperature you want then you just keep a steady supply of wood in the burn chamber. This will take a little practice to learn how much wood and what size of wood each temperature requires. It should not take long to get comfortable with it. The big advantage of this system is that you can use relatively small pieces of wood that would be easy to grow and harvest on your own property - especially if you setup a coppice system.

Here is a great video showing how the cooking process works for a bunch of pizza



And one all about how rocket oven's work:

Keeping a rocket oven at a particular temperature is just a function of how much wood you feed it. However this requires experience and the right dryness of wood.

I've been roasting just fine in my oven which meant maintaining a temperature of 230 deg C for 1.5 hours.

https://permies.com/t/93105/Cooking-inch-batch-rocket-stove

Though this is now a 5 inch batch box.

Thanks for all of the replies.  I'll read through them and watch the videos to see what steps are needed to use the heat from a rocket stove to provide the heat needed for oven style cooking.

Jason, what sort of food are you cooking?  And what temperatures do you want to reach?

Earth/brick based ovens are used somewhat differently from your electric oven.  Once you reach the hottest temperatures you can cook pizza.  As it cools down, you can roast, and then when it cools down further you can bake.  So, you normally time your cooking with the natural firing and cooling temperatures of the mass of the oven.

If you want precise temperature control then that's going to be harder but I think it's doable.  You just need to keep watching the oven temperatures.  It's not set a dial and timer style cooking.

A lot of the stuff I have cooked in an oven is of the "slow roast" variety.  The typical example is where you put a whole chicken or other sizable hunk of meat in a covered roasting pan, with mushrooms, vegetables and maybe a cup or two of water, then roast it at 250 or 275 for 3 or 4 hours.  This is usually started just before going out for the afternoon sit in a blind or treestand.  

Most of the cooking I have done on my rocket stove is grilling meats, the way one would in a Weber grill, or simmering a stew or soup for an hour or two.  Those are two different uses for a rocket stove and require different "feeding habits", such as smaller pieces of really dry wood and a personal fan (for grilling) or larger/wetter pieces that burn slower for the soup.  I have found it to be challenging to run a rocket stove any other way besides full bore, unless you are OK with smoky results.  They are kind of fussy, in that regard, at least from my experience.  

When I think of an oven I think 350F (250f - 450) for 1hr (0.5hr to 3hrs).
I might put a pot of boiling water for moisture/humidity and to keep the temp stable.
I can do the same with a lid/foil paper.

Temporal Control (feeding pattern- frequent breaks possible by small diameter)
Conductivity Control. (Thermal Mass - makes it slow for temp to go up/down)
Moisture Control (seems like a type of thermal mass, but also affects "crusting/searing/flavor" and internal food moisture level).

I look forward to other type of tips/tricks that help rocket oven, woodstove, grills, rocket stove, and others in general.

The temp of a flame in regular oven is 2000F-3500F
https://en.wikipedia.org/wiki/Gas_burner

For the temperatures you are looking at, a solar oven make work for you as well.

I have an evacuated solar tube as a solar cooker, and I'd have to say that only works midday for me on sunny days i.e. not often.  The only place I have full day sun is on the roof but I don't plan on cooking there.

Smoke can be an issue if the fire dies down and you put more wood in the batch box.  That's quickly fixed by using a fan to get the fire up again.  But if you cook inside a dutch oven, then smoke won't be a problem taste wise.  Or, I wonder if you can use charcoal to add to the fire since with charcoal all the wood gas has been removed.

I've cooked over 4 hours in my dry stacked batch box rocket stove.  I roasted pork for 1.5 hours and then cooked pizza and finally baked potatoes in the coals. Now, I've found I can use the riser as a tandoor and BBQ skewered meat in the start up phase of the fire.  Lots of flexibility with a rocket stove oven of the right geometry