RM Stove question, maximizing air flow

I've done some reading around on this site and others but haven't found a satisfactory answer to my question. I'd eventually like to make a permanent RMS to complement my back yard fire pit because we do a fair amount of cooking outside all year long, but I want to get a feel for design first so I'm going to build a few of the tin can models to see what I like or don't like. My question is related to maximizing efficiency and minimizing smoke.

It seems to me that the diameters of the horizontal and vertical pieces would affect air flow, as well as chimney height. What I'm wondering is this...to maximize draft, it seems that the chimney should be higher, right? If so, what's the commonly accepted practice in terms of the diameter of the vertical and horizontal pieces (again, using the basic coffee/soup can idea). Should they be the same diameter? Would it draw better if one or the other was narrower? Fluids (gases) travel faster in smaller diameter pipes, but the trade off of narrowing pipe diameter would be either having a smaller area for the flame to contact a pot or pan on top, or else having even less space to put fuel.

What are your thoughts?

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My riser was higher than normal at 41 inches. I could do that as there is no 55 gal. drum on top of it. My burn box is way bigger than normal and horizontal. It produces an awesome rocket effect.

Jeffery Roberts : It seems that we have given you bits and pieces of good answers ! Let me see if I can help , 1st you are talking about the Rocket Stove, not the
Rocket Mass Heater RMH, The Rocket Stove came 1st, and was designed to be used out of doors or in very well ventilated spaces !

The Rocket Stove, especially in its portable Tin can configurations is much loved by Survivalists/Preppers/ Zombie Hunters, and Ice Fishers !

For cooking purposes, a 3-4 inch Rocket stove is more then sufficient for most cooking duties, By making a tall chimney you increase draft and efficiency, BUT-
You will soon have to deal with the danger of tipping the Stove over if you extend the Stoves Chimney too high !

A good place to look for more information exclusive to the Rocket Stove and Rocket Stove Ovens, Is at Aprovecho.org - -> Good Hunting !

Allan Mikolet is I THINK describing the outdoor use of a Rocket Mass Heater RMH, that when you remove the Barrel -Can act very much like a Rocket Stove,
also when the Rocket Burner of A RMH is completed by adding the barrel (And a final vertical chimney) the top of the barrel can be heated to a glowing cherry red
and can be used as a cooking surface !

This is where I recommend going to rocketstoves.com to Download a PDF Copy(s) of The 3rd Edition of Evans' And Jackson's Great Work "Rocket Mass Heaters"
After you have had a chance to read though the great depth of material in this pamphlet you will be able to come back here and know that you can use and understand
The words we use to describe the size, shape and orientation of the parts of the Rocket Mass Heater RMH, which is Probably what you will be using as a platform to
make an outdoor Cooker !

Finally one of the Core Ideas to grasp in the construction of any Permanent Outdoor Heater / Cooker is Need for a Constant Cross-Sectional Area ( C.S.A. ) in your
Feed Tube, Burn Tunnel and Vertical Chimney/Heat Riser !

Get the Pamphlet, and Come Back here often, With Over 25,000 Members World wide you can expect to come here 24 / 7 and find someone who wants to talk about
what you want to talk about ! For the Good of The Crafts, Big AL !

Allen, it's not outdoors, rather in my one room cabin. The hybrid heater using 3 water tanks. Alan

Alan Mikoleit : your build probably needs to be addressed in a New topic Thread, as this started out to be a Rocket Stove discussion, do you have a link to
pictures of your build ? Big AL !

Yes, under the title of hybrid double barrel stove heater. The whole build is documented with lots of pictures.