http://www.smokingmeatforums.com/t/...others-ready-to-use-rev5-6-19-15#post_1264161
http://www.1728.org/circsect.htm
Mark, afternoon..... First, when looking at the tutorial for building a RF smoker, ONLY use the first post...... IGNORE the other posts for the build...
The first post is a step by step how to calculate each number for the build....
Gallons x 231 = 115,000 cubic inches..
115,000 X 0.004 = 460 cu. in. FB/CC opening / area under the RF plate / area at end of RF plate...
115000 X 0.33 = 38,000 cu. in. for the FB.... (24 x 40 pipe is 18,000 ) too small (36x36x36 is a great size)
115,000 X 0.001 = 115 sq. in. for the FB inlets...
115,000 X ( .017 to .022 ) = 2,000 to 2,500 cu. in.. I lean toward the larger volume to insure good air flow..
Exhaust Stack Volume ...
2500 / 0.7854 = 3180 cu. in. / 81 (9x9) = 39" of stack ABOVE the Cook Chamber... That's what I would use....
FB/CC opening...
Inside diameter of your tank is approx. 36" ... use 18" for the radius.....
16" segment height works well... but it can be safely lowered to give more room where the food is cooked.... Because the diameter of the CC is wide, there is reduced friction..... Also, if you slide the FB into the CC, that will reduce surface area and friction loss under the RF plate...
I would slide the FB into the CC until it has passed the welded bead so you are now into the straight section of the tank... That will make this build soooo much easier... the RF plate will now be a rectangle, the friction will be reduced and I'm going to say the Segment Height can be reduced to 14", giving you 21" above the RF plate for food racks... The RF plate width will then be 35"... It can then be welded directly to the top plate on the FB for easy fitment and the FB will be 1" wider than the CC for easy fitment...
For the air inlets to the FB, I would put ~20 sq. in. of opening directly across from the FB/CC opening ...
I would put ~80-90 sq. in. about 4-5" above the floor of the FB and have the wood grate about 6-7" above the floor of the FB....