Cook Chamber to Fire box half moon calculation

[Bombtech]

Hey folks,
The Feldon numbers confused me for the formula to half moon cut a CC/FB opening on my RF project. I recently looked at a circle calculator link commonly shared on BBQ sites often shared along with the feldon link. I did not care for it.

I figured the math using these calculators from a few sites. I found it simpler than the chord/height variables on the commonly shared calculator site.

I figured I would put them up here and share my numbers for anyone who cares to review and give me some feedback on practical use on previous builds.


http://www.feldoncentral.com/bbqcalculator.html
http://www.mathopenref.com/segmentarea.html
http://planetcalc.com/1421/

My numbers are (roughly):
24" ID Cook Chamber of 120 gallons total = 22,720 CI Volume
FB 22' square box = 10,640 CI Volume
SO....
Half moon cut is figured for a 12' Radius, 6" height, 20.7" chord = 88.4" area. The 88 is higher than the Feldon recommended 85.

DOES THIS SOUND EFFICIENT ENOUGH? FELDON IS SAYING A 14 INCH DIAMETER HALF MOON, WHICH MAKES NO SENSE TO ME.... I feel like I am splitting hairs here, but you only build it once.

 

[Smokin J's PIts]

What I do is I measure 4" down from the center of the pipe, and measure straight across, in this instance its 22-5/8", I would then round up to 23 just to keep it simple. This is also the same calculation I use for RF, the baffle would be 23" and for the opposite end I divide the pipe size by 4, and that gives me the distance I need from the end of my RF plate to the end cap. I hope this makes since.

 

[Bombtech]

Smokin J,
See that's what I was looking for. 4" down, as a rule, would seem to work on a 24 ID, but on a smaller or much larger tank it would seem wrong if you considered the ratio we are shooting for. Sort of a sliding scale kinda thing. But...you build these things and you cook on them. I am a rookie trying to remember trig class in HS. I got hung up on the math and forgot practicality... I'm just welding up a big old BBQ smoker, not building a spaceship. Your number (23") and my number (21") are close enough for me to fire up the Lincoln Cut 55 and split the dif. I can't wait to get this project off the ground. Thanks for the response.