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Planning A Medium Size RF

post #1 of 7
Thread Starter 

Please forgive me, my math skills are poor when it comes to formulas. If someone could either tell me the sq in's or even tell me the formula so I can calculate it out I would appreciate the help.


Here is the calculator so I don't have to retype the info. And then a pic of the damper I would like to have on the intake for the fire box. Half guess, half math I think I am close.


One other question that probably makes a big difference is when I mount the fire box to the cook chamber, I would like to mount it as low as possible. How do I figure the area for a tear-drop shape. I will be using flat plate for my ends so the fire box will just sit flush to the cook chamber and not actually enter the chamber like seen on a propane tank.


spread sheet calculator.jpg


And here is what I would like for a damper.


Fire box damper 1.jpg


I know this is asking alot, so if someone could at least point me in the right direction I would appreciate it greatly.

post #2 of 7

Tom...did you ever get this figured out?  *bumping* for the math whizzes just in case.  

post #3 of 7
Thread Starter 

No Abi I have not. With any luck at all I will get a good go at it this weekend.



post #4 of 7

The full opening of the 7 1/2" diameter circle is 44.2 square inches.

The portion covered in the center by the 1/2" diameter piece is about 0.2 square inches.


So the available portion of the opening would be about 44 square inches.  The baffle plate appears to cover about half of this, leaving a maximum opening area of 22 square inches.

Area = \pi r^2.\,

(I think the Radius measurements you give are actually diameters...)


post #5 of 7
Thread Starter 

Thank You roklimo,


I greatly appreciate the help. Yes you are correct on the radius/dia issue. Sorry about that. Based on approx 22 square inch's I should have roughly twice the air intake that the calculator shows.


This is one of those things that I did not have the ability to do, and that makes me want to do it even more. And to understand how and why the math works.

Thanks again


post #6 of 7
Thread Starter 

Guys I am almost ashamed to admit this but, If it helps someone else down the road then its all good.


I sat here with my 14 year old, for a couple hours. We made a drawing in sketch up and then dimensioned it and started working on the math for a sector.


WOW, the little smarty pants says Dad its just algebra!!!!!!  And I had to remind him that class was almost 24 years ago. Anyways the little turn was just writing away while tellin me to change this line and add this and so on.


Well after a little mishap with sketch up and doing a google search we found this freaking thing.


This is for the fire box to cook chamber. Right now we are at a segment height of 2 and a radius of 9 with a segment area of 15.4 X 2  and I need 28.5. I am thinking this is close enough.


http://www.1728.com/circsect.htm  This will calculate any part of a circle into area.


If you study this page for just a sec or two its a piece of cake. We used the calc for radius and segment height to verify his calculations. Man, he was right on.


Let me tell ya all something, I had to work my tail off in school to get d's and c's. I can't even begin to tell ya how proud it makes me to know he is on the presidents honors list for this year and I believe the lowest grade he has received in the last four years has been a B+.


Maybe I have retarded ideas but it made me feel pretty darn good for him to sit down here with me and rattle off and crunch numbers like he did.

Edited by Tom37 - 6/5/10 at 4:22am
post #7 of 7

hey Tom, i just now seen this thread. man that is an awesome link! i have always just guessed, this will make this a lot easier for me! thanks for the info,


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