FAQFAQ   SearchSearch   MemberlistMemberlist   UsergroupsUsergroups   RegisterRegister 
 ProfileProfile   Log in to check your private messagesLog in to check your private messages   Log inLog in 


30"x60" CC RF Build Questions

 
Post new topic   Reply to topic    The Smoke Ring Forum Index -> Tech-Talk
View previous topic :: View next topic  
Author Message
PitPartyQ



Joined: 21 Nov 2017
Posts: 3
Location: West Michigan

PostPosted: Thu Nov 23 17 3:44 am    Post subject: 30"x60" CC RF Build Questions Reply with quote

Hello all. I have been lurking around the forum for some time now trying to make sure i have my design points correct before i get too far into the build. At this point i am planning to build a trailer mounted RF Smoker with a warming box attached. The CC is coming from a 325 LP tank cut down to 30"x60" with a FB that is 26Hx24Wx24D. I have included the link below for the Feldon calc's. I have a few questions that i'm not easily finding answers to.

1. The calculator says i need a 17.47" Half Moon. I understand from reading around that it is recommended to increase that by 50% to 1.5x17.47 due to the reverse flow drag. so first part of the question is i know the volume in a cylinder doesn't increase linearly so i am unsure how to calculate that (Sorry it's been a long time since Geometry. The second part is if the "diameter" is what is given on the calc would i just go up to the point on the 30" tank from the bottom until i reach the 21" or so that that likely will come out to and that's the height for my RF plate? If so that's around 5.5"-6" up total. does that sound possible? Or am i truly needing half of a 21"ish diameter circle meaning it will be cut out 21" wide and 10.5" high? I tried to find a similar build to glean from but most were either larger diameter tanks or if they had a 30" it was full length which makes for larger calcs.

2. Related to the above question i am trying to layout grate heights. I've seen numerous posts with seemingly wide discrepancies on where that bottom grate should be in relation to the RF plate. I've seen everything from "You want it within 2-3 in max so you don't waste the radiant heat" to you need 8"-10" so you don't have flare ups. Like everyone else i would like to maximize the cook options in this unit. I cook mostly BB's and i would guess 6" of free space would be enough for those between racks (open to input). That said what i am hoping for is enough room for Butt's on the bottom rack and then 2 closer together racks above with maybe 4" of clearance for Ribs, Chicken & Sausage etc. that would allow me to remove the top rack to create another Butt capable rack as needed. so in a perfect world that would look like from the bottom of the tank 6" to RF plate, 6" to Bottom Grate, 6" to 2nd Grate and 4" to 3rd optional Grate.

3. looking at "Typical" round air intakes. the calculator shows Qty-2.29 5" intakes to achieve 44.93" of intake. that calculates out about right for a 5" hole but most of the vents i see only allow for 50% flow when wide open so wouldn't even qty-4 5" be slightly less than needed for actual SQ In. of inlet?

Sorry for the questions being in novel form I appreciate any input. These i suspect will create further questions


Feldon Calc's.

Link to BBQ Pit Calculator
Back to top
View user's profile Send private message
k.a.m.
BBQ Mega Star


Joined: 12 Dec 2007
Posts: 25981
Location: Southeast Texas.

PostPosted: Tue Nov 28 17 8:37 am    Post subject: Reply with quote

On your firebox to cooking chamber I would use a 18" wide x 9" tall half moon. This will allow for a 1.5" to 2" tall grease bridge.
I would also increase the exhaust to 6" ID x 30" tall.

I place my reverse flow plates at 4.5" below the top of the grate at the firebox end with a 1" fall to the opposite end.

You can put three grates in a 30" but the two top ones are pretty much useless except for ribs. I would aim for two lower and two uppers. Make your door cut 6" below 12:00 for the top cut and 1" below 3:00 for your lower cut.

When you say only 50% open on a 5" hole you must be referring to spinner intakes with 4 openings the calculator is figuring a 5" open hole. Personally I prefer rectangle horizontal slides if you choose these then you would need three at 7" tall x 2.5" wide.

Dont think I missed anything if I did I apologize just ask another question. Very Happy
_________________
Always remember slow and steady wins the race.

Hybrid Cooker
Back to top
View user's profile Send private message
PitPartyQ



Joined: 21 Nov 2017
Posts: 3
Location: West Michigan

PostPosted: Wed Nov 29 17 10:12 pm    Post subject: Reply with quote

K.A.M. thanks so much for the response and awesome input.
1. On the CC -> FB opening being the FB will be 24" wide would it be better to use the width of the CC tank to allow a wider but shorter opening allowing the grate heights to be lowered? I'm not sure if there is a downside to that. I have tried to muddle my way through the Trig Functions to calculate that sq. In. opening given the 30" tank and have not been able to. For instance if i measure a 21" opening its approx 6" tall from the bottom. I don't however know how to figure out the Sq. In in that as its not as simple as Pi r2 since the "Radius" in this case isn't half the Diameter. i can certainly just go with the 18x9 just wondering if i could widen and shorten that opening a bit in the planning stage here and gain some functionality. My best efforts at calculating it show that if i went 27 1/4" Wide by 9 1/8" that would yield approx. 180 Sq. In.
2. Awesome input on the RF plate thank you!!
3. Are the top 2 racks worthless except for ribs due to space constraints or is it too hot at the top?
4. Yes i was referring to rounds as that was an option i was looking at. It just seemed odd to me the calc suggested what amounts to only 50% of what you would really need if using spinners perhaps there is another type of round vent cover i'm not familiar with that allows full flow.
5. One added question if i could. i am planning a warming box on top of the FB (approx 24W 24Dx 30H). There will not be a FB -> WB opening just a CC -> WB Damper . any suggestions given the dimensions of this rig on smoke stack sizing and placement? given the recommendation to go 1.5x the size for FB -> CC and end of RF plate openings for RF cookers i am assuming a similar accommodation must be required for the chimney pipe outlet to carry that increased air volume. I'm figuring i will need to have a cap for the main chimney when using the WB? I'm understanding i can greatly reduce the Chimney height leaving the WB as it will act as a plenum as well. Sorry to abuse your generosity for info just don't want to build a large paperweight Smile.

Thanks again for all the input!
Back to top
View user's profile Send private message
k.a.m.
BBQ Mega Star


Joined: 12 Dec 2007
Posts: 25981
Location: Southeast Texas.

PostPosted: Thu Nov 30 17 1:04 am    Post subject: Reply with quote

You can use a trapezoid opening to shorten the hole. Pete Mazz has a great tool listed in the welding section.
http://planetcalc.com/5155/
_________________
Always remember slow and steady wins the race.

Hybrid Cooker
Back to top
View user's profile Send private message
k.a.m.
BBQ Mega Star


Joined: 12 Dec 2007
Posts: 25981
Location: Southeast Texas.

PostPosted: Thu Nov 30 17 1:10 am    Post subject: Reply with quote

Using a trapezoid with a 1.5" grease bridge your opening would be.
Top Length
24
Bottom Length
13.077
Height of cut-out
6.5
Throat area of cut-out.
120.50
_________________
Always remember slow and steady wins the race.

Hybrid Cooker
Back to top
View user's profile Send private message
Display posts from previous:   
Post new topic   Reply to topic    The Smoke Ring Forum Index -> Tech-Talk All times are GMT + 8 Hours
Page 1 of 1

 
Jump to:  
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum


Powered by phpBB © 2001, 2002 phpBB Group