Beginning thoughts of my RF Trailer build

Discussion in 'Reverse Flow' started by fobar22, Apr 22, 2011.

  1. fobar22

    fobar22 Newbie

    By no means will I be completing this project anytime soon, but I stumbled across a 250 gal tank, and I have been wanting to upgrade from my small 6 month old SFB. I have had a lot of successful cooks on it, but it requires constant monitoring and a lot of charcoal to cook through the night. I'm guessing because of the thin metal its built from. And I always seem to run out of usable cooking area!

    I took this picture after smoking 3lb of hamburger for some chili I made the other day.


    The other day I was kicking around ideas for a biodiesel processor I'm going to try to build, and while of craigslist looking for parts I came across this bad boy.


    I got it for $100, so until I start construction the thing is going to sit right on my trailer. Hopefully I can now stumble across a decent trailer that I can use! Sadly I will be moving soon though, and while my truck can pull with no problems, I don't think I want to get into pulling two trailers so I think I will hold off on looking for a trailer until I get to Tennessee.

    I'll continue with another post of where I stand in the design, just have to type it up.

    Oh I asked the owner of the Ford Raptor in the background if he wanted to trade trucks... I love seeing those things driving around town. He said no, which I was happy to hear, I love my truck too much.
  2. fobar22

    fobar22 Newbie

    Ok, so I am thinking first the basic design will be a 24x24x24 firebox mounted at the back end of the trailer feeding into the tank, there will be the fat drip pan stretching the length of the smoker slanted toward the front of the trailer slightly, this making the RF portion of the smoker. I like the idea of using angle iron to direct the fat into a pipe leading out the bottom of the tank a lot, so I plan on doing that. I want to have one big door, right now I'm thinking about 72" long and having it wrap just about a quarter of circumference of the tank. Right now I am thinking a single 6" diameter exhaust pipe pulling the smoke from the center-line of the tank.

    Now past the basics I have a few ideas I have been kicking around and I am going to try them out individually on my small SFB if possible. I will list them and then talk about them each on their own.

    -pre-heating the incoming air

    -pulling fans under the drip pan

    -mechanically monitoring a water pan

    -optional hanger for adding upper cooking racks

    -convection oven style fans in the cooking chamber

    -electronic monitoring the conditions in the smoker

    -insulating everything!

    I have a background in mechanical engineering, and everything is about efficiency, so why not preheat the air before hitting the fire. The only thing that worries me is the air getting too hot, but I imagine I could just have a smaller fire once the smoker is going. I'm thinking right now to have the inlet be on the bottom side of the firebox, then I will route the air to travel up to the top, across the top, then pass back under itself towards the rear of the trailer again, and then back down to the bottom of the firebox chamber before it is exposed to the fire (if your looking at the side it will go up 24", left 24", down 2", right 22", down 22", and then into the fire itself). Basically rather than building a warmer box, I will use the radiating heat from the fire to pre-heat the air.

    I am thinking about pulling fans under the drip tray to help move air if I only need a small fire because of the pre-heating. I am working on a homebrew electronics thing that will control the speed of the fans, more below...

    I like the idea of a water pan in my smoker, but rather than having a big one that will last a long time, or opening the smoker to refill it, I have a plan to mechanically monitor the water level, kind of like a toilet bowl. I will have a large external water reservoir that is connected by copper tubing to a tub in the bottom of the smoker. Using a cork and float the water level will be maintained at a certain level as the water constantly boils/evaporates off. My first experiment has been successful so far, but I need to make sure my cork and float will be safe at the temperatures they are going to see.

    The main cooking surface is going to be two wide trays, but I want to be able to have upper trays as well, without limiting putting something across the main trays, say a whole pig. I want to make a hanger that I can take in and out that will support the center parts of the upper trays.

    I have been searching and I have yet to find any definitive bottom line about convection fans in the cooking chamber, I can see nothing but benefits as long as we are cooking with moist indirect heat. I am thinking about having four fans along the length of the smoker, each pointed against and pushing the air into the wall. None of them will blow directly on the food, or towards the inlet or exhaust. I have been looking for a motor that I can mount out of the heat, and then maybe connecting the fans all to that one motor (fan belt of some sort?). Not sure, but I may have to get one for each fan to limit the number of things moving in the cooking chamber. This is probably the least on my priority list, but one I see as being beneficial.

    I would call myself a hobby electronics kind of guy, though I have yet to get anything more that a blinking light of a fan of changing speed, I am still learning. And this is the cheapest thing to work on right now until I gather all of the big parts. I want to have a few temperature sensors through out the smoker to monitor the temperatures in the cooking chamber and the current temperature of multiple temp probes in the food. Then I want the little gadget to control the speed of the pulling fans, as the cooking chamber cools, the fans speed up pulling more air into the smoker, or slow down if its getting warm. Also I want it to control the air inlet dial, I'm thinking a servo fits this task perfectly. Then, this is the big lofty goal, I want the little gizmo to update me on the conditions of the smoker on my phone... I have some work to do on that one... If I get that working, I should also be able to change the desired cooking temperature from my phone as well.

    Basically, if the smoker is cooling off, the fans speed up, if it is getting too hot it closes the air inlet, otherwise they find a happy medium and keep the temperature steady through out the cook.

    For my current smoker I am using red bricks to act as an insulator but I may look into fire bricks for the fire box, or I might use sand. But in the tank I think I am going to do something like BBQ Engineer and use superwool to line the inside of it. Then I would have to add a skin of metal over the insulation, but it could be something pretty light I'm thinking.

    Wow, that is a lot of stuff. I am still kicking around ideas and testing them out, probably a few months from any real construction of my RF, but I would like some criticism of my ideas and help improving the design. I am trying to build a 3D model of this in AutoCad Inventor, but I haven't use the program yet so it may take some time.

    Thanks for making it to the end of the post!

  3. 2bears

    2bears Smoke Blower

    I don't think you will need any liner/insulator for that LP tank. It will be plenty thick enough to retain the heat for you.
  4. daveomak

    daveomak Smoking Guru OTBS Member SMF Premier Member

    Morning, There are many successful builds on this site. Searching their builds and avoiding pitfalls made in the past should save you some headaches. Looks like you are on the right track. I do not have a reverse flow.

    This attached build got some really good reviews as to consistency and efficiency. 

    I enjoy reading about others builds and will be following yours also.

    Hope the move to Tennessee goes well.
  5. fobar22

    fobar22 Newbie

    I agree and know from others successes that no insulation of the LP tank would be perfectly fine, but since I'm still at the concept level on this smoker I am looking at all ideas and weighing the long term benefits, in both  cost and handiness throughout the smokers life.

    Using a very simple heat transfer model and material property values I pulled from various sources, I found that insulating the tank with 1" of Superwool insulation could reduce the wood needed for a 20 hour cook session on the order of 50 lbs. (some assumptions I made, cooking temp 250F, outside temp worst cast 32F, there were a few others but I will save all of the details) I can organize my stuff to make it presentable if anyone is curious in my math.

    Considering that I have heard of getting half a cord of wood (~2000lbs of hickory?) is less than $100, and the cost of time, labor, and materials to insulate the tank would probably cost on the order of a few hundred dollars (a few cords of hickory) I can live with building a bigger wood bin, and skip the insulation on the tank itself.

    Maybe if I want to cook in the winter I could get some wool blankets from an Army surplus and build the tank a jacket! I will still be looking to insulate the firebox, and invest my efforts on sealing the doors.

    Still working on the 3D model, maybe I can get a picture of my progress up sometime tomorrow.
  6. tom37

    tom37 Master of the Pit OTBS Member SMF Premier Member


    I'm thinkin this is gonna be an awesome build.
  7. sunman76

    sunman76 Master of the Pit

    +1 sounds awsome can't wait

Share This Page