Office of Steam Forum for Model & Toy Steam Gas & Hot Air Engines

Hello ,
 I am contemplating my first steam build, and have the first, of what I am sure will be many questions. The build I am thinking of will be to power a stern wheeler paddle boat. Something at least 4 foot range and radio controlled. My first thoughts are for a slow rpm engine. so I think that translates to low pressure and long stroke.
 I have researched some but have not found answers to some basic questions so I thought I might find some answers here.
  1st.   I see that a lot of the steamers use cast cylinders with a thick wall area . is there a need for them to be thick? I am thinking that it may help with heat loss and condensation issues but I am just guessing.
  2nd. When steam pressure is reached in the boiler, and then is transferred to the cylinders, and the input valve closes, does the pressure increase or spike [through expansion and because the crank is not yet at TDC.] above what was delivered or is the maximum steam pressure always at the boiler?
  3rd. Is there a formula to determine the size of the orifices in the valve body and pluming ,as it compares to the displacement of the cylinders? 
  4th. Any ideas on using the paddle wheel itself as the flywheel? [picture two flywheels with the paddles between them.]
 
 That is enough for now,
  Thanks in advance for any replies and advice. Hopefully I will be able to post some pictures of my progress as the build goes on.

Thank you  for the reply, I am now retired so I have some time to play with. While I do not own a milling machine as of yet, my shop includes a 13 inch Sheldon lathe, a drill press, a bed sander, a MIG welder, a oxy-acetylene outfit, a band saw , lots of hand tools and so forth. [Because as we all know,, he who dies with the most tools wins] . My trade as a millwright put me in quite a few electrical power generation stations. Most of which ran on steam. They however, are turbines and most being in the 60 ton range, so not to much in small stuff.
 As for my experience with models , I have 12 or so scratch built RC airplanes. All built from purchased plans . war birds, trainers, biplanes, low wing and high. Only one model boat so far, that being a 40 inch  RC sailboat with electric assist .it was scratch built from  red cedar and ply, but without plans. This build  hinge on the power plant. After it is built [at least on paper] I should have a better idea on the size of the boiler needed . That, in turn, should tell me the size of the hull and what it will build it from. 
 I am posting here because I do not wish to "reinvent the wheel" I had thoughts of using pneumatic cylinders for the power but I think perhaps that is not a good idea. I tested them and they appear able to withstand the heat and pressures that I am expecting, but again the temperature difference I think might cause problems of excess condensation inside the cylinders. That is the basis for my 1st question on my original post.
 The second question originates  because I am assuming that the pressure that is shown on the boiler is the highest in the system. it seems to me that as the steam travels its path from the boiler, through the engine it should do nothing but decrease. but I am not 100% positive on this. What I have read so far makes me believe that the inlet valving closes just before TDC on the crank, so there should be some compression going on there. How much? HMMMM.
 The third has to do with straight mechanics. How big do the inlet and exhaust ports [and plumbing] have to be for a given displacement
 The final question is just out of curiosity, I have looked at quite a few pictures of stern wheelers trying to prepare for this build. I have not seen one with the paddle wheel being used as the flywheel. I think this my be because in full sized stern wheelers , the paddles were chain driven . Most likely  from a reversible gearbox and a higher RPM motor.

Thanks for the information . But this raises another thought. If the steam is expanding as it cools, then it stands to reason that you would want to cool it as much as possible while in the cylinder. That would mean that thinner walled cylinders might be advantageous.

  This whole question comes to mind because I have on hand several double acting pneumatic cylinders that I thought of using for this build. the walls of the cylinders are about 1/8th of a inch thick. They are rated at 250 psi of air pressure. I have submerged them in a heated oil bath at 300 degrees with no apparent lost of integrity .
  I was thinking that steam pressure of less than 50 psi should make them produce. that would keep the temperature down to approximately 250 degrees or less. The available long stroke of 8 inches and bore of 1-1/4 should allow me to make the rpm output rather slow .
   I might have issues with the flywheel / paddlewheel setup not having enough inertia to carry the crank through its cycle However with the paddles in the water and the boat in motion the water hitting the paddles might help.
 So for now the question still stands.
 Does the walls of the cylinders need to be thick to hold the heat, and aid in limiting condensation inside of the cylinders? or are they that thick just for appearance . or maybe some other reason ?

Regarding the cylinders and heat...

  If you take a look around you will find that many 'Model' engines
have cylinders that are clad with an insulating material, in most
cases wood.  I've read that doing so increases the efficiency of
the engine.  I've also read that steam condensing in the cylinder,
which can often happen when steaming a cold engine, could cause a
hydraulic lock problem to occur.  So, a warm cylinder is a friendly
cylinder, so it seems.

  Maybe, you should start with simple steam engines, quick and easy
projects for someone who knows their way around a machine shop.
Try 'Making Simple Steam Engines' by Stan Bray as a reference.  It
covers simple engines and boilers.

Good Luck,
Wayne

I would definitely go with a proven design for your engine.
There are plenty available as casting kits and from drawings you build from bar and round stock.
They are a lot work either way and when well finished, your reward is a great looking fully functional piece of hardware.

Regarding steam expansion, more heat is your friend.
Cooling a charged steam cylinder will be the death of your power. The faster it cools, the quicker the stored energy is vanquished.

Temperature drop is not what makes the pressure drop. It is the pressure drop that makes the temperature drop.
Steam can exist at 212 degrees F but only at atmospheric pressure. For example, steam at 120 psi is 354 F.
You can find charts showing steam pressures with the corresponding temperature.

We are looking forward to following your build so please keep us updated.
Best of luck with your ambitious project.

Gil

I know the feeling of I built it myself snd adding I tidied the design too .  I’m very new to this fascinating hobby too . There are not many steamers near me just the hot rod racer guys. There is so much to learn about . I did purchase a paperback book that covers a lot of early steam developement that was informative but I think mormodern approach is the basic automotive things regarding engines is important to understand. Valve timing and how ignition timing affects cylinder pressure thus ultimate torque then calculated horse power . For model steamers in Rc boats I’d guess you need to decide what you want. An African queen river boat chugged or a smoking battle ship under full power. Maybe a harbor tug.  Each will need their own features I just ordered two turbines and maybe a third the issue with these is they spin really fast so are going to need precision gear boxes just as the battle ships. The big problem is the tiny shaft size. Of course metric then between any common frill size so couplers will need to be custom made they rotate so fast that the slightest imbalance will be disastrous. I haven’t seen many steamer in real life except at farm shows  but seeing a great big steam tractor with 50+feet of flat belt between centers running a complete saw mill was pretty impressive . So I think maybe scalping up an existing engine might be the way to go. This book I got covers many different valve designs so I think valuable in the knowledge part is good it readily available on Amazon   Just remember how thing s so from Rc model building some things don’t scale well physical size works but function , not always I just saw a new jet bot trial. It drives props and provides thrust .but it’s in a class I can’t even afford to take pictures of .

So you have some decisions to make.

Byron