Stirlingengineforum.com

I have recently constructed my first engine and am 'hooked'. But I was wondering if I have the right size/weight flywheel. How do you determine the size? Thanks for your help.

Hi Donnie,

The answer is that it depends on your engine. More specifically, what its power output is and its intended use. Most "hobby" sized engines are going to have a flywheel under 6 inches in diameter and less than a pound in mass.

BUT, this varies significantly from case to case. One thing I can tell you is that there are two basic functions for flywheels which require different designs. The flywheel is there to smooth out the motion of the reciprocating parts of the engine and get it "over the hump". Its also there as a storage device of kinetic energy or momentum.

Depending upon your intended use, you can vary where the majority of the wheel's mass is placed. Wheels with most of their mass at the outside rim will generally store more kinetic energy but at a slower revolutions. Wheels with more evenly spread mass will spin more quickly (higher rpms) but are more easily stalled.

Hope this helps!

-Stefan

Thanks, Stefan. Just what I needed.

Donnie

Hi Donnie,

Stefan is exactly correct. Donnie built the tin can engine I believe. As for the flywheels on the tin can engine….

Heavier the flywheel the slower it will turn.

Lighter the flywheel the faster it turns (sound right! LOL )

The flywheel on the tin can engine was selected because:

If you go heavier, the flywheel will drag because of friction (if you are using the designs and not altered) . The engine will suffer from this drag and you will lose power or the ability to do work. Add a better bearing and you can go to a heavier flywheel and do more “work”. Too heavy and the engine will not be able to keep the flywheel turning. :-(

If you go to a lighter flywheel you will pick up rpm’s on the engine but you will not be able to do as much work and the engine will stall more often. If the tin can engine goes too fast (lighter flywheel) it becomes inefficient. The cycles become too quick and the air really doesn’t have time to completely heat to its max or cool down. So you loose some of its potential. The tin can design is not extremely efficient exchanging heat.

Better bearings and a heavier flywheel is a better way to go. It slows down the engine and gives more time for the cycles to complete and allows more “potential work” because of the stored energy in the heavier flywheel.

Remember this is a demonstration engine. It really was not designed to “do work”. The plans at http://boydhouse.com/stirling/ were designed to be as easy to build as possible, not efficiency. There are dozens of ways to improve this engine and learn.

Have fun! \:D/

Darryl Boyd

I was doing a bit of surfing on the web and found a great place to get cast flywheels http://www.pmresearchinc.com/store/cust ... php?cat=34 I think they would be easy to dress up with just a drill press. Most of you would rather make your own and I am one of them but for the right engine, they would make things much easier. I use 1/8 inch sheet aluminum cut with a jig saw about 5 and a half inches diameter then center drilled and with a nut and bolt attached, I spin them in my drill press and true them with a file. I suggest cutting them close though, it's a bit tricky to get them real round otherwise. You can then add holes for looks or? Sand paper gives a nice finish too.

Using the info here, I decided to try a heavier fly wheel. So I glued 8 1 inch washers around the rim and the engine running at its best speed with a can of sterno, would get about 150 to 180 rpm. I have removed 2 of the washers, and now after warming up, it gets 250 rpm.

DonnieB

Whether the flywheel in question is a flat disc or a spoked heavy rim it is the "Moment of Inertia" that matters.

A thin flat disc has a low value and take the same amount of material and reform or reshape it to a spoked rim design and the Moment of Inertia increases dramatically!

stanhbaker

I found a great and cheap product to add weight or balance your flywheels. They are golf club weights, they are thin lead bars that have a thin glue tape on them, just peel and stick. Perfect for disk type flywheels. They even look okay. Check the golf or sports section for them.

Brilliant! Thanks Cartech.

-Stefan

Hi Cartech,

Thanks for the info. I have been looking on the internet for the weights but so far, all I get are the kind that screw on. Do you have a link where they can be found??

Thanks,
Donnie

The ones I got came from Wal-Mart in the sporting goods, golf stuff. It was my boss actually that found them and brought them to me. He knew what I was looking for, something thin and easy. He said they cost about a buck. A balance kit for a ceiling fan would work too but they are thicker and not as pretty. For that matter, you can use tape on wheel weights for car wheels but those are also thick and ugly. The golf weights are about as thick as a paper match stick and the glue tape layer is so thin, you can't see it. They also have a silver/gray outter coating, not just the lead exposed.

Thanks. That is a great idea. I will be checking out Wal-mart tomorrow. I have just about finished my second engine and am using large washers for counter balance, but this sounds much better.

thanks for the information,

Donnie

I needed to make the weights a little flatter, the glue side is a little convex from being "stamped" out. Take a piece of wood and cover it with a soft rag and tap them flat with a hammer on a flat surface. It won't take much. You will need the glue area nice and flat or they don't stick all that great. I also made sure I was at room tempeture or they fall off if you stick them on in a cold garage. They made my engine run smoother and start at a lower temp. May have cut the RPM's slightly though. Still worth doing if your using a disk.