Offset Flywheel

[Brian Rupnow]

Conventional wisdom has it, that engine flywheels belong on the end of the crankshaft. I don't have any problem with that, and have built a number of engines exactly that way. I have an idea in my head for a new, rather strange i.c. engine to build, and it will be air cooled. I don't want to install a separate belt driven fan. It would suit my purpose extremely well, If I had a 2" diameter spur gear on the end of the crankshaft, meshing with a second 2" spur gear which was attached to the face of a flywheel running on a dummy shaft with ball bearings. This would put the flywheel in line with the cylinder. Instead of conventional spokes in the flywheel, I would use flatbar spokes set at a 45 degree angle, thus creating a powerful little "fan" to blow air over the cylinder. I don't see any reason that it wouldn't work, but I have never seen an engine arranged that way either. I believe the spur gears would have to be made from some relatively strong, tough steel, perhaps 4140, or even purchased hardened steel gears. Has anyone ever seen an engine set up like this?---Brian

 

[dnalot]

If the fan were to be on the top and rather large in diameter you would be describing a helicopter drive train. So long as the drive for the flywheel is robust there should be no problem. The flywheel would provide the momentum to run smoothly but I would wonder about the loss of the balancing effect to the crankshaft.

Mark T

 

[Longboy]

Model engines ( to a certain # of cylinders I'm sure) tend to have flywheels that are heavier than the crankshaft itself. Making the flywheel a 1:1 driven object instead of part of the drive of the crank by direct attachment doesn't sound right. It would be interesting to have someone with a math & physics backround answer......Per Brians description, is a remote flywheel as effective as a crank centerline mounted one?

 

[Scott_M]

Hi Brian
Not sure about IC engines or if you mean mounted 90 degrees from the crank centerline but, my air compressor has about a 16" pulley on the pumps crankshaft and its spokes are fan blades and blows air over the intercooler and cooling fins on the pump. It is pretty much "an engine" and it seems to work well in that application.

Mine looks like the image on the left, my intercooler is between the pulley and pump, not around it.

Scott

 

[Brian Rupnow]

I have decided not to go with this idea. The engine which this would have been potentially fitted to is going to be a hit and miss engine. Experience has shown me that model hit and miss engines simply don't run as well as I like them to when there are too many moving parts. The less parts that have to be spun either directly or indirectly, the longer the engine will run between "firing" cycles. Also, with a hit and miss style engine, there is a constant acceleration/deceleration cycle that is not a good thing with gear drives. I THINK at this point, I will just design with a larger diameter flywheel and build the "vanes" into the flywheel, which will be mounted on the crankshaft. Jason--Interestingly enough, I grew up in the era of gasoline engine powered washing machines (no hydro-electric in the part of Ontario I grew up in at the time), however all the engines I seen were either Briggs and Stratton or Iron Horse. I never seen a Maytag engine.---Brian

 

[nemoc]

Brian, I like the idea, but agree with your analysis. I don't think it would work well on a hit & miss engine. I had the idea of gearing a flywheel on a stirling engine so I could have 2 counter rotating flywheels. Maybe in the future. Any way, I was wondering why you think there is a need for additional cooling on a hit & miss engine? Many I have seen running on display with a water jacket are run dry because they never really get hot.

 

[Brian Rupnow]

Nemoc--You are right. However--I have built quite a few water cooled hit and miss engines, and after half an hours running in a cool shop, you can visibly see steam rising from the water tank. An air cooled hit and miss probably doesn't need a fan, but it adds a bit of fun to the build.---Brian

 

[Jasonb]

I feel one reason we can get away without filling the hopper with water is that most engines you see running are just for display and not powering something else. As soon as you put a load onto a hit and miss engine you will get more hits and less misses so its firing more often and generating more heat.

As for seeing a bit of steam rise out of the hopper it really only gets to a certain temperature and then stays constant which is still relatively low, if it starts to boil you have got problems.