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

[cheepo45]

Sounds like an interesting idea, Brian.
I would be a little concerned about the gear lash causing some odd noises and wear because of the uneven nature of an I.C. engine.
Maybe some sort of anti-backlash gear would work?
cheepo45

[mklotz]

Wouldn't a pulley/belt system driving a lightweight fan do the job and eliminate unnecessarily stressed gears?  Or are you going for maximum visual complexity?

[Jasonb]

Or a short stroke and conrod combined with a large dia flywheel so the cylinder is behind the flywheels aero spokes, bit like a maytag.

The gears may get a bit clanky if you go for hit & miss but throttle governed should be a bit smoother

[Brian Rupnow]

Jason---the "clanky" bit is what concerns me.--It will be a hit and miss. Marv--I have two engines now with a belt driven fan, and was trying to avoid that. Visual complexity is fine, but not if it results in an ill running (or sounding) engine.---Brian

[MMan]

Perhaps not quite what you were asking but my mind went to the Boulton and Watt in the Sydney Powerhouse museum (http://commons.wikimedia.org/wiki/File:Boulton_%26_Watt_steam_engine,_Sydney_Powerhouse_Museum,_2014_(15860996071).jpg).

It turns a reciprocating motion into 2 times revs of the flywheel using two spur gears. You could put a crank on the end of your crankshaft to get reciprocation and then use the double gear mechanism to get a faster fan (more blow) and more energy stored in the flywheel for a more chilled hit and miss.

Mman.

[Jasonb]

This is what I had in mind



Another option is instead of using two 2" gears make use of the timing gears which could be larger dia than usual to get the required spacing and have the fan/flywheel on the larger of the two. Still not a constant load on te gears as it hits and misses but two less gears.

[Admiral_dk]

Regarding the noise - a toothed belt could do the trick.

If you gear the flywheel down, you'll have to increase it's size in order to get the same inertia / energy stored.

I think the idea of a nice fan as spokes with a solid rim outside should work and look nice.

If you don't like a belt - consider two gears on the same axel, with one fixed and the other with a spring to "push" against the opposing gear wheel - this has been used in high speed four-stroke racing engines as a solution to gear-driven camshafts.

Looking forward to see your next project 

[mklotz]

Keep the flyfan on the crankshaft and use a drain trap to direct the air to the cylinder. 

[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

[sshire]

Maytag engine. Maytag washing machine. Sounds correct..

[Jasonb]

If you fancy adding a bit of interest what about the angled fins like a single cylinder Maytag which would allow a longer stroke/conrod or smaller flywheel. Like the gas tank too.

[steve-de24]

Brian,
A model aircraft engine uses the propeller as the flywheel and the airflow from the prop cools the cylinder. Some include gears to reduce the RPM to allow a bigger prop to be used. Take a look at:-

   images.rcuniverse.com/forum/upfiles/445518/Ge95832.pdf 

Pictures at the end of the article, I'm sure a trawl of the net would produce other makes of engine and more pics.

Regards,
Steve

[Admiral_dk]

Another option would be either a fan at the centre of the flywheel on the crank moving air via a deflector towards the cylinder or a centrifugal blower on the side of the flywheel a la an old Puch MS moped - again with a deflector.