Prop to wheel replacement for aero engine

[nfk]

Hi gents,
A few months ago i finished my boxer air engine.
It run well but i`m a bit scared of starting it again because of the big air screw it needs to run smoothly.
The current prop is a 20x9 and i found quite dangerous to run the engine on my crawled home shop.
I was thinking of turning a brass wheel to replace the prop and been able to show the engine to friends without make them to pee his pants
Which wheel size you think could fit? The engine is a opposed 2 of 14cc.
I`ve tried with a 55mm diameter brass wheel but i couldn`t make it pop more than a few times (seems small to me) and before going to buy some stock for it i rather ask here before scraping another small wheel

Thanks!
Norberto

 

[Swede]

I know what you are proposing is possible. Maybe someone with some engineering can suggest a replacement flywheel. The thing that scares me a bit is that while the flywheel has inertia and load, once it is up to speed, it's not doing much "work" and it might have the potential to overspeed a bit. I just am not sure, but no doubt someone here knows.

How about this... build (or buy) a little dynamo or generator for it? Use a belt and a set of sheaves for proper RPM, and attach the dynamo to a load, like a set of incandescent lights. That way, the engine is doing real work, and it'll add to the display as well.

 

[Maryak]

A couple of very very rough starting points.

15cc approximates 1hp

15lbs effective peripheral flywheel weight approximates 1hp.

Seems to me this could be a lot more dangerous than your propeller at model aircraft engine rpm, (engine breakup).

If is feasible, why not fit a propeller guard. ???

Hope this helps

Best Regards
Bob

 

[Kmot]

Look for a model boat flywheel for a CMB or OPS .90 nitro engine (15cc). Run your engine with a rich mixture to help keep the cylinder cool. You can also add a water jacket around the cylinder head, and use an electric pump to circulate cooling water. Do not try to reach peak rpm as you may overspeed the engine. But you can run it fairly fast enough to impress.

[ame]http://www.youtube.com/watch?v=IzSygqHvLPY[/ame]

 

[Jasonb]

As Swede says I would have thought that once the flywheel is upto speed it will not put any load on the engine unlike a prop, maybe go for a 4 blade prop which will be smaller dia or a fan type.

Can't see why you would want cooling on an air engine

 

[kherseth]

I Think you could use magnetic damping to prevent overspeed. Make a medium sized aluminium flywheel and mount a neodymium magnet close to it, by adjusting the distance between the magnet and flywheel you could effectively make a adjustable speedlimiter.

 

[Kmot]

Can't see why you would want cooling on an air engine

If it is going inside a closed boat hull, you would want water cooling. That is the purpose of my conversion.

 

[Jasonb]

Ah, when he said air engine I assumed it was not IC but infact its an aero engine

 

[nfk]

Thank you all for your comment, now i know there are plenty of options
I think my best choices are, in order of availability and practicality using own skills, the following:
A) Use a 4 blade prop. ( using a 4 blade means i can cut half the prop size? 2 blade 20' to 4 blade 10'?)
B) Build a prop guard. I`m not sure if its practical for a 20' prop, but for a 10' sounds good.
C) Flywheel + dynamo + fancy neon lights. (aka pimp my engine! trust me, i would do it!)

I got a D option for someday in the future.. build a plain for the engine and show it outside of my small shop...
I would also need to learn how to fly a model... but if i can build the engine for it i can do anything...right?

Thanks,
Norberto