School me on propellers

[kvom]

As I get closer to the completion of the Halo radial, it seems "natural" that it should drive a propeller eventually. The question of what size to shoot for becomes important as I need to design and make a mount that's high enough to clear the prop when the engine is running.

In watching videos of other radial models, it seems as if a propeller that's twice the diameter of the engine looks "right". The total diameter of the Halo will be around 4". Does an 8" prop seem reasonable?

The end of the steel crankshaft is 3/16" in diameter, so the prop needs to be attached here. I'm iugnorant about how model propellers are attached. Obviously a fast turning propeller is a lot more dangerous than a steam engine model flywheel, so a safe attachment will be critical.

Any advice will be appreciated.

 

[gbritnell]

You're right about the safety aspect. The fellows who runs gas radials generally have a safety loop around them or the engines are run where the spectators can't get in line with the prop. Another option is to stub the prop off. It still looks like a prop but is a little bit safer to spin.
gbritnell

 

[kf2qd]

For a Propeller just go to your local Hobby Shop and look for and Gas Model Airplane Prop. Good to around 20,000 RPM.

3/16 shaft might need a bushing, an 8" prop with be either 3/16 or 1/4.

Most model props are held on with a single nut and no safety wire or anything else to cause balance problems.

Just Remember - When it is spinning it almost seems to disapeer and if you aren't careful you will be the one sticking you finger in it.

The first number on a prop is teh diameter, and the second is the pitch (or how fast it wants to move the air)

 

[ozzie46]

Get A wood prop and balance it. All props need balanced. Then paint at least the outer 3/4 inch ends of the prop white or yellow. The color will still be visible when spinning. It will create a circle of color when spinning. The painting is used on full scale props as well to keep ground crew from walking into the spinning prop. Would ruin your whole day.

The reason I say get a wood one is that the molded nylon/fiberglass props have flashing on them that is as bad as a razor blade and will cut you quick. For this reason wood ones are safer (IMHO) if you are not used to working with props.
Ron

 

[shred]

Unless you plan to fly anywhere, I'd put a restrictor in the airline so it can't turn the prop very fast without a lot of intervention... A friend built a radial and it looks cool just ticking over. You can still get whacked good, but less likely for permanent injury.

 

[bentprop]

Ozzie,the frp props should ALWAYS be deburred before use.Just use sandpaper to dull the edges .I also round the tip away from the running direction,this is supposed to make them more efficient.
I'm with Shred,it would look much nicer if you can"count the blades".It could also save embarassment ,with too much power your engine could tear of the display table :big:

 

[ozzie46]

Ozzie,the frp props should ALWAYS be deburred before use.Just use sandpaper to dull the edges .I also round the tip away from the running direction,this is supposed to make them more efficient.
I'm with Shred,it would look much nicer if you can"count the blades".It could also save embarassment ,with too much power your engine could tear of the display table :big:

Yes, I know I fly Rc planes too. I mentioned the flash problem for anyone not familiar with these kind of props. I have deburred them for years. Anyone not used to them might not know this, so good advise.

On another note I think(IMHO) that a wood prop would look much better than a composite one.


Ron

 

[cfellows]

These make very nice props for display and slow runner model engines. I've bought three of them on ebay over the years and they appear there quite regularly. They are made out of chrome plated metal, probably zinc alloy. They are pretty heavy and also behave as a good flywheel. I believe it could be bored out to 3/16" easily.

http://cgi.ebay.com/HAMILTON-STANDARD-STEEL-PROPELLER-LETTER-OPENER_W0QQitemZ380173136571QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item588415b2bb

Chuck