Re: Propeller dynamics

gcb Sun Sep 18, 2011 9:35 pm

SuperDave wrote:In the OLDEN days there was no such thing as a prop balancer. We flew props that came directly from the source unbalanced. I'd only be concerned if there were excessive vibration...

SD

More ramblings - Of course OLDEN depends on your age...for me it was the mid nineteen fifties.

My first prop balancer was two single edge razor blades imbedded in a chunk of balsa and leveled before use. Prop was on a piece of piano wire. For some reason, I still have that balancer, plus a few others.

In those days, wooden props were often a bit off due to manufacturing or finishing. Sometimes you could sand ff some excess varnish...or add some to the light blade...or both. I have seen guys clip off the tip with a pair of dykes.

As Mark mentioned, it was not unusual to move a prop on the crankshaft, usually heavy blade opposite the piston position (heavy blade up, piston down).

So far, we only discussed weight balance. For those heavily into competition, you might want to consider dynamic balance also.

George

fred Sun Sep 18, 2011 10:09 pm

Interesting Forum here guys.
IMO a Cox Black 5 x3 is the prop for a TD. It flattens at hi rpm .. nicely, ergo a variable pitch prop :-)
Plus it's durable, unlike a COX grey.. or an APC, which is a decent prop if you get the right one.
Also be careful with rpms as imo no TD 049/051 will survive beyond an actual 27k rpms... the crank WILL snap and g'luck getting a replacement.

Mark Boesen Sun Sep 18, 2011 11:00 pm

Years ago when I raced 1/2a R/C Pylon, the hot set-up was a plastic Master Airscrew 5.5"x 4" or a 4.5" pitch cut down to about 4-1/2" or 4-5/8" with a nice tapered scimitar tip...unfortunately at the high RPM's the TD's ball/socket joint would often fail, more so it seemed then the crank, even with a well lapped engine.

Somewhere in my pile (collection) I have a nice never mounted wood Top Flite Power Prop 4.5"x7" ...I wonder what a hot Tee Dee would turn it?

Mark

nitroairplane Mon Sep 19, 2011 1:51 am

SuperDave wrote:In the OLDEN days there was no such thing as a prop balancer. We flew props that came directly from the source unbalanced. I'd only be concerned if there were excessive vibration then I'd use the one that I have been GIVEN me by one of also-aging friends leaving the hobby for the nursing home.

Ditto a laser incidence meter, digital tach, Hobbico DeLuxe Flight Box, 12V starter motor and more. My only guilt is that my friends aren't flying any more.

SD

I have never bought a prop balancer either I made mine ages and it still works,
Two rasor blades and some piano wire.
Buta ibreally don't balance props much I don't see the need because I don't fly competitions.

nitroairplane Mon Sep 19, 2011 1:54 am

gcb wrote:
SuperDave wrote:In the OLDEN days there was no such thing as a prop balancer. We flew props that came directly from the source unbalanced. I'd only be concerned if there were excessive vibration...

SD

More ramblings - Of course OLDEN depends on your age...for me it was the mid nineteen fifties.

My first prop balancer was two single edge razor blades imbedded in a chunk of balsa and leveled before use. Prop was on a piece of piano wire. For some reason, I still have that balancer, plus a few others.

In those days, wooden props were often a bit off due to manufacturing or finishing. Sometimes you could sand ff some excess varnish...or add some to the light blade...or both. I have seen guys clip off the tip with a pair of dykes.

As Mark mentioned, it was not unusual to move a prop on the crankshaft, usually heavy blade opposite the piston position (heavy blade up, piston down).

So far, we only discussed weight balance. For those heavily into competition, you might want to consider dynamic balance also.

George

Oops just read this after posted the same thing.

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