The "counter-rotating" prop I saw in a video had the second prop just free wheeling.. It certainly looked cool, and seemed practical, but I don't remember it being overly noisy.
However, how about the efficiency of such props, free wheeling or driven? I know we tend to not be terribly concerned with propellor efficiency in CL Stunt (exception for electrics, right). But it seems like a lot of energy would be lost just correcting the airstream.
Of course, with a driven version, you have the gears associated with the reverse drive, which means mechanical loss of efficiency not even considering the aerodynamics of the system.
Interesting thread.
L.
"Sometimes you get shown the light in the strangest of places if you look at it right." -Jerry Garcia
Hi Larry
Your not correct about the contra system freewheeling, It was a fluid drive system, the same system that runs your car , automatic transmissions in Cars are not direct coupled, they are driven by fluid , air for all intents and purposes in this use is a fluid
It does ,and will drive props, the prop went from 0 RPMs to about 10,000 RPMs in a matter of about 1.5 seconds, If you think it is just freewheeling and not driven ,stick your finger in the "freewheeling blade" only, It will take a good chunk of it off.
I have held the blade (on the bench)still while the engine was running and there is a hard force trying to drive that rear blade, as soon as you let go the blade will shoot to 10 grand immediately...doesn't sound like free wheeling to me.
The only time it free wheels is when the front drive prop stops, then it spins down.
And the only thing that is important is the blade spin, it does not matter how it spins, GP forces have NO idea how a prop is being turned
As far as efficient, the Homemade .64 driving the props had more than enough power to do so, with much in reserve if needed, and if that didn't work I had 2 74s that would have :-)
As I stated earlier the plane flew tremendously better with the contra props
Just for info , there is/ was a geared engine system, a belt drive system, a fluid drive, and a traction drive, props used ranged from 12 inch to 15 inch
regards
Randy