Interesting prop idea

[MadMuz]

http://www.sunflightcraft.com/en/coaxp.phpI just found this on the US rotary wing forum.....Reminds me of their big V8 airboats with these things on the back of a 510 ci engine

[gyroo]

Thanks for spotting that Muz!It"s a neat idea but the ratio of 1:3.7 means a 582 flat out will only be spinning these props at 1756 rpm. That"s way, way too low.In fact, it has been a concern of mine for a long time that gyro props on C boxes at the usual 1: 2.68 ratio are spinning too slow. With a 582 at 6500 this gives 2425 at the prop, and 6000 engine you get 2238 at the prop. My own personal preference would be that the prop - at full throttle - should be turning 2600-2700, and 2400 in cruise. I cautiously base my "theory" on personal experience in GA fixed wing PLUS I once again I refer to the range of standard texts available on propeller theory, such as the absolutely outstanding EAA series or the RAAus technical papers. The standard calculations seem to suggest that prop rpms several hundred revs higher than what we are used to might be a bit better for us.I know, I know - GA fixed wings are all direct drives and engine manufacturers say the prop manufacturers want their engines to turn too slow, while prop manufacturers say that engine manufacturers want their props to turn too quick! So, 2700 or even 2800 is the usual full throttle compromise. And, smaller Recreational fixed wings like Jabirus turn their smaller diameter props into the 3000s.I also agree that paddle blade props can efficiently turn much slower, but my "opinion" that our relatively short-chord prop blades (Warp drive / Ivo standard, etc) could usefully spin several hundred rpm quicker.What do people think?Mark R

[MadMuz]

The 582 seems to produce a heck of a lot of thrust with the c box, I wonder what they could do with better ratios?The contra rotating box would probably not be able to push a gyro needing lots of power all the time, would probably wear the box out or cook it in no time, I would think?

[aussie_paul]

It"s a neat idea but the ratio of 1:3.7 means a 582 flat out will only be spinning these props at 1756 rpm. That"s way, way too low.Mark it does depend on the prop diameter, BUT yes, for our normal prop size which is limited by rotor clearance etc.Aussie Paul.

[tonydenton]

another timely post. the new guy care taker came up to me on sunday, yeah I never had my bollards and yellow safety chain out again, he asked about prop diameters and ratios . I spoke of tip speeds and then he

[aussie_paul]

another timely post. the new guy care taker came up to me on sunday, yeah I never had my bollards and yellow safety chain out again, he asked about prop diameters and ratios . I spoke of tip speeds and then he

[MadMuz]

another timely post. the new guy care taker came up to me on sunday, yeah I never had my bollards and yellow safety chain out again, he asked about prop diameters and ratios . I spoke of tip speeds and then he

[gyroo]

Yep Paul -You put it better than me - I should have said that "..... and with our generally constrained prop diameters between the rotor and keels".Still, that counter-rotating prop would have enormous curiosity value, and maybe if a really really effective 2 stroke muffler / silencer could be engineered, we might be on our way to a stealth gyro!Which, given the occasional noise complaints that filter through to ASRA, might not be a bad thing.Everybody"s gettin" far too sensitive and whingey in the wider community.MR

[MadMuz]

Here you go, all you need is a big block chev and you can run this lot

[MadMuz]

Or even one of these

[davidbuzz]

...or one of these...