Alternate propeller designs

[cudabean]

All aircraft propellers that I've seen revolve around a drive shaft aligned with the longitudinal axis. Has anyone seen a propeller that operates more-or-less like a sternwheeler paddle? I've seen windmills that revolve around a vertical axis, but I suppose the problem with using that type of design in reverse is that I suppose that if you apply power directly to it, it would sling out the air in all directions at once and provide no net thrust.

cudabean

[Mike Everman]

You'd do that with a cyclic pitch change, though as a driver it would be less than stellar in terms of thrust per parasitic pound. Helicopter rotors are very efficient owing to the long aspect ratio, and the axiom: it is more efficient to move alot of air slowly than a little very fast.
-Mike

[Bruno Ogorelec]

it is more efficient to move alot of air slowly than a little very fast.

If I can amend that:

It is more efficient to move a lot of air at about the speed you intend to travel than a little air much faster, even though the total momentum may be the same. This covers the entire spectrum of airspeeds.

Bruno

[Mike Everman]

I sit corrected.

[cudabean]

Thanks for the responses. Another problem, besides efficiency, with small area velocity greatly exceeding the flight speed is noise.

One possibility for alternate forms of thrust generation is a squirrel cage blower.

cudabean

[Peter Hanely]

I've considered propellers with an axis crosswise to flow.

Advantages:
- thrust can be quickly changed to any direction crosswise to direction.
- for a helicoptor such a blade can avoid retreating tip stall.

Disadvantage:
- each blade must constantly cycle between pulling air in and pushing it out the other side.

[Mike Everman]

Centrifugal forces unfortunately limit how fast you can spin it, putting the blades in bending, and all things being imperfect, some will bend out slightly more than others making for catasrophic imbalance. there's damned little better than a ducted fan, but I search too...

[Hank]

Hello- The only propulsion assembly that popped into my head even near what you mention is one constructed by a fellow-member of a model aircraft club I once belonged to.
Though centerline thrust it is still interesting re this topic.
The assembly consisted of a ducted fan with the blades mounted in a ring.
The tips were close to the centerline. power transmission was through a rubber wheel fed by a flexible shaft from the engine. This unit worked, but stability in flight was near nonexistent due to the torque.

Kudos Mike Kirney for mentioning eBay re sheet metal tools. There is not much out there now. Does anyone know of any manufacturers of small crank operated beading tools?

Hank

[nmasters]

All aircraft propellers that I've seen revolve around a drive shaft aligned with the longitudinal axis. Has anyone seen a propeller that operates more-or-less like a sternwheeler paddle? I've seen windmills that revolve around a vertical axis, but I suppose the problem with using that type of design in reverse is that I suppose that if you apply power directly to it, it would sling out the air in all directions at once and provide no net thrust.

cudabean

It's been tried a few times with limited success. Too many highly stressed moving parts without any gains. Here are some links


The Caldwell "Cyclogyro":
http://www.ufx.org/maryland/caldwell.htm

The "Fanwing":
http://www.fanwing.com/ann_exclusive.htm

Some NACA tech reports of wind tunnel testing of the "Cyclogyro":
http://naca.larc.nasa.gov/reports/1935/naca-tn-528/
http://naca.larc.nasa.gov/reports/1930/naca-tn-467/

[nmasters]

Here's a picture of the Cyclogyro

http://www.aerofiles.com/schroeder.jpg

[Mike Everman]

Very nice links, Norm. I enjoyed that a lot. The fan wing reminds me of a shred of an idea I had a long time ago, but replace the fan with a cylinder. No blast down the upper surface with mine, but huge lift from Magnus. Lift unfortunately = drag still.

[Mike Everman]

Hey, coincidentally enough, the new Popular Science showed up yesterday with an old PS cover with a paddle-wheel propeller flying boat. I'll scan it and post when I get a minute.

[Peter Hanely]

Here's a picture of the Cyclogyro

http://www.aerofiles.com/schroeder.jpg

Different from the arangement I was thinking of. Mine would feather the airfoils 'above' and 'below' the airstream so as to not stall them, tilting for angle of attack up or down relitive to the circle, and would always keep one edge foreward into the airstream.

Looks like the aircraft pictured places the advancing blade for lift and the retreating blade paddlewheel style, the airfoil spinning about it's pivot on the circle.

[nmasters]

The fan wing reminds me of a shred of an idea I had a long time ago, but replace the fan with a cylinder.

That would be a variation on a flettner rotor. There was an experiment to do exactly what you describe with an OV-10 "Bronco". I don't know how it turned out but there is a picture of it on Rex Research's flettner rotor page.

http://www.rexresearch.com/aero/1aero.htm#thompson

That page has got a lot of flettner related images on it and loads really slow so here's the link to the Bronco picture:
http://www.rexresearch.com/aero/magnus1.gif

[Mike Everman]

Well, I declare, Norm, another "nothing new under the sun" in living color. Please visit the Valveless section, PJ alternators thread; maybe your considerable archive could save us there...
Thanks, that was a cool one!