I had been told back in the mid 60s when I was starting flying that theoretically the single blade prop is the most efficient, but that the practical application of that concept presented almost insurmountable problems.....

This picture is the first indication to me that there were actually some that were put into use at all.
Thank you for posting the picture of one!

lc

Another interesting tidbit...Everts sold the technical aspects of his prop to Kopper's who went on to use that information to develop the Aeromatic prop.

How is it variable pitch? It looks like solid wood. Does the entire prop twist at the end of the crank?

Samintel - yep, pretty much. See the top photo. The two small silver plugs (buttons) is the hinge point. It works on centrifugal force more or less. There is no controls or linkages. On take-off it is flat, and in cruise it moves forward at the tip for more bite.
There must be 10 inches of forward back and forth travel at the tip when on the ground.

They had an identical Tayor Cub with a standard prop do a drag race start with this one. This one pulled away both on the ground and in climb.

Amazing some of the cool things that just seem to disappear.

The Alisport self-launch glider uses a single blade. Seems to work pretty well. See the URL below and page down a few pages . . .

http://www.alisport.com/pdf/sha.pdf

bumper

it's very cool but it just looks wrong.

I just read a story about this prop. On the 40hp engine and in the J-2, the company "claimed" it increased the speed by 25%, increased the rate of climb by 30%, and cut the take-off roll by 50%!! Those are some claims.

Maybe I'm just ignorant. I just can't see how a single normal sized blade would provide more thrust and be more efficient than two considering the speed of the prop is limited to the maximum RPM's of the engine.

Hey one of you experimental guys need to make on of these to try out.... if they really work like they claim you would have a new "borer" prop.

GroundLooper wrote:I just can't see how a single normal sized blade would provide more thrust and be more efficient than two considering the speed of the prop is limited to the maximum RPM's of the engine.

The engine speed itself is limited by the tip speed of the blade(s).
It probably has something to do with the fact that the blade gets to operate in clean air, rather than in the wash of the other blade(s).
In theory I guess it must be heavier than a two bladed prop too. The angular accelleration is less at the counterweight's location, so the counterweight must be heavier than a blade to create the same force.

Maybe I'm just ignorant. I just can't see how a single normal sized blade would provide more thrust and be more efficient than two considering the speed of the prop is limited to the maximum RPM's of the engine.

I'm thinkin'.... that the preceeding blade interferes (aerodynamically) with the following blade, and it was thought, at one time, that one blade would be more efficient. It may be true.... but I think the nose bearings take a beating. Still an interesting proposition.

Single blade propellers are quite prevalent in the competitive free flight modeling scene. I think there is something to it when it comes to low horsepower.

The underlying rule of fewer fewer blades being more efficient is at work, and works nicely unless one has an abundance of power (energy) to transfer from engine to air and must keep the prop arc a reasonable size.

With a multi-blade prop, each blade passes near air that has been disturbed by the preceding blade*. The more blades, the closer this disturbed air is to each blade and the more pronounced this "interference drag" is. Interference drag also occurs were surfaces join (wing to fuselage) and fairings help reduce it. And of course between the upper and lower wings of a biplane, which was the reason Walter Beech staggered his wings to help minimize it.

*This is also one of the reasons that using a courser prop pitch in cruise results in more efficient operation, as a slower turning higher pitch prop results in a reduction of both parasitic and interference drag.

Disclaimer: I'm not an engineer, my simplistic explanation leaves out a bunch of stuff.

bumper