I have heard that 1 blade props are more efficient than their two blade counterparts which is all very believable, but how much more efficient? I was running a 9x5 MA on a 25 FX, I think that it was running around 13500 ( i havent tached it for a while) I made a one blader from an APC 10x5 and that was swinging at 14200.
anyway, it makes sense that for racing props spinng at 28k single blade props would make quite a difference, but what about normal engines running in the mid teens? is there much to be gained from one bladers for the average flyer? Am i wasting my time making these carbon fiber oddities?

Mr. Moose,

Methinks that by virtue of the fact that we don't see any one bladed examples in full scale applications, all is not rosy with the statement we hear about one blade being more efficient. One blade may in fact be more effecient, but is just not practical.

How did the one bladed example you made fly? The only place I know of where one bladers are are flown is in controll line speed. You are one of the few who have actually went to the trouble to make a prop to test. Interesting stuff.... I'm still looking for the "magic bullet" to make my 1/2a pylon racer really go..... good flying...... Jeff

You can increase the radius (Can't really call it diameter with 1 blade, eh? hehehe) by 15% and get 10% more static thrust, same as going from 4 blades to 2. I reckon the problem would be balance and vibration?

The prop i made seemed to do quite fine in the air. It sounds different though. My theory to that is that it may be louder since higher tip speeds, but having only one blade cuts the frequency in half. It might be louder but it is less shrill than the two blade prop.
I think the reason that they are not used more often in full scale aircraft is ground clearance. Also maybe at the lower RPMs that full scale props are used the benifits of a one bladed propeller are minimal. But they are used, I have seen a powered sailplane that uses a folding one blade propeller.

Canada did a bit of experimentation with single blade props during the 40's, mostly on aircraft like Cubs and taylorcrafts. Yes, the results did show greater efficiencies but evidently not enough to overcome the manufacturing problems with balance and with the uneven wear on the prop shaft bearings caused by the flexing or wobble of the shaft caused by unequal bending forces.

As I understand it, the efficiency is improved as the number of blades is reduced because the trailing blade is moving through through dirtier air (more turbulant, altered angles of attack relative to the airstream, etc.) due to the prop blade ahead of it. The degree of inefficiency is relative to RPM as well...the higher the RPM, the more pronounced the inefficiency. In extreme, some of the really high RPM engines use single blade props (CL guys use them in some events).

Full scale planes really don't have high enough RPM to warrant the need for a single blade prop. In some cases, such as in warplanes, the engine is so strong they need multiple blades for prop clearance despite the reduction in efficiency (the Corsair is an example of how an engine choice drove the design properties of the airframe).

The theory that less blades is more efficient only at high revs is interesting but it doesn't explain why rubber duration models use (or used to use) single bladers. They run rather low revs.

If you read Martin Hepperle on propellers (http://beadec1.ea.bs.dlr.de/Airfoils/propuls1.htm) you'll find that the improved efficiency is due partly to the larger diameter of the prop disc but even more to the fact that you can run a wider blade which gives you a higher Re on the prop's airfoil.

However the improvement is not great and hardly likely to be worth the effort unless you need to wring the last possible drop of power out of the system.

Steve

I think the reason why we don't see more one bladers is due to the complexity of building one that runs balanced. Unlike a two blader, you have to balance the two sides of a one blader so that the center of mass on each side is equal. Other wise, the vibrations get worse at higher RPMs. If the c. of mass is further out on one side, the prop will want to wobble and vibrate. There is also the assymetric force of lift that the one blade produces and is not evened out by "another" blade. This probably isn't too much of a problem if you have a beefy enough prop shaft to handle the loads but it does wear the bearings a lot more. I have built a couple one bladers for S-400 pylon planes that worked pretty good. I have also seen some used for faster pylon planes. If there was an easy way of making them balanced out of the mold, I wouldn't mind building some more for testing.