Prop out of one piece?

[Ontheronix]

Hi all,

for a fun project, I'm looking for a small propeller. Something like 40-70cm (15-25").
DIY propellers require a lot of work, and balancing isn't that easy too in my experience For that reason, I was thinking about a pre-cast propeller, something like this: http://www.gotwind.org/diy/12-inch-mini-turbine.htm
This one used a propeller of an RC-airplane, thus the airfoil is inverted (for thrust). And therefore I was wandering if a similar design with an airfoil for wind is for sale somewhere. Anybody knows this? 

[john8750]

I made a test prop from paint stirrer sticks and a square hub, about 20 inches. It is terribly out of balance. The blades are flat and square, but seems to catch plenty of air. I need to use some brass tubing for bearings.  I like the coils the guy made, so simple.

[CraigM]

You could check out RC helicopter main rotor blades. They're much larger in diameter but I believe most use a symmetrical airfoil and have zero twist. May be similar to using a GOE222 profile. With the right angle of attack they may work well.

[tanner0441]

Hi

You can also get three bladed props for RC fixed wing planes, I think way back on the old site there was an article showing one of these it was 12 or 15in.

One thing to remember propellers for RC planes are designed to put energy into the air not collect it, there is a difference.


Brian.

[SparWeb]

 You could also make a series of sheets, each cut in a Y shape, then stack them.  Each sheet maybe 1/16" thick.  The top and the bottom in the stack have "arms" that aren't very wide, which the middle piece in the stack has fat "arms".  Instead of stacking them symmetrically, you would sweep the stack "clockwise" a little.  The combination would give you an approximation of an airfoil.  After gluing the stack together, all you have to do is sand down the 1/16" steps into a smooth profile.

Sort of like this:   https://www.google.ca/url?sa=i&rct=j&q=&esrc=s&source=images&cd=&cad=rja&uact=8&docid=x79C3ja4Ku-YNM&tbnid=XOB5YL4-uvEgTM:&ved=0CAUQjRw&url=http%3A%2F%2Fnotplanejane.com%2Ffleet60fort.htm&ei=jh9QU_KTC8-gyAT1uoLICw&bvm=bv.64764171,d.aWw&psig=AFQjCNEK0iLaUJQDxiAgRJT4ysV9SH_opQ&ust=1397846243816133

Real aircraft propellers were made this way...  in the 1930's.

[Ontheronix]

You could check out RC helicopter main rotor blades. They're much larger in diameter but I believe most use a symmetrical airfoil and have zero twist. May be similar to using a GOE222 profile. With the right angle of attack they may work well.

Thanks, good idea! Although I'm not able to find 3-blade props with that or a similar profile 

You can also get three bladed props for RC fixed wing planes, I think way back on the old site there was an article showing one of these it was 12 or 15in.

One thing to remember propellers for RC planes are designed to put energy into the air not collect it, there is a difference.

That's what I meant with the 'inverted airfoil' in my original post, if propellers (for thrust) are used as blades for windpower, they go in the wrong direction.

You could also make a series of sheets, each cut in a Y shape, then stack them.  Each sheet maybe 1/16" thick.  The top and the bottom in the stack have "arms" that aren't very wide, which the middle piece in the stack has fat "arms".  Instead of stacking them symmetrically, you would sweep the stack "clockwise" a little.  The combination would give you an approximation of an airfoil.  After gluing the stack together, all you have to do is sand down the 1/16" steps into a smooth profile.

I like the idea, but there is still quite some room for error. (Certainly in my hands  )

[tanner0441]

Hi

I made a garden ornament using a fan from a car. it was a one piece plastic molding with five blades  and asymmetrically spaced, drove an old cycle dynamo and lit a couple of little bulbs, before the days of bright LEDs.

I never worried when the speed went stupid, decided if it was capable of 5000/6000 RPM on an engine a couple of thousand RPM or so no matter how noisy wasn't going to be a problem.

Brian