I am just getting into electric, and am having clearance problems with the recomended APC 12x6e. My thought is to get a 4 bladed prop for better ground clearance. I know that twice the blades does not equate to half the diameter. My question is; does it equate to half the swept area?

I take the sqaure of the radius of the 12" prop (36''), divide by two to get 18'' and take the square root which gives me about 4 1/4''. Rounding up to acount for the loss of efficiency, I get 9'' diameter.

There is enough thread on my drive shaft to ''gang up'' a couple of 9" APC's. Is this a valid method for aproximating the 4-blade equivalent for a recomended 2-blade? Does APC make 4-blade e-props? (If so, my LHS does not carry them)

Before going to a multi blade prop, have you tried using larger wheels and/or bending the landing gear to get more prop clearance ?

"There is enough thread on my drive shaft to ''gang up'' a couple of 9" APC's. Is this a valid method for aproximating the 4-blade equivalent for a recomended 2-blade?" DO NOT DO THIS. If you want/need a multiblade prop purchase one.

I don't know about 4 blade props, however for going from a 2 blade to a 3 blade, either drop 1" in diameter OR 1" in pitch. In your case you would go to either an 11x6E OR a 12x5E.

Multiblade props are A LOT LESS efficient than a 2 blade prop.

The usual rule-of-thumb is to go down 1" in diameter for every blade you add. So, you would be running a 10x6 4-blade.

Yes, APC makes 4-bladed props, but I'm not sure if they make them in a diameter you can use.

Another alternative is Vario props. In addition to 4-blade props, they're also adjustable pitch (on the ground only).

It's been my experience that 4-bladed props are less efficient than their 2-bladed counterparts, but they look a lot cooler.

Dan

Those vario props were fancy looking but the blade shapes were terrible.

It won't cost you much to try the stacked props. While you're at it try to use somthing other than a right angle so they form sort of a dragonfly like pair of V's. It may help with any blade wash conflicts.

I seem to remember reading a while back that Chip Hyde and Jason Shulman were doing something like this on their big electrics. I'll try it. I have also re-mounted the motor 3/8'' higher. Now an 11x7 just barely clears.

I try to resolve stuff like"prop efficiency" by testing
the math is a poor second on these questions
On my electrics, I simply stacked 2 blade props some with same pitch some with different pitches and diameters
The way I checked the results, was by measuring thrust and watts consumed at given thrust. I made a device to check this type of stuff.
My thrust stand -which I developed and shared over the internet - is now available (some body glommed onto it) is now available commercially!
my, my.
The really funny part --
when I first showed the device to the internet-- a number of guys doubted it could be accurate because the thrust was not measured in direct pull.
Anyway -the mixed props were pretty similar in thrust with 2 blade props-IF you compared watts to thrust
said differently - the thrust was the same when the power used to turn the prop(s) was the same.

Can anyone give me a couple of good resources for 4-blade warbird electric props????