I sat through a talk by Paul Lipps at Gene Nevada at the alternative engine seminar put on by Contact Magazine several years ago.

 

He flew in his home built, with his propeller. Its outer blades were the size of a 12" ruler. Imagine model sail plane wings, or bread knife blades. He placed split tennis balls on the tips so guests did not stab themselves on the blades.

 

Later, he helped a guy design new wings for a biplane racer, and those wings looked just like his propeller

blades. It had a 4 bladed Lipps propeller as well.

 

Not mentioned was the low wetted area of the blades would allow greater span with less drag. The high angle of attack at the root allowed playing card sized cooling inlets.

 

In the event of failed engine his prop has less than a 3rd of the frontal area of a conventional prop.

Not exactly full feathering, but better than anything else.

 

So, if the blade has less drag for each unit of lift, then you could add span until you get close to the ground, and then add blade count until you have accounted for all of the available HP. Then you port the rotary to get more HP.

 

Warning, looking at a Lipps propeller blade may hurt your mind......................

 

 

Lynn E. Hanover