The effieciency would be infinate because the airfoil shape would make "some" foreward lift, and the pitch is zero... any number divided by zero is infinity. Well that's one way of doing it anyways.

The idea of pitching a prop at zero is silly. There are basically two ways to look at prop efficiency. One is to use the slip to calculate how far the prop moves foreward per rotation compared to the pitch of the blade... example an 18x10 prop that is only moving foreward 8 inches per rotation has an efficiency of 80%(8/10). But, this method is flawed in some ways. An 18x10 prop that is mounted to a plane in a hover for example is not moving foreward at all so it's efficiency would therefore be 0/10 which is zero... yet the model stays in the air... hmm that doesn't make sense. A better way to measure prop efficiency would be to compare brake horsepower to thrust horsepower. THP=BHPxprop efficiency. This can be done static by using a fish scale to meauser the thrust, and compare that to the brake horsepower if that data is available... I don't know if anyone has ever put an OS on a Dyno to create the tables needed to do these calculations.

Ty