Don`t know the aircraft, but it is clearly calibrated to drive a 500 watt generator, the pitch setting corresponding to the airspeed you want it to be driven at.

I would tend to agree that it is for a wind-driven generator as 500 Watts is a fairly ‘sensible’ output for a generator of the 1920-1930 era.

And as you say the table seems to be advising the pitch setting to give 500 Watts for a given airspeed.

I doubt very much that with a 500 Watt motor this propeller could produce a wind speed of 324km/h (200mph) at a pitch of 38° (in a wind tunnel for example).

Could it be something to do with a wind tunnel by any chance? Perhaps the table referring to blade angle and scale speed?

Just re-read your comments about scale-speed. It’s possible but wouldn’t it be more useful to have the absolute-speed on the propeller and then work out the scale-speed from the scale of the model. Also the fact that it is only a 600mm propeller would tend to make the tunnel small so the absolute-speed would need to be very high to give a reasonable scale-speed.

It is a long time since I did anything with a wind tunnel so I could be very, very wrong though! 🙂