Quote Originally Posted by desbromilow View Post
anyone ever built one of these sirens? specifically I want to know how close fitting the rotor and vane need to be for it to work well? the one I want to make is a version of the handcranked air raid type siren (about 75mm (3") rotor diameter.

thanks,
Des
Mattias Wandel has several videos on sirens. IIRC it was a side quest while working out geometry for a Thien baffle type dust separator for his wood shop. I don't have the link to the videos but you can get to them via his website https://woodgears.ca. He gets a bit into the weeds of math and theory, but in layman's language.

Neil