Whistling blades on wind direction weather vane
I have a propeller with four blades that acts as a wind direction weather vane.
What I would like is for the propeller to make a whistling noise when it is rotated by the wind.
Someone told me if I put a small hole or a slit in each of the blades it will make a whistling noisy which should change with wind speed.
Can anyone tell me what size hole/slit I would need?
Also at what angle would the slit have to be?
Or can you tell me any other way to get a whistle from the blades when the wind is blowing?
The blades are metal and about 200mm long (400mm overall diameter).