Bedsheet windmill

[kirk]

The oldest windmachine was drag operated. While I have a nifty way of collapsing the "bedsheet" on the return portion of the cycle I don't know how to calculate the work out.

How is the drag on a rectangular sheet calculated?

Thanks

Kirk

[windstuffnow]

 Hi Kirk,

    This formula is fairly basic and doesn't take into account the upwind drag but will get you into the ballpark.

.00492 x area x windspeed^2 = lbs of force

where area is in sq ft and windspeed in mph.

Once you have the lbs of force against the sheet you multiply that by the arm length to the center.  ( i.e.  4ft diameter would be 2ft to the center or a 2ft arm ).  This will give you ft/lbs

Then you take the ft/lbs x rpm / 5252 to find hp then to convert to watts multiply hp by 746.

Hav e fu n

Windstuff Ed