A Maritime U-V-W Measuring System

The angular response of a fixed axis anemometer is strongly affected by the vortices from the hub and blade tips. These vortices interact with neigh- boring blades. The amount of the effect can be changed by altering the total angular blade twist, the blade angle of attack, by cutting a thin slot at the hub-base juncture, and by changing the number of blades (blade spacing). Other changes are ineffective or deleterious. Accurate wind component response to within 2.5 per cent is obtained most closely with eight rectangular blades with 45 degrees of helicoidal twist, offset 0.8 percent of the span from a rough ellipsoidal hub, whose diameter is 22 percent of the total span. Continuous electronic display of wind speed is accomplished by accurately timing each revolution and computing the reciprocal of that period.