The Whirling Arm

It’s easy to imagine early man standing on a hill, twirling a rock on a tether over his head to gauge its performance in a hunt. Easier still to fast forward to the Middle Ages and imagine early theorists examining the concept of centrifugal force. Jump ahead in time yet again and you’ll find man using a mechanical device in lieu of their own arms. What is this device? The whirling arm.

A whirling arm functions much like a person spinning in one place with an object attached to a long string circling above him. The source of power on a whirling arm is at the center point (fulcrum). The arm of a whirling arm either Robins Whirling Arm extends with a counterweight at one end or extends from the fulcrum as in the whirling arm pictured here. The object whirling around on the whirling arm is not of interest because of the centrifugal force generated, but rather because of the behavior of the air as it flows past the object. Because of this, whirling arms were the first machines used to test the aerodynamic properties of objects.

The whirling arm pictured above is the Robins whirling arm. The first whirling arm, English mathematician and military engineer Benjamin Robins, used it in his work in the field of ballistics in 1742.

More whirling arm info and diagrams to come! For more information now, check out my book.


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