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Smeaton's Coefficient

In 1759, the British engineer John Smeaton published a paper titled "An Experimental Enquiry Concerning the Natural Powers of Water and Wind to Turn Mills and Other Machines Depending on Circular Motion" that addressed the relationship between pressure and velocity for objects moving in air. Others later used the concepts and data in this paper to arrive at a constant of proportionality with the value 0.005 to describe his basic notion of pressure varying as the square of the velocity when it was applied to objects moving in air. (A constant of proportionality is a multiplying factor that allows the general relationship of pressure and velocity to be applied to the specific medium being studied.) Although derived by others than Smeaton, this constant was called Smeaton's coefficient. The Wright brothers had used the established value in designing their first two gliders. An error in this constant, which had remained unquestioned for almost 150 years, would have explained the less-than-expected lift of these machines.

From Peter L. Jakob, Visions of a Flying Machine, Washington and London: Smithsonian Institution, 1990.