Smeaton's coefficient

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The Smeaton coefficient , named after John Smeaton , describes the relationship between pressure and aerodynamic resistance of a body in a gas flow. However, the dynamic pressure of the medium is not taken into account.

  • Air resistance in lbs
  • Speed ​​in mph
  • Area in square feet
  • Drag coefficient (for the reference environment = 1). Corresponds to today's value

The resistance equation

gives k for the Smeaton coefficient

In 1759, Smeaton gave in his work An Experimental Inquiry Concerning the Natural Powers of Water and Wind to Turn Mills and Other Machines Depending on Circular Motion a value of k = 0.005.

Up to about 1900, after further experiments, the value k was found to have a scatter of 0.0027 to 0.005. The Wright brothers trusted the value of k = 0.005 and initially built two gliders, but they did not fly. Extensive experiments then resulted in a value of k = 0.0033, which corresponded to the current value of k = 0.00327 with sufficient accuracy.

Because of its limited usefulness, the Smeaton coefficient has not been used since around 1920. Instead, the Bernoulli equation was used.

Individual evidence

  1. ^ A b John David Anderson: A History of Aerodynamics: And Its Impact on Flying Machines . Cambridge University Press, 1998, ISBN 978-0-521-66955-9 , pp. 58.313 f . ( limited preview in Google Book search).