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   Compute the Reynolds number for an aircraft at altitude.
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   Form:
   Re = Reynolds( h, u, L );
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   Inputs
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   h             (1)     Altitude           [m]
   u             (1)     Velocity           [m/s]
   L             (1)     Reference length   [km]

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   Outputs
   -------
   Re            (1)     Reynolds number

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