=+69. Let x denote the vibratory stress (psi) on a wind turbine blade at a particular wind speed in a wind tunnel. The article “Blade Fatigue Life Assessment with Applications to VAWTS” (J. of Solar Energy Engr., 1982: 107–111) proposes the Rayleigh distribution as a model; the density function is f(x) 5 c x

2 ? e 2x 2

y(22

)

0 x . 0 otherwise