Repeat Prob. 6–85 for an air-flow velocity of 10 m/s.

Data from problem 85

A metallic airfoil of elliptical cross section has a mass of 50 kg, surface area of 12 m², and a specific heat of 0.50 kJ/kg · K. The airfoil is subjected to air flow at 1 atm, 25°C, and 5 m/s along its 3-m-long side. The average temperature of the airfoil is observed to drop from 160°C to 150°C within 2 min of cooling. Assuming the surface temperature of the airfoil to be equal to its average temperature and using momentum-heat transfer analogy, determine the average friction coefficient of the airfoil surface.