In early development of gas turbine engines, the pressure ratio was low, the isentropic efficiency of components was low, and metallurgy limited upper operating temperature of gases entering the turbine. Consider standard inlet conditions of 1.0 atm, 25 C, a pressure ratio of 4 across compressor, and an upper operating temperature limit of 600 C, what is the minimum isentropic efficiency of compressor and turbine (assume equal for simplicity), for which the engine will just begin to produce net power output, i.e., break-even?