3.4 Under take-off conditions when the ambient pressure and temperature are 1-01 bar and 288 K, the stagnation pressure and temperature in the jet pipe of a turbojet engine are 2-4 bar and 1000 K, and the mass flow is 23 kg/s. Assuming that the expansion in the converging propelling nozzle is isentropic, calculate the exit area required and the thrust produced. For a new version of the engine the thrust is to be increased by the addition of an aft fan which provides a separate cold exhaust stream. The fan has a bypass ratio of 2.0 and a pressure ratio of 1.75, the isentropic efficiencies of the fan and fan-turbine sections being 0-88 and 0.90 respectively. Calculate the take-off thrust assuming that the expansion in the cold nozzle is also isentropic, and that the hot nozzle area is adjusted so that the hot mass flow remains at 23 kg/s. [0-0763 m², 15-35 kN; 24.9 kN]