Preliminary fan design for a silent aircraft

Preliminary fail design for a,functionally silent aircraft has been performed with reduction as the primary goal. For such an aircraft the fan design must, in addition delivering low cruise fuel burn, enable low jet and fan source noise during takeoff. requires the fan to be operating at low pressure ratio and high efficiency during and, for conditions where the relative tip Mach number onto the fall is ensuring the primary shock structure is ingested into the blade passage. To meet requirements, flyover and cruise flow coefficients are matched using a variable nozzle at the same time as delivering low takeoff FPR. This places the sideline point near the shoulder of the characteristic and fixes the top of climb and cruise pressure ratios. For a 4-engine, 250 pax, 4000 nm silent aircraft this approach leads a top of climb FPR of 1.45, requiring a 39% increase in nozzle area at takeoff. A fan has been designed for this cycle with 20 blades, low tip loading during takeoff and 350 m/s top qf climb tip speed.