An aero-propulsion system includes a drive shaft, a low-pressure compressor, a fan shaft driving a fan, a reduction device that couples the drive shaft and the fan shaft, and an inlet channel which extends between the fan and the low-pressure compressor, the inlet having a predetermined mean radius, a ratio between a mean radius of the inlet channel and the mean radius of the low-pressure compressor, on the one hand, and the reduction ratio of the reduction mechanism, on the other hand, being less than 0.35.