A disclosed propulsion unit includes a pylon having a blade presenting a chord Cx and a downstream arm having a structural arm. The pylon has a first distance D between a trailing edge of a fan blade and a leading edge of the fan blade, a second distance d between said trailing edge of the blade and a leading edge of the structural arm, and a third distance L between the trailing edge of the blade and a mark located at a maximum thickness of the downstream arm. The pylon is dimensioned according to: a first quotient between D and Cx between 2.2 and 2.6, a second quotient between d and Cx between 1 and 1.2, and a third quotient between L and Cx between 4 and 7.