Aeronautical propulsion system

A method of manufacturing an aeronautical propulsion system comprising:

• a stator;
• a fan section comprising a fan shaft extending along a longitudinal axis, the fan section being unducted;
• a first guiding system supporting and rotationally guiding the fan shaft, the first guiding system comprising a fixed part which is fixed with respect to the stator and an active part configured to transmit a force between the fan shaft and the fixed part;
• a drive shaft extending along the longitudinal axis and configured to be driven by a turbine of the aeronautical propulsion system;
• a second guiding system supporting and rotationally guiding the drive shaft;
• a reduction structure coupling the drive shaft to the fan shaft such that a rotation of the drive shaft at a first speed drives a rotation of the fan shaft at a second speed which is less than the first speed;
• a support attaching the reduction structure to the stator;
• and
• a coupling device connecting the drive shaft to the reduction structure and configured to compensate for a misalignment between the drive shaft and the reduction structure, the coupling device comprising a plurality of shaft sections and a plurality of radial flexibility elements, each of the plurality of shaft sections extending along the longitudinal axis, each of the plurality of radial flexibility elements connecting two of the plurality of shaft sections to one another and being configured to compensate for a misalignment between the two of the plurality of shaft sections;
• wherein the active part of the first guiding system has a first axial end and a second axial end, a reference plane orthogonal to the longitudinal axis being axially positioned at equal distance from the first axial end and from the second axial end of the active part of the first guiding system;
• wherein the second guiding system comprises a plurality of thrust bearings, a first thrust bearing of the plurality of thrust bearings being axially positioned nearer to the reduction structure than the others of the plurality of thrust bearings, the first thrust bearing comprising a fixed part which is fixed with respect to the stator and an active part configured to transmit a force between the drive shaft and the fixed part, the active part of the first thrust bearing having a first axial end and a second axial end, a first plane orthogonal to the longitudinal axis being axially positioned at equal distance from the first axial end and from the second axial end of the active part of the first thrust bearing, the first plane being further axially positioned at a first distance from the reference plane;
• wherein the support has a first end connected to the stator and a second end connected to the reduction structure, the first end of the support being axially positioned at a second distance from the reference plane and the second end of the support being axially positioned at a third distance from the reference plane;
• wherein the reduction structure is an epicyclic gear train comprising a ring gear having a first axial end and a second axial end, a second plane orthogonal to the longitudinal axis being axially positioned at equal distance from the first axial end and from the second axial end of the ring gear, the second plane being further axially positioned at a fourth distance from the reference plane;
• wherein the first guiding system comprises a plurality of rolling elements aligned in a third plane orthogonal to the longitudinal axis, the third plane being axially positioned between the reference plane and the reduction structure, the third plane being further axially positioned at a fifth distance from the reference plane;
• wherein a first radial flexibility element of the plurality of radial flexibility elements of the coupling device is positioned nearer to the first guiding system than the others of the plurality of radial flexibility elements, the first radial flexibility element comprising a first axial end and a second axial end, a fourth plane orthogonal to the longitudinal axis being axially positioned at equal distance from the first axial end and from the second axial end of the first radial flexibility element, the fourth plane being further axially positioned at a sixth distance from the reference plane;
• wherein a second radial flexibility element of the plurality of radial flexibility elements of the coupling device is positioned nearer to the second guiding system than the others of the plurality of radial flexibility elements, the second radial flexibility element having a first axial end and a second axial end, a fifth plane orthogonal to the longitudinal axis being axially positioned at equal distance from the first axial end and from the second axial end of the second radial flexibility element, the fifth plane being further axially positioned at a seventh axial distance from the reference plane;
• and
• wherein the method comprises dimensioning the aeronautical propulsion system, and
• wherein a ratio of a difference between the seventh distance and the fourth distance to the fourth distance is determined to be greater than or equal to 0.55 and less than or equal to 2.0.