Abstract: A gas turbine engine comprises a gearbox comprising a sun gear, an annulus gear, a plurality of planet gears and a carrier. Each planet gear is rotatably mounted in the carrier by a bearing. The sun gear meshes with the planet gears and the planet gears mesh with the annulus gear. The sun gear, the planet gears and the annulus gear comprise helical gear teeth. The annulus gear is secured to a surrounding structure by a radially extending member. A face of the flange nearest the middle of the annulus gear is axially spaced from the middle of the annulus gear by a first distance. The reference diameter of the annulus gear is radially spaced from a point at which the radially extending member is secured to the surrounding structure by a second distance. The ratio of first distance to second distance is between and including 0.5 and 1.2 such that misalignment between the annulus gear and the planet gears is reduced to minimise vibrations, noise, stress and wear of the gearbox.

Abstract: A gas turbine engine includes gearbox including sun gear, annulus gear, plurality of planet gears and carrier. Each planet gear is rotatably mounted in carrier by bearing. The sun gear meshes with planet gears and planet gears mesh with annulus gear. The sun gear, planet gears and annulus gear comprise helical gear teeth. The annulus gear secured to surrounding structure by a radially extending member. A face of the flange nearest the middle of the annulus gear axially spaced from middle of annulus gear by first distance. The reference diameter of the annulus gear is radially spaced from a point which the radially extending member is secured to the surrounding structure by second distance. The ratio of first distance to second distance is between and including 0.5 and 1.2 such that misalignment between annulus gear and planet gears are reduced to minimize vibrations, noise, stress and wear of gearbox.