A coupling device for rotably coupling a shaft with a gearbox in a geared turbo fan aircraft engine, wherein the coupling device includes a connection to the shaft at a first end and a connection to the gearbox at a second end, the first and the second ends being axially separated and at least one curved shape between the first end and the second end extending from the gearbox radially inwards to the shaft and the at least one curved shape including at least one cross-section in the axial direction of the engine with a logarithmic profile or a power profile.