The Boeing Company
Aircraft turbofan engine having variable pitch fan and method of over-pitching the variable pitch fan in an engine out condition to reduce drag

Abstract:

There is provided a turbofan engine for an aircraft. The turbofan engine has a core with a fan cowl and a variable pitch fan (VPF) configured to only rotate in a first rotation direction. The VPF has a plurality of fan blades each configured to over-pitch to an over-pitch position relative to a feathered position. The turbofan engine has outer guide vanes (OGVs) axially disposed downstream of the VPF, and has a rotation control device to prevent the VPF from rotating in a second rotation direction opposite the first rotation direction, during an engine out (EO) condition of the turbofan engine. When the VPF is prevented from rotating during the EO condition, the fan blades are over-pitched to the over-pitch position relative to the feathered position, to achieve no or minimal air flow separation about the OGVs, and to reduce drag of the turbofan engine during the EO condition.