A turbofan engine according to an example of the present disclosure includes, among other things, a fan section including a plurality of fan blades, the plurality of fan blades having a fixed stagger angle and a design angle of incidence, a low pressure turbine driving the plurality of fan blades through a gear train, a fan nacelle and a core nacelle extending along an engine axis of rotation, the fan nacelle at least partially surrounding the core nacelle and the plurality of fan blades, a fan bypass flow path defined between the core nacelle and the fan nacelle, the core nacelle contoured along the fan bypass flow path with respect to the engine axis of rotation, and a fan variable area nozzle in communication with a controller and with the fan bypass flow path, and defining a fan nozzle exit area between the fan nacelle and the core nacelle.

Provided are methods and systems for measuring and controlling nozzle areas of variable area fan nozzles. A control system attached to a nozzle may include a cable having one end connected to a linear displacement measuring device, such as a string potentiometer. The other end of the cable may be connected to a petal. A reference portion of the cable extends across multiple petals of the nozzle and, in some embodiments, substantially parallel to the nozzle circumference. The linear displacement measuring device measures any changes in the length of this reference portion as the petals actuate outwardly or inwardly during operation of the nozzle. The output of the linear displacement measuring device may be used to control actuators that move the petals. In some embodiments, potentiometer's output may be combined with one or more outputs from other sensors, such as a linear variable differential transducer and/or thermocouple.

Provided are methods and systems for measuring and controlling nozzle areas of variable area fan nozzles. A control system attached to a nozzle may include a cable having one end connected to a linear displacement measuring device, such as a string potentiometer. The other end of the cable may be connected to a petal. A reference portion of the cable extends across multiple petals of the nozzle and, in some embodiments, substantially parallel to the nozzle circumference. The linear displacement measuring device measures any changes in the length of this reference portion as the petals actuate outwardly or inwardly during operation of the nozzle. The output of the linear displacement measuring device may be used to control actuators that move the petals. In some embodiments, potentiometer's output may be combined with one or more outputs from other sensors, such as a linear variable differential transducer and/or thermocouple.

A turbofan engine includes fan section including a plurality of fan blades, a gear train, a low spool including a low pressure turbine and a low pressure compressor, the low pressure turbine driving the plurality of fan blades through the gear train, and a high spool including a high pressure turbine driving a high pressure compressor. A fan nacelle at least partially surrounds a core nacelle to define a fan bypass flow path. A fan variable area nozzle is in communication with the fan bypass flow path and defines a fan nozzle exit area between the fan nacelle and the core nacelle. The fan variable area nozzle varies the fan nozzle exit area.

A turbofan engine includes fan section including a plurality of fan blades, a gear train, a low spool including a low pressure turbine and a low pressure compressor, the low pressure turbine driving the plurality of fan blades through the gear train, and a high spool including a high pressure turbine driving a high pressure compressor. A fan nacelle at least partially surrounds a core nacelle to define a fan bypass flow path. A fan variable area nozzle is in communication with the fan bypass flow path and defines a fan nozzle exit area between the fan nacelle and the core nacelle. The fan variable area nozzle varies the fan nozzle exit area.

A turbofan engine includes a fan variable area nozzle includes having a first fan nacelle section and a second fan nacelle section movably mounted relative the first fan nacelle section. The second fan nacelle section axially slides aftward relative to the fixed first fan nacelle section to change the effective area of the fan nozzle exit area.

A turbofan engine includes a fan variable area nozzle includes having a first fan nacelle section and a second fan nacelle section movably mounted relative the first fan nacelle section. The second fan nacelle section axially slides aftward relative to the fixed first fan nacelle section to change the effective area of the fan nozzle exit area.

A turbofan engine includes a fan variable area nozzle includes having a first fan nacelle section and a second fan nacelle section movably mounted relative the first fan nacelle section. The second fan nacelle section axially slides aftward relative to the fixed first fan nacelle section to change the effective area of the fan nozzle exit area.

A turbofan engine includes a fan variable area nozzle includes having a first fan nacelle section and a second fan nacelle section movably mounted relative the first fan nacelle section. The second fan nacelle section axially slides aftward relative to the fixed first fan nacelle section to change the effective area of the fan nozzle exit area.

A turbofan engine includes a fan variable area nozzle includes having a first fan nacelle section and a second fan nacelle section movably mounted relative the first fan nacelle section. The second fan nacelle section axially slides afterward relative to the fixed first fan nacelle section to change the effective area of the fan nozzle exit area.