A turbofan engine for an aircraft includes a fan and a fan actuation system. The fan has a plurality of fan blades coupled to a fan shaft having one or more fan bearings. The fan blades are rotatable about a pitch axis. The fan actuation system is disposed within a fan hub and includes one or more actuators for rotating the fan blades about the pitch axis and one or more radial thrust bearings. The fan actuation system is characterized by a fan actuation system length envelope in a range of 8.5 to 24 and given by

[00001]$\frac{N_{\mathrm{FB}}{D}_{\mathrm{FT}}}{L_{\mathrm{AXIAL}}\left(\frac{R_{\mathrm{TB}}}{N_{\mathrm{FB}}}\right)}.$

N.sub.FB is a number of the fan blades, D.sub.FT is a fan tip diameter of the fan blades, R.sub.TB is a thrust bearing radius of the radial thrust bearings, and L.sub.AXIAL is an axial length from a fan hub tip to the fan bearings.

The invention provides a method and a device for fault diagnosis of a yaw system in a wind turbine, and relates to the technical field of wind turbines. The method comprises the following steps: acquiring monitoring data collected in a yaw system, inputting the monitoring data into a yaw fault diagnosis model, and outputting a fault diagnosis result, wherein the fault diagnosis model is obtained by training known fault diagnosis results and corresponding monitoring data, and the fault diagnosis result comprises at least one of the following: the position of a yaw sensor is shifted, the yaw sensor is damaged, the yaw contactor is stuck, the hardware of a yaw motor/reducer is damaged, and the yaw motor is braked, In the working process, the monitoring data collected by the yaw system can be input into the yaw fault diagnosis model in real time, and the yaw fault diagnosis model can be used to determine whether the yaw system has a fault and the specific fault diagnosis results when the fault occurs. In this way, the operation and maintenance personnel can be prevented from going to the aircraft seat for inspection, and the fault diagnosis efficiency of the yaw system can be improved.

The invention provides a controller for a wind turbine having three rotor blades, the controller being for controlling activation of individual pitch control of the rotor blades. The controller is configured to receive a flap load signal, from a flap loading sensor of each of the three rotor blades, indicative of flap loading on each of the respective rotor blades. The controller is configured to determine, based on the received flap load signals, a statistical dispersion parameter of flap loading for each of the rotor blades, the statistical dispersion parameters being indicative of a wind event in a wind field in which the wind turbine operates. The controller is configured to control activation of individual pitch control based on the respective statistical dispersion parameters.