## Time Series Data

Because furling is a transient phenomena, analysis of time-series data can be more useful than that of 10-minute mean data. In the time-series data, thrust and furl are often correlated but not always. For example, the second furling event of about 14 degrees shown in Figure 28 occurs when the thrust is relatively low and the rotor speed is decreasing, whereas the large furling event of 36 degrees occurs when the thrust is high and the rotor speed is increasing immediately preceding the furl, as would be expected. Yaw error changes occur rapidly and affect furl.

Calculated channels for shaft thrust and shaft 0- and 90-degree bending moments are used to calculate the center of thrust angle (CenThrAng) and center of thrust length (CenThrLen) as follows:

CenThrAng = ArcTan2 (shaft tilt moment/thrust, shaft yaw moment/thrust) (1)

CenThrLen = Sqrt [(shaft tilt moment/thrust) 2 + (shaft yaw moment/thrust) 2] (2)

These equations are only valid when inertial forces can be ignored during steady-state operation with negligible yaw rate, otherwise the gyroscopic forces on the shaft have too large an effect and invalidate the equations. Figure 29 shows a time-series furling event with a low yaw rate before the furling event and how CenThrLen plots in relationship to furling. Additional data analysis, using equations (1) and (2), is needed to characterize the effect of aerodynamic thrust on furling behavior during low yaw rates.

sonicwsmet (m-s Furl (deg ShftThrus2 (N yaw error (deg

3000

sonicwsmet (m-s Furl (deg ShftThrus2 (N yaw error (deg

3000

320.0 330.0 340.0 350.0 360.0 370.0 380.0 390.0 400.0 410.0 420.0

Time, seconds

Figure 28. Time series furling events

320.0 330.0 340.0 350.0 360.0 370.0 380.0 390.0 400.0 410.0 420.0

Time, seconds

Figure 28. Time series furling events

35 30 25

35 30 25

Figure 29. Furling with center of thrust

11 13 15 Time, seconds

Figure 29. Furling with center of thrust

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