B. Bland, J. Kissel, N. Roberston, T. Sadecki

As discussed yesterday, today in one last bit of effort to understand which the lowest pitch mode frequency is lower than expected, we flipped the M3 dummy mass upside-down, in efforts to change the height of the suspension point between M2 and M3 at that mass ("d4"). The solid works model predicted that this flip would increase d4 from 1 mm above the COM to 2 mm above the center of mass. However, recall from yesterday that a model that best fit the measured data showed that d4 was in fact ~0 +/- 0.1 mm, i.e. dead even with the center of mass.

The attached plot shows the results of the flipped M3. The result is that the pitch frequency did increase, but only by 0.01 Hz up to 0.47 Hz, as opposed to the expected 0.50 Hz. Hence, as with adjusting the M1 blade tip heights, the lowest pitch frequency moved quite a good deal less than expected. Further, a model matching the data shows that d4 had actually increased only from -0.1 mm (GREEN/PURPLE) to 0.4 mm (CYAN/GOLD), a 0.5 mm change, where a 1 mm change (from 1 mm (BLUE) to 2 mm (RED)) was expected.

This concludes our foray into investigating this particular mode, as achieving a 0.48 Hz lowest pitch mode (where the lowest longitudinal mode remains at 0.41 Hz) was a goal, not a requirement. Hence, we will settle for the first pitch mode being at 0.46 Hz, in which the M3 mass is returned right-side up, and the M1 blade tip heights are set to 23.6 mm from the M1 base plate, making that the new baseline.

Because we're going with a M1 lower blade tip height, we must now recalculate the appropriate wire lengths for the stages below M1, to restore the nominal heights of M2 and M2. We will do so, and remeasure the pitch frequency response to ensure that the lowest mode frequency remains *at least* above 0.46 Hz.