The Dutch-roll oscillation may from a piloting standpoint be termed a nuisance factor. Its oscillatory nature is not purposely induced to perform any maneuver, and its presence may hinder the maintenance of precise flight-path control. Originally attempts were made to correlate pilot opinion with the ratio фЦЗ of the eigenvector and the damping of the oscillation. However, when it was found that pilots desired more damping for a given фІ@ at lower flight speeds, the parameter ф/(и0р) or ф/v was introduced to replace фЦЗ. Additional studies indicated that the altitude was also important with more damping being desired at higher altitude. This lead to the us

of plp0 or <f>/vE. Further refinement then replaced cycles to half amplitude

by the inverse of the time-to-half-amplitude, 1/Tj. Figure 12.20 illustrates the pilot rating boundaries plotted on a l/T^ vs. <f>/vE diagram. This is typical for fighter-type aircraft.

As is often the case in the field of handling qualities, this is not the final answer. In fact some results can be shown to correlate better with bank angle response to rudder input and root-mean-square bank angle response to random gust inputs.