Interesting thread on dutch roll testing. I wonder if going back to basics will shed any light on the discussion. I thought that DR was driven by sideslip since direction response is a second order system, and lateral response a first order system. With that in mind you could trigger a DR response via any mechanism which creates sideslip. These include rudder doublet, release from SHSS, turbulence or aileron inputs (if AAY is bad).
I thought that the test fraternity settled on a rudder doublet as the chosen DR test as it allowed a nice DR response with AoB variations about wings level, thus negating any spiral stability effects. Easy to fly, easy to count and time. However not the only means to excite.
Am I missing something here?
------------------