ORIGINAL: redcommander
Yes, I was invisioning, for example, flying into a headwind, then making a turn such that now you are in a crosswind and your airplane now has some crab angle (since you aren't holding any rudder). This would not happen on a neutrally stable (directionally) airplane. If that crosswind then dissappeared, a stable airplane will then return to zero crab (again witout inouts from pilot)
another way to think of it is by applying a rudder singlet. an unstable airplane will spin as a result of a rudder singlet, while a stable vehicle will recover and resume with the pointy end forward. These cases are not steady state.
Respectfully, I'm not sure I follow you. Crab angles have nothing to do with stability. Are you sure you don't mean
sideslip, or
skid, instead of
crab? A crab is only relevant with respect to an airplane's path over the ground - something the airplane has no "knowledge" of, unless in contact with it.
Also, I had to look up
singlet, and I have not found a definition that seems to fit the context above. One defition is
tank top, or
sleeveless undershirt, and the other has to do with atomic physics and particle spin. There is some mention of particulate angular velocity, but I wasn't smart enough to apply it in a straighforward way to a rudder. Care to elucidate? I suppose if I tossed up a tank-top just as the airplane was flying overhead, and it caught on the rudder, it might enter a spin.
(showing my ignorance). I'm sure I just missed a general enough definition to be able to understand it in the way you mentioned it.