Slips, sideslips & crosswind landings.
I attended an FAA instructor seminar yesterday. One of the FAA guys gave a brief (or lecture, if you like) on slips. I had no issue with most of his talk ie slips/skids/forward/side, however when it came to wing down crosswind landings he stated that the aircraft was in a zero slip condition during this phase of flight, a position with which I disagree. He states that the aircraft is unable to determine crosswind and only experiences wind parallel to the longitudinal axis ie 'on the nose' - which is true in normal balanced flight, however this is not the case here. The aircraft has crossed controls applied.
I think that it is still a sideslip, and only appears not to be slipping because the sideslip speed balances drift speed and the flight path is being referenced to the runway. In other words, I think his error is that he's jumping between frames of reference which is masking the aerodynamics.
Am I wrong? Have I misunderstood something all these years? Anyway, we a have bet over who pays for lunch, to be won (or lost) one day when it's breezy & we have a plane available to which we'll attach a yaw string. I say the string will not be parallel to the longitudinal axis, he says it will...