Flying for fun must have posted as I wrote my waffle. He/she said exactly what I wanted to, though I can't expree myself nearly so clearly!
say in one particular leg of the flight
In flight it doesn't matter what the crosswind is doing. However, if it is very very strong, a light aircraft may not be able to make headway over the ground.
As far as on the runway is concerned, the crosswind limit is the point up to which a particular type can safely maintaine the runway centreline. If the crosswind is slightly above limits, say 18/19 kts, providing the ailerons are held fully into wind to prevent the upwind wing lifting, at best, the plane would deviate from the centreline due to insufficient authority from the rudder.
I'm sure there's much more to it though, ie, fuesalage cross section, aircraft lenghth, (moments around the main gear) and of course runway surface and tyre pressure and strength. ANd that old twin engine chesnut - pilot competancy!
I suppose if there was say a 30kt crosswind component, on the approach, a warrior or similar could track the extended centreline, albeit with horrendous crab. But it would be imposible to land wing down with opposite rudder and zero drift and then maintain the centreline.
Going off at a tangent, I once landed a warrior at Le Touquet at its limit, (i think it was 30/40 degrees from the right and 19kts gusting 27) Now, I said to myself, I'll approach, and if at anytime I dont like it I'll divert. However, as I flared and was pretty much committed, I began to feed in increasing ammounts of right aileron and left rudder. It surprised me when I reached the rudder stops, but what surprised me more was that my damm knee borad prevented me from getting full aileron deflection so as I touched down in 27kt gusts I had to remove my kneee board. Now of course, its just habbit pre landing to chuck all the maps and crap in the back