Back onto the subject of written references, and back onto my own suggestion of Langewiesche. (I've spelt his name correctly this time, since I've got his book in front of me!) What he has to say on the subject is:
The rudder is also used in cross-wind landings. In order to have the airplane going straight over the ground at the moment when it makes contact with the ground, it is made to sideslip through the air......
He doesn't appear to use the term "forward slip" at all, but he does use the time "sideslip" to refer to the cross-wind landing technique as well as the technique for loosing height.
Incidentally, though, one thing I had forgotten (since it's been a while since I read his book) is that he is not a big fan of the rudder at all. His vision of the aircraft of the future doesn't have a rudder. He sees ailerons designed well enough that adverse yaw becomes negligable, the use of side-slip to loose height replaced by flaps, and no need to straighten up the nose prior to landing because the "new" tricycle undercarriages which were being used could land crabbed. So he may not be the best reference to quote on this particular subject!
FFF
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