Originally Posted by
Flap40
There isn't one. An Aeroplane, or Airplane for those on the other side of the pond, is an Aircraft as is a balloon, airship and glider (and if you believe our CAA, as is a hovercraft).
In my younger days we were taught that "aircraft" referred to anything, aerostat or aerodyne, that moved through the air and aeroplane referred to aerodynes only. As they say these days, the clue is in the name - and "plane" is a term for "wing" as in mainplane, tailplane etc.
Not sure what the US usage implies