Called a phugoid, test of aircraft stability in longitudinal axis, I have carried out this test on various aircraft. Similar to what you are seeing with T foils I guess.
http://en.wikipedia.org/wiki/Phugoid When it occurs, it's a pure nuisance mode, and in lighter aeroplanes (typically showing a shorter period) it can be a cause of pilot-induced oscillation
When skipper-induced oscillation occurs on our boat it is of particular nuisance to my crew! <img src="http://www.catsailor.com/forums/images/graemlins/smirk.gif" alt="" /> <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />
