I am going to take a really good guess at what "helicopter flapping" is.
Helicopters, when they are overloaded - you see it in war movies where medivac is taking place and the helicopter is in fact, overloaded, and all it can do is get a few feet above the ground. The pilot tries and tries again until finally (only in the movies) does the helicopter take off....just a few feet off the ground, of course.
I could be so seriously wrong with that description, but, hey.....