...you get a bit of a nodding dog effect as it disrupts the flow over the elevators.
In my younger, and more adventurous days I found the effect varied from one aircraft/model to another. Some didn't show any unusual effects, some just did the 'nodding dog' thing to a varying degree, but the one that 'impressed' me most, suddenly pitched down and took 200-300 feet to recover.
Although the 40 flap setting had it's uses, I was, on balance, glad when they reduced it to 30.
MJ
