The act of making a "raspberry"
sound with one's mouth, while it is between a pair of
labia. The vaginal equivalent of the "
motorboat".
"Her baloney flaps were so
large, I couldn't help planting my face in there and doin' the twatcopter." or "It's a lot harder to pull off a resonant twatcopter if she's
got a 70's
porno bush."