Happy Thanksgiving ! !! I ' m most grateful for Giovanni ' s <| sep |> I really like the Autumn leaf sticker on the right <| sep |> I didn ' t watch the video closely , but helicopter blades absolutely flap up and down as they go around to maintain lift symmetry during forward flight , and yes , this flap motion is extremely fast . Feather adjusts the individual blades ' pitch angle , and flap essentially addssubtracts angle of attack in the retreatingadvancing portions of blade motion . Actually , I ' m pretty sure flap is the larger contributor to lift symmetry than feather . It ' s certainly more safetycritical anyway , so in my line of work I focused way more on flap angle . Source former flight test instrumentation engineer for attack helicopters