Expert: Mark Janus - 7/9/2006

Question
I am confused by the explanation of the term flapping, as regards the stabilising effect this has on a rotory wing. With the processive rotor exerting more lift causing downward pressure on the recessive, does this cause a pitch change or an angle of attack variation from one side to the other. What confuses me is that in flight the rotor disc assumes a positive angle of attack at the leading edge and what appears to me to be negative at the retreating?     Cliff.  

Answer
I was tempted to respond that this is outside my expertise...but I'd like to give some response...  I'm not very familiar with rotary wing dynamics.... but a pitch change is a change in angle of attack....  a flapping wing generally means the wing is translating vertically pivoting about the hinge point (the root)....pitch oscillations are another thing ...  both will cause changes in local angle of attack (AoA)  flapping has bigger changes at the tip than at the root, and pitch oscillations generally would cause AoA uniformly from root to tip....

also, everything must be viewed from the blade relative frame of reference to determine the AoA

best that I can do...  :)
mj