delta3
Helisphere
I would like to add to the previous posts
- the "positive delta 3" reduces indeed flapping. This can be understood by the geometry and feedback logic. I also can refer to the graphs I posted on the delta3 of the main rotor of the R44-I (quite a while ago) which confirm this when effectively running the math in a simulator
- the way delta3's are rigged however create secondary effects : they introduce cyclic offsets. Of course the tail rotor has no cyclic steering so why bother about cyclic offsets? A tail rotor will also have not a lot of coning in order to avoid blow backs.
One line of thinking could be as suggested, to create such an offset that the max flap happens aways from the boom. I have to agree that using a destabilizing feedback to achieve this kind of puzzles me. I have asked the details of the 407 TR, and will look at it later this week.
B540
I am not fully following your logic. From a resonance stand point rotors are considered resonant, this is why they listen so fast to control inputs. Where aero forces primarily act at the base frequency, this is not the only one. A coned rotor has a strong second aerodynamic harmonic in forward flight. (note : asymmetries for instance in the blades provoke still other highers harmonics) Looking at a simple second order resonant system dampening will change the resonant frequency, but in the case of a rotor this will always be the base frequency I think, so I think we only have to look at dampening here.
d3