To: Grey Area
Thanks for the explanation. Dave Jackson also provided a similar definition via email. Perhaps I should have used the term lead angle as opposed to phase angle as it caused a bit of confusion. What I was describing was the relationship between the direction of movement of the swash plate relative to the longitudinal and lateral axes of the helicopter and the angular lead of the pitch horn relative to the blades. On all helicopters that I am familiar with the swashplate angular deflection and the pitch horn lead add up to 90-degrees. All except the Robinson. I also understand that aerodynamics can play a part relative to actual disc deflection as well as the effect of coupling will have an effect. The certification documents allow for this difference in movement relative to command and they limit it to several degrees all of which can be compensated for by cyclic input.
To: Dave Jackson
What you say about the Robinson head is true but I must add that all helicopters have a delta (hinge) effect as this is the way they compensate for flapping by neutralizing (my word) the flapping through pitch flap coupling. If a blade flaps up the pitch is reduced. If a blade flaps down the pitch is increased. This increase or decrease is caused when the blade flaps up or down and the pitch link / pitch horn connect point is above the coning or flapping axis. I had made this same statement on several occasions and likened it to the tail rotor which has a delta relationship between the flapping axis and the location of the pitch input to the tail rotor blades.
[ 04 December 2001: Message edited by: Lu Zuckerman ]
[ 04 December 2001: Message edited by: Lu Zuckerman ]