Regarding the two pictures:
On both the Robinson and the Bell the blades are shown in the low pitch or, full down collective. On the Robinson head, the pitch horn attachment to the pitch link is almost coincident with the axis of the flapping hinge. On the Bell the same point is almost coincident with the axis of the teeter hinge.
When the rotor is turning and the blades are in an aerodynamic state , and the pilot pulls in collective the points referenced above are now above the respective axis points. Whenever the pilot introduces cyclic there is in effect a coupling caused by the delta hinge effect. This is common to all helicopters and is called pitch coupling. Because of this coupling the pilot must make a correction in his cyclic stick position. The coupling also tends to restore the individual blade when some external force tries to perturb it from the normal tip path just like the tail rotor.
Regarding your observation of the Robinson rotorhead and the relationship of the pitch horn to the teeter hinge, the pitch horn has to be in this position because if the horn was in line with the teeter hinge the coupling would be so massive as to render the helicopter uncontrollable.
This rotorhead is totally unlike any other rotor head and the rules in your textbooks don't apply. If you read the report I sent to you, you would have seen the reference to the fact that the FAA required special tests in order to certify the design. My question in the report was ," Was this testing done?"
It is my contention that the rotor design and the control rigging procedures are the root cause of the rotor incursion incidents and loss of control incidents.
Go back to your basic aerodynamics and determine if pitch coupling influences phase angle. Then, diagram a Bell rotor system and a Robinson system to see the differences.
Oh yeah, I forgot I sent those diagrams to your email site along with the report.
Talk to your professors and present the problem to them. As I said to you in the email, "don't always believe your text books".
Text books define the problems under ideal conditions and they don't always cover the total picture.
You will find this out when you get your first job. Just like lawyers making new law you will on occasion make new engineering in order to meet design requirements and/or in order to correct a design problem.
Do your text books cover rotor blade design where the blades have a negative twist and a constantly changing camber from the root to the tip or, do they just deal with negative twist and a constant camber. The blade described above was created to overcome a design restriction that limited the rotor span. The design was created by Ray Prouty who is one of the best aerodynamicists. Much to his chagrin, the design was a failure and caused a lot of problems from an aerodynamic standpoint. Two helicopters were lost due to this design. One had the blade hit the fuselage and partially destroy the wind tunnel at the Ames Research Lab. and the other had a blade hit the cockpit due to divergence and killed the pilot. The problems were so severe that they cancelled the program. This was mentioned posts above and, it was the Cheyenne.
The Robinson has the same problem of rotor blade divergence. In fact there have been 32 cases to my knowledge where the rotors hit the fuselage. What do they teach about divergence and what do they teach about how to correct it?
I have stated this in a previous post, " if I am proven wrong like a good dog I will drop this bone and look for another bone".
------------------
The Cat
[This message has been edited by Lu Zuckerman (edited 21 November 2000).]