To: Eurocopter
The reason the pitch horn leads by 72 degrees (approximately) is because the pitch horn can not pass the flapping hinge. On a Bell the pitch horn leads by 90 degrees and there is a small amount of pitch coupling.
That is caused by the fact that under certain pitch settings the pitch horn attachment to the pitch link is not coincedent with the teeter point.
On the Robinson, since the pitch horn is not always coincedent with the flapping hinge, you will get a slight amount of pitch coupling. However, if the pitch horn crossed the flapping hinge the helicopter would be uncontrolable due to massive pitch coupling. That is the explanation for the difference of 18 degrees (approximatly)
I can't say other than what I stated above. Why someone would give the explanation you provided,is either they didn't understand or, they were covering up the truth.
Here is a suggestion to not only Eurocopter but to all of you:
Go on the internet and on the address bar, type in helicopter frontiers-aerodynamics or,
http://www.hfi.ca/training/helo_aero.html
Either one will get you to the right place.
Some of what you see on this site contradicts what I say in my report as the web page is run by a Robinson dealer. I will admit it has a lot of good stuff that can't be contradicted. However, there is one point. When they explain the functions of the rotorhead, and they have some good pictures, especially if you have never seen one. they also describe gyroscopic precession. The illustration of swashplate movement relative to gyroscopic precession is for a Bell rotorhead and not a Robinson rotorhead.
They also have a lot of self serving verbage on the safety of Robinson helicopters. It's interesting reading so check it out.
After checking out the website, come on back and let me know what you think.
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The Cat
[This message has been edited by Lu Zuckerman (edited 10 November 2000).]
[This message has been edited by Lu Zuckerman (edited 11 November 2000).]
[This message has been edited by Lu Zuckerman (edited 11 November 2000).]