OH NO, HERE WE GO AGAIN.
You may remember me shooting my mouth off disagreeing with Frank Robinson when he said he had considered a 90-degree pitch horn on the R-22 rotorhead.
(See link below.)
I responded that if the pitch horn reached beyond the cone hinge there would be problems related to controllability. It has been brought to my attention that on the R-44 the pitch horn extends beyond the cone hinge by approximately 28mm and this got me thinking. What effect does this have on delta-3 pitch coupling and blade flap?
When the blade flaps on the teeter hinge the up flapping blade would have a pitch decrease and the down flapping blade would have a pitch increase, which is what you would expect. However the blade is capable of flapping on the cone hinges and herein lies a problem.
On the R-44 if the helicopter enters into a loss of control situation and
there are extreme changes in blade position relative to the cone hinges the
pitch changes due to delta-3 will be exacerbated. You would expect that
when a blade flaps up the pitch will decrease due to delta-3 but in this
case it will increase increasing the upward flap. Conversely if the blade
flaps down the pitch decrease will also be exacerbated causing the blade to
flap downward even further. In a loss of control situation this would help speed up the process resulting in rotor incursion, mast bumping and contact with and fracture of the blade tusks.
Here is another example. Let's say the pilot at startup increases blade pitch to say 10+ degrees in order to hover. The blades cone up and in doing so increase the pitch to 12+degrees causing the helicopter to rise. What does the pilot do?
Please tell me I am wrong. Explaining why I am wrong with technical statements and not vitriol.
Original thread is here.
See response by Frank Robinson posted 30th November 2000.
Heliport