To: Helo Teacher
Point 1) What you stated about the rigging of a helicopter to counter translating tendency is correct. On some helicopters this is built into the mixing unit so that when the pilot pulls collective there is a left bias on the swashplate causing the disc to tip left. On others, the pilot must move the cyclic left to counter the movement of the helicopter. On the Robinson however the Helicopter has a 2-degree left bias on the mast to do the same thing. When the Robbie is rigged, the helicopter is leveled so that the rotorhead is level and the helicopter is leaning 2-degrees to the right. In this position the swashplate is adjusted to conform to a specific setting which in effect makes it parallel to the disc when it is rotating. In this condition the cyclic is placed slightly right of center of the longitudinal centerline of the aircraft. The control linkages are adjusted to obtain this relationship. In the process of setting blade angles the blades are disposed 18-degrees ahead of the respective axes. On a Bell undergoing the same settings the blades are disposed directly over the respective axes. If a Bell has a phase angle of 90-degrees the blade disc will tilt down over the nose. Assuming the Robinson conforms to the laws of physics the disc will tilt down and to the left when the cyclic is pushed forward from the rigged neutral position.
Point 2) According to the documentation transverse flow effect diminishes after about 20 Knots. But on the other hand if you are correct in you assumption about the 18-degree offset countering the transverse flow effect at speeds higher than 20 knots then my argument goes out the window. However, my source on the transverse flow effect is the FAA Rotorcraft handbook and it says that transverse flow effect stops around 20 Knots.
Point 3) Frank Robinson brought it up in his response on the Robbie certification thread. He said it was the delta 3 effect that caused the rotor disc to tip down over the nose even though it defied the laws of physics, (90-degrees of precession). I said the 18-degree offset would cause the disc to tip left because that is what the laws of precession would dictate. He said the delta 3-hinge effect would cause the disc to tip down over the nose.
Point 4) this was taken from the website of RW-1. I never discussed this phenomenon in my threads nor, was it discussed in my report to the NTSB.
Point 5) regarding the stick plotting board what you say is true. My reference to the plotting board was in reference to the 18-degree offset and what it recorded when the cyclic was pushed forward.
Thanks for responding.
------------------
The Cat