Originally Posted by JamesT73J;[url=tel:11882801
11882801[/url]]Juan Brown has picked up the VHA angle:
https://youtu.be/z7A7j253jT0
Something I need a bit of education about. I understand the 2/rpm bounce from aerodynamic loads on a 2-bladed rotor, There's some reference to the accident aircraft exhibiting tail wag at ground idle. I'm a little confused about the dynamics here; there's no aerodynamic load, is this just balance of a rotating mass? How would composite blades exacerbate this, compared to the OEM aluminium honeycomb blades?
The tail wag on the ground is due to an RPM-dependent lateral imbalance caused by uneven fore-aft positioning of the blades, called Sweep. Incorrect sweep can be canceled out by lateral balance weights on the hub/in the blade pins, but they’re not effective until you are at 100% rpm (which is also what you balance the rotor for). Sweep can be tough to set properly when setting up a rotor head without the proper fixture, and I’ve met many a mechanic that doesn’t believe in adjusting sweep during rotor smoothing.
Van Horn has stated in their IL that incorrect sweep of the blades can exasperate the in-flight vertical hop occurrence rate/severity.