Sovietjet From Bulgaria, joined Mar 2003, 2577 posts, RR: 17 Posted (8 years 7 months 3 weeks 2 days 21 hours ago) and read 1515 times:
I have noticed something about this Mi-8 helicopter(as wel las a couple of others). This Mi-8 LZ-CAE has these sorta brown small round-looking things attached to the top of the propeller blades. There's five total following the pattern of the blades. However, in a previous picture it doesn't have them. What are they and why were they added? Some sort of balance weights or floating devices?
Airgypsy From United States of America, joined Nov 1999, 130 posts, RR: 2
Reply 2, posted (8 years 7 months 3 weeks 1 day 2 hours ago) and read 1428 times:
Those weights seem to be part of the rotor pitch change mechanism. Loss of a connection could be catastrophic but a flyweight could provide a very good safety by commanding the blade to a safe pitch. (Dassault Falcons have springs that neutralize control surfaces if they get disconnected from the control rod.) Could just provide some pitch input dampening to improve handling. If they have a website, don't be bashful.
AeroWeanie From United States of America, joined Dec 2004, 1607 posts, RR: 52
Reply 4, posted (8 years 7 months 3 weeks 6 hours ago) and read 1377 times:
The things you see are called bifilars. They are weights on short arms that are free to move in two axes. The weights move to cancel out vibrations emanating from the rotor system. Sikorsky pioneered the use of bifilars, but they actually date back to radial piston engines - they were used on crankshafts to dampen vibrations. One of the Sikorsky dynamicis engineers who was a key player in developing the concept was Bill Paul, who later served as President of Sikorsky for a short period in the 1980s.
Bifilars were retrofitted to some S-61s and were designed into the UH-60/SH-60, S-76 (the S-76 has a double stack) and S-92: