HH-60G tail rotor 3° bias degradation
 

Greetings! Question for the engineers: what would cause a 3 degree bias to go out over time? Main rotor rig is in check, tail rotor rig is in check, all pins slip fit, cable tension is fine, but the bias when checked is out by between half and a full degree around the whole tail rotor. And yes, it was rigged and biased correctly the first time. The time frame I speak of its just over a year. Thanks!

Tried sending a PM with a thought, but you have that option shut down.

@Pavehawk: I am reaching back into a few decades ago of Navair manuals and doing maintenance on Seahawks (IIRC, the bias is the same on Pavehawk, but maybe not) but can't the bias be reset/re-established by a procedure in the TM/TO at the unit level? (What we used to call O level maintenance).

@JohnDixson: I tried finding the PM settings under my profile but was unable to locate anything with regards to that. I enabled receive emails from administrators but I'm not sure that was the correct option. If you can direct me to the appropriate option editor I would greatly appreciate it.

@Lonewolf_50: yes the bias is set with TO procedures we have within rigging the flight controls, which i have since done, but my question was regarding how the bias could degrade over time with both main and tail rotor rigging still in check. The bias is set with hard pitch control links (elastomeric rod ends) so if cable tension or rig is not out, what would cause that?





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Senior Pilot

99 times out of 100, it was set improperly the first time. Usually by setting the protractor on the wrong part of the blade or retention plate while setting the bias, or with a protractor thats got a less than optimal battery - or a straight bad protractor. Also, the procedure is consistently being rewritten on the Army side (which I'm sure gets transferred over to the Pave side) and gets quite confusing at times, even for experienced mechs. Hence the QA call for verifying the bias angles. We always used a second protractor to verify blade angles at that point and found some pretty interesting results some times.

Would still check clamp up and for broken TRB spars as the movement of the paddles in the retention plates can cause an altering of the blade angles. If it's just one paddle that is off, it could be a migrating spar plug - though usually this is found by an uncorrectable TR vibe level.

Mike

Star Shifted
 

Many years ago we investigated a mishap where a reduction in tail rotor authority was the result of a tail rotor star assembly that shifted due to improper torque. A small shift could in the star would effect TR pitch at its limits.

Solution
 

Thank you to everyone for your responses. After rigging was checked, torques checked and verified, I have come to the conclusion that the initial bias was set incorrectly by taking measurements over the pivot bearing cover and not the blade cuff forward of the bolts. I asked various mechanics how they have taken measurements in the past and most of them have admitted to taking them incorrectly. Corrective training was implemented and the bird has been flying beautifully with ips levels well below goal. Thanks again!