MD80 NLG Vibrations 1

[formentera27]

As some of you know, the MD80 has the generic problem of NLG vibrations during T/O. This sometimes translates into aborted T/O. From my experience, this generic problem could be due to many factors....wheel balancing,type of tyre (new or rethread), difference in wear between both wheels, defective bearings, nlg excessive play(between links).
What do you guys think according to your experience?
Any new suggestions?
Thanks and take care you all.

 

[av8rbpm]

At my carrier, we had this same problem. We implemented a policy that drove Mx to always change nose wheels as a set. The other big thing to watch for is that the mechanics are servicing the NLG strut properly, and not just adding more nitrogen every time it gets low.

 

[sam9]

Another area worth considering is the steering system. A very small amount of trapped air in the hydraulic system is sufficient to significantly change the steering damping characteristics - leading to the problems described.

 

[ABXLiaison]

The policy at our airline is not to intermix the bridgestone and goodyear tires. There is a circumferential size difference that causes the aircraft to pull to one side. We also have reported vibrations that may be due to this.

 

[davidjh]

If the NG tires sit for any hours they will "take a set", then as the airplane taxis the "set" on one will move away (rotate) away from the other setting up a good vibr. On the flight program I was involved with, we would jack the NG just enough to reduce the load. We had unusual situatiopn in that we loaded the airplane the night before a flight and thus had long set times.

 

[graemew]

Nosewheel tyre flat spots and LH to RH differences get my vote as the most significant driver of shimmy but usually in association with higher than acceptable NLG torsional free-play.
Experience on F28, BAE146, and B737 has led me to believe that the limits set by the OEM are often initially a stab in the dark based upon history upon other programs (it is certainly the case with the 737).
As a NLG becomes worn, the trigger threshold for shimmy initiation lowers but the damping of the tyres and the shimmy damper will mask this somewhat until a tyre imbalance occurs.
Consider the NLG to have a tyre imbalance margin that is eroded by an increase in NLG torsional free-play and a reduction in shimmy damper condition.
Rectifying any of the factors will have a beneficial effect. The trick for an airline is to select the best overall strategy that will minimize overall cost and pilot reports.
At one airline I worked with, I implemented a strategy of scheduled mid-life torque-link changes (a relatively quick job ) to get new bushings installed and reduce the torsional free-play. It was effective, and cheaper for them than playing clever tricks with tyres (and suffering delays on-line ).
Best of luck.