Helicopter Maintenance Blog*
Posted 4 years 268 days ago ago by Scott Skola
Well, I hope this New Year brings a much needed uplift to the helicopter industry. It’s definitely been a rough ride. With a stabilizing oil price and the potential of a better business climate ahead, I wish them the best of luck.
One programing note: updated the blog email below.
As I mentioned last month, we will be focusing on SA315B Lama tips and tricks. But first, a note from our sponsor: the Lama is technically an Alouette III. Believe it or not!
Look for a future tip on the commonality of the Alouette/Lama family.
So whether you call it a Lama, or a Wyoming Sky Tractor, I think we’re in for a helluva ride this year. That is… if reading about a couple old guys talk about turning wrenches on old helicopters is your thing.
And now… The Lama-Nator!
TIPS and TRICKS
Airbus (Sud Aviation)
Our first Lama tip for 2017 is on the sometimes fickle T/R pitch change bearings. Although referred to by the manufacturer as a “battery of angular contact bearings”--because it consists of three full inner and outer race ball bearings stacked on top one another--they are commonly referred to as the stack bearings (#3).
The oscillation of T/R pedal inputs over time wears the bearing races in the area that the balls travel back and forth during the common pitch change range required for external load operations. The pilot may mention the pedals are “starting to notch” a little, or that it takes additional force to push past a resistance in the tail rotor control system, which on the Lama is not boosted. Regardless, the situation deteriorates from a PITA to the helicopter being unable to conduct normal safe operations.
The longevity of the stack bearings in service is maximized by frequent greasing, keeping the tail rotor under .2 IPS, and what is called “rotating the stacks.”
To rotate the stacks: every 25 hours (or sooner if desired or required) disconnect the T/R P/C links (#1) and while pulling down on the bearing housing (to simulate centrifugal force) rotate it three or four times. If there is a notch in one or more of the bearings, you will feel it, if not, this procedure at least changes the location of the balls relative to the bearing race.
Again rotate the housing while greasing the stack bearing zerk fitting (#7) to get full grease coverage and force out stiff or congealed grease that accumulates between the balls. At the same time, swap the pitch change links end-for-end. This will increase their life since the inboard PC link bearing wears much faster than the outboard.
By this regular rotation of the bearings, a good Lama mechanic can feel the wear or notch in a stack bearing before the pilot sometimes. The notch is a dent in the races that the balls settle into.
A worn stack bearing will quickly notch the other two in the set on one blade, and subsequently the remaining stacks. Rotating the stacks can relieve lightly notched bearings for a time, but since the notch is a low area on the race the balls will settle in the notch again after a few hours of flight.
The main cause of premature wear in the bearings, besides tail rotor imbalance and worn PC links, is insufficient lubrication or a grease leak. It is imperative to maintain both the stack bearing lip seal and the blade cuff Teflon gasket. Loss of grease robs the bearings of lubrication, plus causes an imbalance in weight among the three blades.
The stacks should be greased every time the Lama shuts down. Keep a “fly kit” onboard the aircraft so the pilot can grease them when shutting down away from the mechanic.
By keeping the tail rotor head and blades immaculate, frequently greased, well-maintained, and well-balanced, a mechanic will enjoy improved stack bearing life, a happy pilot, and more free time. [Submitted by Lama-Nator]
We’ll start the year off with one Airbus Journal and one AgustWestland newsletter:
SUBMITTING MAINTENANCE TIPS/TRICKS/QUESTIONS/INFO:
Have an old tip or trick you’d like to share with your fellow mechanics? Or maybe a question that you can’t seem to find an answer to? Or just some info to pass on? Send an email to: [email protected]
About the author: After 32 years maintaining helicopters in various capacities, Scott concluded a full time career with a major operator in 2014. When not pursuing future writing projects, he can still be seen around the flight line tinkering on aircraft for beer money.
*To keep the hounds at bay, the information contained in this blog is for discussion purposes only.