Helicopter Maintenance Blog*
Posted 275 days ago ago by ScottSkola 0 Comments
The next time you run across a pilot who complains about the navigation equipment in his aircraft—right after he enters his coordinates into the panel mounted Garmin 430, the backup windshield RAM mounted Garmin 695, and the backup-backup glare shield mounted I-Phone—ask him what he would have done during the time of the Transcontinental Airway System.
Back in the day, to aid real aviators, the government placed concrete arrows and lighted beacons on the ground to guide US Air Mail pilots along their route. No GPS, RNAV, ADF. Nothing. But a map, a mag compass, and looking out the window. I wonder how the new breed would do…
Now if your pilot flies offshore where surface based concrete arrows were not an option, you can always bring up LORAN C. And before LORAN there was “looking for smoke” and watching the white caps for course corrections. But then again those were also the days of gauge runs requiring 150 takeoffs a day. Glad I stayed on the rig.
TIPS and TRICKS
Airbus (Sud Aviation)
Last month, we had removed the MRH damper in preparation for bleeding. Some say you can bleed a damper on the helicopter, I say not.
Put a strip of tape over the bleed hole on the damper reservoir. Situate the damper in a vise, near vertical with the bleed port at the highest point and the piston extended. Remove the bleed screw and top off with fluid, tapping the sides with plier handles to dislodge any air bubbles clinging to the internal sides.
Re-install the bleed screw, and cycle the piston 2 or 3 times. Remove the bleed screw again and check the level. When it stays up after cycling the piston, it is good to go. The bleed screw has a crush seal too and you’ll see it bubble if it’s leaking.
With all dampers installed, the next check on the MRH is the sleeves (grips) for grease inside. Tap the bottom of each sleeve with a quarter and note the result. A ringing sound indicates an empty sleeve. A dull or muted sound means grease has passed the sleeve seal at the pitch change bearings and is collected in the sleeve inside.
Take the sleeve apart that fails the tap test, clean it out, and inspect the seal. Sometimes the seal passes some congealed grease and/or separated oil (usually from sitting idle for months) but is otherwise okay. If so, put it together and try it.
Or, you may see that the sleeve seal is obviously distorted, however, you don’t have a new seal and the tools available. Now you have a quandary. Do you put it back together and refrain from greasing this sleeve, knowing it’ll just end up inside the sleeve and imbalance your main rotor?
Most make the mistake of not greasing this sleeve’s pitch change bearings until they can get the problem fixed, but by then you’ll likely trash the bearings and/or spindle. Which is very expensive. You should continue to give that sleeve the same number of pumps it takes to purge the other sleeves, thus running some grease through the bearings.
Ideally, you should remove and empty the grease from the sleeve with the bad seal every night or so, to preserve main rotor balance. Alternatively you can wait until the balance is objectionable, then empty the grease from the sleeve. But after you’ve taken one apart, you’ll want to change the seal next time.
If you starve a sleeve pitch change bearing of grease for an extended period, you can cause tens of thousands of dollars damage to the MRH. And if you run that helicopter with an imbalance for an extended period, who knows what other damage you’ll do, in addition to increasing the susceptibility to ground resonance. Always check the balance of the M/R after emptying/replacing the seal in a sleeve.
If your Lama has the old 11.30 factory MR blades, they are matched sets and can be tracked with a flag while light on the skids and everything will be hunky-dory. Many operators mixed blades from 11.30 sets, but until digital track and balance equipment was available, these Lamas flew noticeably worse.
The later 11.40 blades could be changed one at a time with better results. The LOM composite blades often require some attention, but today’s technology such as the DSS will allow you to get them flying together in harmony with chord-wise balance and tab adjustments as well as span-wise balance.
Don’t buy into the notion that it’s “just a Lama” with intrinsic vibratory issues. If you take your time, you can make that Lama as smooth as a car ride. Like a Peugeot. [Submitted by Lama-Nator]
The Airbus Rotor-Journal Volume 106:
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: firstname.lastname@example.org
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.
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