Helicopter Maintenance Blog*
Posted 186 days ago ago by ScottSkola 0 Comments
Well, thankfully, it appears not all helicopter legacy airframes are headed for pasture. Two tried and true models just celebrated their 50th birthday since first flight.
The brick-shithouse MBB BO-105 made 50 on February 16, 1967 and the Sud Aviation SA.341 Gazelle, sleek cousin to our featured Lama, hits the big 5-0 on April 17, 1967. Both models now fly under the Airbus logo, but suffice to say these aircraft made the industry what it is today.
The original Gazelle prototype, SA.340, had a conventional T/R set-up. But it was soon replaced with the first ever fenestron. Some may not know, but under its Hollywood make-up in Blue Thunder was in fact a Gazelle.
As for the BO-105, I have a soft spot for it. I cut some of my mechanic teeth on a CB-2, along with a few fingers on those beloved firewalls. Not to mention losing a few hydraulic pack microswitch springs, getting drenched by a stuck main transmission chip plug check-valve, and wondering who the *bleep* invented those sealing “donuts” in the fuel cells.
Some didn’t care for the Bolkow, but I stayed close as it was stretched and upgraded until the CBS-5. Even turned a wrench or two on the LS version. The best part, it was one of the few airframes out there, in my opinion, that was either broke or was flying. No gray areas.
Ahhh… the memories.
And now some more memories.
TIPS and TRICKS
Airbus (Sud Aviation)
The maintenance of the Lama is largely a bag of tips and tricks. We’re going to go around the Lama as if we’re performing a daily inspection and talk about the tips and tricks associated with the prime items. Of course take a fuel sample before disturbing the aircraft.
We’ll start with the tail rotor driveshaft (T/R D/S) hanger bearings: plain Oilite sleeves in housings that take 10W machine oil. Originally, the manufacturer supplied a hand pump with a nipple and a corresponding concave fitting on each hanger bearing assembly. With this tool, called a “pussy pump” after the French “pompe puissance”, you could dispense more oil on yourself and the surrounding areas than into the bearings. In the US, operators went to a lever type grease gun sealed at the butt end that dispenses oil when inverted and installed grease zerks. This method purges the bearings under pressure and with less mess.
Tuck a paper towel under each hanger bearing. As you apply oil to each hanger bearing, watch for the oil to show clean, plus check that the two rubber seals on the housing are contacting the polished surface of the T/R D/S hanger bearing journal.
If one seal is “pooched” out and not contacting the journal, it indicates the plain bearing has migrated in the housing and is sticking out one end, pushing the seal lip out. This hanger bearing will not hold oil.
First, increase the frequency of oiling that bearing to keep it lubricated and cool. Continue this treatment until you can schedule removal of the T/R G/B and end coupling in order to slide off and replace that hanger bearing assembly, or to press the bearing back into place. Sorry, no in-place trick for this fix. Insufficient oil causing the bearing to run hot is the reason for this and you’ll find that it is almost always the middle hanger bearing due to the engine exhaust heat.
Here’s a tip for the T/R D/S. Carry a spare coupling o-ring on the forward seal of the #1 hanger bearing and the rear seal of the #5 hanger bearing. This will allow replacement a defective o-ring in the forward or aft T/R D/S coupling without removing the T/R G/B and ensures you will always have a spare available.
On the daily lubrication of the helicopter, you should pump all required zerks with grease till it shows somewhere. Where it shows matters, so pay attention to that for each zerk. Of course, inability to apply grease to a zerk means it’s plugged up or the item it lubricates is blocked. This condition must be remedied immediately. On the Main Rotor Head Drag Damper, there are several points where a bushing can shift and block the grease.
Count the pumps it takes to grease each zerk. This will tell you when there is a potential problem by comparing what it takes each day over time. Every 25 hours you purge lubricate, which means you grease the item till it shows grease, then keep pumping till the grease comes out clean.
The most overlooked lubrication point is the upper rod ends of the vertical flight control tubes (C5, C6, and C7) at the stationary star. These are a daily requirement. And don’t forget the scissors bearings get the same every 200 hours, so hit these with the acid brush you’re using to clean up after yourself.
The most neglected grease zerk on the lube chart is the lower mixing unit crank arm (irreversibility link) a.k.a. the disc rod. It needs to be purged daily to get gritty grease out from between the disc and the side plates.
[Submitted by Lama-Nator]
A couple FAA InFOs for your reading pleasure.
1) Electronic signatures, recordkeeping, and manuals:
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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