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ROTORwrench…Tips, Tricks, and Info - November 2018

Posted 4 years 316 days ago ago by Scott Skola

Helicopter Maintenance Blog* 
November 2018

Being a history buff, I run across some unique stuff. Like this one: This past October, 62 years ago, the first Bell Huey flew as the XH-40. 

While the Sikorsky R-4 and the Bell 47 gave the world a viable helicopter, it was the Huey and its performance in Vietnam that gave us the industry we call home. 

Some click bait:


And now… the Lama-Nator is back in the house.

ATA 57 
Main Rotor
Airbus (Sud Aviation)
SA315B Lama/SA316 Alouette III

The previous tip on the aftermarket main rotor blades, the LOMs, prompted me to remember a couple of other experiences with Lama main rotor blades.

And it doesn’t matter whether you have the factory blades or the LOMs on your Lama or Alouette. If you start the engine with one parked over the exhaust, you’ll heat-damage a blade because the blades don’t move during engine start. 

Besides requiring a clutch to engage the rotors after start (due to the single-shaft design of the Artouste engine (no free-turbine)), this is the other major drawback to this type of engine, the pilot can forget to park a blade out front and it will fry one if one’s directly over the exhaust.

First, a word about the factory blades. As mentioned in the previous post, the 11.30 blades were delivered in matched sets (until later part numbers enabled single-blade replacement and finally full interchangeability).  

If you changed the mast, say, and weren’t able to trammel the pitch change links for duplication, you could track the 11.30 matched-set blades with a flag and they would be just fine and dandy. A roll of paper towels duct-taped to a broomstick, and the blades marked with three different colors of grease pencil (preferably red, yellow, and blue). Brought to harmony by PC link adjustments. 

One year, in the early 90s, the manufacturer of the LOMs sent out sets of blades that were not balanced at all. A helicopter could not be run-up with these blades installed due to the extreme imbalance. I’m talking about just a couple of revolutions and the pilot was applying the rotor brake. 

They apologized and said their balance device was defective and was being repaired, and they had sent sets out anyway, just to fill orders, hoping they would be OK. They said to send them back and they’d balance them now that their balancer was operational.  I knew if I sent them in I wouldn’t get them back in time.

I had several Lama old-timers in the Lama shop at that time, the two of them were my mentors. One of them said he could bring those blades to balance enough to get a Chadwick reading. I accepted the challenge. 

He proceeded to put about ten wraps of duct tape around the red blade out at the tip. The following operation highlights a benefit of having a clutch: you can run-up, stop the rotors, make weight changes, repeatedly, without shutting down the engine, until the clutch gets hot, after 4 or 5 runs. 

They engaged the rotor just enough to know whether it was better or worse, then he removed and applied duct tape to other blades until he found the light blade. He then moved to the other two blades, adding and subtracting tape, trial and error, until the helicopter could run-up to RPM and a Chadwick reading acquired. At that point he weighed the duct tape and added that weight to the two blades he identified as requiring weight. Chadwick balance then proceeded and the blades were placed into service.

My employer had two bases of operation at the time, and the other base had chosen to send their two new out of balance LOM blade sets back to the factory for balance. The other base later called me and asked if they could borrow one of my two sets and they’d then give me a set when theirs came back.  

Well, thanks to John McNamara, I was able to honor this request and make everyone happy.

[Submitted by the Lama-Nator*]

* For those who would like to contact the Lama-Nator directly: [email protected]

A couple newsletters: Airbus Apr/May/Jun and Leonardo Spring:



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.