Posted 4 years 13 days ago ago by Scott Skola
Helicopter Maintenance Blog*
As it seems I always have extra time on my hands since retiring, I tend to spend more time than I care to admit surfing the internet for interesting aviation stories. Here’s a couple.
The first is of an antenna replacement in Atlanta. Having worked in and around external lift ops at times, I’m still in awe of a good long-line crew. And this crew doesn’t disappoint.
The second video I ran across is an older movie conversion of the birth of Bell Helicopters. While not as old as Sikorsky, it still makes for an entertaining view.
In the history corner:
TIPS and TRICKS:
We left off last month with completing the ground (initial) M/R track and balance with RADS. Now we move onto flight.
And the same general tips we used during the ground work apply to flight as well.
In most cases, with the aircraft ready/legal to fly, once the RADS gives you the okay on the ground readings you’ll continue on and hit the “hover” button. However, here’s a few more tips for flight work.
To keep things on an even keel, maintain a fairly consistent aircraft weight by keeping extra onboard personnel to a minimum and refuel as needed during the flight track and balance process. There’s no need to be A-retentive about it, but keeping the fuel load within a normal operating range and no joy-riders will help in the process.
And just as we torque-checked the M/R mast nut after the first ground run, torque-check it again after the first flight. But don’t forget you still have a required “after-maintenance” torque check due within one to five flight hours.
The RADS flight process will take you through various conditions from a hover through a number of specific airspeeds and finish with a letdown reading. In a perfect world, RADS will allow you complete all flight levels. However, in the real world, it may take a little reading between the lines.
The biggest difference between these worlds is if your flying an aircraft with all new elastomerics from the transmission deck up and a matched set of blades versus an in service aircraft with elastomerics of various ages/condition and unmatched M/R blades. It is what it is, but not necessarily a dead end.
This is where having a basic understanding of track and balance comes into its own. And just as we learned during the ground RADS process: vertical vibrations are track; lateral vibs are hub weight; plot move lines on a paper chart; and, use the RADS recompute and view predictable options when cycling between solutions. You either got it or you don’t. Just never give up until you do!
One tip in the hover regime is to tell the pilot to nose the aircraft into the wind and don’t fight the aircraft to hover over the same point. Each control input changes how RADS records the readings. Allow the aircraft to drift a bit with minimal control inputs. But just be sure you have the room to do that without running into something.
With the hover recorded, get to the next level and hit the button. And so on. But all the while don’t turn of your built-in senses that you can see with your eyes (blade track) or feel with your butt (vibration).
If it’s obvious you’re fighting a blade out of track, turn off the hub weight (lateral) readings and recompute for just vertical adjustments (PC link or tab). Hit “view predictables” to see where RADS thinks it will go. Verify that on your paper chart. Can you see the method from the madness now?
Okay, so now you’ve made it through several flights and everything is within limits…except the letdown readings are out of limits and any attempt to correct the letdown causes one or more of the other regimes to go out of limits. Now what?
My tip, it’s more important to have the best vibration levels where the aircraft flies the most. If after looking over the aircraft per the MM vibration troubleshooting chart and if all looks good then you may just have to live with a rough letdown. Especially on an in-service aircraft with tired rubbers.
So there you have it, RADS 101. Just remember, RADS is always lying to you and it’s your job to find out where and why. Good luck!
A couple 2019 Airbus newsletters:
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.