Helicopter Maintenance Blog*
Posted 3 years 166 days ago ago by Scott Skola
A lot of flying going on in California last month covering the fires. While I never directly worked in that type of ops, I have seen them in action during the day and the mechanics during the night. A sight to see.
Plus there are a number of videos out there. Here’s one:
Also noticed that HAI has gone through a makeover. While I’m no longer a member since I retired, for those of you who are looking to expand their helicopter career, outside just turning wrenches, being a member to HAI can have its benefits. Especially on the networking side. It’s not for everyone, but check it out one day: www.rotor.org
And finally in the history corner: Operation Kingpin
TIPS and TRICKS:
As mentioned in October, this month’s tips will be on balancing the oil cooler blower shaft.
This is directed to those 407s modified with blower balance plates and using RADS. I know, most people don’t like RADS. But I do. It’s one of the few balance systems that can be field customized and compute multiple move solutions. So I’ve thrown in a few RADS tricks below.
Also if you have a flywheel adapter or air conditioning installed, a different setup or RADS software may need to be used.
The number one tip, ensure you follow the OEM procedures to the letter. Especially when viewing the blower and indexing/numbering the balance wheels. When the book states: “view looking aft” or “view looking forward,” do not confuse the two (see figure). Otherwise your aircraft will not match the RADS software indexes. Do that once and you’ll never forget it.
If there are multiple existing indexes on the balance wheels or shafts remove them and apply your own. Also check the wheel’s four weight studs (item 1). Only two should have weight with the other two having a nominal stack-up. If more than two have weight, remove the lesser stack and subtract that same weight from the opposite stud. Now’s the time to do this, not afterwards.
Another quick check: verify the T/R D/S mount flanges are properly orientated at 90 degrees to each other from the engine to the T/R gearbox. As with adjusting the weights above, correcting these items prior to balancing reduces your future workload.
With the RADS installed and powered up, here are several more tips. RADS is simply a very basic computer. Think Windows 3.1 or DOS 6. So it has a tendency to get full quick. Prior to use, delete any previous balance data if possible. Also, performing a hard reboot of the CADU prior to use can usually speed things up. FYI: a soft reboot can be used during balancing if things lock up or run slowly.
Two more quirks with RADS: it doesn’t technically “correct the clock” after the first run like you did with an old Chadwick 177. Plus, all balance solutions try to achieve a perfect balance of 0 IPS.
And a third sometimes quirk, RADS can be “insensitive” to weight amounts and their respective move lines. For example, if RADS calls for a 2 gram weight addition on stud #1 but the actual move line extends through the balance center axis, remove half of the original weight (1 gram) and run balance again. If the reduced weight gives the desired move then use half weights for all subsequent runs until complete. Sometimes it’s quarter weights or in rare occasions could be double weights.
If having trouble “seeing the move lines” scroll through the CADU screens to find the IPS reading and clock angle. Or, make your own polar chart and physically plot the IPS, clock angles, and move lines on it.
Another tip, put together a balance weight kit. Simply putting a supply of recommended balance washers by P/N in separate bottles can speed up the balancing process. If on the other hand, you are in a situation where the recommended washers are in short supply, other type washers could be used provided you weigh each washer prior to installation. It’s the total weight that is important not the number of washers. However, there still are stated OEM maximum limits on balance weights/washers per stud.
A final tip. It is very important to follow the first two solutions provided by RADS. Most balance equipment needs three runs to work: 1st run gives initial clock/IPS; 2nd run verifies 1st run data; 3rd run is the first attempt at a balance solution by the software. With practice, you can cut this learning curve a bit. But until then, follow the first three runs and then look for weight sensitivities, plot move lines, etc.
A couple FAA SAIBs on dye penetrant inspection and tailboom attach structure failure.
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.