Helicopter Maintenance Blog*
Posted 2 years 309 days ago ago by Scott Skola
A quick reminder: I’m still chasing salmon and beer in Alaska. Will get to your emails when I get back.
For all you drone enthusiasts out there, there have been a few changes to the recreational side rules. While personally I haven’t been bitten by that bug yet, it will be interesting whether there will be a FAA regimented maintenance side to the equation as these drones grow in size. Time will tell.
Also ran across an interesting article as I was putting to together this month’s blog. Takes place in 1993 Somalia and is about a US Army mission with several “secret” helicopters.
In the history corner:
And off we go…
TIPS and TRICKS:
Got a leftover tip on the rotor-brake system from last month’s blog.
While there are several methods to bleed the 407 rotor-brake system, most mechanics seem to prefer using a pressurized back-bleed tool, where you push hydraulic fluid from the rotor-brake fluid reservoir back to the caliper bleed screws.
I prefer to use the rotor-brake master cylinder as it is always available and is never back at the main shop getting repaired as most back-bleed tools seem to always be located.
Once the rotor-brake is installed and serviced, pump the master cylinder handle with rapid, short strokes, but never allowing the brake handle to “over-cam” to the full-on position. This is key. As the handle transitions to the full-on position, the internal fluid pressure head momentarily reduces and in most cases the hydraulic fluid will actually suck back toward the reservoir--dragging any trapped air back along as well.
When you start to feel resistance in the brake handle, give a heads up to your helper to get ready. As you initiate the next pump stroke, yell “open” which signals your helper to crack open the aft upper bleed screw on the R/H side caliper. Without reducing pressure on the handle, slowly pull the brake handle toward the full-on position. You’ll feel the handle resistance lessen as the fluid/air flows out the bleed screw.
Prior to the brake handle hitting the full-on “cam-over” point, yell “close,” signaling the helper to close the bleed screw. Remember, never put the handle into full-on position during the bleed procedure.
If the system has excessive air, it may take several attempts initially to get fluid squirting out the first bleed screw. Be sure to always check your reservoir level in between each bleed cycle. A hand powered oil can or squirt bottle with hydraulic fluid works great to service the rotor-brake reservoir.
Once you are showing no air escaping at the R/H caliper aft bleed screw, move over to the forward bleed screw on the same caliper. By now you should feel resistance through the entire handle stroke short of the full-on position. With no air at the R/H forward screw move over the L/H caliper, starting with the aft bleed screw then moving to the forward screw.
After bleeding the system, the rotor-brake handle should be “tight” to actuate. Matter of fact, after moving the handle from the full-on position toward the closed position, the handle should snap back with some force into the closed detent.
It takes a bit of practice, especially to not move the brake handle into the full-on position during bleeding. But after several aircraft you should be able to bleed a system rather quickly.
A couple side tips. When installing rotor-brake brake calipers ensure the bleeder screws are installed on the top ports of caliper housings. And if you want to limit your mess during the bleeding process, take an AN3-7A bolt, cut the head off, and drill the center of the shank out with a #30 drill bit. Stick one end into some clear tubing then screw the “bleeder tube” into the caliper bleed screw and capture the fluid in a cup.
Some more FAA InFOs: ELT False Alerts and portable Fire Extinguisher Maintenance.
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.