Damage to gyro instruments

[yellowbird135]

Hello to all,

Section 9 (Towing) of the AMM contains the following:

CAUTION
TO AVOID DAMAGE TO ANY GYRO INSTRUMENTS DO NOT MOVE HELICOPTER ABRUPTLY FOR 10 MINUTES AFTER SWITCHING OFF THE BATTERY OR EXTERNAL POWER SUPPLY.

I know that the OEM is allways right, so follow up on this instruction, but I keep wondering; considering the run down time of a gyroscope, what are the additional stresses to the instruments when you move the machine within, let's say, 5 minutes after power down.
Is anyone aware of some general guideline about this topic?

[RWJackOfAllTrades]

From previous experience with several different employers over the years, the general rule of thumb I have come to use is to let the machine run down for 15-20 minutes before moving it FULLSTOP!!!, or simply switch the master switch back on and allow the instruments adequate time to run up before moving. A few pilots I have worked with in the past have also shut down the machine and left the master and strobe light on (good reminder that battery is still on) and move the machine once the blades have stopped turning, but the instrument gyros are still spinning at operating RPM.

[Helinut]

It pops up as a problem in various types. If you think about what is happening, then you need to wait until the gyros have stopped to make sure. It will take more than one case of moving it to break the thing - presumably it causes acclerated wear in the bearings.

[yellowbird135]

I really think I remember :ugh: that as long as the gyro has at least something like 75% of nominal revs, excessive precession forces to the cardanic ring bearings and gyroscope body bearings are not really an issue in additional wear to the thing.
Back in the old days (late eighties) in the Air Force as a -16 crew chief, I remember the machine being shut down in front of those shelters, attach the winch ropes to the main gear, and a bar to the nose gear, then winching the aircraft tail first into the shelter. (That took a couple of minutes to achieve) I'm sure that they were still equipped with conventional gyroplatforms instead of them ring state laser ones. It could well be possible that the Master switch remained on until fully parked, I don't remember that well:\ )

[MightyGem]

Would this apply to FOGs as well?