Spins and avionics

[FenderManDan]

Hi,

Would doing the spins affect older instruments and compass adversely, given they are all fully functional?

[cgzro]

Yes- and the G on recovery is not helpful either.
Many expensive aerobatic planes like Extras have quick removable gyro packages.

[PilotDAR]

FWIW, I've looped and rolled my 150 regularly for 25 years, and never had a problem with the gyros which I can attribute to the aerobatics. It's not great for them, but I don't see a problem of consequence either. The C 150 Aerobat I used to fly had a full panel of what seemed to be the regular gyros, and never a problem.

[photofly]

The OP said compass... nobody is talking about the whisky compass here, right?

[GyvAir]

By compass, I took him to mean the directional gyro, although aerobatics probably don't extend the life of the whisky compass any either.

I've heard two schools of thought about caging or not caging while performing aerobatics. Some say to cage before performing a maneuver, some say just cage it back to erect when you're done.
Caging would prevent the gimbals reaching travel limits, but unless you can turn the gyro off while caged, I would imagine the gyroscopically induced bearing loads would be destructive.

Another thing I've heard about gyro care that I've never been sure about, is that a float plane sitting idle (not running) on open water should always have the gyros caged to prevent damage to the bearings from constant wave action. Thoughts?

[PilotDAR]

How many vacuum gyros in GA aircraft these days can be caged? Very few that I have seen in the last few decades!

The "old" gyros (typically larger around than 3 1/8") did not have internal freedom of motion through 360 degrees, so past roll and pitch angle exceeding 90 degrees, internally, they would come to a hard stop. So caging them just put that hard stop at the beginning of the maneuver, rather than the middle. But the very high loads on the bearing still occurred.

All of the 3 1/8" vacuum driven gyros I have seen have a full range of motion in all axis, so although they might "roll over" during some aerobatics, none come to a hard stop inside. Therefore, caging is not required, so it's no longer a function available on the instrument. So don't worry about it.

As for the innards of the instrument moving while a float plane floats, they're just moving the way they are supposed to. I think they will suffer from the more moist environment, or lack of regular use, (like most planes), long before bearing wear is a worry.

After all is said and done, instruments, like engines, and whole airplanes are consumable. We'd like them to last forever, and we can work toward that with care and repairs, but nothing lasts forever. Fly it and wear it out, before it dies of boredom!

[FenderManDan]

Thanks for the replies. I have to prep for my CPL ride and this cold wx combined with tumbling of gyros is new to me. Whiskey compass went to chits, it is showing 30 deg off. I have to swing it again before the test.

In addition to my original question is there a limit on doing the spins in cold Wx. POH does not say anything about that type of ops. Yesterday I had -32 OAT, climb rate was pegged at over 1000 fpm at Vy (awesome for C172)

[CFR]

Many AI's will tumble during aerobatics but usually recover in a few minutes or so of straight and level flying (mine has taken up to 10 minutes). At one point my AI remained slightly tipped to the left and stayed that way until another aerobatic session corrected it (clearly something wrong with the instrument). Currently it is showing a slight nose down when in level flight. I intend to complete my Instrument Rating in this aircraft so it needs to be repaired or replaced. I had considered a cageable AI but they start at around 2500.00 A rebuilt replacement for mine is around 500.00 meaning I can have a shelf load of spares for the price of one cageable one!

[PilotDAR]

At one point my AI remained slightly tipped to the left and stayed that way until another aerobatic session corrected it (clearly something wrong with the instrument)

There are four paired vanes inside the instrument, which act by gravity to very slowly erect the instrument. this takes many minutes, intentionally, by design. Occasionally, they stick a bit, and do not erect perfectly. This is an indication that it's time for the instrument to go to the shop for a cleaning.

You can spin at any temperature, but be extremely aware of the affect of shock cooling resulting from a long slow climb, then closing the throttle to a power off dive. I do not do aerobatics in cold weather for this one reason. If you must, allow many minutes of temp stabilization, as you slowly reduce power at altitude before slowing to enter the spin

[iflyforpie]

The turn and bank indicator/turn coordinators will have the toughest time.. since they will have forces applied to the bearings during maneuvers. This is why they typically wear out faster than the other gyro instruments...

I've found that spins/steep turns/spirals usually reveal 'unhealthy' gyros... like the DG that starts spinning at around 720 degrees a second... or the AI with a case of the leans.

[FenderManDan]

You can spin at any temperature, but be extremely aware of the affect of shock cooling resulting from a long slow climb, then closing the throttle to a power off dive. I do not do aerobatics in cold weather for this one reason. If you must, allow many minutes of temp stabilization, as you slowly reduce power at altitude before slowing to enter the spin.

Thanks buddy, the way I would do it (trying of course not to f..up my engine) is to have an altitude set and do some warm up with the other required maneuvers, then do the spin with 1500 rpm on entry, go idle for a 2-3 sec and quick recovery. I have a tough time entering a nice clean spin at idle. Time is the issue here, so I have to do the test before my annual.

[CFR]

At one point my AI remained slightly tipped to the left and stayed that way until another aerobatic session corrected it (clearly something wrong with the instrument)

There are four paired vanes inside the instrument, which act by gravity to very slowly erect the instrument. this takes many minutes, intentionally, by design. Occasionally, they stick a bit, and do not erect perfectly. This is an indication that it's time for the instrument to go to the shop for a cleaning.

You can spin at any temperature, but be extremely aware of the affect of shock cooling resulting from a long slow climb, then closing the throttle to a power off dive. I do not do aerobatics in cold weather for this one reason. If you must, allow many minutes of temp stabilization, as you slowly reduce power at altitude before slowing to enter the spin

Thanks.

I suspected it was something like that. I will likely do a repair/exchange with it. It is a pretty basic, non-lighted unit.

I don't do aerobatics in the winter for exactly the reason you suggest.

[PilotDAR]

then do the spin with 1500 rpm on entry

Okay, but use caution with this. If you elect to spin with the torque, it could be a little more "crisp" an entry than you expect. It'll work, but be on your game. Your key is to prevent sudden power reductions, particularly at faster speeds, where cooling is even better. Allow cooling to happen slowly. From my Aztec days, the rule was one inch of manifold pressure reduction (equates to about 100 RPM) per minute maximum in cold conditions. We never had a problem with the Aztec engines.

I was once required to demonstrate spins in a modified 210 HP IO-390 engined Lake Amphibian, entering at 75% power. I did against the torque first, and it would not even enter. Then with the torque, and I had a prompt snap roll. That was enough of that - spins demonstrated.

[cgzro]

None of my instruments lasted 1000hrs of acro but if you are just doing a few spins is not likely an issue.