bnicolette Posted March 2, 2011 Report Posted March 2, 2011 Hello all, I was out flying a couple different times today and noticed that my attitude indicator was going a skew. It spun up and errected quickly on the ground but even before I took off (within 10 minutes), it was showing a bit of a turn. While flying it would show a turn in either direction (up to 5 - 10 degrees) and a slight climb on occaision. I tried switching to the AUX vacuum system, but that didn't help the matter. I just bought the airplane in the end of January and it went through a pre buy/annual in the beginning of February. This instrument was replaced as when I was taxiing it around on the ground I noticed it doing the same thing so we had it swapped out for an exchange unit from Precision Avionics. It is a vacuum unit model #: 52D267M Edo Aire Attitude Indicator which is connected to the Century 31 Autopilot System. Are there multiple vacuum filters that I might try replacing or should I just have the instrument swapped out again. It is obviously still under warranty. Thank you for any and all input!!! Brett Quote
Jeff_S Posted March 2, 2011 Report Posted March 2, 2011 Well, the most obvious question is whether or not your vacuum pump is actually operating. Since you have said two different AIs have exhibited this behavior, are you sure the main pump is still working? Are you getting adequate pressure readings? Even if you are getting adequate pressure readings, there could still be something in the lines that is preventing the airflow from fully activating the gyro in the AI. Just a thought. Quote
bnicolette Posted March 2, 2011 Author Report Posted March 2, 2011 That's a good question. I don't have a vacuum gauge in the airplane but I could get a mechanic to check that reading for me. I just wasn't sure how the plumbing for the AUX vacuum pump was routed? I tried the AUX vacuum pump and it didn't seem to make any difference although I suppose there could be something in the line aft of where the regular pump and the AUX pump come together. I guess the real confusing part is that the instrument errects right away after start up, but within 15 minutes starts to act erratic? Quote
MooneyMitch Posted March 2, 2011 Report Posted March 2, 2011 Just a thought for you. How's your Heading Indicator behaving? The AI and HI are vacuum operated. If the HI is fine, it just might be a clogged air line. The vacuum feeding tubes are T'd together and hence run to each instrument. It could possibly be a loose clamp on the tube [either end] and leaking. Also, you might consider having a vacuum gage installed at this point. I believe most Mooney's, have or had, either Hi/Lo vacuum lights or a dial type vacuum gage. Please let us know how this turns out. Quote
sleepingsquirrel Posted March 2, 2011 Report Posted March 2, 2011 It could be spinning up and working with little or no pitch and roll input , but not fast enough to overcome the precession caused by bearing friction over a priod of time. Like having to reset a working gyro compass over a long period of time. Does it have a caging mechanism? Like the old days? Probably not getting enough vacuum to spin up to proper speed. Possibly the bearings are needing service, but I would leave that for last (not likely since this is the second instrument with the same symptom). Remember that VACUUM MAY LOOK GOOD ON A GAGE (dead head) BUT IT MUST ALSO HAVE THE PROPER FLOW RATE AT THAT VACUUM READING. Quote
sleepingsquirrel Posted March 2, 2011 Report Posted March 2, 2011 Quote: Bnicolette I guess the real confusing part is that the instrument errects right away after start up, but within 15 minutes starts to act erratic? Drifting like a gyro compass? not tumbled? Quote
MooneyMitch Posted March 2, 2011 Report Posted March 2, 2011 Hey Brett. Great looking family [Future Mooney Pilots?] and terrific looking Mooney. Have tons of fun with your new Mooney. Quote
thinwing Posted March 2, 2011 Report Posted March 2, 2011 Hi there Brett,....without an actual vac guage to show what your pulling...this one tough to dx...I would recomend a mechanic connect up a guage and take a reading..probably what needs adjusting (after verifying lines are clear and not kinked closed)is the vacumn regulator.This has a spring operated dump valve with a garter type filter.The vac pump itself is usually all or none,and of course you could still have a bad gyro..my money is on the regulator...kp couch Quote
kortopates Posted March 2, 2011 Report Posted March 2, 2011 Bret, Its very common to have leaky vacuum lines. You might even find some rotted hoses. So after checking for vacuum at the gauge then be sure to rule out leaks before adjusting the regulator; especially when you see significant drop in vacuum all of a sudden - which you won't be able to notice though without a gauge. Quote
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