NicoN Posted September 1, 2022 Report Posted September 1, 2022 We have a Century 21 A/P installed. Part of it is a directional gyro (type is not available for me at the moment). This guy is drving me crazy. Especially during take-off it drifts a lot; sometimes its off by 30-40 degrees while climbing to F060 or so. After 30 minutes, I see less drfiting but that might be wishful thinking. The A/P keeps the heading pretty well, following the drifting DG :-( NAV mode is even more buggy: It was always necessary to keep the heading bug under the current course - this seems to be by design. Now - with the drifting Gyro NAV mode is difficult as the heading bug is drifting ayway from the 12 o clock position. The maintenance manual asks to clean the filters of the instruments regularly. It was definitely not done with the last annual/100h check. according to the manual, there are filters on the back side of AI and DG and also a filter on the vacuum regulator itself. Q1: Is this behaviour a typical failure for a gyro? What can be done besides of an overhaul? To be honest - we are discussing an upgrade and we want to avoid wasting money Q2: A friend recommended cleaning the filters first. I don't think that this is helpful, but it sounds quick and easy. Can I access those filters without removing the glareshield? This as always PITA with a risk of damaging the galreshield on this "slot". Any further ideas for diagnosing this problem? The DG runs absoulutely quiet We have 1980 M20K
carusoam Posted September 1, 2022 Report Posted September 1, 2022 Typical of gyro asking for an OH… So many gyro systems coming out of old panels… You might find a short term solution by finding a similar take-out… Find out what you have…. See if Alan has one on the shelf… Best regards, -a- 1
81X Posted September 1, 2022 Report Posted September 1, 2022 Garmin fixed this recurring issue. Replace with G5 or GI275. You also get GPSS as a sweet bonus! I had a similar issue on my KFC150 and went the G5 route as the overhaul of the DG and remote slave unit was almost as much as the G5 setup.
NicoN Posted September 1, 2022 Author Report Posted September 1, 2022 Our shop said something of 8-10 weeks overhaul time and around 1000€ . They did not offer us a replacement but gave a quot for a Gi 275 setup (which is nice). Of course, we all appreciate the idea of our hangar neighbour that a clogged filter might be the reason. That's why I was asking for the procdure and whether thhose filters are accessible.
DCarlton Posted September 1, 2022 Report Posted September 1, 2022 My DG is having issues a year after overhaul. I just talked to the instrument overhaul shop yesterday. I'm not expert but if the compass card is rock steady and not drifting, it may not be the gyro part of the DG. There is a "clutch" that holds the heading bug in place when you release the knob. That clutch could need overhaul. Also check and see if the shaft for the heading bug is binding at all on the instrument panel or overlay. If it doesn't release all the way back out, the clutch may not engage properly. Bottom line, you'll probably need to overhaul the gyro; sounds like your compass card is drifting from your description. Mine is exceedingly difficult to remove. The entire radio stack and trays needs to come out first. I'm keeping my vacuum driven DG though because it drives my Brittain Autopilot. I'm also trying to get some intell on the output of the Garmin GAD-29 (G5 autopilot interface) just to see if the analog course deviation output is similar to the existing DG. The Garmin G5 and GAD29 is not approved for use with the Brittain Autopilot but there is a remote chance field approval might be possible. I'm investigating it. BTW, if I pull my vacuum DG again, I'm buying a new one. Not going with another overhaul. Too difficult to remove and replace. You could do that if you want a quick turnaround time.
N201MKTurbo Posted September 1, 2022 Report Posted September 1, 2022 25 minutes ago, DCarlton said: My DG is having issues a year after overhaul. I just talked to the instrument overhaul shop yesterday. I'm not expert but if the compass card is rock steady and not drifting, it may not be the gyro part of the DG. There is a "clutch" that holds the heading bug in place when you release the knob. That clutch could need overhaul. Also check and see if the shaft for the heading bug is binding at all on the instrument panel or overlay. If it doesn't release all the way back out, the clutch may not engage properly. Bottom line, you'll probably need to overhaul the gyro; sounds like your compass card is drifting from your description. Mine is exceedingly difficult to remove. The entire radio stack and trays needs to come out first. I'm keeping my vacuum driven DG though because it drives my Brittain Autopilot. I'm also trying to get some intell on the output of the Garmin GAD-29 (G5 autopilot interface) just to see if the analog course deviation output is similar to the existing DG. The Garmin G5 and GAD29 is not approved for use with the Brittain Autopilot but there is a remote chance field approval might be possible. I'm investigating it. BTW, if I pull my vacuum DG again, I'm buying a new one. Not going with another overhaul. Too difficult to remove and replace. You could do that if you want a quick turnaround time. I assume the trouble with R&R ing the DG is the hoses. I quit trying to save them. I just cut them off and buy new hoses. The new hoses are soft and supple and slide on the hose barbs with little effort. The new hoses don’t cost much.
DCarlton Posted September 1, 2022 Report Posted September 1, 2022 18 minutes ago, N201MKTurbo said: I assume the trouble with R&R ing the DG is the hoses. I quit trying to save them. I just cut them off and buy new hoses. The new hoses are soft and supple and slide on the hose barbs with little effort. The new hoses don’t cost much. I'm flying a '67F with the sloped windshield mod. Avionics access on the top row of instrument is very difficult. It seems easier to remove the CDI and the radios to get at the DG. I'm more than willing to learn from an expert though.
Unit74 Posted September 2, 2022 Report Posted September 2, 2022 There are several overhaul shops in the United States fully capable of taking care of this problem. In addition, they OH sell units as well if the shipping yours across the world is not desirable on your time frame needs. Some that come to mind are: https://rudyaircraftinstruments.com https://flyaqi.com Or you could always just purchase a new DG. or like others mentioned, step up to a digital HSI like a Garmin display.
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