nels Posted October 22, 2017 Report Posted October 22, 2017 I noticed some drift in the directional gyro during a cross country last week. Not sure how much but after reading up on it it should be no more than 3 degrees every 15 minutes. Does too much vacuum influence the amount of drift? Also, what is the overhaul cost and what is typical turn around time to expect? The plane is a 78 J with autopilot so the gyro has a heading bug. Quote
takair Posted October 22, 2017 Report Posted October 22, 2017 Too much vacuum could be a sign of not enough flow. While vacuum is a good indication of health, the gyro also needs a certain amount of flow. A kinked line or plugged filter could reduce airflow and reduce gyro speed. Check under the panel to see if the line to the DG is kinked. Mooneys are also susceptible to compass error. So be sure to verify it is not a directional issue. More maneuvering will also cause some drift. For example, if you are out doing air work, vs point to point cross country. Quote
nels Posted October 23, 2017 Author Report Posted October 23, 2017 In case I need it, what's the cost of an overhaul and where do I go? Quote
takair Posted October 23, 2017 Report Posted October 23, 2017 25 minutes ago, nels said: In case I need it, what's the cost of an overhaul and where do I go? I recently used Century Instrument for a turn coordinator. Good customer service after I had a problem with the first one. Don’t know about the longevity yet. You may also want to look at new. Every so often the new prices approach overhaul. Also, look at outright or exchange units to speed things up. Quote
Browncbr1 Posted October 23, 2017 Report Posted October 23, 2017 I have a rca g-502a dg with heading bug (works with Britain AP). coming out of my panel next month if interested. (Recently overhauled with few hours) Quote
N201MKTurbo Posted October 23, 2017 Report Posted October 23, 2017 Overhauling gyros is part of owning an airplane. They typically need to be overhauled every 1000 hours or so. I haven't had one done in a while but I would expect to pay between $250 and $500 Quote
pinerunner Posted October 23, 2017 Report Posted October 23, 2017 On 10/21/2017 at 10:13 PM, takair said: Mooneys are also susceptible to compass error. I hadn't heard this. Could you expand on it. I think I've seen my compass get off on east west headings, but assumed ti was because of acceleration. It would be good to know if it were common and even expected. I've been thinking about remote flux gate based solutions but haven't been able to find lower priced versions. Quote
Mooneymite Posted October 23, 2017 Report Posted October 23, 2017 The steel cage can become magnetized and play havoc with your magnetic compass, or even a flux gate compass. A pure DG shouldn't be affected, except by the fact you don't have a valid reference to update to. I bought the compensating balls from Spruce after @Marauder told us about them to take care of the magnetized roll cage. 1 Quote
takair Posted October 23, 2017 Report Posted October 23, 2017 8 hours ago, pinerunner said: I hadn't heard this. Could you expand on it. I think I've seen my compass get off on east west headings, but assumed ti was because of acceleration. It would be good to know if it were common and even expected. I've been thinking about remote flux gate based solutions but haven't been able to find lower priced versions. As Mooneymite said, the steel tubes become magnetized and cause compass errors. They can frequently be corrected with a proper compass swing and a correction card. The magnetism does not affect the DG, but may change your reference and cause it to look like drift. As an example, if you set your DG while heading north, but then turn east, your DG May appear incorrect unless you check against the corrected compass. Turning things like the landing light on or off can change the error as well, so you need to know the condition under which the compass swing was done. The best way to check for dg drift is on a long, straight cross country while tracking the GPS. A really good DG can go 30 minutes or longer without requiring adjustment. If you start making corrections of more than 5 degrees every 15 minutes or there is a trend of degradation then something is changing. If the vacuum system and hoses are good then it may be bearing degradation in the gyro and you are prone to it tumbling, which is no fun if you are IMC. Often a tumbling DG will just spin like a top. Quote
carusoam Posted October 24, 2017 Report Posted October 24, 2017 Somewhere along the way Mooney changed the construction of the tube the compass is mounted on. Stainless and non-magnetic (?) I believe.... My 65C had a problem with the tube setting up a shadow. When flying 360s using the compass, the compass would hang, then release...twice each turn... making the compass navigation completely useless as a smooth skill demonstrator... Best regards, -a- Quote
nels Posted October 25, 2017 Author Report Posted October 25, 2017 On 10/21/2017 at 10:00 PM, nels said: I noticed some drift in the directional gyro during a cross country last week. Not sure how much but after reading up on it it should be no more than 3 degrees every 15 minutes. Does too much vacuum influence the amount of drift? Also, what is the overhaul cost and what is typical turn around time to expect? The plane is a 78 J with autopilot so the gyro has a heading bug. To rephrase part of my question....does too much vacuum ruin or wear out a DG quicker? Are they real finicky as to exactly the required vacuum number? Quote
takair Posted October 25, 2017 Report Posted October 25, 2017 I would think that going over the 5.0 psi limit might run the gyro speed higher than it should and might contribute to wear. What are you seeing for vacuum and did it happen suddenly? You could also have instrument error. The small 1” ones tend to be worse than the larger ones. Quote
nels Posted October 25, 2017 Author Report Posted October 25, 2017 I don't have a vacuum gauge on the panel so I really don't know what the vacuum is. I did hook up several vacuum gauges awhile back to check vacuum but each one gave me a different reading. I'm not sure I would trust any vacuum gauge to be accurate at low vacuum numbers. What would a professional use... maybe some sort of monometer? Quote
takair Posted October 25, 2017 Report Posted October 25, 2017 36 minutes ago, nels said: I don't have a vacuum gauge on the panel so I really don't know what the vacuum is. I did hook up several vacuum gauges awhile back to check vacuum but each one gave me a different reading. I'm not sure I would trust any vacuum gauge to be accurate at low vacuum numbers. What would a professional use... maybe some sort of monometer? What do you have for vacuum indication? Older Mooney’s had high/low lights but most have a gauge now. An indicator is required. I use a spare gauge as a test gauge. The gauge typically is attached to a spare port on the back of one of the gyros. It should be quite stable. Please tell more about your situation, you aircraft and your setup so we can help better. Quote
N201MKTurbo Posted October 25, 2017 Report Posted October 25, 2017 I bought a WWII suction gauge on EBAY. It is always correct. after 40 years of airplane ownership I've decided that running your suction at the lowest level allowed does make your gyros last longer and doesn't affect their operation. I always set it to the very bottom of the green. Quote
MyNameIsNobody Posted August 2, 2018 Report Posted August 2, 2018 On 10/23/2017 at 7:37 AM, Browncbr1 said: I have a rca g-502a dg with heading bug (works with Britain AP). coming out of my panel next month if interested. (Recently overhauled with few hours) Did you part with this? Quote
ragedracer1977 Posted August 2, 2018 Report Posted August 2, 2018 2 hours ago, MyNameIsNobody said: Did you part with this? @MyNameIsNobody I’m out of town right now, but I think I have one of these in the hangar too. If you still need it, send me a message and I’ll look when I get back beginning of next week. 1 Quote
Browncbr1 Posted August 2, 2018 Report Posted August 2, 2018 7 hours ago, MyNameIsNobody said: Did you part with this? Sorry, i don’t have that anymore. I do have one of the original style horizontal card DGs available though if anyone needs it. 1 Quote
1964-M20E Posted August 2, 2018 Report Posted August 2, 2018 Rudy aircraft instruments in AR is a good place I just had my AI overhauled by them. My DG tends to drift as well I guess I should have sent that to them at the same time. http://rudyaircraftinstruments.com/Home_Page.html Quote
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