Relay breaker pops on retraction 1984 M20J

[maceman]

'84 M20J pops gear relay breaker when gear switch moved to retract in flight. No problem when plane is on jacks. Swung gear 20 times after first time it happened without problem but popped breaker again on next flight. Need suggestions how to troubleshoot. Thanks.

[TTaylor]

The loads on the gear retract are higher in flight than on the ground. Several possible problems:

1. The gear system is either dirty or worn to the point the motor is drawing too many amps and causing the breaker to pop.

2. The motor is getting bad and causing the breaker to pop.

3. The breaker has gotten weaker and is popping at a lower than rated amps.

I would start by pulling the gear motor and cleaning, inspecting, and lubing it. If the gears are good, lube the entire landing gear system.

Is this the 20:1 or the 40:1 gear drive? The 20:1 system is likely to have more problems. There is a technical note on inspecting the gear drive.

[Marauder]

23 years ago I chased this demon. Don't rule out a slipping alternator belt.

[ShermAv8tor]

without having a wiring diagram to see what feeds off this relay, its hard to say. Question is whats different from airplane on jacks and airplane in flight? Answer is the engine is running and you have a different electrcal source (previously stated) and the throttle position is in the takeoff or max power position. Is there a switch in the throttle? And of course while flying the aircraft is vibrating so a wire which could be shorting to ground is possible. Just thoughts.......

[Andy95W]

The loads on the gear retract are higher in flight than on the ground. Several possible problems:

1. The gear system is either dirty or worn to the point the motor is drawing too many amps and causing the breaker to pop.

2. The motor is getting bad and causing the breaker to pop.

3. The breaker has gotten weaker and is popping at a lower than rated amps.

I would start by pulling the gear motor and cleaning, inspecting, and lubing it. If the gears are good, lube the entire landing gear system.

Is this the 20:1 or the 40:1 gear drive? The 20:1 system is likely to have more problems. There is a technical note on inspecting the gear drive.

+1, any of the above.

Also, if you have inner gear doors, those can increase the load on the system, particularly if not lubricated or if worn attachment fittings.

[maceman]

Thank you everyone! I will call the A&P tomorrow to share your thoughts and recommendations so he can start the troubleshooting. I will report back once the situation is remedied.

[Blackhawk]

Get this fixed. Now. For too long pilots (including myself), have pooh poohed popped circuit breakers. A circuit breaker popping means something in the electrical system is getting too hot. Something in the electrical system getting too hot means something might catch on fire.

As an example from the NTSB there is this:

http://www.ntsb.gov/news/press-releases/Pages/Airplane_Crash_that_Killed_Five_Due_to_Corporate_Flight_Department_Practices_and_Poor_Pilot_Decisions_NTSB_Says.aspx

 

From a personal experience, again in a C310 not a Mooney, I had a situation in a 310 where there were electrical problems that kept coming up. Circuit breakers popping when the gear was retracted, etc. It turned out the problem was an old, and failing GCU (generator control unit), located under the left, forward seat. When it finally failed it caught on fire and the entire electrical system went dead. Fortunately this was day VFR.

[ShermAv8tor]

Get this fixed. Now. For too long pilots (including myself), have pooh poohed popped circuit breakers. A circuit breaker popping means something in the electrical system is getting too hot. Something in the electrical system getting too hot means something might catch on fire.

As an example from the NTSB there is this:

http://www.ntsb.gov/news/press-releases/Pages/Airplane_Crash_that_Killed_Five_Due_to_Corporate_Flight_Department_Practices_and_Poor_Pilot_Decisions_NTSB_Says.aspx

 

From a personal experience, again in a C310 not a Mooney, I had a situation in a 310 where there were electrical problems that kept coming up. Circuit breakers popping when the gear was retracted, etc. It turned out the problem was an old, and failing GCU (generator control unit), located under the left, forward seat. When it finally failed it caught on fire and the entire electrical system went dead. Fortunately this was day VFR.

+1

 

My rule of thumb…..if you dont see smoke and you cant smell an electrical burning odor…..you can try a 1 time reset of the affected CB, if it trips again…..thats it, no more resets and Maintenance action is required. If you reset the CB and then you smell electrical burning odor or see smoke pull the CB back out……Depending on which CB, phase of flight, etc. Pilot should use best judgement on the above actions and feel comfortable to do so, if not just get the Maintenance action done. If it cannot be duplictaed on the ground during troubleshooting, your missing something that comes into play while the aircraft is flying…..if it really cannot be duplicated on the ground at the least, replace the CB and/or relay

[RobertGary1]

If you don't see anything obvious, changing the breaker may be a good bet. Hopefully the motor is fine. We have a place near Sacramento "George's Electric" that is one of the few that overhauls Mooney gear motors. I recall the price quoted me 5 years ago was around $500. Mine still works fine so I opted out.

 

-Robert

[richardheitzman]

Wind loads on the gear will increase the needed amperage to the motor. All comments above are correct. Clean, lube, inspect. CB do go bad and it might be a combination of increased load with a bad CB.

[maceman]

Problem found and solved. Two of the wires coming off the gear switch on the panel were shorting against a radio rack that had worn the insulation away from vibration over time. You can notice the small burnt spots on the wires in this photo http://www.imgivingnotice.com/wp-content/uploads/2015/01/gear-wires-Mooney.jpg

 

Apparently, the wires were moved away from contact when the A&P wiggled them on the jacks. That's why 20 gear retractions went fine. Starting the engine and taxiing created the short again. It took a little digging, probing, and moving things around behind the panel to find this, but my A&P persisted. 

 

He replaced both wires from the switch to the cannon plug and all is good.

 

Makes me wonder about other wires in this 1984, 30 year old airplane!

[carusoam]

Thanks for sharing the picture!

Any insight on why it popped in flight but not on Jacks? Just flight angle vs. gravity?

Go MS!

-a-

[Marauder]

Thanks for sharing the picture!

Any insight on why it popped in flight but not on Jacks? Just flight angle vs. gravity?

Go MS!

-a-

My bet, no vibration.

[Marauder]

Problem found and solved. Two of the wires coming off the gear switch on the panel were shorting against a radio rack that had worn the insulation away from vibration over time. You can notice the small burnt spots on the wires in this photo http://www.imgivingnotice.com/wp-content/uploads/2015/01/gear-wires-Mooney.jpg

Apparently, the wires were moved away from contact when the A&P wiggled them on the jacks. That's why 20 gear retractions went fine. Starting the engine and taxiing created the short again. It took a little digging, probing, and moving things around behind the panel to find this, but my A&P persisted.

He replaced both wires from the switch to the cannon plug and all is good.

Makes me wonder about other wires in this 1984, 30 year old airplane!

Thanks for reporting back with your findings. Will help the next guy dealing with this issue.