Gear motor blowing CB

[Gordon C Keymer]

Gear retracts three quarters and trips CB. Putting gear switch down and reactivating CB causes gear to go down normally. Works ok on jacks prior to flight. Once in flight problem recurs and remains when aircraft returned to jacks. Different motor on same aircraft works ok in flight.

[JIMICS2452]

When I had that problem it was a broken wire in the harness in the wheel well. Call Matt Kurke (Comanchegear.com) and order a set of new harnesses.

[N3322G]

ditto on trusting Matt - he is the guru

[Charles Schefer]

I agree with all the post thus far but beyond electrical, when were the gear ADs last complied with and / or when was the gear last serviced including bungie replacement? Another possibility is there is too much mechanical resistance raising the gear and the motor becomes overworked and trips the breaker. At each annual there is a load retraction test to be performed. Bogert has a tool for this and a torque wrench is used to measure the load to fully retract. I forget the numbers off the to of my head but I think something like 120 ft-lbs is the max. Fresh bungies help take the load off the transmission. If any bushings are out of spec there may be additional resistance.

Definitely take Matt Kurke's guidance, check the wiring - perhaps put the plane on jacks retract and see what happens, if it stops short - ohm out the wires. Beyond that look for something mechanical and check the retraction loads.

- Charles

[William Hughes]

I have had very similar issues very recently. Gear would pop the breaker on the way up in flight, but would work just fine on the ground.

Check your generator, regulator, and battery.

The shunt wound motor in the gear transmission will pull enough amps as required to keep moving as the field coil voltage drops or as the rotor stalls. If you have a low battery, weak regulator, dirty brushes then the voltage drops, the gear motor pulls a massive amount of amps, enough to trip the breaker.

Your regulator should keep the bus voltage around 14.7 volts when charging the battery.

My original equipment regulator was completely shot. Replaced with new electronic one and my gear issues (and another of other electrical issues) went away.

Once I correlated it to the electrical system I could even repeatedly make it occur, for example, by turning on all the electrical loads such as the nav lights and pitot heat, which draw huge current, load the system, and drop the voltage. With all that on the gear would pop the breaker on the way up. With it off it would work - most times.

During the gear swing on jacks, there is less load on the gear and on the electrical system and the battery can do the job as the generator and regulator isn't involved. So the breaker doesn't pop during the gear swing.

Measure the bus voltage while the generator is allegedly charging the battery and see if the voltage is below specification.

There is nothing more frustrating than fixing something that isn't broken. I'd make sure your electrical system (battery, generator, regulator, wiring) is up to snuff before getting into the really expensive stuff...