Landing gear CB

[Kurt Garbin]

Hello All, and Happy New Year....
This is my first post, as I am a new Comanche owner (Aug, 2016). I have a 62 250B, and have just had a new prop gov cable installed. Flew her this am to check out the cable, and all was good. Mid field as I attempted to lower the gear, I didn't get the green. I went around and checked the CB. It had popped. After pushing the breaker back in, I noticed my transponder light came on as well. The gear cycled as normal, and the landing was uneventful. I will have the airplane jacked, and cycle the gear to see if we can find a culptet?? Anyone else ever have this happen? OAT was 8F and I was at 8000' on a L downwind.

One more question.... I read another Comanche owner discussing his gear bouncing. In his description, he mentioned moving his gear selector to "neutral" for flight?? I have not been told this by instructors, nor read this in the POH?? Is this common practice?

Thank you for any info and direction you may have for me!!

Kurt Garbin

[N3322G]

Kurt,

Suggest you resolve before flying again and definitely study the POH emergency gear procedures. Service manual available on the home page here under Tech Tab gives tests as do many generous posters here. The best source is Comanchegear.com and owner Matt Kurke.

[LeWayne Garrison]

I have seen numerous causes for this, but I agree the airplane should be put on jacks before further flight and the gear cycled multiple times. At this time make sure you know the exact procedure for emergency gear extension. Possible causes are a weak circuit breaker (unlikely, but possible), a dirty landing gear cable conduit causing binding issues, a possible bad gear motor, poor gear lubrication (both in the undercarriage and inside the airplane with the transmission or jackscrew, or the bushings in the gear are excessively worn, also causing binding. Usually the sloppy bushings make collapse more likely, not binding. It is also possible the bungees are installed incorrectly, although that again usually make collapse more likely. Also be sure the circuit breaker is the correct amperage (I believe 30 amps, but check it out in the manual).

If everything checks out on the ground, I would take it up again and watch carefully the load on the ammeter on retraction and extension. it should not peg the ammeter. If it does that is an indication of either a dirty conduit or binding somewhere in the system, probably due to poor lubrication. I say to do this in the air because even though you can monitor the ammeter on jacks the air loads are significant and will cause higher current draws.

Good luck

[LeWayne Garrison]

In response to second question, I do not recommend leaving gear switch in neutral. This position is mostly used for maintenance.

[Kurt Garbin]

[Kurt Garbin]

[JIMICS2452]

There is a small brake on the side of the jack screw on the landing gear motor/transmission. It is pulled back by a solenoid when the gear is in transition and held in place by a spring when the landing gear motor is off. This bake prevents the jack screw from turning while the gear is up in cruise. There are no up locks in the system. Make sure the brake is making good physical contact and has the rubber rub surface in place.

Jim Hiatt

[Kurt Garbin]

[Kurt Garbin]

[Kurt Garbin]

[Zach Grant L1011jock]

Kurt,
On the gear selector switch "off" position, it is exactly what it says it is. Starting somewhere around '65, all Comanches came with just an up/down two position switch. With the two position switch, you have to pull the breaker, or kill the master to remove all power from the gear system. With the 3 position switch it is as easy as placing the switch to OFF. In the case of having the three position switch, there have been several gear ups caused by people not looking for a green light and just moving the switch from up to the next position down, which unfortunately is off. For that reason, as most GA pilots are used to a two position switch, I have the gear to "off" as part of what I teach as an after takeoff flow if the selection is available. This is a common procedure on many larger aircraft with hydraulic gear, so it is common for many who transition from Large Pipers ( PA23/27,PA31) Boeing types etc. There are other reasons to place it to off, including removing the chance of having an electrical issue develop in the system in flight, but that is a rarity if you maintain the gear and harness properly. Whichever way you choose to operate your aircraft, you can do it that way. The switch is there, and there is no mandate using the off position, for or against.

-Zach

[William Hughes]

I'd like to offer, based on recent experience, that a cause of circuit breaker popping can also be due to the DC electric motor stalling. At which point it will pull 90 odd amps before tripping the breaker after a few seconds.

The motor can stall because it is old and dirty inside the motor and the commutator and brushes have difficulty in transferring the power. Due to the way shunt wound DC motors work, if they can't carry the load, they stall and pull a huge quantity of amps. Which is why there is a circuit breaker. But also due to the way they are wound they will simply pull more amps and carry on at a constant speed under increased load - until they get a load they cannot carry any more. This usually happens at the end of the cycle where the load goes up naturally due to the way the jackscrew and torque tube work.

Now, causes of increased load on the motor are many and varied. Conduits, brake lines, cold, lubrication, bungie's, bungie pulleys, rigging, speed, weak battery, weak generator etc. The most common seem to be brake lines jamming and old conduits. But as the motor keeps getting weaker due to a dirty commutator/brushes/windings, it will take less and less increased force to jam it. So it will start popping the circuit breaker for lots of different and seemingly random reasons which are tough to track down.

You can check it during a gear swing by placing a bit of opposing force on the manual gear swing handle. Not much, just a bit. If it stalls near the end with a circuit breaker pop you probably have a dirty motor. Note that you generally can't load the motor enough at the wheels as all the mechanical leverage is in the motor's favor there. But the manual gear extension handle is designed to be in the pilot's favor, so you can load the motor quite a bit with a small force on the handle.

The motor can be pulled, disassembled, cleaned, reassembled, and tested with not too much hassle in a day by an AME. Worth trying before you get into more expensive things. Plus it is satisfying seeing the commutator go from dirty to bright, and see the dust and grime blast out of the windings using compressed air, and even more satisfying seeing it operate with some authority. Plus it might be quite a while before you start getting "random" gear circuit breaker pops on retraction.

[Kurt Garbin]

[Kurt Garbin]