Separate names with a comma.
Discussion in 'Maintenance Bay' started by azure, Feb 27, 2018.
Ya, OP stated that motor stopped after running a few seconds.
Perhaps this manual will help solve the problem. It is a PDF of the service manual for 177's.
Thanks Norm, but my plane is a 1976 model, and that manual is for 1975 and before.
Yep, and I am the OP.
I don't think so. The gear cycle takes about 12 seconds, and that sounds just about right from what I've observed, though I haven't timed it with a clock.
BTW this is a little embarrassing to admit, but I have a gear running light too. I'm rusty enough from so little flying over the last few months that I actually forgot to check it, relying on hearing and feel instead. But I'm pretty sure it would have caught my attention if it had continued running indefinitely. That's why I would be very surprised if the problem were inadequate pressure.
Even if you could have accessed the pump it would have been a poor decision to fly.
Yeah, probably so.
BTW, just to clarify: based on what I knew then, another lap in the pattern seemed a reasonable thing to do given that this has happened before and there were no obvious signs prior to this of gear malfunction or imminent failure. I discussed this with the mechanic and specifically asked him if there were any failure modes he knew of that would cause the manual extension system not to work as long as there was fluid in the system. He said he wouldn't personally do it but that he knew of no such failure modes, and we checked the fluid level. He added that I should make sure I could get to and operate the manual system first, which is how we found out the handle was jammed.
That said, based on what Dan has posted here, and what others on CFO have said, it's probably not wise for me to trust Steve's word about much that is specific to make and model. Apparently such failure modes do exist, and as I've said, he really knows nothing about Cardinals that he hasn't learned from working on my plane.
Any new information on the issue?
None, unfortunately. The FBO confirmed that the emergency gear handle was just jammed due to pressure in the system, but the mechanic is out sick and so they haven't been able to get my plane into the shop yet.
So my plane finally got into the shop today. The owner just emailed me to say they cycled the gear about 20 times, and nary once did it fail to retract. So the cause is unknown, as is how long it will be til it recurs. But I'm not inclined to throw any more money at trying to figure it out until it does.
However, at annual I'm going to insist that all the hoses and seals be IRANed at the very least - the hoses should probably be replaced, as it's been at least 8 years and I believe Cessna recommends they be replaced every 5 years.
So it happened again yesterday, on my first post-annual (test) flight. Took off, pulled the lever up... nothing. The wheels stayed down and locked, the green stayed lit, and this time I was careful to glance at the gear running light. Nothing. As before I put the gear lever down and landed. This time the mechanic who did the annual was standing by and came out, checked a number of things including the hydraulic fluid level (though it had just been serviced at annual, so EXTREMELY unlikely to be the problem) and the external electrical connections to the power pack and the solenoid.
He came up with what struck me initially as a truly hare-brained scheme to troubleshoot the problem. Since it seems to never happen when the plane is jacked up on the ground, we would do it in the air. He would sit in the right seat, and we would cycle the gear repeatedly in the air, and if the gear failed to come up he would slither back and go to work. His main suspicion was that the solenoid might be intermittently opening up, so he brought along a jumper, and a hammer to rap the gear motor housing in case the problem was a dead spot in the winding. I couldn't think of any better idea, so that's exactly what we did, as crazy as it sounds. (We did make sure ahead of time that he would be able to make his way out of the right seat to the tailcone, but I was still very concerned about the effect of the shifting of his weight on the CG and the plane's handling characteristics.)
Long story short, we cycled the gear at least 10 times in the air and it worked like a charm every time. Ditto on the trip home. So I am no closer to an answer. One thing that is clear though, I was imagining the feel and sound of the gear running when it happened earlier this year. The motor simply does not run when the gear lever is pulled up. But it happens so infrequently that reproducing the problem seems to be a hopeless task.
The one thing I will try next time it happens is to cycle the landing gear breaker, as it is the original breaker and could possibly be getting flaky. Other than that, I truly have no clue as to how to proceed.
Once in a blue moon problems are the worst.
Get an inexpensive volt meter (or three), attach to yea olde gear motor and leave it sitting between the seats. Next time it happens, you can look at the motor (and pressure switches, and solenoids, and...) and see if it is getting power. If it doesn't move the meter upstream, etc. Eventually you should be able to narrow it down.
I would have suggesed that you tie a bosun's chair to the struts so your mechanic could observe from outside, but your airplane has a strut deficiency.
Those sound like good suggestions, thanks. My Fluke and B&G multimeters are sitting in a friend's upstairs in Michigan, but I could borrow a couple of student meters from the teaching labs. The only thing I can't think of a way to monitor in flight is the electrical integrity of the squat switch wire. That was one of the first things my local mechanic checked back in February, but of course only on the ground. If the stresses applied by the windstream in flight are just enough to open it up...I'm not sure that we've eliminated that possibility, nor really how to do so.
As you say, the fact that it so rarely happens - and seems to happen randomly - makes it all the harder...
Harbor Freight has the "buy anything get this meter for free" coupon every once in a while. Not exactly quality, but they seem to work.
Not sure how the squat switch is wired - look for open / closed across the switch itself?
I don't think anyone has actually posted a wiring diagram from the manual either.
AFAIK the squat switch runs a solenoid that locks the selector lever from being moved and that's all it does.
If that's the case my next question is the pump motor powered off the same breaker as position indicating system? (She stated the lights stay on during the event so I want to know where motor power comes from witch breaker) Breakers are typically cheap and easy to replace so a quick eliminator if desired to replace it.
Corrosion of wiring?
Does the motor have its own thermal switch? Is it bad?
(ask 20 questions lol)
I'd post the diagram if I had it, but I don't have the service manual. (I used to, but loaned it to my mechanic in Michigan - I think - and never got it back.)
Clearly the gear breaker does not power the indicator lights as the green stayed on, as you said. The gear breaker is a separate breaker.
If we replaced the breaker now we might "never" know it wasn't the culprit, depending on how long it waits before acting up again.
Wiring corrosion is always possible. The only way we'll know is to reproduce the problem with a bunch of meters monitoring continuity at various points.
Not sure whether there is a thermal switch and not sure exactly what you mean. Do you mean something that protects the motor in case of overheating?
Edit: I don't think it's true that the squat switch prevents the selector lever from moving. If that were the case then it should be impossible to accidentally select gear up when on the ground. That would be nice, but I don't think it's true. I think it just prevents the gear motor from running until the weight is off the nose.
I think it does, because on the 76 and later the selector is actually a hydraulic halve, correct? Must lock the valve in down position.
I'm thinking it is an electrical problem. The solenoid that controls power to the pump motor (slave) or the system that controls power to pump motor solenoid (master). What switches control power to the motor pump solenoid? The system pressure switch, and what else?
It certainly operates the hydraulic system but I don't think the squat switch prevents the lever from moving. All it says about it in the POH is: "A safety switch, actuated by the nose gear, electrically prevents inadvertent retraction whenever the nose gear strut is compressed by the weight of the airplane." It doesn't say anything about the solenoid preventing the lever from moving. About the lever, it says "After the lever has been repositioned, it directs hydraulic pressure within the system to actuate the gear to the selected position."
Looks like an electronic copy of the service manual is available for $38
Thanks, it might be worth the investment.
It looks like they have printed copies as an option, too.
Just an FYI, the expense of replacing the seals is nowhere near the expense of a perfect belly landing. Been there, done that. One failure point in the nose bit us even though we had a full tank of fluid. Tried to get the gear down for a solid hour before accepting we couldn't fix it.
There are internal seals that can be an issue in the Cardinal. If I understand what my mechanic told me on a similar problem recently the RG system requires a significant amount of greater pressure to keep the gear up than to put it down. Wonder if perhaps the hydraulic pump isn't quite meeting the PSI needed to push it up?
Wonder if perhaps the hydraulic pump isn't quite meeting the PSI needed to push it up?[/QUOTE]
It seems like if it worked with the mechanic in the right seat, it would show the pump is "up to snuff", but it's impossible to troubleshoot setting in front of a computer
Its gotta be an electrical problem based on what the OP has posted. We don't have a print or know where the motor pump run light is wired in but IIRC she said it wasn't on during the event.
I had a talk with the annual mechanic about that when I dropped the plane off, encouraged him to IRAN the hoses and replace any that looked at all questionable. When I picked the plane up he reported that he'd inspected them all thoroughly and they seemed to be fine.
The way the Cardinal gear up mechanism is designed, I believe that if insufficient pressure was the problem, the pump would be running continuously to try to get the pressure up to spec. In any case, the motor would run, and the problem was that it didn't. At all. I'm far from an expert on the RG gear system, but I think @bnt83 is correct that it is some kind of electrical issue, the circuit that supplies power to the gear motor intermittently opens up somewhere. The question is whether the break or disconnect is in the wiring or internally in a winding or something.
Does the pump run when power is tuned on before the first flight of the day?
Once in a blue moon. I was told that was normal.
I would assume it would most of the time, depending on how quickly hydraulic pressure decreases of course. If it sits overnight I would expect it to run, if it doesn't I would be suspicions like maybe the motor pump solenoid is stuck open.
My 50 year old battery contactor sticks open about three times a year.
I can't be 100% sure how often it actually does it, but the only time I notice it is when I turn the master on to check the lights and put down the flaps. The sound is unmistakable, and the first time I heard it I was a bit alarmed. But as I said, it's a once in a blue moon thing.
The system uses a pressure switch on the powerpack that closes when you select gear up or down. The selector is a hydraulic valve, so moving it causes hydraulic flow, which drops the pressure, which activates the pressure switch. Power runs from the bus though the breaker, throught the pressure switch, through the squat switch to the solenoid that controls the pump motor. (The order might be slightly different, but that's the general idea. I retired recently and don't have the manual handy anymore.) Your problem is something loose, worn or misadjusted somewhere between the bus and the pump motor. There's a remote possibility that the nosegear strut is sticking (182RG struts are sometimes sticky for some reason, even after overhauling them) and it might not be extending all the way after liftoff, especially with the drag. Or the squat switch is adjusted so that it just barely actuates even when the strut is fully extended, and sometimes it won't close. Or the squat switch wiring is tired of being flexed every time the nosegear goes up or down and the copper strands have become fatigued and have broken and are making contact within the insulation, except when they don't. That scenario is a common one in older cars, when the door locks or electric windows stop working. The wires in the cable bundle at the door hinges will fail.
Or the motor brushes are worn out and sometimes not making contact with the commutator. That's a 500-hour inspection item.
Yes, good summary of most of the different possibilities. Also points to why it's so difficult to find the problem, since it happens so rarely.
I didn't know the pump motor brushes were a 500 hour inspection item. In fact I thought the motor housing was sealed, didn't know there was any way to inspect them except at a specialty shop that could open the unit up.
I would NOT expect it to run often. I've got two Cardinals in hangars right now and I've only had a gear pump run when I turned the master on once in the last year that I can recall - and we fly an average of 3-6 flights a week.
If this is Cessna gear operated by an electric motor. the motor is going bad.
Thanks for that. That reaffirms its not a hydraulic system tightness issue.
If so I'd expect to see the motor running light on and nothing happening.
There can still be an issue in one direction, not affected by the other. We had one bird that never ever ran the pump on start up, or while the gear was down but was running the gear UP pressure every 5-6 minutes in flight to maintain the up pressure. It took the mechanics several tries before that issue finally got resolved, but I'd hear clicks in my headset and see the pump running light very briefly all the time, which really got on my nerves.
It's caused by a tiny leak somewhere. The accumulator on the powerpack is tiny and doesn't store much volume, so any internal leakage will trigger the pump occasionally. The way to find the leak is when the airplane is on jacks and the gear is up or down as applicable, and using a mechanic's stethoscope you poke at all the various hydraulic components and listen real close. Need the shop quiet, of course. A leak will be heard as a hiss or whistle at the component affected. Fluid at such pressures will make noise when it's squeezing through tiny gaps. We had a leaking check valve in the hand pump and found it that way. $1100 check valve, IIRC.
@azure I've been having a similar problem recently. Turned out that occasionally the pump was not running, or not running long enough. It was intermittent at the start, and then a total failure. When we opened the motor up one of the brushes was completely worn, so it was making occasional contact (or occasionally not making contact).
Just an idea for you.
Thanks. This was indeed one of @Dan Thomas 's suggestions.
BTW Dan, I asked on CFO about this, and the list moderator who replied said he was not aware of any 500 hour inspection item regarding the gear motor brushes. Nonetheless, it's something I'm going to ask to be looked at.
Section 2 of the Service Manual has the inspection details in the last 10 or 12 pages or so. One of those items will be a check of the motor brushes, with a note number that leads you to the notes section giving more detail. One model of motor, IIRC, wasn't easily opened up without taking it right out and maybe sending it for service. The other type is easily inspected by removing the top cap and getting a look at the brushes. Gotta have at least the right front seat out. There are other inspections, too, that are usually ignored; the self-relieving check valve filter, the pressure switch cutoff point, the main and thermal relief valve pressure settings. It all takes time, it all costs money, and if ignored long enough it can add up to serious difficulty and expense. Chapter 5 (landing gear and hydraulics) is a long chapter and details all of the stuff that needs checking.