RG gear issues

Discussion in 'Maintenance Bay' started by azure, Feb 27, 2018.

  1. azure

    azure Final Approach

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    I'll be posting this question to Cardinal Flyers later on, but for now just wanted to relate what happened today and ask a couple of questions.

    I was going to make a fuel run to a field about 50 nm south, but upon takeoff, when I raised the gear handle... nothing. I'm sure I heard/felt the gear motor running, but when I glanced at the indicator after a few seconds, the green light was still on, and the main gear was still down. (On the Cardinal, the green light goes out when the gear starts to travel, and the yellow only comes on when locked in the up position.) My first instinct was to reach for the handle, put it down, and try again as this had happened once before, about 7 years ago, and never happened again until now. But there was resistance in the handle for a few more seconds. Finally I was able to put the handle down. Once again the feel of the gear motor running, but of course the gear was down, the light was still green, and nothing happened other than the motor stopped after a few seconds. So I scrapped my planned fuel run, flew the pattern and landed uneventfully.

    I asked the local mechanic what he thought, and then decided I would try another lap in the pattern and see if the problem was a one-time event, like 7 years ago. But first I wanted to make sure that I could pump the gear down manually in case the gear motor was faulty and could only manage to raise the gear, maybe part way. We checked the hydraulic fluid, and then tried to extend the manual gear pump handle. Here I was in for a shock: the thing was absolutely stuck. I could not budge it at all. Steve was able to twist it a bit, and after applying a little WD-40 was able to pull it out an inch or so, but no further.

    So I scrapped the idea of a lap in the pattern too, and taxied back to the hangar ramp.

    So my questions:

    1) Do any likely causes come to mind for the failure of the gear to come up? Steve thought the motor was likeliest, but I wonder, since I definitely heard/felt the motor running, yet the green light never went out as it would if the downlock had at least released. So I wonder if one of the downlocks might have failed to release.

    2) What in the heck would cause a manual gear extension lever to freeze up like that?? It was definitely checked (and worked) at last annual in May, 2017.

    This is a 1976 177RG.
     
  2. Dan Thomas

    Dan Thomas En-Route

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    The manual pump is in the gear-down hydraulic line. Pressure in that line will put pressure on the pump piston and try to force it up a little, which drives the end of the pump handle against the belly and makes it stick there. The manual pump, when it's needed, is used after the gear lever is lowered and pressure in the system falls off, not when the gear is already down and there's lots of pressure in the system.

    I would get the airplane on the jacks and troubleshoot the system. Flying it around and fooling with the gear is risking a failure to extend and a belly landing. There are several seals in that system that can fail and let the pressure bypass, and if that happens the manual pump can't extend the gear either. Your symptoms are in line with a failing seal. If, for instance, one of the actuator piston O-rings has worn or shrunken, it can let fluid bypass once the pressure falls off when you select gear up, and the fluid then just flows past it to the return line. The system can't build pressure and the downlocks won't release. That seal might or might not suddenly catch and seal up again and make things work. I ran into this on a Lake Amphib a couple of years ago.

    On older retracts Cessna used seals that should be changed every five years. That stopped in 1979, I think.
     
    Last edited: Feb 27, 2018
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  3. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Just a wag but something is not releasing the gear down latch system which physically retains the gear in the locked position, it is not releasing the gear so the hydraulic pressure can bring it up. I agree with Dan, get it up on some jacks and trouble shoot it there!
     
  4. azure

    azure Final Approach

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    I could swear that I've extended the end of the pump handle on the ground before, with the gear down and everything off. It's never been stuck like that before.

    Certainly the next step is to jack it up and troubleshoot - but that won't happen for at least a couple of weeks as the maintenance hangar is full at the moment. I don't have access to jacks, personally. Only other way would be to fly it with the gear down to another field, but getting in at the only other nearby field is difficult and I'd probably be looking at a two month wait, at least. That's where I plan to have it annualed this year, but that will have to wait.

    @Briar Rabbit I agree, that was my thought too - downlock latch system not releasing for some reason. The motor itself seems to be working.
     
  5. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Wait a couple of days to let the pressure bleed off a bit and then try to extend your manual pump handle, I will bet you can pull it out then. I do not recommend using it to pump more pressure though. As I remember an RG does not have main gear doors that open with hydraulic pressure, is this correct?
     
  6. azure

    azure Final Approach

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    There is only a nose gear door, no gear doors for the main gear. And the nose gear door is mechanically actuated, according to the POH. I wasn't intending to try to pump more pressure (don't think that would be easy with the gear down anyway), just to verify that I could extend the handle. You could be right; I'll try to make it up there over the weekend and see if it's easier to pull out.
     
  7. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    If you have main gear doors it probably is hydraulic pressure that opens them. You may have a stuck main gear door, and it is better to have a gear door stuck with the gear down than a door stuck with the gear up obviously. On 210’s prior to the 78 models you can use the hand pump to open the gear doors when on the ground to perform maintenance. I just don’t recall if the gear door systems on an RG are the same as a 210? But I still recommend that you not try to cycle the gear until you have additional help from an A&P familiar with your gear system! Probably something as simple as a pressure switch - be glad you didn’t remove some metal from your belly. RG’s are one of the sweetest flying airplanes in the air as long as you don’t overload them.
     
  8. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Yes just nose gear doors and probably not the problem then, but still suspect a problem in your down lock system?
     
  9. azure

    azure Final Approach

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    I deleted the post you replied to after a moment's thought -- as the post now reads, there are no main gear doors. There is a downlock mechanism though, that has to release for the gear to retract normally. I believe the main gear downlocks and the release mechanism are hydraulically actuated, but there is no detailed description in the POH and I don't have the maintenance manual.

    According to the POH it should always be possible to extend the gear manually if there is hydraulic fluid in the system. But no, I'm not going to try it until we've at least tested the system on jacks.

    As I said, the exact same thing happened about 7 years ago, once and then never again. Unless the failure happens consistently (or at least frequently) I'm not going to let Steve waste my money trying to figure it out. He is good, but must be the slowest mechanic on the planet. I would rather take it to someone with Cardinal experience.
     
  10. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    I still think it will be something relatively easy to fix. I had a nose gear cylinder on my 210 develop a leak last year, found some hydraulic oil leaking on the ramp when I returned from a short trip to visit a customer. That darn cylinder lists retail for about $11,000 and No used ones to be found. So be glad it is probably just an inconvenience. Good luck and let us know what you find?
     
  11. Brad Smith

    Brad Smith Pre-takeoff checklist

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    Time to put it up on jack stands and find out what the real culprit is. I would definitely ground it for now. After the problem is corrected the mechanic will run some gear swings on the jack stands to ensure the entire system is working as it should. Intermittent problems always become real problems if they're not addressed. Also, much cheaper than a belly landing and a rise in insurance premium.
     
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  12. azure

    azure Final Approach

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    Just an update - one of the experts on CFO mentioned that there is a ring in the back of the emergency gear extension handle that prevents the front part from coming out accidentally. If pressure in the system forces the handle down against the floor, that ring can come up and bind the front part very tightly. There is supposed to be a bumper that keeps the handle from going too far down, but my plane doesn't have it and the 1976 model I flew years ago didn't either.

    He also said that the gear retraction failure is likely to be the squat switch, or the wire leading to it, as that switch must disengage or the pump won't run. I doubt this as I'm pretty sure the pump was running.

    Anyway it's good to know that the gear handle is probably not an issue - though it's not clear how to test whether it will be available in case of emergency if it binds readily like that when the system is pressurized. Maybe after the pressure bleeds off it will be easier to move. Regardless, I want to at least test the system on jacks before flying it again. My main concern now is whether the problem is reproducible or whether, like 7 years ago, it will prove to be something that happened "just once". If it's not readily reproducible I really would rather take the plane somewhere that has experience with Cardinals. Steve is a good mechanic but his only Cardinal experience is on my plane, and he is EXTREMELY slow and thorough. I really don't want to have to pay him to learn the Cardinal gear system.
     
    Last edited: Feb 28, 2018
  13. Cruzinchris

    Cruzinchris Pre-Flight

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    If I had a retract, I would invest in jacks. Heck, I am fixed gear and I have jacks to do an effective lube on the gear.
     
  14. Dan Thomas

    Dan Thomas En-Route

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    Is there any record of the rubber seals in the system having been replaced since the aircraft was new? That's the first thing I'd be looking at. 40 years is way too much to expect from Buna O-rings.
     
  15. azure

    azure Final Approach

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    I am pretty sure they were replaced by Bob Russell during an annual about a decade ago, by the last owner. I know none have been replaced since I have owned the plane, though.
     
  16. donjohnston

    donjohnston Pre-takeoff checklist

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    Looks like you got a low wing there...

    FYI, swinging the gear on a high wing Cessna is not for the faint of heart. It almost has to be jacked up the the flight levels to swing the gear.
     
  17. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    I can not think of a reason that a bad seal or o-ring would prevent the gear from retracting. I am still going with a downlock that is stuck, pressure sensor or switch of some sort.
     
  18. azure

    azure Final Approach

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    Pressure allowed to bypass so not being applied to the gear? That was suggested on CFO as well. I would think, though, that there would be enough pressure to disengage the downlocks, barring some stuck condition. Based on the indicator light (and Mark-1 eyeball), the gear (at least the mains) never budged even though the pump was (apparently) running.

    There was certainly plenty of hydraulic fluid, so though I can't be certain about internal seals, there are no large leaks in the system.
     
  19. Dan Thomas

    Dan Thomas En-Route

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    Then you have no experience with this stuff. I work on Cessnas all day. Have done so for almost 22 years.
     
  20. Dan Thomas

    Dan Thomas En-Route

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    The downlocks are in the main gear up pressure lines. If they both don't unlock, it would be really unusual. Most likely they weren't getting any pressure, or not enough to do anything. If the green light didn't go out, none of the wheels retracted or even unlocked. The nosegear downlock is a function of a cam in the ram connection to the gear leg. No separate hydraulic downlock. Each gear has a switch in the downlock mechanism to fire the green light, and they're all wired in series. If any one unlocks, the light is out.

    If the pump was running and nothing moved, the drive coupling between the motor and pump might be sheared.

    Internal leaks don't make any mess under the airplane and don't lose fluid. An internal leak is between the pressure and return side of the system, and happens when a piston O-ring isn't sealing properly. It can seal intermittently if the flow is high enough to cause it to suddenly seat.
     
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  21. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Dan, you probably do have more recent experience than I do. My thought was that if the system is developing enough pressure to lock up the emergency hand pump system then there is probably enough pressure developed to run the system. Obviously if the pump is not developing enough flow & pressure things are not going to happen. I still think it is something like a pressure switch but I don’t have a diagram to study it. It will be interesting to hear what the issue is.

     
  22. azure

    azure Final Approach

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    Yes that was my thought as well. The plane was flown less than a week ago and the gear system functioned perfectly at that time. HOWEVER, I only performed one gear cycle, and between that flight and the one before that, we have had some extremely cold weather here in VT. As anyone who remembers the Challenger disaster knows, O-rings can fail to seal if exposed to cold temperatures, or seal only intermittently, as Dan says. I don't really have enough recent experience with the plane to say whether that possibility is likely or unlikely. The test will be getting the plane on jacks and testing the system out. If it doesn't work at all, then I'd favor some kind of switch failure. If it works intermittently, then possibly a poorly functioning seal in the system.

    (And of course, the problem may be completely irreproducible, in which case... well, as I said, I had a gremlin long ago too. That kind of problem I wouldn't give this FBO money to chase, it's just not an efficient use of my money. Better to inspect the entire system at annual, hopefully at a more reasonably priced shop, coming up in May.)

    For those who think I should invest in jacks, I'm not that much into performing my own maintenance, and in any case I can't imagine how I would transport them if I have to move. The jacks my old mechanic in Michigan owned were large enough and heavy enough that I would want a truck to move them. And then there's the fact that I'm in a community hangar... don't really have enough space to store them anywhere.
     
  23. Dan Thomas

    Dan Thomas En-Route

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    That manual pump is, as I said, in the pressure line. If the system developed pressure after you selected gear down (which it would have if the pump shut off, since it's a pressure switch that operates it) then the pressure in that down line would force the tail of the pump handle, in its retracted position, against the belly. Jams it tight. It's a sign that one of the check valves in the pump leaks a tiny bit. It's never an issue in an emergency or when on jacks and you test the manual system: Gear is up. Pull the breaker, select gear down (which takes the pressure off that line), pull the handle out and pump.

    Your mechanic might find something wrong with the manual pump, but the the jamming is common enough with gear down.

    If you go here: cavok.hu/wp-content/uploads/C177_AFM.pdf

    and scroll down to page 131, Figure 7-7, you'll see the system schematic.
     
    Last edited: Mar 1, 2018
  24. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Dan, thanks for sending the link to the schematic. Do you think the hand pump is jamming at less than 1,000 psi and the system is not getting adequate pressure to energize the pressure switch which appears to be in series with the squat switch? But then if the pump is kicking off doesn’t the system have to reach 1,500 psi to hit the high end of the pressure switch? What else is automatically shutting off the hyd pump if the pressure is not hitting the 1,500 psi called out in the schematic? Couldn’t the problem be this pressure switch not recognizing the 1,000 psi activation level or the squat switch is bad or there is a broken wire/open in the squat switch safety circuit?
     
  25. Kritchlow

    Kritchlow Final Approach

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    After a known gear problem you opted to go for another lap in the pattern and try to pull the gear up????

    Maybe I’m misunderstanding. I hope that I am.

    I do see you took some precautions then decided to scrap the mission.
    That said, I would never have done it even if all was well with the pump down.

    —JMO
     
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  26. azure

    azure Final Approach

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    You are misunderstanding. I did one lap, then landed when the gear failed to retract and never took off again. I considered it, then thought better of it when it was unclear whether I would be able to access the emergency pump.
     
  27. azure

    azure Final Approach

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    That's my understanding too and why I don't follow what Dan is saying. It seems that if there were insufficient pressure to activate the pressure switch to "on", then (a) the gear motor would never have started running, and (b) if it did, there would be insufficient pressure to stop it. Even if the problem were intermittent, the gear motor stopped on the retraction cycle, when the gear failed to retract. Unless pressure in excess of 1500 psi is needed to disengage the main gear downlocks... but the nose gear is electrically actuated as I understand it, and the fact that the green light stayed on says that NONE of the downlocks released.

    Which leaves me... totally confused as to what might be wrong. :confused:
     
  28. azure

    azure Final Approach

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    Incidentally, Cessna's recommendation if the gear fails to retract is basically to try it again while still in flight. They do not say what to do if the gear retracts on the second try, implying (to me anyway) that a single failure to retract may not mean gear system failure. They also don't seem concerned about a catastrophic event unless the gear fails to retract again AND the gear motor keeps running, in which case they recommend flying it with the gear down and not re-attempting the retraction. I did not even give the retraction cycle a second try, and the only thing I'm sure of is that the gear motor stopped running.
     
  29. bnt83

    bnt83 Final Approach

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    Do you have the service manual? IDK know what you mean by "nose gear is electrically actuated" but the nose is moved up and down by a hydraulic cylinder. There are two hydraulic cylinders that move all three landing gear legs in the 177RG. Many 177RG have electrically actuated main gear downlocks, only the very late models have hydraulic downlocks. Read the description and operation section of the retraction/extension system in the manual.

    I'd be curious exactly how much pressure the hydraulic pump is making. I've heard more than once a guy can hold the tail down and swing the nose gear for troubleshooting but I would definitely be prepared for a nose gear that won't come back down.

    The RG is a simple system but troubleshooting without the manual is futile
     
    Last edited: Mar 2, 2018
  30. bnt83

    bnt83 Final Approach

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    We have two high wing cessnas, niether are retracts, and I still want a set of wing jacks.
     
  31. azure

    azure Final Approach

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    I do not have the service manual, unfortunately. I was going by the POH. It's a 1976 model, and I'm pretty sure the main gear downlocks are hydraulically actuated. On the nose gear being electrically actuated, I was referring to the downlock release, not the moving of the gear itself which I know is hydraulic. Again, that is per the POH, not the service manual which I don't have. Unfortunately here at work I don't have quick access to my POH and I'm not sure what year models the version that Dan posted applies to.
     
  32. azure

    azure Final Approach

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    As I posted before, I'd LIKE to own a set of jacks, I just don't think it's very practical in my situation.
     
  33. Skip Miller

    Skip Miller En-Route

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    @Briar Rabbit: From message 6 in this thread:

     
  34. Briar Rabbit

    Briar Rabbit Pre-takeoff checklist

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    Yes I could not remember as I have not worked on or flown an RG since the mid 70’s. My 70 model 210 has gear doors which are operated hydraulically. Much simpler system without doors.

    When they are discussing the nose actuator and referring to electric down locks I think they are really referring to the safety squat switch on the strut?
     
  35. coloradobluesky

    coloradobluesky En-Route

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    It may end up that you will have the plane jacked up and swing the gear successfully and then fly merrily on your way. I had that happen on my Amphib. The gear didnt go up all the way, so I put it back down, flew to an airport (I was on a cross country far from home). The mechanic swung the gear, declared it ok, and it never happened again.
     
  36. azure

    azure Final Approach

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    Here is the relevant passage from the POH (it's the one Dan posted, but I think it's the same as in mine):
    And later:
    It sounds to me as if the nose gear downlock is NOT actuated hydraulically, since they say only that the main gear downlocks are, but it's not entirely clear to me how it is actuated. It may all be connected via a linkage to the hydraulically-actuated nose gear mechanism and the nose gear "wheel well" door; I assumed the release was electrically driven, but that may not be true. (Not sure why the POH uses the plural there, on my plane there is only one nose gear door AFAIK.)
     
  37. azure

    azure Final Approach

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    Yes, considering that this happened once before long ago, that's very possible. As I recall the symptom was the same, green light never went out. Not sure if the gear motor was running that time. I did as Cessna recommends, tried it again, and it worked. I put it down and landed, debated whether to take off again, but I was not at home base, so I launched. Until this week, that failure has not happened since.

    I certainly want to test it thoroughly before ungrounding it, but I'm not going to throw away money trying to reproduce the problem if it appears to pass all tests and works consistently. As I've said, the local mechanic can spend hours and hours digging into every nook and cranny of a system and the usual result is just a large bill.
     
  38. Capt. Geoffrey Thorpe

    Capt. Geoffrey Thorpe Touchdown! Greaser!

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    "The nose gear incorporates an over-center mechanical linkage which provides a positive mechanical up and down lock"
    That would imply that there is no separate latch hardware - the linkage is arranged in a way that when it is up or down it stays in place on it's own.
     
  39. Dan Thomas

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    The pressure switch is normally closed, which means that it runs the pump anytime the pressure is below about 1500 PSI. If you select gear up, the pressure falls because the valve has redirected fluid from gear down to gear up, the pressure falls, and the pump runs and pushes fluid until the gear is up and pressure builds to the shutoff point. If there's an internal leak of any significance that pump will continue to run, and if the gear doesn't even unlock due to a massive internal leak, it will run forever. The OP didn;t say that he heard the motor stop, only that he heard it running.

    The only guy that is going to figure this out is the guy that actually jacks the airplane up and troubleshoots the system. Symptoms described by pilots are often ambiguous. And I'm a pilot that has sometimes been fooled by symptoms experienced in flight, leading eventually to an "Aha!" moment.
     
  40. Ravioli

    Ravioli En-Route

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    Technically the gear requires electricity since the hydraulic pump is not engine driven.

    Ours has a hydraulic pump indicator light. Have you noticed the pump running longer than normal during gear movement? Also, has it come on when the gear was not being cycled? Could indicate leakage.