If this is your first visit, be sure to check out the FAQ by clicking the link above. You may have to register before you can post: click the register link above to proceed. To start viewing messages, select the forum that you want to visit from the selection below. |
|
|
Thread Tools | Display Modes |
|
#1
|
|||
|
|||
Wanted clever PA32 engineer's thoughts - Gear extention problem on Piper Lance
Others may be able to give more knowledgeable advise, but I am somewhat
familiar with the gear system on the PA28R, and I believe the system on the PA32R is similar. As I see it, you have expressed two problems. The first is that the gear won't extend reliably with the normal hydraulic activation (accompanied by the squeal from the pump). The second, potentially more dangerous problem is alluded to at the end of your post when you state, "however once released with the emergency extension lever the hydraulic pump would push them to the locked position if required." The whole idea of the emergency extension system, which is essentially a valve that releases the hydraulic pressure holding the gear up and thus allowing it to free-fall into the extended (and locked!) position, is that it works independently of both the pump and the electrical system. Your statement seems to suggest that the gear will free-fall, but may not lock unless given a "boost" from the pump. Bad situation if you ever loose your pump! This second problem may in fact be related to the first problem. If you can figure out why the gear does not reliably free-fall to a down and locked position, you may also find the reason why the hydraulics won't reliably extend the gear down. Once place it start looking would be the pressure switch, which is common to both the main hydraulic circuit and the emergency bypass circuit. One more thing: I do not believe it is normal for the pump to squeal, even momentarily, at the end of the gear cycle, since the pressure switch should cut it off immediately when pressure spikes upon full extension, but I could be wrong. Anyway, this would also point to the pressure switch as the culprit. I presume your mechanic has checked to make sure the system is purged of air and is not leaking. Hope this might be of help. Good luck. -Elliott Drucker |
#2
|
|||
|
|||
("Richard Kelly" wrote)
snip Gear allways retracts correctly and without problems. On occasions when extending the landing gear it does not come down at all, all you can hear is a loud squeal as the hydraulic pump appears to pumping against a brick wall (similar noise to when holding a car's power steering against the stops) It allways extends with the emergency extention without problems. Whether it's computers, boats, cars, plumbing, etc, it seems when sh%* happens to me, mystery problems invariably have 2 (unrelated) things going on - at the same time. Trips me up every time - until I figure it out ....or stumble upon the (hidden) second problem. Good luck solving your mystery. Ass-u-me nothing!!! -- Montblack |
#3
|
|||
|
|||
On Thu, 17 Jul 2003 13:43:23 +0100, "Richard Kelly"
wrote: Will you settle for another Usenet junkie's thoughts? Worth exactly what you paid for 'em... On a retract PA28 or 32, the retraction cycle starts by picking up the gear handle. The pump will run in "up" mode, high (compared to extension) pressure is applied to the "up" side of the retract cylinders picking up the gear. For the pump to stop running, the required pressure must be seen at the pressure switch. Am reasonably sure that the "up" switches are for position indication only, the "high" pressure switch is what stops the pump. If the pressure bleeds off in flight, the pressure switch logic changes, the pump runs, pressure builds back up, switch shuts pump off. Pressure in the system is all that holds the gear "up". Emergency extension is accomplished by manually opening a valve in between the "up" side and the "down" side of the hydraulic system and also by actuating a switch turning on the pump in "down" mode. It is a semi-crappy valve, and you will not find a parts breakdown on it from Piper (unless things have changed in the last couple of years). I could tell you that it is likely similiar to a park brake valve on an Aztec (sharing the same seals), but then I would have to kill you. The gear should indeed extend and lock properly when this valve opens, with- or with-out assistance from the pump. If your aircraft has not been modified to remove auto gear extension, "too slow" results in only the mechanical valve opening, the fluid passes from the "up" side of the pistons in the retract cylinders, through the open valve, and back into the cylinders on the "down" side of the pistons and the gear extends via gravity, and with some spring assist. Before I forget, it is typical for the powerpack to squeal slightly at the end of the normal retraction cycle. The gear is mechanically rigged to be in the proper position with the pistons in the retract cylinders at full travel-when the pistons smack the ends of the cylinders, the pressure builds rapidly, the switch makes, pump shuts off. Absolute max retract pump pressure is regulated by a "high" pressure relief valve (part of the pack).. The gear's "up", the handle's "up", there is trapped "up" pressure holding the gear "up" until you select gear "down". Pump supplies reduced (compared to retraction) pressure to the "down" side of the cylinders, as there is no up-lock system, the gear immediately begins to extend. The pump will run , generating volume of flow, but not a lot of pressure, as the gear will pretty much extend and lock itself (remember?). When all three gear down-and-locked switches are actuated, the pump will shut off. There is no "down" pressure switch, however extension pressure is limited by another relief valve. The down-and-locked switches should actuate slightly before the extension mechanism/cylinder pistons run out of "travel". For the normal extension cycle, the pump should shut off electrically before it bangs up against the relief valve. If the gear is sloppy mechanically (common on the nose gear), and/or a d-&-l switch is rigged on the edge of being actuated, the switch relaxing will cause the pump to immediately run until the related cylinder/extend mechanism moves enuff to actuate the switch. There is no system pressure supplied to the properly down-and-locked gear, it is secured by mechanical means only. The book gives the range for proper extension pressure. This is typically checked by plumbing a gage into the extend side of the system, holding a main gear leg physically "up" and selecting gear down. Once the other two gear legs are down and stopped, the relief valve will be limiting the pressure, as indicated on the gauge. A leaking emergency extension valve can also "bypass" extension pressure, causing a lower indication. The high points are pressure switch "up" limit (pump shut-off), d-&-l switches "down" limit, emergency extension is a valve in the center leg of the "H" connecting the extend and retract hydraulic lines. This is only a general system overview, subject to subsequent technical correction, as I haven't had access to a Piper manual (or worked on one) for several years. I'm sorry but I cannot recall if the extend relief valve is an internal (to the pack) or external relief valve. I also am not sure how the powerpack/system mechanically "swaps" from "extend" pressure to "retract" pressure. My long distance usenet diagnosis is that electrically the gear system logic is to extend, but it is hanging hydraulically somewhere in between-the up pressure switch is electrically out of the system, and the d-&-l switches aren't able to shut the pump off. Hope this helped; TC Help !!! Anyone ever heard of this one. big snip |
#4
|
|||
|
|||
I think my closing statement may have been slightly confusing, in that when
I said if the gear is released with the emergency extention the power pack will push them into place. This gave the impression that the gear will not free fall into the down and locked position - It will. However what was missing from the statement is that if I prevent the gear from falling ie hold the nose leg back (simulating too fast an airspeed) and then someone resets the circuit breaker the pump will happilly power the leg into position. In other words I am not able to extend the gear using the pump because it just sits and squeals but if this situation occurs and the gear is released using the emergency extention the pump is then happy to continue push the gear into its down position Ric "Richard Kelly" wrote in message ... Help !!! Anyone ever heard of this one. snip |
#5
|
|||
|
|||
On 18-Jul-2003, "Richard Kelly" wrote: This gave the impression that the gear will not free fall into the down and locked position - It will. However what was missing from the statement is that if I prevent the gear from falling ie hold the nose leg back (simulating too fast an airspeed) and then someone resets the circuit breaker the pump will happilly power the leg into position. Oh! Well, given that new info I would guess that the most likely culprit is the shuttle valve in the power pack. This is the valve that directs the pump's pressure to the retraction or extension sides of the hydraulic circuit. The high pressure with the gear retracted may be somehow preventing the valve from moving from the "retract" to the "extend" position. However, when you reduce the pressure (with the emergency extension valve) the shuttle valve is then freed up to move to the proper position. Actually, given all your symptoms the problem could be with the pressure switch (external to the power pack) being set too high, so that the hydraulic pressure with the gear retracted is excessive, which might be what keeps the shuttle valve from moving properly. I am sure that Piper specifies a correct pressure range in its service manual, and this can be tested by a qualified A&P (err... "engineer"). All of the above are just the musings of an amatuer, of course, but hopefully it might help. -Elliott Drucker |
Thread Tools | |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Wanted: Gear Legs C-150 (1959) | Burt Compton | Aviation Marketplace | 0 | December 29th 03 04:18 PM |
Aluminum vs Fiberglass landing gear - Pro's and cons. | Bart Hull | Home Built | 1 | November 24th 03 02:46 PM |
Aluminum vs Fiberglass landing gear - Pro's and cons. | Bart Hull | Home Built | 2 | November 24th 03 05:23 AM |
Aluminum vs Fiberglass landing gear - Pro's and cons. | Bart Hull | Home Built | 0 | November 24th 03 03:52 AM |
Aluminum vs Fiberglass landing gear - Pro's and cons. | Bart D. Hull | Home Built | 0 | November 22nd 03 06:24 AM |