|
|
|
Bill,
What was the cause of the engine failure?
Jeff
-----Original Message-----
From: GT Phantom <gt_phantom@hotmail.com>
To: lml@lancaironline.net
Sent: Tue, Apr 19, 2011 5:13 pm
Subject: [LML] Re: Gear operation fix for the LNC2
Wolfgang,
I know that this was discussed a while back, but it occurs to me that this module could induce catastrophic failure if it activates a few times in flight, e.g. if the pressure for some ungodly reason is NOT relieved the pump could build up so much pressure that it blows a seal or worse.
Bypassing the pressure switches AUTOMATICALLY is not, IMHO, an actual solution but rather a work-around that could unintentionally cause unexpected consequences. While fixing the pump with the latest mods and installing the three-way dump valve is probably the best actual solution (fix the problem, not the symptoms), if you want to do a work-around it's probably safer to use the momentary push-button solution (e.g. manually bypassing the pressure switch by intentional pilot command) than to have an automatic system repeatedly exercising a workaround without the pilot's knowledge.
Everyone,
By now some of you know that I experienced engine loss a few months ago and ended up attempting to land on a highway. Unfortunately an SUV pulled onto the highway at the last moment, and the energy spent waiting to get past the SUV was simply too much to leave enough for a flare. The result was a hard touchdown, breaking off the left main and slamming the left wingtip onto the highway. The plane pulled hard left, leaving me concerned that the plane would cross the grass median into oncoming traffic. There was just enough energy left to momentarily re-raise the left wing, apply the right brake and rudder to straighten out, and make a split second decision as to whether I could land on two wheels safely or whether attempting that would result in either resuming course towards oncoming traffic or result in flipping in the median. Given the choice, I chose to raise the remaining gear and slide rather than risk flipping and being trapped in a scenario that might possibly have involved gasoline leaking on a hot engine with us trapped inside. Google N351E for photos of the result.
Why is that pertinent to this discussion?
Prior to that I had had a gear-up landing from pump failure and other factors involving a potential partner. I spent 3 yrs of weekends rebuilding and a year flying before this incident. In the mean time, I became VERY familiar with my systems. And, I just don't want to see any more of our community end up busting their ass if it is avoidable or spending your time fixing what might have remained a perfectly good airplane.
SOooooooo....
Chris has made an EXTREMELY generous offer to all of you. If you don't KNOW that your pump has the latest mods, take him up on it. He is sharp and an obsessively careful individual.
Install the 3-way valve if you have the time and inclination. Install the push-button override, too.
But do NOT install automated work-arounds that may be disguising or exacerbating real problems.
Please.
Blue skies,
Bill Reister
From: Wolfgang <Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Sun, April 17, 2011 10:13:18 AM
Subject: [LML] Gear operation fix for the LNC2
Here are some details on the Gear Fix Module - - - - -
There is a potential for the landing gear to fail to operate in the LNC2.
The spool in the hydraulic pump can come off it's end position and seal the fluid volume in the lines. When the system incurs a large temperature rise, the trapped fluid expands raising the pressure in the lines, tripping both pressure switches open and making the hydraulic pump inoperable.
A module to fix this gear operation failure in the LNC2 using the standard hydraulic system is now available. It is installed across the pressure switches and monitors their operation. If both switches are tripped open by high pressure, the pump is made to run in the direction set by the gear switch re-seating the spool in it's end position restoring normal pump operation and relieving pressure in the offending side. This happens automatically without pilot intervention.
The module is 2.5" x 1.5" x .75", weighs 2.3 oz. and has two pairs of leads that connect directly to each pressure switch with 1/4" spade terminals. No other wiring is necessary. Price is $250.00 each. Simple installation instructions included.
----- Original Message -----
Sent: Saturday, April 16, 2011 8:24 PM
Subject: Re: [LML] Re: LNC2 Gear Hydraulics
Wolfgang,
What is your gear fix module?
Bryan
On Fri, Apr 15, 2011 at 10:11 AM, Wolfgang <Wolfgang@micom.net> wrote:
From a design point of view, I still have a big concern about relying on the friction from an O-ring to keep the landing gear functioning properly. Vibration levels can exceed 70 G's. I would be much happier with a spring loaded ball detent or something similar.
That's why I came up with the gear fix module.
Wolfgang
----- Original Message -----
Sent: Wednesday, April 13, 2011 8:25 AM
Subject: Re: [LML] Re: LNC2 Gear Hydraulics
A symmetric back-pressure circuit and spool will eliminate the possibility of installing the spool backwards as happened with pumps manufactured in about the '96 through '98 time frame. The spool must still remain in place after the pump shuts down to prevent both high and low circuits from locking up simultaneously.
Using o-ring 013-70 requires 30 g's to move the spool.
Using o-ring 013-90 requires 70 g's to move the spool.
This includes the return force generated by the poppet springs (410462).
The difference between the two o-rings is durometer. I have been using the softer one without any problems. The stiffer o-ring (intended for pumps with back pressure circuits) should leave no doubt. The first thing to do with a pump that has a history of locking up both sides is to measure the return force for the spool and make sure it has an o-ring installed.
Chris Zavatson
N91CZ
360std
From: Wolfgang <Wolfgang@MiCom.net>
To: lml@lancaironline.net
Sent: Mon, April 11, 2011 4:56:57 AM
Subject: [LML] Re: LNC2 Gear Hydraulics
When I first got into this problem with the hydraulic pumps last year, I had a few conversations with the product manager of the Oildyne 108 pump. There have been many changes in it's production life and one of them was to make the spool symmetrical and have the relief circuit the same both ways.
Wolfgang
Wolfgang,
Yes, I have considered this. The spool with O-ring is a very tight fight. While I have not tried to measure the force to move it, I would estimate something over 50 g's to move it (I'll measure this the next time I have a pump opened up) Could it be that a pump somehow ended up mounted such that it was subjected to some resonant frequency? Seems like a remote possibilty given all the variables and the mass of the pump. How about wear and tear? Perhaps sitting dry and idle for ten years would do it. A missing O-ring or a spool that doesn't utilize an O-ring would allow the spool to move very easily. Parker does make spools that don't even have O-rings. Did these end up getting installed by chance?
Based on reports from the LML, the behavior seems to be rather binary. On the one hand we have planes with over 1000 hours and more than ten years of service that have never once had the spool move off the poppet. On the other hand, we have planes with circuits that lock up right out of the box (put into service).
This leads me to believe there is a difference in configuration. The easiest way to verify this is to simply open up a pump that is known to lock up hi and low circuits simultaneously.
While I have opened up several pumps (primarily to flip around spool valves), I have not yet worked on one that had this lock up issue. I am optimistic the difference will be quite obvious upon inspection.
Chris Zavatson
N91CZ
360std
Sent from my iPad
Chris, have you considered what effect airframe vibration has on the position of the spool in the pump and the problem in general ?
Wolfgang
|
|
|
I would like to extend the offer to the whole group. I think the entire community would benefit from understanding why some pumps are allowing the system to lock up. If anyone has a pump that exhibits this behavior and could part with it for a week, I am willing to check it out on the test stand and examine the internal configuration.
Chris Zavatson
N91CZ
360std
|
|
|