X-Virus-Scanned: clean according to Sophos on Logan.com Return-Path: Sender: To: lml@lancaironline.net Date: Wed, 18 Apr 2012 13:01:28 -0400 Message-ID: X-Original-Return-Path: Received: from mta4.srv.hcvlny.cv.net ([167.206.4.199] verified) by logan.com (CommuniGate Pro SMTP 5.4.4) with ESMTP id 5487184 for lml@lancaironline.net; Wed, 18 Apr 2012 11:45:15 -0400 Received-SPF: none receiver=logan.com; client-ip=167.206.4.199; envelope-from=Adam@ValidationPartners.com Received: from VpiWorkstation1 (ool-4351a46d.dyn.optonline.net [67.81.164.109]) by mta4.srv.hcvlny.cv.net (Sun Java System Messaging Server 6.2-8.04 (built Feb 28 2007)) with ESMTP id <0M2O00BYUMEBDOG0@mta4.srv.hcvlny.cv.net> for lml@lancaironline.net; Wed, 18 Apr 2012 11:44:37 -0400 (EDT) X-Original-Date: Wed, 18 Apr 2012 11:46:05 -0400 From: Adam Molny Subject: RE: [LML] Excessive down hydraulic pressure In-reply-to: X-Original-To: lml@lancaironline.net X-Original-Message-id: <8901937227B24EC195E554DEC7A75AC2@VpiWorkstation1> MIME-version: 1.0 X-MIMEOLE: Produced By Microsoft MimeOLE V6.00.2900.6157 X-Mailer: Microsoft Office Outlook 11 Content-type: multipart/alternative; boundary="Boundary_(ID_S4zyCZGg0SK/pFyN4nbeLQ)" Thread-index: Ac0dYDOM7+n2SguYTNeutEQ3lB+VwQAFI+2g References: This is a multi-part message in MIME format. --Boundary_(ID_S4zyCZGg0SK/pFyN4nbeLQ) Content-type: text/plain; charset=us-ascii Content-transfer-encoding: 7BIT Hi Jeff - Yes, I'm using my Sequenced Gear System in this plane. The inner gear doors close after the landing gear is extended for landing. I can say from experience that it provides a huge reduction in wind noise and cockpit drafts. Naturally I investigated whether my system could be contributing to the problem. During system development I changed to a down pressure switch with a set point of 650psi. The stock 550psi switch didn't provide enough 'oomph' to close the inner gear doors against the emergency opening springs. I have an older kit with the narrow diameter door cylinders. Customers with the newer style large-diameter cylinders are able to use the stock pressure switch. Theoretically, having a down pressure with a higher set point should help alleviate this problem since the system would be less sensitive to pressure buildup on the down side. I believe we can also rule out pressure buildup due to thermal expansion. My early flights never went above 5000' so there wasn't a big temperature swing. Also, you would expect to see a gradual rise in pressure due to cold soaking, which wasn't the case. Partway through the build process I also modified my hydraulic pump by installing the high capacity impeller. As part of the troubleshooting process I have removed the inner gear door springs. The gear still extend quickly in both ground and flight tests as seen in my fourth flight video. http://www.youtube.com/watch?v=fo1qnhBuqS8. While developing the sequenced gear system I learned that the pressure switches can be wildly inaccurate, and they behave oddly at the limits of their adjustment range. As you turn the adjusting screw to increase the pressure the hysteresis decreases. In other words, the pressure difference between turning off and turning back on again gets smaller. This can lead to pump chatter where the gear hit their stops, the pressure rises and the pump shuts off. Then the pressure drops slightly and the pump kicks in again. This can happen several times per second and last several seconds. The solution was to make sure the adjustable pressure switch was set near the middle of its pressure range. I don't have a solution yet but I'm reading through Chris Zavatson's excellent write up on the Lancair hydraulic system http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf. I'm beginning to suspect a sticky shuttle valve or some other internal pump problem, with the pressure switches as a secondary suspect. On my fifth flight yesterday I had to crack the dump valve to get the doors to close completely with the gear retracted - and this was with the door springs removed! -Adam Molny 7.6hrs Hobbs time and counting _____ From: Jeffrey W. Skiba [mailto:jskiba@icosa.net] Sent: Tuesday, April 17, 2012 9:52 AM To: lml@lancaironline.net Subject: RE: [LML] Excessive down hydraulic pressure Adam, Are you running the Stock Lancair gear system or are you using your gear system ? Do you have the first generation pump or the high capacity one ? --Boundary_(ID_S4zyCZGg0SK/pFyN4nbeLQ) Content-type: text/html; charset=us-ascii Content-transfer-encoding: 7BIT

Hi Jeff –

 

Yes, I’m using my Sequenced Gear System in this plane. The inner gear doors close after the landing gear is extended for landing. I can say from experience that it provides a huge reduction in wind noise and cockpit drafts. Naturally I investigated whether my system could be contributing to the problem. During system development I changed to a down pressure switch with a set point of 650psi. The stock 550psi switch didn’t provide enough ‘oomph’ to close the inner gear doors against the emergency opening springs. I have an older kit with the narrow diameter door cylinders. Customers with the newer style large-diameter cylinders are able to use the stock pressure switch.

 

Theoretically, having a down pressure with a higher set point should help alleviate this problem since the system would be less sensitive to pressure buildup on the down side. I believe we can also rule out pressure buildup due to thermal expansion. My early flights never went above 5000’ so there wasn’t a big temperature swing. Also, you would expect to see a gradual rise in pressure due to cold soaking, which wasn’t the case.

 

Partway through the build process I also modified my hydraulic pump by installing the high capacity impeller.

 

As part of the troubleshooting process I have removed the inner gear door springs. The gear still extend quickly in both ground and flight tests as seen in my fourth flight video. http://www.youtube.com/watch?v=fo1qnhBuqS8. While developing the sequenced gear system I learned that the pressure switches can be wildly inaccurate, and they behave oddly at the limits of their adjustment range. As you turn the adjusting screw to increase the pressure the hysteresis decreases. In other words, the pressure difference between turning off and turning back on again gets smaller. This can lead to pump chatter where the gear hit their stops, the pressure rises and the pump shuts off. Then the pressure drops slightly and the pump kicks in again. This can happen several times per second and last several seconds. The solution was to make sure the adjustable pressure switch was set near the middle of its pressure range.

 

I don’t have a solution yet but I’m reading through Chris Zavatson’s excellent write up on the Lancair hydraulic system http://www.n91cz.com/Hydraulics/Lancair%20Hydraulics.pdf. I’m beginning to suspect a sticky shuttle valve or some other internal pump problem, with the pressure switches as a secondary suspect. On my fifth flight yesterday I had to crack the dump valve to get the doors to close completely with the gear retracted – and this was with the door springs removed!

 

-Adam Molny

7.6hrs Hobbs time and counting

From: Jeffrey W. Skiba [mailto:jskiba@icosa.net]
Sent: Tuesday, April 17, 2012 9:52 AM
To: lml@lancaironline.net
Subject: RE: [LML] Excessive down hydraulic pressure

 

Adam,

 

Are you running the Stock Lancair gear system or are you using your gear system ?

 

Do you have the first generation pump or the high capacity one ?

--Boundary_(ID_S4zyCZGg0SK/pFyN4nbeLQ)--