---------------------------------------------------------- Commander-List Digest Archive --- Total Messages Posted Wed 08/04/04: 1 ---------------------------------------------------------- Today's Message Index: ---------------------- 1. 10:05 AM - Re: landing gear cylinder removal (Scott Dickey) ________________________________ Message 1 _____________________________________ Time: 10:05:29 AM PST US From: "Scott Dickey" Subject: Commander-List: RE: landing gear cylinder removal --> Commander-List message posted by: "Scott Dickey" Hi Larry, If you have pressure indicated on your hydraulic gauge, there will be pressure on the extend portion of the inboard gear cylinders (when the gear is down). The outboard gear cylinders have N2 pressure on the extend side all the time from the emergency gear extend bottle in the baggage compartment. If you want to remove the landing gear cylinder on the ground, just bleed the pressure from the system using the following procedure: With all power OFF (engine driven and aux pumps), move the flap handle from the neutral position up or down VERY slowly until you hear the pressure bleed down to zero (you can see this happen on the gauge and you can hear it through the flap valve). It turns out the flap valve has a bleed port which bleeds pressure just before going to the flap UP or flap DOWN position. If you move the handle slowly, you will hear pressure relieve and see the gauge go to zero 1/4" or so before getting to the flap UP or DOWN position. Now the piston in the accumulator is at the end of its stroke with 600 psi nitrogen on one side and 0 psi hydraulic fluid on the other. There is no danger having the gear cylinder off on the ground because the bungees hold the drag brace locked in the over center position. In addition, you will still have the other cylinder on which is pressurized with N2 so you couldn't retract the gear even if you wanted to. The only thing I wouldn't do is remove both cylinders and the bungees at the same time. If you go to the trouble of removing the gear cylinder and disassemble it, you might as well just reseal the whole thing. Commander Aero has reseal kits that contain all the o rings you need to do the job. If you take the cylinder apart and metal parts look damaged, badly scored, etc. they have exchange cylinders and piston rods for reasonable $$. Don't forget to remove the hydraulic fittings before trying to disassemble the cylinder. The fittings thread through the outer aluminum tube into an inner piston cap and it won't come apart unless they are removed first. Personally, I am not a big fan of reusing old, relatively cheap parts like hydraulic fittings, fasteners, etc so I would replace them. Let me know if you want me to fax you the pages from the parts manual. When you replace the hydraulic fittings, you need to use some kind of sealant on the tapered threads. I have used Fuel Lube and Hugh from Merlyn Products had the name of some kind of thread sealant for hydraulic fluid use but I don't have it with me at the moment. Maybe some of the other folks on the list have recommendations. There should be no need to recharge the hydraulic accumulator after you do this. However, this is not a bad time to make sure you have a good charge of 600 psi as it must be checked/filled when the hydraulic system pressure is at 0 psi. If you don't have a 600 psi source of N2 at the avionics shop, I wouldn't worry about it. Just put everything back together, top off the reservoir, and cycle the gear in flight a few times to get rid of the air. That is the great thing about the commander hydraulic system - you don't have to bleed any part of the system except the brakes and nose wheel steering cylinder after servicing. This job shouldn't take more than a couple hours if you have all the parts and a good supply of sockets, stubbie wrenches, and open end wrenches. Have fun. Scott Time: 08:26:02 AM PST US From: "Larry Wokral" Subject: Commander-List: Landing Gear Cylinder --> Commander-List message posted by: "Larry Wokral" I have a 500B with a new Merlyn 320 conversion that is currently at Aerotronics in Missoula MT for a major avionics upgrade (CNX80, MX20, PS Engineering 7000B intercom & PXE7300 entertainment center, GTX330 transponder). While visiting it last Friday, I noticed that the left side inboard MLG cylinder had a pretty good leak at the piston (forward) end of the cylinder. Since they will want me to fly it with their technician onboard to test the IFR functions of the new CNX80 for certification before I can get it back to its home field (Hamilton MT, 6S5) for a repair, I may need to remove it while it is there and reinstall it before that flight. My service manual is in California, so my question to the list: Is there constant pressure on these lines when the electric pump isn't running? Can I remove the hydraulic lines to this cylinder and the cylinder itself without having to bleed down any high pressure? If not, will I have to recharge the accumulator before flying it after reinstallation? Lastly, is there any danger in the landing gear stability of the plane on the ground while this cylinder is removed? I know this is a pretty simple concept that I should already understand, but I am still new with Commander flying and service and am still learning. I'd rather take the cylinder to my home field mechanic for repair than to have some local mechanic in Missoula do it if it is possible. Thanks, Larry Wokral (who wants to make it to the TCFG fly-in if I can get it all together my the August 25 commitment time) PS: I read the Aeroshell report on 5606 hydraulic fluid alternatives that someone here provided. If there are so much better alternatives, why hasn't there been a universal substitution? I remember a wheel fire on a C119G after the pilot's hard braking heated up the magnesium wheels and ignited the fluid in the lines.