320tech From Turks and Caicos Islands, joined May 2004, 491 posts, RR: 5
Reply 10, posted (10 years 12 months 4 days 15 hours ago) and read 5855 times:
What is a strut charge?
In airliners, the landing gear shock strut (aka oleo, gear leg, etc) is filled with hydraulic fluid (H-515, MIL-H-5606, AeroShell Landing Gear Fluid, "red stuff"), then topped off with nitrogen.
The fluid provides the main shock absorbing function on landing, while the nitrogen smoothes out lesser bumps, eg during taxi.
To fill it, the strut is compressed (we use a platform that can be pumped up to three feet or so), then filled with hydraulic fluid. The strut is then "blown down" using about 50 psi of nitrogen. Once it's fully extended, the strut is charged with nitrogen - around 1200 psi or so.
The process is a little more involved than what I've described, but it gives you the idea, I hope.
The strut charge, then, is the pressure of nitrogen in the strut. It's supposed to correspond to the strut extension. If extension is too low, either you're low on fluid or low on nitrogen. If it's too high, you've got too much nitrogen (can't really have too much hydraulic fluid).
And for the other A320 AME's, yes, I know, upper and lower chambers, etc, but just trying to keep it simple.
The primary function of the design engineer is to make things difficult for the manufacturer and impossible for the AME.
So, in short they are sort of pressurized chambers filled with nitrogen and then hydraulic fluid?
When the aircraft touches down, if all of the fluid takes the force only relying on its ability to compress or absorb the shock would that not pose a problem? Does it have like an overflow system which combines the viscous nature of the fluid to slow the rate of overflow, thus absorbing the force and also creating room for the strut to compress into the chamber resulting in absorbing of more force?
OK, did y'all get that or am I looking stupid right about now? Not sure if I am explaining this right? I need a whiteboard...
I'm all in favour of keeping dangerous weapons out of the hands of fools. Let's start with keyboards.
FredT From United Kingdom, joined Feb 2002, 2185 posts, RR: 26
Reply 12, posted (10 years 12 months 4 days 3 hours ago) and read 5826 times:
The fluid does not compress to any significant degree. That's one of the main criteria for a hydraulic fluid to be a good hydraulic fluid. It flows through valves to create a resistance as the strut is compressed, just as in any hydraulic damper/shock absorber.
The fluid is damping, the nitrogen is the "spring".
I thought I was doing good trying to avoid those airport hotels... and look at me now.
HAWK21M From India, joined Jan 2001, 31875 posts, RR: 54
Reply 14, posted (10 years 12 months 3 days 3 hours ago) and read 5783 times:
Quoting 320tech (Reply 13): As FredT says, the fluid doesn't compress. The fluid is forced through an orifice which decreases in size as the gear is compressed. This provides the shock absorbing action.
Also a snubber valve in the strut to reduce Oleo extension speed in Air.