N2 pressure

[Jdm]

How much regulator pressure capability is required to service most GA main struts? Not on jacks, on the bench, or lifting the wing from below. I’m talking general weight on wheels servicing.
Asking because I can’t exactly remember for GA airplanes. Now I need a new regulator, and want to make sure it’s capable of normal servicing without going overboard.
Thanks!

 

[Dan Thomas]

How much regulator pressure capability is required to service most GA main struts? Not on jacks, on the bench, or lifting the wing from below. I’m talking general weight on wheels servicing.
Asking because I can’t exactly remember for GA airplanes. Now I need a new regulator, and want to make sure it’s capable of normal servicing without going overboard.
Thanks!

I remember using over 250 psi sometimes. But the service manuals often told you to jack the airplane to get the weight off the wheels, and bring the pressure up to a certain point, a lot lower than it would be with the weight on the strut. 40 psi in the 172 nose strut, I think.

Most struts are sticky enough (with the wheels on the ground) that you have to raise the pressure until it starts to raise the airplane, and then it shoots to full travel, and now you have to fool with releasing nitrogen, then it unsticks again and now it's too low. Sometimes it's easier just to do as the manuals say.

 

[Jdm]

struts are sticky enough (with the wheels on the ground) that you have to raise the pressure until it starts to raise the airplane, and then it shoots to full travel, and now you have to fool with releasing nitrogen, then it unsticks again and now it's too low. Sometimes it's easier just to do as the manuals say.

That I understand. Good reminder! Servicing Bonanza mostly. Wishful thinking I suppose

 

[Gary Ward]

How much regulator pressure capability is required to service most GA main struts? Not on jacks, on the bench, or lifting the wing from below. I’m talking general weight on wheels servicing.
Asking because I can’t exactly remember for GA airplanes. Now I need a new regulator, and want to make sure it’s capable of normal servicing without going overboard.
Thanks!

IMO you need 2 different regulators depending on what plane your working on.
Some planes need 1000-1200 psi sitting on the wheels. Not a cessna 172 but some beechcraft models do. So you need a reg that can go up to at least 1200psi if you want to add gas with the weight on the wheels.
The one I use on my 172 is 400 psi regulator and the pressure gauge is small enough increments to be somewhat interpreted down low. Mine has been set for approx 50 psi and I bled my strut down on my 172. Trying to put it in with weight on the strut makes harder to accurately do it. IMO
A higher pressure reg gauge will hardly read at 45 psi, so the need for different regulators depending on the plane.

I would think it would better to take the weight off, add pressure which won't be real high pressure then bleed the gas down for the right height.

 

[Jdm]

Good points Gary. I’m spoiled with airline experience! Never really looked at the gauges much. Just bumped the struts up to chart values.

 

[geezer]

For the 172 and other Cessna pilots here, a couple of tricks.

2 guys, no guage needed, but a quick and reliable valve in the gas line.
Mags checked off, Idle cutoff. Fuel line off. Propeller horizontal, and one guy stays in front of it.
Second guy connects the gas line to the fitting, signals to the first to start bouncing the nose slightly up, as he gives small squirts of gas.
Eventually, the nose will approach the desired height, the first guy tapers his bumps to zero, and the GUY BEHING THE PROP measures the extension.
Be sure that the distance is correct for your model and year, they do vary.

Wipe the strut clean, then moisten with fluid

Good pressure guage? Alone? You need a smooth strong rope and smooth tie down ring in the pavement.
Tie the rope to the fixed tie down ring, and position tail directly over the ring. The rope goes up through the tail ring, back down, and through the fixed ring.
Place the heel of one hand exactly on the rivet line of the stabilizer spar. Press down and pull the rope at the same time, until the nose wheel is several inches in the air.
Shift the hand on the rope next to the fixed ring, and wrap a loop of the loose portion of the rope around the vertical portion several times, and tie the loop to the loose end.

Fill to the correct pressure, and done.

If you leak fluid, this is a good time to remove the fill plug, measure the level, an correct that.


There were at least half a dozen Cessna owners at the field at one time who shared parts of the above tools and equipment. Most time ther4e were3 or more to share the work, so much easier than described above.

 

[NordicDave]

..the service manuals often told you to jack the airplane to get the weight off the wheels, and bring the pressure up to a certain point, a lot lower than it would be with the weight on the strut. 40 psi in the 172 nose strut, I think.

..Sometimes it's easier just to do as the manuals say.

Dan is correct as he commonly is on MX issues. A couple of sandbags over the elevator spar holds a 172 tail down /nose up.

My own 182P nose strut was 100% overhauled, including the placard with a summary of the service manual instructions for filling:



The strut should be disassembled every 1000 hours or sooner if flown infrequently. That old 5606 hydraulic is black and nasty on too many planes. Plus the rebuild kit from McFarlane is not very expensive.

Here's what too many Cessna nose bearings look like:
When dissembled, it's prime time to replaced the 2 needle bearings that are likely impacted with rust & grit and dry of any grease. Greasing these bearings are 1000 hours maintenance items. NO SPL spray, needs to non-water soluble grease.



Replacement:

 

[Dan Thomas]

Wipe the strut clean, then moisten with fluid

A wet strut attracts dust and grit which is then carried up and grinds away at the scraper ring. It gets embedded in the ring and scores the strut. Once the scraper is shot, the grit eats into the O-ring and bearing. Besides that, 5606 dries to a sticky gum that makes strut operation jerky. It's best left dry.

Place the heel of one hand exactly on the rivet line of the stabilizer spar. Press down and pull the rope at the same time, until the nose wheel is several inches in the air.

Cessna forbids pushing down on the stab, even on that forward spar. It's a much higher load than flight puts on it, and the spar cracks in the center. I have encountered too many cracked spars caused by people pushing down on it to turn the airplane. I once ferried a 172 in which I subsequently found that spar broken clear through. The stab skins were taking the loads, Could have failed any time. If you're going to push down, do it on top of the fuselage bulkhead adjacent to that spar.

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=22210

 

[Gary Ward]

A wet strut attracts dust and grit which is then carried up and grinds away at the scraper ring. It gets embedded in the ring and scores the strut. Once the scraper is shot, the grit eats into the O-ring and bearing. Besides that, 5606 dries to a sticky gum that makes strut operation jerky. It's best left dry.



Cessna forbids pushing down on the stab, even on that forward spar. It's a much higher load than flight puts on it, and the spar cracks in the center. I have encountered too many cracked spars caused by people pushing down on it to turn the airplane. I once ferried a 172 in which I subsequently found that spar broken clear through. The stab skins were taking the loads, Could have failed any time. If you're going to push down, do it on top of the fuselage bulkhead adjacent to that spar.

https://support.cessna.com/custsupt/contacts/pubs/ourpdf.pdf?as_id=22210

I agree with Dan's advise which is always spot on.
5606 hydraulic oil in some sticky stuff not at all like say aw32 hydraulic oil as a example. Which is 10w oil basically.
I like using mineral spirits on the chrome shaft on my strut, cleans bugs off, provides just the right amount of lubrication and drys quickly so dust and dirt does not stick to it. Keeps your strut nice and clean and free moving.
I have improvised several times with my 50 pound tool box to hold down the rear end of my 172 since I don't have a eye bolt in the floor of my hangar. Holds the rear down nicely. I agree putting weight on the stab is not a good idea.

It was just heavy enough.

 

[schmookeeg]

That I understand. Good reminder! Servicing Bonanza mostly. Wishful thinking I suppose

bonanzas are 100psi per the shop manual, but as noted, that's with weight off of wheels. I can only imagine how much pressure is in those struts with weight on.

 

[Gary Ward]

This thread reminded me to dig this steel plate out of my garage. It is a left over light pole base. I blew a square into them and welded square light poles to them years ago. It weighs way more than 50lbs I'd say. I am going to put it on a furniture dolly to move around the hangar. I have some other plate I can add if need be.
I will use it at the hangar to hold rears down for gear swings when the plane is on jacks and front tire changes. It is heavy, soon to be in my hangar.

 

[Gary Ward]

bonanzas are 100psi per the shop manual, but as noted, that's with weight off of wheels. I can only imagine how much pressure is in those struts with weight on.

I believe 95 psi on the front and 175 psi on the mains on some with no weight on them. Put em the ground and the mains can go up to 1000 psi. Much better to work with 175 psi than 1000 plus when adding gas IMO. But much quicker cheaper to have a reliable setup and not have to jack em up. I can see it both ways.

 

[Magman]

There are quite a few aircraft with “ damage holes “ near jack points.

When jacking 1 wing ; as the jack extends the geometry changes and causes the

jack to tip. I’ve seen aircraft where the owner holed the wing; twice!

The Bogert Strut Service Kit works great . You can fill fluid or ( air/N1) w/o

disturbing gaskets or removing valves.

 

[Jdm]

I appreciate the replies. Good tips about rebuilding the 172 strut. I did the same thing already. Took it ALL THE WAY down. Cleaned and greased the collar bearings, new seals, hardware kits, everything from McFarlane. It’s amazing now. Wish I had blasted and painted it, but I wasn’t set up for that at the time.

The nitrogen regulator OP however was aimed towards bonanza and other low wing strut servicing.

 

[geezer]

The Geezer, yields graciously to the greater knowlege of Mr. Thomas.

Fortunately, we were usually over supplied with manpower, and two pressed dpow on both the fuselage and stabilizer spar, so we SEEM not to have damaged a spar.

Fond memories of the days when if you unloaded some tools beside the plane, a crowd would form and OFFER TO HELP. They often had the correct tools, too.

You did learn who not to use for anything touchy.

 

[3393RP]

This thread reminded me to dig this steel plate out of my garage. It is a left over light pole base. I blew a square into them and welded square light poles to them years ago. It weighs way more than 50lbs I'd say. I am going to put it on a furniture dolly to move around the hangar. I have some other plate I can add if need be.
I will use it at the hangar to hold rears down for gear swings when the plane is on jacks and front tire changes. It is heavy, soon to be in my hangar.

That plate is proof if you keep stuff around long enough, there will eventually be a use for it.

You just need to own a big enough shop or hangar.

 

[Doug Reid]

Not sure about your Cessna, but around 150-160 psi on my Bonanza main struts fully extended on jacks, and 100-120 on nose strut fully extended.

I remember inflating the nose strut on a C150 with an air tank back in the day.

 

[Jdm]

Thanks Doug. I’m not worried about the Cessna. It’s the Bonanza numbers I’m interested in.