Nose wheel oleo wont hold

Nose wheel oleo wont hold

<HTML>The nose wheel oleo on my 1972 172L consistently loses its air or oil.  My mechanic has tried several possible  solutions, but the problem keeps recurring.  Initially, the hydraulic fluid would leak, but this seems to be resolved with the installation of new seals (for a second time), however, each day, especially after large temperature swings, the plane lowers an inch or so, until it is almost completely metal to metal.  Does any one have any suggrestions.  Of course, I want to avoid changing the entire nose wheel assembly.

Any help would be greatly appreciated.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Just went through the same thing... first fix was to change the schrader valve, that didn't solve it... it turned out to be the rubber ring under the schrader valve causing all of my problems..

Jeff</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Thanks for the advice Jeff. 

Do you by chance have the Cessna part number, in order to be very specific with my mechanic.

Thanks</HTML>

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<HTML>Start by replacing the valve, part#0543036-1(a common schrader valve - cost me $2.56) and the gasket part#AN901-5A(under $1.00)(these are on a 1980 152). Total cost with labor under $10.00.

Jeff</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Just rebuilt the nose strut on my 172. The big deal I found was making sure when you put it back together that the cylinder walls are honed out very smooth. If not, they will pinch the o-rings when you slide them together. There is a very, very small tolerance between the housing and the piston.  I messed up two o-rings before I figured out what was going on. Also, I've noticed that people who use air instead of nitrogen in the strut get a lot of variation (up & down) in the strut depending on the temp. Hope this helps.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Peter:

As Greg mentioned, there are people who use air instead of nitrogen when servicing the nose strut.  I would never use compressed air in my strut unless is was an emergency.  Nitrogen should be used because it is dry and containes no moisture.  The moisture in compressed air will eventually lead to corrosion.  This is also the case if you have tubeless tires.  I have seen what the inside of a wheel looks like where compressed air was used, and its not a pretty picture. 

Another good practice for your strut is to wipe the piston with Hyd fluid (5606) after each flight.  I am sure you have seen struts that have all kinds of dirt on the piston.  The o-rings do not act like wipers and push away the dirt when the strut compresses.  Instead, the dirt will get between the o-rings and act like sand paper, eventually wearing the o-rings with the end result of leakage. 

Sal</HTML>

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<HTML>Hummm!  - maintain three 182RGs - Combined time is 30,800 hrs.  Always used compressed air in the nose struts  and tires.  No corrosion - original wheels and struts still look and work great.  Prefer Tubes to tubeless... Just another opinion! Jack</HTML>

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<HTML>I would assume that the internal piston assembly in the nose struts are Stainless Steel or some kind of chromium finish and it is not just a low alloy or Carbon Steel.  Stainless steel or chromium finish in not prone to corrosion.  (That is of course unless you are near the sea.  Sea water environment is the pits when it comes to corrosion.)  In which case use nitrogen.  The nitrogen blanket will prevent corrosion since you need oxygen inorder to have corrosion.  It's the dissolved oxygen in the water that causes the corrosion.

Greg, in your statement:

"Also, I've noticed that people who use air instead of nitrogen in the strut get a lot of variation (up & down) in the strut depending on the temp."

I can not understand any physical reason for this.  air is ~78% nitrogen and the thermal expansion coefficients of air and nitrogen are approximately identical.  The difference is not noticeable.  Something else must be going on if you are seeing this.

As noted above, nitrogen precludes corrosion and that's why it is preferable to air, but according to Jack's experience, the design of the metal alloys used seems to do a pretty good job of inhibiting corrosion.

my 2 cents</HTML>

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Re: Nose wheel oleo wont hold

<HTML>The compressed air will have a moisture content which will affect pressure and volume according to tempreture. The Nitrogen will not have a moisture content.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Joe,

I'm not sure I buy your explanation entirely.  If the air in the oleo were completely saturated at the various temperatures, you would add the vapor pressure to the pressure of the air to get the change in oleo pressure. 

At 32 degrees F, vapor pressure is about 0.09 psia,
At 99 degrees F, vapor pressure is about 0.9 psia, and
At 117 vapor pressure is 1.5 psia. 

The change due to moisture content can be estimated by adding the partial pressure to the air pressure in the oleo.

You can estimate the effect by dividing the 1.5 by the nominal value for the oleo gage pressure. I'm stuck here because I do not know what that pressure is.  But since the change in pressure is relatively small for most temperature ranges, I can't see how this can be a major effect.  I guess it all depends on what Greg means by a lot of variation.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Barry, You seem to have some very factual information regarding why compressed air should not be any more subject to temperature change than nitrogen. I am definately not a physicist, nor will I attempt to hold a debate with one. All I know is what I have seen through personal observation here with the guys who use air; Low air temp = Low nose strut, Warm air temp = High nose strut. The guys that I know without doubt who use nitrogen (including myself) do not experience this. Please do not ask me to explain why, because I cannot. But I can also see what you are saying, Barry, with air being 78% nitrogen and thermodynamics and so forth. Although what Joe says above also makes sense to me also. I don't know!!!</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Greg,

You sound frustrated.  Sorry, I'm not trying to frustrate you nor do I doubt your experience.  When I hear something that sounds strange to me I want to understand it.  I am new to owning an air plane.  I want to learn as much as the next that's why I participate on this website.  Hopefully, it will help me to make better decisions.  I do appreciate your input.

I was trying to understand what a lot of variation is by your experience.  You say low temp = low strut;  High temp= high strut.  Are you saying that there is so much variation with air that you need to add air or bleed some off or are you saying about an inch difference between air and nitrogen?  Just trying to understand the magnitude of the question.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Is it LEGAL to use air, instead of nitrogen, in landing gear oleos?</HTML>

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Re: Nose wheel oleo wont hold

<HTML>In the 100-Series Service Manual, Section 2 - Ground Handling, Servicing, Lubrication, and Inspection, paragaph 2-20 - Nose Gear Shock Strut refers to ensuring that the strut is filled with hydraulic fluid and is inflated to the correct "air pressure".  Use of air sure sounds legal to me.  In fact, the service manual doesn't mention the use of nitrogen, although it sure makes sense to use it if it's available.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>My guidelines - If you own a Falcon 50 (or real expensive) - use Nitrogen.
      If you have kind of a "basic" Cessna - Air in the strut will suffice. Speaking of Cold or Hot temps - bigger issues of concern are preheating , proper engine cooling. carb ice, low batteries etc.  Struts will vary - no matter what you do.   If Nitrogen is available - use it. If not, there's always plain old air.  Last checked today,  It's still legal. Jack</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Stan,

You brought the piece of information I was missing.  Some moisture that may be in the compressed air will condense and then sink to the bottom of the hydraulic fluid.  It will for all intents no longer be available to evaporate again into the air.  As long as the water is not in contact with a metal prone to corrosion there should be no problem.

Bottom line, I agree with both you and Jack air is probably a good substitute. If the components were very susceptible to corrosion the service manual should specify nitrogen.  Having said that, nitrogen cylinders should be relatively inexpensive because it is use in industry routinely just for these purposes.

Jack,

Yes there are much bigger issues, but sometimes its the smaller ones that can be costly.  "The devil is in the details."  And if I owned a Falcon 50, someone else would be concerning themselves with what they should put in the damn oleos!  (And who came up with the word Oleo anyway?)

Miriam-Webster dictionary on the web says "Etymology: short for oleomargarine
Date: 1884

MIGARAINE:  a food product made usually from vegetable oils churned with ripened skim milk to a smooth emulsion and used like butter.</HTML>

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Re: Nose wheel oleo wont hold

<HTML>Stan,

You brought the piece of information I was missing.  Some moisture that may be in the compressed air will condense and then sink to the bottom of the hydraulic fluid.  It will for all intents no longer be available to evaporate again into the air.  As long as the water is not in contact with a metal prone to corrosion there should be no problem.

Bottom line, I agree with both you and Jack air is probably a good substitute. If the components were very susceptible to corrosion the service manual should specify nitrogen.  Having said that, nitrogen cylinders should be relatively inexpensive because it is use in industry routinely just for these purposes.

Jack,

Yes there are much bigger issues, but sometimes its the smaller ones that can be costly.  "The devil is in the details."  And if I owned a Falcon 50, someone else would be concerning themselves with what they should put in the damn oleos!  (And who came up with the word Oleo anyway?)

Miriam-Webster dictionary on the web says "Etymology: short for oleomargarine
Date: 1884

MIGARAINE:  a food product made usually from vegetable oils churned with ripened skim milk to a smooth emulsion and used like butter.</HTML>

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Re: Nose wheel oleo wont hold

I clean the strut of my old 210 A after or before every flight but I never use hydraulic fluid I prefer avgas. I have been flying for 6 years after rebuilding my aircraft and I never added hydraulic fluid in the strut I only inflated it once two years ago.
Alain

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