Squirrel - Hydraulic Fluid Contamination

[pitchlink]

Hey guys,

 

MNR has grounded their entire a-star fleet pending results of the cold weather testing.

 

I just heard that one of the operators is focusing on the moisture levels in the hydraulic fluid.

 

Some of the highlights I received are attached below.

 

An internal technical review of recent incidents concerning hydraulic/ flight controls problems experienced on the AS350 series aircraft has identified water contamination (moisture) of the hydraulic fluid to be the most probable cause. Transport Canada and Eurocopter are presently conducting an official investigation including cold weather testing.

 

Remove any “Tanis” heater pads from “metal” hydraulic oil tanks (if equipped). These pads are not to be used any longer as they may promote condensation in the fluid.

 

Hydraulic oil change interval is “each 100 hours”. The Company has decided to use Royco 756 hydraulic oil across the fleet.

 

 

Safe flying,

pitchlink

[skullcap]

Am a little confused about water contamination.

 

I understand that if water is turned to vapor it would become an issue as any gas compresses and is not a "good" hydraulic fluid and the controls would become sloppy and cause mucho grief(this is another reason why you shut off hydraulic switch when you have a failure, you do not want to have a possibility of pump pumping air into system). Water on the other hand is a "good" hydraulic fluid(the original I believe).

 

So my point is that water does bring with it all sorts or other problems such as corrosion which would cause a FOD problem, but water in itself,,,how does it cause problem directly? If the system to be overheated then obviously it would turn to vapor, there is not any direct tempurate indication of oil, so cannot say exactly what it runs at, but doubt strongly that ever gets to 100' C. Maybe there are some pilots out there who operate aicraft with temp sensors and could shed to light on this? Purhaps they are worrying about ice forming and causing fod or blockage of filters but "water" I don't get.

 

As #### stated some systems contained up to 40% water, I can only assume that these systems were operating properly and in warm climates. The recommendations of changing oil and removing heater of metal tank is great though it precludes moisture forming. But to my limited background water itself is not the culprit. It is a link in the chain of problem which eliminated, could further prevent degradation of the system.

 

sc

[CTD]

I'm going to say very little about this - but the whole story will soon be out.

 

What I will say is that 100 ml of water in a 3 litre system turns the fluid from a nice translucent red colour to a strawberry milkshake.

[skullcap]

Sorry CTD I have to bite;

 

Can a strawberry milkshake not have hydraulic ability, ahhh....maybe is oxygen mixed into the system? This would allow some sort or bad stuff to happen me thinks, please explain. Foaming usually affects lubrication abiltiy of oil, and has tendancy to blow seals(anyone see the monkey joke about the penguin...its just ice cream,,,sorry).

 

sc

[Guest CHEVY II]

Water in Hydraulics? Possibly @ sub zero temps...there's a mix for a whole lot of grief! :shock:

 

I'm not endorsed on the A-Star, so I remain ignorant to it's systems, nor am I an engineer, so my comments are from personal experience only

 

In past experiences, where water contamination was discovered in various hydraulically operated machinery I've had the pleasure to operate...water and oil just doesn't mix, especially in hydraulic systems!

 

The effects that I've felt on controls were far outside what they were supposed to be.

 

Just the viscosity alone when the two mixed and turned essentially to foam, gave the controls a "blind spot" or faded momentarily with little or no response.

 

Water in itself is a great hydraulic fluid and is used in several applications where fluid contamination must be kept to a minimum in the event of a leak, but the two can never be mixed and expect to have "descent" or acceptable hydraulic control because both fluids have "good" properties.

 

The damage that occurs, that often goes unnoticed in the valve bodies and tiny orfices which is corrosion and the weakening of your fluid capabilities, once explained to me as "hydrolysis" which I believe is the decomposition of the hydraulic fluid because of a chemical reaction with the water when heated.

 

This has caused hydraulic systems to fail at the worst times...Murphy's Law

 

With this scenario present at sub-zero temperatures :shock: I've had all kinds of problems before the "system" had a chance to warm up. These systems had no additional heaters, the fluid only heated due to friction as the fluid passed through the system. If there was enough water present in the oil, it naturally would attempt to freeze causing a sticky, sluggish or frozen...(literally) feeling. This in turn caused all sorts of problems that cost all kinds of money but I was happy to be on the ground when it happened and not flying around with Pax.

 

Anyway...just my 2 cents worth from personal, "non-aviation experiences".

[skullcap]

Thanks chevy, very informative.

[skullcap]

Chevy;

 

I would think that since there is a change in viscosity of oil then the pump may even have cavitation problems which would be bad as well, maybe this is one reason that mere were mixed forces on hydraulics? Astar oil is temperature regulated by running the hyd oil lines on the inside case of transmission so if trans oil is warm then you should have warm hyd oil.

[Guest CHEVY II]

Thanks chevy, very informative.

No problem...like I said, just personal experience!

 

ps: always, always, always refuse to "run" junk. Might just save you a whole world of grief :up:

[Guest CHEVY II]

I suspect there would be a cavitation issue as the "milkshake" try's to pass through a pump...not really sure what would happen in the servos. I'm sure it would result in some of the wierd control responses I've felt.

 

But I'll leave that one up to the "guys in the know" :hide:

[skullcap]

One thing forgot to mention; hydraulic is only warmed by trans oil is if you are actuating controls, so if sitting on ground for extended time the oil in servos may cool enough to cause the freezing of any h20 contamination in servos. Stirring the stick lots prior to flight would seem like not a bad idea.