Engineers - any sign of ash damage so far?

[smudgethecat]

Gavthespotter, gas turbine engines employ labyrinth seals which rely on air tapped of the compressors to function ,this air actually enters the bearing sumps therefore any contaminants which are in that air will possibly enter the engine oil system, hence the reason for checking the filters ,now be a good chap and get off back to the spotters forum

[BOAC]

A crippling set of first 7 posts..............................

The world has really gone mad - we've got a spotter on 'Airlines, Airports' asking about a g/a at BHX and some sort of 'Secret Service' war going on on the Polish 154 thread.

Now, about the British General Election.....................

[Landroger]

Ash in pressurised oil system?

I have to admit, it is pretty counterintuitive that any one atmosphere contaminant can get into a pressurised lubrication system. What is the average sort of pressure in an aeroplane engine (high bypass fan jet)? A modern car is between 60 and 100 psi.

Having said that, I am an MRI engineer and our magnet cryogen recombinant systems work at about 4 psi. Given that Helium is the second smallest atom in the periodic table, it can leak through pretty much anything - outwards. However, magnets have personalities and some of them have an amazing propensity to suck atmospheric pressure air into them.

How do we know its there? Because various electrical ports that we need to use from time to time, become blocked with ice, but don't go thinking its just plain old frozen water. Oh dear me no. The water vapour freezes out long before it gets very far into the magnet. No, the ice we are talking about is where air (per se) has somehow got past 'O' rings into a 4 psi over ambient environment and the oxygen has condensed out, dripped about a foot deeper into the magnet and hit a metal surface somewhere where it freezes solid. Ever seen frozen oxygen? Its blue.

Can anyone actually explain how any ambient pressure contaminant can get into otherwise sealed, pressurised systems?

Roger.

[Landroger]

Smudgethecat.

Gavthespotter, gas turbine engines employ labyrinth seals which rely on air tapped of the compressors to function ,this air actually enters the bearing sumps therefore any contaminants which are in that air will possibly enter the engine oil system, hence the reason for checking the filters ,now be a good chap and get off back to the spotters forum

A little harsh Smudge, I feel. I am not an aero engineer and I didn't know that - see my post above - but I was still interested. Now I know, I won't trouble you again. Want to ask me about 30,000 Gauss magnetic fields? Careful, I might give a short sharp answer, because you ought to know.

Those of us on this forum may not be aircraft engineers, but we are engineers and we are interested. Bask in the knowledge that others are asking you the question.

Roger.

[lomapaseo]

People that ask to learn get answers. People that ask questions and then disparage the answer get put down as trolls. There is enough knowlege on PPRune for a reasonable balanced explanation to come out among multiple posters without retorts.

[john_tullamarine]

I don't think that one needs to add anything much to the previous post by lomapaseo.

For those who see the need to wave their arms and froth a bit at the mouth .. all you succeed in achieving is making a bit of a fool of yourself.

The knowledge base in PPRuNe varies from the highly expert to the abjectly ignorant but, even then, we all can learn a bit from each other. Many of our aeronautical new chums are, of course, knowledgeable or highly expert in other, unrelated, fields.

A touch of humility all around goes a long way in such an environment I suggest ?

[spannersatcx]

gav" i know how plane engines work" the spotter, anybody is welcome on these forums, no laws against it.

My knowledge is limited, I only have 32 years experience in aviation maintenance, and I don't pretend to know it all as that would be dangerous, and I don't pretent to know what Landroger is talking about, but I would respect his knowledge in his field.

There are ways to ask questions and to take that information to learn from it, unfortunately the abrupt and agressive attitude that is shown by some posters doesn't do them any favours. I'll help anybody glean knowledge I don't have a problem with that, that's how we all learn, and if I don't know something I will ask that's how I learn.

I could show you some pics taken during a borescope inspection (you know what that is don't you?) the other day from a CF6-80 as fitted to a 747-400 after a suspected ingestion of something, we also had to replace the oil system scavenge filter and drain, flush and replace the engine oil, I wasn't sure what was ingested by the engines, but made the call to ground the a/c and carry out the necessary checks, really pissing off the 450 pax that had been waiting for 4 days to fly, but hey what do I know.

By the way the check is the same if ingestion is volcanic ash or sand, so prey tell why do I have to drop the engine oil and filters on a gas turbine engine as fitted to the 744?

[mad_jock]

Can anyone actually explain how any ambient pressure contaminant can get into otherwise sealed, pressurised systems?

Theory alert could be bollocks.

Surface tentsion allows fluids to do some very strange things when in capillarys liquified gases are famous for it. They will allow fluid to travel uphill so to speak.

My theory is that they have a slight leak and there is Oxygen fluid forming, if it manges to bridge the hole the surface tension will start doing its work and cappilary action will work pulling it up stream. Now because the fluid will be travelling into a cooler temp it will aid heat transfer to the outside it will cause even more oxygen to become liquid and supply the capilary action. Once its inside if there is any sort of height difference between top and bottom of the seal you will have started a syphon. Liquid oxygen being relatively heavy compared to He will have no probs overcoming the 4 psi differential. And thus you have an up hill (in pressure differential terms) leak. Look on the bright side though it means your not loosing highly expensive He through a seal leak.

[lomapaseo]

Can anyone actually explain how any ambient pressure contaminant can get into otherwise sealed, pressurised systems?

I never did quite understand what this question was about, so my answer may be missing the mark.

For starters the oil system is not sealed from outside air. It does have a scavenge just like your car engine. It does rely on knife edge seals as well as friction carbon seals. It does not only provide bearing lubrication but also adjusts the thrust load on the bearings via air pressure internally to the gas path.

For the thrust load balance as well as cooling of hot metal parts behind the combustor, pressurized air is drawn off the gas path (typically in the high pressure compressor rotor). This air can entrain dirt and this dirt can flow through the labryinth seals between the oil system and the internal pressurize cavity of the rotors. Note you want any air flow to come out the breather rather than oil flow inside a hot rotor compartment.

[FE Hoppy]

Are there any partial oil loss or total oil loss engines still in use?

[411A]

gavthespotter
Probationary PPRuNer
Join Date: Apr 2010
Location: formby
Age: 25
Posts: 7

Look at the stated age.
About says it all, really...a youngun' who thinks he knows it all.

Are there any partial oil loss or total oil loss engines still in use?

Still quite a few Darts in service, worldwide.
A really fine engine.

[barit1]

Can anyone actually explain how any ambient pressure contaminant can get into otherwise sealed, pressurised systems?

Think about it. Where do you think the pressurizing air comes from? Have you studied how the sump sealing system really works?

Here's a good introduction

[Agaricus bisporus]

Mods, please close this thread if it doesn't come back onto topic.
I asked a topical question that had nothing to do with odd behaviour in gas capilliary action or labyrinth seals.

[forget]

AB.

I asked a topical question that had nothing to do with odd behaviour in gas capilliary action or labyrinth seals.

But it does. As Smudge said -

gas turbine engines employ labyrinth seals which rely on air tapped of the compressors to function ,this air actually enters the bearing sumps therefore any contaminants which are in that air will possibly enter the engine oil system,

[L337]

I am reluctant to copy from the BA company forum, but I think on balance it helps clear up some of what is being discussed, and shows what a "major" carried out prior to the ban being lifted. The post relates directly to the test flight BA carried out in a 744.

All the filters in the aircraft were replaced before the flight. After the flight, they were all removed and sent for analysis - the theory being that any contamination of the filters could only have occurred on that flight. Nothing was found. Fuel and oil samples were also taken and they came back clean too. The engines were boroscoped and showed no evidence of any damage or accumulations of ash deposits. The airframe (including windows) was examined for any signs of abrasion - none was found. The QAR and FDR data was sent for analysis to detremine is there was any abrormal relationship between engine parameters (eg erroneous EGT for the N1) or air data parameters (eg Angle of Attack incompatible with IAS) - again nothing has been found.

The aircraft was deliberately flown in areas where the Met Office Model showed that ash encounters were likely, but outside the areas where the WSI model showed ash encounters were likely (you might like imagine these areas as being similar in principle to the Enhanced Procedures Zone and the No-Fly Zone respectively, which the CAA has mandated in FODCOM 12/2010 )

[fflyingdog]

Thats pretty much exactly what we found ...........................absolutely nothing.

[lomapaseo]

Mods, please close this thread if it doesn't come back onto topic.
I asked a topical question that had nothing to do with odd behaviour in gas capilliary action or labyrinth seals.

You could always try steering the thread to something more specific to your interests by asking more questions that somebody might have an answer

Looks like this technical discussion is of more interest to the participants.

Of course a Mod could always change/merge the thead title to something more generic, where a variety of similar questions to yours might be asked

[Niallo]

I too support a return to the original question.
Presumably current jet engines are highly instrumented and these readings are recorded for later analysis.
I expect that airline engineers and engine manufacturers are now routinely analysing the recorded engine operating data from all their flights to identify any change in trends pre and post ash exposure.
Have they noticed any changes?

[Pugilistic Animus]

I've learned so much from this thread

[ZQA297/30]

411A

Are there any partial oil loss or total oil loss engines still in use?
Still quite a few Darts in service, worldwide.
A really fine engine.

Its been thirty-odd years, but I am pretty sure the RR Dart was not a total or partial loss system.
I think you may be mixing it up with the Viper as fitted to Jet Provost, and some earlier powerplants.
Re; Dart
Within its limits (cycles) it was a simple and dependable powerplant