From the thread:
Emirates A380 new-generationThank you for your input on the EK T900 problems, mario. Your
post is particularly helpful, since it answers some of the question we are debating in the 'Emirates RR-engines issue' thread, and I wish you copied everything in your post about RR engines to that thread, to feed the discussion there.
I have two questions for you on this topic.
- Have you any idea how of how long it would take to test engine wear in a specialised facility, as you suggest EK did ? It could explain the timing ...
- Do you think a new coating might be enough to solve this kind of issue ?
Thank you again, Mario !
You are welcome my dear philidor! As indeed always, I am so glad, You have found something useful and interesting for Yourself in this post.
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Part 1 - from the
post... There is no doubt that the ´next generation´ of the
Emirates´
A380 ULR frames represents a significant step forward for the company in an effort of more efficient use of the cabin space of this unique aircraft.
And the whole story would have been great if another and very significant problem had not appeared, and this is the one with the
Trent 900 engines and all that just before the delivery of the first aircraft with this type of the engines to the airline.
Pretty bad and, for the most, unexpected introduction to the new chapter. And some questions impose on its own; Why just now? ... What´s the problem? ... How could they discover this kind of problem at all, since there was no aircraft of that type in use with this airline and in this particular environment conditions? ...
Qatar has no experience with this type of aircraft and neither the
Etihad. Their
A380s are all powered with
GP7200 engines just as those existing
Emirates´.
So what´s the problem? Is that all just because of many billions of high-velocity, abrasive dust and sand particles impacting the critical airfoil surfaces of compressor blades and vanes, eroding away the exposed surfaces, thin metal tips and trailing edges? Just because of the cooling system in the turbine that might become seriously threatened, undermined and ultimately completely incapacitated because of the clogged cooling channels? Does inevitable result might be really so progressive and rapid degradation of engine performance to the extent of premature engine failure or at least unacceptably common and expensive visits to the engine shop? Yes, that´s right! And this is the serious problem now. And if I start to talk about it now from the technical side, it will last too long. Not now. Not here...
So, we have no aircraft tested with the engine in the question and in the particular climate and environment conditions, but there is a big concern because of the potential problem. Hm... Sir Tim Clark is not willing to accept the aircraft with the engines on which might appear, already shortly described, phenomena and problems. He is an very wise, experienced and technically very well educated person who wants to get the best for the money he has on disposal. Behave in such a way, is his right. And his duty. The fact he is at the head of such a company, gives him the freedom to be sometimes very, very demanding and complicated to talk to. And why is he so sure all of a sudden he might have the problems with the new engines? Where was he until now and what was he waiting for?
I am absolutely sure that, at least one,
Rolls-Royce Trent 900 engine has been exposed, since it was announced that the future
Emirates´
Airbus A380 aircraft are going to be powered by new type of engine, to those simulated conditions, so specific and characteristic for the environment in which it should work safely, reliably and that for a long period of time. Is it possible to create such a specific testing conditions at all? Of course it is! Take a look at this
(click on the images)I believe no one has remembered, exactly at this point, of all this just to create some new terms, circumstances and positions for the new negotiations. This situation has been conditioned by the defectation of the engine(s) on which the testings were performed. This is not just one of those stories which is the purpose to itself. No. I am sure that the tested engine(s) was thoroughly dismantled and carefully inspected to the smallest detail, leading the engineers to those recorded and significant changes on some of the engine parts...
And what now? Those engines could work, but with the significantly more frequent inspections and services, all until the appearance of the revised and redesigned engines or ... to send them all to the factory to make all the necessary improvements and changes on them. The big question is if the Emirates and Sir Tim Clark are willing to wait for the new aircraft with the expected specifications, and that should bring the profit to the company in the meantime.
And what are the questions so necessary to be raised at this point? Is it technically feasible to make all the necessary finishing and modifications on the engines? Of course it is. Is it simple to realize all that? Not at all. What is the main concern now? Who will pay for all this, and how long it will take? Am I, personally, surprised with all this? Unfortunately, I am not. Disappointed? Exceptionally.
What would I do if I was Sir Tim Clark? I would say:´
The features and the specifications of the engines are as expected, but their planned and expected durability and reliability are, not only questionable, but almost entirely unacceptable. I need those aircraft now and I want You to deliver them with the existing engines, and how those redesigned engines will become available, You will deliver me the new aircraft with the modified new engines and over the time those existing and already delivered engines You will return to the factory just to perform all the necessary modifications on them. On Your own expense, of course. I sincerely believe and hope in our future and successful cooperation. I think that would be all. For now. Thank You... ´
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Part 2 Here, specifically, we are talking about an very wide, interesting and highly important area related to the construction of the aircraft engines. All of these coatings: erosion, corrosion and thermal (-barrier) coatings are used in order to keep compressors´ and turbines´ blades integrity. Lately, the new ´Surface Finish Improvement Coating´ (SFIC) for super polished blades in the engine's high-pressure compressor, a process projected to significantly improve the engine's efficiency and fuel burn alongside with reduced maintenance costs, has been applied on some of the engines since the improving of the surface of compressor blades reduces the inner friction of the engine. But, providing compressor blades with a super polished surface has never really lasted for a long as the surface quickly became eroded from contaminated air flowing through the engine. Thus the benefit of the polishing soon becomes compromised, producing harmful effects, such as reduced compressor efficiency and higher SFC. That is why it´s necessary to resort to the use of all those coatings...
One of the requirements to the coating is that it must have the same maintenance requirements as the engine itself, i.e. at least withstand the same amount of flight hours as the compressor blades themselves. Newly developed multilayer coating systems feature excellent hardness but also provides the flexibility to withstand vibrations, preventing the coating from separating from the airfoil.
Another expected benefit, besides the reduced SFC, of the new coating process is a significant reduction of maintenance costs through a nearly complete elimination of airfoil erosion and what is so important, the airfoil geometry is expected to stay true for a significantly longer amount of time, resulting in a slower decrease of the compressor's efficiency throughout an engine's life cycle.
The recent trends in the application of the blade coatings are focused on erosion and corrosion resistant composite nano-structured coating (nano-coating) for application on compressor airfoils for the gas turbines, in both industrial power generation and commercial aviation applications. Such a coated blades have to be resistant to erosion, corrosion, vibration and fatigue.
Generally, compressor section airfoil surfaces are subjected to a hostile, erosive environment that implies ingestion of dust, sand, abrasive and fluid particles, especially during the takeoff, respectively in the phase when the engines are mechanically and thermally most loaded. This results in degradation of the compressor airfoils from erosion, resulting in a marked decrease in engine efficiency – decrease in fuel efficiency and increase in CO
2 emissions.
The nano-structured coatings have the ability to tailor features of the material to achieve specific properties, such as strength, durability and reactivity among other material characteristics. Of particular interest is the designing of composites with the different phases, and on the nano-meter scale, in order to produce materials with enhanced properties. The hard phase provides the hardness necessary for the coating to resist impact from the impinging erodent particle. The softer phase by itself would have little or no resistance to an erosive particle. However, when the materials are woven together, in the composite, the softer, more ductile phase absorbs the impacts and keeps any initial cracks from propagating directly to the substrate material. Interestingly, a high hardness material is not necessarily the predictor of erosion resistance, and that lower hardness can provide superior erosion properties. The composite material provides a combination of hardness and toughness, which results in a more erosion-resistant coating than could be provided by the monolithic component alone.
The tip of the blade has the greatest effect on efficiency, but it is also the region most affected by the erosion. The coating that the material has been formulated to has a good balance of hardness and toughness to resist particle impact, as well as being sacrificial in a corrosion sense in relation to steels to provide corrosion resistance. And how are those coatings applied? By a proprietary method using a physical vapor deposition process, a vaporization coating technique in which a high purity solid coating material is evaporated under high vacuum and subsequently attaches onto the substrate material on a nano-level (10
-9 m). The coating structure can be varied according to the required properties and is optimized to counter the erosion pattern exhibited on a compressor airfoil. The total coating thickness can vary according to the engine type and compressor stage, but as a general rule these types of coatings have to be at least 10 micrometers (10
-6 m
) thick to provide sufficient protection. The coating preserves the overall shape of the airfoil during operation, which in turn retains compressor efficiency.
And how all this relate to the current situation in which
Rolls-Royce has found itself with the
Trent 900 engines. Are those
Trent 900 engines going to be the first
Trents used in those specific climate and environment condition? Is that quite a new situation for the factory? Well, I don´t think so.
-
Emirates was using or still use
Trent 500 (
Airbus A340-541),
Trent 700 (
Airbus A330-243) and
Trent 800 (
Boeing 777-21H(ER);
Boeing 777-31H) engines;
-
Etihad was using or still use
Trent 500 (
Airbus A340-541;
Airbus A340-642) and
Trent 700 (
Airbus A330-243/F;
Airbus A330-343) engines and finally
-
Qatar Airways was using or still use
Trent 500 (
Airbus A340-642) and
Trent XWB (
Airbus A350-941) engines on their aircraft.
So? The most of these engines have already been in the use for a long time (except
Trent XWBs on the
QR´s
Airbus A350) so we can conclude that the appropriate technical solutions have already been applied on those engine series, otherwise the problem with the blade erosion, as and some other problems also, would have already appeared since long time ago. It means that already existing, as well as that new, technology should be applied on the
Trent 900 engines´vulnerable parts
(I would really like to know if the blade erosion problem has been possible noticed on QR´s Trent XWBs). I strongly believe that all the problems and side effects related to the specific parts of the
Trent 900 engine, modifications of each demand special approach, were addressed in the factory. And what are the main concerns in this moment? Compressor blade erosion and turbine cooling system. I believe the technical solutions for the modifications of all the parts of the engine on which were identified material degradation, and after the dismantling of the test engine, have been collected and reviewed. Also, because of the possibility of the appearance of the doubts and uncertainty how could any specific problem could be solved, I'd go, at the same time, with the three test engines, exposed them to the simulated environment conditions they will be exploited in, simultaneously performing the ´triple red-line test´ (maximum speed of the fan, maximum speed of the core and maximum temperature, all at the same time) pushing the engine to its limits. Rigid and brutal testing! After every 100 hours of day-and-night testing, dismantling and the inspection of the engine parts on the table. 1.000 hours of testing, on each engine. In the end of testing, after the multidisciplinary approach inspection of all engine parts, the final configuration has to be defined, the one that will enter the serial production.
I am absolutely sure that all the noticed and detected problems are solvable, and the new technical solutions and redesigned parts will provide the quality, durability and reliability to the
Trent 900 engine, introducing it to the new chapter of its life. From
Rolls-Royce´s engineers I expect a high-quality, devoted and meaningful effort because this is the opportunity that must not be missed...
Kind regards
Mario