Last year, during the one of the aeronautical fairs,
Emirates´ president and COO, Sir Tim Clark, was asked on the
Emirates’ requirement for a twin-aisle medium/long range complement to their
Airbus A380 and
Boeing 777 fleets, respectively on the competition in between
787-10 and
A350-900, in the 300-seat segment. Namely, somehow conventional wisdom has been created that
Emirates firmly leans towards
Boeing 787-10, especially after they canceled their order for the 70
A350-900s in 2014. However, Sir Clark responded that he doesn’t know where that comes from because the
Boeing 787-10 is not coming up with the thrust requirements
Emirates find necessary for their needs, whereas the
Airbus A350-900 has more than enough supply of thrust. Now, the most people could wonder how come the
Boeing 787-10 can be short of thrust since no other customer has raised this issue.
That what Emirates are looking for is 84.00 lbf of thrust out of
Boeing 787-10´s engines,
Trent 1000(
-TEN) three-shaft turbofans (fan diameter: 2.844,8 mm / 112,0 in; eng. architecture: F-8IPC-6HPC ^ 1HPT-1IPT-6LPT) or
GEnx-1B twin-shaft turbofans (fan diameter: 2.821,9 mm / 111,1 in; eng. architecture: F+4LPC-10HPC ^ 2HPT-7LPT), thrust that would be needed to assure take-off with full loads all year round. It is interesting to note that
Emirates’ Gulf neighbor,
Etihad, which has an almost identical climate and elevation to the Emirates base in Dubai, is a launch customer of the
787-10 and plans to deploy the jets on routes similar to those Emirates has in mind. However, the people in Emirates are well aware of the fact that a few other airlines, if any, have such a requirement and that neither the
Boeing nor the
787-10 engine-makers,
and
, are going to essentially develop a new engine just for Emirates.
Allow me to detain here for a moment longer; the indisputable fact is that both engines,
GEnx-1Bs and
Trent 1000s, certified for
Boeing 787-8 Dreamliner and
Boeing 787-9 Dreamliner aircraft are already at their upper limit, but still in the anticipated working area where you can expect them to be highly reliable and safe in their exploitation. It is difficult to speculate how much more thrust could be extracted out of those
GEnx-1B and
Trent 1000(
-TEN) engines, but the value of 84 x 10
3 lbf, and that was mentioned, seems to be pretty high for both of those engines, especially if the same expected time of the reliable service and maintenance intervals, what is quite realistic to expect, would be required.
Those recently certified and more powerful
General Electric´s engines are
GEnx-1B75/P2, rated at 345,20 kN / 35.200 kgf / 77.604 lbf and
GEnx-1B78/P2, rated at 357,60 kN / 36.465 kgf / 80.392 lbf. The later have not been installed yet on any of the
Boeing 787-9 aircraft delivered to any of the customers. There are several possible reasons for that, and just one of them is that the higher thrust ratings and increased engine´s structural load capabilities would require a somewhat redesigned engine´s nacelles, but it is also quite possible that this version is intended for the new
Boeing 787-10 aircraft. Those, so far, delivered
Boeing 787-9s, and powered by the
GEnx-1B engines, use
-1B74/75P1(
P2) version, rated at 341,20 kN / 34.793 kgf / 76.700 lbf and quite recently,
-1B76(
A)
/P2 version, rated at 349,19 kN / 35.607 kgf / 78.500 lbf .
On the other side, some delivered
Boeing 787-9 Dreamliners are powered by the
Trent 1000-J2/
K2 engines (Package C), rated at 347,54 kN / 35.439 kgf / 78.129 lbf. It is expected that those most powerful versions of the new
Trent 1000-TEN engine,
Trent 1000-M3/
N3 rated at 354,65 kN / 36.164 kgf / 79.728 lbf and
Trent 1000-R3 rated at 360,43 kN / 36.754 kgf / 81.028 lbf will be certified with the new
Boeing 787-10 aircraft...
There is no doubt that the development of those two engines will remain very strong.
Trent 1000-TEN engine is, in a much greater extent, a derivative of the
Trent XWB engine, rather than the evolution of the existing
Trent 1000 engine, and that speaks enough how much dedicated
Rolls-Royce remains to the
Boeing 787 Dreamliner aircraft and how well prepared they are waiting for the new
Boeing 787-10. On the other side,
General Electric, in the order to achieve even higher engine´s thrusts, is ready to increase the mass-flow through its
GEnx-1B engine, searching for, not only the higher thrusts, but the increased propulsive efficiency of the engine. Will it be enough to implement in
GEnx-1B´s further redesign all the modern technology aimed for the future
GE9X engine as and that already applied on the already existing
engine, especially the utilization of the new
CMC material in the engine´s hot section (already widely tested on the
GEnx-1B engine), making that way the engine thermally more efficient or it will be unavoidable to increase fan´s diameter, redesign core´s geometry, BPR and the overall engine´s architecture, remains to be seen. Personally, I just can´t see
going so far with the development of their
GEnx-1B engine...
Comparing the
Trent 1000 and the
GEnx engine, it is noticeable that the
GEnx´s LPC´s rotation speed is limited by its fan´s maximum speed limit, resulting with the very low pressure gains per stage, about 10%, compared with 30-40% per stage for an optimal spinning compressor, like the ones in
GEnx´s HPC. This results in more stages for a given pressure ratio and to not lose even more efficiency, the LPC´s diameter is kept as large as possible, thereby rendering all discs and frames heavier then the comparable three-shaft compressor part. Three-shaft engine design does not have such a defects, and therefore its length and weight are less than those of the engines with the standard two-shaft configuration and which are comparable by their performances and the thrusts to the three-spool engines.
Finally, since the
Boeing has recently expressed its unreadiness and unwillingness to adjusts
Boeing 787-10 just to the
Emirates´ needs excessively, and aircraft itself was not designed for the MTOW higher than the one of the
Boeing 787-9 (557.000 lb / 252.657 kg, according to Boeing´s ´
Airport Compatibility Brochure - 787-10 Dreamliner´), I wonder how realistic is it, at all, to expect
Boeing 787-10 with the engines rated at the thrusts higher than those mentioned. However, I take into account the possibility that neither
Rolls-Royce nor
General Electric haven´t revealed all their aces yet…
Part 4Emirates are everything but an ordinary airline by any of the benchmarks. Their main hub, Dubai International Airport (
DXB) experiences the ground temperatures of over 45°C degrees (113°F) on many days of the year, and this affects in a great extent and in the same way both, aircraft and engines.
The decreased air density directly impacts on the foreseen and necessary difference of the pressures on the top and the bottom of the wings, the difference that creates a lift-off force on the wings. So, to get to the same lift force, the aircraft has to go faster. Higher take-off speed requires stronger engines or longer runways. Those
Dubai International´s runways are long (
12L/30R - 4.000 m / 13.123 ft;
12R/30L - 4.450 m / 14.600 ft), but there are other limits. Try to go too fast down the runway and you´ll find the tires everywhere. And if you want to reduce take-off speed, the TOW has to be reduced. And who wants to reduce TOW?
And when it comes to the engines, it is even worse. The lower air density not only lowers engine´s thrust but the engine also suffers internally from the increased air temperature. The air of the higher temperature enters the intake and passes through the whole front section of the engine - fan and LPC. As it passes the HPC, it can cause the engine computer (FADEC) to lower engine rotation speed since the HPC also increases the air´s temperature as the part of the compression, and that temperature can easily exceed the last HPC stages´ allowed maximum. On the other side, lower rotation speed, and which saves the last stages from being thermally overloaded, means disturbed/reduced air-flow, possible compressor´s stalling and/or surging, lower CR (compression ratio), OPR (overall pressure ratio), TIT (turbine inlet temperature) and consequently SFC.
That´s the main reason why I have pointed out, in my previous post, at which temperatures
Trent 900 engines achieve their highest thrusts. Generally, this flat rating max. temperature is normally set to happen at outside temperature of +15°C over ISA temperature (the worldwide agreed standard) and Dubai has +30°C, i.e. 45°C, on a large part of the year, what represents three to four times higher values. In the case the compressor alone ´has no problem´ with the higher temperatures, the engine´s turbine will not accept those higher temperatures without the engine computer´s throttling back. This results in reduced thrust from the engine and what we have seen is that we need more thrust just to compensate for the thinner air. That reduced thrust comes from the engine´s computer injecting less fuel in the combustor just to save the compressors´and especially HPT´s blades from melting. Don´t forget to add on all that the dust and the sand filling the turbines´ blades cooling system …
The final result is that the engine loses the power and that the aircraft has to take-off with the lower TOW. The only way to compensate for the thinner air and thrust loss is to haul less payload or to have stronger engines on an aircraft with a bigger wing. The problems with a very high thrust requirement for take-offs from Dubai International are especially known from the larger aircraft.
´
The temperatures are not EK's concerns.´ Oh, yes they are. A great concern and to a great extent!
What is the conclusion we could derive from all the above mentioned? No matter of the fact that the higher OPR (combustor inlet pressure / intake delivery pressure) makes the engine thermally more efficient, and what, consequently, improves engine´s SFC, yet there are some limiting factors because of which the engine´s OPR needs to be controlled. As I have already described, high temperatures, developed at the last compressor´s stages, condition large thermal load on the compressor blades, posing the possibility of a the material failure risk, and just this value, the one of the outlet temperature from the last compressor´s stage, is one of the most important conditions for the final design of the engine´s core and overall engine´s architecture. In the case of the civilian engines, the pressure ratio can be adjusted through the aircraft´s climb, because some of the heat load can be offset through the lower high-altitude air´s pressure and temperature. This is one of the many reasons why the airliners climb to high altitude as quickly as possible.
The development of the material technology, to a large degree, condition the efficiency of the construction of the modern turbofan engine, and searching for more power and thrust out of the existing or completely new engines designs, implies the existence of the higher thermal and mechanical stresses of the engines´construction, and all because of the increasing of their operating parameters (FPR, CR, OPR, TIT, flow speeds, rotational speeds…). In the same way as the increased mechanical stresses may affect the fractures and tearing-offs of the materials, the increased long-term temperature stresses could easily cause a change in the structure of the materials, leading to their disintegration. Besides, to have a thermally efficient engine does not mean that it is, in the same time, a propulsive efficient engine, just for every purpose. It is not that simple at all, is it?
Regardless of the engine´s limitations, conditioned by its architecture and the core´s geometry, there are still many opportunities for the engine´s improvements, such as in its aerodynamics, higher rotational speeds, improved combustors, higher working parameters (temperatures, pressures - FPR, CR and OPR, TIT, mass flow...), stronger cooling of the thermally most loaded engine´s sections, using of the new sophisticated materials like the CMC (Ceramic Matrix Composites) in the hotest engines´sections …
Replacing the certain metal components in the hot section of the engine by those made of the CMC material brings a lot of advantages to the engines. CMC material itself, made as strong as the metal, at the same time being much lighter, and withstanding higher temperatures, allows lower fuel burn and the lower emissions of NOx and CO, while increasing the efficiency of the engine. This material can withstand some 110-170°C (200-300ºF) higher temperatures compared to the ceramic coated nickel/titanium super-alloys. Combined with a new swirl pattern and increased air volume through the combustor, it eliminates the need for cooling bleeds. The higher temperature capability and simpler component´s cooling requirements allow a more spacious combustor´s design so it can be run more efficiently. Less cooling flow to the component enables more HPC´s flow to be put into the combustion process through the combustor mixing nozzles. Namely, the present-day metal parts of the HPTs need extensive amount of the cooling air, directly taken from the primary engine airflow, thus reducing engine´s SFC, CR, OPR and TIT. CMCs can operate with the much less or even no cooling, providing a significant efficiency boost to the cycle and simplifying a complex cooling system of the engine´s hot sections. CMCs, also one-third the weight of the nickel, deliver a truly revolutionary leap in temperature capability, beyond any advanced metal alloy and its durability has been already proven through the significant testing in the
aeroderivative gas turbine engines (
LM2500,
LM6000-PF/
PF+,
LMS100 and
TM2500). The biggest benefit of CMCs is in the significant weight savings they can give, as well as CFRP-made fan blades and fan case, but also Ti-Al HPC´s and LPT´s blades.
The main advantage of using CMC materials is not in enabling higher peak cycle temperatures of the engine, but in the improving cycle efficiency by reducing the thermal losses caused by the bringing the compressed air into the hot sections of the engine. The peak combustion cycle temperatures in commercial TFs are currently limited by NOx formation, and NOx compounds only form in the presence of too high amount of the oxygen at the front of the flame and with the temperatures greater than some 1.560°C (2.800°F). In the order for the combustion system to operate with the lowest emissions, it must operate at a specific flame temperature, balancing the generation of NOx with the generation of CO. This is very difficult to achieve if fuel and air are injected directly into the combustion chamber, and therefore a pre-mixing of the fuel and the air has to be accomplished just to create a uniform mixture that, once it enters the combustion chamber, is ideal for complete low emissions combustion...
As we could have already noticed, the thrust difference in between
Trent 9XX-84 engines rated to ISA +15°C and
Trent 9XXB-84 engines flat rated to ISA +10°C is about 4,5%. You can just imagine how much less are the engines´thrusts at + 45°C of the ambient temperature. I strongly believe if the
A380 aircraft was certified with any of those higher thrust
Trent 900 engines (fan diameter: 116,0 in / 2.946,4 mm; eng. architecture: F-8IPC-6HPC ^ 1HPT-1IPT-5LPT):
Trent 977-84, rated at 359,33 kN / 36.641 kgf / 80.781 lbf,
Trent 977B-84, rated at 372,92 kN / 38.027 kgf / 83.835 lbf or
Trent 980-84, rated at 374,09 kN / 38.147 kgf / 84.098 lbf, one of them would be
Emirates´ choice.
This way, they simply chose the higher thrust version of the two existing engines, and certified with the
Airbus A380 aircraft:
Trent 972B-84 rated at 356,81 kN / 36.384 kgf / 80.213 lbf …
After a certain time of the extensive and intensive exploitation and experiences with the
Trent 972B-84 engines, it will be very interesting to see the different comparisons with those existing
GP7270 twin-shaft turbofans (fan diameter: 116,0 in / 2.946,4 mm; engine architecture: F+5LPC-9HPC ^ 2HPT-6LPT), rated at 332,44 kN / 33.899 kgf / 74.735 lbf, and installed on
Emirates´
A380-861 aircraft...
At the end of
Part 4, I would like to say just a few more words on that, and by which we have cut into this subject at all:
Recently, the two companies,
and
, have reached an agreement, involving both technical and commercial elements, that the later will finance, respectively pay for fixing everything that
Emirates objected to, the measures to counteract the performance and maintenance issues that were addressed and to improve the performance of the engines in question, and that were the subject of an historic $9,2 billion (€8,7 billion) deal between
Emirates and
Rolls-Royce for 217
Trent 900 engines and a long-term TotalCare package. The engines will be used to power 50
Airbus A380s ordered at the Dubai Air Show in 2013, and which will begin entering service, let´s hope, very soon.
And ... this is it. Is it? It would be logical to think whether
Rolls-Royce has managed to solve, in this short period of time, all the problems that
Emirates objected to. No way! They are still just as present, and resolving the observed problems requires several months of dedicated, comprehensive and multidisciplinary work, all until the modified engines start to roll-off the production line (until then they will deliver what they have and what they are able to produce). Anyone who thinks that
Rolls-Royce is not going to do anything and will not implement any or all of the necessary modifications to their
Trent 900 engine design, to meet the demands of exploiting the engine in a new, very specific and demanding, environment, but will just bear the costs of the more frequent services and repairs, is not right and is miles away from the truth.
Rolls-Royce can not afford it in any sense! Nor will…
And, if anyone might have been expecting an official statement and confirmation of what we have here, I believe correctly and accurately, concluded … it is not going to happen. All involved in this story,
Emirates,
Rolls-Royce and
Airbus, function on a extremely high, exceptionally professional and very enviable level, and that does not imply revealing such a details on which we were talking and discussing here…
How do the recent statements and the events fit into what I have said in
Part 1, judge for Yourself…
... 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... ´
Kind regards
Mario
P.S. As the year nears to its end, somehow all sort slowly ...
MSN 221 has returned from its mission :-) and was recently rolled-out.
MSN 225 and
MSN 226, those first
´
powered
A380s, are near the delivery...