Who Will Power the Aircraft of the Future?!
- This video is brought to you together with Squarespace. Are we right now seeing the very first stages of a new jet engine war? That might sound like a strange question since neither Boeing or Airbus have announced any new aircraft designs and they basically just finished re-engineing their flagship MAX and neo variants. But that doesn't mean that there is no movement on the engine development side. On the contrary, the case might well be that Boeing and Airbus are basically waiting for the winner of this new engine war before making their own move.
Or it could also be the other way around. Stay tuned. (delightful tune) In the past few weeks and months, we've been hearing some quite unusual news about issues involving, among others, the engines of the latest editions of the 737 and the Airbus A320 families. And to be perfectly honest, that wasn't completely unexpected. It always takes a bit of time for engine and aircraft manufacturers to learn all the ins and out of anything new really, and especially something as complex as new versions of modern turbofan engines. Now, to be perfectly clear here, as a passenger, you don't need to worry.
The electronic management systems in these new engines is very good. And it would only shut an engine down if it deemed that that would be the most safe option to keep both the passengers, aircraft and the engine in itself safe. Now, it might sound a little bit strange. You wouldn't want your engine to ever shut down itself.
But that happening is extremely rare. And in the extremely unlikely situation that one of these engines would decide to shut itself down, well, then all of us pilots are trained to deal with that and to continue to fly the aircraft safely on the remaining engine. But there's no question that there has been some teething issues with these new engines, so let's look at what's going on. To understand this, you first need to remember that the engines that are powering the previous generations of the 737s and the Airbus A320s have been in service for about three to four decades already.
And these trusty engines that we're now talking about are of course the mighty CFM-56. And in the case of some Airbus 320s, the IAE V2500. The first CFM-56 actually flew as early as back in the 1970s.
And today, the CFM-56 is the most popular commercial jet engine in the world, with over 30,000 of them having been produced up until today. But for the new generations of these single aisle bestsellers, the aircraft manufacturers needed something new. That's why the 737 MAXes are instead using the CFM LEAP-1B engines, while the Airbus A320neo operators have a choice between the CFM LEAP-1A and the Pratt & Whitney Geared Turbofan, or GTF. These are more advanced but also brand new engines. And as with any new technology, they will naturally need some time before they can achieve the same level of durability as the old, tried and tested CFM-56 had. But crucially, we're talking about durability here, not reliability, because all of these engines are extremely reliable.
So what I mean by the teething problems have to do not so much with actually inflight faults, but instead, mainly with how frequently these new engines require maintenance. At the moment, it seems like these service intervals have turned out to be a little bit more frequent than the airlines would like them to be. It seems like the heat and other environmental conditions that the engines are operating in are a big factor in this. And for that reason, both CFM and Pratt & Whitney are currently redesigning a number of parts to improve their time-on-wing, meaning the time between each time that the engine needs to be taken off as well as overall durability. But this work is taking some time. And in the meantime, some airlines have had to ground a part of their fleet simply because they haven't been able to get their hands on spare parts to be able to service their engines fast enough to get them back into the air.
And at the moment, the engine maker that seems to be most affected by this is Pratt & Whitney. According to some recent reports earlier this year, as many as 10% of all aircraft in service with Pratt & Whitney's Geared Turbofans were grounded. Now this doesn't only affect the airline customers. It also has a knock-on effect on how quickly Airbus and also to a smaller extent, Embraer, have been able to deliver new aircraft to their customers. And that's because Pratt & Whitney have had to divert some of their parts production to the in-service fleet instead of using those parts in the production of new engines. Beside the Airbus A320neo family, other aircraft that are using versions of Pratt & Whitney's GTF are the Airbus A220 and the Embraer E2 who are also suffering from these same delays.
The Geared Turbofan was also supposed to be the engine for the Mitsubishi SpaceJet, which unfortunately, was recently cancelled. And until February last year, the Russian MC-21 was also supposed to enter service with the GTF. But obviously, that is not happening. Now, the airlines who rely on aircraft with these latest CFM and Pratt & Whitney engines are understandably a bit frustrated with these teething issues. So at this point, you might be wondering if it was really worth replacing those engines in the first place.
The simple answer to that is a resounding yes. And the airlines are proving this by the extensive use of their wallets. If we look at Pratt & Whitney, for example. Despite them suffering much more from these early durability issues than CFM did, they recently announced that they had secured over 800 orders and commitments for its Geared Turbofan engines, and that was only in the first half of 2023.
It really seems like the airlines really want their aircraft to use these newer engines, but why is that? Well, to understand this we have to look a bit closer at how they differ from the previous engines and why these differences could be leading towards a new engine war with the next generation of engines. If you simply look at aircraft with either CFM LEAP or Pratt & Whitney GTF engines, you might notice that they are larger in diameter than the older generation were. As I've explained in previous videos, to make a jet engine more powerful, the manufacturers really only have two ways of doing that. They can either push the same amount of air out of the back of the engine faster, or they can try to push more air backwards at the same speed. It has been shown that the latter option is far more efficient.
So to do this, modern turbofans needs a way to achieve a higher bypass ratio. That's the ratio of air that is driven by the big fan at the front around the engine core versus the air that actually goes through the core part. To achieve this higher ratio, modern turbofan engines have a much larger diameter than the older ones to fit this giant new fan in the front. And on top of that, some like the Pratt & Whitney GTF also use a smaller engine core. This has led to engines which are up to 15% more fuel efficient, which is of course, what the airlines are really after.
But achieving a bypass ratio as high as this also runs into some practical problems. Now without getting too deeply into the physics of both propulsive and thermal efficiency here, there are two factors in these modern engines that you really need to understand. Firstly, the jet engine engineers wants the turbine part in the engine's core to spin really fast because this will allow them to simplify its design, making it lighter and also more efficient.
But conversely, they also want the huge fan in the front to spin relatively slowly because when that one goes too fast, it starts to lose its efficiency. This has historically been an issue because the turbine part of the engine is normally what drives the fan in the front. This means that historically, jet engine designers have had to compromise between the ideal speed of the fan and the turbine inside of the core. But there is a way to let each part of the engine rotate at the best speed possible, and that is through the use of a gearbox or a gear reduction system.
Adding this to the construction also adds some complexity which has taken engineers years to perfect and it also adds weight. But the extra efficiency is absolutely worth it. So rotation speed is the first factor you need to understand, and the second is temperature. To get the most efficiency out of the engine core, the engineers needed to enable it to run hot, and I mean really hot. Turbine blades and other engine parts often operate at temperatures that would normally cause even the most advanced metal alloys to melt.
And in order to keep that from happening, turbine blades and other parts often have to incorporate various cooling methods into their design. But to make the engine core even more efficient, it would be much better if the internal components didn't need that cooling, or if the engine could be made to run even hotter in some type of way. The physics of this topic are seriously advanced. And if you want to learn more about that part, I highly recommend Bjorn Fehrm's work over at Leeham News.
He is currently running a series on the ways future aircraft and engines will become more efficient and what they will look like. It's really fascinating. You should check it out. So now that we know about the two factors that need to be taken into account in order to make an even more efficient jet engine, then let's look at how CFM and Pratt & Whitney have tried to solve it.
In the case of Pratt & Whitney with its Geared Turbofan, it's pretty obvious what they have done. You can actually hear it in the name, the geared turbofan. The advanced gearbox that they use in these engines have allowed a bypass ratio as high as 12.5:1 in the version used in the Airbus A320neo family. That's huge; and even the A220 and the Embraer E2 who needed a smaller overall engine diameter, still achieved a bypass ratio of 12:1. And it's not just the geared fan that made that happen.
Pratt & Whitney also spent a lot of effort to miniaturize the core as much as possible in order to further increase this ratio. But what about CFM's LEAP engines then? Well, CFM did not design its LEAP-1 engine family to use a geared turbo fan. But even though they didn't, CFM still managed to increase the LEAP engine's bypass ratio compared to the CFM-56 from around 6:1 to 11:1. These numbers are for the engines used on the Airbus A320 family.
The 737 engines needed to be a bit smaller in diameter to avoid them dragging on the ground. So its bypass ratio went from around 5.5:1 to 9:1, which is still fantastic but not quite in the same level as Pratt & Whitney managed to achieve with their Geared Turbofan.
CFM did this by focusing their development efforts on the other factor that I mentioned previously, core temperatures. General Electric and Safran, which are the two companies making up CFM, have done a lot of work over the past years aiming to replace parts made of advanced metal alloys with materials called ceramic matrix composites or CMCs. These CMCs can withstand enormous stresses, vibrations, and all kinds of other abuses, which makes them absolutely perfect for the harsh environment inside of a jet engine core.
And they can also withstand insanely high temperatures and are considerably lighter than the metal alloys that they are starting to replace. On top of this, there are, of course, many more advances inside of the LEAP family, including the use of more composites and other clever materials. So even without a geared fan, the LEAP-1 engines can still achieve that 15% efficiency improvement that I mentioned earlier over the CFM-56 engines that they're replacing.
So before we continue, let's recap. In the most modern engines that we're using in today's single aisle aircraft, Pratt & Whitney focused their efforts on miniaturizing the core and perfecting the Geared Turbofan design. And by contrast, CFM concentrated their efforts on more advanced internal components. So makes the engines lighter and also allows them to run hotter and more efficient. Now of course, ideally, to be even more efficient than that, a jet engine would need to use both of these technologies together. That would make sense, right? Well, that combination is, of course, exactly what both CFM and Pratt & Whitney want to do, but in two very different ways.
In General Electric and Safran's case, the next project that they are working on is the CFM RISE open fan, which I already made a video about a few months back. Like I explained in that video, the CFM RISE project follows much older open fan project by General Electric and Snecma, which is, by the way, what Safran was called back at that time, and also actually separately by Pratt & Whitney. Back in the late 1980s and early '90s, Boeing wanted to replace the 727 and the 737 with a design that they called the 7J7. That design would have made use of this new engine technology. McDonnell Douglas also looked at the possibility of an MD-80 variant that would use an open fan design. Now what makes these open fans very attractive is that by removing the engine cowling, they can increase the effective bypass ratio much, much more, potentially as high as 70:1 giving a potential efficiency increase of 20% above the current LEAP engines, which would be insane.
But of course, back in the '80s and '90s, the technology just wasn't there yet, neither in materials or aerodynamic modeling, leading to high noise levels due to counter rotating propellers and also unreliability in the gearboxes. By now, computer modeling has allowed CFM to eliminate that second counter rotating fan, replacing it with a set of variable pitch but non-rotating blades or veins to deswirl the airflow, fixing that huge noise issue. Again, Bjorn Fehrm explains this in Leeham News in great detail if you want to learn more. But on top of that, now gear reduction systems for the fan are also much more reliable, allowing fans with their new, lightweight composite fan blades to work even better thanks to slower rotation speeds.
But what about Pratt & Whitney? What are they going to do then? Well, it turns out that for now at least, Pratt & Whitney aren't at all interested in revisiting the open fan concept. Instead, they want to build on their work, which they had already done on its geared fan and miniaturized cores by adding the kind of ceramic matrix composites that CFM is already using. Pratt & Whitney wants to use these CMCs to a much greater extent. CFM is currently only using these ceramic composites for the turbine shrouds to its LEAP engines.
But what Pratt & Whitney wants to do is to also make these materials for bigger parts, like the turbine blades for example. This is a project that Pratt & Whitney is working on right now with collaboration from NASA. Remember, CMCs are not just capable of handling super high temperatures, they're also lighter than metal alloy parts, which means that they will be very handy for high energy rotating parts, which is why Pratt & Whitney are looking at them specifically for the turbine blades.
Now to be perfectly clear here, CFM also plans to use ceramic matrix composites in their RISE engine. In fact, General Electric has been testing CMC turbine blades for many years at this point, and will probably also use them for larger parts inside of the core. But of course, it's not as simple as just starting to use these new materials.
We also have to take into account factors like the very sensitive technology necessary to produce it, both in the right quality, volume and also in price. But what Pratt & Whitney are betting is that their geared fan and other innovations combined with more advanced CMCs will bring enough improvements in efficiency to keep aircraft designers from choosing the CFM RISE open fan, even if they can't match the insane increase in efficiency. And they might actually be on to something with that bet. You see, the CFM RISE engine brings out some question marks, specifically about its installation on the aircraft.
It has a really large diameter, so fitting it under the wings of many smaller planes would bring some complications with it. Now fitting them near the plane's tail will work, but aircraft that have rear-mounted engines generally need a more robust fuselage structure, which adds weight. By contrast, Pratt & Whitney's next engine, when it comes, will still be a turbofan, which the aircraft manufacturers already know how to fit onto their designs.
So does this mean that Pratt & Whitney have a real advantage here? Well, it turns out that it's not that simple. The CFM RISE engine could end up being so much more efficient that even if its installation to the aircraft brings a small weight penalty, it would still be worth it. And even that weight penalty is not a given because future aircraft won't simply benefit from a new engine design, they might also look different.
I recently made a video where we looked at Boeing's and NASA's new Transonic Truss-Braced Wing, or TTBW, which by the way, has recently been renamed the X-66A. The engines that this aircraft will have when it first flies will be a version of the Pratt & Whitney Geared Turbofan. But according to Jon Ostrower in The Air Current, at a later stage, Boeing is planning to test this aircraft with the CFM RISE engine. The high-mounted wing of the X-66A, which is a modified MD-90 airframe, by the way, should give the RISE engine the necessary clearance that it needs. And Airbus will also test the RISE engine on its A380 test bed. So in reality, whether or not the unique design of the CFM RISE engine will bring a weight penalty in its installation or not, and how big that penalty might be really depends on what the aircraft will look like.
Finally, there is another side to this engine war, which has to do with how engine manufacturers actually earn their money. You see, engine manufacturers earn revenue not just by selling engines, but also by servicing them over their lifetime. So if these newer engines enter service in the middle of the next decade, as the plan is at the moment, well, then our current newest engines will be less than 20 years old. Could that spell a problem of income for the engine manufacturers who still haven't been able to reap the income from all of those extra juicy years of engine maintenance? Well, that's a very complicated question to answer this early in the process. But there's no question that there are already calls for newer, much more efficient engines as the industry drives towards a very challenging net zero emission target for 2050.
One way or another, newer engines are coming and I am for one looking forward to it. I just operated the 737-8-200 for the first time this week and it was absolutely mind-blowing how low the fuel burn of its new LEAP engines were and also how insanely cool looking they are. Oh, and by the way, did you know that Ben from Airline Pilot Performance and me are running virtual type rating courses for computer sim pilots a couple of times every year? Well, the last one we did was so much fun to do and really appreciated by the students. So we're planning to run another course very soon. And to show you what it's all about and to allow you to register your interest we have created a new website called virtual737course.com. Now making this website was made so much easier, by the help of today's sponsor, Squarespace.
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Bye-bye.
2023-07-21 17:29
