15 ms·

Why it's so hard to build a jet engine

444 points by mhb 2y ago

jmward01 2y ago
The physics of gas turbine engines is one reason I am really excited about electric aviation. People don't realize that you are temp limited at altitude. They think the air is cold, but it is about getting mass through that engine so compressing that air to the density needed brings its temp way up. Electric doesn't have that issue so electric engines could go much higher which means those aircraft could become much more efficient. People focus on the problem of putting enough energy into an electric airframe, but they don't realie the potential massive efficiency gains that it can bring because of the physics of flight.
- sokka_h2otribe 2y ago
  I am not clear about your description. Electric propellor planes have similar problems at high altitude that you're pushing thin air. What are the efficiency gains you're thinking about?
  - russdill 2y ago
    The thinner the air, the more efficient your flight can be, but I never saw this as a temperature problem. My understanding is that there just isn't enough oxygen. Maybe there's an issue with the amount of heating that occurs when you try to compress enough air to get enough oxygen to run your engine? In any case, electric engines don't need oxygen.
    - zeusk 2y ago
      thinner the air, harder it is to generate lift as well. Coffin corner is a real thing.
      - mhandley 2y ago
        Unless you're prepared to go supersonic. Not easy to do with electric propulsion though.
        namibj 2y ago
        Scimitar props are pretty tame, though, or what part do you mean is hard?
        russdill 2y ago
        Pretty sure for electric aircraft to do anything useful at supersonic speeds you'd need beamed energy. Which would be a pretty cool technology
      - jmward01 2y ago
        if you stay subsonic. I hear the U-2 has like 1-2kt of leeway when it is at its max altitude because if it went faster it would be supersonic but any slower and it would fall out of the sky.
        tonyarkles 2y ago
        To the point where, if you turned too hard, you could stall one wing tip while Mach buffeting the other.
        FredPret 2y ago
        Obligatory plug for the excellent book Skunk Works by its former director, Ben Rich.
        sidnb13 2y ago
        +1, immensely satisfying read for any aviation nut
    - 0manrho 2y ago
      > can be Theory != Practice. If that were the only variable, then yes. Electric would be great. But it's not. It's far from the only thing in play. Lift also suffers from thinner air. Pure electric (as-in battery/solid state energy storage) could have 100% efficiency (specifically in converting prop/turbine torque to thrust of moving air), and it'd still have a terrible efficiency problem with current day tech. Electric's primary efficiency and efficacy issue is regarding the total operating weight of the aircraft compounded by how that weight does not meaningfully decrease as the battery banks are depleted as compared to consumable fuels. Weight is your biggest enemy in flight, not power nor mechanical efficiency. Hybrid electric (be it consumable fuel through a generator or fuel cells) is much more promising, but rarely what people mean when discussing "electric propulsion" (without the hybrid qualifier), and still has issues of it's own.
  - jmward01 2y ago
    Think of it this way, if I took 1lb of air on the ground and put it into a box that box would have sides of x. As I go up x gets bigger because pressure is dropping with altitude so to get the same mass of air I need a bigger box. When you burn fuel you need a ratio of fuel to air that is determined by mass, not volume so I need to take that really big box at altitude and squeeze it down a lot to get the same density as at sea-level (and then squeeze it even more to get the right mixture in the combustion section). The thing is though, 'hot air rises' so just squeezing down to 1 atmosphere of pressure air at altitude is way hotter than the air on the ground and then you squeeze it even more to get it to the density you need for the engine and it is -really- hot. Engines are generally torque limited on the ground and TIT limited at altitude because as they go up you are power limited by TIT (turbine inlet temp, or some other temp limit related to the engine) because of this compression. Designing engines that can handle that massive heat and that massive force is really hard, but electric has the huge benefit of just needing to produce torque so it is way easier to build and can keep producing power at much higher altitudes. There are definitely challenges there, but they are likely much easier than solving both the heat and torque problems that jet engines have.
    - scarier 2y ago
      Duuuuuude, TIT is the temperature after combustion, not compression. Adiabatic compression isn't even close to the main contributor to TIT--heat input from burning fuel is. Also you may be confusing turbofans and turboshafts--helicopters have torque limits (not a helo guy, but my understanding is this is a gearbox or masthead structural limit rather than an engine limit), but if your turbofan can't hit RPM limits on the ground on a cool day you should seriously consider bringing it back for maintenance instead of going flying.
      - jmward01 2y ago
        There are a lot of variations. I am most familiar with turbo props so shaft hp is the limiter on the ground and TIT is the limiter at altitude. TIT, of course, gets most of the heat from burning and I did mess up my explanation a bit. Sorry about that! You may be surprised how much of that TIT comes from compression though. The main point still stands, check the temp of that compressed air at sea level vs at altitude and for the same PSI out of the compressor you get a lot more heat at altitude. Either way though, the original point remains, electric has no TIT limit and you don't have to deal with 1000c materials spinning at 100k RPM so way simpler and easier to build something that keeps delivering thrust at extreme altitudes.
- 55873445216111 2y ago
  Can you recommend a place to learn more about this? I have been curious about this topic but have struggled to find resources online describing the basic physics of electric flight propulsion.
- iancmceachern 2y ago
  They are not temperature constrained at altitude. It's much colder up there. They are air, oxygen really, constrained. You are right that the electric motors themselves won't suffer from the same oxygen starvation, but as the other commenter noted, the props or impeller blades will. They need something to push, there isn't much up there.
  - numpad0 2y ago
    I think he's talking about aerodynamic heating. Turbines compress air, and exhaust generates more thrust than resistance, so it's sort of obvious that compressor stages can be temperature limited where the airframe that hosts it is temperature constrained or something. I'm not sure how it has to do with electric propulsion, though - I'd think systems like NERVA is a more exciting solution in this kind of domain(jk).
- TylerE 2y ago
  Electric has the virtually insurmountable problem that they have to haul the entire weight of the batteries around even if they are drained. This is a MASSIVE loss as itliners can burn off over half their weight during the flight.
  - mhandley 2y ago
    You need the electric equivalent of a glider tug plane to get you up to altitude. It can then return to base taking its drained batteries with it while you continue to your destination with fully charged batteries.
    - nickff 2y ago
      If that sort of complexity were viable for commercial aviation, we’d be air-to-air refueling airliners.
      - namibj 2y ago
        Air-to-air is way more difficult than just a tug, though.
        nickff 2y ago
        If that’s the case, why doesn’t the Air Force tug up its fighters? It’d be a huge advantage.
        deleted 2y ago
        [deleted]
        usrusr 2y ago
        Why? Energy density way beyond anything battery, and power headroom way beyond anything designed for frugal transport. Short haul passenger flights are not about speed but about getting directly to the stopover, without the unpredictability of ground transport. A "powered glider" with separating assist for the climbout could be a great match for that task. And the tug would obviously not really be a tug, but a winged battery directly attached to the aircraft it supports, with barely enough wing for a controlled return. An electric drop tank. Not exactly unheard of in military aviation (except for the "electric", obviously)
- bilsbie 2y ago
  Would electrics be ducted jet engines but with a motor instead of a gas turbine?
  - rich_sasha 2y ago
    I think they would basically be just the fan bit of a turbofan (where they replace a turbofan). A turbofan generates some of its thrust from the fast, hot exhaust, which you wouldn't have in an electric fan engine. Not sure about electrifying engines for slower planes, that currently use turboprops. Would that be an electric prop too?
- tekla 2y ago
  You have absolutely no idea what you are talking about. Literally made up.
adiabatichottub 2y ago
For anybody interested in gas turbine engineering, I recommend Gas Turbine Theory by Cohen & Rogers. https://archive.org/details/gasturbinetheory0000sara https://archive.org/details/gasturbinetheory0000sara
ge96 2y ago
[flagged]
orbital-decay 2y ago
One important point is missing from this: building a cheap and good engine is not enough, there are more companies and industries that can do this than it seems. But you also need the maintenance and logistics network, with a ton of professionals trained for your engine type in particular. And for that you need to penetrate the market that is already captured. This is what stopping the most.
avmich 2y ago
> Developing a new commercial aircraft is another example in this category, as is building a cheap, reusable rocket. Cheap rockets can be vastly simpler than turbojet engines. Reusability (I'm talking about reusability of an orbital rocket, suborbital reusable rockets can be rather simple, as e.g. Armadillo Aerospace and Masten Space achievements show) adds a lot to the order, but increasing the size the square-cube law improves things to an extent.
- kragen 2y ago
  Are you talking about cheap liquid-fueled rockets?
  - avmich 2y ago
    Yes.
    - kragen 2y ago
      Interesting! How do you make those cheaper than jet engines?
      - avmich 2y ago
        The simplest rocket engine doesn't really have moving parts. It's a chamber where the fuel burns and the nozzle which shapes the exhaust. The moving part is the valve somewhere which turns it on. The more complex rocket engine includes a pump. But today it's feasible not to make a turbopump, but instead use electric pump - batteries get better, and Electron rocket from Rocket Lab uses this approach for years already. With jet engines you necessarily have to accept incoming air, compress it and burn with fuel - otherwise it's not a jet engine. Batteries are unfortunately still a bit heavy, so electrical aviation is just getting off the ground slowly.
        kragen 2y ago
        You can't build a liquid-fueled rocket engine without a pump, can you? The liquid will just stay in the tank unless there's something pressurizing it to a higher pressure than you achieve inside the rocket's combustion chamber, won't it? An electric pump still sounds much more complex than a jet engine, which has, I believe, one moving part to both compress that incoming air and harness the exhaust. Admittedly, it's a moving part subject to high stresses, high temperatures, stringent balancing requirements, and demanding aerodynamics, so the larger number of parts in the electric pump might still be easier to make. Ultimately I think long-distance aviation will probably get electrified by way of abundant renewable energy powering electrical synthesis of synfuel on the ground which its engines burn.
smitty1e 2y ago
> Building the understanding required to push jet engine capabilities forward takes time, effort, and expense. This occurs in a broader cultural context. A society that dreams, enjoys science fiction, rewards hard study of advanced topics and so forth, can produce the work force to staff companies capable of going to the stars. Let us encourage that.
- kragen 2y ago
  You're describing Russia and China, but the US still seems to be doing okay at producing spaceships. Maybe that's because many of the dreamers who enjoyed science fiction in India, Ukraine, Russia, South Africa, France, Germany, Mexico, etc., moved there. Will that continue?
  - avmich 2y ago
    Russia lags far behind the US in producing spaceships for some decades. There are other things necessary for the society to build and maintain companies capable of going to the stars.
    - kragen 2y ago
      Starting 14 years ago, Russia had crewed spaceflight capability, and the US didn't; that situation persisted until less than 5 years ago (Crew Dragon Demo-2). There are other things necessary, but Russia wasn't "lagging", except in the sense that they hadn't backslid as quickly as the US. They are now, of course.
      - avmich 2y ago
        Soyuz spacecraft was technologically simpler - yet safer - than Space Shuttle. It can be argued that US had technically superior, but safety-wise inferior access to space capability until 2011, when the last Space Shuttle flight happened, then US had zero crewed spaceflight capability until 2020, and after that US again had technically superior access to space capability. Russia in contrast didn't develop its crewed spaceflight capability, it uses the technology left from the USSR. Russia maintains that technology, but progress with the improvements is rather slow. So Russia wasn't lagging in a sense of having - and using - a technology, but definitely was and is lagging in a sense of developing a new technology. As we see, the lagging of US - in a sense of having and using a technology - was for 9 years, and lagging of Russia - in a sense of having and using technology - for now is about 5 years. In a sense of developing new crewed space technology Russia is lagging roughly since the dissolution of the USSR, so 30+ years. There were quite a few attempts - again, in crewed space technology - but little results.
bob1029 2y ago
I've always been fascinated by the power density potential of the gas turbine. Especially the micro turbine class. > The MT power-to-weight ratio is better than a heavy gas turbine because the reduction of turbine diameters causes an increase in shaft rotational speed. [0] > A similar microturbine built by the Belgian Katholieke Universiteit Leuven has a rotor diameter of 20 mm and is expected to produce about 1,000 W (1.3 hp). [0] Efficiency is not fantastic at these scales. But, imagine trying to get that amount of power from a different kind of thermodynamic engine with the same mass-volume budget. For certain scenarios, this tradeoff would be amazing. EV charging is something that comes to mind. If the generator is only 50lbs and fits within a lunch box, you could keep it in your car just like a spare tire. I think the efficiency can be compensated for when considering the benefits of distributed generation, cost & form factor. One of the other advantages of the smaller engines is that you can use techniques that are wildly infeasible in larger engines. For example, Capstone uses a zero-friction air bearing in their solutions: > Key to the Capstone design is its use of air bearings, which provides maintenance and fluid-free operation for the lifetime of the turbine and reduces the system to a single moving part. This also eliminates the need for any cooling or other secondary systems. [1] [0] https://en.wikipedia.org/wiki/Microturbine https://en.wikipedia.org/wiki/Microturbine [1] https://en.wikipedia.org/wiki/Capstone_Green_Energy https://en.wikipedia.org/wiki/Capstone_Green_Energy
- nick3443 2y ago
  Tiny nitro RC engines can produce 1+ horsepower in engines that weight 1/2 lb.
  - esperent 2y ago
    I guess nobody cares about efficiency in their model car engine, so it doesn't matter if you need to refuel every 5-10 minutes. But that would be a problem for pretty much any other use case. Does anyone know how the efficiency per liter of engine volume compares to these small turbine engines?
    - nick3443 2y ago
gtirloni 2y ago
Aren't these engine designs patented very heavily? How were clones popping up less than a decade later?
sitharus 2y ago
A very good article, but I was disappointed to see the misunderstanding about the de Havilland Comet failures repeated > fatigue failures around its rectangular windows caused two crashes, resulting in it being withdrawn from service While the accident investigation reports refer to "windows", which really doesn't help matters, the failure point was the ADF antenna mounting cutout. The passenger windows had rounded corners and did not fail in service. The Comet was not withdrawn from service, they re-engineered and launched the Comet 4 (with oval windows, but that choice was to reduce manufacturing costs) in 1958, but the Boeing 707 was introduced that year and the DC-8 in 1959, ending the Comet's status as the only in-service jet airliner it held between 1952 and the grounding of the Comet 1 in 1954. The Comet 4 continued to fly in revenue service until at least the mid 1970s with lower-tier airlines. The decision to bury the engines in the wings was one of the deciding factors for airlines - engines in nacelles are easier and cheaper to service and swap if required. Re-engining the Comet 4 to new more efficient turbofan engines the DC-8 and Boeing 707 introduced in 1960 and 1961 respectively required a new wing, but a podded engine was much easier to swap on to an existing airframe and this was done for many of the Boeing and Douglas aircraft. The last Comet-derived aircraft - the Hawker Siddeley Nimrod - flew until 2011 in the RAF. They did look at upgrading them with new wings and avionics, but the plan was scrapped when they discovered that in the grand tradition of British engineering every fuselage was built slightly differently and they couldn't make replacement parts to a standard plan. Anyway that's my rant in to the void today :)
- ggm 2y ago
  As i am sure the OP and GP know pprune has much of this, and concord related stories from a cohort of engineers and pilots who worked on these aircraft. They did have a "best of" collection at one point, not sure now. Also a lot of flight test stories, ATC stories.
wyager 2y ago
What's beautiful to me is that that combustion turbines have the simplest possible thermodynamic cycle in theory (a steady input flow of X fluid/sec at pressure P, and a steady output flow of Y>X fluid/sec at pressure P), yet it turns out to be one of the most complex cycles to harness in practice!
- eternauta3k 2y ago
  Is that really the thermodynamic cycle of the turbine? My understanding is that a cycle is something like "adiabatic compression followed by isothermic expansion, followed by ...", i.e. the details of what happens to the working fluid.
  - adrian_b 2y ago
    In a gas turbine, the phases of the thermodynamic cycle happen simultaneously in time, but in different places inside the turbine. While a portion of air progresses through the turbine, it passes through the phases of the cycle. During the first phase, the air passes through the compressor section of the turbine, where it is compressed adiabatically. During the second phase, fuel is added to the air and it burns, heating the air, which expands at an approximately constant pressure. During the third phase, the exhaust gases pass through the expander section of the turbine, being expanded adiabatically. The last phase of the cycle, which closes the thermodynamic cycle, by reaching the ambient temperature and pressure, happens in the external atmosphere, for the exhaust gases. The meaning of this phase for an open-cycle engine is that its computation provides the value of the energy lost in the exhaust gases, which reduces the achievable efficiency. This thermodynamic cycle, which approximates what happens in a gas turbine, is named by Americans the Brayton cycle, even if the historically-correct name is the Joule cycle. (George B. Brayton has patented an engine using this cycle in 1872, without explaining it, but James Prescott Joule had published an article analyzing in great detail this cycle, “On the Air-Engine”, already in 1851, 21 years earlier. Moreover, already in 1859, a textbook by Rankine, “A Manual of the Steam Engine and other Prime Movers”, where all the thermodynamic cycles known at that time were discussed, attributed this cycle to Joule, 13 years before the Brayton patent. Not only the work of Joule happened much earlier than that of Brayton, but the publications of Joule and Rankine have been very important in the development of the industry of thermal engines, unlike the engines produced by Brayton, which had a very limited commercial success and which had a negligible contribution to the education of the engineers working in this domain. Therefore, the use of the term "Brayton cycle" does not appear to be based on any reason, except that Brayton was American and Joule British.)
deleted 2y ago
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divbzero 2y ago
Related: See Thru Jet Engine [video] - https://news.ycombinator.com/item?id=32145297 https://news.ycombinator.com/item?id=32145297 - July 2022 (70 comments)
I_dream_of_Geni 2y ago
Funny, if you mouse over the graph of transistor costs, they become free in 2005! Cool!
- moffkalast 2y ago
  Transistor manufacturers are like, "hey free transistors" then they bill the entire cost as shipping fees like the average aliexpress store.
drysine 2y ago
>Depending on how you count, there are just two to four builders of large commercial aircraft (Airbus, Boeing, Embraer, and now COMAC). Where is Russian Sukhoi?
- D_Alex 2y ago
  It is part of UAC, along with Ilyushin and Yakovlev.
  - drysine 2y ago
    Still not in the list)
    - D_Alex 2y ago
      Yes, and they are ahead of COMAC in the number of aircraft produced. It will be interesting to see if UAC emerges as a serious competitor to Boeing and Airbus (and COMAC) in the near future.
      - drysine 2y ago
        Yeah, waiting to see if the current iteration of PD-14 engine[0] is finally up to the task. Two years ago UAC tested them and found to be in the need of improvement. [0] https://rostec.ru/media/news/rostekh-peredal-partiyu-seriynykh-aviadvigateley-pd-14-dlya-ms-21/ https://rostec.ru/media/news/rostekh-peredal-partiyu-seriyny...
        D_Alex 2y ago
        Yep... it is hard to build a competitive jet engine. If the Russians manage to do this, it would be another example of the stupidity of the sanctions. I bet COMAC is cheering them on too.
      - notahacker 2y ago
        Seems unlikely. They had their window of opportunity when they had an active Western marketing arm, Russia wasn't a sanctioned nation, COMAC was barely getting started and the early reports of the Superjet were quite positive. Suffice to say the airlines that passed on the opportunity aren't regretting it and the couple that bought them did regret it.
mppm 2y ago
One important aspect of modern jet engines that the article only mentions on the periphery are the materials engineering problems in the hot section. There are many metals (not to mention ceramics) that can survive 1000C temperatures, but there are not many that can permanently resist creep at these temperatures under high tensile loads. The only really viable class of materials at the moment are Nickel-based single-crystal superalloys that contain rare metals like Rhenium and Ruthenium. This comes with serious supply limitations and rather complex manufacturing, where the molten metal is solidified directly in the shape of a turbine blade from a single seed crystal. Fun stuff, in other words :)
- eutectic 2y ago
  Silicon carbide fiber reinforced silicon carbide is also being increasingly used.
  - mppm 2y ago
    In production?
    - credit_guy 2y ago
      I think eutectic is referring to the ceramic matrix composites (CMC) used in the General Electric's engine LEAP. Here's some quotes from [1]: > The engine has one CMC component, a turbine shroud lining its hottest zone, so it can operate at up to 2400 F. The CMC needs less cooling air than nickel-based super-alloys and is part of a suite of technologies that contribute to 15 percent fuel savings for LEAP over its predecessor, the CFM 56 engine. > GE’s CMC is made of silicon carbide (SiC) ceramic fibers (containing silicon and carbon in equal amounts) coated with a proprietary material containing boron nitride. The coated fibers are shaped into a “preform” that is embedded in SiC containing 10–15 percent silicon. [1] https://www.ornl.gov/news/ceramic-matrix-composites-take-flight-leap-jet-engine https://www.ornl.gov/news/ceramic-matrix-composites-take-fli...
      - Invictus0 2y ago
evnix 2y ago
I feel, What's more harder are the jet engines on fighter planes. These are usually a decade or two ahead in terms of advancements. The technology here trickles down to commercial jet engines slowly. Things like Metullargy for blades etc are a closely guarded secret. China and India are pouring billions into research just to get theirs close to even the lower end of what GE has to offer.
- dguest 2y ago
  One of the figures in the article [1] adds something to this point: military engines have much shorter lifetimes. So it seems it's not just "trickle down" technology, there's also some redesign for reliability. A commercial engine can operate for a cumulative 1 year between overhauls, according to that figure, as of 2010. The military ones last 1/10th as long. I can only imagine how much more challenging it is to iterate on designs when you are dealing with problems that take 10 times longer to manifest. [1]: https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F968978db-8b83-450c-9640-5528a17e10a0_745x560.png https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_pr...
betimsl 2y ago
Material tolerances.
alkonaut 2y ago
> There’s no point in designing a new engine if it doesn’t significantly improve on the state of the art Oh but there is. I would love to see more European alternatives to US designs even at 5% less efficiency and power. Surely it can’t be that expensive to create an engine in 2025 similar to the state of the art 2005, when you have all the hindsight plus unlimited access to the original design? Events of this week show that this will be very important.
- varjag 2y ago
  Rolls Royce is British.
  - venv 2y ago
    And PBS is Czech, to name one.
- 6SixTy 2y ago
  There's sort of two tracks when it comes to jet engines: commercial aviation and military. Commercial just focuses on efficiency, while military has other considerations to account for. And in both sectors there's plenty of European competition, US/EU joint ventures, and subcontractors/licensed manufacturing going on. Europe does have enough aerospace talent to make a jet engine especially at the cutting edge, but there's a significant amount of tech transfer between the US and Europe happening at the same time.
- Epa095 2y ago
  I agree, but it does not seem so bleak. According to Wikipedia[1]: The manufacturers market share should be led by CFM with 44% followed by Pratt & Whitney with 29% and then Rolls-Royce and General Electric with 10% each. CFM is a 50/50 American/French joint venture, and Rolls-Royce is British. 1: https://en.m.wikipedia.org/wiki/List_of_turbofan_manufacturers https://en.m.wikipedia.org/wiki/List_of_turbofan_manufacture...
  - class3shock 2y ago
    Safran can not make a competitive commercial jet engine on their own and Rolls Royce is a generation behind both GE and P&W, and given the state of the UK not likely to catch up. Right now there is really P&W and GE and then everyone else.
1024core 2y ago
How many countries make their own jet engines? US, UK, France ... anyone else?
- philwelch 2y ago
  Russia and China
  - themgt 2y ago
    I was intrigued by an above comment about miniature jet engines - Iran last year announced a jet-powered Shahed drone variant, which uses an engine that has an interesting backstory: There are many variants of [the French Microturbo TRI 60] engine and it is used in many missiles and UAVs, as listed below. Aside from the known uses listed below, it is widely speculated that Iran illegally purchased many TRI 60 engines from Microturbo to assemble C-802 cruise missiles purchased from China. It is unclear which variant was purchased. Iran also reverse-engineered this engine as the Toloue-4 turbojet engine. Toloue-4 is used in several Iranian military equipment including Iran's copy of C-802, the Noor missile. It's fascinating how many engineering artifacts turn out to have been invented just once. This is the same engine used in Storm Shadow / SCALP EG, so both sides in the Ukraine war are firing variants of a 1970s miniature French jet engine at each other. https://en.wikipedia.org/wiki/TEM_Toloue-4 https://en.wikipedia.org/wiki/TEM_Toloue-4 https://en.wikipedia.org/wiki/Microturbo_TRI_60 https://en.wikipedia.org/wiki/Microturbo_TRI_60
- t43562 2y ago
  The German part of Rolls Royce - that's where the new B-52 engines are coming from for example.
- missedthecue 2y ago
  Russia, China, India, both South and North Korea, Iran, Turkey, Israel, and Czech Republic all manufacture jet engines domestically.
paulpauper 2y ago
It's hard not because the technology is so special , but because the tolerance for errors is so small . Jet failure can mean loss of many lives and little room to rectify the situation in flight ,whereas an automobile or train engine failure is a more manageable situation.
Animats 2y ago
And why they are so expensive. General aviation is still running on pistons. Not because small jet engines can't be built, but because they don't get cheaper as they get smaller. 6-passenger bizjet sized engines seem to be the lower economic limit. Williams tried and tried. They built good small jet engines, all the way down to jetpack size, but those never got cheap.[1] There are "very light jets", but the smallest in production, the Cirrus Vision Jet, is around US$2 million. [1] https://en.wikipedia.org/wiki/Williams_International https://en.wikipedia.org/wiki/Williams_International [2] https://en.wikipedia.org/wiki/Very_light_jet https://en.wikipedia.org/wiki/Very_light_jet
- hnuser123456 2y ago
  I wonder, as batteries and electric (BLDC) motors get better and better, if we will find applications where electric ducted fans outperform (electric driven) propellers, since electric motors are the same complexity regardless of application.
  - geocrasher 2y ago
    Ducted fans are by nature less efficient than propellers. This is one reason that the next big leap in engine efficiency may come from what are essentially unducted fans.
    - Manuel_D 2y ago
      I thought adding a shroud to propellers increased efficiency? That's why we use turbofan engines instead of turboprops.
      - consumer451 2y ago
        One of the latest designs appears to do away with the duct/shroud, for the thrust creation part of the engine. It also hopes to achieve a 20$ decrease int fuel usage. https://en.wikipedia.org/wiki/CFM_International_RISE https://en.wikipedia.org/wiki/CFM_International_RISE https://www.cfmaeroengines.com/rise/ https://www.cfmaeroengines.com/rise/
anon_cow1111 2y ago
For young aspiring engineers here who may read this and just like the sound of "building jet engine", look into building a pulse jet first. They're extremely easy to build, having no moving parts, and only requiring some steel tubing, a welder and a large propane tank. I've already done it and can attest to this being true. The "best" part is that they're incredibly, obnoxiously loud. Like wear earplugs and ear muffs at the same time loud. Efficiency isn't great, you can expect maybe 20-100 lbs thrust from larger models but I suppose that's more than enough for "let's grab an old bicycle and do something really stupid" (oh and look pulsejets up on youtube for sure, it'll open up a whole world for you in under 20 minutes)
- gosub100 2y ago
  https://youtu.be/xJhazf0apN8?si=fcb8vehZbqUFRhIy https://youtu.be/xJhazf0apN8?si=fcb8vehZbqUFRhIy A great DIY from a great YouTuber
  - physicsguy 2y ago
    https://youtube.com/watch?v=-fDM9Eb16Do&t=176s&pp=ygUcY29saW4gZnVyemUgcHVsc2UgamV0IGtldHRsZQ%3D%3D https://youtube.com/watch?v=-fDM9Eb16Do&t=176s&pp=ygUcY29saW... I like this one
gunian 2y ago
because it flies away
anovikov 2y ago
It's not all that hard to build a jet engine. Nazi Germany built them being constantly bombed, with actively sabotaging slave labor. Starving North Korea builds them. War-torn Ukraine builds them. What's hard is to build a competitive jet engine. And there, it happens naturally, by itself: the best marketable jet engine is the one where marginal increase of complexity and cost matches marginal fuel savings: buy simpler/cheaper ones and you waste more money on fuel than you save buying the engine, buy a more complex/expensive one and you don't justify the costs with your fuel savings. Because an engine runs for tens of thousands of hours - some over 100K hours - so 1% of performance improvement is worth ~1000 tons of fuel - there is a lot of complexity that can be pushed into the solution while still being profitable - and competition ensures this is the case. That's why it is incredibly hard to make a competitive jet engine.
- maxglute 2y ago
  IIRC leading fuel efficient turbo jet cost like ~10m + 1m for maintenance and consumes 70m worth of fuel over 30k hour life time. An engine 15% less fuel efficient would have to cost $0 to be competitive.
  - anovikov 2y ago
    See. But building a jet engine that "just works" without a particular profitability is not at all hard. Like, one that burns 50% fuel for same thrust than the best state of the art. That's about the level of disposable engines used in cruise missiles and drones.
DeathArrow 2y ago
I wonder if there aren't other propulsion principles to pursue in modern aircrafts beside the jet engine.
maxglute 2y ago
May countries got domestic turbojet running, but most engine projects fail because there wasn't political will eat the billions to keep a competitive program going, especially as complexity increase in turbofans.

444 points by mhb 2y ago

The physics of gas turbine engines is one reason I am really excited about electric aviation. People don't realize that you are temp limited at altitude. They think the air is cold, but it is about getting mass through that engine so compressing that air to the density needed brings its temp way up. Electric doesn't have that issue so electric engines could go much higher which means those aircraft could become much more efficient. People focus on the problem of putting enough energy into an electric airframe, but they don't realie the potential massive efficiency gains that it can bring because of the physics of flight.

sokka_h2otribe 2y ago
I am not clear about your description. Electric propellor planes have similar problems at high altitude that you're pushing thin air. What are the efficiency gains you're thinking about?
- russdill 2y ago
  The thinner the air, the more efficient your flight can be, but I never saw this as a temperature problem. My understanding is that there just isn't enough oxygen. Maybe there's an issue with the amount of heating that occurs when you try to compress enough air to get enough oxygen to run your engine? In any case, electric engines don't need oxygen.
  - zeusk 2y ago
    thinner the air, harder it is to generate lift as well. Coffin corner is a real thing.
    - mhandley 2y ago
      Unless you're prepared to go supersonic. Not easy to do with electric propulsion though.
      - namibj 2y ago
        Scimitar props are pretty tame, though, or what part do you mean is hard?
      - russdill 2y ago
        Pretty sure for electric aircraft to do anything useful at supersonic speeds you'd need beamed energy. Which would be a pretty cool technology
    - jmward01 2y ago
      if you stay subsonic. I hear the U-2 has like 1-2kt of leeway when it is at its max altitude because if it went faster it would be supersonic but any slower and it would fall out of the sky.
      - tonyarkles 2y ago
        To the point where, if you turned too hard, you could stall one wing tip while Mach buffeting the other.
        FredPret 2y ago
        Obligatory plug for the excellent book Skunk Works by its former director, Ben Rich.
        sidnb13 2y ago
        +1, immensely satisfying read for any aviation nut
  - 0manrho 2y ago
    > can be Theory != Practice. If that were the only variable, then yes. Electric would be great. But it's not. It's far from the only thing in play. Lift also suffers from thinner air. Pure electric (as-in battery/solid state energy storage) could have 100% efficiency (specifically in converting prop/turbine torque to thrust of moving air), and it'd still have a terrible efficiency problem with current day tech. Electric's primary efficiency and efficacy issue is regarding the total operating weight of the aircraft compounded by how that weight does not meaningfully decrease as the battery banks are depleted as compared to consumable fuels. Weight is your biggest enemy in flight, not power nor mechanical efficiency. Hybrid electric (be it consumable fuel through a generator or fuel cells) is much more promising, but rarely what people mean when discussing "electric propulsion" (without the hybrid qualifier), and still has issues of it's own.
- jmward01 2y ago
  Think of it this way, if I took 1lb of air on the ground and put it into a box that box would have sides of x. As I go up x gets bigger because pressure is dropping with altitude so to get the same mass of air I need a bigger box. When you burn fuel you need a ratio of fuel to air that is determined by mass, not volume so I need to take that really big box at altitude and squeeze it down a lot to get the same density as at sea-level (and then squeeze it even more to get the right mixture in the combustion section). The thing is though, 'hot air rises' so just squeezing down to 1 atmosphere of pressure air at altitude is way hotter than the air on the ground and then you squeeze it even more to get it to the density you need for the engine and it is -really- hot. Engines are generally torque limited on the ground and TIT limited at altitude because as they go up you are power limited by TIT (turbine inlet temp, or some other temp limit related to the engine) because of this compression. Designing engines that can handle that massive heat and that massive force is really hard, but electric has the huge benefit of just needing to produce torque so it is way easier to build and can keep producing power at much higher altitudes. There are definitely challenges there, but they are likely much easier than solving both the heat and torque problems that jet engines have.
  - scarier 2y ago
    Duuuuuude, TIT is the temperature after combustion, not compression. Adiabatic compression isn't even close to the main contributor to TIT--heat input from burning fuel is. Also you may be confusing turbofans and turboshafts--helicopters have torque limits (not a helo guy, but my understanding is this is a gearbox or masthead structural limit rather than an engine limit), but if your turbofan can't hit RPM limits on the ground on a cool day you should seriously consider bringing it back for maintenance instead of going flying.
    - jmward01 2y ago
      There are a lot of variations. I am most familiar with turbo props so shaft hp is the limiter on the ground and TIT is the limiter at altitude. TIT, of course, gets most of the heat from burning and I did mess up my explanation a bit. Sorry about that! You may be surprised how much of that TIT comes from compression though. The main point still stands, check the temp of that compressed air at sea level vs at altitude and for the same PSI out of the compressor you get a lot more heat at altitude. Either way though, the original point remains, electric has no TIT limit and you don't have to deal with 1000c materials spinning at 100k RPM so way simpler and easier to build something that keeps delivering thrust at extreme altitudes.
55873445216111 2y ago
Can you recommend a place to learn more about this? I have been curious about this topic but have struggled to find resources online describing the basic physics of electric flight propulsion.
iancmceachern 2y ago
They are not temperature constrained at altitude. It's much colder up there. They are air, oxygen really, constrained. You are right that the electric motors themselves won't suffer from the same oxygen starvation, but as the other commenter noted, the props or impeller blades will. They need something to push, there isn't much up there.
- numpad0 2y ago
  I think he's talking about aerodynamic heating. Turbines compress air, and exhaust generates more thrust than resistance, so it's sort of obvious that compressor stages can be temperature limited where the airframe that hosts it is temperature constrained or something. I'm not sure how it has to do with electric propulsion, though - I'd think systems like NERVA is a more exciting solution in this kind of domain(jk).
TylerE 2y ago
Electric has the virtually insurmountable problem that they have to haul the entire weight of the batteries around even if they are drained. This is a MASSIVE loss as itliners can burn off over half their weight during the flight.
- mhandley 2y ago
  You need the electric equivalent of a glider tug plane to get you up to altitude. It can then return to base taking its drained batteries with it while you continue to your destination with fully charged batteries.
  - nickff 2y ago
    If that sort of complexity were viable for commercial aviation, we’d be air-to-air refueling airliners.
    - namibj 2y ago
      Air-to-air is way more difficult than just a tug, though.
      - nickff 2y ago
        If that’s the case, why doesn’t the Air Force tug up its fighters? It’d be a huge advantage.
        deleted 2y ago
        [deleted]
        usrusr 2y ago
        Why? Energy density way beyond anything battery, and power headroom way beyond anything designed for frugal transport. Short haul passenger flights are not about speed but about getting directly to the stopover, without the unpredictability of ground transport. A "powered glider" with separating assist for the climbout could be a great match for that task. And the tug would obviously not really be a tug, but a winged battery directly attached to the aircraft it supports, with barely enough wing for a controlled return. An electric drop tank. Not exactly unheard of in military aviation (except for the "electric", obviously)
bilsbie 2y ago
Would electrics be ducted jet engines but with a motor instead of a gas turbine?
- rich_sasha 2y ago
  I think they would basically be just the fan bit of a turbofan (where they replace a turbofan). A turbofan generates some of its thrust from the fast, hot exhaust, which you wouldn't have in an electric fan engine. Not sure about electrifying engines for slower planes, that currently use turboprops. Would that be an electric prop too?
tekla 2y ago
You have absolutely no idea what you are talking about. Literally made up.

adiabatichottub 2y ago

For anybody interested in gas turbine engineering, I recommend Gas Turbine Theory by Cohen & Rogers. https://archive.org/details/gasturbinetheory0000sara https://archive.org/details/gasturbinetheory0000sara

ge96 2y ago

[flagged]

orbital-decay 2y ago

One important point is missing from this: building a cheap and good engine is not enough, there are more companies and industries that can do this than it seems. But you also need the maintenance and logistics network, with a ton of professionals trained for your engine type in particular. And for that you need to penetrate the market that is already captured. This is what stopping the most.

avmich 2y ago

> Developing a new commercial aircraft is another example in this category, as is building a cheap, reusable rocket. Cheap rockets can be vastly simpler than turbojet engines. Reusability (I'm talking about reusability of an orbital rocket, suborbital reusable rockets can be rather simple, as e.g. Armadillo Aerospace and Masten Space achievements show) adds a lot to the order, but increasing the size the square-cube law improves things to an extent.

kragen 2y ago
Are you talking about cheap liquid-fueled rockets?
- avmich 2y ago
  Yes.
  - kragen 2y ago
    Interesting! How do you make those cheaper than jet engines?
    - avmich 2y ago
      The simplest rocket engine doesn't really have moving parts. It's a chamber where the fuel burns and the nozzle which shapes the exhaust. The moving part is the valve somewhere which turns it on. The more complex rocket engine includes a pump. But today it's feasible not to make a turbopump, but instead use electric pump - batteries get better, and Electron rocket from Rocket Lab uses this approach for years already. With jet engines you necessarily have to accept incoming air, compress it and burn with fuel - otherwise it's not a jet engine. Batteries are unfortunately still a bit heavy, so electrical aviation is just getting off the ground slowly.
      - kragen 2y ago
        You can't build a liquid-fueled rocket engine without a pump, can you? The liquid will just stay in the tank unless there's something pressurizing it to a higher pressure than you achieve inside the rocket's combustion chamber, won't it? An electric pump still sounds much more complex than a jet engine, which has, I believe, one moving part to both compress that incoming air and harness the exhaust. Admittedly, it's a moving part subject to high stresses, high temperatures, stringent balancing requirements, and demanding aerodynamics, so the larger number of parts in the electric pump might still be easier to make. Ultimately I think long-distance aviation will probably get electrified by way of abundant renewable energy powering electrical synthesis of synfuel on the ground which its engines burn.

smitty1e 2y ago

> Building the understanding required to push jet engine capabilities forward takes time, effort, and expense. This occurs in a broader cultural context. A society that dreams, enjoys science fiction, rewards hard study of advanced topics and so forth, can produce the work force to staff companies capable of going to the stars. Let us encourage that.

kragen 2y ago
You're describing Russia and China, but the US still seems to be doing okay at producing spaceships. Maybe that's because many of the dreamers who enjoyed science fiction in India, Ukraine, Russia, South Africa, France, Germany, Mexico, etc., moved there. Will that continue?
- avmich 2y ago
  Russia lags far behind the US in producing spaceships for some decades. There are other things necessary for the society to build and maintain companies capable of going to the stars.
  - kragen 2y ago
    Starting 14 years ago, Russia had crewed spaceflight capability, and the US didn't; that situation persisted until less than 5 years ago (Crew Dragon Demo-2). There are other things necessary, but Russia wasn't "lagging", except in the sense that they hadn't backslid as quickly as the US. They are now, of course.
    - avmich 2y ago
      Soyuz spacecraft was technologically simpler - yet safer - than Space Shuttle. It can be argued that US had technically superior, but safety-wise inferior access to space capability until 2011, when the last Space Shuttle flight happened, then US had zero crewed spaceflight capability until 2020, and after that US again had technically superior access to space capability. Russia in contrast didn't develop its crewed spaceflight capability, it uses the technology left from the USSR. Russia maintains that technology, but progress with the improvements is rather slow. So Russia wasn't lagging in a sense of having - and using - a technology, but definitely was and is lagging in a sense of developing a new technology. As we see, the lagging of US - in a sense of having and using a technology - was for 9 years, and lagging of Russia - in a sense of having and using technology - for now is about 5 years. In a sense of developing new crewed space technology Russia is lagging roughly since the dissolution of the USSR, so 30+ years. There were quite a few attempts - again, in crewed space technology - but little results.

bob1029 2y ago

I've always been fascinated by the power density potential of the gas turbine. Especially the micro turbine class. > The MT power-to-weight ratio is better than a heavy gas turbine because the reduction of turbine diameters causes an increase in shaft rotational speed. [0] > A similar microturbine built by the Belgian Katholieke Universiteit Leuven has a rotor diameter of 20 mm and is expected to produce about 1,000 W (1.3 hp). [0] Efficiency is not fantastic at these scales. But, imagine trying to get that amount of power from a different kind of thermodynamic engine with the same mass-volume budget. For certain scenarios, this tradeoff would be amazing. EV charging is something that comes to mind. If the generator is only 50lbs and fits within a lunch box, you could keep it in your car just like a spare tire. I think the efficiency can be compensated for when considering the benefits of distributed generation, cost & form factor. One of the other advantages of the smaller engines is that you can use techniques that are wildly infeasible in larger engines. For example, Capstone uses a zero-friction air bearing in their solutions: > Key to the Capstone design is its use of air bearings, which provides maintenance and fluid-free operation for the lifetime of the turbine and reduces the system to a single moving part. This also eliminates the need for any cooling or other secondary systems. [1] [0] https://en.wikipedia.org/wiki/Microturbine https://en.wikipedia.org/wiki/Microturbine [1] https://en.wikipedia.org/wiki/Capstone_Green_Energy https://en.wikipedia.org/wiki/Capstone_Green_Energy

nick3443 2y ago
Tiny nitro RC engines can produce 1+ horsepower in engines that weight 1/2 lb.
- esperent 2y ago
  I guess nobody cares about efficiency in their model car engine, so it doesn't matter if you need to refuel every 5-10 minutes. But that would be a problem for pretty much any other use case. Does anyone know how the efficiency per liter of engine volume compares to these small turbine engines?
  - nick3443 2y ago

gtirloni 2y ago

Aren't these engine designs patented very heavily? How were clones popping up less than a decade later?

sitharus 2y ago

A very good article, but I was disappointed to see the misunderstanding about the de Havilland Comet failures repeated > fatigue failures around its rectangular windows caused two crashes, resulting in it being withdrawn from service While the accident investigation reports refer to "windows", which really doesn't help matters, the failure point was the ADF antenna mounting cutout. The passenger windows had rounded corners and did not fail in service. The Comet was not withdrawn from service, they re-engineered and launched the Comet 4 (with oval windows, but that choice was to reduce manufacturing costs) in 1958, but the Boeing 707 was introduced that year and the DC-8 in 1959, ending the Comet's status as the only in-service jet airliner it held between 1952 and the grounding of the Comet 1 in 1954. The Comet 4 continued to fly in revenue service until at least the mid 1970s with lower-tier airlines. The decision to bury the engines in the wings was one of the deciding factors for airlines - engines in nacelles are easier and cheaper to service and swap if required. Re-engining the Comet 4 to new more efficient turbofan engines the DC-8 and Boeing 707 introduced in 1960 and 1961 respectively required a new wing, but a podded engine was much easier to swap on to an existing airframe and this was done for many of the Boeing and Douglas aircraft. The last Comet-derived aircraft - the Hawker Siddeley Nimrod - flew until 2011 in the RAF. They did look at upgrading them with new wings and avionics, but the plan was scrapped when they discovered that in the grand tradition of British engineering every fuselage was built slightly differently and they couldn't make replacement parts to a standard plan. Anyway that's my rant in to the void today :)

ggm 2y ago
As i am sure the OP and GP know pprune has much of this, and concord related stories from a cohort of engineers and pilots who worked on these aircraft. They did have a "best of" collection at one point, not sure now. Also a lot of flight test stories, ATC stories.

wyager 2y ago

What's beautiful to me is that that combustion turbines have the simplest possible thermodynamic cycle in theory (a steady input flow of X fluid/sec at pressure P, and a steady output flow of Y>X fluid/sec at pressure P), yet it turns out to be one of the most complex cycles to harness in practice!

eternauta3k 2y ago
Is that really the thermodynamic cycle of the turbine? My understanding is that a cycle is something like "adiabatic compression followed by isothermic expansion, followed by ...", i.e. the details of what happens to the working fluid.
- adrian_b 2y ago
  In a gas turbine, the phases of the thermodynamic cycle happen simultaneously in time, but in different places inside the turbine. While a portion of air progresses through the turbine, it passes through the phases of the cycle. During the first phase, the air passes through the compressor section of the turbine, where it is compressed adiabatically. During the second phase, fuel is added to the air and it burns, heating the air, which expands at an approximately constant pressure. During the third phase, the exhaust gases pass through the expander section of the turbine, being expanded adiabatically. The last phase of the cycle, which closes the thermodynamic cycle, by reaching the ambient temperature and pressure, happens in the external atmosphere, for the exhaust gases. The meaning of this phase for an open-cycle engine is that its computation provides the value of the energy lost in the exhaust gases, which reduces the achievable efficiency. This thermodynamic cycle, which approximates what happens in a gas turbine, is named by Americans the Brayton cycle, even if the historically-correct name is the Joule cycle. (George B. Brayton has patented an engine using this cycle in 1872, without explaining it, but James Prescott Joule had published an article analyzing in great detail this cycle, “On the Air-Engine”, already in 1851, 21 years earlier. Moreover, already in 1859, a textbook by Rankine, “A Manual of the Steam Engine and other Prime Movers”, where all the thermodynamic cycles known at that time were discussed, attributed this cycle to Joule, 13 years before the Brayton patent. Not only the work of Joule happened much earlier than that of Brayton, but the publications of Joule and Rankine have been very important in the development of the industry of thermal engines, unlike the engines produced by Brayton, which had a very limited commercial success and which had a negligible contribution to the education of the engineers working in this domain. Therefore, the use of the term "Brayton cycle" does not appear to be based on any reason, except that Brayton was American and Joule British.)

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divbzero 2y ago

Related: See Thru Jet Engine [video] - https://news.ycombinator.com/item?id=32145297 https://news.ycombinator.com/item?id=32145297 - July 2022 (70 comments)

I_dream_of_Geni 2y ago

Funny, if you mouse over the graph of transistor costs, they become free in 2005! Cool!

moffkalast 2y ago
Transistor manufacturers are like, "hey free transistors" then they bill the entire cost as shipping fees like the average aliexpress store.

drysine 2y ago

>Depending on how you count, there are just two to four builders of large commercial aircraft (Airbus, Boeing, Embraer, and now COMAC). Where is Russian Sukhoi?

D_Alex 2y ago
It is part of UAC, along with Ilyushin and Yakovlev.
- drysine 2y ago
  Still not in the list)
  - D_Alex 2y ago
    Yes, and they are ahead of COMAC in the number of aircraft produced. It will be interesting to see if UAC emerges as a serious competitor to Boeing and Airbus (and COMAC) in the near future.
    - drysine 2y ago
      Yeah, waiting to see if the current iteration of PD-14 engine[0] is finally up to the task. Two years ago UAC tested them and found to be in the need of improvement. [0] https://rostec.ru/media/news/rostekh-peredal-partiyu-seriynykh-aviadvigateley-pd-14-dlya-ms-21/ https://rostec.ru/media/news/rostekh-peredal-partiyu-seriyny...
      - D_Alex 2y ago
        Yep... it is hard to build a competitive jet engine. If the Russians manage to do this, it would be another example of the stupidity of the sanctions. I bet COMAC is cheering them on too.
    - notahacker 2y ago
      Seems unlikely. They had their window of opportunity when they had an active Western marketing arm, Russia wasn't a sanctioned nation, COMAC was barely getting started and the early reports of the Superjet were quite positive. Suffice to say the airlines that passed on the opportunity aren't regretting it and the couple that bought them did regret it.

mppm 2y ago

One important aspect of modern jet engines that the article only mentions on the periphery are the materials engineering problems in the hot section. There are many metals (not to mention ceramics) that can survive 1000C temperatures, but there are not many that can permanently resist creep at these temperatures under high tensile loads. The only really viable class of materials at the moment are Nickel-based single-crystal superalloys that contain rare metals like Rhenium and Ruthenium. This comes with serious supply limitations and rather complex manufacturing, where the molten metal is solidified directly in the shape of a turbine blade from a single seed crystal. Fun stuff, in other words :)

eutectic 2y ago
Silicon carbide fiber reinforced silicon carbide is also being increasingly used.
- mppm 2y ago
  In production?
  - credit_guy 2y ago
    I think eutectic is referring to the ceramic matrix composites (CMC) used in the General Electric's engine LEAP. Here's some quotes from [1]: > The engine has one CMC component, a turbine shroud lining its hottest zone, so it can operate at up to 2400 F. The CMC needs less cooling air than nickel-based super-alloys and is part of a suite of technologies that contribute to 15 percent fuel savings for LEAP over its predecessor, the CFM 56 engine. > GE’s CMC is made of silicon carbide (SiC) ceramic fibers (containing silicon and carbon in equal amounts) coated with a proprietary material containing boron nitride. The coated fibers are shaped into a “preform” that is embedded in SiC containing 10–15 percent silicon. [1] https://www.ornl.gov/news/ceramic-matrix-composites-take-flight-leap-jet-engine https://www.ornl.gov/news/ceramic-matrix-composites-take-fli...
    - Invictus0 2y ago

evnix 2y ago

I feel, What's more harder are the jet engines on fighter planes. These are usually a decade or two ahead in terms of advancements. The technology here trickles down to commercial jet engines slowly. Things like Metullargy for blades etc are a closely guarded secret. China and India are pouring billions into research just to get theirs close to even the lower end of what GE has to offer.

dguest 2y ago
One of the figures in the article [1] adds something to this point: military engines have much shorter lifetimes. So it seems it's not just "trickle down" technology, there's also some redesign for reliability. A commercial engine can operate for a cumulative 1 year between overhauls, according to that figure, as of 2010. The military ones last 1/10th as long. I can only imagine how much more challenging it is to iterate on designs when you are dealing with problems that take 10 times longer to manifest. [1]: https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_progressive:steep/https%3A%2F%2Fsubstack-post-media.s3.amazonaws.com%2Fpublic%2Fimages%2F968978db-8b83-450c-9640-5528a17e10a0_745x560.png https://substackcdn.com/image/fetch/f_auto,q_auto:good,fl_pr...

betimsl 2y ago

Material tolerances.

alkonaut 2y ago

> There’s no point in designing a new engine if it doesn’t significantly improve on the state of the art Oh but there is. I would love to see more European alternatives to US designs even at 5% less efficiency and power. Surely it can’t be that expensive to create an engine in 2025 similar to the state of the art 2005, when you have all the hindsight plus unlimited access to the original design? Events of this week show that this will be very important.

varjag 2y ago
Rolls Royce is British.
- venv 2y ago
  And PBS is Czech, to name one.
6SixTy 2y ago
There's sort of two tracks when it comes to jet engines: commercial aviation and military. Commercial just focuses on efficiency, while military has other considerations to account for. And in both sectors there's plenty of European competition, US/EU joint ventures, and subcontractors/licensed manufacturing going on. Europe does have enough aerospace talent to make a jet engine especially at the cutting edge, but there's a significant amount of tech transfer between the US and Europe happening at the same time.
Epa095 2y ago
I agree, but it does not seem so bleak. According to Wikipedia[1]: The manufacturers market share should be led by CFM with 44% followed by Pratt & Whitney with 29% and then Rolls-Royce and General Electric with 10% each. CFM is a 50/50 American/French joint venture, and Rolls-Royce is British. 1: https://en.m.wikipedia.org/wiki/List_of_turbofan_manufacturers https://en.m.wikipedia.org/wiki/List_of_turbofan_manufacture...
- class3shock 2y ago
  Safran can not make a competitive commercial jet engine on their own and Rolls Royce is a generation behind both GE and P&W, and given the state of the UK not likely to catch up. Right now there is really P&W and GE and then everyone else.

1024core 2y ago

How many countries make their own jet engines? US, UK, France ... anyone else?

philwelch 2y ago
Russia and China
- themgt 2y ago
  I was intrigued by an above comment about miniature jet engines - Iran last year announced a jet-powered Shahed drone variant, which uses an engine that has an interesting backstory: There are many variants of [the French Microturbo TRI 60] engine and it is used in many missiles and UAVs, as listed below. Aside from the known uses listed below, it is widely speculated that Iran illegally purchased many TRI 60 engines from Microturbo to assemble C-802 cruise missiles purchased from China. It is unclear which variant was purchased. Iran also reverse-engineered this engine as the Toloue-4 turbojet engine. Toloue-4 is used in several Iranian military equipment including Iran's copy of C-802, the Noor missile. It's fascinating how many engineering artifacts turn out to have been invented just once. This is the same engine used in Storm Shadow / SCALP EG, so both sides in the Ukraine war are firing variants of a 1970s miniature French jet engine at each other. https://en.wikipedia.org/wiki/TEM_Toloue-4 https://en.wikipedia.org/wiki/TEM_Toloue-4 https://en.wikipedia.org/wiki/Microturbo_TRI_60 https://en.wikipedia.org/wiki/Microturbo_TRI_60
t43562 2y ago
The German part of Rolls Royce - that's where the new B-52 engines are coming from for example.
missedthecue 2y ago
Russia, China, India, both South and North Korea, Iran, Turkey, Israel, and Czech Republic all manufacture jet engines domestically.

paulpauper 2y ago

It's hard not because the technology is so special , but because the tolerance for errors is so small . Jet failure can mean loss of many lives and little room to rectify the situation in flight ,whereas an automobile or train engine failure is a more manageable situation.

Animats 2y ago

And why they are so expensive. General aviation is still running on pistons. Not because small jet engines can't be built, but because they don't get cheaper as they get smaller. 6-passenger bizjet sized engines seem to be the lower economic limit. Williams tried and tried. They built good small jet engines, all the way down to jetpack size, but those never got cheap.[1] There are "very light jets", but the smallest in production, the Cirrus Vision Jet, is around US$2 million. [1] https://en.wikipedia.org/wiki/Williams_International https://en.wikipedia.org/wiki/Williams_International [2] https://en.wikipedia.org/wiki/Very_light_jet https://en.wikipedia.org/wiki/Very_light_jet

hnuser123456 2y ago
I wonder, as batteries and electric (BLDC) motors get better and better, if we will find applications where electric ducted fans outperform (electric driven) propellers, since electric motors are the same complexity regardless of application.
- geocrasher 2y ago
  Ducted fans are by nature less efficient than propellers. This is one reason that the next big leap in engine efficiency may come from what are essentially unducted fans.
  - Manuel_D 2y ago
    I thought adding a shroud to propellers increased efficiency? That's why we use turbofan engines instead of turboprops.
    - consumer451 2y ago
      One of the latest designs appears to do away with the duct/shroud, for the thrust creation part of the engine. It also hopes to achieve a 20$ decrease int fuel usage. https://en.wikipedia.org/wiki/CFM_International_RISE https://en.wikipedia.org/wiki/CFM_International_RISE https://www.cfmaeroengines.com/rise/ https://www.cfmaeroengines.com/rise/

anon_cow1111 2y ago

For young aspiring engineers here who may read this and just like the sound of "building jet engine", look into building a pulse jet first. They're extremely easy to build, having no moving parts, and only requiring some steel tubing, a welder and a large propane tank. I've already done it and can attest to this being true. The "best" part is that they're incredibly, obnoxiously loud. Like wear earplugs and ear muffs at the same time loud. Efficiency isn't great, you can expect maybe 20-100 lbs thrust from larger models but I suppose that's more than enough for "let's grab an old bicycle and do something really stupid" (oh and look pulsejets up on youtube for sure, it'll open up a whole world for you in under 20 minutes)

gosub100 2y ago
https://youtu.be/xJhazf0apN8?si=fcb8vehZbqUFRhIy https://youtu.be/xJhazf0apN8?si=fcb8vehZbqUFRhIy A great DIY from a great YouTuber
- physicsguy 2y ago
  https://youtube.com/watch?v=-fDM9Eb16Do&t=176s&pp=ygUcY29saW4gZnVyemUgcHVsc2UgamV0IGtldHRsZQ%3D%3D https://youtube.com/watch?v=-fDM9Eb16Do&t=176s&pp=ygUcY29saW... I like this one

gunian 2y ago

because it flies away

anovikov 2y ago

It's not all that hard to build a jet engine. Nazi Germany built them being constantly bombed, with actively sabotaging slave labor. Starving North Korea builds them. War-torn Ukraine builds them. What's hard is to build a competitive jet engine. And there, it happens naturally, by itself: the best marketable jet engine is the one where marginal increase of complexity and cost matches marginal fuel savings: buy simpler/cheaper ones and you waste more money on fuel than you save buying the engine, buy a more complex/expensive one and you don't justify the costs with your fuel savings. Because an engine runs for tens of thousands of hours - some over 100K hours - so 1% of performance improvement is worth ~1000 tons of fuel - there is a lot of complexity that can be pushed into the solution while still being profitable - and competition ensures this is the case. That's why it is incredibly hard to make a competitive jet engine.

maxglute 2y ago
IIRC leading fuel efficient turbo jet cost like ~10m + 1m for maintenance and consumes 70m worth of fuel over 30k hour life time. An engine 15% less fuel efficient would have to cost $0 to be competitive.
- anovikov 2y ago
  See. But building a jet engine that "just works" without a particular profitability is not at all hard. Like, one that burns 50% fuel for same thrust than the best state of the art. That's about the level of disposable engines used in cruise missiles and drones.

DeathArrow 2y ago

I wonder if there aren't other propulsion principles to pursue in modern aircrafts beside the jet engine.

maxglute 2y ago

May countries got domestic turbojet running, but most engine projects fail because there wasn't political will eat the billions to keep a competitive program going, especially as complexity increase in turbofans.