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 <i>creep</i> at these temperatures under high tensile loads. The <i>only</i> 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 :)
I've always been fascinated by the power density potential of the gas turbine. Especially the micro turbine class.<p>> 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]<p>> 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]<p>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.<p>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:<p>> 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]<p>[0] <a href="https://en.wikipedia.org/wiki/Microturbine" rel="nofollow">https://en.wikipedia.org/wiki/Microturbine</a><p>[1] <a href="https://en.wikipedia.org/wiki/Capstone_Green_Energy" rel="nofollow">https://en.wikipedia.org/wiki/Capstone_Green_Energy</a>
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.
And why they are so expensive.<p>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.<p>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.<p>[1] <a href="https://en.wikipedia.org/wiki/Williams_International" rel="nofollow">https://en.wikipedia.org/wiki/Williams_International</a><p>[2] <a href="https://en.wikipedia.org/wiki/Very_light_jet" rel="nofollow">https://en.wikipedia.org/wiki/Very_light_jet</a>
For anybody interested in gas turbine engineering, I recommend Gas Turbine Theory by Cohen & Rogers.<p><a href="https://archive.org/details/gasturbinetheory0000sara" rel="nofollow">https://archive.org/details/gasturbinetheory0000sara</a>
A very good article, but I was disappointed to see the misunderstanding about the de Havilland Comet failures repeated<p>> fatigue failures around its rectangular windows caused two crashes, resulting in it being withdrawn from service<p>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.<p>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.<p>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.<p>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.<p>Anyway that's my rant in to the void today :)
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.<p>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.<p>The "best" part is that they're incredibly, <i>obnoxiously</i> 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)
> Developing a new commercial aircraft is another example in this category, as is building a cheap, reusable rocket.<p>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.
> Building the understanding required to push jet engine capabilities forward takes time, effort, and expense.<p>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.<p>Let us encourage that.
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!
> There’s no point in designing a new engine if it doesn’t significantly improve on the state of the art<p>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 <i>that</i> 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?<p>Events of this week show that this will be very important.
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.
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.
>Depending on how you count, there are just two to four builders of large commercial aircraft (Airbus, Boeing, Embraer, and now COMAC).<p>Where is Russian Sukhoi?
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.
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.
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.<p>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.<p>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.<p>That's why it is incredibly hard to make a competitive jet engine.