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As far as I know, only 4 countries can build aircraft jet engines on their own:
All other countries use jet engines bought from companies of these 4 countries.
Is that true?
Are German, Japanese, and Chinese companies not able to build aircraft jet engines on their own?
Why is building jet engines so tough for companies from other countries?
Well Rolls Royce designs and builds jet engines in Germany with their RR Deutschland division. Rolls Royce Deutschland is a subsidiary of Rolls Royce and is a collaboration between RR and BMW.
The Shenyang Aerospace Corporation and Aero Engine Corporation of China are homegrown Chinese jet engine manufacturers, making their names largely for the manufacture of copies of Russian military jet engines for PLAAF need, but are now manufacturing their own designs for military and civilian applications.
Japan’s Aero Engine Corp is a partnership between Rolls Royce and several Japanese industrial powerhouses, most notably Mitsubishi Heavy Industries, who has begun to develop a line of small to medium thrust high bypass turbofan engines for regional airliners use.
While the basics of a jet engine are fairly well understood - it is, after all just a Brayton Cycle gas turbine - the details of designing and manufacturing modern high efficiency jet engines requires quite a bit of technical talent and capital to accomplish. A new engine program often takes longer, and is more expensive than, the aircraft program it is being designed to power. Most likely many entrepreneurs and prospective OEMs are deterred by this as any improvement they are likely to offer can be either bought out by an existing engine OEM eg Pratt and Whitney, etc. or simply crushed by the economies of scale.
This is an interesting question, but I also think it's the wrong question.
Firstly, even despite the tight and complex relationships between governments and aerospace companies, it's not nations that build jet engines, but aerospace companies.
Aerospace engineering and manufacturing know-how doesn't stop at national borders, especially not when it's inside a large multi-national corporation.
So, I think you should be asking questions about why jet engine manufacturers do their production.
Secondly, the question should be about why they don't, not whether they can.
The fact that a nation (or a company) doesn't do something doesn't necessarily mean that it is unable to.
It could also be economically preferable, practically advantageous or even politically expedient not to.
In the case of building jet engines, it's a combination of these; certainly in the case of building jet engines in European Union countries, where interests and projects are bound together in tight and complex agreements, it's all three.
You might equally well ask why countries in the EU can't build cars on their own, because they pretty much all use parts manufactured in other EU countries.
Sometimes even the same parts make multiple cross-border trips for different stages of the manufacturing process.
This isn't because they can't make crankshafts or whatever in France or Germany, but because it suits them to do it otherwise.
I have no doubt whatsoever that if China needed to produce its own jet engines without recourse to foreign industry, it could and would. Until it needs to though, it won't.
it's not nations that build jet engines, but aerospace companies The UK gov saved the RB211. :)
$\endgroup$
What they can't build is a gas turbine that is competitive with the existing engines from companies that have been developing them for decades.
China has a strategic interest in developing military gas turbine engines. Right now, they are totally dependent on Russia. If the two nations have a falling out, as they have in the past, then the PLA's air force could be in some amount of jeopardy if their primary source of engines is cut off.
Japan and Germany have no real reason to get into the aircraft engine market, although Japan does manufacture smaller gas turbines under license from RR, P&W, and GE. Both nations are on good terms with multiple engine suppliers in multiple countries, so their military engine source is very unlikely to be cut off due to political reasons. As for commercial gas turbines, neither nation could justify the considerable funds required to field a competitive aircraft engine.
The gas turbine market is fairly mature, and fiercely competitive. To build a turbofan that can rival the existing products in size, weight, capacity, and especially fuel usage requires the cumulative experience of the last 70 years. Such an effort needs the sort of knowledge that you just can't pick up in an internet search, because the organizations that make the best engines guard their designs very closely.
As the market is both mature and very competitive, the profit margins are not so high that a new company could be set up to make gas turbine engines and expect to show enough profit to offset the considerable expense. It would take decades of expensive development just to try to match what the current producers make, and they aren't just sitting on their laurels. P&W is trying to work out the kinks in a geared turbofan that promises to be more efficient than current ones, and GE just made the first flights with the GE9X, a huge engine to power the 777X that's due out in a few years.
This competitiveness also holds true for military engines, as a better power to weight ratio means a better performing aircraft, while a more efficient engine means greater range and less refueling. If you want to build your own military gas turbines, you had best be sure they're in the vicinity of a possible opponent's engines, or you'll be at a distinct disadvantage. That homegrown engine isn't very useful if the planes it powers keep getting shot down due to inferior performance.
So, unless a nation has a strategic reason to get into this very difficult field of engineering (as China does), it's just not worth the expense when you can buy state of the art engines already fully developed, from a reliable source.
Ukraine also produces jet and heli engines:
https://en.wikipedia.org/wiki/Ivchenko-Progress
https://en.wikipedia.org/wiki/Motor_Sich
Why is building jet engines so tough for other countries?
Military export regulations prevent US companies and companies located within countries allied with the US from exporting or sharing the engines themselves, and the technology to design and manufacture them.
The espionage committed by other countries in attempting to obtain engines, designs, and other information has resulted in convictions as recently as 2016:
The conviction of Man is the latest development in an ongoing saga of corporate espionage between the U.S. and China. Experts say spying has played a role in China's strategy to modernize the country in recent decades. The illicit acquisition of technology has helped China accelerate the process, bypassing problems that would otherwise require years of research and development to resolve, according to analysts.
...
Boosting jet engine capabilities has long been a priority for China as it seeks to increase its military clout. The most recent five-year development plan for the country identifies domestic development and production of engines and planes as a major goal.
But it's a difficult area to master, forcing China to rely heavily on importing technology. Over the last four years, engines accounted for 30% of all its imports, according to the Stockholm International Peace Research Institute.
It's easy enough to build simple jet engine models, but the high performance high thrust to weight combinations used in modern military aircraft - and even commercial aircraft - combine well protected secrets with state protections to prevent other countries from obtaining them either through their own design and development or import.
Jet engines are complex systems that require lots of knowledge across different fields (aerodynamics, metallurgy, advanced manufacturing techniques). Especially the turbine and compressor blades operate at the edges of what's physically possible.
Even for an experienced company like Pratt & Whitney, developing a new fighter powerplant costs in the region of a billion dollars. Setting up a new jet engine manufacturer and making it competitive is likely a much bigger investment than that, and a major commitment even for large countries. So there's a cost/benefit analysis: is the strategic advantage of having a national source for jet engines worth the gigantic investment?
The Germans are very capable of designing any sort of complex engines,no doubt they are the pioneer of jet engine technology, but inter political and economic agreement discourage then from doing so,I have to come to realize that the Germans are the best when it comes to highly sophisticated technologies,history has always shown what their engineers are capable of doing, they are also the pioneers of gas turbine technology, the Germans are just too awesome when it comes to advanced engineering.. The US and Russian space programme and technology were made possible by means of abducted German scientist and engineers infact critical observation of the nazi Luftwaffe aerospace engineering technology at the end of ww2 was what helped the allies nation to establish their own, the Germans are incomparable genius when it comes to complex innovation and technology,but economic and government boundaries limit them from re establishing their jet engine production once again
Another fantastic nation filled with mouth opening innovations and unbelievable technology these nation is extremely capable of building even the most advanced jet engine in the world no doubt they are the most advanced country in the world right now, the Japanese are just too amazing when it comes to technology, but also the reason why they aren't building or haven't build there own jet engines is not as a result of inability no far from it rather as a result of eco- political reasons coupled with the fact that they don't see much reason to waste resources to establish theirs when they can actually import quality jet engine from others
Jet engine technology is often related to military application and not civilian application so which means it is only countries that grow interest in investing heavily in their military budget that end up showing great interest in building or accumulating jet engine technology, Germany and Japan those two tech giants are not for now investing heavily or have interest in making their military a world recognized one as before unlike Russia, US,Britain, France china that quest for military supremacy hence they source for means to achieve their quest by building a powerful jet engine to air supremacy.
