SDF Aerospace and Aerodynamics Corner

Originally Posted by MiG-29

it does not make sense at all, most J-10s are less than a decade old some are less than 1 year old, same is J-11/Su-27, tell me why you replace engines that have 7-5 years old?

That does not make sense at all, aircraft like the F-14 were re engined but if China has WS-10 why you will spend money in a foreign engine? you will re engine 120 J-10 that have less than 7-5 years? that is just fantasy, tell me how many J-10s are build in China annually?
China might built 100 J-10s if the J-10 is exported, the F-16 is exported and build in Europe, Turkey, Korea and Japoan (AKA F-2) but F-16s use american engines.

why you will re-engine a mere 120 aircraft if you can build 100 J-10s with WS-10?

So the mostly likely reality is China builds 20-30 annualy and the Al-31s are going to be used for new J-10s and perhaps iin 2015 they will use WS-10s, but now the WS-10 is not ready an if WS-10 is not ready WS-15 is not even flying.

Because Russian engines are cheap to buy but expensive to maintain with short lives.
Many will not last 5-7 years even with expensive maintenance.
Old J10s, J11s and Su27 which cannot use WS10 will need new Al31s very often. It's cheaper to buy them than re-design to use WS10s or even to maintain the Al31s.

Originally Posted by Quickie

IMO, some people have to realize that the technological transfers between countries are actually the purchase of high tech equipment or its kits and basic component modules. Take the case of the flankers between China and Russia. Russia would sell the flanker aircrafts or its basic kits and modules to build the aircrafts, but she would not be so generous as to actually teach China the process of designing the aircrafts or how to design and build their basic components itself.
.....................

China orders basically kept the Russian defence industries alive during those tough years of the 90s.

Originally Posted by latenlazy

A production capacity problem is the more likely reason why they bought more AL-31s. They're probably making more J-11s and J-10s than the production of WS-10s can keep up, particularly as they only just resolved their production quality problems. There's a reason why the J-10B is being tested with the WS-10. Opening up new lines of production will take time (factories don't just spring up at the snap of a finger), and the time frame probably matches with the induction of the J-10B. Until then they can't simply halt the production of new J-11s and J-10s.

This does not mean the WS-10 is not ready however. If it were not ready we wouldn't see them on so many J-11s equipped with them. It's very clear that the WS-10 has already entered mass production. It's probable that due to the limitations on production capacity the WS-10 is only going to J-11s until manufacturing of the engine can be expanded. That said, engine R&D and production is not a serial process, but a parallel one. Using the WS-10's production time to gauge the WS-15s is nonsensical and pointless.



I think some people are touchy about the word "help". For a lot of people in China it's usually loaded with the connotation that China can't do anything on its own. To extend that analogy about the Harvard undergraduate, for a lot of them it's like your professor treats you like you're an undergrad even after you've completed your dissertation :P

that is no realistic at all, if WS-10 is ready for production then building J-10s with WS-10 is logic, China does not build 100 J-10s a year, if the J-10 is an equivalent of F-16A maybe, but J-10 has more advanced avionics than F-16s of 1980s and 1990s, J-10 has avionics of 2000s, similar to Gripen, LCA of F-16 of latest blocks, this means it is not as easy to build, so i think China builds 20-30 jets a year for its force alone, avionics is what really raises the price of modern jets, today an F-22 is expected to do the job of 3-4 F-15s, a J-10 in 2011 must be as good as 2 to 3 F-16As in fighting capability just simply by radar, F-16As of 1980s are not even as advanced as a JF-17 or a modern F-16 block 60, China is not building many J-10s too because you only have a production line in China, F-16 were built in Europe and many other countries.

these leaves you with Al-31s for the next 3-4 years of J-10s　production, do i think WS-10 might start production in 2011? maybe but for test aircraft but the WS-10 is clearly not ready most likely the Ws-10 will be ready in 2-3 years time and that shows why they bought 123 Al-31s.
However they were discussing a further batch of 150 Al-31s, if that happens means WS-10 is a failure.
Engines under this contract will be assembled by the Ufa-based UMPO factory
The second contract is for more than 120 AL-31FN engines to power newly built Chengdu J-10 fighters. Engines under this contract are already being delivered, from the Moscow-based Salut plant.

Speaking to AIN at the Aviation Expo 2011 in Beijing, Salut general director Vladislav Masalov said that negotiations continue on a second batch of nearly 140 AL-31FNs and that a follow-on contract is expected to be signed in October.

http://www.ainonline.com/?q=aviation...ighter-engines
So tell me why we have not heared of another engine from China for J-10s? the US had F-110 and F-100s, but China still relies on Al-31s.


So now do you think J-20 has Ws-15, i do not think so.

Originally Posted by MiG-29

...........
Engines under this contract will be assembled by the Ufa-based UMPO factory
The second contract is for more than 120 AL-31FN engines to power newly built Chengdu J-10 fighters. Engines under this contract are already being delivered, from the Moscow-based Salut plant.

Speaking to AIN at the Aviation Expo 2011 in Beijing, Salut general director Vladislav Masalov said that negotiations continue on a second batch of nearly 140 AL-31FNs and that a follow-on contract is expected to be signed in October.

Big New Chinese Order for Russian Fighter Engines | Aviation International News
So tell me why we have not heared of another engine from China for J-10s? the US had F-110 and F-100s, but China still relies on Al-31s.


So now do you think J-20 has Ws-15, i do not think so.

Russian sources, especially on China related news, are known to be unreliable. They'll say anything for marketing purposes. So the figures above don't mean much really and most Russian fanboys know that but don't like to admit to it. That's why unfortunately you see more of them coming to forums like this for real PLA news.

Originally Posted by Schumacher

Russian sources, especially on China related news, are known to be unreliable. They'll say anything for marketing purposes. So the figures above don't mean much really and most Russian fanboys know that but don't like to admit to it. That's why unfortunately you see more of them coming to forums like this for real PLA news.

this proves why Al-31s are still being order.

Originally Posted by MiG-29

..........
this proves why Al-31s are still being order.

J10S which is a twin seater J10A are designed to only use Al31. Pointless to redesign them to use WS10 when Al31 can be had cheaply and that the J10A may not be in production for much longer.
WS10s on J10 will be for later J10B or any future J10 models.

Originally Posted by MiG-29

that is no realistic at all, if WS-10 is ready for production then building J-10s with WS-10 is logic, China does not build 100 J-10s a year, if the J-10 is an equivalent of F-16A maybe, but J-10 has more advanced avionics than F-16s of 1980s and 1990s, J-10 has avionics of 2000s, similar to Gripen, LCA of F-16 of latest blocks, this means it is not as easy to build, so i think China builds 20-30 jets a year for its force alone, avionics is what really raises the price of modern jets, today an F-22 is expected to do the job of 3-4 F-15s, a J-10 in 2011 must be as good as 2 to 3 F-16As in fighting capability just simply by radar, F-16As of 1980s are not even as advanced as a JF-17 or a modern F-16 block 60, China is not building many J-10s too because you only have a production line in China, F-16 were built in Europe and many other countries.

Just because it has more advanced equipment does not mean it's harder to build. Regardless, the 20-30 air frames a year is probably an accurate number (anyone want to confirm). However, you have to keep in mind that the J-11 also uses the WS-10, and we have seen many instances of the J-11 with WS-10s already. The J-11 uses two engines to the J-10s one, so if we assumed that they built 30 J-10s and 30 J-11s, that would mean they need 90 WS-10s a year to keep pace with the air frames. 90 turbofans a year sounds like a pretty hard number to keep pace with if you only have one line of production.

these leaves you with Al-31s for the next 3-4 years of J-10s　production, do i think WS-10 might start production in 2011? maybe but for test aircraft but the WS-10 is clearly not ready most likely the Ws-10 will be ready in 2-3 years time and that shows why they bought 123 Al-31s.
However they were discussing a further batch of 150 Al-31s, if that happens means WS-10 is a failure.

Actually, all the examples of new WS-10 equipped J-11s we've seen were inducted airplanes. In that sense, the WS-10s seems clearly ready for regular service.

Keep in mind that not all 123 new AL-31FNs are going into new airplanes. The oldest J-10s are nearly a decade old already, and will probably be in need of re-engining. If this is the first cycle of re-engining for older air frames, presuming that initial production was half the rate of current production (which is an assumption on my part, anyone remember how many J-10s were inducted in its first year?), that means they would need an addition of 15 new turbofans a year. That bumps up the turbofan requirement per year for J-10s to 45, which means 123 new AL-31FNs would last short of 3 years, assuming that the re-engining requirements aren't higher or that they don't intend on further accelerating the J-10's production (which is a distinct possibility given a potential naval variant of the J-10).

2 years is probably the window for the J-10B's induction, and there's no guarantee the WS-10 could ramp up production to fulfill the engining of both old and new air frame by then, though that's probably the target. As a thought experiment lets assume they wanted to re-engine old J-10s with the WS-10 while engining both new J-11s and new J-10s with WS-10s. That would bump up the number of WS-10s per year needed to keep up with engining requirements to 105 turbofans. Then if we presume just 15 old J-11As that need re-engining every year, the number of WS-10s needed every year would bump up to 145. If we add reserve requirements for turbofans, that means they would have to produce more than 145 new WS-10s a year to keep up with the production and maintenance of new and old fighters. That's a pretty tall order if they only have one production line for a turbofan.

This discussion then goes to the 150 new AL-31s (not FNs) orders. That would be enough for 75 flankers, most of which will probably be new, but many of which will also be old air frames that need re-engining. With that in mind, 150 might only be enough turbofans for less than two years. What's interesting to note here is the 150 AL-31 orders cover fewer planes than the AL-31FN orders (due to the J-11 needing two engines for every J-10's one). This seems to imply at least that 150 new AL-31 orders seem insufficient for long term production and maintenance of flanker air frames, excluding the possibility that more flanker lines open up for naval purposes (J-11BHs, J-15s), which would fit well with the idea of splitting engine supply between a WS-10 that's still expanding production and AL-31s that can immediately fulfill supply shortages to prevent bottle-necking of production.

It's unnecessary to assume the WS-10 is a failure simply because more AL-31s are being ordered. Given the number of new turbofans that would be needed to keep up with the production of new air frames and the maintenance of old ones it's unlikely the WS-10 could immediately fulfill demand by itself this early in its production run. Limited production capacity of the WS-10 is a better fit explanation. Otherwise, they wouldn't already be flying J-11s with WS-10s and testing the J-10B with it.

So tell me why we have not heared of another engine from China for J-10s? the US had F-110 and F-100s, but China still relies on Al-31s.

So now do you think J-20 has Ws-15, i do not think so.

Well, that's certainly an intelligent argument. Clearly, the only way we can say the WS-10 is a success is if China is fielding another indigenous design.

The US had F-110s and F-100s because they needed to keep two defence contractors happy while trying to leverage each company to cut costs (whether that worked or not is another matter). In other words, it has nothing to do with whether the WS-10 is ready, since its clearly being used in new J-11Bs. We have not heard of "another engine" for China because there is no need for some other engine. The J-11s are already flying with the WS-10.

In case you didn't hear the news, here's an inducted J-11B flying with the WS-10



WRT to the F-110 and F-100.
"The F-16 Fighting Falcon entered service powered by the Pratt & Whitney F100 afterburning turbofan. Seeking a way to drive unit costs down, the USAF implemented the Alternative Fighter Engine (AFE) program in 1984, under which the engine contract would be awarded through competition. The F110 currently powers 86% of the USAF F-16C/Ds (June 2005)."

And no, I do not think the J-20 is powered by the WS-15. I was saying the WS-15's success is tied to the WS-10s, not that the J-20 is already flying with the WS-15 (I don't know you concluded that)

Originally Posted by Schumacher

J10S which is a twin seater J10A are designed to only use Al31. Pointless to redesign them to use WS10 when Al31 can be had cheaply and that the J10A may not be in production for much longer.
WS10s on J10 will be for later J10B or any future J10 models.

how much do you think a J-20 costs?

a F-22 cost as much as a Boeing 777, a Eurofighter cost as much as as 3 Embraer E-190, a F-16 is actually more expensive than a Bombardier global express, so a J-10 probably is as expensive as a global express.

So do you think they use Al-31s for 5-7 years? do you think a jet that probably is as expensive as a ARJ-21 29 million dollars

With an official price tag of between $27 million and $29 million, the ARJ21 holds an acquisition cost advantage over its peers in the international market.

China pushes towards delayed ARJ-21 certification | Aviation International News
Saab AB (SAABB), which won a 3.1 billion Swiss-franc ($3.41 billion) order for 22 Gripen fighter jets this week, will keep competing on price to lure buyers as governments Saab
those 123 engines are for new J-10s, WS-15 is a very ambitous program and J-20 must be as expensive as 2-3 ARJ-21

Originally Posted by MiG-29

those 123 engines are for new J-10s, WS-15 is a very ambitous program and J-20 must be as expensive as 2-3 ARJ-21

...Or for old J-10s that need new engines.

Originally Posted by latenlazy

Just because it has more advanced equipment does not mean it's harder to build. Regardless, the 20-30 air frames a year is probably an accurate number (anyone want to confirm). However, you have to keep in mind that the J-11 also uses the WS-10, and we have seen many instances of the J-11 with WS-10s already. The J-11 uses two engines to the J-10s one, so if we assumed that they built 30 J-10s and 30 J-11s, that would mean they need 90 WS-10s a year to keep pace with the air frames. 90 turbofans a year sounds like a pretty hard number to keep pace with if you only have one line of production.

Actually, all the examples of new WS-10 equipped J-11s we've seen were inducted airplanes. In that sense, the WS-10s seems clearly ready for regular service.

Keep in mind that not all 123 new AL-31FNs are going into new airplanes. The oldest J-10s are nearly a decade old already, and will probably be in need of re-engining. If this is the first cycle of re-engining for older air frames, presuming that initial production was half the rate of current production (which is an assumption on my part, anyone remember how many J-10s were inducted in its first year?), that means they would need an addition of 15 new turbofans a year. That bumps up the turbofan requirement per year for J-10s to 45, which means 123 new AL-31FNs would last short of 3 years, assuming that the re-engining requirements aren't higher or that they don't intend on further accelerating the J-10's production (which is a distinct possibility given a potential naval variant of the J-10).

2 years is probably the window for the J-10B's induction, and there's no guarantee the WS-10 could ramp up production to fulfill the engining of both old and new air frame by then, though that's probably the target. As a thought experiment lets assume they wanted to re-engine old J-10s with the WS-10 while engining both new J-11s and new J-10s with WS-10s. That would bump up the number of WS-10s per year needed to keep up with engining requirements to 105 turbofans. Then if we presume just 15 old J-11As that need re-engining every year, the number of WS-10s needed every year would bump up to 145. If we add reserve requirements for turbofans, that means they would have to produce more than 145 new WS-10s a year to keep up with the production and maintenance of new and old fighters. That's a pretty tall order if they only have one production line for a turbofan.

This discussion then goes to the 150 new AL-31s (not FNs) orders. That would be enough for 75 flankers, most of which will probably be new, but many of which will also be old air frames that need re-engining. With that in mind, 150 might only be enough turbofans for less than two years. What's interesting to note here is the 150 AL-31 orders cover fewer planes than the AL-31FN orders (due to the J-11 needing two engines for every J-10's one). This seems to imply at least that 150 new AL-31 orders seem insufficient for long term production and maintenance of flanker air frames, excluding the possibility that more flanker lines open up for naval purposes (J-11BHs, J-15s), which would fit well with the idea of splitting engine supply between a WS-10 that's still expanding production and AL-31s that can immediately fulfill supply shortages to prevent bottle-necking of production.

It's unnecessary to assume the WS-10 is a failure simply because more AL-31s are being ordered. Given the number of new turbofans that would be needed to keep up with the production of new air frames and the maintenance of old ones it's unlikely the WS-10 could immediately fulfill demand by itself this early in its production run. Limited production capacity of the WS-10 is a better fit explanation. Otherwise, they wouldn't already be flying J-11s with WS-10s and testing the J-10B with it.



Well, that's certainly an intelligent argument. Clearly, the only way we can say the WS-10 is a success is if China is fielding another indigenous design.

The US had F-110s and F-100s because they needed to keep two defence contractors happy while trying to leverage each company to cut costs (whether that worked or not is another matter). In other words, it has nothing to do with whether the WS-10 is ready, since its clearly being used in new J-11Bs. We have not heard of "another engine" for China because there is no need for some other engine. The J-11s are already flying with the WS-10.

In case you didn't hear the news, here's an inducted J-11B flying with the WS-10



WRT to the F-110 and F-100.
"The F-16 Fighting Falcon entered service powered by the Pratt & Whitney F100 afterburning turbofan. Seeking a way to drive unit costs down, the USAF implemented the Alternative Fighter Engine (AFE) program in 1984, under which the engine contract would be awarded through competition. The F110 currently powers 86% of the USAF F-16C/Ds (June 2005)."

And no, I do not think the J-20 is powered by the WS-15. I was saying the WS-15's success is tied to the WS-10s, not that the J-20 is already flying with the WS-15 (I don't know you concluded that)

Saab AB (SAABB), which won a 3.1 billion Swiss-franc ($3.41 billion) order for 22 Gripen fighter jets this week, will keep competing on price to lure buyers as governments adapt to shrinking budgets, its chief executive officer said.

Saab

You think engines are dipers, and aircraft can change them see the price of only 22 Gripen, how much for 30 J-10s?


“The Air Force says the F-22 cost $44,259 per flying hour in 2008; the Office of the Secretary of Defense said the figure was $49,808. The F-15, the F-22’s predecessor, has a fleet average cost of $30,818.”

The F-22 Raptor: Program & Events

how much do you think it cost to fly J-10s an hour?



China has maintanaince centers to keep those Al-31 working for at least 15 years


“The current cost for a single copy of an F-22 stands at about $137 million. And that number has dropped by 23 percent since Lot 3 procurement, General Lewis said. “The cost of the airplane is going down,” he said. “And the next 100 aircraft, if I am allowed to buy another 100 aircraft… the average fly-away cost would be $116 million per airplane.”

Depending on which “dollar-year” those fly-away cost figures represent, actual amounts may vary, since current year dollars include inflation. Recent budgets suggest current-dollar figures of $150-180 million per plane, but a July 2009 USAF response [PDF] gave the F-22A’s current flyaway cost as $142.6 million each. Over the last few years, Pentagon documents list F-22 budgets as follows:






Boeing (NYSE:BA) said Monday that the national airline of the United Arab Emirates, Etihad Airways, has ordered 10 Boeing 787-9 Dreamliners and two Boeing 777 Freighters, in a deal valued at $2.8 billion.

http://www.proactiveinvestors.com/co...ine-22360.html

The catalogue price of the A330-200 is about $180.9 million. http://www.aljazeera.com/focus/2009/...354903514.html

Originally Posted by MiG-29

Saab AB (SAABB), which won a 3.1 billion Swiss-franc ($3.41 billion) order for 22 Gripen fighter jets this week, will keep competing on price to lure buyers as governments adapt to shrinking budgets, its chief executive officer said.

Saab

You think engines are dipers, and aircraft can change them see the price of only 22 Gripen, how much for 30 J-10s?

Umm. No. I think engines are like anything else. Perishable after a certain amount of time. When they reach their life expectancy, you replace them, and given that the J-10 is a decade old, that means at least a few of their engines have reached life expectancy.

Regardless of how expensive the J-10 is, the 30 a year rate seems about right given observations. (Though someone like Deino who follows this more carefully could either confirm or deny that). You're trying to argue with facts, assuming I got the 30 a year number right.

“The Air Force says the F-22 cost $44,259 per flying hour in 2008; the Office of the Secretary of Defense said the figure was $49,808. The F-15, the F-22’s predecessor, has a fleet average cost of $30,818.”

The F-22 Raptor: Program & Events
how much do you think it cost to fly J-10s an hour?

Not as much as it costs to fly the F-22 obviously. Remember one of the biggest costs of maintenance for the F-22 was its RAM.

China has maintanaince centers to keep those Al-31 working for at least 15 years

Evidence that they could keep them working for 15 years?

The life expectancy of an AL-31 is 3000 hours. Let's say they fly 1 hour a day. That's 3000 days. That's less than 10 years per engine.

Originally Posted by latenlazy

Umm. No. I think engines are like anything else. Perishable after a certain amount of time. When they reach their life expectancy, you replace them, and given that the J-10 is a decade old, that means at least a few of their engines have reached life expectancy.

Regardless of how expensive the J-10 is, the 30 a year rate seems about right given observations. (Though someone like Deino who follows this more carefully could either confirm or deny that). You're trying to argue with facts, assuming I got the 30 a year number right.

Not as much as it costs to fly the F-22 obviously. Remember one of the biggest costs of maintenance for the F-22 was its RAM.

Evidence that they could keep them working for 15 years?

The life expectancy of an AL-31 is 3000 hours. Let's say they fly 1 hour a day. That's 3000 days. That's less than 10 years per engine.

Joel detailed how in the UK a Typhoon typically flies 24 hours per aircraft per month, whereas in Libya they are notching up 84 hours per month The EuroFighter Typhoon : Troodon Best Articles from the Globe


Flying Hours. Views on the number of required live flight hours (see Figure
D.1) vary widely. The NATO minimum is 180 hours (15 per month). RAF flying
hours for jet pilots is between 180 and 240 per year (18.5 month on average). Of
these hours, 150 hours (12–14 hours per month; 12.5 on average) are felt to be a
safety-of-flight minimum (instruments, takeoffs, landings). The RAF also feels
the additional increment for military elements of flying (e.g., warfare tactics) is
about three hours per month or 36 per year for a total of 186 annual hours (15.5
hours monthly). The 180–240 hours include all flying (e.g., transit and overhead
flights) not just military elements or high-quality flying, which is estimated at
75–80 percent of the total. http://www.rand.org/content/dam/rand...R1441.appd.pdf

Easily you have more than 10 years for each Al-31, engines are not nappies

Originally Posted by MiG-29

......
So do you think they use Al-31s for 5-7 years? do you think a jet that probably is as expensive as a ARJ-21 29 million dollars
...........those 123 engines are for new J-10s, WS-15 is a very ambitous program and J-20 must be as expensive as 2-3 ARJ-21

Yes, Russian engines are not known for long lives.
If from Russian sources, the 123 figure is quite meaningless.
Any new J10s with Al31 are likely to be J10As which can't use WS10, with some maybe for PAF. With Al31's low reliability, you may see higher number of Al31 needed as spares.

Originally Posted by MiG-29

Joel detailed how in the UK a Typhoon typically flies 24 hours per aircraft per month, whereas in Libya they are notching up 84 hours per month The EuroFighter Typhoon : Troodon Best Articles from the Globe


Flying Hours. Views on the number of required live flight hours (see Figure
D.1) vary widely. The NATO minimum is 180 hours (15 per month). RAF flying
hours for jet pilots is between 180 and 240 per year (18.5 month on average). Of
these hours, 150 hours (12–14 hours per month; 12.5 on average) are felt to be a
safety-of-flight minimum (instruments, takeoffs, landings). The RAF also feels
the additional increment for military elements of flying (e.g., warfare tactics) is
about three hours per month or 36 per year for a total of 186 annual hours (15.5
hours monthly). The 180–240 hours include all flying (e.g., transit and overhead
flights) not just military elements or high-quality flying, which is estimated at
75–80 percent of the total. http://www.rand.org/content/dam/rand...R1441.appd.pdf
Quoting tphuang here. I presume the elite forces are piloting J-10s and J-11s.
Easily you have more than 10 years for each Al-31, engines are not nappies

"It's really hard to say how many flight hours they get per year right now. Also as I mentioned, the intensity and the type of training they do is probably more important. I have read that some of the elite forces are getting as many as 200 hours a year, although my guess is that most of the 4th generation pilots are getting less than that (more like in the 160 hours range). The J-7 pilots are getting probably in the 120 to 130 hours a year range if I was to guess."

http://iis-db.stanford.edu/pubs/12078/phadke.pdf

" At the rate of approximately 1.5 pilots per aircraft, the PLAAF would have to provide a minimum of 120 to 150 flight hours annually to 4,500–5,000 of its active-duty pilots. Allowing for those employed on staff and headquarters appointments it would mean that at least 4,000 pilots would need regular flight training. A “back-of-the-envelope” calculation would show that to provide 150 hours of flying to 4,000 pilots at 60–70 percent rate of serviceability/availability, the PLAAF fleet would have to fly some 285 to 333 hours per serviceable aircraft per year, or 24 to 28 hours per month—a huge task by any standards. "


While the figures themselves are disputable, the key take away is that flight hour per pilots is not equal to flight hour per plane.

Even if we assume just 240 hours per plane (1.5 times the 160 per pilot figure we got from tphuang) at most that stretches out the AL-31s to 12.5 years. Furthermore, as the engine ages it would be operating at less than 100% capacity. At some point even before it reaches its maximum life expectancy the engine would probably be replaced for performance and safety reasons. Engines may not be nappies, but when they're no longer sufficient for their role we replace them all the same.

Also keep in mind that the engines were ordered in 2011. That means they will take time to deliver (it's not like they snap their fingers and 123 new AL-31FNs magically appear). By the time they are delivered some J-10s will very well need new engines. The oldest J-11s meanwhile were in production three years before the J-10. It could explain why we saw an old J-11A with the WS-10s.