Shenyang / Chengdu 6th Gen Demonstrators?

jmspeedfreak said:
Can Sundog or anyone in general chip in as to why employing blanking off doors on the 2 caret inlets is so crazy?
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Its technically feasible, but you've missed out any consideration of the drag impact this causes. This is a very large impact, especially transonic/supersonic. Even without blanking 2/3 intakes, then for such fixed geometry intakes its very important to size them correctly to ensure that spill drag is minimsed.
 
red admiral said:
Its technically feasible, but you've missed out any consideration of the drag impact this causes. This is a very large impact, especially transonic/supersonic. Even without blanking 2/3 intakes, then for such fixed geometry intakes its very important to size them correctly to ensure that spill drag is minimsed.
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Appreciate that, I was only thinking under 350kts in the loiter search mode. Also if you interpreted blanking someway down the inlet that wasn't my intention. I meant a door closing the inlet off right at the lips. I think your point about spill drag is still somewhat valid but I was wondering if there is still some rcs implication of the inlet ducts whether an emission minimised mode with the inlets closed could have a benefit. Thanks for replying of course!
 
red admiral said:
Its technically feasible, but you've missed out any consideration of the drag impact this causes. This is a very large impact, especially transonic/supersonic. Even without blanking 2/3 intakes, then for such fixed geometry intakes its very important to size them correctly to ensure that spill drag is minimsed.
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Also the top intake would need to be able to pass enough air to supply all 3 engines. It obviously isn't sized for that, so this discussion is null and void.

Equally there's no compelling reason to blank the lower intakes if they are designed correctly.
 
jmspeedfreak said:
Also if you interpreted blanking someway down the inlet that wasn't my intention. I meant a door closing the inlet off right at the lips. I think your point about spill drag is still somewhat valid
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Sealing the intake at the lips will produce a large bluff surface with similarly negative drag impacts. Especially transonic/supersonic if you can visualise that this produces a rapid increase in cross sectional area over the course of the length, and produces a large increase in maximum cross sectional area as you're no longer swallowing the intake stream tubes. Both very bad for wave drag.
overscan (PaulMM) said:
Also the top intake would need to be able to pass enough air to supply all 3 engines.
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Quite. Or the top intake needs to be massively over sized for when operating with only 1 engine, which will again give large spill drag.

If turning off 2 engines for efficiency then I'd think that loss of thrust would limit to quite low altitudes - seems unlikely

Much more likely 3 separate ducts
 
jmspeedfreak said:
Appreciate that, I was only thinking under 350kts in the loiter search mode. Also if you interpreted blanking someway down the inlet that wasn't my intention. I meant a door closing the inlet off right at the lips. I think your point about spill drag is still somewhat valid but I was wondering if there is still some rcs implication of the inlet ducts whether an emission minimised mode with the inlets closed could have a benefit. Thanks for replying of course!
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Those doors would have edge discontinuities and corners where they unfold from the skin.

And that completely misses the point of the caret inlets, that of minimizing the numbers of gaps and corners and other discontinuities.

So bad idea from both drag and from RCS standpoints.
 

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Deino said:
IMG_8374.jpeg
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So I guess this eliminates the claim that this has a foldable vertical stabiliser then?
 
VTOLicious said:
My attempt :)

This 3D model is based on the planform @paralay posted previously. It is a solid body with a volume of 218,55 m³ (!) Further, please note that all three air intakes have the same area of 0,656 m², which equals a circle of 0,914 m (36") diameter.
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Another one for the fun of it :)
 

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Did a run with movable wing tip spoilers, no adjustable tail, made the control surfaces similar to the image. Low speed handling is great, needed a good gyro to keep it stable. Maneuverability is amazing minus occasional departure from controlled flight. Supersonic flight isn't terrible, requires the tips to work overtime to keep it from adverse yaw.
 
Jason Dykstra (Wyvern) said:
So I guess this eliminates the claim that this has a foldable vertical stabiliser then?
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Looks like this platform has a blended canopy with possibly limited pilot visibility instead of a bubble-type canopy found on other fighters. Won't know until we get better images of what the upper surface looks like. Is this possibly unmanned?
 
Fantastic and very detailed CGI of J-50 as a UCAV (i think).

【六代机】沈飞六代机外形猜想_哔哩哔哩_bilibili

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jmspeedfreak said:
Can Sundog or anyone in general chip in as to why employing blanking off doors on the 2 caret inlets is so crazy? I realise that achieving a perfect match across the closure would be very hard and so on, but if the aircraft is at high altitude wouldn't this be an advantage operating on only the dorsal inlet? Would the dorsal inlet system need to have internal mixer doors to still feed flow through the inactive engines to mitigate base drag? Could these doors also enable the (high AoA effective) lateral inlets to feed air to the centreline engine during high Alpha maneuvers.

My thoughts looking at J-36 are:

1) Three engines with vectoring gives more redundancy which may be important.

2) Comparing three engines to two larger engines produces a flatter overall propulsion package for given overall mass-flow. Also the lateral inlets are presumably 30% smaller if sized for 1/3rd total mass flow.

3) Commonising engines across multiple platforms is probably cheaper (economies of scale etc) and allows the fleet of different aircraft to leverage technology improvements on that engine family as they come through more quickly.

4) Long range, deep magazine and VLO characteristics would be key objectives if you were designing a system to act as counter to B-21. I would imagine the PLAAF would be very concerned with deterrence vs that system more than say 5th generation fighters. The J-20 may be acceptable solution for conventional air battle, but you would want a system able to get well out from the Chinese mainland and picket with a high degree of stealth if you were first searching and then aiming to take down B-21 incursions. Long range strike of naval forces etc is plausible but there are already many discussed options that expose a less expensive asset to do this and we've already seen the prototypes for RQ-180 analogs that can handle search and targeting support for these missions. To me the compelling target for this weapon system seems to be the most stealthy and hardest to pin down target, the B-21. You have much less clarity where it's coming from, a huge area of sky to cover and you need to stay on station a long time and potentially deal with several targets in the same mission with relatively few aircraft. Getting on station quickly to maintain sortie rate and response effectiveness will be important but the marginal benefit of M2.2 over M1.7 will be very little. Main issue is to get on station quickly, stay there a long time and be hard for the opposing force to find and vector their bombers around.

5) IRST triangulation is plausible but I would expect that altering the search aircraft track is also a key part of building up a solution on the target course and having high performance IRST on both sides of the nose may be part of this?

For all the talk about DEW and enormous power requirements, I would still have thought that 1 to 2 MW with high efficiency PMSM generator is not a huge power drain off the engine given the total installed power in watts of a fighter engine is measured in tens of thousands of Watts. What's the issue? (I appreciate there will be impacts from shafting some of the power off the turbine but still that doesn't seem horrendous). A dedicated engine just for this seems unlikely but I could be overlooking something.

I hate putting my head above the parapet, so please appreciate I'm just a humble Mech engineer whose company develops high performance motor generators and power electronics, but I'm interested why this doesn't make sense.
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You should not hate putting your head above the parapet but some posters here are so nasty, intolerant, and narcissistic that they want to smack down anything that triggers them, either because it hurts their feelings or they see as inferior.

The criticism I have of your idea is that the Chinese will be going after the weak links in the US system. The B-21 in flight is probably the strongest link. It is essentially untouchable and sending an expensive interceptor to go looking for it is a waste of resources. The same plane could be sent on another mission that is more likely to succeed.
 
Airbus A340 said:
You should not hate putting your head above the parapet but some posters here are so nasty, intolerant, and narcissistic that they want to smack down anything that triggers them, either because it hurts their feelings or they as inferior.

The criticism I have of your idea is that the Chinese will be going after the weak links in the US system. The B-21 in flight is probably the strongest link. It is essentially untouchable and sending an expensive interceptor to go looking for it is a waste of resources. The same plane could be sent on another mission that is more likely to succeed.
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I know! It would be much more enjoyable if it wasn't quite as fiery an atmosphere but I love the fact people are passionate and thoughtful. It's difficult when folks don't really know each other and there is a surplus of strong opinions. But you guys (not everyone but nearly everyone) are awesome. Always love this site.
 
I have a question that I was wondering about.
Imagine you're the head of the PLA. You're developing new generation of combat planes. You're possibly in midst of an arms race with the US.

Why do you go so public about it all, the way China has gone public? Why don't you you try to test fly those things as covertly as possible?
What is it to be gained from being so open about it?
Sure, the US intelligence community might be tracking your progress nevertheless. Though it's doubtful they'd necessarily get as good photos of the prototypes through their regular spy channels this quickly and this easily.

But why show it off to the wider audience? Doesn't that only create further political pressure on the US congress and then the DoD so US next gen programs get more financing and get a kick in the butt? How does that benefit you, as the head of PLA who presumably wants to win the next war?

Lets for a moment forget the inner chinese politics and grandstanding angle of it all. If that stuff is excluded, what palpable benefit does PLA get in going public? How does going public in this way help you win that next war?
 
Airbus A340 said:
You should not hate putting your head above the parapet but some posters here are so nasty, intolerant, and narcissistic that they want to smack down anything that triggers them, either because it hurts their feelings or they see as inferior.

The criticism I have of your idea is that the Chinese will be going after the weak links in the US system. The B-21 in flight is probably the strongest link. It is essentially untouchable and sending an expensive interceptor to go looking for it is a waste of resources. The same plane could be sent on another mission that is more likely to succeed.
Click to expand...
You have to consider many have been online for decades and have answered the exact same questions/theories many, many times. Twenty years ago you might have got a five paragraph, well articulated, polite response. Now you just get a, "STFU newb". ;)
 
totoro said:
I have a question that I was wondering about.
Imagine you're the head of the PLA. You're developing new generation of combat planes. You're possibly in midst of an arms race with the US.

Why do you go so public about it all, the way China has gone public? Why don't you you try to test fly those things as covertly as possible?
What is it to be gained from being so open about it?
Sure, the US intelligence community might be tracking your progress nevertheless. Though it's doubtful they'd necessarily get as good photos of the prototypes through their regular spy channels this quickly and this easily.

But why show it off to the wider audience? Doesn't that only create further political pressure on the US congress and then the DoD so US next gen programs get more financing and get a kick in the butt? How does that benefit you, as the head of PLA who presumably wants to win the next war?

Lets for a moment forget the inner chinese politics and grandstanding angle of it all. If that stuff is excluded, what palpable benefit does PLA get in going public? How does going public in this way help you win that next war?
Click to expand...
Well it could cause knee-jerk reactions from the West rather than well thought out strategies.
 
For what it's worth (not a huge amount), I'm a professional engineer developing systems for F1, Indycar and road going sportscars so I know a fair amount about high power propulsion (used to design engines including aero-engines, later electric machines) and I have a very substantial library with many of the books people recommend on this site.

I get (and made originally) the point about the complexity of sealing an intake door. I don't doubt it. I also know as does everyone else here that weapon bay doors are also complex, and also solveable. So my take is that isn't a showstopper but it certainly is a challenge.

The angle of the closed inlet is not bluff or perpendicular to the airflow, and in the loitering mode the speed is relatively low (or at least IAS is) so the drag is hardly a given to be higher than the intake duct viscous drag / crubbing losses or the drag of windmilling turbines.

The SFC of these engines operating at 66% output is far lower than all three at 22%, that is my expectation based on normal turbomachinery characteristics. I apprecate what inlet guide vanes and variable stator blading can do to broaden the efficiency map, but I would be very interested if anyone here knows a lot about the thrust specific fuel consumption benefits or otherwise of shutting down engines for loiter. I've done plenty of efficiency / fuel consumption analysis in the past for turbomachinery in aerospace so very interested to hear if the forum can explain why this wouldn't be extremely beneficial to reduce fuel consumption at low speeds - just to be clear I'm talking about the loiter segment of a CAP, not trying to go M1.5 on 1 engine!

I appreciated Paul's point that a well designed inlet with suitable RAM and/or Compressor shielding technologies should do the job perfectly well. I take that and I accept that might be fact (and would definitely be the position of the airframe team unless there were really compelling benefits), but I also consider it not a certainty that the component of the RCS due to reflections from inside the duct is perfectly attentuated (unless Quellish or Hydroman for instance confirm otherwise). It may well be that this is the case, but a lot of work is put into this detail so I don't know whether or not it's possible to improve the RCS with a 'total blocker' as opposed to the existing solutions. This is basically my question open to all, and not the typical statement of an opinion being a prediction - I'm just interested if there is an angle here. Since I bought a second hand copy of the Future Fighters Salamander back in the late 80's there have been plenty of aircraft with dorsal as opposed to convential intakes. To have both seems like an unexpected outcome and not one the designers would have decided upon lightly. To have this just to support the third engine seems a bit like shallow foundations. Normally in this space you need several good reasons to underpin a design decision, not just one.

Airbus A340's point about the complexity of challenging the B-21 is perfectly valid. If I were in the PRC shoes though I wonder if they would be so comfortable (betting there kids lives as someone said today) on just letting it operate unchallenged. The other targets for this aircraft are difficult for me to justify a whole new aircraft over say more J-20's. What is this aircraft bringing to the fight that is unavailable in an adequate capability level in a lower cost and in greater numbers.

Is it the size - longer ranged, UHF band benefits as Quellish's explanation would support this larger aircraft having some scale advantage compared to J-20?. If it's just to be longer legged to strike ground targets in the enemy operating bases why not 100% dorsal intake, and for that matter why not two engines if it's a glorified modern day Vigilante or FB-111 analogue.

I think a concept that fits with the observed features could be.... Design aircraft to transition at high speed (to get substantially east of Taiwan) at supercruise speeds (with all engines running and all inlets open, to be clear) and then loiter for as long as reasonable on one engine in an attempt to act as pickets using IRST to identify B-21's at high altitude (which may have a harder time identifying and avoiding the threat than 4th or 5th gen fighters). Then the aircraft could restart the engines and operate on all three engines with all inlets very much open. The supercruise is also obviously a strong benefit for lob range of AAMs etc etc as well as allowing groups of these aircraft to revector/pivot once a set of targets are identified. Clearly whether or not intake doors are shut, open or flapping about in the wind(!) is hardly a key point, but it's interesting to me because I'm interested in the RCS discussions to (and always have been).

Please bear in mind I am not hammering on about this at of some narcisistic design to be right, or to proclaim that this is the gospel according to me. In engineering there are some certainties and then there are many cases where it's a case of deciding how to make a best stab of optimising for complex and usually very interesting trade-offs, primary and secondary benefits and so-on. I am interested in your opinions mainly because I find the details very interesting in a purely engineering context.

I definitely wasn't thinking the dorsal inlet would need to be sized for all engines demand, only the centreline unit.

I do think there is thrust vectoring but I suspect they could make a case for only caring much about deflecting in pitch up and that pitch down doesn't need to be as effective given the other limits of negative g and the concept to operate primarily at high altitude where upward IR emissions might not be their concern.

Lastly (and back to A340's point) if they're right then does this mean the B-21 is welcome to know on China's door with impunity and do they have a different strategy to deal with B-21 or can someone elaborate?
 
sferrin said:
You have to consider many have been online for decades and have answered the exact same questions/theories many, many times. Twenty years ago you might have got a five paragraph, well articulated, polite response. Now you just get a, "STFU newb". ;)
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That's the sad thing sferrin, there are probably many people like me who have been on this site a long time, but we don't say anything because as you say the response is STFU. For what it's worth I generally expect to see it and honestly it was there 5 years ago too (just go look), but maybe 15 years ago it read as quite civilised and cloisterly!

At least it's not just aerospace forums this happens, it's everywhere, and in the workplace too to a good degree. It's human nature.
 
sferrin said:
Well it could cause knee-jerk reactions from the West rather than well thought out strategies.
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I thought the same. Always going to be a trade-off.

China's strategists maybe deciding a puff the chest out and look fierce is the best strategy to encourage the west to think more than twice about escalating a defence of Taiwan. There is a benefit to having Excaliber hidden away so that your enemy doesn't have free reign to develop a counter strategy but equally a couple of gatling guns on your front porch is quite a good burgler deterent. Might also be as simple as domestically this is a good lift for Xi and plays well politically with Trump taking the reins soon.
 
quellish said:
You’re actually describing a video I intend to shoot to help explain this, though I will also have shiny models of the F-1117 and other things as well.
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That exact image was used to help explain RCS in a book published 38 years ago. I'll think of the author's name in a bit.

Also, the fact that people are still standing on their hind legs and saying "it must have a bigger RCS because of its size" is either a testament to the effectiveness of security or a sign of continued Internet-induced brain rot.
 
The 3 engines is very difficult to analyze. If they are 3 of the same engine, then I am stumped. What makes sense to me, although the sameness of the nozzles suggests this is not the case, is to have 2 low bypass turbofans for supercruise and a higher bypass engine for loiter. What do the low bypass engines do will the plane is loitering? I do not know. Closing the intakes seems to add weight and complexity. How bad would it be to let air flow into the low bpr engines and windmill them? How much fuel would it take to inject a little fuel and have the engines essentially idle so that they essentially produce enough thrust to equal the drag and have it be neutral? I suspect that windmilling the engines is better. It's possible that the third engine is mainly for power generation for a future DEW or the third engine is just a measure to get the plane into service ASAP because they are in a hurry.
 
LowObservable said:
That exact image was used to help explain RCS in a book published 38 years ago. I'll think of the author's name in a bit.
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I recall a popular science article in the early 90s that used a similar explanation but with a hose of water instead of light (IIRC).

LowObservable said:
Also, the fact that people are still standing on their hind legs and saying "it must have a bigger RCS because of its size" is either a testament to the effectiveness of security or a sign of continued Internet-induced brain rot.
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Maybe because of the “myth” that cruise missiles are hard to detect (which is more of a clutter issue than RCS or size)
 
totoro said:
But why show it off to the wider audience? Doesn't that only create further political pressure on the US congress and then the DoD so US next gen programs get more financing and get a kick in the butt? How does that benefit you, as the head of PLA who presumably wants to win the next war?
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Why did the US engage in a very public arms build up under Reagan?
 
quellish said:
I recall a popular science article in the early 90s that used a similar explanation but with a hose of water instead of light (IIRC).
Click to expand...

January 1989 Popular Science article "Revealed: Secret F-117A Stealth Fighter"

books.google.com

Popular Science

Popular Science gives our readers the information and tools to improve their technology and their world. The core belief that Popular Science and our readers share: The future is going to be better, and science and technology are the driving forces that will help make it better.
books.google.com

I'm not sure why I remembered it being a hose of water instead of a light.
 
Ainen said:
3rd engine is a giveaway.
Strike aircraft, supercruising or not, just won't need it - but it takes helluva fuel and weapon bay volume.
You only need this 3rd engine for onboard power and fighter dynamics.
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This is flatly false, if you're looking for an configuration to use an existing engine to supercruise with and the size of the vehicle is too large for two of the existing engines.
 
totoro said:
I have a question that I was wondering about.
Imagine you're the head of the PLA. You're developing new generation of combat planes. You're possibly in midst of an arms race with the US.

Why do you go so public about it all, the way China has gone public? Why don't you you try to test fly those things as covertly as possible?
What is it to be gained from being so open about it?
Sure, the US intelligence community might be tracking your progress nevertheless. Though it's doubtful they'd necessarily get as good photos of the prototypes through their regular spy channels this quickly and this easily.

But why show it off to the wider audience? Doesn't that only create further political pressure on the US congress and then the DoD so US next gen programs get more financing and get a kick in the butt? How does that benefit you, as the head of PLA who presumably wants to win the next war?

Lets for a moment forget the inner chinese politics and grandstanding angle of it all. If that stuff is excluded, what palpable benefit does PLA get in going public? How does going public in this way help you win that next war?
Click to expand...

Obviously the PLA chief desperately wants the US to spend $300+ million per NGAD fighter (before cost overruns). Either to bankrupt the US through excessive defence spending or he just owns a lot of shares in Lockmart.
 
Sundog said:
This is flatly false, if you're looking for an configuration to use an existing engine to supercruise with and the size of the vehicle is too large for two of the existing engines.
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You can build a like twice heavier (longer-ranged) aircraft, shaped for supersonic flight, with way more space inside, and it'll supercruise faster than numbers in this thread.

Concorde did exist.
 
totoro said:
I have a question that I was wondering about.
Imagine you're the head of the PLA. You're developing new generation of combat planes. You're possibly in midst of an arms race with the US.

Why do you go so public about it all, the way China has gone public? Why don't you you try to test fly those things as covertly as possible?
What is it to be gained from being so open about it?
Sure, the US intelligence community might be tracking your progress nevertheless. Though it's doubtful they'd necessarily get as good photos of the prototypes through their regular spy channels this quickly and this easily.

But why show it off to the wider audience? Doesn't that only create further political pressure on the US congress and then the DoD so US next gen programs get more financing and get a kick in the butt? How does that benefit you, as the head of PLA who presumably wants to win the next war?

Lets for a moment forget the inner chinese politics and grandstanding angle of it all. If that stuff is excluded, what palpable benefit does PLA get in going public? How does going public in this way help you win that next war?
Click to expand...

I have a question -- why did you ask it here on Secret Projects? If you're wanting to get into the head of the PLA, this isn't the best place for it lol.

But to address your questions, my answers are from two complementary directions:
1. Due to the practical necessity of having it be built and tested at Chengdu's factory, and the need to have it tested during day time for its first flight (risk reduction and all that), it would be virtually impossible for it to not be leaked out by the public anyway. Which is to say, I suspect they realized the effort to genuinely, fully conceal it would take far too much effort for questionable and unknown benefits. Furthermore, it is virtually guaranteed that people have already taken better quality images of this thing but were warned to not share it, and it's possible that people who took and shared some of the imagery that we do have, were given warnings already as well -- but once footage is out there, you can't truly take it down.
2. The PLA themselves have not actually been particularly open or public about this new aircraft -- I would say that when we account for differences in social media and smartphone prevalence today, the amount of information and imager we got of this thing is about similar to what we got for J-20 back 14 years ago. Things are just way harder to conceal these days.
Certainly, comparing J-36 with other big ticket US projects such as B-21 (official name and concept art in 2016, rollout in 2022 with official pictures, first flight in 2023 with official pictures and news), or even NGAD (we've gotten play by plays of its developmental process and updates over time), J-36 is positively secretive. We don't even know its official name yet, which is par for the course.

So I suppose my answer is a combination of "they haven't been very public or open about it to begin with" and "concealing it more than they already have would be very difficult".
 
quellish said:
January 1989 Popular Science article "Revealed: Secret F-117A Stealth Fighter"

books.google.com

Popular Science

Popular Science gives our readers the information and tools to improve their technology and their world. The core belief that Popular Science and our readers share: The future is going to be better, and science and technology are the driving forces that will help make it better.
books.google.com

I'm not sure why I remembered it being a hose of water instead of a light.
Click to expand...
That's the name I was thinking of...
1736028839262.png
 

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