Official Chengdu J-20 Discussion Thread

King Comm

New Member
The IRST on an Su-27SK can be called "something similar to EODAS"
The all aspect missile approach warning system on the FC-1 is essentially a cheap and simple EO DAS, four optical apertures mounted around the fuselage provide 360 degree detection of incoming missiles, and the onboard computer display the information to the pilot..
 

Pathfinder-X

Tribal Warlord
Verified Defense Pro
Only visually? So this is the Chinese equivalent of the Su-34?
Yes, only the airframe will be the same (different FBW, avionics, radar, engine etc...). I wouldn't consider it Su-34 equivalent, more in the lines of F-15E. They want to retain J-11's air superiority capability while expanding its multirole capability.

Anyways my main point was that the J-15 is likely to have less in common with the Su-33 (especially if their recent upgrade plans materialize) and more in common with the Su-27SK, T-10K, and indigenous Chinese technology.
They were able to manage to obtain a single Su-33 from Ukraine in the mid 2000's I think. No doubt the experience they had with developing the J-11 line will speed up the process.

The IRST on an Su-27SK can be called "something similar to EODAS"... Granted you mention him as a reliable source, but I'm honestly very hesitant. As it stands the Chinese have yet to serially produce any sophisticated indigenous EO sensor.
The system on J-20 has sensors throughout the body of the aircraft, offering 360 degree coverage. It's not a simple IRST like the ones on the Su-27SK. The source I've mentioned revealed details about J-20 two years prior to the first photos being seen. He's considered one of the best sources available, given the government's secretive nature. So far, he hasn't been wrong about anything yet. As far as China producing an EO sensor suite, J-11A, J-10B and J-11B are already being equipped with indigenously produced IRST. J-20 would be its first attempt to build something as complicated as EODAS.

With J-20 slated to enter service around 2018-2020 period, there are plenty of time for improvements.

Flew for the first time with landing gear up today: http://img3.imageshack.us/img3/3506/11050602362cb96611962ff.jpg
 
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Feanor

Super Moderator
Staff member
Yes, only the airframe will be the same (different FBW, avionics, radar, engine etc...). I wouldn't consider it Su-34 equivalent, more in the lines of F-15E. They want to retain J-11's air superiority capability while expanding its multirole capability.
The Su-34 has air-to-air capability. Not great but some. So the J-16 is to be a multi-role strike fighter?

They were able to manage to obtain a single Su-33 from Ukraine in the mid 2000's I think. No doubt the experience they had with developing the J-11 line will speed up the process.
They obtained a T-10K prototype. Yes it definitely helped.

The system on J-20 has sensors throughout the body of the aircraft, offering 360 degree coverage. It's not a simple IRST like the ones on the Su-27SK. The source I've mentioned revealed details about J-20 two years prior to the first photos being seen. He's considered one of the best sources available, given the government's secretive nature. So far, he hasn't been wrong about anything yet. As far as China producing an EO sensor suite, J-11A, J-10B and J-11B are already being equipped with indigenously produced IRST. J-20 would be its first attempt to build something as complicated as EODAS.

With J-20 slated to enter service around 2018-2020 period, there are plenty of time for improvements.

Flew for the first time with landing gear up today: http://img3.imageshack.us/img3/3506/11050602362cb96611962ff.jpg
Interesting. I suppose we will see.
 

gf0012-aust

Grumpy Old Man
Staff member
Verified Defense Pro
J-20 recently revealed its advanced EODAS system, which in the past F-35 exclusively owns.

Pics:
J-20... The New Generation Fighter II

And it's rumored that J-20 will also incorporate a laser jammer in the near future, which is used to defeat the current AA missiles with imaging infrared seeker.
Its not even remotely en EODAS.

this silliness has been claimed on some other forums as well. Have a close look. - again and again and again.
 

plasmafish

New Member
shock ramps don't look like that. this has been discussed to death when the FC-1 was out - which does have shock ramps
Apologies. I meant to say "adjustable DSI" but I confused them with shock ramps.

What is your opinion on this adjustable DSI?
 
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gf0012-aust

Grumpy Old Man
Staff member
Verified Defense Pro
Apologies. I meant to say "adjustable DSI" but I confused them with shock ramps.

What is your opinion on this adjustable DSI?
I'm not qualified to pass on technical comment as its not my background. But from what I've seen in the past, shock ramps and DSI's are generally attempts to get around engine management issues in certain parts of the performance envelope - esp with shock ramps as they are a less graceful way to "boot" a performance requirement.

movable DSI's are in the same boat for me as it seems to indicate the engine management systems of the engines are unable to deal with performance demands and so are used as spikes to control the rate and compression flow of air into the intakes.

to me that smells of a mismatch of components and a hail mary attempt to patch a solution because its cheaper etc.....

wrt to DSI's I'm referring to movable shock ramps, rather than the movable spikes that used to exist on older centrig jet engines or ramjets
 

latenlazy

New Member
I'm not qualified to pass on technical comment as its not my background. But from what I've seen in the past, shock ramps and DSI's are generally attempts to get around engine management issues in certain parts of the performance envelope - esp with shock ramps as they are a less graceful way to "boot" a performance requirement.

movable DSI's are in the same boat for me as it seems to indicate the engine management systems of the engines are unable to deal with performance demands and so are used as spikes to control the rate and compression flow of air into the intakes.

to me that smells of a mismatch of components and a hail mary attempt to patch a solution because its cheaper etc.....

wrt to DSI's I'm referring to movable shock ramps, rather than the movable spikes that used to exist on older centrig jet engines or ramjets
Not to draw comparisons, but wouldn't that imply that the aircraft like the F-15 and the Eurofighter have engines that "are unable to deal with performance demands" and are thus "mismatch of components and a hail mary attempt to patch a solution because its cheaper etc.....".

My understanding is that all turbofans need subsonic air flow and a fixed inlet design can only do so much to make sure the engine is being properly fed before hitting a certain speed envelope. It has less to do with the engine and more to do with the inlet design?
 

gf0012-aust

Grumpy Old Man
Staff member
Verified Defense Pro
My understanding is that all turbofans need subsonic air flow and a fixed inlet design can only do so much to make sure the engine is being properly fed before hitting a certain speed envelope. It has less to do with the engine and more to do with the inlet design?
I guess thats my point.

if you look at what its trying to achieve it is attempting to compensate for the inlet design, you either redesign the inlet (and you've quoted some good older examples) or you change the way that air enters the inlet (ie secondary management)

movable inlets and shock ramps are analogous to a defibrilator - ie shock loading and compressing air at different stages of the performance envelope. shock ramps are like speed bumps, they will have a different impact depending on the speed and performance flight parameters at a point in time - eg combinations of speed, altitude, AoA etc etc... but they are a one time event - you can't move the "speed bump" - it will kick in and influence flight handling characteristics at "xx" and will always do so at "xx"

a movable inlet at least gives some control that can be coupled to the FADEC

coarsely speaking, modern FADECs should be able to handle and manage far more effectively than 2 these structural opportunities will although these plus FADEC would obviously make an improvement as well.

I see them as compromises in the design process - at some point someone realised that the inlet size and engines couldn't cope with certain flight requirements and these were bolted on to get around a fundamental engineering problem.

again,. the DSI analogy I refer to is basically a moving shock ramp as opposed to a managed inlet
 

latenlazy

New Member
I guess thats my point.

if you look at what its trying to achieve it is attempting to compensate for the inlet design, you either redesign the inlet (and you've quoted some good older examples) or you change the way that air enters the inlet (ie secondary management)

movable inlets and shock ramps are analogous to a defibrilator - ie shock loading and compressing air at different stages of the performance envelope. shock ramps are like speed bumps, they will have a different impact depending on the speed and performance flight parameters at a point in time - eg combinations of speed, altitude, AoA etc etc... but they are a one time event - you can't move the "speed bump" - it will kick in and influence flight handling characteristics at "xx" and will always do so at "xx"

a movable inlet at least gives some control that can be coupled to the FADEC

coarsely speaking, modern FADECs should be able to handle and manage far more effectively than 2 these structural opportunities will although these plus FADEC would obviously make an improvement as well.

I see them as compromises in the design process - at some point someone realised that the inlet size and engines couldn't cope with certain flight requirements and these were bolted on to get around a fundamental engineering problem.

again,. the DSI analogy I refer to is basically a moving shock ramp as opposed to a managed inlet
A compromise maybe, but also an innovation I think. If we ask what the purpose of using a DSI is, it's to achieve a similar performance with a lighter weight solution. My understanding is that FADEC cannot adjust the speed of the airflow coming into an engine. That's purely left to inlet design, and a movable DSI sacrifices a bit of the weight benefits to make the DSI, a fixed solution to controlling airflow, more flexible through different speed envelopes. In this case it might be more a trade off between simplicity and flexibility.

In any case, we're talking about a purely hypothetical solution here. We have no confirmation that the J-20 actually has an adjustable DSI (though I've always been intrigued with such a concept).
 

Pathfinder-X

Tribal Warlord
Verified Defense Pro
Its not even remotely en EODAS.

this silliness has been claimed on some other forums as well. Have a close look. - again and again and again.
They don't have it on yet, but they are working towards it. That bit has been confirmed by someone working with CAC. To be able to mimic EODAS is one of the primary goal they have at improving situational awareness.

The Su-34 has air-to-air capability. Not great but some. So the J-16 is to be a multi-role strike fighter?
Yes, it will be a multirole strike platform. They weren't happy with the air-to-air performance of Su-30MKK and MK2. Because of their added weight, they are not as agile and fast in the air as the Su-27/J-11 series.
 

Feanor

Super Moderator
Staff member
Yes, it will be a multirole strike platform. They weren't happy with the air-to-air performance of Su-30MKK and MK2. Because of their added weight, they are not as agile and fast in the air as the Su-27/J-11 series.
So their main means of improving air-to-air performance is agility? Not new or more powerful radars, longer range BVR missiles, or any RCS reduction techniques? Agility is their focus?
 

latenlazy

New Member
So their main means of improving air-to-air performance is agility? Not new or more powerful radars, longer range BVR missiles, or any RCS reduction techniques? Agility is their focus?
From what I've read about China's air doctrine it sounds like they believe all else being held equal agility becomes the deciding factor in A2A combat. This kind of doctrine would make sense as it assumes China can only match the best avionics, missile, and RCS reduction technologies from other countries at this point in its development instead of besting them. (Of course, the overall system matters too, but if you think about it China doesn't have as many modern or advanced support assets in the air as the rest of the developed world.)
 
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Pathfinder-X

Tribal Warlord
Verified Defense Pro
So their main means of improving air-to-air performance is agility? Not new or more powerful radars, longer range BVR missiles, or any RCS reduction techniques? Agility is their focus?
New sensors, weapons and various improvements come without a question, but sustained manoevurability is deemd to be the deciding factor in A2A encounters by PLAAF. The most important addition to J-16 would be a new variant of WS-10 engines with improved thrust.
 

MiG-23MLD

Banned Member
Not to draw comparisons, but wouldn't that imply that the aircraft like the F-15 and the Eurofighter have engines that "are unable to deal with performance demands" and are thus "mismatch of components and a hail mary attempt to patch a solution because its cheaper etc.....".

My understanding is that all turbofans need subsonic air flow and a fixed inlet design can only do so much to make sure the engine is being properly fed before hitting a certain speed envelope. It has less to do with the engine and more to do with the inlet design?
All jet engines need subsonic flow unless they are ramjets that can use supersonic flow, in example is the SR-71 which only uses the Ramjet at high supersonic speeds.
Why they need subsonic flow? simple at subsonic speed they need to compress the air, at high supersonic speeds there is no need for compression, the air speed is enough to compress the air, In a Ramjet this translates into no need of turbine blades.
Fighters with turbofans and turbojets require an inlet that can slow down the air for the engine to handle the air pressure so they need to slow the supersonic flow to subsonic speeds.
The DSI inlet main advantage is weight reduction because it lacks moveable parts and lacks a boundary layer diverter, the bump does work in the same way as a regular shock cone of the inlet of a Mirage III or 2000, however it is fixed, it can not move as the shock cone of the Mirage III inlet, thus it is limited to supersonic speeds below Mach1.7 or Mach 2 at most, as speed increases the supersonic wake does change profile, it does reduce its angle of incidence, this requires a variable geometry inlet that keeps the supersonic flow out of the engine so the Mirage III`s inlet shock cone moves forward as the shock wave changes incidence angle.
see picturehttp://history.nasa.gov/SP-4302/p254.jpg
The Moveable DSI will requiere a moveable inlet lip, but this will cancel out the simplicity of the DSI inlet and will make it redundant.
 
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latenlazy

New Member
4302/p254.jpg"]http://history.nasa.gov/SP-4302/p254.jpg[/URL]
The Moveable DSI will requiere a moveable inlet lip, but this will cancel out the simplicity of the DSI inlet and will make it redundant.
Not if the DSI allows for a simpler movable inlet lip mechanism.
 

MiG-23MLD

Banned Member
Not if the DSI allows for a simpler movable inlet lip mechanism.
The DSI inlet main advantage is it is fixed and lighter, it has no moveable parts or splitter that increases maintainance, of course, you can add moveable parts, but these will add weight and vastly increase maintainance and costs, so then why you need a DSI? it is better to have then a F-22`s type inlet.
As speed increase the shock wave will reduce its angle, a Mirage III or MiG-21 will move forward the shock cone forebody to avoid supersonic flow entering the inlet, on the SR-71 this will be the opposite, it needs supersonic flow for the ramjet, so it moves rearward to allow the supersonic flow into the engine.
Since the DSI has no moveable cone and the bump is fixed the inlet lip cowling has to move, this will add weight, increase maintainance and RCS signature.
Then the regular F-22`s inlet type makes more sense.

If you need a fighter with Mach 1.8 speed the DSI makes sense. a max speed of Mach 2 probably is attainable, but the engine thrust at that speed will suffer, in example Mirage 2000 and F-16, the Mirage having lower thrust weight ratio, is faster than the F-16 thanks to a variable geometry inlet.
 

latenlazy

New Member
The DSI inlet main advantage is it is fixed and lighter, it has no moveable parts or splitter that increases maintainance, of course, you can add moveable parts, but these will add weight and vastly increase maintainance and costs, so then why you need a DSI? it is better to have then a F-22`s type inlet.
As speed increase the shock wave will reduce its angle, a Mirage III or MiG-21 will move forward the shock cone forebody to avoid supersonic flow entering the inlet, on the SR-71 this will be the opposite, it needs supersonic flow for the ramjet, so it moves rearward to allow the supersonic flow into the engine.
Since the DSI has no moveable cone and the bump is fixed the inlet lip cowling has to move, this will add weight, increase maintainance and RCS signature.
Then the regular F-22`s inlet type makes more sense.

If you need a fighter with Mach 1.8 speed the DSI makes sense. a max speed of Mach 2 probably is attainable, but the engine thrust at that speed will suffer, in example Mirage 2000 and F-16, the Mirage having lower thrust weight ratio, is faster than the F-16 thanks to a variable geometry inlet.
What I'm saying is that given how the DSI works, having an movable inlet lip is still probably a much simpler and lighter solution than say variable shock ramps. Why would a solution like this be necessary? Probably because part of the requirements for the plane is to have it move at speeds beyond what a fixed DSI would allow, or perhaps it has to do with how capable the engine is.

I don't know how much more or less such a small change as a moving lip will increase RCS, especially if it's properly managed. Finally, the F-22 has a fixed inlet design with diverters. Perhaps a DSI offers better control of RCS (by controlling the direction of radar reflection entering the inlet?)
 
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