Chengdu J-20 pictures, analysis and speculation Part II

[chuck4]

I don't think it is a missile rail because i can't see any separate openned missile bay door, which has to be there for the rail to show. I think more likely it is actually just the lower half of an openned missile door.

 

[Deino]

I think You are correct ... if You slow down the video image by image it seems as if the door is closing just before landing and what looks like attachments of the rail are a gap between fuselage and closing door.

Then the question howeber would by WHY ?? was there a malfunction and the doors only closing so late or was it again to initiate additional discussions at the forums since flight testing beacme almost boring in recent times ?

Deino

 

[Deino]

Now I'm no longer sure ... seems indeed like a rail !

 

[chuck4]

Maybe the pilot fat fingered his touchscreen?

 

[Thorvic]

Looks like its bolted on to the fuselage below the side bay, could they be using it to intergrate missiles with the on-board systems possibly for targeting before they test them in weapon bays ?

 

[chuck4]

Now I'm no longer sure ... seems indeed like a rail !

But where is the door? The rails can not be exposed without the door being open. I think it is just the door seen at an angle that reduced its profile and made it look like a rail.

 

[chuck4]

Looks like its bolted on to the fuselage below the side bay, could they be using it to intergrate missiles with the on-board systems possibly for targeting before they test them in weapon bays ?

It's not seen on the jet after it landed. So it can't be bolt on. Must be something that either folds into the plane or retracts into the plane.

Also, it seems a bit early in the development cycle to worry about weapons integration, if you ask me.

 

[Sundog]

It could be a pod attached to the rail for loads/accoustic measurements with regards to the weapons bay, so they know what the "environment" will be for the weapons when tested.

 

[Deino]

There's currently an interesting theory going on some discussion if the missile could possibly be launched with the doors closed:

http://lt.cjdby.net/thread-1568080-1-1.html

If true indeed an interesting theory ... something like that attached below !

Deino

 

[2IDSGT]

There's currently an interesting theory going on some discussion if the missile could possibly be launched with the doors closed:

http://lt.cjdby.net/thread-1568080-1-1.html

If true indeed an interesting theory ... something like that attached below !

Deino

That's pretty cool, but might it reflect a limitation of some kind in their missiles/launch-systems?

 

[Deino]

Here's a new image which seems to confirm this theory ... attached are the original (huge one) + two smaller ones I tried a bit to modify ! ???

Deino

 

[latenlazy]

There's currently an interesting theory going on some discussion if the missile could possibly be launched with the doors closed:

http://lt.cjdby.net/thread-1568080-1-1.html

If true indeed an interesting theory ... something like that attached below !

Deino

That's pretty cool, but might it reflect a limitation of some kind in their missiles/launch-systems?

I can't imagine what kind of launch system limitation would such a solution would address...It seems to be meant to maintain RCS during launch...

 

[2IDSGT]

There's currently an interesting theory going on some discussion if the missile could possibly be launched with the doors closed:

http://lt.cjdby.net/thread-1568080-1-1.html

If true indeed an interesting theory ... something like that attached below !

Deino

That's pretty cool, but might it reflect a limitation of some kind in their missiles/launch-systems?

I can't imagine what kind of launch system limitation would such a solution would address...It seems to be meant to maintain RCS during launch...

...Which begs the question: why do their missiles need to hang on the outside prior to launch and for how long? Of course, the old Sidewinders on the F-22 need to hang out; but should things come that point, VLO wouldn't be much of a concern.

 

[latenlazy]

There's currently an interesting theory going on some discussion if the missile could possibly be launched with the doors closed:

http://lt.cjdby.net/thread-1568080-1-1.html

If true indeed an interesting theory ... something like that attached below !

Deino

That's pretty cool, but might it reflect a limitation of some kind in their missiles/launch-systems?

I can't imagine what kind of launch system limitation would such a solution would address...It seems to be meant to maintain RCS during launch...

...Which begs the question: why do their missiles need to hang on the outside prior to launch and for how long? Of course, the old Sidewinders on the F-22 need to hang out; but should things come that point, VLO wouldn't be much of a concern.

*Shrug* Maybe it's not meant to address any problems. Maybe it's just a better solution? For example, in a mission where VLO isn't as important they can probably use those hardpoints to mount weapons that don't fit in the bay. Or perhaps at BVR closing the bay doors minimizes the chance that you'd be detected, thereby maximizing your ability to hit a target without giving it a heads up?

 

[chuck4]

Still seems more likely to me that what we are seeing is the missile bay door itself, not a launch rail.

 

[LowObservable]

It might give you a more benign aero environment for launch. Or limit any aero effects from the open door, or aero loads on the door, hinges and actuators, to a transient. Or not expose the open door to blast. In short a lot of potential reasons for doing it that way.

 

[chuck4]

It might give you a more benign aero environment for launch. Or limit any aero effects from the open door, or aero loads on the door, hinges and actuators, to a transient. Or not expose the open door to blast. In short a lot of potential reasons for doing it that way.

If this is true, then it implies the launch arrangement is designed to hold the missile in the airstream for a certain amount if time. This in turn implies the j-20 wasn't designed with lock-on after launch missile in mind.

 

[latenlazy]

It might give you a more benign aero environment for launch. Or limit any aero effects from the open door, or aero loads on the door, hinges and actuators, to a transient. Or not expose the open door to blast. In short a lot of potential reasons for doing it that way.

If this is true, then it implies the launch arrangement is designed to hold the missile in the airstream for a certain amount if time. This in turn implies the j-20 wasn't designed with lock-on after launch missile in mind.

Not mutually exclusive. It gives the J-20 the option to keep the missile in the airstream. I'm doubtful that the J-20 doesn't have lock on after fire capability, since that's needed for weapons fired from the belly bays.

 

[chuck4]

I am talking about ir missiles from side bays. The ability to close the missile bay doors with missile held in the airstream does not exclude lock-on after launch IR missiles, but is redundant if the missiles can be simply ejected into the airstream and then be commanded by data link to acquire their Lock-on during free flight.

 

[latenlazy]

I am talking about ir missiles from side bays. The ability to close the missile bay doors with missile held in the airstream does not exclude lock-on after launch IR missiles, but is redundant if the missiles can be simply ejected into the airstream and then be commanded by data link to acquire their Lock-on during free flight.

Still not sure we can conclude that. It would imply the J-20 couldn't launch missiles with IR seekers from its belly bays, and I'm somewhat doubtful such a limitation would be acceptable for the main weapons bay.

 

[Blitzo]

I am talking about ir missiles from side bays. The ability to close the missile bay doors with missile held in the airstream does not exclude lock-on after launch IR missiles, but is redundant if the missiles can be simply ejected into the airstream and then be commanded by data link to acquire their Lock-on during free flight.

My hypothesis is that the launch mechanism will keep the bay door open in the airstream a shorter overall time compared to F-22's mechanism. It will be beneficial for drag and leave another extra reflection surface exposed for a shorter amount of time.


This is assuming J-20 and F-22 have similar overall launch times for their side bays of course.


Also, F-22 side bays do not simply eject sidewinders like you described either, I believe. It too "holds" the missile on a rail for a brief moment until the motor ignites. J-20 I imagine works the same, but allows the door to close for the few milliseconds between lowering the rail out and missile launch.

 

[chuck4]

I am talking about ir missiles from side bays. The ability to close the missile bay doors with missile held in the airstream does not exclude lock-on after launch IR missiles, but is redundant if the missiles can be simply ejected into the airstream and then be commanded by data link to acquire their Lock-on during free flight.

My hypothesis is that the launch mechanism will keep the bay door open in the airstream a shorter overall time compared to F-22's mechanism. It will be beneficial for drag and leave another extra reflection surface exposed for a shorter amount of time.


This is assuming J-20 and F-22 have similar overall launch times for their side bays of course.


Also, F-22 side bays do not simply eject sidewinders like you described either, I believe. It too "holds" the missile on a rail for a brief moment until the motor ignites. J-20 I imagine works the same, but allows the door to close for the few milliseconds between lowering the rail out and missile launch.

Aim-9X is based on missile bodies of older aim-9 version that isn't cleared to be ejected rather than rail launched.


However, that is not the point. The point is is if the missile can lock on after launch, then it won't need to remain attached to the aircraft and exposed to the airstream for any significant amount of time whether it is ejected or rail launched. In this case The missile can go off the rails the moment it is extended into the airstream. it seems hardly worth while to close the missile bay doors first before sending the missile on it's way. In fact, having to open and close the door twice during each launch would only lengthen the launch cycle and extend the period of vulnerability.


However, if the missile must take time to lock on while attached to the aircraft, then it makes more sense to extend the rails, close the door to improve the aerodynamics and stealth characteristics while waiting for the missile to seeks and locks on, and then open the doors and retract the rails after the missile leaves the rail.

 

[latenlazy]

I am talking about ir missiles from side bays. The ability to close the missile bay doors with missile held in the airstream does not exclude lock-on after launch IR missiles, but is redundant if the missiles can be simply ejected into the airstream and then be commanded by data link to acquire their Lock-on during free flight.

My hypothesis is that the launch mechanism will keep the bay door open in the airstream a shorter overall time compared to F-22's mechanism. It will be beneficial for drag and leave another extra reflection surface exposed for a shorter amount of time.


This is assuming J-20 and F-22 have similar overall launch times for their side bays of course.


Also, F-22 side bays do not simply eject sidewinders like you described either, I believe. It too "holds" the missile on a rail for a brief moment until the motor ignites. J-20 I imagine works the same, but allows the door to close for the few milliseconds between lowering the rail out and missile launch.

Aim-9X is based on missile bodies of older aim-9 version that isn't cleared to be ejected rather than rail launched.


However, that is not the point. The point is is if the missile can lock on after launch, then it won't need to remain attached to the aircraft and exposed to the airstream for any significant amount of time whether it is ejected or rail launched. In this case The missile can go off the rails the moment it is extended into the airstream. it seems hardly worth while to close the missile bay doors first before sending the missile on it's way. In fact, having to open and close the door twice during each launch would only lengthen the launch cycle and extend the period of vulnerability.


However, if the missile must take time to lock on while attached to the aircraft, then it makes more sense to extend the rails, close the door to improve the aerodynamics and stealth characteristics while waiting for the missile to seeks and locks on, and then open the doors and retract the rails after the missile leaves the rail.

I get that point, but it doesn't square too well with missiles that are stored in the main weapons bay. If the missile needs to seek and lock on its own then how do they fire from the mwb?

I have another hypothesis. What if the side bays can fit a mraam, but it can't clear safely from the fuselage when fired from the bay? Such a solution would make the side bays more versatile.

 

[Blitzo]

I get that point, but it doesn't square too well with missiles that are stored in the main weapons bay. If the missile needs to seek and lock on its own then how do they fire from the mwb?

maybe IR AAMs will not be fired from the belly weapons bay?

I have another hypothesis. What if the side bays can fit a mraam, but it can't clear safely from the fuselage when fired from the bay? Such a solution would make the side bays more versatile.

I sincerely doubt the side bays will be able to fit an mraam.

I am talking about ir missiles from side bays. The ability to close the missile bay doors with missile held in the airstream does not exclude lock-on after launch IR missiles, but is redundant if the missiles can be simply ejected into the airstream and then be commanded by data link to acquire their Lock-on during free flight.

My hypothesis is that the launch mechanism will keep the bay door open in the airstream a shorter overall time compared to F-22's mechanism. It will be beneficial for drag and leave another extra reflection surface exposed for a shorter amount of time.


This is assuming J-20 and F-22 have similar overall launch times for their side bays of course.


Also, F-22 side bays do not simply eject sidewinders like you described either, I believe. It too "holds" the missile on a rail for a brief moment until the motor ignites. J-20 I imagine works the same, but allows the door to close for the few milliseconds between lowering the rail out and missile launch.

Aim-9X is based on missile bodies of older aim-9 version that isn't cleared to be ejected rather than rail launched.

What if the new SRAAM is developed to be rail launched rather than ejected? That would explain everything quite handily.

However, that is not the point. The point is is if the missile can lock on after launch, then it won't need to remain attached to the aircraft and exposed to the airstream for any significant amount of time whether it is ejected or rail launched. In this case The missile can go off the rails the moment it is extended into the airstream. it seems hardly worth while to close the missile bay doors first before sending the missile on it's way. In fact, having to open and close the door twice during each launch would only lengthen the launch cycle and extend the period of vulnerability.

That really depends on how fast they can make the doors open and close, I think.
Does opening and closing the door twice during the launch cycle lengthen the overall launch time, or was the door speed dependent on a set launch time they were required to achieve?

However, if the missile must take time to lock on while attached to the aircraft, then it makes more sense to extend the rails, close the door to improve the aerodynamics and stealth characteristics while waiting for the missile to seeks and locks on, and then open the doors and retract the rails after the missile leaves the rail.

That is definitely one possible answer, but let's give benefit of the doubt that PL-10 has LOAL ability as rumours of the years have suggested. For the purposes of discussion, what else could justify this unique mechanism?
The only benefits I'd see, would be the reduced drag and door reflections of leaving them open for the entire launch cycle, assuming:
-overall launch time of J-20 is comparable to F-22 (i.e.: door opening and closing is very, very fast, but considering the side bay door seems to only open some 45 degrees relative to the side fuselage this may be possible)
-missile is LOAL



Btw, have there been any existing aircraft with dedicated SRAAM side bays that "eject" the missile out? Two problems with that come to mind, one, ejecting the missile from a side bay may launch it into any aircraft flying level with you (for belly weapon bays it's less of a problem, as flying in formation or with a wingman means your allies won't be beneath you). Two, would the aggressive maneuvering you'd expect in a WVR combat situation necessitate rail launch in any way?

 

[chuck4]

An alternative explanation may be the Chinese wanted the flexibility to lock the missile on either before or after launch, depending on the tactical situation. I imagine in very close quarter combat, it may be advantageous to lock on the missile before it departs the rail.


I think we should reserve judgement until a better photo of the side bay on the j-20 appears.

 

[latenlazy]

maybe IR AAMs will not be fired from the belly weapons bay?

Maybe, but I have doubts about that given what we know about China's intended datalink capabilities. What's so different about post release lock on for an IR missile vs a radar guided one? The inability to lock on after fire from the side bays implies the inability to lock on after fire, period.

I sincerely doubt the side bays will be able to fit an mraam.

You're probably right. Just checked my rough estimates and the numbers don't fly.

 

[overscan (PaulMM)]

Maybe they want to be able to fire PL-8s from the sidebays, they have a few kicking about, and PL-10s only could also go in the main bay if wanted.

 

[chuck4]

maybe IR AAMs will not be fired from the belly weapons bay?

Maybe, but I have doubts about that given what we know about China's intended datalink capabilities. What's so different about post release lock on for an IR missile vs a radar guided one? The inability to lock on after fire from the side bays implies the inability to lock on after fire, period.

The technical challenge is more complicated then you think.

The missile can't just lock onto the first target it sees. It must not only communicate with the launching plane with datalink, it must also have a sufficiently accurate inertial navigation system onboard the missile so as to preserve the orientation of the reference frame of the launching aircraft so when launch aircraft gives a target direction to lock to, the missile, through high g maneuvers, would still keep track of what that direction ought to be in common terms with the airplane. It muust also calculate the displacement with respect to the lunching aircraft, so that when it receive lock on instructions from the launching aircraft, the missile's seeker can correct for parallex amd point to the same target as stated in the instruction. It has to do this in a package that fits inside a 5 inch tube and survive many Gs and severe vibration and temperature environments.

 

[latenlazy]

maybe IR AAMs will not be fired from the belly weapons bay?

Maybe, but I have doubts about that given what we know about China's intended datalink capabilities. What's so different about post release lock on for an IR missile vs a radar guided one? The inability to lock on after fire from the side bays implies the inability to lock on after fire, period.

It's more complicated then you think.

The missile can't just lock onto the first target it sees. It must not only communicate with the launching plane with datalink, it must also have a sufficiently accurate inertial navigation system onboard the missile so as to preserve the orientation of the reference frame of the launching aircraft, and calculate the displacement with respect to the lunching aircraft, so that when it receive lock on instructions from the launching aircraft, the missile's seeker will point to the same target as stated in the instruction.


In a dog fight, where targets and friendlies can to intermingled, and both friendlies and targets can make large angular movements with respect to the radial coordinate system centered around eith the missile or the launching aircraft in very short time. The challenges to a IR LOAL missile will be much greater those facing a LOAL medium range missile like the AMRAAM.

So you're suggesting that there's a limitation in communicating the inertial data from the launching aircraft to the missile, or a limitation in the missile's ability to figure out its own inertial frame of reference relative to the plane? I somehow find that hard to believe. Even if the problem exists now, I can't imagine it persisting throughout the lifetime of the J-20's service life.

 

[chuck4]

Yes, I think the problem of accurately retaining a inertial reference frame through high g maneuvers in a package that fits inside a 5 inch tube is not trivial. It has clearly been solved because LOAL short range IR missiles exist. But the Chinese may not be sufficiently close to state of the art in technologies critical for this purpose to garranty the j-20 won't have to use LOBL IR missiles for some time aft the Le enters service.


Also, the design of j-20 has to consider what weapon will be available when the plane enters service, not just what will become available before j-20 leaves service, in perhaps 50 years.

 

[latenlazy]

Yes, I think the problem of accurately retaining a inertial reference frame through high g maneuvers in a package that fits inside a 5 inch tube is not trivial. It has clearly been solved because LOAL short range IR missiles exist. But the Chinese may not be sufficiently close to state of the art in technologies critical for this purpose to garranty the j-20 won't have to use LOBL IR missiles for some time aft the Le enters service.


Also, the design of j-20 has to consider what weapon will be available when the plane enters service, not just what will become available before j-20 leaves service, in perhaps 50 years.

Oh, I'm sure it's not trivial. I'm just not sure that China would be so behind. I'm not going to play the China copies everything card, but they have acquired a lot of knowledge about missiles by reverse engineering the ones they've bought. It's not like the the capabilities you're speaking about are new either. The US figured them out early enough, and I can't imagine the solution to the problem being that different from eject and fire SRAAMs that have been around for a while.

China isn't THAT behind in its electronics capabilities either. If they're not there yet a combination of espionage, and growing engineering capabilities will probably get them there soon enough. The J-20 will have to account for the weapons available upon entering service, but that isn't sometime in the near future either. Accelerated timeline or not, the J-20's induction is still years away.

 

[overscan (PaulMM)]

More photos and guesswork...

[attachment deleted by admin]

 

[Deino]

A new nearly front view !

 

[overscan (PaulMM)]

Better, I think.

 

[Mat Parry]

Regarding the "China copies everything card" taken at face value this innovation would seem to show otherwise (unless this idea was lifted from elsewhere and we just haven't seen it disclosed before). I'm not optimistic but I'll do a patent search and post if anything pops out.
Assuming this is one of the first examples of China inventing in an aviation context, I would expect other nations would have similar "intel gathering capabilities" as China, so no doubt one of the Western alphabet agencies is well aware of the thinking behind this set up.

 

[overscan (PaulMM)]

Here's my rather crude sketch of how I think it works.

 

[chuck4]

Regarding the "China copies everything card" taken at face value this innovation would seem to show otherwise (unless this idea was lifted from elsewhere and we just haven't seen it disclosed before). I'm not optimistic but I'll do a patent search and post if anything pops out.
Assuming this is one of the first examples of China inventing in an aviation context, I would expect other nations would have similar "intel gathering capabilities" as China, so no doubt one of the Western alphabet agencies is well aware of the thinking behind this set up.

There is nothing wrong with copying. If the backward country try to reinvent each wheel, it will either take an inordinately long time to, or never, catch up. We are just alarmed that they are catching up so fast, so we disingenuously belittle their sound strategy to feel better.

 

[Mat Parry]

Yep fully agree, it's not just China, Even between major corperations in the west "Competitive Intelligence" is a highly valued tool. Of course nowadays the sources of competitor information is only ever openly published material.... ;D For example from published patents, the context of the patents and the names of the inventors you can map out discrete groups within an organisation and their main research interests, it's actually quite fun to do this for aerospace companies and you do find some surprising themes.

 

[Sundog]

The problem with copying is that most of the advanced tech is being developed in the U.S., therefore American taxpayers are paying for it. None of those countries develops near as much as the U.S., so the U.S. loses a hell of a lot more than it gains as a result. Then again, we did train many of their Aero-engineers, so this is what we get for doing that.

 

[Mat Parry]

I fear this may only be the start of our copying opportunities