Chengdu J-20 pictures, analysis and speculation Part II

[sferrin]

The simple answer is that the J-20 is optimized for supercruise where as the F-22 isn't, as it's designed to supposedly do everything well. Unfortunately, the F-22s fuel fraction was marginal to begin with, you want a fuel fraction greater than .25 for a supercruise fighter, but due to weight increases the F-22 is now below that number. Providing the Chinese were able to control the weight of their aircraft well it should prove to be a very capable supercruise fighter if they can get engines up to the task..

So the J-20 being optimized for supercruise means it can't manuever? Wut?

 

[Kryptid]

How are you calculating the wing area? Are you just using the dimension of the wings, or are you including the fuselage area between the wings? If the former, are you doing the same with the F-22, or did you get pull that number from a reference? Regardless, good thorough work!I think we've tried to calculate the wing area of the F-22 before just using the wing dimensions and got results that didn't match the reference.

I used the 3-view available on Wikipedia. Probably a fan-made drawing. If one assumes a given length, it's fairly straightforward to calculate reference wing area (which does include the "wing" covered by the fuselage) if one has a drawing available. The F-22 wing area was pulled from Wikipedia as well (not extracted from a drawing).

 

[overscan (PaulMM)]

A closeup of the J-20 engine exhausts shows them to be AL-31 exhausts, as I insisted from the beginning.

I believe they are likely to be higher thrust AL-31F derivatives from Salyut.


(Via CDF forum)

 

[chuck4]

I think there isn't serious doubt that AF-31s are fitted on the prototype most of the time. The only uncertainty was whether a different nozzle with LO serrated trailing edge, probably belonging to WS-10, was briefly fitted.

 

[Sundog]

So the J-20 being optimized for supercruise means it can't manuever? Wut?

My comment didn't get into any investigation of the maneuverability of either aircraft, so I understand your confusion. My comment was strictly about supercruise ability, as clearly written in the comment itself.

 

[JFC Fuller]

A closeup of the J-20 engine exhausts shows them to be AL-31 exhausts, as I insisted from the beginning.

I believe they are likely to be higher thrust AL-31F derivatives from Salyut.

AL-31FM1 is definitely a possibility, AL-31FM2 will apparently not start flight tests until this year so I would suggest that's out as even for a technology demonstrator it wouldn't be mature enough. The other alternatives would be that its a custom job done by Salyut for the Chinese (possibly in return for further AL-31FN orders) or the Chinese diverted AL-31FNs from the J-10 programme and modified them for higher thrust- with reduced fuel efficiency and a shorter MTBO.

 

[chuck4]

A closeup of the J-20 engine exhausts shows them to be AL-31 exhausts, as I insisted from the beginning.

I believe they are likely to be higher thrust AL-31F derivatives from Salyut.

AL-31FM1 is definitely a possibility, AL-31FM2 will apparently not start flight tests until this year so I would suggest that's out as even for a technology demonstrator it wouldn't be mature enough. The other alternatives would be that its a custom job done by Salyut for the Chinese (possibly in return for further AL-31FN orders) or the Chinese diverted AL-31FNs from the J-10 programme and modified them for higher thrust- with reduced fuel efficiency and a shorter MTBO.

I wonder why Russians do not use their engine leverage over the Chinese to force more concessions from the Chinese in the area of purchases of large number of complete aircrafts.

 

[quellish]

As far as stealth, i would even say the J-20 is Stealthier than the Sukhoi T-50.

No, and they are designed for different threats. This is like saying the F-22 is stealthier than the B-2.

 

[Sundog]

I don't know if you guys already saw these. Some nice close up pictures at the link. Those of you at CDF probably have already.

http://news.xinhuanet.com/english/photo/2013-01/17/c_132108052.htm

 

[chuck4]

I wonder what sort of actuator arrangement they used to facilitate plus minus 85 degree deflection on those canards, provided the canards can deflect as much up as down. Also there are no big bulges or fairing above to accommodate a linear actuator and pivot sweep arms to provide moment arm for the actuators. Must be some sort of rotary actuator.

 

[Sundog]

I wonder what sort of actuator arrangement they used to facilitate plus minus 85 degree deflection on those canards, provided the canards can deflect as much up as down. Also there are no big bulges or fairing above to accommodate a linear actuator and pivot sweep arms to provide moment arm for the actuators. Must be some sort of rotary actuator.

The actuator could easily be positioned below the canard.

 

[Sundog]

The "new" engine. Any ideas, as I haven't been following the powerplant choices too closely. Indeginous Chinese design, or Russian?

http://alert5.com/wp-content/uploads/2013/03/578415_10151478128839043_1735289026_n1.jpg

 

[chuck4]

I wonder what sort of actuator arrangement they used to facilitate plus minus 85 degree deflection on those canards, provided the canards can deflect as much up as down. Also there are no big bulges or fairing above to accommodate a linear actuator and pivot sweep arms to provide moment arm for the actuators. Must be some sort of rotary actuator.

The actuator could easily be positioned below the canard.

Linear actuators would be very ineffecient if the canards can deflect up and down by 85 degrees around a pivot. At extreme of deflection the moment arm of the linear actuators would be almost nothing, and they would be excerting their force in a direction almost orthogonal to the desired direction.

 

[latenlazy]

The "new" engine. Any ideas, as I haven't been following the powerplant choices too closely. Indeginous Chinese design, or Russian?

http://alert5.com/wp-content/uploads/2013/03/578415_10151478128839043_1735289026_n1.jpg

Uh. No. That's still the old engines, AL-31.

 

[overscan (PaulMM)]

Yep, still AL-31.

 

[chuck4]

Is it possible to estimate the intended thrust of J-20's ultimate engine from the size of the intake on the prototype and thus the flow rate of the engine? Admittedly the size of the intake could change during production, but they may not have customized the intake to a temporary engine, and the intake may represent the intended production size.

 

[latenlazy]

Is it possible to estimate the intended thrust of J-20's ultimate engine from the size of the intake on the prototype and thus the flow rate of the engine? Admittedly the size of the intake could change during production, but they may not have customized the intake to a temporary engine, and the intake may represent the intended production size.

I don't think so. Too many other variables, like the temperature of the combustion chamber.

 

[sferrin]

Is it possible to estimate the intended thrust of J-20's ultimate engine from the size of the intake on the prototype and thus the flow rate of the engine? Admittedly the size of the intake could change during production, but they may not have customized the intake to a temporary engine, and the intake may represent the intended production size.

And it's not always that clear-cut. Take the F-14 and F-15. One went from the 20k TF-30 to the 28k F110 with no intake change. The other went from a 23k F100 to a 30k F100 also with no intake change.

 

[chuck4]

Is it possible to estimate the intended thrust of J-20's ultimate engine from the size of the intake on the prototype and thus the flow rate of the engine? Admittedly the size of the intake could change during production, but they may not have customized the intake to a temporary engine, and the intake may represent the intended production size.

And it's not always that clear-cut. Take the F-14 and F-15. One went from the 20k TF-30 to the 28k F110 with no intake change. The other went from a 23k F100 to a 30k F100 also with no intake change.

F-14 and F-15's intakes were clearly overdesigned for their original engines to permit later upgrades. But can one establish an upper limit to how much thrust any engine of a given state of technology, sucking through those intakes, and operating normally could possibly generate?

If one could do that with F-14 and F-15, one ought to be able to do it more easily with the J-20 because:

1. J-20 probably has a fixed inlet because it is stealthy. So inlet maximum massflow is probably easier to estimate.

2. If the J-20 is indeed optimized to supercruise, as its length suggests, whatever engine it uses ought to be closer to a pure turbojet than the F100 or F110. As a result, there is less room for the engine thrust limit to be effected by the bypass ratio of the engine. So there would be fewer variables that could upset maximum thrust estimates besides intake mass flow and turbine inlet temperature.

 

[Trident]

And it's not always that clear-cut. Take the F-14 and F-15. One went from the 20k TF-30 to the 28k F110 with no intake change. The other went from a 23k F100 to a 30k F100 also with no intake change.

Both have variable intake geometry (capture area and bypass, respectively) which allows a measure of adaptation to a new engine with different airflow requirements without hardware changes, simply by matching the scheduling of aforementioned features appropriately. In the F-14's case, there's also the fact that the inlets were actually sized for an engine much closer to the eventual F110 than the (notionally interim) TF30s it got stuck with for so long.
A better example is probably the Eurofighter Typhoon, which went from a high bypass ratio interim engine (RB.199) in the early prototypes to a low bypass ratio power plant (though with considerably more thrust), despite fixed intakes.

 

[latenlazy]

Is it possible to estimate the intended thrust of J-20's ultimate engine from the size of the intake on the prototype and thus the flow rate of the engine? Admittedly the size of the intake could change during production, but they may not have customized the intake to a temporary engine, and the intake may represent the intended production size.

And it's not always that clear-cut. Take the F-14 and F-15. One went from the 20k TF-30 to the 28k F110 with no intake change. The other went from a 23k F100 to a 30k F100 also with no intake change.

F-14 and F-15's intakes were clearly overdesigned for their original engines to permit later upgrades. But can one establish an upper limit to how much thrust any engine of a given state of technology, sucking through those intakes, and operating normally could possibly generate?

If one could do that with F-14 and F-15, one ought to be able to do it more easily with the J-20 because:

1. J-20 probably has a fixed inlet because it is stealthy. So inlet maximum massflow is probably easier to estimate.

2. If the J-20 is indeed optimized to supercruise, as its length suggests, whatever engine it uses ought to be closer to a pure turbojet than the F100 or F110. As a result, there is less room for the engine thrust limit to be effected by the bypass ratio of the engine. So there would be fewer variables that could upset maximum thrust estimates besides intake mass flow and turbine inlet temperature.

And what if the J-20 is using an internal bleed system for mass flow control like the F-22, or some other novel inlet control system?

And it's not always that clear-cut. Take the F-14 and F-15. One went from the 20k TF-30 to the 28k F110 with no intake change. The other went from a 23k F100 to a 30k F100 also with no intake change.

Both have variable intake geometry (capture area and bypass, respectively) which allows a measure of adaptation to a new engine with different airflow requirements without hardware changes, simply by matching the scheduling of aforementioned features appropriately. In the F-14's case, there's also the fact that the inlets were actually sized for an engine much closer to the eventual F110 than the (notionally interim) TF30s it got stuck with for so long.
A better example is probably the Eurofighter Typhoon, which went from a high bypass ratio interim engine (RB.199) in the early prototypes to a low bypass ratio power plant (though with considerably more thrust), despite fixed intakes.

I thought the EF had variable intakes? The F-16 would be a good example.

 

[Trident]

I thought the EF had variable intakes? The F-16 would be a good example.

The Typhoon's intakes have moveable lips, but they aren't really supposed to change the capture area (resulting in a pronouced throat!) so much as act like airflow smoothing devices. Think of them as "LE flaps" for the inlet lip, to avoid flow separation at high AoA and/or low forward speed, when air may be arriving at an angle to the edge.
The F-16 is a poor example, as it did require the inlet to be enlarged to take full advantage of the F110

 

[chuck4]

And what if the J-20 is using an internal bleed system for mass flow control like the F-22, or some other novel inlet control system?
.

F-22's bleed system is manifest in the obvios serrated bleed doors on the upper fuselage surface. Don't see anything similar on the j-20. If j-20 use internal bleed, the air has to come out somewhere.

 

[chuck4]

.
A better example is probably the Eurofighter Typhoon, which went from a high bypass ratio interim engine (RB.199) in the early prototypes to a low bypass ratio power plant (though with considerably more thrust), despite fixed intakes.

I think we can assume j-20 would also get a low bypass engine eventually for the same reason. Fixed intake without visible flow control, low bypass engine of somewhere between f100 and f119 technology. Is that enough to put a narrow confidence band on maximum thrust?

 

[Sundog]

F-22's bleed system is manifest in the obvios serrated bleed doors on the upper fuselage surface. Don't see anything similar on the j-20. If j-20 use internal bleed, the air has to come out somewhere.

The serrated doors on top center of the F-22 are not bleed doors. They are "suck in" doors, or extra inlets, since having fixed inlets, the engines need another way to get the mass flow they need when it's sitting on the ground, since you don't get the ram affect sitting still/without airspeed. Not all planes with fixed inlets have them. It's a function of the mass flow rate required by the engine and what the intakes have been optimized for, which is usually the cruise design point.

 

[sferrin]

F-22's bleed system is manifest in the obvios serrated bleed doors on the upper fuselage surface. Don't see anything similar on the j-20. If j-20 use internal bleed, the air has to come out somewhere.

The serrated doors on top center of the F-22 are not bleed doors. They are "suck in" doors, or extra inlets, since having fixed inlets, the engines need another way to get the mass flow they need when it's sitting on the ground, since you don't get the ram affect sitting still/without airspeed. Not all planes with fixed inlets have them. It's a function of the mass flow rate required by the engine and what the intakes have been optimized for, which is usually the cruise design point.

They are bleed doors as well. Look at which way they open. They operate the same way as the doors on the XF8U-3 Crusader. Just a different way of accomplishing the same thing a VG intake does.

 

[latenlazy]

And what if the J-20 is using an internal bleed system for mass flow control like the F-22, or some other novel inlet control system?
.

F-22's bleed system is manifest in the obvios serrated bleed doors on the upper fuselage surface. Don't see anything similar on the j-20. If j-20 use internal bleed, the air has to come out somewhere.

I thought the dorsal exhausts on the J-20 might be bleed doors, but they're probably too small for that purpose huh?

 

[Sundog]

They are bleed doors as well. Look at which way they open. They operate the same way as the doors on the XF8U-3 Crusader. Just a different way of accomplishing the same thing a VG intake does.

I'll check it out. I would have thought the inlets on the F-22 would have been better matched, due to the amount of drag caused by dumping low energy air overboard. Thanks.

 

[Trident]

F-22's bleed system is manifest in the obvios serrated bleed doors on the upper fuselage surface. Don't see anything similar on the j-20. If j-20 use internal bleed, the air has to come out somewhere.

The serrated doors on top center of the F-22 are not bleed doors. They are "suck in" doors, or extra inlets, since having fixed inlets, the engines need another way to get the mass flow they need when it's sitting on the ground, since you don't get the ram affect sitting still/without airspeed. Not all planes with fixed inlets have them. It's a function of the mass flow rate required by the engine and what the intakes have been optimized for, which is usually the cruise design point.

They are bleed doors as well. Look at which way they open. They operate the same way as the doors on the XF8U-3 Crusader. Just a different way of accomplishing the same thing a VG intake does.

They are bleed doors as well. Look at which way they open. They operate the same way as the doors on the XF8U-3 Crusader. Just a different way of accomplishing the same thing a VG intake does.

I'll check it out. I would have thought the inlets on the F-22 would have been better matched, due to the amount of drag caused by dumping low energy air overboard. Thanks.

It's an interesting issue - as you say, you'd expect inlets as small as possible on an aircraft optimised for high speed cruise. Depending on what source you look at you'll find them labelled as one or the other, and even on photos it's not easy to tell - take this close up:
http://www.af.mil/shared/media/photodb/photos/080608-F-0154C-104.jpg
They look as though they'd open the way auxiliary inlet doors would, judging by how the edges overlap. Then again:
http://cdn-www.airliners.net/aviation-photos/photos/9/4/6/1790649.jpg

 

[sferrin]

They look as though they'd open the way auxiliary inlet doors would, judging by how the edges overlap. Then again:
http://cdn-www.airliners.net/aviation-photos/photos/9/4/6/1790649.jpg

I'd wager in that shot they're just open as part of the control surface test routine. Notice the horizontal stab and TVC are angled down and the rudders are toed out.

 

[chuck4]

I am not sure how louvre flaps that seem to be hinged at the front and swings outwards at the rear could appear to be suck in doors. It seems to me this arrangement is intended to operate with airflow coming from lower front through the flaps exiting upper rear, ie from inside of the plane up and back out of the plane.


Suck in doors would operate the other way, hinged at the front and swings inwards, such as those on av-8b's dumbo ear intakes. This way they operates best with airflow coming from upper front in through the door towards lower rear.


You can see the doors on f-22 only swings outwards because the trailing serrated edge of each flap overlaps the hinge of the flap behind it.

 

[Trident]

They look as though they'd open the way auxiliary inlet doors would, judging by how the edges overlap. Then again:
http://cdn-www.airliners.net/aviation-photos/photos/9/4/6/1790649.jpg

I'd wager in that shot they're just open as part of the control surface test routine. Notice the horizontal stab and TVC are angled down and the rudders are toed out.

Yes, that's what I meant: they appear to be power-operated bleed doors as opposed to spring-loaded suck-in doors - they open the wrong way to be the latter, at least on this picture.

 

[sferrin]

Yes, that's what I meant: they appear to be power-operated bleed doors as opposed to spring-loaded suck-in doors - they open the wrong way to be the latter, at least on this picture.

They are definitely powered. Flateric used to have a video of them in operation on his Youtube channel.

Here it is:
http://www.youtube.com/watch?v=BKZrr4WbGYo&[/quote]

 

[chuck4]

So f-22 has internal bleed that exits through dorsal bleed doors. J -20 probably doesn't as there areno visible doors. That ought to mean j-20's maximum thrust is more tightly constrained by inlet dimension than f-22. No?

 

[Trident]

Yes, that's what I meant: they appear to be power-operated bleed doors as opposed to spring-loaded suck-in doors - they open the wrong way to be the latter, at least on this picture.

They are definitely powered. Flateric used to have a video of them in operation on his Youtube channel.

Here it is:

Interesting, thanks for pointing that one out (& to Flateric for sharing it)![/quote]

 

[Deino]

An interesting info was posted today at the SDF regarding the J-20's flight requirements and esp. a comparison to its competitor from Shenyang (posted by "Engineer"):

This is written by one of SAC's engineers, which talked about their tri-surface design that competed with J-20. The most important piece of knowledge in the text is that PLAAF gave a requirement that China's forth-generation must be able to fly in 60° AoA. From this, we can see the capability of J-20.

CAC's proposal uses canard configuration right from the beginning, but SAC's original proposal was a traditional layout with LERX. The traditional layout was found to be uncontrollable between 40° ~ 45° AoA and didn't meet the requirement. So, SAC modified the design to include canards, resulting in a tri-surface layout that remained controllable up to 65° AoA. So once again, a configuration with canard proved to be superior to a traditional layout.

Deino

 

[Deino]

New video

http://www.youtube.com/watch?feature=player_embedded&v=lzlAwi6Qna0

with some discussion if at 4:26 the side door is open or not. However it seems as if there's something looking out of the fuselage and if I would not know better I would say it could be a launch rail of an AAM from the side bay !??

Deino

 

[JFC Fuller]

Having watched the video, 4.26 to 4.32 being the pertinent section, it certainly looks very much like there is a missile launch rail protruding from the starboard side weapons bay.

 

[Deino]

Agreed ... but I'm surprised why this rail is shown during landing ? ... since right after landing the bay is closed again.

Deino ???

 

[Grey Havoc]

Some sort of drag test?