Official Chengdu J-20 Discussion Thread

[Chrisious]

Awang se

Assume we are referring to Syahbana's comment, have noted 'Hardware', 'ex lavi' etc. Interesting suppose it would be up to the sender to translate, which is why I've not bothered on this one. Pretty sure the moderators would step in if it was inappropriate in some way. Now what was this thread about?

 

[Feanor]

This thread is about a next-generation Chinese fighter plane, that is allegedly ready for testing. The debate is how advanced this fighter is, or rather can be, and how soon it will be ready.

 

[syahbana]

The Reply

This thread is about a next-generation Chinese fighter plane, that is allegedly ready for testing. The debate is how advanced this fighter is, or rather can be, and how soon it will be ready.

Ok, well, one day I would like to try to write in english, I bag your pardon, to all.
thanks.

 

[dingyibvs]

Experience is passed down through the institutions and the training, as well as being stored and codified in manuals, books, etc.

The point is that this collective volume of information creates a culture, and an environment. When taken outside of this context it becomes hard to interpret and use. Not to mention without this context the information itself is not enough to produce the desired results.

It's the same thing that you could technicaly take an African country, spend tens of billions on modern infrastructure and development, and then come back 10 years later and find it to still be a third world hellhole.

The thing you appear to be overlooking is that experience is not something that can really be stolen. It is an intangible asset that is built up by personnel over time and after exposure to situations.

I do not doubt that China (or most anyone else for that matter) could get their hands on US military training manuals. That might have guides for how to do certain things, fix or employ some weapons and systems, etc. However, there is an enormous difference between what one can get from a book, and reality. Particularly with something as significant as military operations. In the US, and many western countries there are of course significant numbers of new recruits and/or conscriptions. However, there is usually some group which forms the 'backbone' of a military where traditions, methods of operating, and experience is shared. For some militiaries, there is a professional officers corps, others rely upon the NCO's (non-commissioned officers) some use both. Whatever it is, there is usually some system or mechanism by which those with experience are able to share and pass on that experience to those following after them.

In the case of forces like the USAF, The lieutenants and junior captains of yesteryear who flew air superiority and strike missions are now majors and colonels who conduct flight planning for currents ops while drawing up doctrine to employ upcoming systems. Those same majors and colonels will in latter years be the general officers in charge of theatres and other major commands and/or force elements.

There are also courses which officers at least will be run through to teach how certain types of things are to be conducted (at least at certain levels) like the Command and General Staff College, or the various Army, Air and Naval War Colleges. Much of the information from such courses is classified AFAIK, but still it is just theoretical unless there is some foundation upon which to use the knowledge.

Consider this. Assuming that China was able to successfully acquire the printed materials and tech sheets for the HARM, as well as the doctrine the US military uses for SEAD/DEAD missions and IADS roll-back operations. Assuming that China had a comparable weapon system, but little or no practical experience in employing the weapon, would China be successful in adapting US doctrine? IMO ultimately they would, and having the US doctrine available would likely allow China to accomplish their objectives and/or develop their own doctrine more quickly. But it would not be as efficient/effective or rapid as if Chinese forces went in already experienced with the weapon(s) in question.

-Cheers

Thanks for the answers! I think that it will be easier to play catch up than to be the pioneer, so it should take China less time to build up that experience due to having American experiences to learn from, but it won't eliminate the learning curve.

Also, after looking through some Chinese military forums, it appears that the most likely design for the Chinese plane is a delta-wing in-line canard design. So I kind of wonder, how come none of the U.S. planes have canards? The Chinese seem to be pretty enamored with it with the J-10 and now it seems the J-XX as well.

 

[Chrisious]

Due to the protracted time line and general 'balls up' of the EF don't think the US has had time to work out whether canards are a good thing or bad. Think there is a criss-crossing of design times between what the US has been doing and that of Europe. Given the time and cost of getting EF off the ground most of it's military customers are slightly sore, so good or bad is again difficult to judge. Think most of the problems were around political, financial and commercial interest in the project.

 

[Todjaeger]

Due to the protracted time line and general 'balls up' of the EF don't think the US has had time to work out whether canards are a good thing or bad. Think there is a criss-crossing of design times between what the US has been doing and that of Europe. Given the time and cost of getting EF off the ground most of it's military customers are slightly sore, so good or bad is again difficult to judge. Think most of the problems were around political, financial and commercial interest in the project.

I am not so sure that is true. Canards have seen use in a number of (mostly European) jets for some time. The recent European canard users have been the EF Typhoon, Dassault Rafale and Saab Gripen, but these are not the only ones. The Saab Viggen also features a canard, as did some Dassault Mirage variants, and Israeli versions of Mirage aircraft.

IMO the US just has a different design philosophy (note US fighters are not delta-winged) which makes a feature like canards less useful.

-Cheers

 

[Kilo 2-3]

I am not so sure that is true. Canards have seen use in a number of (mostly European) jets for some time. The recent European canard users have been the EF Typhoon, Dassault Rafale and Saab Gripen, but these are not the only ones. The Saab Viggen also features a canard, as did some Dassault Mirage variants, and Israeli versions of Mirage aircraft.

IMO the US just has a different design philosophy (note US fighters are not delta-winged) which makes a feature like canards less useful.

-Cheers

The US has been doing some research on canards and deltas with the X-31, so it isn't as if the technology has been totally ignored. However, I do agree with you that US design philosophy is not one which seems to place top priority on ultra-agility and/or canard-and-delta designs.

 

[Todjaeger]

The US has been doing some research on canards and deltas with the X-31, so it isn't as if the technology has been totally ignored. However, I do agree with you that US design philosophy is not one which seems to place top priority on ultra-agility and/or canard-and-delta designs.

There was also a test version of the F-15 which had canards circa ~1989, and there is a form of canard located on the B-1 bomber for stability. As I understand it, canards are only applicable for some airframes. For whatever reason, a delta-wing seems to benefit from canards than aircraft with vertical stabilizers.

-Cheers

 

[Chrisious]

J-11's

Slight update - looks like photos are coming out of new build J-11's in naval colours, Janes has a report, though quite a small photograph. Another is Global Times which is slightly clearer, don't have anything further to add myself.

 

[MiG-23MLD]

Thanks for the answers! I think that it will be easier to play catch up than to be the pioneer, so it should take China less time to build up that experience due to having American experiences to learn from, but it won't eliminate the learning curve.

Also, after looking through some Chinese military forums, it appears that the most likely design for the Chinese plane is a delta-wing in-line canard design. So I kind of wonder, how come none of the U.S. planes have canards? The Chinese seem to be pretty enamored with it with the J-10 and now it seems the J-XX as well.

I think it is too early to say it will have canards, there reason is many people posting on internet forums hardly have some basic knowledge of aerodynamics and sometimes even basic physics, most of them think canards are new or kind of revolutionary, the reality is canards are very old as old as powered flight, if it is true you can use canards on a stealth aircraft, in terms of limitations and trade offs canards usually offer the most difficulties to harmonize with stealth.
On aircraft like the Eurofighter and J-10 stealth is not the main factor on its aerodynamic configuration, the main factor influencing it, it is performance.
In the other hand in aircraft like the F-22 stealth is a big factor in the aircraft aerodynamic configuration; the main difficultines canards have are in shape and position, a canard requieres a position with respect the wing and a shape that offers the best lift and least drag, these requierements make canards more difficult to harmonize with stealth.
Both PAK FA and F-22 chose the use of tailplanes because it is easier to adapt stealth to a conventional configuration, on the T-50, LEVCONs are used, these offer some aerodynamic characteristics seen too in canards but without the disadvantages canards have.
Both designs see more advantages in tailplanes because they have the least trade offs in performance with respect stealth.

Are canards good? the answer will depend in the aircraft mission and requirements.

 

[latenlazy]

I think it is too early to say it will have canards, there reason is many people posting on internet forums hardly have some basic knowledge of aerodynamics and sometimes even basic physics, most of them think canards are new or kind of revolutionary, the reality is canards are very old as old as powered flight, if it is true you can use canards on a stealth aircraft, in terms of limitations and trade offs canards usually offer the most difficulties to harmonize with stealth.
On aircraft like the Eurofighter and J-10 stealth is not the main factor on its aerodynamic configuration, the main factor influencing it, it is performance.
In the other hand in aircraft like the F-22 stealth is a big factor in the aircraft aerodynamic configuration; the main difficultines canards have are in shape and position, a canard requieres a position with respect the wing and a shape that offers the best lift and least drag, these requierements make canards more difficult to harmonize with stealth.
Both PAK FA and F-22 chose the use of tailplanes because it is easier to adapt stealth to a conventional configuration, on the T-50, LEVCONs are used, these offer some aerodynamic characteristics seen too in canards but without the disadvantages canards have.
Both designs see more advantages in tailplanes because they have the least trade offs in performance with respect stealth.

Are canards good? the answer will depend in the aircraft mission and requirements.

Wouldn't canards sitting on the same plane as the main wing act like tailplanes but smaller? I don't know much about aerodynamics, but if that were the case there's the possibility that using a same-plane delta canard instead of a tailplane could serve as a weight reduction measure?

 

[MiG-23MLD]

Wouldn't canards sitting on the same plane as the main wing act like tailplanes but smaller? I don't know much about aerodynamics, but if that were the case there's the possibility that using a same-plane delta canard instead of a tailplane could serve as a weight reduction measure?

There are many myths about canards that you will find on the internet claimed by people who love the Eurocanards or J-10, this does not mean that canards are not useful, they are useful and in some configurations you can get outstanding aircraft.

If you look at the basics you will find that canards have advantages and disadvantages.
In modern fighter aircraft canards are used as vortex generators, it means as a way to increase wing lift at high AoA, in most cases are used on Delta wing aircraft, like the Rafale and J-10.
Canards are used also as pitch control, in this case they are very useful as a pitch up force in turns, this gives an aircraft excellent instantaneous turn rates, they can also be used as STOL devices reducing Take off or landing approaching speeds.
In the case of the Su-34 and B-1B, they are used as turbulance dampers at low altitude and high speed.
Now these are canard`s main advantages, the main disadvantage is they reduce wing lift at level flight, thus having more drag.

Shape and position are also constraigns and limits they have, the best position for a canard is above wing level, thus its low preassure vortex increases wing lift at high AoA.

The Shape is also very important, for an aircraft in order to reduce drag at level flight while using a canard , it needs a small high aspect canard with weak wingtip vortex downwash but this means it will generate less wing lift at high AoA due to the same weaker wingtip vortex.

If the canard needs to create more lift at high Ao A a big low aspect canard is used but this generate more drag at level flight.
canard wing distance is also important a closer position to the wing means more drag and less lift at level flight but better wing lift at high AoAs.

On aircraft with tailplanes you can use LERXes sometimes called wing strakes and LEVCONs to increase wing lift at high AoA, these wing strakes generate low preassue vortices like canards do therefore increasing wing lift at high AoA.
The LERX by its self can not be uses as a pitch control device, but if used on an aircraft with tailplanes that disadvantage does not exist.

The LERX does not generate downwash, and the same is for the LEVCON, reducing thus drag and wing size.

Canards also limit the max lift potential of the wing, this makes canards highly mission dependant, as you can see stealth aircraft have shape and position limitations that will impact an aircraft with canards in a greater way than one with tailplanes.
Now the use of thrust vectoring aids by reducing the pitch control tailplanes do thus reducing trimming drag and allowing the tailplanes to be used as roll devices.

In the T-50 you will find it has LEVCONs and LERXes, so these devices are increasing wing lift at high AoA as a canard would do but without the canard generated downwash.
In both the F-22 and T-50 you will find the use of thrust vectoring for pitch and yaw control.

So in my opinion i do not think the JXX will have automatically canards, most representations i have seen are early studies or fan art, could it use canards, yes it could, but it will be more difficult to achieve the same level of performance the T-50 has achieved without the use of thrust vectoring control anf i do not think it will represent a better solution, the T-50 is very advanced more than a simple canard delta wing concept might suggest to many J-10 enthusiasts.

 

[latenlazy]

If you look at the basics you will find that canards have advantages and disadvantages.
In modern fighter aircraft canards are used as vortex generators, it means as a way to increase wing lift at high AoA, in most cases are used on Delta wing aircraft, like the Rafale and J-10.
Canards are used also as pitch control, in this case they are very useful as a pitch up force in turns, this gives an aircraft excellent instantaneous turn rates, they can also be used as STOL devices reducing Take off or landing approaching speeds.
In the case of the Su-34 and B-1B, they are used as turbulance dampers at low altitude and high speed.
Now these are canard`s main advantages, the main disadvantage is they reduce wing lift at level flight, thus having more drag.

I thought that was more dependent on the configuration, shape, and position of the canard? I've read that non-static canards can be either used to improve either lift or drag depending on how they're configured.

Shape and position are also constraigns and limits they have, the best position for a canard is above wing level, thus its low preassure vortex increases wing lift at high AoA.

That's assuming the use of canards for max maneuverability though? What about as maneuverability assists or for lift?

The Shape is also very important, for an aircraft in order to reduce drag at level flight while using a canard , it needs a small high aspect canard with weak wingtip vortex downwash but this means it will generate less wing lift at high AoA due to the same weaker wingtip vortex.

Would a lifting body help resolve some of these issues?

If the canard needs to create more lift at high Ao A a big low aspect canard is used but this generate more drag at level flight.
canard wing distance is also important a closer position to the wing means more drag and less lift at level flight but better wing lift at high AoAs.

Wouldn't that still be less drag than larger tailplanes?

On aircraft with tailplanes you can use LERXes sometimes called wing strakes and LEVCONs to increase wing lift at high AoA, these wing strakes generate low preassue vortices like canards do therefore increasing wing lift at high AoA.
The LERX by its self can not be uses as a pitch control device, but if used on an aircraft with tailplanes that disadvantage does not exist.

The tradeoff is a canard which does both though. This seems to be a draw.

The LERX does not generate downwash, and the same is for the LEVCON, reducing thus drag and wing size.

I'm not sure, but I thought downwash is only created when the canard sites on a different plane than the main wing?

In the T-50 you will find it has LEVCONs and LERXes, so these devices are increasing wing lift at high AoA as a canard would do but without the canard generated downwash.
In both the F-22 and T-50 you will find the use of thrust vectoring for pitch and yaw control.

So in my opinion i do not think the JXX will have automatically canards, most representations i have seen are early studies or fan art, could it use canards, yes it could, but it will be more difficult to achieve the same level of performance the T-50 has achieved without the use of thrust vectoring control anf i do not think it will represent a better solution, the T-50 is very advanced more than a simple canard delta wing concept might suggest to many J-10 enthusiasts.

What's the difference between a movable LERXes and a canard sitting on the same plane as the main wing? Aren't they both just control surfaces that perform similar functions?

 

[MiG-23MLD]

I thought that was more dependent on the configuration, shape, and position of the canard? I've read that non-static canards can be either used to improve either lift or drag depending on how they're configured.


That's assuming the use of canards for max maneuverability though? What about as maneuverability assists or for lift?

Would a lifting body help resolve some of these issues?

Wouldn't that still be less drag than larger tailplanes?

The tradeoff is a canard which does both though. This seems to be a draw.

I'm not sure, but I thought downwash is only created when the canard sites on a different plane than the main wing?


What's the difference between a movable LERXes and a canard sitting on the same plane as the main wing? Aren't they both just control surfaces that perform similar functions?

To understand canards we first have to understand they are wings, as a wing they have trailing edges, at the end of any trailing edge the upper wing`s low preassure and the lower wing`s high preassure meet, this creates the downwash, at the tip of any wing you also have a place where the wing`s difference of preassure meet, this usually create downwash too, on straight wing or a very high aspect wing this is a realtively weak vortex and therefore generates weaker downwash; the F-14 will sweep its wing at 16 degrees to make it straight basicly reducing its swept thus reducing the relative AoA of the wing and induced lift drag.
So the F-14 wing at 16 degree of swept does not need a higher AoA to achieve higher lift as a delta wing will, a higher AoA also induce low preassure wing separation and stall the wing at very high AoA.

A highly swept wing generates a strong low preassure vortex that moves diagonally with respect the aircraft flight path until its shed behind the wing.

Delta wings are this type of wing, so a highly swept LERX or canard generate stronger low preassure vortices than a a lower swept LERX or Canard.

Now, the canard low preassure vortex appears the strongest at high angles of attacks. it means that the canard vortex will only increase the wing lift above 5 degrees of AoA up to 40 degrees of AoA, however the canard downwash affects mostly at level flight or 0 degrees of AoA, this kills wing lift at level flight.

The LERXs has no trailing edge, thus it has no downwash.

Now a canard as a pitch control is positioned with the certer of gravity in a way it can balance the aircraft as it pitches up or down, this is achieved by increasing or reducing lift.
A LERX can not do that because it is part of the wing and it shares a common center of preassure with the main wing, therefore you need tailplanes or elevons.

The Canard and wing do not share a common center of lift , so they can be used as the tips of a seesaw or two boys each one seated at each extreme of the seesaw, with the center of gravity balanced by these two lifting surfaces basicly working like a fulcrum of a lever.
Now at turns, the wing is at higher AoAs so the canard aids the wing by increasing its lift as it is while landing or taking off.
The reason why canards are prefered over tailplanes is since they generate lift ahead of the center of gravity they generate a pitch up force so while turning the response is quicker than a tailplane this will increase Instantaneous turn rates.
the problem of this is most modern fighters with canards have delta wings, a delta as i told you before gets stalled faster than a straight wing because of the downwash it generates, if you are flying a F-14 you will set the wing at mid settings around 45 degrees or 16 at very low speeds so you wing has the lowest drag lift.

Most canard delta wing aircraft bleed energy fast in turns so the have a big difference in instantaneous turn rates and sustained turn rates.

Now if you possition the canard at lower levels than the wing the lower preassure vortices it generates goes under the wing thus reducing even further the wing lift, that is the reason canards are set above the wing level.

The canard generates a pitch up force so as control surface to pitch up the aircraft it is easier but not pitching down, so their size is reduced as a pitch up force but not as pitch down control, An aircraft with canards can use the wing elevons too as pitch devices like are used on a tailess delta wing. most aircraft have small canards to reduce drag. Because canards need to be very close to the wing like in the Rafale, so in order to reduce downwash a small size is recomended.

 

[latenlazy]

To understand canards we first have to understand they are wings, as a wing they have trailing edges, at the end of any trailing edge the upper wing`s low preassure and the lower wing`s high preassure meet, this creates the downwash, at the tip of any wing you also have a place where the wing`s difference of preassure meet, this usually create downwash too, on straight wing or a very high aspect wing this is a realtively weak vortex and therefore generates weaker downwash; the F-14 will sweep its wing at 16 degrees to make it straight basicly reducing its swept thus reducing the relative AoA of the wing and induced lift drag.
So the F-14 wing at 16 degree of swept does not need a higher AoA to achieve higher lift as a delta wing will, a higher AoA also induce low preassure wing separation and stall the wing at very high AoA.

A highly swept wing generates a strong low preassure vortex that moves diagonally with respect the aircraft flight path until its shed behind the wing.

Delta wings are this type of wing, so a highly swept LERX or canard generate stronger low preassure vortices than a a lower swept LERX or Canard.

Now, the canard low preassure vortex appears the strongest at high angles of attacks. it means that the canard vortex will only increase the wing lift above 5 degrees of AoA up to 40 degrees of AoA, however the canard downwash affects mostly at level flight or 0 degrees of AoA, this kills wing lift at level flight.

The LERXs has no trailing edge, thus it has no downwash.

Now a canard as a pitch control is positioned with the certer of gravity in a way it can balance the aircraft as it pitches up or down, this is achieved by increasing or reducing lift.
A LERX can not do that because it is part of the wing and it shares a common center of preassure with the main wing, therefore you need tailplanes or elevons.

The Canard and wing do not share a common center of lift , so they can be used as the tips of a seesaw or two boys each one seated at each extreme of the seesaw, with the center of gravity balanced by these to lifting surfaces basicly working like a fulcrum of a lever.
Now at turns, the wing is at a higher AoAs so the canard aids the wing by increasing its lift as it is while landing or taking off.
The reason why canards are prefered over tailplanes is since the generate lift ahead of the center of gravity they generate a pitch up force so while turning the response is quicker than a tailplane this will increase Instantaneous turn rates.
the problem of this is most modern fighters with canards have delta wings, a delta as i told you before gets stalled faster than a straight wing because of the downwash it generates, if you are flying a F-14 you will set the wing at mid settings around 45 degrees or 16 at very low speeds so you wing has the lowest drag lift.

Most canard delta wing aircraft bleed energy fast in turns so the have a big difference in instantaneous turn rates and sustained turn rates.

Now if you possition the canard at lower levels than the wing the lower preassure vortices it generates goes under the wing thus reducing even further the wing lift, that is the reason canards are set above the wing level.

The canard generates a pitch up force so as control surface to pitch up the aircraft it is easier but not pitching down, so their size is reduce as a pitch up force but not as a pitch down control, canards can use the wing elevons too as pitch devices like are used on a tailess delta wing. most aircraft have small canards to reduce drag. Bbecause they need to be very close to the wing like in the Rafale, so in order to reduce downwash a small size is recomended.

Ahh, I see. I've asked those questions numerous times and it's the first time someone explained it to me proper. Thanks a lot!

I've heard the J-xx might use a bigger lifting body than any other 5th generation design (with the top view basically making it look like a triangle). I wonder if that could counteract some of the potential lift problems a same plane canard could create. Conversely, I wonder if there's a way to make the canard sit above the plane and still make it stealthy.

 

[MiG-23MLD]

Ahh, I see. I've asked those questions numerous times and it's the first time someone explained it to me proper. Thanks a lot!

I've heard the J-xx might use a bigger lifting body than any other 5th generation design (with the top view basically making it look like a triangle). I wonder if that could counteract some of the potential lift problems a same plane canard could create. Conversely, I wonder if there's a way to make the canard sit above the plane and still make it stealthy.

no problem if you want i can recommend you a few webpages, in reality canards are not so difficult to understand but usually you will find many myths of half trues, perhaps the Chinse will include other technologies, if they are succesful that will show they have reached maturity as an aerospace power.
But in my opinion the smartest solution is the PAK FA

 

[Chrisious]

Just to keep the topic up to date, possibly been seen already.

[nomedia]http://www.youtube.com/watch?v=bPrLY566SUU&NR=1[/nomedia]

 

[SURB]

If the fighter jet is cruising and the canards are steady will it effect it's RCS?

I personally think that canards only increase the RCS when it's "flapping" so they shouldn't decrease a plane's level of stealth during cruise flight (when they are held level).

And what about something like retractable canards.I mean when you need them you can apply them as an option and whenever not required ,it just retracts and becomes part of the plane.Is it practical? (i never listened about it, just an idea came to my mind.)

 

[weasel1962]

Re:

If the fighter jet is cruising and the canards are steady will it effect it's RCS?

I personally think that canards only increase the RCS when it's "flapping" so they shouldn't decrease a plane's level of stealth during cruise flight (when they are held level).

And what about something like retractable canards.I mean when you need them you can apply them as an option and whenever not required ,it just retracts and becomes part of the plane.Is it practical? (i never listened about it, just an idea came to my mind.)

The concept of retractable canards is not new (more than a decade old with existing patents). There are design issues eg when the canards are in the process of retracting, how does the plane fly? At the same time, it may not be easy to optimise an airframe to perform safely with and without the canards.

Also, what happens if the canards get stuck. How to house them etc. When the optimum time to utilise the canard etc. The use is possible but a lot of issues to consider and test.

Any additional surface increases RCS. Aircraft like the typhoon may use software to calculate and control the surface to minimise RCS. Retracting it just to minimise RCS may not be beneficial when compared to the loss of flight control.

 

[gf0012-aust]

I personally think that canards only increase the RCS when it's "flapping" so they shouldn't decrease a plane's level of stealth during cruise flight (when they are held level).

That won't achieve anything. it assumes that other systems are only working on the perpendicular axis. that's impossible.

that would only achieve a partial effect if both planes were fixed on the same approach axis and bolted on the ground facing each other. it has no chance of working in the air