J-20 5th Gen Fighter Thread IV (Closed to posting)

[plawolf]

Regarding the so often mentioned engine-issue/-question - as again in the Su-35-tread - I did this one ...



As far on what I read, what I learned from different sources (including Russian ones) and after some loooong observations and even more discussion with friend I came to the conclusion ... it IS the AL-31FN !!!

I remember a close up picture where someone compared the internal structure of the engines in the J20 to AL31s, and they were identical and significantly different from the internal structure of the WS10A. That, more than anything, convinced me that the J20 uses a variant of the AL31. Whether it's the AL31F, FN or a new specialist sub-variant is hard to say, but imo, the fact that it is an AL31 is undeniable.

The reason for the slightly different coloured afterburner flame I cannot say, but it is possible that that may be caused by overtuning to the AL31s to burn hotter to gain greater thrust at the expense of service life. But that would just be a guess.

 

[delft]

I thought yellow flames means incomplete combustion due to insufficient mixing or excess fuel.

 

[Air Force Brat]

Quite true. The real limiter here will be whether China can get an engine in the 140kn, 10:1 TW class like the F135.

Well the latest agreement in China Daily did seem to mention the F-117, bingo, you're in the ballgame, add OVT and your in Hog Heaven, this will be interesting to the max! Brat

 

[Air Force Brat]

I thought yellow flames means incomplete combustion due to insufficient mixing or excess fuel.

Quite right but the AB injects raw fuel into the AB section, allmost all US powerplants seem to have a red/yellow/blue flame, and in he case of F119 and F-135, not shortage of thrust...... So, a richer mixture runs MUCH COOLER! BRAT

 

[Quickie]

The reason for the slightly different coloured afterburner flame I cannot say, but it is possible that that may be caused by overtuning to the AL31s to burn hotter to gain greater thrust at the expense of service life. But that would just be a guess.

I believe the slight difference is due to the foggy weather in the J-20 picture. In contrast, the J-10 picture was taken in clear blue sky.

I thought yellow flames means incomplete combustion due to insufficient mixing or excess fuel.

IMO, ultimately the colour of the exhaust plume depends on its chemical composition and temperature. One can imagine a fuel that produces an orange flame even when the combustion is 100% complete.

 

[Scratch]

A generall observation I think I can make is that western fighters have a more yellowish AB plume, while russian jets have a more blueish one. The B-1 AB plume is also rather blueish actually, and Tu-22 has a really blue one. I seem to recognize that these tones go with bigger by-pass ratios the russion engines have when compared to western ones. The B-1's engines also have a bigger BPR then their fighter counterparts.
With a bigger BPR, there might be more oxygen readily available for a more complete combustion. Just a guess.

 

[leibowitz]

Well the latest agreement in China Daily did seem to mention the F-117, bingo, you're in the ballgame, add OVT and your in Hog Heaven, this will be interesting to the max! Brat

Heh. This sort of thing is a capability China would do better to have on an indigenous basis.

 

[Air Force Brat]

Heh. This sort of thing is a capability China would do better to have on an indigenous basis.

Roger that, but remember LockMart bought Yaks lift fan rights, and maybe the prototype aircraft, you lads make entirely to much of the indigenous deal, we used to refer to that as NIH or not invented here. Sometimes you have to pay for something you want, its not all about the deal, its about capability and if you have to buy it to get where you need to go, thats no big deal....get out the checkbook dudes?? Brat

 

[Air Force Brat]

A generall observation I think I can make is that western fighters have a more yellowish AB plume, while russian jets have a more blueish one. The B-1 AB plume is also rather blueish actually, and Tu-22 has a really blue one. I seem to recognize that these tones go with bigger by-pass ratios the russion engines have when compared to western ones. The B-1's engines also have a bigger BPR then their fighter counterparts.
With a bigger BPR, there might be more oxygen readily available for a more complete combustion. Just a guess.

I'll buy that, and Happy Easter, hope you got a chocolate bunny, Brat.

 

[MiG-29]

My point exactly! MIG-1.44 has a similar size and build to the J-20 and also employs a canard configuration. It also has internal weapons bay in the belly. Yet you don't hear the "experts" calling the MIG-1.44 a fighter bomber of pure interceptor (even those why say that the J-20 is a MIG-1.44)!

Those so-called experts also screw themselves up with their own arguments:



1. The J-20 must be a fighter-bomber. (what about the dedicated SRAAM bays and shallow main bay?)
2. That means it must be an interceptor that can't turn. However, it also employs DSI so it can't go faster than MACH 2.

You see! They don't even know what they are talking about half the time. As long as they get to bash the J-20 everything is fine with them (even if their arguments conflict with one another).

There are a couple of things you do not consider in your assesment, first is the position of the landing gear in both designs, second is the position of the canards in both designs and third is the fact MiG-1.44 had Al-41s with TVC nozzles.

These differences are quiet important to consider at the moment of the type of optimization of an aircraft.

Another thing is the fact the MiG-1.44 had hinged ventral fins and the wings had trailing edge extensions hinged flaps between the fuselage and tail booms.


If you want to be fair, today`s aircraftt are not single role, they are multirole, but many solutions are related to avionics and weaponry.

J-20 is a multirole aircraft, as is PAKFA, however there are some aerodynamic features that shown some limitations and some optimizations based upon compromises.


As a last thought, i give you the puzzle, why the landing gear position in both fighters is different, why the canard position is also different and why the MiG-1.44 has an oval frontal cross section and J-20 a diamond one.

IF you are fair you can see the optimization, compromises, up to what level avionics will play a role in the multirole capability as well as weapons.

Otherwise i can not help you more

as an addendum.

Panavia tornado ADV and MiG-31 do use short range dogfight missiles and are interceptors, Panavia ADV used, ASRAAM AIM-132 and MiG-31 uses AA-8s Aphid, AJ-37 Viggen also was an interceptor but it used AIM-9