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

[thunderchief]

Hmm I think both of you are saying the same thing just worded differently thus causing confusion amongst yourselves.
T/W, cd, shape, wing thickness and a dozen other factors ALL play a role in speed, supercruise availability etc.

Yes they do , but with given fifth generation fighter shape and materials you cannot achieve much with fourth gen engine like AL-31 .

 

[Air Force Brat]

Well , actually it does not save a lot of fuel , because you will need more time to accelerate to supersonic speed with just dry power . Lesser force , more time , same amount of energy (although afterburner wastes more energy then military power) . I might save some wear and tear on engine though .

But , in real life pilots would need every second . Therefore they would engage afterburner to quickly achieve speed and them continue to cruise on military power .

Actually it saves a tremendous amount of fuel, but go ahead and be pig-headed about it,,the aircraft is able to accelerate and maintain supersonic without engaging the AB, and that is supercruise, it was developed in order to function the aircraft with-out engaging AB, the real beauty of the F-22 is the ability to maintain supersonic cruise of approx. mach 1.8 for an extended period of time, rather than the full AB dash, which will very quickly deplete your prescious fuel, the guy hoping to run the F-22 down in Full AB will soon have to break-off, the F-22 will simply be GONE! The F-22 is a very "slick" aircraft, its top speed remains classified, but if it is offensive and enters the target area supersonic, delivers its weapons at supersonic and departs the area still supersonic, with-out AB, and as stealthy as it is, supercruise not only saves fuel, it saves aircraft and airmen, you prolly ought to lay off that Clint Eastwood movie?????
"real life", hummh??? brat

 

[kwaigonegin]

Yes they do , but with given fifth generation fighter shape and materials you cannot achieve much with fourth gen engine like AL-31 .

True, however even with a weaker engine those factors all still play the same role regardless of engine power. Besides we all know AL-31F is just a 'transitional' engine. I hope no one here is foolish enough to think AL31 would be the final engine for the J-20.

 

[plawolf]

Yes they do , but with given fifth generation fighter shape and materials you cannot achieve much with fourth gen engine like AL-31 .

Thrust isn't the only factor that affects speed and super cruise potential. To be sure, thrust is a big factor, but the drag coefficient is just as important if not more so. Strap some F119s on a 787 won't make it go supersonic, but the concord with a far lower TWR than conventional fighters managed super cruise with second generation airframe and engine technology.

The Typhoon, with fourth gen EJ2000s engines can achieve super cruise with limited payload, yet the F35 with its fifth gen F135 cannot, there is simply no categorical limitation or cut off that says a fourth gen engine cannot achieve super cruise while a fifth gen engine can.

A J20 with AL31s may not be able to super cruise on dry thrust alone, but it would not be unreasonable to think that with a slight boost from the afterburners to punch through the sound barrier, a J20, which would have an airframe optimised for super cruise, cannot maintain level supersonic flight with dry thrust alone.

 

[Engineer]

Typo on my part . I meant to say I have read the article , but I disagree with claims they have made , especially with 40% reduced weight of parts and 90% less material used .

Yes , real weight savings of the parts is around 5% (depends on shape of the part) . It is quite simple : let say you have traditional cast part and same 3D printed part . You will need to mill both of them to achieve required dimensions and tolerances . But , you will have to mill cast part more , because it is thicker and casting cannot be that precise as 3D printing . You will have more waste with cast part and you will spend more energy and time . But , at the end , both parts would have same dimensions and weight (with reasonable tolerances) . Only place where you would save weight on 3D printed parts are some very thin parts and joints which cannot be cast . Therefore , when you prepare your casting , you would have to make them thicker . But this is not 40% ,it is somewhere in 5% range

The issue is reality is not that simple. With a complex part, such as one with a lot of concavities, the part made using traditional method would see welding of multiple parts together. A part made with joints is weaker than one made from a single piece, and must be designed to be bulkier from the start to account for the lost in strength. Your assumption suppose that the parts made by different methods would use the exact same design, but in reality the two methods would result in completely different designs. Moreover, even a 5% weight saving from your 4300 kg figure translates to a weight reduction of 215 kg. This is more than twice the amount of your 100 kg claim.

Btw , your 1720 kg is 8.73 % of F-22 (empty)weight . But AL-31 has just 71.63 % of F119-PW-100 power , so even that extreme and unlikely weight save would not be enough to compensate , especially if you load both planes with fuel and missiles .

That is entirely irrelevant since thrust-to-weight ratio does not correlate with ability to supercruise, and therefore does not support your conclusion.

Look at the shape of Concorde and the shape of F-22 . It is self explanatory :

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What is self explanatory is that the Concorde can still supercruise despite its lower thrust-to-weight ratio compared to F-22. This shows thrust-to-weight ratio does not support your claim that J-20 cannot supercruise with AL-31 engines.

J-20 is a fighter for God's sake It is designed to maneuver , not to fly straight from one city to another .

Maneuverability and flying straight are not mutually exclusive.

Do you expect from Concorde to pull 9g ? That is way F-22 and J-20 have a thicker wings and fuselage (relative to length )then Concorde .

This does not support your argument that lower thrust-to-weight ratio being an obstacle to supercruise.

 

[Engineer]

Yes they do , but with given fifth generation fighter shape and materials you cannot achieve much with fourth gen engine like AL-31 .

You claimed that J-20 cannot supercruise with Al-31 engines. You are now making your argument vague in an attempt to distract others from your originally flawed claims. It is not helping your argument in anyway.

 

[hardware]

official claim that J-20 capable of supercruise up to speed mach 1.2,(compare with F-22 of m. 1.9) was he refering to ws-10X or WS-15?

 

[siegecrossbow]

I don't really understand what the concern is about. According to Doctor Song's paper, the J-20's layout is designed to optimize high velocity flight and maneuverability even in the absence of advanced engines.The plane will certainly suffer performance penalties with an interim engine, but it'll hardly be the end of the world.

 

[latenlazy]

official claim that J-20 capable of supercruise up to speed mach 1.2,(compare with F-22 of m. 1.9) was he refering to ws-10X or WS-15?

Where'd you get that information?

 

[hardware]

info was posted on wmf,probably around mid-january 2012.