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

[thunderchief]

You recalled wrong then. Main advantage of 3D printing is weight reduction. From a post on this very board:

Here is the original

Please, Log in or Register to view URLs content!

.

Read the article , but those are wild claims , especially that you going to save up to 90% in material . Author is not aware that direct metal laser sintering does not give a "clean" crystal structure like traditional casting and that you sometimes need to increase tolerances to achieve same tensile strength . Also 3D printed part needs to be machine-milled afterwards . That doesn't say that 3D printing is not revolutionary technology (it is) , but actual weight savings in this case are around 100 kg , not 1000 as you assume . And even if it is true , F-22 would still hold significant T/W advantage over J-20 with AL-31 .

Mind you, the Concorde being a much bigger and sluggish aircraft can still supercruise at Mach 2.0. So, I wouldn't be so quickly to assert J-20 to be unable to supercruise with Al-31 engines.

Comparing apples and oranges . Concorde had turbojet engines . Turbojet engines don't get that much thrust with afterburners . In this case Rolls-Royce/SNECMA Olympus 593 had 140 kN dry thrust and 169 kN afterburner thrust (D/A coefficient 0.828 ) . AL-31 is turbofan with 74.5 kN dry ,and 122.58 kN with afterburner (D/A coefficient 0.608)

Not to mention Concorde had pencil shape optimized for speed and nothing else , while J-20 is a fighter with totally different requirements . Basically Concorde would lit up afterburners to get supersonic and with low drag and high dry power it would slowly de-accelerate crossing the Atlantic . Fighters like J-20 have larger drag coefficient and cannot just run straight . Because of that supercruise is a such a big deal .

 

[thunderchief]

Actually I think the Raptor can achieve supersonic at altitude strictly just on military power alone i.e W/O the use of afterburners.

Probably yes , but this is not that important - in real life F-22 would use afterburners to get supersonic as fast it could , and then use military power to maintain the speed for prolonged periods of time .

 

[drunkmunky]

did someone just say that 200 kg of weight is nothing?

ugh... the plane can do 7 g plus turns.... that's 1400 kg of torsional and gravimetric force....

 

[thunderchief]

did someone just say that 200 kg of weight is nothing?

ugh... the plane can do 7 g plus turns.... that's 1400 kg of torsional and gravimetric force....

I doesn't go that way Think about it , whole J-20 is somewhere around 17 000 kg . That would be a lot of force at 7g , but fortunately it is spread around . You would need to calculate pressure , longitudinal force , torsion etc ... at each point of interest . And then imagine what would happen if you sling two 500 kg bombs on your J-20

 

[Engineer]

Read the article , but those are wild claims , especially that you going to save up to 90% in material .

Yes, I read the article, which clearly stated weight saving as one of the main advantages, invalidating your claims.

Author is not aware that direct metal laser sintering does not give a "clean" crystal structure like traditional casting and that you sometimes need to increase tolerances to achieve same tensile strength . Also 3D printed part needs to be machine-milled afterwards . That doesn't say that 3D printing is not revolutionary technology (it is) , but actual weight savings in this case are around 100 kg , not 1000 as you assume .

The article says 40% weight reduction. So, using your figure and let say the total weight of Titanium parts on the F-22 is 4300kg, the actual weight reduced is around 1720 kg of weight. Even if the weight reduction is only 4%, the actual weight reduced is still 172 kg, higher than the 100 kg that you assumed. Whether 3D printing requires post processing has absolutely nothing to do with the weight reduction of the aircraft as a whole.

And even if it is true , F-22 would still hold significant T/W advantage over J-20 with AL-31 .

Comparing apples and oranges . Concorde had turbojet engines . Turbojet engines don't get that much thrust with afterburners . In this case Rolls-Royce/SNECMA Olympus 593 had 140 kN dry thrust and 169 kN afterburner thrust (D/A coefficient 0.828 ) . AL-31 is turbofan with 74.5 kN dry ,and 122.58 kN with afterburner (D/A coefficient 0.608)

Not to mention Concorde had pencil shape optimized for speed and nothing else , while J-20 is a fighter with totally different requirements . Basically Concorde would lit up afterburners to get supersonic and with low drag and high dry power it would slowly de-accelerate crossing the Atlantic .

Excuses. The fact is quite simple, and that is Concorde can supercruise at Mach 2.0 with lower thrust-to-weight ratio than a fighter such as F-22. In other words, thrust-to-weight ratio does not correlate with supercruise ability.

Fighters like J-20 have larger drag coefficient and cannot just run straight . Because of that supercruise is a such a big deal .

Flying straight has nothing to do with drag coefficient, and I fail to see how J-20 cannot fly straight.

 

[Air Force Brat]

Probably yes , but this is not that important - in real life F-22 would use afterburners to get supersonic as fast it could , and then use military power to maintain the speed for prolonged periods of time .

Yes it can, and yes it is important, supercruise saves fuel and wear and tear on your hot section, it also decreases your visual and heat signature, so requiring AB to accelerate to supersonic and then slowly decelerating is not supercruise, accelerating through and maintaining supersonic with-out AB is SUPERCRUISE, and yes it is important, as speed is life! brat

 

[Air Force Brat]

Were you responding to me or cyan? LOL I'm pro Raptor all the way. Even my avatar is a Raptor albeit a lesser threatening now and it AINT easy for a squid to admire the AF.


Our drill instructor was at the end of his rope: An airman’s ineptitude was driving him crazy. Getting in the airman’s face, he demanded, “Whoever told you to join the Air Force?!”

Snapping to attention, the airman proclaimed, “The Navy recruiter, Sir.”

—James Hetlinger, Webb City, Missouri

One of my parishoners was a retired Marine, he was in Korea and his brother Ehlbert wrote and asked Herb what branch of service he should join, Herb told Ehlbert to join the Air Force as they're the only ones not doing anything over here. Ehlbert ended up being a crack shot on the Air Force pistol team under old Bob Day who was the lead armorer. Kwai I was responding to the the fellows who presume that defense analysts are cry babies, just because big whup, the J-20 prototypes actually have weapons bays, I know you are also a Raptor fan, it will remain penultimate fifth gen, likely for my life time. brat LOL

You are also quite right about supercruise.

 

[thunderchief]

Yes, I read the article, which clearly stated weight saving as one of the main advantages, invalidating your claims.

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 .

The article says 40% weight reduction. So, using your figure and let say the total weight of Titanium parts on the F-22 is 4300kg, the actual weight reduced is around 1720 kg of weight. Even if the weight reduction is only 4%, the actual weight reduced is still 172 kg, higher than the 100 kg that you assumed. Whether 3D printing requires post processing has absolutely nothing to do with the weight reduction of the aircraft as a whole.

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 .

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 .

Excuses. The fact is quite simple, and that is Concorde can supercruise at Mach 2.0 with lower thrust-to-weight ratio than a fighter such as F-22. In other words, thrust-to-weight ratio does not correlate with supercruise ability.

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

Please, Log in or Register to view URLs content!

Please, Log in or Register to view URLs content!

Flying straight has nothing to do with drag coefficient, and I fail to see how J-20 cannot fly straight.

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

 

[thunderchief]

Yes it can, and yes it is important, supercruise saves fuel and wear and tear on your hot section, it also decreases your visual and heat signature, so requiring AB to accelerate to supersonic and then slowly decelerating is not supercruise, accelerating through and maintaining supersonic with-out AB is SUPERCRUISE, and yes it is important, as speed is life! 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 .

 

[kwaigonegin]

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 .

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 .




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

Please, Log in or Register to view URLs content!

Please, Log in or Register to view URLs content!

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

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.