J-20... The New Generation Fighter III

@ Airforce Brat:

Personally I think that a second J-20 prototype probably won't appear until a sufficiently powerful engine appears. One could only do so much using the AL-31. Perhaps the WS-10 will be used as a stop-gag measure until the WS-15 is ready.

Good News and Bad News.

The good news is that the wingspan is about 13 meters. The bad news is that the J-20 is about 18.7 meters long, if you go by satellite photos and use the J-10 to compare, using the J-10 wingspan as a measuring stick. This results in 64.7m^2 wing area. On a 25k combat weight, this translates to a mediocre 386 kg / m^2. On a 30000 kg combat weight, this translates to a 463 m^2. Even if you add in the canards, a 70 m^2 on 30000 kg only gives you 428 kg / m^2.

Wing loading is pretty severe on this fighter. Hopefully the Rafale-lite config can cancel this out.

You cannot do simple minded wind loading calculation with aircraft that uses vortex generators such as LERX and canard -- vortex wash over the wing will increase the lift.

that only further points to j20 being optimized for supersonic performance and manouvering at transsonic and supersonic speeds, like the eurofighter. small wing loading is more important if a fighter is optimized for subsonic manouvers and dogfighting at sustained turn rates. The philosophy of newer fighters like Typhoon and f22 is more geared towards greater speeds and high instantenuous turn rates. J20 fits there quite nicely.

Totoro said:

that only further points to j20 being optimized for supersonic performance and manouvering at transsonic and supersonic speeds, like the eurofighter. small wing loading is more important if a fighter is optimized for subsonic manouvers and dogfighting at sustained turn rates. The philosophy of newer fighters like Typhoon and f22 is more geared towards greater speeds and high instantenuous turn rates. J20 fits there quite nicely.

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Raptor has very high sustained rate of turn (around 30 degrees per second) as well. I think it comes down to engine power.

Inst said:

Good News and Bad News.

The good news is that the wingspan is about 13 meters. The bad news is that the J-20 is about 18.7 meters long, if you go by satellite photos and use the J-10 to compare, using the J-10 wingspan as a measuring stick. This results in 64.7m^2 wing area. On a 25k combat weight, this translates to a mediocre 386 kg / m^2. On a 30000 kg combat weight, this translates to a 463 m^2. Even if you add in the canards, a 70 m^2 on 30000 kg only gives you 428 kg / m^2.

Wing loading is pretty severe on this fighter. Hopefully the Rafale-lite config can cancel this out.

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Do one for the F-22. I'm still suspicious about the way in which they calculate wing area (I suspect at least for the F-22 they didn't just take the wings but the body in between)

siegecrossbow said:

One thing I don't understand is why they aren't using the rear control surfaces to do anything during a turn.

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IMO, using the canards in the turn maneuovre introduces less trim drag than if the large tail control surfaces are used. This is different from the case during landing when the tail control surfaces are used to generate lift at low speed and trim drag contributes to the overall braking force.

latenlazy said:

My guess is the air frame is generating so much lift it doesn't need to?

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the maximum lift config would probably look like this (take off and landing config) :

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same like siege, also wonder what the trailing edge is (not) doing
can't get my head around this picture, the more i look at it the more confusing

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Maybe this is just my imperfect areodynamics understanding, but for delta canards at least, I always thought that for sustained turns, only the leading edge flaps are used, whereas the trailing edge flaps are more reserved for things like roll or instantaneous stuff.

I certainly cannot remember seeing a picture of any delta canard using their trailing edge flaps for a hard sustained turn, and a quick yahoo image search didn't yield any either.

Here is a snap of the Typhoon during a hard turn. Notice the nice flat training edge flaps.



And here is one of a Rafale about to go into a roll. Notice the different deflections on the trailing edge flaps.



Just while I was at it, here is a picture of an F16 turning hard. Again, no use of the trailing edge flaps.

AFAIK, trailing edge is rarely changed during manouvers, except for pure deltas which don't have any other options, because it screws up the lift. That is precisely why pure deltas have fairly bad sustained turn rates - because their lift keeps dropping during the turn as their control surfaces screw up the airflow over the wing. delta canards and conventional layout planes don't need to do that.