Asoka
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a lot of folks here are saying canards increase the rcs and therefore it contributes to the fighter not being stealthy. it is true canards to increase the rcs, thats and fact, and they increase drag too.
people must understand one thing, purpose. what is it designed to do? now my opinion is that its a high endurance front line fighter/interceptor. this makes it perfect for use on the scs.
looking at the image below it is evident that its size would suggest its role in a high endurance interceptor/fighter
now since this is their first fifth gen fighter. this can also be seen as it being a test platform. developing something thats not critical as there are other platform that can do the job like the h-6. where as something like a full on air superiority fighter like the f22 and pak-fa is something that would be in the early stages of development. which i would assume would be fully Chinese including the engines. i suspect they have the ability to manufacture most of the engine components such as the main fan and the lp and hp compressors but the hp and lp turbines would be the problem and running them at cooler temperatures would increase their life but reduce their power. this being a fighter jet they need to be powerful so must run at much hotter temperatures but this greatly reduces the life of the turbines/engine.
The canards at the front are used 1.) to create vortexes to increase the lift, 2.) to balance the airplane to make it level, 3.) and to increase maneuverability when turning.
When placed close to the main wings, the canards do wonder to increase goals #1 and #2, but it also drastically increase drag during transonic and supersonic phase, so it's not good for supersonic flight. And it's also not so good at goal #2, to balance the plane because of the shorter moment arm.
When the canards are placed far away from the main wings, the drag effect is dramatically reduced, but the goal #1 and #3 of having a canard is also greatly weaken, but goal #2 is increased.
Aircraft designers have been bedeviled by this conflicting goals of incorporating the canards for some times. They know about advantages and short coming since the 60's.
Chinese designers solve this dilemma by using Leading Edge Extension between the canards and wings to create vortexes and use the far away placement of the canard to balance the plane.
Thus, it has predicted that J-20 will have excellent supersonic maneuverability because of its far away placed canards, and low speed maneuverability because of its leading edge extension like those of the F-18.
So far, the low speed, post stall maneuvers, made famous by the Flankers and Raptors, have not been demonstrated publicly by J-20.
One of the member of the design team has written a book which revealed one of the requirement of J-20 is that it must have the range to reach the islands of Japan or the first island chain without refueling, and able to reach Tokyo with just one refueling. So long range is a built-in feature like the Mig-31.
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