J-20 5th Gen Fighter Thread V

[delft]

Maybe the wrong place to discuss this specific detail, or perhaps I'm plainly wrong altogether. But in my (old fashioned?) understanding the higher pressure air from under the wing streaming around the tip to the top is exactly not what is creating lift, rather the exact opposite.
You do want to keep that pressure difference to experience lift. Hence all the effort with winglets and what not, on subsonic aircraft.
That vortex, by trying to balance that pressure difference is reducing lift and inducing additional drag.

Also, while the airstream tries to balance that pressure diffetential along all paths - and I'm not really firm as regards airfoil properties in relation to vortex creation - I was so far always under the impression that vortecies are created by airflow around the tip, and not primarily the trailing edge.

The lift is created by a vortex around the wing. Imagine a two dimensional airfoil in an air steam under an angle of attack. The speed of air on the suction side is larger than on the pressure side. If you subtract the free airflow you see a vortex around the airfoil, with something strange near the trailing edge.
At some higher angle of attack the flow will detach and the airfoil will stall. By creating vortices that run from some vortex generator, in the case of J-20 the canard surfaces, in the case of C-17 little half delta wings on the engine cowlings, in the case of humpback whales lumps on the leading edges of the breast fins, the stall is delayed to a higher angle of attack and the lift is increased at the price of some increase in drag. All engineering and all life is a matter of compromises.

 

[janjak desalin]

Are there any news about '2016' ... or at least some rumours ?? (...)

I'm thinkin' we'll see 2016 in 2016 and she'll be numbered as the first of an initial production batch.

 

[SpicySichuan]

Few New Photos of 2013
A Min Late, Deleted.

On the last image, what's that dangling thing right behind the weapons bay?

 

[kyanges]

On the last image, what's that dangling thing right behind the weapons bay?

It's a device to increase visibility on radar, IIRC. I forget the actual term for the device though...

 

[Deino]

On the last image, what's that dangling thing right behind the weapons bay?

That's a Luneburg lens mostly used by stealthy types in order to increase their RCS for for air traffic control and safety reasons.

We have already seen them on the J-20 ...


... and the F-22 carries such a device sometimes too:

 

[Air Force Brat]

The lift is created by a vortex around the wing. Imagine a two dimensional airfoil in an air steam under an angle of attack. The speed of air on the suction side is larger than on the pressure side. If you subtract the free airflow you see a vortex around the airfoil, with something strange near the trailing edge.
At some higher angle of attack the flow will detach and the airfoil will stall. By creating vortices that run from some vortex generator, in the case of J-20 the canard surfaces, in the case of C-17 little half delta wings on the engine cowlings, in the case of humpback whales lumps on the leading edges of the breast fins, the stall is delayed to a higher angle of attack and the lift is increased at the price of some increase in drag. All engineering and all life is a matter of compromises.

well put, Master Delft, and Master Scratch is right on, as per Bernoulli's Theorum as the velocity of a fluid increases the pressure decreases. Master Scratch in ground school we were given to imagine the the air molecule was bisected by the leading edge with 1/2 going over and 1/2 going under the wing, the curvature of the top of the wing meant the 1/2 going over the wing had to accelerate in order to meet the bottom 1/2 at the trailing edge, so the top of the wing having accelerated airflow has lower pressure. As the angle of attack is increased and airspeed is decreased the airflow toward the trailing edge separates or departs, and the wing is considered to have stalled??? The Canard, LERX, or LEVCON does create a vortices that is used to "energize" the airflow, and in the process helps to keep the flow "attached" and developing lift longer, it will soon "depart or separate" as well, but as long as that airflow is "attached" will make lift??? oversimplified Sunday afternoon explanation, but the real reason I have desired to see the blue smoke over the J-20 to actually be able to visualize that very complex airflow, grandkids calling-- brat out!

 

[delft]

OT

Master Scratch in ground school we were given to imagine the the air molecule was bisected by the leading edge with 1/2 going over and 1/2 going under the wing, the curvature of the top of the wing meant the 1/2 going over the wing had to accelerate in order to meet the bottom 1/2 at the trailing edge, so the top of the wing having accelerated airflow has lower pressure.

Of course they only meet at the trailing edge if the wing is infinitely thin. Otherwise the air on the suction side reaches the trailing edge before that on the pressure side. This increases the lift gradient over the theoretical thin wing case. And if that trailing edge is thick the difference in velocity on both sides induces a vortex there and this increases the lift gradient further. Remember how effective is the split flap.
On the other side there are viscosity effects: the lift gradient is lower at a lower Reynolds Number.

 

[Air Force Brat]

That's a Luneburg lens mostly used by stealthy types in order to increase their RCS for for air traffic control and safety reasons.

We have already seen them on the J-20 ...
View attachment 13499

... and the F-22 carries such a device sometimes too:

View attachment 13498

Outstanding article in Air Combat Monthly Deino, just a great overall compilation of solid information, and why I encourage these fine young gentlemen to only use good sources and to "always" guard your credibility, between TP, Jeff, BDPopeye and others the Sino Defense Forum has made a name for integrity and honest debate, well done Master Deino, good show!

I would ad that our other non-published posters push the bar up as well on a day to day basis, I would name names but you know who you are, and it would break my heart to leave even one of you out of this list of "extraordinary gentlemen", each of you have a place of honor and my deepest respect, not only as brothers, but true friends!

 

[Deino]

Ohhhh ... and now without that nasty watermark on it !!

 

[Jeff Head]

Very nice...let me clean up the watermarks that are there:

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The J-20 is certainly a beautiful bird!

That pic would make a heck of a wallpaper/background image.