J-20 5th Gen Fighter Thread V

[GreenestGDP]

Is this J-20 * 2013 still in ChengDu skyline ??

Source: HuanQiu.com

 

[Quickie]

Lower, actually.

We'll have to agree to disagree because without the wind tunnel / flight test data, no one can know for sure, short of an official announcement of the J-20's specs and capabilities.

Lower, actually.


At very high AOA, vertical stabilizers aren't going to do anything regardless of whether they are placed more forward or more aft. This is where the ventral fins come in.

It still does matter at high or very high AOA. The air stream should still be moving over the vertical stabilizers at high angle of AOA, and even at very high AOA, with the difference that now much more of the air-stream is now coming through the bottom of the aircraft

Furthermore, the small and fixed ventral fins won't be able to prevent the aircraft from yawing in a straight line flight (whether during a level flight, or during a steep climb at high AOA) due to any kind of changing external forces, and also can't be used to prevent the aircraft tail from yawing out during a right or left turn, since the ventral fins are not movable in the required direction and degree, not to mention its too small a surface area.

 

[by78]

A few more from 2016's latest flight:

 

[siegecrossbow]

A few more from 2016's latest flight:

Guess they are sticking with the black nozzles.

 

[by78]

Guess they are sticking with the black nozzles.

For now, at least.

 

[Air Force Brat]

We'll have to agree to disagree because without the wind tunnel / flight test data, no one can know for sure, short of an official announcement of the J-20's specs and capabilities.



It still does matter at high or very high AOA. The air stream should still be moving over the vertical stabilizers at high angle of AOA, and even at very high AOA, with the difference that now much more of the air-stream is now coming through the bottom of the aircraft

Furthermore, the small and fixed ventral fins won't be able to prevent the aircraft from yawing in a straight line flight (whether during a level flight, or during a steep climb at high AOA) due to any kind of changing external forces, and also can't be used to prevent the aircraft tail from yawing out during a right or left turn, since the ventral fins are not movable in the required direction and degree, not to mention its too small a surface area.

You will NOT find any firm data on an aircrafts manners in official spec sheets, further the Eng knows what he is talking about, the SAC bird has an additional control surface for pitch, and yes that does likely make it more effective, if draggier.

In addition at very high alpha, there is very little if any air flowing over the verts to push the nose either right or left, and YES those small vents are very effective at maintaining longitudinal stability at high alpha, that my friend is their only function, the verts are blocked by the wing and fuse??? jus simple physics bruda.

If you wish to discuss this in more detail, we should go to the aerodynamics thread??? perhaps the mods can help us? I am glad to see you are at least cogent and interested in these very important characteristics of the J-20, it is a very interesting and progressive aircraft in this realm. keep up the good work!

 

[Quickie]

In addition at very high alpha, there is very little if any air flowing over the verts to push the nose either right or left,

That would already be in the stall condition with the air stream completely separated from the wing surface. Under normal condition with no layer separation, the air stream should be close to the wing, and then go further downstream to the vertical stabilizers.

Really, it makes no sense and serves no purpose to have a high alpha design but then you lose control of the stabilizer. As an example, a jet fighter making a tight turn is already at a high alpha and at this instant it needs a fully effective vertical stabilizer to prevent its tail from yawing out of the turn. Without an effective vertical stabilizer at this critical moment to control the strong yaw force, the aircraft would just spin out of control.

I think I have enough of this. (Btw, it seems like nobody understands what I'm trying to explain. )

 

[latenlazy]

That would already be in the stall condition with the air stream completely separated from the wing surface. Under normal condition with no layer separation, the air stream should be close to the wing, and then go further downstream to the vertical stabilizers.

Really, it makes no sense and serves no purpose to have a high alpha design but then you lose control of the stabilizer. As an example, a jet fighter making a tight turn is already at a high alpha and at this instant it needs a fully effective vertical stabilizer to prevent its tail from yawing out of the turn. Without an effective vertical stabilizer at this critical moment to control the strong yaw force, the aircraft would just spin out of control.

I think I have enough of this. (Btw, it seems like nobody understands what I'm trying to explain. )

I understand what you're trying to say. I think the disagreement is semantic. One side presumes we're talking about flow just before critical alpha while the other presumes just after.

 

[Engineer]

We'll have to agree to disagree because without the wind tunnel / flight test data, no one can know for sure, short of an official announcement of the J-20's specs and capabilities.

I am simply going by what big shrimps said over the years.

It still does matter at high or very high AOA. The air stream should still be moving over the vertical stabilizers at high angle of AOA, and even at very high AOA, with the difference that now much more of the air-stream is now coming through the bottom of the aircraft

Through?! I hope I misunderstood you, but that's a physical impossibility. Consider what happens if air passes through the aircraft. The plane could not fly because no lift could be generated.

Furthermore, the small and fixed ventral fins won't be able to prevent the aircraft from yawing in a straight line flight (whether during a level flight, or during a steep climb at high AOA) due to any kind of changing external forces, and also can't be used to prevent the aircraft tail from yawing out during a right or left turn, since the ventral fins are not movable in the required direction and degree, not to mention its too small a surface area.

That's like saying wing can't generate lift because it is attached rigidly to the airframe.

There is vertical stabilizer, and then there is rudder. The two are not the same even though they are mounted at the same place. Vertical stabilizers, or in this case, ventral fins do exactly what you claimed they cannot do. They keep the aircraft from yawing through weathercock effect. External forces are naturally counteracted, hence the term "stabilizer" because such airfoils add stability. Rudder actually does the complete opposite, adding yaw moment where there is none to force the nose to point away from equilibrium.

Finally, ventral fins are smaller than traditional stabilizers because ventral fins are more effective.

Please, Log in or Register to view URLs content!

Really, it makes no sense and serves no purpose to have a high alpha design but then you lose control of the stabilizer. As an example, a jet fighter making a tight turn is already at a high alpha and at this instant it needs a fully effective vertical stabilizer to prevent its tail from yawing out of the turn. Without an effective vertical stabilizer at this critical moment to control the strong yaw force, the aircraft would just spin out of control.

Yes, that last part is exactly what happens, hence those other means to enhance directional stability at high alpha.

 

[AssassinsMace]

So what's the new thing under the wing on the fuselage behind the rear landing gear? It's not on earlier pics of the 2016.