J-20 5th Gen Fighter Thread V

[b787]

That's correct, and that distant coupled canard gives the J-20 an outstanding rate of "pitch transition", as its also a very long throw, allowing the canard to maintain lift in addition to the forward fuselage to a very high angle of attack. So as others here have stated, the distant coupled canard is the real secret to the J-20s very agile pitch transitions.

The philosophy configuration of J-20 is the sharp wing LEX will energize the delta much better than the canard will do. shaper the wing sharper the vortex. (i mean the angle of wing sweep) and the long couple canard will be used as a pitch canard or control canard with a dihedral to position the vortex above the wing.

So the canard is not a close couple canard but still generates a vortex. add the the ruddevators and you have kind of a triplane configuration reducing the size of the long couple canard and to some degree drag, thus improving the drag/lift ratio

 

[Jeff Head]

What do you guys think about this theory? Is it possible that the gunpod is mounted within the main bay?

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Extremely doubtful.

The gun would then extend into the bay and limit the ordinance load therein.

 

[Deino]

To admit I saw these images yesterday but did not think that t was something special ...

Can anyone confirm that yesterday two J-20s were delivered to PLAAF Cangzhou test and training base ??

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[b787]

Aren't inward-canting vertical stabilizers detrimental to maneuverability?

not necessarily but there are reasons why the J-20 has its vertical tails canted outward and the SR-71 inward. everything depends in two factors, its position respect the longitudinal axis and the vortex system position,on the SR-71 the fuselage is slim and the chines vortex system is not that far from the longitudinal axis, the SR-71 has its vertical fins mounted on the engines quiet far from the fuselage so the chines vortex system is between the chines and engines, canting them inward makes sense, on the J-20, the vortex system of the LEX and canard are farther from the fuselage, over the wing, thus canting them outward is needed.

A third factor is the lever arm distance from the longitudinal axis, the F-117 had early concepts with inward canted fins, by canting them outward, vertical fin reduction size was achieved and thus drag was reduced.

But stealth forces some compromises, canting the sides o the flat fuselage is also influencing the angle, thus they have to make a compromise between the vortex system needs, the distance needed for the lever arm highest effectiveness and the radar RCS.
J-20 has a broad fuselage thus canting them outward avoids the small all moving vertical tail from being blanketed by the fuselage wake turbulence, thus the J-20 has ventral fins to augment the longitudinal stability at high AoA and level flight

 

[Air Force Brat]

not necessarily but there are reasons why the J-20 has its vertical tails canted outward and the SR-71 inward. everything depends in two factors, its position respect the longitudinal axis and the vortex system position,on the SR-71 the fuselage is slim and the chines vortex system is not that far from the longitudinal axis, the SR-71 has its vertical fins mounted on the engines quiet far from the fuselage so the chines vortex system is between the chines and engines, canting them inward makes sense, on the J-20, the vortex system of the LEX and canard are farther from the fuselage, over the wing, thus canting them outward is needed.

A third factor is the lever arm distance from the longitudinal axis, the F-117 had early concepts with inward canted fins, by canting them outward, vertical fin reduction size was achieved and thus drag was reduced.

But stealth forces some compromises, canting the sides o the flat fuselage is also influencing the angle, thus they have to make a compromise between the vortex system needs, the distance needed for the lever arm highest effectiveness and the radar RCS.
J-20 has a broad fuselage thus canting them outward avoids the small all moving vertical tail from being blanketed by the fuselage wake turbulence, thus the J-20 has ventral fins to augment the longitudinal stability at high AoA and level flight

actually Master Siege is right here 787, the inward canted verts are in the "dirty air" of the aft fuselage, and they are much less effective. Your example of the SR-71 as opposed to the J-20 is actually very good, and you reach the right conclusions in your last paragraph, which contra-indicates your initial statement.

The SR-71 was NEVER intended to be an A2A platform that excelled at ACM, but was an interceptor, hence the tails were canted inward. The SR-71 was actually the first stealth fighter, and that was the genesis for the inward canted tails, less RCS. Now the SR-71 had sufficient longitudinal stability, but at the altitudes it operated, aerodynamics were somewhat dicey. To lose and engine at speed could very well cause a yawing moment that might not be recoverable?? and there were "controllability" issues.

The J-20 on the other hand was designed from the outset to compete with the F-22 and to excel at Air Combat Maneuvering, hence the outward canted tails, which also reduce rcs, but do in fact increase longitudinal stability, particularly in concert with the Ventral fins. Those outward canted tails/vents enable the J-20 to excel at low speed maneuverability, with outstanding longitudinal stability, and enable it to recover from vigorous post-stall maneuvering with-out OVT.

The F-117 was less than affectionately called the "wobbling goblin", a reputation that likely cropped up with the inward canted verts, in fact it was NOT intended to engage in ACM, but was instead a small, very L/O bomber. I would point you to the airshow out East where the Wobblin Goblin lost an outer wing panel, likely on the application of a healthy amount of aft stick. Lost an airframe, thankfully the pilot was able to punch out.

 

[Air Force Brat]

actually Master Siege is right here 787, the inward canted verts are in the "dirty air" of the aft fuselage, and they are much less effective. Your example of the SR-71 as opposed to the J-20 is actually very good, and you reach the right conclusions in your last paragraph, which contra-indicates your initial statement.

The SR-71 was NEVER intended to be an A2A platform that excelled at ACM, but was an interceptor, hence the tails were canted inward. The SR-71 was actually the first stealth fighter, and that was the genesis for the inward canted tails, less RCS. Now the SR-71 had sufficient longitudinal stability, but at the altitudes it operated, aerodynamics were somewhat dicey. To lose and engine at speed could very well cause a yawing moment that might not be recoverable?? and there were "controllability" issues.

The J-20 on the other hand was designed from the outset to compete with the F-22 and to excel at Air Combat Maneuvering, hence the outward canted tails, which also reduce rcs, but do in fact increase longitudinal stability, particularly in concert with the Ventral fins. Those outward canted tails/vents enable the J-20 to excel at low speed maneuverability, with outstanding longitudinal stability, and enable it to recover from vigorous post-stall maneuvering with-out OVT.

The F-117 was less than affectionately called the "wobbling goblin", a reputation that likely cropped up with the inward canted verts, in fact it was NOT intended to engage in ACM, but was instead a small, very L/O bomber. I would point you to the airshow out East where the Wobblin Goblin lost an outer wing panel, likely on the application of a healthy amount of aft stick. Lost an airframe, thankfully the pilot was able to punch out.

You note that canting the vertical stabs outward allowed them to be reduced in size??? wouldn't that imply that they were in fact much more effective??? of course it would! brat

 

[b787]

actually Master Siege is right here 787, the inward canted verts are in the "dirty air" of the aft fuselage, and they are much less effective. Your example of the SR-71 as opposed to the J-20 is actually very good, and you reach the right conclusions in your last paragraph, which contra-indicates your initial statement.

The SR-71 was NEVER intended to be an A2A platform that excelled at ACM, but was an interceptor, hence the tails were canted inward. The SR-71 was actually the first stealth fighter, and that was the genesis for the inward canted tails, less RCS. Now the SR-71 had sufficient longitudinal stability, but at the altitudes it operated, aerodynamics were somewhat dicey. To lose and engine at speed could very well cause a yawing moment that might not be recoverable?? and there were "controllability" issues.

The J-20 on the other hand was designed from the outset to compete with the F-22 and to excel at Air Combat Maneuvering, hence the outward canted tails, which also reduce rcs, but do in fact increase longitudinal stability, particularly in concert with the Ventral fins. Those outward canted tails/vents enable the J-20 to excel at low speed maneuverability, with outstanding longitudinal stability, and enable it to recover from vigorous post-stall maneuvering with-out OVT.

The F-117 was less than affectionately called the "wobbling goblin", a reputation that likely cropped up with the inward canted verts, in fact it was NOT intended to engage in ACM, but was instead a small, very L/O bomber. I would point you to the airshow out East where the Wobblin Goblin lost an outer wing panel, likely on the application of a healthy amount of aft stick. Lost an airframe, thankfully the pilot was able to punch out.

let me reply you on this, the SR-71 has podded engine nacelles, J-20 has conventional fuselage with buried engines in the fuselage, not on pods like SR-71 like the engines of SR-71.

Vertical fin has to bear torsional forces, so most fighter aircraft will have them on the fuselage like J-20 or F-22, but SR-71 has a strong engine pod, away from the main fuselage chine structure, these engine nacelles on Sr-71 can bear torsional forces and are far away from the main fuselage thus increasing the lever arm used for roll.
on the F-117 the vertical fin is over the longitudinal axis, and have blue inward canted fins were on the fuselage, this reduced the lever arm and were blanketed by the fuselage.

inward canted vertical fins are not worse or better it depends where you put them on the aircraft, but since wings get thinner at the tips, the torsional forces they can bear reduce, thus wingtips are usually small and without rudders and fixed and not movable, and therefore they are there to increase range rather than as vertical stabilizers

 

[Air Force Brat]

actually Master Siege is right here 787, the inward canted verts are in the "dirty air" of the aft fuselage, and they are much less effective. Your example of the SR-71 as opposed to the J-20 is actually very good, and you reach the right conclusions in your last paragraph, which contra-indicates your initial statement.

The SR-71 was NEVER intended to be an A2A platform that excelled at ACM, but was an interceptor, hence the tails were canted inward. The SR-71 was actually the first stealth fighter, and that was the genesis for the inward canted tails, less RCS. Now the SR-71 had sufficient longitudinal stability, but at the altitudes it operated, aerodynamics were somewhat dicey. To lose and engine at speed could very well cause a yawing moment that might not be recoverable?? and there were "controllability" issues.

The J-20 on the other hand was designed from the outset to compete with the F-22 and to excel at Air Combat Maneuvering, hence the outward canted tails, which also reduce rcs, but do in fact increase longitudinal stability, particularly in concert with the Ventral fins. Those outward canted tails/vents enable the J-20 to excel at low speed maneuverability, with outstanding longitudinal stability, and enable it to recover from vigorous post-stall maneuvering with-out OVT..

No need to resort to aerodynamic "gobble dee gook", lets just keep it simple, the inward canted tail is lowered into the dirty air on the aft fuselage, trust me, there is lots of "turbulent flow", the F-18 had problems with "vortex bursting" placing undo stress on the vertical stabs and causing buffeting. The SR-71 did indeed have inward canted tails, and while they were out of most of the turbulent flow of the fuselage, they would have been much more effective in the cleaner outboard flow.

 

[A.Man]

J-20 High Performance Video:

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[siegecrossbow]

J-20 High Performance Video:

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Deino beat you to this video by two days.