Aerodynamics thread

[Inst]

The scope of the intended discussion was when the J-20 would receive Chinese TVC engines. My view is that at least the initial variants won't be TVC, and that it would take 2-3 years.

The disagreement is over whether the J-20 would benefit from TVC. My argument is that TVC isn't just for post-stall maneuvering; it's useful for any kind of instantaneous turn in general by allowing the aircraft to pitch quickly, as well as to vector thrust in a desired direction, accelerating the turn. Post-stall is merely the flashiest application of TVC.

 

[Brumby]

The scope of the intended discussion was when the J-20 would receive Chinese TVC engines. My view is that at least the initial variants won't be TVC, and that it would take 2-3 years.

The disagreement is over whether the J-20 would benefit from TVC. My argument is that TVC isn't just for post-stall maneuvering; it's useful for any kind of instantaneous turn in general by allowing the aircraft to pitch quickly, as well as to vector thrust in a desired direction, accelerating the turn. Post-stall is merely the flashiest application of TVC.

Cool. That means all discussions around the F-22 should stop because that would be outside scope.
I don't follow the J-20 program and the WS-15 engine development, but wouldn't a key indicator be whether the Chinese engine WS-15 comes with such capability? What we think is not important. If the Chinese thinks that TVC is important for the J-20, the clue would be from the engine that is under development.

 

[Inst]

Well, we're discussing whether or not the F-22 actually benefits from its TVC nozzles, because the counterargument from Engineer is that TVC is worse than useless. It's relevant because the F-22 is a case of an aircraft already operating with TVC.

Another line of argumentation is simply that the Su-35S ditched canards for TVC, even though the Su-30MKI had both TVC and canards. Which, according to Engineer, would be because the Russians are poopyheads or retards or whatever.

 

[b787]

The scope of the intended discussion was when the J-20 would receive Chinese TVC engines. My view is that at least the initial variants won't be TVC, and that it would take 2-3 years.

The disagreement is over whether the J-20 would benefit from TVC. My argument is that TVC isn't just for post-stall maneuvering; it's useful for any kind of instantaneous turn in general by allowing the aircraft to pitch quickly, as well as to vector thrust in a desired direction, accelerating the turn. Post-stall is merely the flashiest application of TVC.

i agree totally with you, turn rates are improved, there is plenty of literature to quote, that is already a fact TVC nozzles increase turn rates, reduce drag and reduce the surface area of control surfaces, Su-35 went from the early Su-27/T-10M to the Su-35S deleting the canards, this also impacts stealth
this is the evolution of thrust vectoring in the Flanker family, this an early non vectoring Su-27B

early flat nozzle with TVC nozzles

Early Su-35 without TVC nozzles but with canards

Su-37 with TVC nozzles and canards

Su-35S with TVC nozzlez but no canards

Basically the jet reduced its drag by adding TVC nozzles and it deleted the canards, entered production as the best flanker ever

 

[b787]

+-

Well, we're discussing whether or not the F-22 actually benefits from its TVC nozzles, because the counterargument from Engineer is that TVC is worse than useless. It's relevant because the F-22 is a case of an aircraft already operating with TVC.

Another line of argumentation is simply that the Su-35S ditched canards for TVC, even though the Su-30MKI had both TVC and canards. Which, according to Engineer, would be because the Russians are poopyheads or retards or whatever.

the Su-35S supercruises, and while they have not released its max speed, it could be Mach 1.1 to Mach 1.4, they needed a cleaner airframe than Su-30MKI or Su-30SM, so the improvements on the airframe were go back to the original canardless Su-27B of 1981 airframe with 117 engines

 

[Inst]

Okay, let me play with Engineer.

When I say that TVC reduces drag compared to canards, the point is cruising drag, not maneuvering drag. If the aircraft is moving level, putting canards in front will necessarily create drag. This is why the Su-35S doesn't have canards; the Russians decided that with TVC, the aircraft was already sufficiently maneuverable and that canards reduced the range of the aircraft.

Second, TVC creates little to no RCS increases when the aircraft is cruising and in proper orientation. Canards, on the other hand, tend to create RCS issues simply because they're in front. "Engineer" seems to think that TVC will cause diffraction from traveling waves more than canards, but in cruise mode, the diffraction is almost entirely covered by the fuselage of the aircraft and the diffraction actually reduces RCS.

When the aircraft actuates TVC, though, the nozzles may extend outside the blocking shape of the fuselage body, but that's not a given and it's dependent on the design of the aircraft.

Third, TVC is not just for rotation. Depending on the design of the aircraft and where the center of gravity lies, TVC can be used to directly change the vector of the aircraft simply because it's changing the direction of thrust. Some of the changed thrust vector may go into rotation, but not all of it.

Fourth, both TVC and canards are means of improving instantaneous turn rates. I misspoke when I said that canards can do TVC; what I meant is that canards do ITR. Canards are large control surfaces that can radically move the direction of air, and canards also help the aircraft to achieve control authority at high AOAs. TVC can do something similar; both by redirecting the direction of thrust and by rotating the aircraft, TVC can allow the aircraft to sustain a higher AOA than normal, while not necessarily stalling, giving it better ITR.

 

[Brumby]

Well, we're discussing whether or not the F-22 actually benefits from its TVC nozzles, because the counterargument from Engineer is that TVC is worse than useless. It's relevant because the F-22 is a case of an aircraft already operating with TVC.

To be fair, I don't think anybody is advocating the non utility of TVC except that it is not everyone's cup of tea because it is a cost benefit trade off. In the case of the F-22, there is obviously good reason(s) for its inclusion and any multi billion dollar program would require due consideration based on relevant data. Having said that, what is good for the F-22 is not necessarily good for other platforms. I would think it is a case by case consideration and not based on some general reasoning. For example, I was just reading a RAND report about the use of Link 16 in improving situational awareness in air to air combat which resulted in a 3 fold increase in kill ratio. This was based on 12,000 simulations.

Another line of argumentation is simply that the Su-35S ditched canards for TVC, even though the Su-30MKI had both TVC and canards. Which, according to Engineer, would be because the Russians are poopyheads or retards or whatever.

I don't remember seeing that piece.

 

[Inst]

@Brumby: Engineer literally said that TVC is useless; note my reply to AFB, as well as his previous statement.

Engineer also said that the Russians are backwards in aerodynamics, which isn't true. The PAK-FA, despite its failings, is highly sophisticated, and unlike the F-22, it deliberately puts its engines off-center, sacrificing some thrust, to enhance the effectiveness of its TVC. What's more, the PAK-FA innovates with LEVCONs.

Engineer is showing his bias when he emphasizes my statement that LEVCONs provide less control authority than canards, without explaining why the Russians chose LEVCONs over canards, when they have canard experience from the Su-30 and the Su-37. Compared to LEVCONs, canards do provide more control, but LEVCONs increase RCS less than canards do, and LEVCONs increase cruising drag less than canards do. The Russian innovation of LEVCONs is a good example of how the Russians remain in the game, aerodynamically, and it's something that China would be wise to adapt and copy, preferably with the J-31 project.

 

[b787]

@Brumby: Engineer literally said that TVC is useless; note my reply to AFB, as well as his previous statement.

Engineer also said that the Russians are backwards in aerodynamics, which isn't true. The PAK-FA, despite its failings, is highly sophisticated, and unlike the F-22, it deliberately puts its engines off-center, sacrificing some thrust, to enhance the effectiveness of its TVC. What's more, the PAK-FA innovates with LEVCONs.

Engineer is showing his bias when he emphasizes my statement that LEVCONs provide less control authority than canards, without explaining why the Russians chose LEVCONs over canards, when they have canard experience from the Su-30 and the Su-37. Compared to LEVCONs, canards do provide more control, but LEVCONs increase RCS less than canards do, and LEVCONs increase cruising drag less than canards do. The Russian innovation of LEVCONs is a good example of how the Russians remain in the game, aerodynamically, and it's something that China would be wise to adapt and copy, preferably with the J-31 project.

i agree but the LEVCON not only increases lift, but also is a control surface, look at the asymmetrically deflection and the Thrust vectoring nozzles and horizontal tail and you will see it is much more advanced than quoted, the jet modifies the aircraft lift asymmetrically

 

[dingyibvs]

None of these arguments is of any use without numbers. Exactly how much more control do canard offer? Exactly how much more stealth do LEVCONs offer? And how much of each is considered an even trade? Is 10% more maneuverability worth 10% larger RCS? Or is it worth 1000%? It doesn't even need to be exact, just rough estimates will do.

Does any of you have answers to any of these questions? Because if you don't, all of you are just a bunch of fanboys using pseudoscience to justify your biases.