Aerodynamics thread
- Thread starter siegecrossbow
- Start date
Dude you just triple posted on the subject of a tailless J-20 with TVC...
My position on the matter is the same as it was when we last discussed it over on CDF a few months back, which is that while the idea of a tailless J-20 isn't inconceivable, there is no reason at this point to strongly suspect any such variant will emerge.
I think given the drastic impact removing the tails would have on the design's aerodynamics a tailless J-20 is inconceivable. It might as well be an entirely different plane.
I use the phrase "not inconceivable" in this case to mean the probability of it occurring is greater than zero... i.e.: not zero.
There's always the chance that some high ranking general in the Chinese Air Force might end up having a particular fetish for a tailless J-20 and enters the high brass around 2020 leading to a pursuit of such a project
Hyperwarp
Captain
Err.....for one, it has one of the most powerful engines fitted on to a modern fighter. Officially the max thrust of F119 is 156kN. In contrast the 117 in the PAK-FA can reach 147kN in an emergency mode. It probably ruins the life expectancy in that mode too. Plus, the 156kN for the F119 is the official value. I've heard chit-chat ranging from 160kN to 175kN.
And, just because the square nozzles have some inefficiencies, it doesn't mean that the overall design of the aircraft is inefficient and those square nozzle do have their advantages. The square nozzles allows for RCS optimization compared to the traditional circular nozzle.
An aircraft is a mass of compromises. Dr Song's article about the design of J-20, indeed it is more than ten years old, shows that the aircraft was designed to work without thrust vectoring. An aircraft that is to use thrust vectoring should be an entirely new design, an entirely new mass of compromises.
I use the phrase "not inconceivable" in this case to mean the probability of it occurring is greater than zero... i.e.: not zero.
There's always the chance that some high ranking general in the Chinese Air Force might end up having a particular fetish for a tailless J-20 and enters the high brass around 2020 leading to a pursuit of such a project
Maybe Inst will be that general
There is likely going to be a tailfinless J-20 one way or another; the question is whether it'll be designated a J-20 or given some kind of sixth generation designation.
It's the same way as with the twin-engined J-10. The project was rumored to exist, but it was canceled and the ultimate result was the twin-engine J-20, which shares many of the same aerodynamic principles as the J-10, but extends on them, is stealth, and is generally more capable.
As to whether the J-20 needs TVC; the J-20 was designed NOT to need TVC, but that won't stop the PLA from putting TVC on the J-20. Consider the Su-33 and the Su-30 series, for instance. These are canard Flankers, but the aircraft they were based on weren't designed as canard aircraft. Consequently, the canard is near-centerline compared to the plane of the main wing, which significantly decreases the benefits of canards to the extent that the Su-35 replaced canards with TVC.
The benefits of TVC are three-fold, first, the combination of TVC and canards enhances maneuverability somewhat above the LERX-Canard-LERX-Delta aerodynamic formula, simply because you now have more control surfaces. Second, TVC allows the J-20 to control trim without resorting to elevators or canards, allowing it to cruise or supercruise more stealthily. Third, TVC potentially enables at least experiments (recall American X-planes based on the F-22 and F-15 to test novel aerodynamics) with tailfinless, a trait that will be critical for a true sixth generation design. I would hope that these experiments lead to functional conversions; i.e, the last J-20s will be designed and programmed as tailfinless, and some of the later generation J-20s will be retrofitted to be tailfinless.
It's the same way as with the twin-engined J-10. The project was rumored to exist, but it was canceled and the ultimate result was the twin-engine J-20, which shares many of the same aerodynamic principles as the J-10, but extends on them, is stealth, and is generally more capable.
As to whether the J-20 needs TVC; the J-20 was designed NOT to need TVC, but that won't stop the PLA from putting TVC on the J-20. Consider the Su-33 and the Su-30 series, for instance. These are canard Flankers, but the aircraft they were based on weren't designed as canard aircraft. Consequently, the canard is near-centerline compared to the plane of the main wing, which significantly decreases the benefits of canards to the extent that the Su-35 replaced canards with TVC.
The benefits of TVC are three-fold, first, the combination of TVC and canards enhances maneuverability somewhat above the LERX-Canard-LERX-Delta aerodynamic formula, simply because you now have more control surfaces. Second, TVC allows the J-20 to control trim without resorting to elevators or canards, allowing it to cruise or supercruise more stealthily. Third, TVC potentially enables at least experiments (recall American X-planes based on the F-22 and F-15 to test novel aerodynamics) with tailfinless, a trait that will be critical for a true sixth generation design. I would hope that these experiments lead to functional conversions; i.e, the last J-20s will be designed and programmed as tailfinless, and some of the later generation J-20s will be retrofitted to be tailfinless.
@Hyperwarp: Do we know that the F119's rated thrust is pre-nozzle or post-nozzle? If it's post-nozzle, I rest my case; the F135 is a high-bypass F119 without TVC. It's not such a big improvement on the F119 engine; if you take the nozzle off the F119 you get the same thrust as a F135.
plawolf
Lieutenant General
Of the 3 main benefits of TVC, I think the only solid one is the stealth trim capability.
Yes, TVC can help agility, but how much so is very relative to the design of the fighter. Modern canards deltas like the J10 and Eurocanards can already turn extremely well, so much so that it's usually the pilot who is the limiting factor rather than the plane.
If your fighter can already turn fast enough to hit 9Gs with conventional controls, adding TVC won't really help agility much since even though the plane with TVC can theoretically turn better than without, in practice trying to do so would merely black out the pilot.
As for tailless, while some US early conceptual designs are indeed tailless, I just don't see it for air dominance fighters. The loss in controllability and corresponding agility would be too much, even with TVC and 9G+ manoeuvring from taking the pilot out. Just look at missiles - they are not limited to 9Gs, and usually come with TVC these days, but all retains conventional control surfaces and many have fixed streaks for stability.
The RCS benefits from taking off the vertical tails are...questionable. Yes it will make the RCS smaller, but will it make it smaller enough to make much appreciable difference to detection ranges and thresholds? Especially in light of modern advances in long wavelength ASEA radars?
Given recent advances in AI technology, I think 6th gen will potentially be the generation where AI starts entering the air to air combat arena.
Take the pilot out of the cockpit and you can instantly make any 4th gen+ fighter significantly more agile by removing the human 9G tolerance limit.
What has held true sir combat UCAVs back has been the lack of any AI who can take on humans in complex air combat maneurvers strategy and decision making. That and the lag inherent in long range communications making remote piloting impractical for air combat applications, where split seconds can be the difference between victory or defeat.
I had imagined twin sweaters becoming important for 5.5gen fighters, so a second pilo can ride in the backseat and remote control an air combat UCAV wingman close enough to the action that communication lag isn't a factor.
The UCAV would operate in front of the manned fighter wings to engage hostiles in both BVR and WVR, hopefully using their superior stealth and agility to clear the skies, removing the need for friendly manned fighters to gen involved.
But the manned fighters will still be more than agile enough to get stuck in themselves and mop up if the enemy survives the UCAV conslaught.
The problem with that concept has always been hard, blanket communications jamming by the enemy and/or hacking.
But if AI gets to a point where it can take on and beat humans in both BVR and WVR air combat, then having AI fighters would make a lot of sense over manned fighters.
People have been wondering when the last generation of manned air combat aircraft would come by, but I think the better questions is when the first generation of unmanned air to air combat drones will appear, and right now, my money is on 6th gen.
Yes, TVC can help agility, but how much so is very relative to the design of the fighter. Modern canards deltas like the J10 and Eurocanards can already turn extremely well, so much so that it's usually the pilot who is the limiting factor rather than the plane.
If your fighter can already turn fast enough to hit 9Gs with conventional controls, adding TVC won't really help agility much since even though the plane with TVC can theoretically turn better than without, in practice trying to do so would merely black out the pilot.
As for tailless, while some US early conceptual designs are indeed tailless, I just don't see it for air dominance fighters. The loss in controllability and corresponding agility would be too much, even with TVC and 9G+ manoeuvring from taking the pilot out. Just look at missiles - they are not limited to 9Gs, and usually come with TVC these days, but all retains conventional control surfaces and many have fixed streaks for stability.
The RCS benefits from taking off the vertical tails are...questionable. Yes it will make the RCS smaller, but will it make it smaller enough to make much appreciable difference to detection ranges and thresholds? Especially in light of modern advances in long wavelength ASEA radars?
Given recent advances in AI technology, I think 6th gen will potentially be the generation where AI starts entering the air to air combat arena.
Take the pilot out of the cockpit and you can instantly make any 4th gen+ fighter significantly more agile by removing the human 9G tolerance limit.
What has held true sir combat UCAVs back has been the lack of any AI who can take on humans in complex air combat maneurvers strategy and decision making. That and the lag inherent in long range communications making remote piloting impractical for air combat applications, where split seconds can be the difference between victory or defeat.
I had imagined twin sweaters becoming important for 5.5gen fighters, so a second pilo can ride in the backseat and remote control an air combat UCAV wingman close enough to the action that communication lag isn't a factor.
The UCAV would operate in front of the manned fighter wings to engage hostiles in both BVR and WVR, hopefully using their superior stealth and agility to clear the skies, removing the need for friendly manned fighters to gen involved.
But the manned fighters will still be more than agile enough to get stuck in themselves and mop up if the enemy survives the UCAV conslaught.
The problem with that concept has always been hard, blanket communications jamming by the enemy and/or hacking.
But if AI gets to a point where it can take on and beat humans in both BVR and WVR air combat, then having AI fighters would make a lot of sense over manned fighters.
People have been wondering when the last generation of manned air combat aircraft would come by, but I think the better questions is when the first generation of unmanned air to air combat drones will appear, and right now, my money is on 6th gen.
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