Aerodynamics thread
- Thread starter siegecrossbow
- Start date
Which is true to an extent, I love to argue. But we're both dealing with speculation.
One other thing to note. Consider the J-20 project. It is starting to become common currency that the J-20 was designed as an ASAP project; i.e, it's not supposed to produce the pinnacle of human fighter engineering for its era. Just from the Song Wencong document, we know that it was designed around limited Chinese engines. That's probably one of the reasons the J-20 came as such a surprise to the US defense establishment; I suspect the US was watching WS-15 maturity and they thought the J-20 couldn't fly without the WS-15.
Yet the aircraft was designed so it didn't need WS-15. The project goal was to bridge the stealth gap with an upgradable stop-gap. This is yet another reason the J-20 probably wasn't trialed with TVC; with TVC coming into maturity now, the earliest I can imagine TVC being ready for the J-20 would be around 2019. Yet without TVC, we are looking at an IOC either at the end of the year or sometime in 2017, a full year before Japan receives its F-35s. Think of the strategic benefits to such an approach!
That's why I think the Chinese didn't stuff TVC onto the initial J-20s; with their iterative build process, there simply wasn't any need to design the aircraft around a technology whose maturity would potentially hold up the entire project. It can occur as an upgrade later, or, as many of you think, it may end up being trialed with the outcome that it doesn't present a significant improvement to the combat capability of the aircraft, despite the greater costs.
One other thing to note. Consider the J-20 project. It is starting to become common currency that the J-20 was designed as an ASAP project; i.e, it's not supposed to produce the pinnacle of human fighter engineering for its era. Just from the Song Wencong document, we know that it was designed around limited Chinese engines. That's probably one of the reasons the J-20 came as such a surprise to the US defense establishment; I suspect the US was watching WS-15 maturity and they thought the J-20 couldn't fly without the WS-15.
Yet the aircraft was designed so it didn't need WS-15. The project goal was to bridge the stealth gap with an upgradable stop-gap. This is yet another reason the J-20 probably wasn't trialed with TVC; with TVC coming into maturity now, the earliest I can imagine TVC being ready for the J-20 would be around 2019. Yet without TVC, we are looking at an IOC either at the end of the year or sometime in 2017, a full year before Japan receives its F-35s. Think of the strategic benefits to such an approach!
That's why I think the Chinese didn't stuff TVC onto the initial J-20s; with their iterative build process, there simply wasn't any need to design the aircraft around a technology whose maturity would potentially hold up the entire project. It can occur as an upgrade later, or, as many of you think, it may end up being trialed with the outcome that it doesn't present a significant improvement to the combat capability of the aircraft, despite the greater costs.
Engineer
Major
That's something Russian arm industry and its fan boys are very guilty of.
Let see some evidence for that first. Most studies were done on traditional configuration, and not applicable for canard configuration.
People say that because they don't consider creeping wave. When that is factored in, then moving nozzle can impact RCS as well. So, people's premises that TVC doesn't produce any return forward of the aircraft is not strictly true to begin with.
The whole point is not to enter into stall, because stall takes energy out of the aircraft and is very bad. In that context, TVC is like having crutches for someone with a broken leg. Sure, that person can do fancy tricks like keeping both feet from touching the ground, but it is so much better not to be crippled to begin with.
It does not matter whether there is an impact. What matters is whether the impact breaks stealth. Given the aircraft is designed to have some freedom in orientation with respects to the enemy, the answer is no. In light of that, advocating how TVC being beneficial to stealth on the J-20 is no different than advocating a way to make a glass of water more wet.
I am not against researches to build up technology reserve. I also did not bring in MTBO to the discussion; you did. What I am saying is that the often repeated benefits of TVC are exaggerated and even non-existent. Take manoeuvrability for example, the F-22 is better off not using TVC.
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About TVC being "terrible", it's called an instantaneous turn. The difference between ITs and STs is that sustained turns can be held indefinitely, because the aircraft's thrust is counteracting the force of drag. ITs of any kind will start to bleed off energy as the aircraft's drag increases. TVC's issue is that it sacrifices thrust to achieve vectoring (thrust is vectored in the turn direction), but canard deflection to achieve TVC also increases drag as well, especially in high AOA regimes. However, that doesn't make instantaneous turns useless to pilots. The ability to rapidly point your nose at an opponent or change your direction in a WVR battle is useful, even if that results in energy bleed and the loss of speed. It's all about trade-offs.
The mistake the pilot is explaining in the video is that beginning pilots rely too heavily on instantaneous turn rate, not acknowledging that the energy loss from IT makes doing so dangerous. It is understandable, because while F-16s and F-15s, the aircraft they're coming from, have adequate instantaneous turn rates, they don't have the same high-AOA performance as Eurocanards so they're not experienced with how dangerous relying on your ITR can be.
As to whether TVC decreases stealth, you're joking, right? TVC has the potential to break traveling waves, true, but it breaks them at the rear end of the aircraft, which is better than breaking traveling waves at the front end of the aircraft, as some of the radar energy will be absorbed by the aircraft and its RAM on its return.
The drag argument is also absurdly specious. Compare the nozzles on the Su-30MKK and the Su-30MKI. One has TVC, the other doesn't. The nozzle sizes are almost exactly the same, meaning there's little difference in drag. Compare canards in the front, where you have large aerodynamic surfaces not only generating additional drag, but generating drag in a bubble ahead of the main wing, whereas LEVCONs and LERXes generate drag in a bubble connected to the main wing.
Also, you're joking, right? I'm not a Russian fanboy, I'm much closer to an American fanboy because the American R&D complex is, as everyone acknowledges, ahead of most of the world, and the US military industrial complex has done a reasonably good job at innovating ahead of all other sectors due to, in part, its superior funding. However, with Lockheed Martin screwing the pooch with the F-35, and with the rapid development of the Chinese aerospace sector, it's viable now for China to briefly come ahead of the United States with J-20 derivatives; we know that in many aerospace technologies, China is only 1-3 years behind the United States.
The "not-invented here" syndrome I am referring to is yours. The J-20 wasn't designed for TVC, so you go on to bash TVC, even though the US air superiority fighter uses it, and the US strike fighter without it is admitted to be an ACM turkey because it doesn't have TVC. The J-31 is expected to use TVC, and the PAK-FA is designed to exploit TVC in novel ways that the Americans hadn't yet thought of.
Thankfully for you, the PLAAF general staff doesn't share your myopia. The TVC technology is mature, and we can almost definitely expect to see the J-20 at least trying TVC technology. As I've said before, the Chengdu is in the unique position where it can combine mature TVC technology and canard technology on its latest fighter for exceptional maneuverability. By doing so, it stands a shot at having the premier air superiority fighter.
The mistake the pilot is explaining in the video is that beginning pilots rely too heavily on instantaneous turn rate, not acknowledging that the energy loss from IT makes doing so dangerous. It is understandable, because while F-16s and F-15s, the aircraft they're coming from, have adequate instantaneous turn rates, they don't have the same high-AOA performance as Eurocanards so they're not experienced with how dangerous relying on your ITR can be.
As to whether TVC decreases stealth, you're joking, right? TVC has the potential to break traveling waves, true, but it breaks them at the rear end of the aircraft, which is better than breaking traveling waves at the front end of the aircraft, as some of the radar energy will be absorbed by the aircraft and its RAM on its return.
The drag argument is also absurdly specious. Compare the nozzles on the Su-30MKK and the Su-30MKI. One has TVC, the other doesn't. The nozzle sizes are almost exactly the same, meaning there's little difference in drag. Compare canards in the front, where you have large aerodynamic surfaces not only generating additional drag, but generating drag in a bubble ahead of the main wing, whereas LEVCONs and LERXes generate drag in a bubble connected to the main wing.
Also, you're joking, right? I'm not a Russian fanboy, I'm much closer to an American fanboy because the American R&D complex is, as everyone acknowledges, ahead of most of the world, and the US military industrial complex has done a reasonably good job at innovating ahead of all other sectors due to, in part, its superior funding. However, with Lockheed Martin screwing the pooch with the F-35, and with the rapid development of the Chinese aerospace sector, it's viable now for China to briefly come ahead of the United States with J-20 derivatives; we know that in many aerospace technologies, China is only 1-3 years behind the United States.
The "not-invented here" syndrome I am referring to is yours. The J-20 wasn't designed for TVC, so you go on to bash TVC, even though the US air superiority fighter uses it, and the US strike fighter without it is admitted to be an ACM turkey because it doesn't have TVC. The J-31 is expected to use TVC, and the PAK-FA is designed to exploit TVC in novel ways that the Americans hadn't yet thought of.
Thankfully for you, the PLAAF general staff doesn't share your myopia. The TVC technology is mature, and we can almost definitely expect to see the J-20 at least trying TVC technology. As I've said before, the Chengdu is in the unique position where it can combine mature TVC technology and canard technology on its latest fighter for exceptional maneuverability. By doing so, it stands a shot at having the premier air superiority fighter.
Let's just put it another way. The biggest drawback of TVC is not high drag during ITR, or weight, or even cost, but rather that TVC is a maintenance hog. The F-35 could have benefitted from TVC nozzles, especially because of its poor basic maneuverability, but TVC on a mass-produced aircraft can easily lead to a maintenance nightmare. MTBR for Russian TVC engines, for instance, are rumored between 250 hours and 1000 hours. The F-22 is known for its extreme maintenance requirements, and part of that is because the F-22 of its TVC nozzles.
And for that matter, if we look at proposed 6th gens by the UNited States, please note that all of them are TVC craft, but the Lockmart proposal has 4 TVC engines and the Boeing proposal has 2 engines + canted canards for controllability. The main challenge with fighter TVC technology is basically getting it to be reliable enough not to inflate operational costs by a factor of two, as well as preventing it from locking up and dooming the aircraft while in flight.
And for that matter, if we look at proposed 6th gens by the UNited States, please note that all of them are TVC craft, but the Lockmart proposal has 4 TVC engines and the Boeing proposal has 2 engines + canted canards for controllability. The main challenge with fighter TVC technology is basically getting it to be reliable enough not to inflate operational costs by a factor of two, as well as preventing it from locking up and dooming the aircraft while in flight.
Brumby
Major
6th gen requirements have not even been defined. Do you have credible reference source to be speaking in such definitive language with regards to the adoption of TVC in both Boeing and LM's proposal?
No, but he has agreed to disagree with himself??? really Inst, your aerodynamics don't add up, and your arguments about canards, TVC, and energy management don't add up. In reality you are in over your head, the very basic physics of flight are simple, but intertwined, and your arguments about instantaneous turn rates as opposed to sustained turn rates are somewhat specious.
The F-22 is a very high energy fighter, it operates at very high altitudes, but the rules of engagement drug it down into a regime where it was possible to over-use the OVT to accelerate the pitch transition at a very rapid rate. Those very rapid pitch transitions enabled by OVT, also bleed energy very rapidly as the aircraft lift is increase dramatically, which increases drag dramatically. Simple physics, pilots understand and must exercise the fundamentals of energy management on every take-off and landing.
The Eng is trying to walk you through this, and if you will listen, I believe he can explain it to you??
Let me put it this way, AFB. Engineer's argument is that TVC is USELESS, that the F-22 would have been better off not having TVC. My point is that that's wrong; TVC has trade-offs, and the point of the video is not to talk about how the F-22 is better off without TVC, but how newbie pilots can misuse TVC and get themselves shot down or killed.
TVC, like canards, can allow an aircraft to achieve control at extreme AOAs. As you've mentioned, at high AOA regimes, both lift and drag increase tremendously, causing the aircraft to bleed energy. This is the definition of an instantaneous turn, a turn that causes the aircraft to lose energy by losing speed. Canard fighters are also capable of high AOA flight; the Gripen, iirc, can achieve 60 degree AOA. They face almost the exact same problem as TVC fighters; the ability to achieve AOAs that are only situationally useful.
Since 4th generation aircraft used by the United States rarely have this kind of AOA capability, this being the preserve of Eurocanards, the newbies don't get it and don't understand that sometimes the instantaneous turn is a bad idea. A J-turn is situationally useful when you're facing a bogie one-on-one, allowing you to change the situation from your opponent being on your six to you being on his six, but the loss of energy means that in a complex WVR melee the ITR is not useful.
However, there are cases where ITR is useful. Imagine a situation where you're being engaged by a missile at the edge of its NEZ, and ECM and chaff have failed to decoy it. An ITR then, in a BVR situation, where the lack of energy cannot be immediately capitalized upon, can allow you to drop the missile's PK to 0, instead of being forced to eject. Alternately, as mentioned before, in small melees or when you have a sufficient energy advantage that high AOA maneuvering doesn't hurt you enough, you can get away with TVC or canard maneuvers.
About the sixth gens, I can certify that the Boeing and Northrop proposals lack tailfins, and the Lockheed Martin proposal has pelikan tails. I could have sworn I had recalled an attempt to achieve XLO through thrust vectoring controls in lieu of conventional control surfaces. I will search further, but here's an old Boeing 6th gen proposal.
The closest I can get to confirmation of TVC on short notice, check out the way the exhaust of the CGI moves as the aircraft twists. It's consistent with TVC, as far as I can tell, and if sixth gen is hypersonic, TVC is probably the best way to handle ultra-high-speed maneuverability, due to control surface lock-up at hypersonic speeds (yes, you technically could do it, but imagine the size of the actuator needed to move the control surface. Bad idea).
TVC, like canards, can allow an aircraft to achieve control at extreme AOAs. As you've mentioned, at high AOA regimes, both lift and drag increase tremendously, causing the aircraft to bleed energy. This is the definition of an instantaneous turn, a turn that causes the aircraft to lose energy by losing speed. Canard fighters are also capable of high AOA flight; the Gripen, iirc, can achieve 60 degree AOA. They face almost the exact same problem as TVC fighters; the ability to achieve AOAs that are only situationally useful.
Since 4th generation aircraft used by the United States rarely have this kind of AOA capability, this being the preserve of Eurocanards, the newbies don't get it and don't understand that sometimes the instantaneous turn is a bad idea. A J-turn is situationally useful when you're facing a bogie one-on-one, allowing you to change the situation from your opponent being on your six to you being on his six, but the loss of energy means that in a complex WVR melee the ITR is not useful.
However, there are cases where ITR is useful. Imagine a situation where you're being engaged by a missile at the edge of its NEZ, and ECM and chaff have failed to decoy it. An ITR then, in a BVR situation, where the lack of energy cannot be immediately capitalized upon, can allow you to drop the missile's PK to 0, instead of being forced to eject. Alternately, as mentioned before, in small melees or when you have a sufficient energy advantage that high AOA maneuvering doesn't hurt you enough, you can get away with TVC or canard maneuvers.
About the sixth gens, I can certify that the Boeing and Northrop proposals lack tailfins, and the Lockheed Martin proposal has pelikan tails. I could have sworn I had recalled an attempt to achieve XLO through thrust vectoring controls in lieu of conventional control surfaces. I will search further, but here's an old Boeing 6th gen proposal.
The closest I can get to confirmation of TVC on short notice, check out the way the exhaust of the CGI moves as the aircraft twists. It's consistent with TVC, as far as I can tell, and if sixth gen is hypersonic, TVC is probably the best way to handle ultra-high-speed maneuverability, due to control surface lock-up at hypersonic speeds (yes, you technically could do it, but imagine the size of the actuator needed to move the control surface. Bad idea).