Aerodynamics thread

[Air Force Brat]

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).

Now that is a much better argument, of course the Eng is a fan of the F-22, but not a fan of OVT. You are "right on" here, without the TVC, the Raptor would never have been the Raptor. I have been up close and personal with the Raptor at Oshkosh, it is "JAW DROPPING". So here you and I are in complete agreement, the OVT enables the Raptor to do some incredible things that no other US aircraft other than "flight test birds" routinely do.

However, if I were doing the F-22B, "Heavy Raptor", I would dispense with the OVT and go for an F-135 upgrade with "kool stealthy nozzles". I would go for more internal fuel, possibly expand the size of the weapons bay to the extant that was possible without major redesign. As the F-35 continues to prove, you can achieve very fine High AOA maneuvering without OVT, in fact that very sweet LockMart airframe is very high lift, and very refined.

Like the Flanker, it is very sound aerodynamically, and very happy to be yanked around and abused, and will recover with little drama, and that brings us to your "disconnect"? When we are talking "IR" vs "STR" every fighter pilot has "energy management" drilled into him from conception, and on "every" landing, you are "bleeding energy", on purpose, from the time you roll the throttle/throttles back and begin your decent, into the approach, and the pattern? In fact the old "360 OVERHEAD", were you are at pattern altitude at 250 kts or so and then "pitch out" and roll in flaps and landing gear as you "bleed energy" off and come rolling down to final at 150 knts is a perfect example of "energy management".

It is simply a matter of how hard you pull on the stick, to enter a low speed engagement, (which most folks agree you probably don't want to do??) you have to pull hard aft stick and get down to where the other guy is, that of necessity "bleeds energy". So on a given day, in a given moment, in any turn, you might have a very high G IR, bleeding off to STR as you attempt to reach a "firing solution". It is not "either or", but a continuous flow as you use thrust and pitch to get where you need to be, we still play these games at Red Flag, etc, etc,? I really think one of the reasons we do, is to allow guys to see what happens when you get drug into one of these "slug fests"

So the Eng's argument, (and I have come to be in complete agreement with him here), is that OVT is heavy, maintenance intensive, and on an aircraft like the J-20, completely unnecessary, and could lead you down the "primrose path" into a low energy, "dead duck" situation??

 

[Engineer]

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.

You are now just throwing together technical terms together to try to retort with something, but your argument is completely meaningless. Canard deflect to achieve TVC? Canard is an aerodynamic control, thrust-vectoring isn't, understand? It's all about trade-offs? Pilots used TVC and lost dog fights in an otherwise unbeatable aircraft. There is no trade-off in that.

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.

The lecturer in the video was pretty clear. Both F-22 pilots and Indian Su-30MKI pilots made the same mistake by going into a stall. The moral of the story is that thrust vectoring does not make the aircraft turn faster.

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.

So you agree TVC impacts RCS. Now you are raising the point that it doesn't make a big enough impact to break stealth. What's the difference between TVC and canard in RCS then? Qualitatively, there is no difference. If you have quantitative data, then let see it.

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.

As you see, there is high inconsistency in the argument about TVC having less drag. On one hand, the argument claims movement of a part of the aircraft produces drag, and on the other, the argument claims movement of another part of an aircraft doesn't create drag.

As you admitted yourself, thrust vectoring transfers thrust into rotation energy. Have you thought about why that is in a wider context? For an aircraft to pitch, there must be a transfer of forward energy into rotational energy. Be it an aircraft with TVC or an aircraft without one, the net effect is the same, which is the lost of forward energy. You can name that lost using whatever word that pleases you, the effect is still a lost.

As to your argument on canard versus LEVCON, let us go back to the point that you admitted yourself, which is LEVCON does not provide the same level of control as canard. There is no comparison in the first place.

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.

No, I did not call you a Russian fan boy, but you are using their dumb arguments.

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.

This is funny coming from the person who first bashed J-10 for its canard configuration, and is now bashing J-20 for the same reason. The "not-invented here" syndrome is just your emotional projection on to me, that's all.

Note how I don't feel compel to bash the PAK-FA like you do with Chinese front line aircraft. I am simply apathetic about it. However, since you brought up TVC, I am simply pointing out the flaws in the arguments that you repeated from others.

The video I have linked to showed what really makes an aircraft ACM turkey is TVC. The fact is, TVC made F-22 lose to more backward fighters when F-22 should have wiped the floor. That demolished the whole argument about how TVC is better for manoeuvrability.

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.

Thankfully for China, military development is based on scientific evaluation, not on the words of some marketing brochure. TVC was offered to China by the then-Saturn for J-10, so it is not like China doesn't have any recourse to gain access to TVC. China engineers simply decided against TVC for J-10 and J-20.

It isn't just the Chinese engineers who rejected TVC. The US had tested out TVC on F-15, F-16 and F-18, yet none of these aircraft ever get retrofitted with TVC. TVC was offered on Eurocanards, and no one showed interested. Air force are unenthusiastic about it, contrary to this whole claim about TVC being the best thing since sliced bread.

 

[Brumby]

Now that is a much better argument, of course the Eng is a fan of the F-22, but not a fan of OVT. You are "right on" here, without the TVC, the Raptor would never have been the Raptor. I have been up close and personal with the Raptor at Oshkosh, it is "JAW DROPPING". So here you and I are in complete agreement, the OVT enables the Raptor to do some incredible things that no other US aircraft other than "flight test birds" routinely do.

However, if I were doing the F-22B, "Heavy Raptor", I would dispense with the OVT and go for an F-135 upgrade with "kool stealthy nozzles". I would go for more internal fuel, possibly expand the size of the weapons bay to the extant that was possible without major redesign. As the F-35 continues to prove, you can achieve very fine High AOA maneuvering without OVT, in fact that very sweet LockMart airframe is very high lift, and very refined.

Like the Flanker, it is very sound aerodynamically, and very happy to be yanked around and abused, and will recover with little drama, and that brings us to your "disconnect"? When we are talking "IR" vs "STR" every fighter pilot has "energy management" drilled into him from conception, and on "every" landing, you are "bleeding energy", on purpose, from the time you roll the throttle/throttles back and begin your decent, into the approach, and the pattern? In fact the old "360 OVERHEAD", were you are at pattern altitude at 250 kts or so and then "pitch out" and roll in flaps and landing gear as you "bleed energy" off and come rolling down to final at 150 knts is a perfect example of "energy management".

It is simply a matter of how hard you pull on the stick, to enter a low speed engagement, (which most folks agree you probably don't want to do??) you have to pull hard aft stick and get down to where the other guy is, that of necessity "bleeds energy". So on a given day, in a given moment, in any turn, you might have a very high G IR, bleeding off to STR as you attempt to reach a "firing solution". It is not "either or", but a continuous flow as you use thrust and pitch to get where you need to be, we still play these games at Red Flag, etc, etc,? I really think one of the reasons we do, is to allow guys to see what happens when you get drug into one of these "slug fests"

So the Eng's argument, (and I have come to be in complete agreement with him here), is that OVT is heavy, maintenance intensive, and on an aircraft like the J-20, completely unnecessary, and could lead you down the "primrose path" into a low energy, "dead duck" situation??

In the Nasa series, the book "Flying Beyond The Stall", in the Epilogue of the book addresses the question why the F-35 program was not interested in TVC :



Essentially there are many ways to skin a cat and in terms of priority it was simply situational awareness and tactics. TVC was just not worth the trouble.

 

[b787]

Now that is a much better argument, of course the Eng is a fan of the F-22, but not a fan of OVT. You are "right on" here, without the TVC, the Raptor would never have been the Raptor. I have been up close and personal with the Raptor at Oshkosh, it is "JAW DROPPING". So here you and I are in complete agreement, the OVT enables the Raptor to do some incredible things that no other US aircraft other than "flight test birds" routinely do.

However, if I were doing the F-22B, "Heavy Raptor", I would dispense with the OVT and go for an F-135 upgrade with "kool stealthy nozzles". I would go for more internal fuel, possibly expand the size of the weapons bay to the extant that was possible without major redesign. As the F-35 continues to prove, you can achieve very fine High AOA maneuvering without OVT, in fact that very sweet LockMart airframe is very high lift, and very refined.

Like the Flanker, it is very sound aerodynamically, and very happy to be yanked around and abused, and will recover with little drama, and that brings us to your "disconnect"? When we are talking "IR" vs "STR" every fighter pilot has "energy management" drilled into him from conception, and on "every" landing, you are "bleeding energy", on purpose, from the time you roll the throttle/throttles back and begin your decent, into the approach, and the pattern? In fact the old "360 OVERHEAD", were you are at pattern altitude at 250 kts or so and then "pitch out" and roll in flaps and landing gear as you "bleed energy" off and come rolling down to final at 150 knts is a perfect example of "energy management".

It is simply a matter of how hard you pull on the stick, to enter a low speed engagement, (which most folks agree you probably don't want to do??) you have to pull hard aft stick and get down to where the other guy is, that of necessity "bleeds energy". So on a given day, in a given moment, in any turn, you might have a very high G IR, bleeding off to STR as you attempt to reach a "firing solution". It is not "either or", but a continuous flow as you use thrust and pitch to get where you need to be, we still play these games at Red Flag, etc, etc,? I really think one of the reasons we do, is to allow guys to see what happens when you get drug into one of these "slug fests"

So the Eng's argument, (and I have come to be in complete agreement with him here), is that OVT is heavy, maintenance intensive, and on an aircraft like the J-20, completely unnecessary, and could lead you down the "primrose path" into a low energy, "dead duck" situation??

TVC nozzles are used to expand the flying ability of an aircraft when its aerodynamic features top up and can not go further.

Take off TVC nozzles from any Su-35S, F-22, Su-30SM and you will see they have lower ITRs and STRs, further more they have more safety restrictions in terms of the flight envelop and a reduced payload capability, then when to fit the thrust vectoring nozzles?

The answer is if you have highly off bored capability on a HMS and Missile you can skip TVC nozzles up to a degree, but it will not give you higher STR or ITR thus your AAM dodging capability will not improve, plus in stealth the TVC nozzles reduce deflection thus your radar signature is greater.

TVC nozzles allows for STOL capability.

So then PAKFA and Su-35 have supercruise, HMS capability and TVC nozzles.


TVC nozzles have different types, you can not lump together all of them, some are simpler than others and some are cheaper than others to operate

 

[Brumby]

The answer is if you have highly off bored capability on a HMS and Missile you can skip TVC nozzles up to a degree, but it will not give you higher STR or ITR thus your AAM dodging capability will not improve,

The whole point is not to go down into an alley where your options are restricted. In other words, post stall maneuvering is not where you want to end up.



This whole conversion seems to be about aerodynamics without a purpose. Aircraft design always come with tradeoffs and the tradeoffs reflect the objectives of the platform in terms of efficiency and cost effectiveness in getting there. Western design does not favour TVC regardless of what your beliefs are about its efficacy. There are fundamental philosophy differences between Western and Russian design. To-date, the limited modern air to air combat statistics reflect a fact that Western approach prevails. When it is all said and done, it is about kill ratio and not how well it turns.

 

[Air Force Brat]

TVC nozzles are used to expand the flying ability of an aircraft when its aerodynamic features top up and can not go further.

Take off TVC nozzles from any Su-35S, F-22, Su-30SM and you will see they have lower ITRs and STRs, further more they have more safety restrictions in terms of the flight envelop and a reduced payload capability, then when to fit the thrust vectoring nozzles?

The answer is if you have highly off bored capability on a HMS and Missile you can skip TVC nozzles up to a degree, but it will not give you higher STR or ITR thus your AAM dodging capability will not improve, plus in stealth the TVC nozzles reduce deflection thus your radar signature is greater.

TVC nozzles allows for STOL capability.

So then PAKFA and Su-35 have supercruise, HMS capability and TVC nozzles.


TVC nozzles have different types, you can not lump together all of them, some are simpler than others and some are cheaper than others to operate

Here again your arguments are more rational, but you also have a disconnect with the finer points of OVT and aerodynamics. OVT does not necessarily give your aircraft better shortfield performance, and the loss of thrust to OVT may honestly hurt your short field performance. All OVT honestly does is increase your pitch authority, very usefull in airshows and also helpful reducing supersonic trim drag on the Raptor. The Flanker, Raptor, and F-35 have very generous pitch authority at all speeds due to the large stabilators and the extremely long throw of those stabilators. So while turn rate may well be enhanced with TVC, the reduction in overall thrust can also lower the sustained rate.

OVT may increase the speed and authority of your pitch transitions, it does not increase usefull load of the aircraft, and will in fact reduce useful load due to its significant weight increase at the very aft end of the aircraft, which also adds mass far out of the cg, and therefore may slow pitch transitions, particularly as you apply forward stick.

In addition, aircraft with significant weight aft, are far more likely to enter an unrecoverable flat spin in the event of an engine failure, particularly in an asymmetric thrust condition. As noted OVT does increase post stall maneuvering, but it also brings with it some decidedly negative side effects??

 

[RadDisconnect]

From what I heard, TVC allows the F-22 to do short takeoff since it allows rotation around the main gears much sooner.

TVC helps trim drag during cruise and potentially during turning as well, but it's ,soy beneficial for low speed and post stall. But the extra weight and expense doesn't justify it, since low speed is something you want to avoid in air combat all together. Pretty much, TVC is really only a big advantage in situation where you're dueling one on one with another plane, which is a very small segment of air combat and not enough to justify its additional complexity.

 

[b787]

The whole point is not to go down into an alley where your options are restricted. In other words, post stall maneuvering is not where you want to end up.

This whole conversion seems to be about aerodynamics without a purpose. Aircraft design always come with tradeoffs and the tradeoffs reflect the objectives of the platform in terms of efficiency and cost effectiveness in getting there. Western design does not favour TVC regardless of what your beliefs are about its efficacy. There are fundamental philosophy differences between Western and Russian design. To-date, the limited modern air to air combat statistics reflect a fact that Western approach prevails. When it is all said and done, it is about kill ratio and not how well it turns.

Western design does not favour TVC? so take the F-22 and get rid of the thrust vectoring nozzles, same Harrier or F-35B

 

[b787]

OVT may increase the speed and authority of your pitch transitions, it does not increase usefull load of the aircraft, and will in fact reduce useful load due to its significant weight increase at the very aft end of the aircraft, which also adds mass far out of the cg, and therefore may slow pitch transitions, particularly as you apply forward stick.

In addition, aircraft with significant weight aft, are far more likely to enter an unrecoverable flat spin in the event of an engine failure, particularly in an asymmetric thrust condition. As noted OVT does increase post stall maneuvering, but it also brings with it some decidedly negative side effects??

You have to differentiate between TVC types, the Su-30Sm, PAKFA, MiG-29OVT, F-15MTD, F-22, X-31, and even Eurofighter have different systems.

Flat nozzles are much heavier, the F-22 has the heaviest while Eurofighter and MiG-29OVT have much lighter systems.

The latest Japanese fighter shows paddles are relatively light

TVC nozzles also require retrofitting thus they cost, the Eurofighter was deemed able to cope with most threats with IRIS-T or AIM-132 missiles cued by a HMS, post stall handling does not represent any drawback, in fact the Indians SU-30MKI proved to be on an equal foot to the Eurofighter.


The TVC nozzles do and always have increased STR and ITR, a gain is a gain, F-22 is a prove of that, it has been able to match the Rafale and Eurofighter despite having higher wing loading and lower TWR; PAKFA will even do better than F-22, with its LEVCONs and Thrust vectoring, and Su-35 the same, but contrary to F-22; Su-30SM, Su-35 and PAKFA do have HMS, so now they can easily boast to trash any euro canard in close combat.

 

[Brumby]

Western design does not favour TVC? so take the F-22 and get rid of the thrust vectoring nozzles, same Harrier or F-35B

There is a cost to every feature and eventually if they add up to be unaffordable, the quantities get truncated as with the F-22. We know from General Mueller's statement that TVC for the F-35 was deemed too costly relative to the benefit. As for your Harrier and F-35B statement, can you not resort to school boy antics?