Topic formely about the PAK FA and now about the aerodynamics of the modern fighters

[PAK FA]

Do you seriously think things are that simple?
When you design a plane you design it with all dimensions in mind.
I wish people would stop believe they can in one glance do the same work than 10 years of windtunnel,CFD and phd+20 years experienced people's work.

What you say is true but remember we are not quantifying concepts just qualifying them, we are not using math to calculate the exact configuration, we are just seeing the aircraft basics.
Aircraft design is slow because it take years for new technologies to mature and new ideas to be proven, true, but basic aerodynamic trends change just very basic concepts, from Biplanes to monoplanes took 20 years that is around 1915-1930, from straight wings to swept wings monoplanes took around 10 years 1945-1955, from swept wings to deltas or trapezoidals around 10 years 1955-1965, from fixed geometry wings to variable geometry wings another 10 years 1965-1977 and from defined fuselages to integral fuselages another 10 years 1974-1985 and from tailplanes to canard in jet fighters 22 years 1964-1986 from high observability to stealth 20 years 1981-2001.

But basicly the concept is simple the design is in esence a simple idea

 

[Ogami musashi]

But basicly the concept is simple the design is in esence a simple idea

No, I disagree, A concept is based on research (and that's why you have patents years before a design is started) and on previous designs shortcomings.


You can't deduce anything by simply looking at it because:

1/you don't know the flows around them (especially Levcons or F-22 wings that are a mix of several naca profiles)
2/you can't predict the way all those systems assembled will behave together


And your exemples of technology transition is a very good example of why you can't judge by the eyes; For each of those technologies, you had aircrafts using the older one that were better performing.
Example in 1918 you had the Fokker VIII which was a parasol wing monoplane, and it was superseded by later biplanes developpment.

Just like saying the F-14 because of his GV would have better turn rate than an F-15/F-16 which was not the case, neither it had the climbing rate.

If we use CFD+windtunnel that is not for fun or for tweaking things (only) this is used to valide some concepts and if it take so long to finish an aircraft it is because it is hard to validate the concept; see the F-35B variant that even in advanced testing needs redesign.

The F-22 raptor is another example of a plane that deep into its design phase was not up to the performance and such needed some RFP requirement tweaking.

 

[PAK FA]

You can't deduce anything by simply looking at it because:
1/you don't know the flows around them (especially Levcons or F-22 wings that are a mix of several naca profiles)
2/you can't predict the way all those systems assembled will behave together

I disagree for the following reason, there are books, internet pages who have written about some basic aspects of aircraft design, results of aerodynamic studies and flight test that explain perfectly some configurations.
These results are explanations of what does happen during those studies.
let us put this example there are reports that say that aircraft have been fitted with thrust vectoring and this has allowed the designers to reduce tail size.
This is the conclusion of the studies that used math, computers, flight tests and wind tunnel tests.

This conclusion simply states modern jets with thrust vectoring can reduce the vertical stabilator size, now you know that the 117S engine has multiaxis thrust vectoring and the PAK FA T-50 has small vertical stabilators, this simple conclusion tells you that the T-50 has for that reason smaller tails than earlier Su-27s.

The LEVCON, it is already a known fact what LERXes do, why they do it, there are many studies about it, now the word LEVCON means Leading Edge Vortex control, we know the PAK FA has a compound wing, which basicly has a LERX, we know what leading edge slats do, now use logic what is a LEVCON? is a LERX with a slat, so it can control the vortex created by the LERX in the same way a slat can reattach the flow over the wing.

Canards do the same, there are studies about it, all over the internet in fact some are patents and some are NASA studies, can we know why it has that configuration? yes, can we know the expecific parameters? no, unless we have the results of the studies and we use some math.

 

[Ogami musashi]

...

Maybe you didn't read enough of those papers because you know no paper is a study on one thing;

Let me take two examples including one you mentionned.

In the late 80's early 90's Nasa studied the Forward swept wing with the X-29; They started this because they had earlier reports that the FSW had many aerodynamical advantages (mostly thanks to german and russian studies after the WWII); Those reports were real...but only very theoritical (they studied only the wing alone) thus when Nasa tested the X-29 and analysed the real flight result (and wind tunnel models results) they actually found that appart from the high AOA possibility NONE of the aformentionned advantages were present;
They placed real hopes on High AOA L/D but found out the F-16 and F-15 were superior even in that; They also hope to resolve the divergence problem of the wings but the weight penalty had many other bad effects.

In the end they concluded that the X-29 configuration (not the FSW) was not up to the exceptations.


Second study, The F-15 active with 3D nozzles; The purpose of this study was not post stall maneuverability but supersonic drag reduction; What they found out was that while the TVC reduced in some parts the drag and allowed for more g's (especially in yaw) the loads on the nozzle actuators were too high and that in supersonic the nozzle movement created huge forces that disturbed the aerodynamics.

The conclusion was that the system was promising but further adaptation were required.

In russia too the theoritical advantages of some elements were adopted then droped; TVC nozzles used on sukhoi planes have their limitations; For example on SU-30 MKI the nozzles NEED to be deflected in yaw because of the plane design which cause huge drag as such the TVC is only activated via a switch when the plane is in post stall regime.

Similarly the SU-37 had only TVC engine in subsonic because of the supersonic loads; The SU-35 itself with its canard finally proved more draggy and the later were dropped.


The pattents of the pak-fa concern the whole plane and not simply levcons or 2D nozzles...

Aerodynamics flow upstream to downstream of the plane and as such each local element will influence the others.


You talk about levcons...what do you know about the influence of the maximum angle at which they can deflect? Their sweep angle? Their position relative to center of pressure? The effect on intakes? The supersonic behavior etc..?

According to you which one of those planes has the best subsonic cruise L/D ratio? F-16 or mirage 2000?
Less sweep (f-16) vs delta and high drag, the F-16 then? NO...this is the mirage 2000 (9 vs 10).

 

[PAK FA]

.Second study, The F-15 active with 3D nozzles; The purpose of this study was not post stall maneuverability but supersonic drag reduction; What they found out was that while the TVC reduced in some parts the drag and allowed for more g's (especially in yaw) the loads on the nozzle actuators were too high and that in supersonic the nozzle movement created huge forces that disturbed the aerodynamics.

These questions have to be addressed with simple answers, first thrust vectoring is used by the F-22 in supersonic flight, this is a real fact not a simple study but a reality of the F-22, its tailplanes are used only in roll, as you can see the americans did perfect the design.
The Su-35BM also uses thrust vectoring and has supercruise not in pitch only but in yaw.
The LEVCON on the LCA naval aircraft: they are used instead of canards, yes they reduce landing speed, what does it tell you, first the LCA uses LEVCONs because they keep the whole design small, second its allows better landing speeds, so the LEVCON does increase lift without pitching excesively the LCA.

HAL could have fitted canards as Sukhoi did on the Su-33, but they used LEVCONS, to achieve the same result, why the Su-33 used canards when it already had a LERX? answer to increase the vortex and control it.
Why Sukhoi deleted the canards on the Su-35BM? first canards increase drag and kill lift, why the Eurofighter has the canard farther ahead than Rafale or Gripen? answer for supersonic flight.
Why then the T-50 does not use canards ? but LEVCONs, simple becasue the LEVCON does not create downwash, canards have trailing and leading edges, LEVCONs do not have trailing edges and are position at the LERX that does create a vortex.
So as you can see, a LEVCON has two main advantages over canards, no down wash and no need to be positioned above wing Level as the canards of the Rafale or Lavi.

look at the planforming alignment of the T-50, the LEVCON does perfect alignement with the wing.
This tells you lots of information if you use logic.

 

[Ogami musashi]

These questions have to be addressed with simple answers, first thrust vectoring is used by the F-22 in supersonic flight, this is a real fact not a simple study but a reality of the F-22, its tailplanes are used only in roll, as you can see the americans did perfect the design.

No. The F-22 doesn't use TVC above Mach 1.4 and it certainly uses the tail planes for pitch!

The Su-35BM also uses thrust vectoring and has supercruise not in pitch only but in yaw.

This sentance says the 35BM has TVC and supercruise, not that it uses it in supersonic;

...

You don't understand: You can't compare two planes simple because one has a technology the other hasn't got and tell the first is superior! I've given you lot's of examples...

You should really read those technical papers...you'd be surprised.

 

[PAK FA]

No. The F-22 doesn't use TVC above Mach 1.4 and it certainly uses the tail planes for pitch

Well Paul Metz says it does http://www.ausairpower.net/API-Metz-Interview.html
and now i ask you do you think if the americans use thrust vectoring at supersonic speeds the Russians would not?
So our Su-35 won`t because the Su-30MKI can`t

 

[Ogami musashi]

No. The F-22 doesn't use TVC above Mach 1.4 and it certainly uses the tail planes for pitch

Well Paul Metz says it does http://www.ausairpower.net/API-Metz-Interview.html
and now i ask you do you think if the americans use thrust vectoring at supersonic speeds the Russians would not?
So our Su-35 won`t because the Su-30MKI can`t

I can't find back the article that was by paul metz on codeonemagazine.com since they seem to have deleted some but your link has nothing against what i say...i say mach 1.4+ and paul metz never says the horizontal stab is used for roll he says that in some conditions it is used to control roll while TVC maitain pitch authority..

And you still do not get my point: You have said the pak-fa is more maneuverable that F-22. According to you it is because it has levcon and TVC...i say to you can't judge a plane's performance just by the presence or not of a technology..i have given you numerous examples of planes that have technologies that would theoritically give them an edge in some department but in reality do not (X-29 with FSW, F-14 with VG, DVIII with parasol wing, F-16 with higher aspect ratio etc...).


Now i think i've done everything i can to show you real examples...If you still want to believe that because pak fa has levcon it will be more maneuverable than the F-22 then go on...It is not the end of the world for me

 

[sferrin]

No. The F-22 doesn't use TVC above Mach 1.4 and it certainly uses the tail planes for pitch!

Source?

 

[Ogami musashi]

No. The F-22 doesn't use TVC above Mach 1.4 and it certainly uses the tail planes for pitch!

Source?

look above, it was an article on codeonemagazine or the official F-22 ...paul metz wasying "at mach 1.5 you have plenty of air so you don't need TVC"..something like that; and i recall a diagram of TVC usage that stopped at mach 1.5

 

[sferrin]

No. The F-22 doesn't use TVC above Mach 1.4 and it certainly uses the tail planes for pitch!

Source?

look above, it was an article on codeonemagazine or the official F-22 ...paul metz wasying "at mach 1.5 you have plenty of air so you don't need TVC"..something like that; and i recall a diagram of TVC usage that stopped at mach 1.5

The article above says this:

"What is not widely known is that thrust-vectoring plays a big role in high speed, supersonic maneuvering. All aircraft experience a loss of control effectiveness at supersonic speeds. To generate the same maneuver supersonically as subsonically, the controls must be deflected further. This, in turn, results in a big increase in supersonic trim drag and a subsequent loss in acceleration and turn performance. The F-22 offsets this trim drag, not with the horizontal tails, which is the classic approach, but with the thrust vectoring. With a negligible change in forward thrust, the F-22 continues to have relatively low drag at supersonic maneuvering speed. . But drag is only part of the advantage gained from thrust vectoring. By using the thrust vector for pitch control during maneuvers the horizontal tails are free to be used to roll the airplane during the slow speed fight. This significantly increases roll performance and, in turn, point-and-shoot capability. This is one of the areas that really jumps out to us when we fly with the F-16 and F-15. The turn capability of the F-22 at high altitudes and high speeds is markedly superior to these older generation aircraft."

 

[Ogami musashi]

I don't speak about that article; I speak about an article that was on codeonemagazine...

The quote you make are interesting, but do not contradict what i'm saying, neither what was said with the F-15 active;

You can read the F-15 active test pdf, i think it is still available @ nasa website.

 

[PAK FA]

And you still do not get my point: You have said the pak-fa is more maneuverable that F-22. According to you it is because it has levcon and TVC...i say to you can't judge a plane's performance just by the presence or not of a technology

I will tell you why i think it is a better fighter, first it is newer, has newer aerodynamic concepts, the LEVCON is one, single piece vertical stabilators slaved to a FCS that use thrust vectoring as control is the other.
Putin declares it will be better, i know this is typical propaganda and adds no veracity to the claim, however is unlikely the Russians made an aircraft than is inferior to the F-22, the T-50 has to be at least as good as the F-22.
Now i will tell you a secret, the F-119 has more power than the current 117 and automatically people think it will add better supercruise, this is true if it has a regular 3D nozzle of rounded cross section however the change of round to rectangular cross section in the F-119 kills thrust, up to 8% of total thrust is lost, now see this if the engine has a thrust of 16 tonnes the nozzle will at least kill 1.2 tonnes of thrust. So if the T-50 has an engine of 15 tonnes and the F-22 one of 16 tonnes the fact it has 2D flat nozzles will even the thrust in both aircraft.
If you add a 2D flat nozzle to the 117 engine the same will happen, so the Russians will develop a new engine that allows the use of flat nozzles by increasing the thrust of this engine with respect the 117.
I know what you are trying to say, and to a degree i think you are right, but my point is technology does give advantages from generation to generation and it is easy to prove.
In 1936 the Me-109 was better than the Rata I-16, difference in technology allowed it, in 1944 jet technology allowed the Me-262 to shoot propeller airplanes with ease like no other propeller aircraft could, the P-51 only could beat it at landing, by 1950, the Jet reigned supreme, the MiG-15 with swept wings was better than any american fighter with straightwings, until the arrival of the F-86
With the advent of the F-16, the MiG-21 was rendered obsolte as a dogfighter. the F-16 has integral fuselage it has the wing and fuselage blended, the MiG-21 a conventional fuselage.
The F-22 has rendered obsolete all previous aircraft except the J-20 and T-50

 

[PAK FA]

The quote you make are interesting, but do not contradict what i'm saying, neither what was said with the F-15 active;

It does not contradict you that is true, however it proves thrust vectoring can be used to control an aircraft and allows for the reduction of vertical stabilator size, so the dorsal fin can be reduced, this explains quit well why the T-50 has such small dorsal fins and the J-20 has small dorsal fins too.
This also explains why the F-22 has tailplanes, people say canards are better for supercruise due to an addition lift center ahead of the main wing, however using thrust vectoring during supersonic trim, no tailplane deflection is used, according to Metz, this obviously allowed the americans to add tailplanes that need no dihedral as the canards of the J-20 do, and are well hidden by the wing of the F-22 reducing radar signals.
The same was used by the Russians on the T-50.
So why then the chinese used canards that usually are only used for pitch control, the Eurofighter only uses its canards for pitch control but not roll.
I think the answer is the engines the WS-10 are not up to the test and they know the J-20 might have its promised WS-15 until perhaps 2025, when they might delete the canards and ventral fins and make the J-20 more akin to the proposed FB-22

 

[AeroFranz]

I think the answer is the engines the WS-10 are not up to the test and they know the J-20 might have its promised WS-15 until perhaps 2025, when they might delete the canards and ventral fins and make the J-20 more akin to the proposed FB-22

I agree in theory. In practice, just looking at the planform, it looks like the canards are currently sharing some of the lift in level flight. Plus where there is a canard, there is structural strengthening, volume for actuators. This is a big penalty to carry around if you don't plan to have it in the final configuration. This is not a trivial thing to change, and of course the aerodynamics would be entirely different.
If we assume that the canards will eventually be omitted, then at the very least a substantial redesign will be needed. This is where i don't think it's worth having them as an interim solution. It's not like the inlet on the J-10, which to a certain extent can be decoupled from the rest of the design.

 

[saintkatanalegacy]

^yep

various parts will also need to be redesigned

eg. nose-fuselage and inlet interactions

 

[PAK FA]

If we assume that the canards will eventually be omitted, then at the very least a substantial redesign will be needed. This is where i don't think it's worth having them as an interim solution. It's not like the inlet on the J-10, which to a certain extent can be decoupled from the rest of the design.

I guess so, but in my opinion despite it looks the J-20 chose "the best configuration" i see it really does not have a really good configuration for high AoA and supercruise.

Let us compare it to the MiG-1.44 and Eurofighter, the chin intake in these two fighters was chosen because at high AoA allows the best flow for the engines combined with sideslip, the PAK FA again has inlets that are little bit ventral and without fuselage obstruction they must also allow good flow even with sideslip.
on the Eurofighter the chin intake gets great degree of pre-compression excellent for pressure recovery, on the MiG-1.44 that is combined with fuselage lift, the forebody of the MiG-1.44 has a almost a flat lower forebody acting on the pre-compression and and adding lift.
The J-20 chose the side intakes mostly because of stealth, to create a single fuselage with faceted engine nacelles and a shoulder mounted wing.

The Eurofighter chose a canard that was small almost at the same level of the wing and very forward, this allows great degrees of unstability and a small canard, excellent for supercruise due to the lower drag it creates and it adds a degree in turn rate compared with an aft placed canard
I do not think the J-20 has the best configuration for supercruise with those large canards

 

[AeroFranz]

I am just as puzzled. This airplane has a mix of contradictory features in the areas of stealth and aerodynamics. I don't think Chinese engineers are stupid, but I don't think they know something US designers don't. The only thing i can think of is that the differences we see are a result of operational considerations that dictate a different CONOPS compared to US aircraft.

 

[PAK FA]

I am just as puzzled. This airplane has a mix of contradictory features in the areas of stealth and aerodynamics.

i agree, i think the Chinese have some technical limitations at the moment, that forced them to try to fix some of the limitations of their engines with some solutions that otherwise the americans would not have taken.
The F-22 is a very well thought aircraft, its F119s add raw power to the limitations stealth imposes, in theory, the 117 engine with rounded nozzles and multiaxis thrust vectoring is a better solution for maneouvrability but not for stealth, the losses in thrust created by the flat nozzles are not worthed if your engines can not deliver, now the 117 can not deliver what the F-119 can, the WS-10 i guess is the same, some solution are quit risky like the stealthy but risky X-32, i do not think the chinese would had made a simple delta like the X-32, specially if they want to compete with the F-22.
I think they want to compensate for the lack of thrust with canards, a delta wing and a twin engined airframe.
If their engines are not as efficient they will need more fuel and therefore a bigger jet, this does not equal necesarally bigger weapons bay automatically as it has been suggested.
I also think their limitations are also in thrust vectoring, this forced them to even add dihedral to the canards, when all the fifth generation fighters hide their tailplanes with the wing or position their canards at the same horizontal level without dihedral like the X-36