Sukhoi Su-57 / T-50 / PAK FA - flight testing and development Part II [2012-current]

[Radical]

kcran567 your observations are very naive and easily turned around.

"The T-50 configuration is clearly superior in agility because the widely spaced engines increase the effectiveness of thrust vectoring. The F-22 and F-35 with their inboard engines can't generate the same roll rates".

In truth, there are pluses and minuses of each layout, but neither layout is clearly superior by eyeballing it. The design driver for inboard engines and boxy fuselage is stealth, not agility. In fact I believe the T-50 configuration is potentially more agile in almost every respect, which would accord with my gut feelings as to the design drivers.

Agreed.

Compared to the F-22's boxy design, the T-50's design of separating the fuselage into pods like the forward fuselage, nacelles, and short range AAM bays allows for a tunnel design that generates a lot more lift since the flat areas connecting these pods act like extensions of the wing. The use of pods also makes it easier to area rule, giving lower drag and better acceleration/maneuver performance. This is pretty similar to the YF-23. It seems like Sukhoi really focused on the kinematic performance of the T-50. I think it's pretty clear that the T-50 has a distinct speed, acceleration, and maneuver advantage over the F-22.

 

[Trident]

The Su-27 had excellent manouverability using traditional measures but compared to the F-16 for instance it was slower to reach maximum roll rate due primarily to the higher aspect ratio wing.

What do you base that on (not trying to argue, I'm genuinely interested)? The two don't seem to be different enough in terms of aspect ratio to account for the difference in agility about the roll axis, my money is on the engine configuration being the main reason, the powerplant/s is/are the biggest mass concentrations in an aircraft after all. I once made an estimate of the impact on moment of inertia from engine offset from the centreline (very crude, scribbled onto the margin of a sheet during a boring avionics lecture) - it was pretty strong! It also indicated that TVC for roll probably cannot fully compensate (weaker dependence of its effect on offset distance), so the T-50 probably has differential TV due to its widely spaced engines, NOT - as is frequently suggested - the other way round.

 

[Avimimus]

He figured the wide-spaced engines were more about Russians sticking with what they know than about providing control authority.

If I recall correctly the widely spaced engines (appearing in the 1980s) were analysed as significantly increasing durability. In fact, aircraft might be able to continue fighting (e.g. with Helmet Mounted Sight and off-boresight missiles) once a missile had destroyed one of the engines. The twin engine requirement also reportedly stemmed from reliability and survivability issues.

So, would it be correct to say that the engine spacing is part of the survivability requirement (and a provides a nicely uninterrupted weapon's bay), rather than being a 'conservative' feature?

 

[kcran567]

kcran567 your observations are very naive and easily turned around.

"The T-50 configuration is clearly superior in agility...


The design driver for inboard engines and boxy fuselage is stealth, not agility...


In fact I believe the T-50 configuration is potentially more agile in almost every respect, which would accord with my gut feelings as to the design drivers...

1) Not proven by you

2) The F-22s fuselage shaping is not a "box" as you say, its an inverted lifting body shape that DOES provide body lift.

3) How do you know it is so agile in every respect. Have you seen any video of the F-22? Pretty good agility if you ask me.

Traditional measures of manouverability we all know:

-
Wing loading
T/W ratio
Maximum climb rate
Maximum instantaneous turn rate
Specific Excess Power (Ps)
-

Note some more modern definitions of agility:

-
Pitch Agility
Time to pitch to maximum load factor plus time to pitch from maximum to zero load factor (i.e. how fast you can get to maximum pitching)

Wing loading is an older requirement for agility. As you know, how unstable the design is is a factor. The T-50 is a more stable design than the F-22/35. The center of gravity is farther forward on the T-50. The F-22/35 have their tail sufaces much further aft on the fuselage. On the F-35, the tail is ALWAYS trimmed upward, providing a LIFTING SURFACE. You never see tail lift on the T-50, Its much more stable for level flight. The T-50 design is conservative, with less nose pitch instability.


F-35: tail farther back, trim up, provide lift. More unstable.
T-50: Tail not so far back, no upward trim, more stable design.

kcran567 your observations are very naive and easily turned around.

"The T-50 configuration is clearly superior in agility because the widely spaced engines increase the effectiveness of thrust vectoring. The F-22 and F-35 with their inboard engines can't generate the same roll rates".

In truth, there are pluses and minuses of each layout, but neither layout is clearly superior by eyeballing it. The design driver for inboard engines and boxy fuselage is stealth, not agility. In fact I believe the T-50 configuration is potentially more agile in almost every respect, which would accord with my gut feelings as to the design drivers.

Agreed.

Compared to the F-22's boxy design, the T-50's design of separating the fuselage into pods like the forward fuselage, nacelles, and short range AAM bays allows for a tunnel design that generates a lot more lift since the flat areas connecting these pods act like extensions of the wing. The use of pods also makes it easier to area rule, giving lower drag and better acceleration/maneuver performance. This is pretty similar to the YF-23. It seems like Sukhoi really focused on the kinematic performance of the T-50. I think it's pretty clear that the T-50 has a distinct speed, acceleration, and maneuver advantage over the F-22.

You have no evidence of kinematic advantage. Basic physics favor a centerline mass more agile than two boxy outboard weights that counteract each other. F-14 had similar centroplane, yet it was not used on any western 5th gen. It is outdated, but as 2idsgt, avimimus, and trident say the Russians went with what they knew and what would basically get the job done no frills with less risk. The T-50 is a less risky design, and is more stable. Outboard engines and less static instability than the f-35/22. F-22 was designed much earlier than the T-50.


My racecar with centerline mass will be much better handling than you're racecar with 2 mass located on the sides.


Also, having a huge pancake between two podded areas provide much more wetted area, which the Russians needed more wing area to make up for lost agility due to less instability built into the design. Just as the F-16 needed a smaller wing due to tail lift and an unstable design, which translated into less supersonic drag. The Russians took simpler approach on T-50.

The entire underside of the F-35 is a lifting shape derived from the lifting body research way back starting w/ M2-F1, M2-F-3 etc.

The T-50 flat pancake is a crude approach, which does work, at the expense of needing much more flat wing area. I think the Russians did it more for weapons space/payload reasons. It was a layout they were familiar with. T-50 More old school F-14 style flat pancake wetted drag than an F-22/35.

 

[overscan (PaulMM)]

The Su-27 had excellent manouverability using traditional measures but compared to the F-16 for instance it was slower to reach maximum roll rate due primarily to the higher aspect ratio wing.

What do you base that on (not trying to argue, I'm genuinely interested)? The two don't seem to be different enough in terms of aspect ratio to account for the difference in agility about the roll axis, my money is on the engine configuration being the main reason, the powerplant/s is/are the biggest mass concentrations in an aircraft after all. I once made an estimate of the impact on moment of inertia from engine offset from the centreline (very crude, scribbled onto the margin of a sheet during a boring avionics lecture) - it was pretty strong! It also indicated that TVC for roll probably cannot fully compensate (weaker dependence of its effect on offset distance), so the T-50 probably has differential TV due to its widely spaced engines, NOT - as is frequently suggested - the other way round.

Yep, it could be that. I read the aspect ratio / time-to-maximum-rate-of-role comment in relation to F-18 versus F-16. It is certain that Su-27 is slower to get to maximum roll rate, though once its there its as good as anything else.

 

[kcran567]

The Su-27 had excellent manouverability using traditional measures but compared to the F-16 for instance...not as

Yep, it could be that. I read the aspect ratio / time-to-maximum-rate-of-role comment in relation to F-18 versus F-16. It is certain that Su-27 is slower to get to maximum roll rate, though once its there its as good as anything else.

We can most assuredly extrapolate this to the T-50. Similar old school F-14 style flat pancake lifting area with podded engines as the SU-27 family. Same design approach.

Again, my racecar with centerline mass more agile than you're racecar with 2 outboard masses.


http://www.nasa.gov/centers/dryden/images/content/328743main_EC66-1567_3x4_946-710.jpg

f-35 lifting body approach


http://air.blastmagazine.com/files/2012/06/fighter_f-14_tomcat.jpg

F-14 old school podded flat pancake T-50 wetted area approach[/quote][/quote]

 

[chuck4]

He figured the wide-spaced engines were more about Russians sticking with what they know than about providing control authority.

If I recall correctly the widely spaced engines (appearing in the 1980s) were analysed as significantly increasing durability. In fact, aircraft might be able to continue fighting (e.g. with Helmet Mounted Sight and off-boresight missiles) once a missile had destroyed one of the engines. The twin engine requirement also reportedly stemmed from reliability and survivability issues.

So, would it be correct to say that the engine spacing is part of the survivability requirement (and a provides a nicely uninterrupted weapon's bay), rather than being a 'conservative' feature?

A single compact fuselage housing both engines is likely to be structurally more efficient and lighter. Two separately podded engines probably impose a weight penalty, both because engine structures can't brace each other, and because there are additional skin area to cover.



But twin podded engines on the T-50 could also shield it's weapon bays from radar in side aspect, and conceivably give it significantly more freedom in launching weapons without breaking stealth

 

[Trident]

The T-50 is a more stable design than the F-22/35. The center of gravity is farther forward on the T-50.

Unlikely - a negative stability margin of up to 15% (which is pretty ambitious) has been claimed in the aerospace press (Butowski, in a FlugRevue issue from last year). Also, as mentioned a while back, with their experience from the Su-27 and Su-47 (which were every bit as unstable as any contemporary, if not more so) means that Sukhoi is pretty much the last company to have to reign in instability due to lack of experience.

The F-22/35 have their tail sufaces much further aft on the fuselage. On the F-35, the tail is ALWAYS trimmed upward, providing a LIFTING SURFACE. You never see tail lift on the T-50, Its much more stable for level flight. The T-50 design is conservative, with less nose pitch instability.

None of these traits are reliable indicators for the degree of (in)stability, so you are basing this argument on a fundamentally flawed premise. Case in point:
The Su-27 and F-16 both have relaxed (neutral) pitch stability, hence are less stable than the contemporary F-15 and MiG-29 which are naturally stable designs. Now go compare tail plane position...

F-35: tail farther back, trim up, provide lift. More unstable.
T-50: Tail not so far back, no upward trim, more stable design.

As mentioned, it does not work that way.

You have no evidence of kinematic advantage. Basic physics favor a centerline mass more agile than two boxy outboard weights that counteract each other. F-14 had similar centroplane, yet it was not used on any western 5th gen. It is outdated, but as 2idsgt, avimimus, and trident say the Russians went with what they knew and what would basically get the job done no frills with less risk. The T-50 is a less risky design, and is more stable. Outboard engines and less static instability than the f-35/22. F-22 was designed much earlier than the T-50.
My racecar with centerline mass will be much better handling than you're racecar with 2 mass located on the sides.

While this is certainly true for roll, I don't see how widely spaced engines would have any effect on pitch whatsoever. As Paul has mentioned, you need to differentiate what you're talking about when you say "agility".

 

[overscan (PaulMM)]

Yes, kcran567 please share how you calculated the CG position of the T-50 without a real one to weigh. I don't even know how much the whole plane weighs, let alone the individual components.

Regarding relaxed stability -

Su-27 - 5%
Su-35 (with canards) - 20%
Su-47 was even higher


X-29 was as high as 35%

15% is roughly comparable to other aircraft. Typhoon is more unstable than F-22 - so is it more agile according to you?

In fact, relaxed stability can help with torsional and pitch agility, but its only one factor.


Note the conclusions of the X-29 report:


http://107.21.31.18/centers/dryden/pdf/88335main_H-1995.pdf

The level of static instability and control surface rate limits did impact the nose up and nose down maximum pitch rates. At low airspeeds, to achieve rates comparable with an F-18, new actuators with at least 50-percent higher rate are required.

The excessive instability of the X-29 meant the control surfaces were too busy keeping it from departing, which actually reduced the maximum pitch rate.

 

[flateric]

T-50 is aerodinamically and structurally more advanced, maneuverable (and risky) design than F-22 using 15+ year gap in aerodynamic development. Just LO variable inlets, LEVCONs and "3D" TVC to mention.

 

[chuck4]

T-50 is aerodinamically and structurally more advanced, maneuverable (and risky) design than F-22 using 15+ year gap in aerodynamic development. Just LO variable inlets, LEVCONs and "3D" TVC to mention.

There is plenty of evidence that the Russians are more than 15+ years behind the Americans in crucial aviation related technologies. In actuators, servos, AESA, for example, amongst others. T-50 was also likely designed under more tighter financial constraints, and likely was mandated to rely more on data originally gathered specifically to support other production programs like su-27, than was the f-22. So t-50 was probably a more constrained design than f-22. Just because t-50 flew 15+ years later doesn't mean anything. Without knowing the alternatives available, examined, and the trade off accepted with each design, it is impossible to say which which design is more advanced, only which design uses more moving parts and employ more buzzwords.

 

[kcran567]

T-50 is aerodinamically and structurally more advanced, maneuverable (and risky) design than F-22 using 15+ year gap in aerodynamic development. Just LO variable inlets, LEVCONs and "3D" TVC to mention.

The only real somewhat new aerodynamic technology used on the T-50 is the Levcons. That's true. Nothing else so groundbreaking. I say somewhat new because the Levcons in themselves are related to the Canard surface, just more well integrated into the fuselage. This would allow a more stable design to be built which is what I meant by less risky The Levcons provide the instability rather than the a dedicated unstable aircraft like the F-35.

Yes, kcran567 please share how you calculated the CG position of the T-50 without a real one to weigh. I don't even know how much the whole plane weighs, let alone the individual components.

Regarding relaxed stability -


X-29 was as high as 35%


Note the conclusions of the X-29 report:

The level of static instability and control surface rate limits did impact the nose up and nose down maximum pitch rates. At low airspeeds, to achieve rates comparable with an F-18, new actuators with at least 50-percent higher rate are required.

The excessive instability of the X-29 meant the control surfaces were too busy keeping it from departing, which actually reduced the maximum pitch rate.

If the F-35 is more unstable than the T-50 it would be able to be controlled due to its highly sophisticated actuators and millions of lines computer code. A number of pilots that have flown the F-35 have said it is the most precise and rapid flight control response aircraft they have flown ( i will try and find the RAF pilot quote or video, it is real). The Russians may have avoided this by taking a simpler approach as they have in the past. The Levcon assembly is part of that approach, albeit with the added mechanical complexity and weight of having a Levcon along with a traditional horizontal tail vs. say having an unstable delta and canard only like the Eurofighter.

 

[Avimimus]

Just because t-50 flew 15+ years later doesn't mean anything. Without knowing the alternatives available, examined, and the trade off accepted with each design, it is impossible to say which which design is more advanced, only which design uses more moving parts and employ more buzzwords.

I agree with the second sentence. We should avoid debates about such vagaries.

However, it should be noted that a lot of information transfer happens accidentally (declassification, academic literature, civilian products) if given enough time. Computational power has also increased, and Russian engineers have always excelled in some areas (Soviet era gun designs and aerodynamics were often quite admirable) and work continued during the collapse of the Soviet Union, partly due to the lack of other employment, albeit the work proceeded at a much reduced rate.

 

[Avimimus]

T-50 is aerodinamically and structurally more advanced, maneuverable (and risky) design than F-22 using 15+ year gap in aerodynamic development. Just LO variable inlets, LEVCONs and "3D" TVC to mention.

The only real somewhat new aerodynamic technology used on the T-50 is the Levcons. That's true. Nothing else so groundbreaking. I say somewhat new because the Levcons in themselves are related to the Canard surface, just more well integrated into the fuselage. This would allow a more stable design to be built which is what I meant by less risky The Levcons provide the instability rather than the a dedicated unstable aircraft like the F-35.

That is quite an assumption.

The LEVCONs can be used at high angle of attacks to control pitch moments (and potentially roll moments), so they allow a smoother transition between normal maneuverability and super-maneuverable flight regimes (something that Russian aerodynamicists have sought for a while - e.g. project Integral, the optimised AOA performance of the Yak-130 and the FSW Sukhoi 47).

I don't think it is defensible to argue that the design is conservative and aims for aerodynamic stability - given that it is designed to be unstable in yaw (even potentially super-maneuverable in yaw) and is the first aircraft to have a G-suit designed to protect the pilot from forces in more than one dimension.

 

[chuck4]

T-50 is aerodinamically and structurally more advanced, maneuverable (and risky) design than F-22 using 15+ year gap in aerodynamic development. Just LO variable inlets, LEVCONs and "3D" TVC to mention.

The only real somewhat new aerodynamic technology used on the T-50 is the Levcons. That's true. Nothing else so groundbreaking. I say somewhat new because the Levcons in themselves are related to the Canard surface, just more well integrated into the fuselage. This would allow a more stable design to be built which is what I meant by less risky The Levcons provide the instability rather than the a dedicated unstable aircraft like the F-35.

I am not sure if one could call an airplane "dedicated unstable". It's either designed to be unstable or not. In all likelihood T-50 was designed to be unstable along 1, 2 or 3 axis. Being unstable in all three axis is also not new. F-117 was unstable in pitch, roll and yaw because aerodyanmic constraints imposed by then state of stealth technology. As F-117 shows, instability is not necessarily correlated to agility. I have a somewhat hard time believing F-35 to be the most agile fighter out there, whatever its instability.

 

[Sundog]

I've yet to see any indications that the T-50 will have 3D TV and what I saw in the patent drawings was studied by the U.S. back in the 80s and discarded. Once again, "better" is something of a dangerous term. Sort of like, the YF-22 was more maneuverable than the YF-23, but it actually wasn't in the entire envelope and where it was wasn't exactly somewhere I would be worried about.


I don't actually see anything new, aerodynamically, with the T-50, other than the levcons, which I still feel are more for controlling the airflow into the inlets at varying alpha than anything else. I don't think they are there to "replace" the canards, like on some of the Flankers, because if you have TV, you don't need them.


What I do see is better optimization of the FCS based on the size of the vertical tails and a more reasonable approach to LO, but it is still proving expensive. Regardless, it appears it will be an excellent fighter design.

 

[flateric]

LEVCONs are being used for roll control as well

 

[Trident]

I've yet to see any indications that the T-50 will have 3D TV and what I saw in the patent drawings was studied by the U.S. back in the 80s and discarded. Once again, "better" is something of a dangerous term. Sort of like, the YF-22 was more maneuverable than the YF-23, but it actually wasn't in the entire envelope and where it was wasn't exactly somewhere I would be worried about.

Assuming that a technology which was tested and rejected by one party cannot be put to very worthwhile use by someone else is also dangerous though By that logic, nobody should be bothered by helmet-mounted sights (VTAS) and high off-boresight AAMs (AIM-95) - or the F-22 fuselage configuration for that matter, which was studied by Sukhoi back in the 1990s (Su-47) and ultimately discarded for the PAK-FA

 

[chuck4]

Assuming that a technology which was tested and rejected by one party cannot be put to very worthwhile use by someone else is also dangerous though By that logic, nobody should be bothered by helmet-mounted sights (VTAS) and high off-boresight AAMs (AIM-95) - or the F-22 fuselage configuration for that matter, which was studied by Sukhoi back in the 1990s (Su-47) and ultimately discarded for the PAK-FA

I suspect PAK-FA configuration was selected in part to allow the maximum reuse of data and research originally gathered specifically for the Su-27/30/33/35 program, perhaps some tooling as well. Su-47 would mean more original research.

 

[Avimimus]

LEVCONs are being used for roll control as well

Thanks! The info is appreciated!

 

[saintkatanalegacy]

LEVCONs aren't simply fancy canards. They also "shift the center of lift" not only to and fro but also sideways and create initial deflection while working in concert with other large control surfaces - Synergism. I find it hard to swallow the idea that its agility and control software are anywhere inferior to its contemporaries.

 

[chuck4]

Moving Canards changes their own lift coefficients independently of the lift coefficient of the wings and tail surfaces. In other words, moving canards change center of lift exactly as you think levcon might do. If canard can move differentially, that would move center of lift to one side or the other, again the same as what you think levcon does. For that matter, ailerons, differential spoilers, elevators can all move center of lift front and back, and side to side.

In what way do normal canards and other control surfaces not move in "synergy"?

So I think there is a lot of bullshit hype surrounding levcons, but nothing really new. It seems to me to be nothing more than an attempt to get some of the benefits of canard while minimizing the RCS penalties of a normal canard.


As to short, non-serpentine intake ducts, on stealth planes, there is a precedence. Boeing x-32 had its engine forward of center of gravity, with an even bigger fan face prscticall under the pilot's ass, fed by an even shorter duct under the chin. The x-32 didn't lose to LM x-35 on account of stealth, so Boeing clearly came up with something that worked. T-50's intake ducts could be at least as stealthy as those on the x-32.

 

[flateric]

http://youtu.be/GclvFf71eT8

 

[chuck4]

The drooping axial symmetric exhaust nozzles in the video are indisputable evidence of 3D TV.

 

[flateric]

http://www.youtube.com/watch?v=g1MmeJcAQNM

 

[flateric]

(c) OKB Sukhoi

 

[flanker]

I find it hard to swallow the idea that its agility and control software are anywhere inferior to its contemporaries.

Looking at Su-35S in real life it would seem to me whoever wrote the codes is a huge nerd. It all looked very very complex.

Not to steal your thunder Flateric, but this is better quality although a bit smaller

http://ic.pics.livejournal.com/bmpd/38024980/471151/471151_original.jpg

He had high res of it it seems, but link died.

 

[flateric]

My racecar with centerline mass will be much better handling than you're racecar with 2 mass located on the sides.

Tell that to Mr.Pugachev
http://youtu.be/fwXLLjOFrZc
http://youtu.be/YJBibMijN6U
http://youtu.be/yMu0YpEjUig

 

[SOC]

The drooping axial symmetric exhaust nozzles in the video are indisputable evidence of 3D TV.

What? The drooping nozzles by themselves would only be evidence of 2D TVC; you're only seeing them "operate" in pitch and can't tell how much they do or do not toe in towards the centerline when drooped. The latter would be indicative of 3D TVC. At any rate all you can tell from that video is that the nozzles move vertically and they relax when power is off.

 

[chuck4]

The drooping axial symmetric exhaust nozzles in the video are indisputable evidence of 3D TV.

What? The drooping nozzles by themselves would only be evidence of 2D TVC; you're only seeing them "operate" in pitch and can't tell how much they do or do not toe in towards the centerline when drooped. The latter would be indicative of 3D TVC. At any rate all you can tell from that video is that the nozzles move vertically and they relax when power is off.

It would be odd for the vectoring nozzle and the sleeve behind the nozzle to be axial symmetric if the nozzle is design to vector in one plane only. In any case, look closer, in the drooped position the nozzles do toe in.

 

[saintkatanalegacy]

They are actually 2D. Just angled. Refer to posted patents

 

[2IDSGT]

They are actually 2D. Just angled. Refer to posted patents

Does anyone know for sure yet?

 

[kcran567]

Cool T-50 3 minute video with short demo and missile test at the end. Just mute the annoying music though.
http://www.youtube.com/embed/dmF4Ql1QgU8

 

[Kryptid]

I'm pretty sure the missile launch footage was computer-generated. Admittedly, whoever made it did a bang-up excellent job.

In regards to the nozzles, being axisymmetric doesn't necessarily mean true 3D-vectoring. Look at the Su-30MKI.

 

[flateric]

Does anyone know for sure yet?

for ages

 

[flateric]

Cool T-50 3 minute video with short demo and missile test at the end.

it's pretty old CGI

 

[flanker]

Nice video of T-50-4 arrival:

http://www.vesti.ru/only_video.html?vid=479833

 

[Wil]

OK

 

[Wil]

From Paralay forum, a great work of Photoshop...!!

 

[saintkatanalegacy]

If it had flat nozzles it would be farther back