Sukhoi PAK FA

arnabmit

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@p2prada @gadeshi noob question...

The engine mount curvature in the lower fuselage is not a stealthy shape. Why is not a simple composite shroud with RAM coating applied on it?

Also why are the internal weapons bay above the engine mount curvature in the lower fuselage? Wouldn't it give much cleaner lines if the internal bays are expanded to carry more/larger weapons upto the level of the engine mount curvature in the lower fuselage?

Something like this... Hope I am able to explain my question properly.



F-22 is like that... much cleaner lines...

 
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gadeshi

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This is because of several reasons:

1 - This place is irrelevent for stealth reasons because it reflects enough energy only under very small angle to radar - the angle distance to radar is simply so small that stealth technology doesn't work on this distance (it reflects only when the radar is almost under the plane).
2 - Raptor-styled flat belly increases Middel cross section (significally reduce supersonic capabilities) and suffers so called bottom suck resistance effect which causes thrust losses up to 25-30%. Americans solved this problem with F-119 rough power in price of giant fuel consumption. Why should Russians rush to step on the same rake?
3 - Tey rumor about flat nozzles which demand significant changes to rear fuselage and will solve all the AD and stealth problems in this region, so there is no reason to do anything untill the final config is introduced.
 

arnabmit

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Where the PAK-FA falls well short of the F-22A and YF-23 is the shaping design of the lower fuselage and side fuselage, where the general configuration, wing/fuselage join angles, and inlet/engine nacelle join angles introduce similar intractable specular return problems as observed with the F-35 Joint Strike Fighter design. These are inherent in the current shaping design and cannot be significantly improved by materials application. .... the PAK-FA prototype design will produce a large specular return in any manoeuvre where the lower fuselage is exposed to a threat emitter, and this problem will be prominent from the Ku-band down to the L-band.

This problem is exacerbated by the inboard ventral wing root fairings, claimed by some Russian sources to be pods for the concealed carriage of folding fin close combat AAMs, such as the RVV-MD/R-74 series. While these fairings do not introduce large RCS contributions from fore or aft aspects, they will adversely contribute to beam aspect RCS, especially for threats well below the plane of flight of the aircraft.

In the lower hemisphere, it will suffer penalties due to the insufficiently obtuse join angles between the wings and stabilators, and outer engine nacelles.

The axi-symmetric 3D TVC nozzles present the same RCS problems observed with the fixed axi-symmetric nozzles used in the F-35 JSF, and the application of serrated shroud treatments and tailpipe blockers as used with the F-35 JSF will not overcome the inherent limitations of this canonical shaping design. Observed from the aft hemisphere in the L-band through Ku-bands, the PAK-FA prototype configuration will produce to an order of magnitude an equally poor RCS as the F-35 Joint Strike Fighter
http://defenceforumindia.com/forum/indian-air-force/43873-pak-fa-preliminary-stealth-assesment-ausairpower.html

This is because of several reasons:

1 - This place is irrelevent for stealth reasons because it reflects enough energy only under very small angle to radar - the angle distance to radar is simply so small that stealth technology doesn't work on this distance (it reflects only when the radar is almost under the plane).
2 - Raptor-styled flat belly increases Middel cross section (significally reduce supersonic capabilities) and suffers so called bottom suck resistance effect which causes thrust losses up to 25-30%. Americans solved this problem with F-119 rough power in price of giant fuel consumption. Why should Russians rush to step on the same rake?
3 - Tey rumor about flat nozzles which demand significant changes to rear fuselage and will solve all the AD and stealth problems in this region, so there is no reason to do anything untill the final config is introduced.
 

gadeshi

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What are you going to say with this? We all have seen this article 2 years ago or even earlier.
Dr. Copp faps on F-22 like the schoolboy on the pornstar, so yes, he stands for extreme stealth even if all the other capabilities are sacrificed to it.
I've wrought the position of Russian specs on it. I think they have the point.
Stealth is not an invisible cloak, it can work on ranges of 90km and farther and doesn't work when the threat emitter is just under the planes belly :)
BTW, it is too early to assess any stealth characteristics of 1-st phase prototype, isn't it? Let's wait for 2-nd phase production aircraft to make a proper oppinion.
 

p2prada

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The engine mount curvature in the lower fuselage is not a stealthy shape. Why is not a simple composite shroud with RAM coating applied on it?
It is too early to talk about the finer points of stealth.

As it stands today, the prototype won't be stealthy from the rear hemisphere. It is yet unknown if the current engines can be equipped with a radar blocker.

The F-35 does not have stealth optimized engines either. Only the nozzles are serrated. They wanted to keep the program cheap after all.

Also why are the internal weapons bay above the engine mount curvature in the lower fuselage? Wouldn't it give much cleaner lines if the internal bays are expanded to carry more/larger weapons upto the level of the engine mount curvature in the lower fuselage?
Sukhoi likes that tunnel effect on the fuselage which generates greater body lift. It is prevalent on their existing Sukhoi designs too.

Some stealth proponents claim it is bad for stealth. But nobody can say they are 100% sure with such a claim because they need a full scale prototype and measure it in a RCS measurement facility to be sure.

We will simply have to wait for official news that is declassified in probably 50 years from now. :p Or go join the air force. :p
 

gadeshi

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Sukhoi likes that tunnel effect on the fuselage which generates greater body lift. It is prevalent on their existing Sukhoi designs too.
Yes, you are right.
And there is another one reason to leave that tunel - if we'll make fat flat belly, this will largely increase Middel cross-section which will immediately drop supersonic charecteristics.
BTW, why should Sukhoi make deeper bays? To cary what??? Existing bays allow to cary 4 RAMs/ASMs/LRAAMs at once. What do you suppose to cary in deeper ones? Brahmos? :p
 

p2prada

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Yes, large fuselage increases drag and that's not a good thing to have when it is unnecessary.

The internal bays are the largest compared to all other 5th gen aircraft in development or planned. If we can pack two nice big 3000 pounders in it, we have all the umpf we need. The A2A missile loadout is very large too.

It would be nice if we make some FGFA versions with a single long bomb bay door instead of the current two. It will allow us to pack Brahmos class missiles.
 

Ganesh2691

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Naval T-50 PAK-FA For Russian Navy's Future Aircraft Carrier?

At the International Maritime Defence Show currently underway in St. Petersburg, Russia unveiled a model [below] of its proposed future Aircraft Carrier. Designed by the Krylov Shipbuilding Research Institute, this Queen Elizabeth-class inspired Carrier would be powered by a Non-nuclear propulsion system &, as it would appear from the picture, have both catapult & ski-jump launch facilities - a throwback to its Ulyanovsk-class Supercarrier. This, however, is one of three designs it has proposed. Details or visuals of the other two aren't yet available on the "Interwebs".



What was interesting, though, was the sight of its flight deck lined with airframes bearing distinct resemblance to the conventional T-50 PAK-FA 5th Gen fighter, under current development. The accompanying article corroborated this. An article claiming that work ondeveloping a Carrier-capable version of the PAK-FA was on the cards, had been floating for some time, though it also claimed it would operate off Russia's present Carrier, the Admiral Kuznetsov - an unlikely proposition. This model & the article does give more credence to the possibility of such a programme being undertaken. One could, perhaps, see it gaining momentum once the current programme attains a level of maturity, indicated by commencement of its serial production, or its thereabout.

Curiously though, all the PAK-FA's are lined along the ski-jump, and what one assumed earlier was a catapult-launch path, actually has a small upward inclination [circled], like a mini ski-jump - uncharacteristic for a catapult-assisted launch. Could they both be ski-jumps with no catapults on this one? If so, the use of a ski-jump, instead of catapults for take-off operations, calls into question the ability of the aircraft to carry any meaningful payload of armaments. In its current form, the empty weight of the PAK-FA equals the Maximum Take-Off Weight [MTOW] of the MiG-29K, that itself stretches the upper weight limits of a ski-jump launched aircraft. Added weight would appear in terms of the delivery payload the aircraft needs to carry. With structural strengthening, that could be required to make the existing airframe carrier-capable, it is only natural for the Naval PAK-FA to gain even more weight. Frankly, a ski-jump launched T-50 makes no sense.



Would India opt into this project, if it 'gets off the ground'? Unlikely. The weight-class this aircraft belongs to would preclude itsoperation from any of the Indian Navy's [IN] planned Aircraft Carriers. The ski-jump equipped 40&45,000 tonne class of vessels - IAC-1 & Vikramaditya respectively - it would operate would be much more suited to play host to the indigenous LCA Navy fighter & the heavier Russian MiG-29K types of aircraft. A successful execution of the LCA Navy project, forked from the original land-based LCA programme, could encourage developers to attempt the same with the heavier indigenous AMCA programme to meet subsequent requirements. In fact, such considerations could be factored into the design process at its current, nascent stage itself. From all available accounts, it appears that the second indigenous Carrier, the IAC-2, could be a much bigger & a more capable platform, possibly even equipped with EMALS [no official confirmation of specifications, so far - all speculations]. Even if it were to be the case, flying the PAK-FA off them would make for a bad choice, not least because of the dissimilar nature of aircrafts that would then be flying off each Indian Carrier - a salad bowl of fighter aircrafts sporting the Indian Navy roundel! The added economic burden of maintaining such a diverse fleet would only reiterate how bad an idea it could be. A much avoidable scenario.



The idea of a landlubber aircraft, which has a variant that is capable of operating from the high seas, could be very appealing to decision-makers. Economies of scale & commonality in major systems, leading to shared supply chain & maintenance regimes are actually compelling, legitimate factors that go in its favour. However, Engineering considerations have shown that such duality are hard to achieve without compromising on certain aspects, that ultimately rob the project of its original goals. Take, for example, the F-111 "Aardvark". Initially began as a common platform for the US Air Force & Navy, the latter eventually rejected it, instead preferring to go with the F-14 Tomcat. Even the current F-35 Joint Strike Fighter programme underway has witnessed increasing dissimilarity in systems between 3 variants - 'A' [Air Force], 'B' [STOVL] & 'C' [Navy] - as the programme has progressed, than originally envisaged. The primary reason for such mismatch in intention-outcome could be attributed to the significant difference in operating characteristics, particularly during take-offs & landings, between land-based & carrier-based aircrafts. They are much more punishing in the latter's case. Therefore, as mentioned above, the need to modify the aircraft for carrier ops, primarily involving structural strengthening, result in increase in weight, causing reduced payload & range performance of the eventual aircraft. With improving computer-based tools for design, testing & optimisation along with the development of new light-weight, high strength materials, we could one day, soon be able to attain the Holy Grail of an ideal balance between duality & performance. But, perhaps, not today. The opposite path, on the other hand, has seen greater success, evident by Air Force versions of the Hornet, the McDonnell Douglas F-4 Phantom II, as also the French Rafale, to an extent. It is not hard to see why. Originally built for the more challenging Naval use, it was easier, thus, to adapt it for the relatively less stressful Air Force application. The Russians, with the years of neglect to their defence R&D setup, following the collapse of the Soviet Union, could face a bigger challenge in ensuring this conversion process actually leads to an as capable platform as its Air force counterpart is projected to be.

On the one hand, with a displacement of 80,000 tonnes, it would be joining the fraternity of Supercarriers, the kind the U.S Navy moves around in. Yet, on the other hand, the designers seem to be sticking with a conventionally fired power plant to move this proposed behemoth. Given the fact that the Russian Navy today operates Nuclear-powered Cruisers, this aversion to go nuclear on this surface vessel leaves one quite flummoxed. Then again, there are two more designs, of which we no nothing. One is hoping that those designs are easier to explain. This particular model could, perhaps, be a case of providing an option for the sake of providing options, making up the numbers.

At this moment in time, all understandings about Navalising the PAK-FA reside in the realms of non-pivoted speculations. The release of this poorly shot photograph of a model has only buttressed this thought-process. Needles to say, one would have to wait for the availability of some amount of authoritative information to be in a position to draw more calculated inferences. All said & done, an interesting development, to say the least.

Naval T-50 PAK-FA For Russian Navy's Future Aircraft Carrier - AA Me, IN
 

arnabmit

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So with that logic you would say that J-20's bathtub like fuselage has major drag and compromises stealth as well (plus cannards)?

Yes, large fuselage increases drag and that's not a good thing to have when it is unnecessary.

The internal bays are the largest compared to all other 5th gen aircraft in development or planned. If we can pack two nice big 3000 pounders in it, we have all the umpf we need. The A2A missile loadout is very large too.

It would be nice if we make some FGFA versions with a single long bomb bay door instead of the current two. It will allow us to pack Brahmos class missiles.
 

p2prada

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In its current form, the empty weight of the PAK-FA equals the Maximum Take-Off Weight [MTOW] of the MiG-29K, that itself stretches the upper weight limits of a ski-jump launched aircraft. Added weight would appear in terms of the delivery payload the aircraft needs to carry. With structural strengthening, that could be required to make the existing airframe carrier-capable, it is only natural for the Naval PAK-FA to gain even more weight. Frankly, a ski-jump launched T-50 makes no sense.
Nonsense. How many aircraft exist in this world that's been designed on 330 KN - 360 KN of thrust?

PAKFA will end up taking off with full fuel complement and full internal bay loadout without any problems at all. With full air loadout, T/W will be greater than 1.3:1. What is the author thinking!!!

And, no. The empty weight of PAKFA is not equal to MTOW of Mig-29K. These people need to do their homework.

So with that logic you would say that J-20's bathtub like fuselage has major drag and compromises stealth as well (plus cannards)?
Like I said. Nobody can eyeball the aircraft's RCS. It is impossible. You can make educated guesses and still turn out to be wrong.

The J-20 may end up being more stealthy than PAKFA even with canards.

The max you can say is that a J-20 without canards will be more stealthy than a J-20 with canards.

When it comes to drag, yeah, the bigger the cross section of the aircraft, the greater is the drag. The bigger the fuselage with respect to the wing, the greater is the drag. But in the end it comes down to how much thrust you plan to use and what you need the aircraft for. Also greater drag does not mean the aircraft is inferior as long as thrust can compensate for it. The aircraft's lift also adds to it.
 

gadeshi

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Yes, large fuselage increases drag and that's not a good thing to have when it is unnecessary.

The internal bays are the largest compared to all other 5th gen aircraft in development or planned. If we can pack two nice big 3000 pounders in it, we have all the umpf we need. The A2A missile loadout is very large too.

It would be nice if we make some FGFA versions with a single long bomb bay door instead of the current two. It will allow us to pack Brahmos class missiles.
Single large bay and Brahmos missile-class loads are impossible for PAK FA due to the force scheme. Just face it. But these loads are unneeded for FDOW (first-day-of war) agressor.
I will describe the main T-50 tactics and purpose when the time will allow me to do it. Those are very different from your point of view on the 5-th gen fighters, I promise :p
 

gadeshi

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Preliminary assessment on PAK FA external and internal structure:





And the main weapons - X-38M and X-58UShK:



So where do you suppose to push BrahMos?

And the AD flow shemes:

 

gadeshi

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More internal structure:



BrahMos external speculations:


Some speculations on T-50M:

 

p2prada

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Single large bay and Brahmos missile-class loads are impossible for PAK FA due to the force scheme. Just face it. But these loads are unneeded for FDOW (first-day-of war) agressor.
So where do you suppose to push BrahMos?
That's the thing. I wanted to point out that Brahmos isn't just one class of missile. It is being planned as a family of missiles.

The current plan has progressed from Brahmos 1. There will be two new projects. One you may already know as the SCRAMJET based Brahmos 2. The third project will be a supersonic Brahmos 1 meant for Mig-29K, Rafale and FGFA called Brahmos 3. It will be much smaller, will have a new engine while still matching Brahmos 1 performance specs. The weight has been reported to be 1.5 tonnes. That's 1 tonne lesser than Brahmos 1 air version. So yeah, I agree that Brahmos 1 can never fit into FGFA's internal bay. But Brahmos 3, may be.

Brahmos-3 Missile - IDP Sentinel
Brahmos - 3 would be smaller and lighter variant of the Brahmos missile currently fitted on Indian Navy warships.

Tass reported on February 20, 2013 that the new missile would be 6 m in length and weigh 1.5 tons. It's range would be the same as Brahmos - 290 km.

The new missile would be capable of launch from standard sized submarine torpedo tube, as is submarine launched version of the Exocet missile to be fitted on Type 75 Scorpene submarines currently under production at Mazagaon Docks in Mumbai.

The smaller size and lighter weight of the Brahmos - 3 will also make it suitable for carriage by smaller aircraft, such as the Indian Navy's MiG-29K and the under-development FGFA.

The current version of Brahmos can only be carried by Su-30MKI Super 30 aircraft.

BrahMos Aerospace chief A. Sivathanu Pillai first announced the new Brahmos version in New Delhi on March 12, 2011. He said plans are afoot to deploy BrahMos on the Fifth Generation Fighter Aircraft (FGFA). [via Hindu]

"If we are able to reduce the weight of the missile below two tons, we can deploy it on the FGFA and we are looking to do that in future," he said.

He reiterated that Brahmos was considering developing a smaller version of the missile to equip newly acquired naval fighters such as the MiG-29K, at a press conference at DefExpo 2012 in New Delhi on March 31, 2012.

New Ramjet Engine

Brahmos-3 will be an altogether new missile that will use technologies developed for Brahmos.

Since Brahmos-3 needs to be considerably smaller, it will need a completely new, smaller sized ramjet engine.

Brahmos Aerospace has already started work on the new engine, which will be developed in Russia. (Brahmos engines continue to be manufactured in Russia, though eventually manufacture will shift to India.)
So a 6m missile weighing 1.5 tonnes can be a suitable missile for internal carriage, but I suppose we will be needing one single bomb bay rather than two. Who knows, perhaps some specific models will be manufactured with one single bay.

Thanks for the images btw.
 

gadeshi

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No, BrahMos 3 also cannot fit T-50 internal bays because internal catapult launchers are of 2 types:
1 - UVKU-50L (up to 350kgs) for light loads like 250kg bombs and MRAAMs
2 - UVKU-50U (up to 750kgs) for heavy loads like LRAAMs / ARMs / ASMs / light ALCMs / 500kg bombs.

I have meningly posted X-58UShK and X-38M missiles - their sizes and weights are almost a maximum that PAK FA can cary internally.

So, if India will develop some BrahMos 4 with the weight and size of Kh-58UShK, then it will be in PAK FA internal weapons list for sure, but not BrahMos 3.
 
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p2prada

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Interesting, so Brahmos 3 is only for external carriage. That would mean two missiles at least.

That's fine by me. :)

Can you provide details about the X-58UShK and X-38M?
 

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