Sukhoi T-50 PAK FA first flight - pictures, videos and analysis

[Abraham Gubler]

As someone has already pointed out, Sukhoi used an S-duct on the Berkut, so the lack of one on the PAK FA can't be blamed on any kind of technical difficulty. For whatever reason, it was a deliberate design preference.

You'd be hard pressed to find anyone in the LO business who would think a beehive box (if that is what Sukhoi plan to stick between the engine and the intake) is a better way to shield the front of the engine from radar than an S-duct. But the limitations of the available volume from reusing the Su-27's seperated engine bay design mean its radar blockers or naught.

[Abraham Gubler]

The engines are widely separated in the T-50 - is there some advantage to wide inlet separation? Survivability? Missile smoke ingestion? Runway debris? Stores placement? Airflow cleanliness at sideslip? I don't know much at all about this, so I'd be interested in hearing from someone who perhaps does...

In choosing the podded engines configuration (303B) for the F-14 Grumman said the reasons over a more conventional fuselage configuration (303C) were:

* supersonic combat ceiling performance (ie more lift less drag)
* isolated inlets and nozzles (precluding the F-111B’s TF30 interference causing maximum performance problems)
* no need for boundary layer diverter (large displacement between inlet and fuselage)
* engine growth potential (easier to fit bigger engine bays with nothing surrounding them but air)

Since the Su-27 and subsequently the T-50 basically copy the F-14’s configuration down to the main gear bays in the wing gloves (with the obvious exception of being fixed wing) the same reasons should apply.

The downside of the configuration is it generates a lot more horizontally facing surface area for reflecting radar. Particularly in the insides of the engine pods which is outer mould line that just doesn’t exist on a box fuselage aircraft. Also much of the interior volume is of very little height (in the area between the pods). This reduces useable volume for things with high height demands like S-ducts and internal weapon bays.

[lantinian]

Another downside to the widely spaced engines is the significant decrease in roll performance, because you are distributing the weight away from the center of rotation.

[Dragon029]

Although with the 3D TV being spaced apart and imparting more direct force, wouldn't that reduced roll effect be negated? I may just be imagining things but I thought that was one of the reasons MiG's and Su's have their nozzles further from eachother compared to western fighters.

[lantinian]

Although with the 3D TV being spaced apart and imparting more direct force, wouldn't that reduced roll effect be negated? I may just be imagining things but I thought that was one of the reasons MiG's and Su's have their nozzles further from eachother compared to western fighters

Your argument has some scientific but not historic basic.
MiG-29 and SU-27 were designed well before trust vector control as we know it today. The reason there was survivability from a catastrophic failure of one engine affecting the other. The russians has always like to build planes that are are likely to be shot at before they can shoot back. Whether that's operational pesimism or simple pragmatism, otherс more qualified here can tell.

Regarding the roll rate influence.
If spacing the engines ever further оут did increase aircraft roll rate, we would be seeing a lot more configurations of fighters with engines on the wingtips The truth is that, aerodynamic surfaces provide just as much control authority without the accompanying weight. You just need to keep the wingspan short. The easiest to maneuver design is the one that has it mass as close to its center of gravity as possible.

The main reason for spacing of the engine on the T-50 is not to enable better use of trust vectoring in roll (that is a side effect) but to create a space where the main weapons bays will be located. Their configuration is the main design driver of the T-50.

[BDF]

I guess YF-23 was also a victim of "parsimonious financial environment" of Northrop/McDonnell Douglas:

Bad example, given that this was not the production intake design.

Perhaps this should be moved to the YF-23 thread but it appears to me, based on the EMD drawing available, that you can still see the engine face from certain aspects.  There may be some caveats here though. One is that return off the engine face may not reflect directly to the source and would be broken up and absorbed by the duct. The other is that the reflection itself may be aligned with the lobe off the wing and other aligned surfaces.  Either way the F-23 apparently was way in the blue in the ATF KPPs and beat the F-22 "on the pole" so its academic in any case.  The F-23's inlet doesn't apply to the T-50s either.

BDF

[donnage99]

Several analysists noted that the high wing sweep are for supercruise.  I think like the x-32, the high wing sweep is so that the wing can be thicker to accomodate the L-band radars and copious amount of fuel without having to pay a drag penalty.  I don't think the higher wing sweep angle indicate a better supercruise or top speed than seen on the f-22.

[Wil]

Hi!

Some interesting images from Paralay site...



The farther away blades look strange. No? 
 


A proposed radar blocker?



To be continued...

 

[saintkatanalegacy]

interesting indeed specially the radar blocker. . .

seems very distortion-ish

[lantinian]

I like that solution. No moving parts, short, light and cheap looking

[dannydale]

I want to see what it does to pressure recovery and airflow characteristics compared to a baseline configuration, preferably in the form of multiple graphs across different AoA and Mach numbers up to the intake's design maximum. I'd also like to see weight and cost figures plotted against an equivalent serpentine duct.

My suspicions are that it'll play merry hell with the PR and airflow while costing less mass, size, and money than a serp duct, but that its aerodynamic performance could be greatly improved on with careful design.

[saintkatanalegacy]

can be quite bleedy and choky imho

[Wil]

Hello...

We remember. Some old pictures (2007 year) of RCS studies on a early model of PAK FA. I do not remember the name of the Russian institute that conducted the studies. 









Good weekend...!

[Trident]

The other is that the reflection itself may be aligned with the lobe off the wing and other aligned surfaces.

That would be my guess as well. There's no point in trying hard to hide a reflection which will coincide with the airframe's leading edge spikes anyway. As you say, of questionable relevance to the T-50 though.

Several analysists noted that the high wing sweep are for supercruise.  I think like the x-32, the high wing sweep is so that the wing can be thicker to accomodate the L-band radars and copious amount of fuel without having to pay a drag penalty.  I don't think the higher wing sweep angle indicate a better supercruise or top speed than seen on the f-22.

Interesting thought, except the T-50 wing is in fact very thin Not sure if it will cruise faster than the F-22, but thickness was apparently not the consideration behind choosing the sweep angle.

[saintkatanalegacy]

see the model flight "demo" in youtube makes me want to see the real thing do the same and even more

(that ofc in behalf of the people who've seen it )