The T-50 (PAK-FA) Thread

[sobek]

I'm sorry, but this is hardly an explanation. What is the physics behind fan blades being the most obvious reflector?

 

I guess because of their form and the material they have to be made of, in addition to that it is probably next to impossible to coat them with absorbant paint.

[tflash]

I can't see how you'd presume to claim that they've come up with magical radio interference from a source that doesn't radiate back to the attacking radar ( ... which just might defeat the purpose of stealth).

 

hello GG,

 

First of all sorry I missed two pages of the discussion, I guess a time zone problem; but I think indeed you misinterpreted somewhat my post. I am not making claims about the PAK-FA. And certainly not that there is some magical trick there unknown to us, since that would be rather a non-statement.

 

In fact I do not really want to reject that canting fins or hiding fan blades or making facetted and aligned planes can contribute to stealth. As a matter of fact, this is precisely what Boeing is proposing for the Silent Eagle.

 

I just wanted to warn that these external indications that we tend now to use to judge the stealth properties of an aircraft rather help to judge whether an aircraft is of a particular geenration rather than really assessing stealth.

 

A canted fin CAN contribute to stealth, but you have to do massive calculations to know how you have to cant and align it to get an overall relevant RCS reduction.

 

If simply applying these rules of thumb would generate a stealth plane, than the whole competition would be fielding these types of aircraft with ease. Which is not the case.

 

Conversely, I would be rather surprised that Russian engineers would be developping Pak-Fa, considering the massive calculations and anechoic chamber visits it presumes, and afterwards would discover "heck, we all forgot about the simple rule of hiding the fan blades, so our plane isn't stealthy!" That just doesn't make sense. So we may be puzzled at best why we still see the blades, but it doesn't learn us much.

[sobek]

If simply applying these rules of thumb would generate a stealth plane, than the whole competition would be fielding these types of aircraft with ease. Which is not the case.

 

You still missed the point. Nobody said you could design a stealthy aircraft by rule of thumb. But it is definately possible to identify by eye if a part is very much not stealthy.

 

E.g., unhidden fanblades. Fact of the matter is, those are not stealthy, if you don't believe it, look at current (proven) stealth designs and try to find the fanblades. Chances are, you won't.

 

I doubt that russian engineers, be they as crafty as they want, can work around that problem with lower funds (translating into less computing power available) in a way that leaves the fan blades completely exposed. It seems *very* unlikely.

[GGTharos]

hello GG,

 

First of all sorry I missed two pages of the discussion, I guess a time zone problem; but I think indeed you misinterpreted somewhat my post. I am not making claims about the PAK-FA. And certainly not that there is some magical trick there unknown to us, since that would be rather a non-statement.

 

Fair enough.

 

Conversely, I would be rather surprised that Russian engineers would be developping Pak-Fa, considering the massive calculations and anechoic chamber visits it presumes, and afterwards would discover "heck, we all forgot about the simple rule of hiding the fan blades, so our plane isn't stealthy!" That just doesn't make sense. So we may be puzzled at best why we still see the blades, but it doesn't learn us much.

 

I don't think they'd miss it either ... which is why believe this is a design compromise: You'll get large RCS from certain small, particular head-on angles. You can hid this with a radar blocker, which will cost you power. Your other alternative is to just mask the blades by turning the aircraft so it isn't pointed nose-on-target. If this guy is cruising around at 50000' with just a few degrees of AoA pointing up, anyone below him will most certainly not have LOS to those blades.

[Weta43]

Drifting slightly off topic, but:

 

And the study of flight originated with the French and the Dutch.

 

Popular history has it that the Wright Brothers at Kitty Hawk [in the United States] were the first to fly [a heavier-than-air craft], but this is not true! The first flight was by a twenty-five year old New Zealander, Richard Pearse on March 31, 1902. Pearse, (1877 - 1953), is not generally known for this wonderful feat as [until recently?] there has been very little publicity about it. In fact the first formal mention of his achievement was some seven years later in the newspapers of 1909.

 

Pearse was an enthusiast, and perhaps a turn of the century 'mad scientist' inventor. Certainly his other creations - mostly farm machinery - were far from the mainstream and thus [ also ] didn't get much credit. But he did get a few things right on his flying machine that were amazingly advanced for the time.

 

Accounts by witnesses of the flight vary, from "50 to 400 yards in length", but it seems most likely that it was around 350 yards long, and ending prematurely when the flying machine landed in a large hedge - 4 metres off the ground ! The aircraft was the first to use proper ailerons, instead of the inferior wing warping system that the Wright's used.

 

 

http://www.ctie.monash.edu.au/hargrave/pearse1.html

[aaron886]

Surprise! You're from New Zealand and you're telling us a New Zealander was the first to fly heavier-than-air. Next a Brazilian will show up and vehemently argue it was Alberto Santos-Dumont in 1898... Everyone just wants to rep their country.

 

Please drop it.

[sobek]

Technically, there were sucessful attempts to glide long before there was powered flight, i wouldn't claim to know who pioneered that, but Otto Lilienthal comes to mind...

[combatace]

I have a documentary where reflectivity of aircraft parts is described.

 

basically light will reflect off in the same but opposite angle as the original emmission. therefore metalic round surfaces, overall are not the biggest RCS features but will always reflect in any direction to the emitter/reciever no matter where it is placed.

 

Blades are rounded, and on top of this do not have any coating to conceal its metallic nature. Since you have dozens of them packed in a small space they will be good reflectors for the wavelength the airborne radars operate at (i.e. <= antenna size and that is inversly proportional to frequency).

 

Also flat surfaces in different aircraft parts should be of same angles so that all reflected energy is concentrated in one direction. Even if a radar reciever is at propper direction to pick this energy up, it will do so only for a fraction of a second (as a blink of light) as the aircraft is moving along the sky. That is insufficient to keep tracking it, and so it remains stealthy.

 

Again, blades are not flat, and are radial mounted which means stable reflection energy levels anywhere you look at it from, of crourse only limited to the nacelle restraints. But then again the T50's nacelles are straight intead of S shaped, and are themselves reflective to the entire 180 degrees from the bottom aspect.

 

You yourself said Radio waves will reflect same as light so why are engine nacelles so big a problem, because the are flat, isn't it better, because I through a wave at it and it will be reflected in opposite direction with same angle as the angle of incidence. Hasn't B-2 designed on same principle? Also, how will engine blades be reflective all the time and contribute to large RCS, they are small and at particular angle only a few blades will be reflective. Also, blades are twisted and their flat surface is not axial to the jet's plane.

[Pyroflash]

Well, for one, take a look at the B-2A, the engine nacelles are most certainly not flat.

 

In talking about the blades, the fan blades are not exactly flat. They are rounded blades with a slight wash out to them. This results in energy being reflected back at multiple angles, some of which include being bounced back at the receiving radar. Couple that with the fact that there are many hundreds of these blades in the same basic location, and you have a mess of radar returns. This in a nutshell is the basic reason why turbines make for a bad RCS.

[Pilotasso]

You yourself said Radio waves will reflect same as light so why are engine nacelles so big a problem, because the are flat, isn't it better, because I through a wave at it and it will be reflected in opposite direction with same angle as the angle of incidence. Hasn't B-2 designed on same principle? Also, how will engine blades be reflective all the time and contribute to large RCS, they are small and at particular angle only a few blades will be reflective. Also, blades are twisted and their flat surface is not axial to the jet's plane.

 

The only thing having flat surfaces are the intakes, the nacelles themselves have different shapes including round portions simirlaly like the original flanker, in addition to the part where the compressor and turbines are exposed. The production model will have to be different if they want it to be stealthy from the sides and bottom.

 

About the blades, your wrong, but even if you were right they spin at thousands of RPM's so you can imagine how many radar sweeps will have a return reflection...

 

The wrong part of your blade assumption is that the angle of twist on a blade leading edge is variable with length which actualy makes it worse, plus the size of each blade is perfectly compatible with the wavelength airborne radars operate at, infact radars are specifically designed to pick them up.

 

The thing about the B2 is that the nacelles are hidden from ground sources, and it employs different stealth techniques: gentle blending and serrated edges.

Edited September 1, 2011 by Pilotasso

[borchi_2b]

well i think this discussion is pointless here.

 

guys, we all do not know what the production fighter will look like. remember, the yf22 is now over 20 years of age. it took 15 years for the lockheed martin group to get the raptor in the air as usual service product.

now think ahead 15 year in terms of the pak-50, which probably will not even be named that way anymore. i guess it will be something more like, SU-60 or something like that.

 

to the radars and the turbines. well, it is very simble. the modern radar systems are that good, that the can even distinguish between f16, f15, mig29, mig21, su27 and so on.

did you guys know that the f15 uses for the ID of the radarcontact, which it shows on mfd screen, also in real life, not just in game, the typical wavelength of the radarreflections of each engine type for the certain opponents, like mig29 and su27 f16 and so on?

 

i hope you guys understand what i mean with that :-), my english just droped in the toilet, lol, but you maybe realise that even an old f15 uses the engines of a bogey to id the type of aircraft. this in mind, makes even doupt that any plane can be stealth the way we think of. the only thing is, what can be done is the change of the time till detection, but stealthy, i think not really.

imagine an arh missile, ok, that is guided maybe and picks up a f16 or mig at 10nm, for example. the thing is, it will pick up the f22 or the t50 at maybe 1nm, but it can still pick up its target, so stealth is no guarantee for

invulnerability. point

[combatace]

@Pilotasso: I was not talking about the engine intakes for B2 I was talking about the plane as whole. Flat surface parallel to radar beams meaning less reflection. About intakes now I get it you are talking they are straight, flat actually means in plane so got confused. and well T-50 isn't exposing the whole first stage there it has main gear space there so come part is compensated.

[aaron886]

now think ahead 15 year in terms of the pak-50, which probably will not even be named that way anymore

 

I think you're right, seeing as it's not even named that right now...! :D

[mikoyan]

@Pilotasso: I was not talking about the engine intakes for B2 I was talking about the plane as whole. Flat surface parallel to radar beams meaning less reflection. About intakes now I get it you are talking they are straight, flat actually means in plane so got confused. and well T-50 isn't exposing the whole first stage there it has main gear space there so come part is compensated.

 

That and the ramps on the intake

[Vekkinho]

PErhaps already posted, Full HD T-50 display at MAKS 2011:

[Antartis]

Look out T-50 air-brakes at 04:20 and 04:45

 

[Antartis]

From http://fotografersha.livejournal.com/152397.html

 

 

 

 

[Vault]

well i think this discussion is pointless here.

 

guys, we all do not know what the production fighter will look like. remember, the yf22 is now over 20 years of age. it took 15 years for the lockheed martin group to get the raptor in the air as usual service product.

now think ahead 15 year in terms of the pak-50, which probably will not even be named that way anymore. i guess it will be something more like, SU-60 or something like that.

 

to the radars and the turbines. well, it is very simble. the modern radar systems are that good, that the can even distinguish between f16, f15, mig29, mig21, su27 and so on.

did you guys know that the f15 uses for the ID of the radarcontact, which it shows on mfd screen, also in real life, not just in game, the typical wavelength of the radarreflections of each engine type for the certain opponents, like mig29 and su27 f16 and so on?

 

i hope you guys understand what i mean with that :-), my english just droped in the toilet, lol, but you maybe realise that even an old f15 uses the engines of a bogey to id the type of aircraft. this in mind, makes even doupt that any plane can be stealth the way we think of. the only thing is, what can be done is the change of the time till detection, but stealthy, i think not really.

imagine an arh missile, ok, that is guided maybe and picks up a f16 or mig at 10nm, for example. the thing is, it will pick up the f22 or the t50 at maybe 1nm, but it can still pick up its target, so stealth is no guarantee for

invulnerability. point

 

It's called non co-operative target recognition (NCTR) which can be used as a basic form of IFF. NCTR is the main reason why engineers prefer to hide the blades.

[combatace]

Yes but you need previous data to compare with, the jet's computer has a database which compares the RCS of the A/c to the ones in its database and tags the Id so when its intercepts a new plane it cannot be tagged more than unknown.

[Vault]

I can't answer that because I don't know the in's and out's of how NCTR works. I've read that NCTR uses the front and rear exhaust blade profiles for identification, I'd be speculating if I said anymore than that.

[GGTharos]

It uses more than that, and it isn't the reason to hide the engine fans. The RCS contribution is.

[combatace]

I can't answer that because I don't know the in's and out's of how NCTR works. I've read that NCTR uses the front and rear exhaust blade profiles for identification, I'd be speculating if I said anymore than that.

 

I find it strange to identify different parts of aircraft just by its radar reflection.

[GGTharos]

They use microdoppler feature extraction. Sort of like submarine/ship ID by propeller sound analysis.

 

They can extract other features as well.

[Vault]

It uses more than that, and it isn't the reason to hide the engine fans. The RCS contribution is.

 

In my country to work on these systems you need to be DV cleared. You can't apply for DV clearance, you're invited to be DV cleared by the goverment. Not even the pilots know how these systems work on a technical level, they just know they work and what buttons to press. I'm always highly sceptical when anyone claims to know how they work.

 

By covering up the turbine blades NCTR and RCS reduction go hand in hand. For 5th gen aircraft what you say is true but not for legacy 4th gen.

[GGTharos]

Get your DV clearance here:

 

http://books.google.ca/books?hl=en&lr=&id=hrp_QP-vz4sC&oi=fnd&pg=PR15&dq=non-cooperative+target+recognition&ots=xuaNOXYLhG&sig=xdfZ62xvyKmUYVbhuaSrlVAhJoA#v=onepage&q=non-cooperative%20target%20recognition&f=false

 

You may need clearance to work on the systems, but you don't need clearance to understand the basics of what they do. These are things that have been tested in academic settings; militaries may employ some very specific techniques and have certain knowledge of their target set which is not shareable for obvious reasons , as well as keeping their capabilities secret to prevent the opposition from knowing how to easily screw up their NCTR - but the general high level ideas behind it, and even specific algorithms are available for viewing in an academic setting.

 

In my country to work on these systems you need to be DV cleared. You can't apply for DV clearance, you're invited to be DV cleared by the goverment. Not even the pilots know how these systems work on a technical level, they just know they work and what buttons to press. I'm always highly sceptical when anyone claims to know how they work.

 

Two birds, one stone. NCTR wasn't the deciding factor. This is nothing other than a basic stealth design feature.

 

By covering up the turbine blades NCTR and RCS reduction go hand in hand. For 5th gen aircraft what you say is true but not for legacy 4th gen.