Sukhoi PAK FA

[gambit]

My questions are -

1. For F-22, the frontal RCS is claimed to be 0.001 m^2 and for F-35 it is claimed to be 0.01 m^2. How do these calculate against your Bowtie DB figures and how accurate are these? Also, what will be the lateral RCS for the F-22 and the F-35?

2. For PAK-FA, what will be the comparable figures, in your opinion?

There are no credible information regarding the F-117's RCS value, let alone the F-22 or F-35. Keep in mind that a 10dB difference mean a %50 difference in detected distance, meaning if A and B are detected at 200 km and A did <something> to drop -10dB in output, A will be detected at 100 km. Give or take a few km. The ONLY way we will know within the accepted %3 range of statistical certainty is to put each aircraft inside a controlled anechoic chamber, like Benefield at Edwards AFB in California, and take our time measuring them.

Edwards Air Force Base - Media Search

We can derive physical dimensions and surface features from photos and insert each aircraft into software written specifically for RCS modeling and estimation, and have no doubt plenty of people have done that, but just as 'Garbage In. Garbage Out.' any data from these calculations should not be construed as the true values because of the differences in physical dimensions between actual and estimated. Saying 'garbage' may be extreme because the commercial software are very well written and even Lockheed uses them so at least we have enough to make these discussions interesting.

 

[gambit]

This is a supplement to post 1516 => http://defenceforumindia.com/indian...soboronexport-hal-jointly-127.html#post310748

Post 1516 was about the X-band as the targeted band and explained it in principle. This supplement will explain the why in the engineering.

It is known that there are several characteristics of a radar transmission that directly affect the quality of target resolutions, the main ones are:

- Beamwidth
- Antenna shape
- Antenna dimension
- Frequency
- Power

The last item 'Power' affect distance. The other items have complex relationships to each other.

Definition: radar resolution cell

radar resolution cell: The volume of space that is occupied by a radar pulse and that is determined by the pulse duration and the horizontal and vertical beamwidths of the transmitting radar. Note: The radar cannot distinguish between two separate objects that lie within the same resolution cell.

The above illustration is about radar resolution cell. In most cases, a narrow beamwidth in both the horizontal and vertical planes are desirable, as in the left situation. When volume search is the mission, the wider the beam the greater the volume that can be scanned per sweep, however, it will be at the expense of target discrimination in a multiple targets environment.

Repair and Maintenance Manuals - Integrated Publishing

Beamwidth varies directly withwavelength and inversely with antenna size. Radarsystems that produce relatively small beam widths generally provide greater target resolution.

Basically, the larger the antenna the smaller the beamwidth, however, the lower the frequency employed, the larger the beamwidth for the same antenna.

Another consideration is beam broadening.

RADAR BEAM CHARACTERISTICS

As pulses travel away from the antenna, the beam takes on a cone-like appearance and expands in all directions. This expansion or beam broadening increases pulse volume, resulting in decreased signal strength (fig. 2-11). Distant targets appear distorted, in fact, they may not be seen at all. Beam broadening also causes "partial beam filling," which implies that distant targets occupy proportionally less of anexpanded beam. Thus, the true characteristics of a target may be hidden or altered during display.

Beam broadening reduces azimuthal resolutionand produces a form of radar nearsightedness. As the beam diameter increases with distance, closely spaced targets may occupy the beam simultaneously and appear as one echo. In short, multiple targets at a distance are difficult to see correctly.

What this mean -- so far -- is that for a 'fighter' class aircraft where internal volume is already limited, the X-band proved to be the most useful in terms of beamwidth for superior target discrimination in a multiple targets environment.

Radar Cross Section

Raleigh region. If the target is a lot smaller than the wavelength of the radar system, the target is said to be in the Raleigh region. If the target is in the Raleigh region, the radar cross section of the target tends to be smaller than the target's physical size.

Resonance region. If the target is of similar dimension to that of the wavelength, the target is said to be in the resonance region. In the resonance region, the radar cross section of the target may vary a great deal but tends to be larger than the physical size of the target.

Optical region. The optical region occurs when the target is much larger than the operating wavelength of the radar. This is quite often the case with operational radar systems whose wavelengths are normally in the order of centimetres in length. When operating in this region, the radar cross section of the target is similar to its physical size.

The X-band is centimetric (cm) which will have any target in the 'Resonance' or 'Optical' region. An aircraft is meters in length and wingspan. In order to place an aircraft into the 'Raleigh' region, the wavelength would have to be in the mhz meters length HF/VHF/UHF bands. The F-15E antenna is 0.9 m in diameter. If this antenna transmit in the mhz bands, the beamwidth would be so large -- double digits of degrees -- that it would be worthless, whereas the more desirable beamwidth is between 1-5 deg.

Diameter of a Raindrop

"A raindrop may have a maximum diameter of 0.25 centimeter."

"Raindrops generally have a diameter greater than 0.5 mm (0.02 in.). They range in size up to about 3 mm (about 0.13 in.) in diameter."

"The 4 mm maximum diameter of raindrops probably results because raindrops larger than this size tend to break up when colliding with other large raindrops."

The higher the freq the more vulnerable to atmospheric attenuation (loss) and the example above is the reason why. The X-band is centimetric and when a pulse encounter a raindrop the raindrop will be in the 'Raleigh' region. However, if a millimetric freq is used, when this millimetric pulse encounter a raindrop the raindrop will be in either the 'Resonance' or 'Optical' region, resulting in a clutter display of weather phenonmena instead of other intended targets such as armed fighters and bombers.

Add all these factors together and there are those complex relationships that system engineers must take into consideration when designing a system for a specific mission. This is why the X-band proved to be the most useful for the 'fighter' class aircrafts and because of this usefulness, RCS shaping must target this particular threat freq.

These factors and their complex relationships are also the reason why AWACS antennas are relatively 'flat' disks that they are: Antenna shape. A 'vertical' fan is from an antenna shape that is 'long'. A 'horizontal' fan is from an antenna shape that is 'tall'. Basically, the fan is always the opposite of the antenna's orientation and each orientation has its purpose. A 'horizontal' fan sweeps in an up-down motion and is useful as a height finding radar. A 'vertical' fan sweeps either side-side or 360 deg is useful in finding targets' locations in respect to one's own position. The wider the fan the more volume is can cover per sweep cycle so a height finding radar can also find target positions but generally if target position and volume search are the goals then a 'vertical' fan is preferred because of the 360 deg ability with the benefit of altitude information per revolution.

 

[SATISH]

Gambit,

Can you please tell me at what range is the F22's rcs 0.0001m^2. Because I know that range is one of the major factor as dissipation of radar waves takes place and it loses power at a certain distance and dosent get reflected back

 

[aimarraul]

 

[p2prada]

Edwards Air Force Base - Media Search

We can derive physical dimensions and surface features from photos and insert each aircraft into software written specifically for RCS modeling and estimation, and have no doubt plenty of people have done that, but just as 'Garbage In. Garbage Out.' any data from these calculations should not be construed as the true values because of the differences in physical dimensions between actual and estimated. Saying 'garbage' may be extreme because the commercial software are very well written and even Lockheed uses them so at least we have enough to make these discussions interesting.

Something that we have here,

This pdf is quite old.

http://faradey.com/files/bkamera.pdf

If you scroll right to the bottom, you will find a reference to Anechoic chambers purchased and installed by our defence industry and air force. HAL will have 2 chambers meant to fit fighter sized aircraft along with a slightly smaller third one. No idea if we have any radar range planned.

As for Russia they have had Anechoic chambers since a long time. The Bars radar was tested in the 5th Central Research Institute nearly 2 decades ago.

 

[p2prada]

Add all these factors together and there are those complex relationships that system engineers must take into consideration when designing a system for a specific mission. This is why the X-band proved to be the most useful for the 'fighter' class aircrafts and because of this usefulness, RCS shaping must target this particular threat freq.

These factors and their complex relationships are also the reason why AWACS antennas are relatively 'flat' disks that they are: Antenna shape. A 'vertical' fan is from an antenna shape that is 'long'. A 'horizontal' fan is from an antenna shape that is 'tall'. Basically, the fan is always the opposite of the antenna's orientation and each orientation has its purpose. A 'horizontal' fan sweeps in an up-down motion and is useful as a height finding radar. A 'vertical' fan sweeps either side-side or 360 deg is useful in finding targets' locations in respect to one's own position. The wider the fan the more volume is can cover per sweep cycle so a height finding radar can also find target positions but generally if target position and volume search are the goals then a 'vertical' fan is preferred because of the 360 deg ability with the benefit of altitude information per revolution.

Larger radars like the Greenpine, Phalcon, M3R, Wedgetail etc use L band. Erieye, Sampson,EL/M 2248(MF-STAR) use the S band. The radars linked to Patriot program, AN/MPQ-53 and 65 work in the C band. Is there any particular reason to why other bands are preferred over X band for such large radar systems?

 

[ace009]

Here's my 2 cents -
The L-band operates at a longer wavelength (15-30 cm) at 1-2 GHz. They have extended range and can pick up bogies at a long distance (300+ km) even from air-turbulence from an approaching aircraft. they might not be well suited to identify the type of aircraft or the exact number, but as an early warning system they can provide the direction of approach, speed, possible size and number for the aircraft.
The C-band operates at "medium" 4-8 cm wavelength 4-8 GHz. Because of the wavelength and freq of this band, this radar maybe able to detect, identify and analyze the flight paths of smaller / leaner flying objects like a ballistic missile at a relatively long distance (200-300 km) Hence the patriot missile systems use this type of radar. However, the C-band is not ideal for small ballistic missiles, which is why the patriots had 10% success rate against the Scuds.
The X-band is much more sensitive with a small wavelength and require less power/ smaller antenna (which is why it is used in aircraft), however, the large freq means it has high attenuation in the lower atmosphere.

 

[gambit]

Gambit,

Can you please tell me at what range is the F22's rcs 0.0001m^2. Because I know that range is one of the major factor as dissipation of radar waves takes place and it loses power at a certain distance and dosent get reflected back

Not possible. Not because I know and refuse to tell because of OPSEC considerations but simply because no one knows. At least no one in the general populace that is not connected to the F-22's program. Based upon my posts 1516 and 1522, we know that a 'fighter' class radar antenna will limit its effective detection range to 150-200 km. A clean F-16 is about 1 meter square in that range and from my experience that was very tough. Once the F-16 dropped below 1000 ft altitude, sea surface clutter hid him completely. So if we are reasonably certain the vast majority of the F-22's opponents are already limited to that 150-200 km detection capable range, we can be reasonably assured that the F-22 is shaped to target that distance.

 

[gambit]

Larger radars like the Greenpine, Phalcon, M3R, Wedgetail etc use L band. Erieye, Sampson,EL/M 2248(MF-STAR) use the S band. The radars linked to Patriot program, AN/MPQ-53 and 65 work in the C band. Is there any particular reason to why other bands are preferred over X band for such large radar systems?

Yes. That antenna dimension and beamwidth relationship as you accidentally answered your own question. For any freq, to get a desired beamwidth, you must either change the freq or change antenna dimensions or work out a compromise between the two. Those lower freq longer wavelengths have more energy to get a longer reach, but to have reasonably accurate target discrimination in a dynamic and multiple target environment, ground radar antennas are usually much larger than its airborne brothers to have the same beamwidth. However, once a missile is launched and if the missile has its own radar guidance it will have one of the X-band freqs. The missile can work in concert with ground radar data, but whether if ground data can override its own data is a different issue.

 

[gambit]

Something that we have here,

This pdf is quite old.

http://faradey.com/files/bkamera.pdf

If you scroll right to the bottom, you will find a reference to Anechoic chambers purchased and installed by our defence industry and air force. HAL will have 2 chambers meant to fit fighter sized aircraft along with a slightly smaller third one. No idea if we have any radar range planned.

As for Russia they have had Anechoic chambers since a long time. The Bars radar was tested in the 5th Central Research Institute nearly 2 decades ago.

What this mean is that NO ONE is going to release their data. The quality of the measurement regime is definitely debatable but no matter the results, NO ONE is going publish the figures.

 

[p2prada]

Yes. That antenna dimension and beamwidth relationship as you accidentally answered your own question. For any freq, to get a desired beamwidth, you must either change the freq or change antenna dimensions or work out a compromise between the two. Those lower freq longer wavelengths have more energy to get a longer reach, but to have reasonably accurate target discrimination in a dynamic and multiple target environment, ground radar antennas are usually much larger than its airborne brothers to have the same beamwidth. However, once a missile is launched and if the missile has its own radar guidance it will have one of the X-band freqs. The missile can work in concert with ground radar data, but whether if ground data can override its own data is a different issue.

Hmm. But I thought there would be more to it depending on how different waves differ over different surfaces. I thought since being stealthy means reducing returns in the X band, the longer wavelengths may work a little better in that respect.

I did not know large arrays were designed with such a simple point in mind. So the Erieye uses the S band as it has a smaller array than say a Phalcon which uses longer wavelength L band on a larger array. All to get a beamwidth of the same size.

From what I know the Erieye pumps out 2.5KW at peak while Phalcon does much higher. So, how would that compare to an aircraft like Su-35 or F-22(maybe) which can deliver 20KW. Does that mean the 2 fighters will have a greater detection range than the Phalcon and Erieye while they all have similar beamwidths? Or is it possible the Su-35 and F-22 will be even better than the AEW&Cs in that aspect?

 

[gambit]

Hmm. But I thought there would be more to it depending on how different waves differ over different surfaces. I thought since being stealthy means reducing returns in the X band, the longer wavelengths may work a little better in that respect.

More precisely -- structures. Keep in mind that an aircraft is the opposite of the sphere, which is the simplest structure in radar detection. All this talk about the L-band being more effective against 'stealth' has more to do with being effective against the many smaller structures on an aircraft than against large expanse of surfaces such as the wings or the fuselage.

For example...

In the above illustration, both the concave and the convex structures may have the exact square surface area but will produce opposite RCS contributorships. The concave structure is called a 'convergent' radiator where any amount of energy is redirected towards the incident direction in a very concentrated manner. The convex structure is called a 'divergent' radiator and the seeking radar will see only that tiny amount of specular reflection and the rest of the signal became assorted surface wave behaviors. The convex structure will produce a much smaller RCS contributing factor than the concave. Obviously, we do not want concave structures of any size at all.

In the above illustration, we have another type of concave structure that will produce similar convergent radiator behavior. Same increasing of RCS contributorship with longer wavelengths.

That is why 'stealth' aircraft maintainers must exercise caution when working to avoid creating gouges of any shape. But in the event that there are any concave structures, no matter how visible they are to the eye or sensitive to the touch, longer wavelengths will produce greater contributorship than shorter ones. Surface expanse does produce greater contributorship with longer wavelengths but not as great as structures does and with the X and L bands, they are still centimetric.

I did not know large arrays were designed with such a simple point in mind. So the Erieye uses the S band as it has a smaller array than say a Phalcon which uses longer wavelength L band on a larger array. All to get a beamwidth of the same size.

From what I know the Erieye pumps out 2.5KW at peak while Phalcon does much higher. So, how would that compare to an aircraft like Su-35 or F-22(maybe) which can deliver 20KW. Does that mean the 2 fighters will have a greater detection range than the Phalcon and Erieye while they all have similar beamwidths? Or is it possible the Su-35 and F-22 will be even better than the AEW&Cs in that aspect?

Essentially -- yes. There are conditions where peak power output is not desirable but essentially, power equals distance. Keyword search for you 'power-aperture product'. This characteristic of radar detection regarding power is so crucial that it was part of SALT 1 treaty...

Theater Missile Defense and the Anti-ballistic Missile (ABM) Treaty | Union of Concerned Scientists

A radar's capability depends strongly on its power and the size of its antenna-- usually expressed in terms of its "power-aperture product," the product of its average power output (in watts) and the area of its antenna (in square meters). The detection range increases as the power-aperture product is increased either by deploying a different radar with greater size or power (or both) or by linking multiple radars electronically (assuming they have been designed to allow this), which will increase the search capability as the square of the number of linked radars.

Basically, SALT 1 said I cannot have my anti-ballistic missile (ABM) defense radar over X power output. It was part of the treaty to allow each side a reasonable chance of destroying the other. A rather bizarre treaty where each side agreed to limit its defensive capability but that is for another discussion.

 

[Anshu Attri]

Indian Air Force to seek engine upgrade for fighter aircraft

Indian Air Force to seek engine upgrade for fighter aircraft - Economy and Politics - livemint.com

New Delhi: The Indian Air Force will seek a more powerful engine for the Sukhoi T-50 fifth-generation stealth fighter jet that is being jointly developed by Russia and India for delivery in 2018, a top government official said.

The air force is aiming to induct 250 Sukhoi T-50s with stealth technology, 126 medium multi-role combat aircraft and 120 indigenously built light combat aircraft, known as the Tejas, in addition to upgrading RAC MiG-29, Dassault Mirage 2000H/TH and Jaguar fighter jets.

India's Hindustan Aeronautics Ltd, Russia's Rosoboronexport and Sukhoi Co. had signed an agreement in 2010 to jointly design and develop the fifth-generation fighter jet.

India hopes to induct the jets from 2017-2018 to bolster its air defences.

Air chief marshal N.A.K. Browne said he was satisfied with the progress of the fighter jet project, but will seek an upgrade of the engine.

"It has flown a number of sorties," Browne said on the sidelines of an aerospace conference in New Delhi. "A lot of changes are going to take place by the time we get the first aircraft. The engine is going to be different. It's going to be a more powerful engine than the one fitted right now. We have selected the engine."

The air force chief did not provide details of the upgraded engine or its capabilities.

"Perhaps what he is referring to is the 117S engine, which is an advanced version of the AL-31F engine," said Deba R. Mohanty, senior fellow in security studies at Observer Research Foundation.

India may learn very little about design from the stealth jet projects as most of the work has already been completed, Mohanty said.

"When we are talking about joint development, three areas are important—upgraded avionics, composite material related to stealth technology and the engine, which could have helped our own Kaveri engine programme," he said. "I don't think India is going to get much in design knowledge, maybe more in the production stage. I wish India could have joined earlier."

Timelines for the delivery of the fifth-generation aircraft to the air force will become clear once the programme moves from prototype to production, Browne said.

"By 2017-2018, we expect the first aircraft to come to us," he said. "The aircraft is still under prototype testing. So, once the prototype is over and it gets into the production phase, then we will be sure of the timelines."

Meanwhile, the bids for the multi-billion-dollar medium multi-role combat aircraft order, which has Eurofighter and Rafale as the two contenders, are expected to be opened by October.

The Eurofighter is built by a consortium of four countries—the UK, Italy, Spain and Germany—whereas Rafale is developed by France's Dassault Aviation.

"On 7th of October, we have a meeting where some of the issues are going to be discussed," Browne said. "Once the issues are cleared by the middle of the month we should be in position to open the bids."

India will need both the medium multi-role fighter jets as well as the stealth fighters, Browne said.

"The medium multi-role combat aircraft does not have stealth features, it does not have super cruise capabilities, whereas the fifth-generation fighter aircraft has all that," Browne said.

"It has (an) armament base, where all the missiles and weapons are inside the aircraft which gives a certain amount of stealth potential. Medium multi-role aircraft has its own set of capabilities. So they are a generation apart," Browne added.

Typically, an air force of India's size should have 30% fifth-generation jets which make up the frontline aircraft and 40% of medium-range aircraft, Mohanty said.

 

[nitesh]

Chindits is reporting that IAF has finalized on the engine of FGFA, which is powerful then the PAK FA one

 

[Galaxy]

 

[Galaxy]

 

[cir]

The pair aren't gonna fly any time soon。

As a matter of fact, they won't resume prototype testing till next Spring the earliest.

It is gonna be a long winter for those who frequent this thread.

 

[nitesh]

Ok here is something very interesting, seems IAF is moving away from 2 pilot systems, seems we will see lot of single seat ones

IAF Chief: 214 FGFAs, HAL Tejas Clearance Delayed, MRCA Deliveries by 2014 and more.. | India Defence

Indian Air Force plans to induct the FGFA / PAK-FA as 166 single-seaters and 48 twin-seaters.

 

[bose]

I think its a very good decision to go for single seater as the twin seater will take some more time to come as it will require design changes to smaller extent... until twin seater comes let us have some of the single seater fighters...

 

[nitesh]

^^ Agree here, also it affects the RCS of the fighter, I guess the single seat ones will form the fighting arm, some twin seat ones as trainers, and some acting as dedicated bombers with relatively lower RCS as compared to other options available