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Radar 101 and DSI intakes discussion

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pegasus

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To anyone who is still listening is the point peagsus trying to make that all “stealth” planes are supposedly more easily tracked than everyone who isn’t wearing a Su-57 t-shirt thinks they are (which appears misguided at best), or is it still all specifically tied up with -anti-DSI-obsession (which makes it concerning from mental well-being perspective, at best)?
https://findpatent.ru/patent/250/2502643.html


The shape of the airframe reduces the number of directions that radar signals are reflected in with the angles of sweep of the wings and the tail plane's leading and trailing edges, the edges of the air intakes and hatch covers being reduced and deflected from the aircraft's axis. Viewing the aircraft from the flank, the fuselage sides, lateral edges of the air intakes and vertical empennage are all deflected at the same angle.

Some openings and slots on the airframe's surface - such as the boundary-layer bleeds on the sides of the air intakes and the openings on the upper fuselage immediately aft of the cockpit - are covered with a thick grid, featuring a mesh of less than one quarter of the wavelength of a search radar, which reduces the reflections from these uneven surfaces. Gaps between the airframe elements are filled with conducting sealants, while the glazing of the cockpit canopy is metallised.

https://findpatent.ru/patent/250/2502643.html

The technical result, which is aimed invention is to provide a prob is gnosti change the angle of the solution steps of one of the arrow-shaped wedges of inhibition and minimum of the cross-section area of the inlet (throat) without education in its channel undesirable longitudinal cracks and stuttering mobile elements. Such regulation would, in turn, to ensure the stable operation of the engine on all flight modes of the aircraft up to Mach number M=3.0 recoveries total pressure at the engine inlet at a level not lower than the standard for adjustable flat intakes and total heterogeneity of the stream below the maximum permitted value ("Aerodynamics, stability and control of a supersonic aircraft", Ed. by Gsena. - M.: Nauka. Fizmatlit, 1998). Thus due to the parallelogram shape of the entrance of the air intake on the front view and make all edges sweep reduced radar visibility of the object on which it is installed. The greatest effect of reducing the radar signature will be achieved when the edge of the inlet parallel to any members of the object (front or rear edges of the wing, empennage, and others).

1572557226688.png

1572556835555.png

1572556891810.png
1572556920946.png

https://findpatent.ru/img_show/11172942.html
https://findpatent.ru/patent/246/2460892.html

https://russianpatents.com/patent/246/2460892.html
© RussianPatents.com - patent search, 2012-2019

The diverterless supersonic inlet (DSI) of the Lockheed Martin joint strike fighter (JSF), which operates mostly at transonic speeds, has been designed taking whatever is mentioned above into enough account. Fundamental researches on this inlet configuration have been continued since the mid-1990s.
The inlet cowl lips are so designed as to allow most of boundary layer flow to spill out of the aft notch. The DSI structure complexity has been greatly reduced by the removal of moving parts, a boundary layer diverter and a bleed or bypass system thus decreasing the aircraft’s empty weight, production cost, and requirements of maintenance-supporting equipment[1-2].

the effects of the free stream Mach number on the mass flow coefficient and total pressure recovery when D = 0º and E = 0º. As the free stream Mach number increases, the mass flow coefficient decreases, and, after reaching the minimum at Mach number 1.000, it increases. Fig.7 also shows that the total pressure rises and remains constant when the free stream Mach number is up from 0.600 to 1.000, and, afterwards, drops sharply while the free stream Mach number approaches the supersonic.

4 Conclusions A wind-tunnel test of a ventral diverterless high offset S-shaped inlet has been carried out to investigate the aerodynamic characteristics at transonic speeds. Some conclusions can be drawn as follows: (1) There is a large region of low total pressure at the lower part of the inlet exit caused by the counter-rotating vortices formed at the second turn of the S-shaped duct. (2) The performances of the inlet reach almost the highest at Mach number 1.000. This renders the propulsion system able to work with high efficiency in terms of aerodynamics. (3) As the mass flow coefficient increases, the total pressure recovery decreases; the distortion increases at Ma0 = 0.850, but fluctuates at Ma0 = 1.000 and 1.534. (4) The total pressure recovery increases slowly first, and then remains unchanged as the Mach number rises from 0.600 to 1.000. (5) The performances of the inlet are generally insensitive to angles of attack from –4º to 9.4º and yaw angles from 0º to 8º at Mach number 0.850, and angles of attack from –2º to 6º and yaw angles from 0º to 5º at Mach number 1.534.


1572557149718.png


A Ventral Diverterless High Offset S-shaped Inlet at Transonic Speeds Xie Wenzhong*, Guo Rongwei College of Energy and Power Engineering, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China Received 13 September 2007; accepted 18 December 2007
 

Ronny

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First let us cool down, we are in no need to convince each other by force.
Let me say your calculations do not prove what is a creeping wave, in no way you have done that. the equation you used only proves an angle and at short distance (1 meter) and few orders, in fact you only calculated one order, the formula it is basically to calculate the distance of any order from the middle order 0, it does not prove what is a creeping wave so you have not proved your conjecture.
you did not prove what is a creeping wave by no means, the NASA documents i gave you, gives a basic definition, but if you open the link is full of differential equations, i only quoted the basic non mathematical definition they gave:
If you look at this laser diffraction it has more than one order
The basic definition of the NASA document is tangents are the equivalents to slits, so the wave is diffracting in each and every tangent that a 180 deg a half circumference has, basically there are plenty of slits, not only one like you are trying to portrait.
And you can clearly see the intensity decrease dramatically as the order number increase so the smaller the angle between each order to the middle order, the quicker the intensity reached 0. Basically the bigger your object compared to the wave, the less diffraction the wave will have when it hit the object, the less likely you have creeping wave. This is quite clear when looking at the RCS value of a sphere vs frequency. At high frequency, there is basically no creeping wave to interfered with specular return, but once the wavelength approaches the sphere dimension, we see a sharp increase in RCS fluctuation range because the creeping wave interfered with the specular return.





Now your statement was DSI intakes are smooth i told you it does not matter, with lidars or powerful radars they become visible and closer to the radar they will be pretty visible.
You can not prove the radar range formula say stealth means invisibility, the only thing i said, is the only real limitation is the electricity an aircraft can provide to its radar, but ground radars do not have such limitations and aircraft work with networks, to exemplify it, imaging you have a hall with many lamps, each light is helping you to see, passive radars basically use that, any frequency they are using to see.
First of all, no one here ever says stealth aircraft is invisible, so please stop making strawman argument. Lidar is laser used as radar, it is affected by atmospheric conditions such as fog, cloud, rains , smokes, snow.... the range is nowhere close to an actual radar.
Second of all, DSI being smooth does matter because it reduces the amount of surface scattering, it is the same reason the surface of stealth aircraft is far smoother than the surface of conventional aircraft. You can't pretend variable inlet are equally as stealthy as a DSI because they aren't.
Finally, it doesn't matter that your powerful radar can detect stealth aircraft because they can't detect stealth aircraft from as far as they can detect a normal aircraft, that what matters.
1.PNG

and RCS make a big difference whether your radar is powerful or not
jamming-burn-throgh311-1.png
 
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pegasus

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Now your statement was DSI intakes are smooth i told you it does not matter, with lidars or powerful radars they become visible and closer to the radar they will be pretty visible.
You can not prove the radar range formula say stealth means invisibility, the only thing i said, is the only real limitation is the electricity an aircraft can provide to its radar, but ground radars do not have such limitations and aircraft work with networks, to exemplify it, imaging you have a hall with many lamps, each light is helping you to see, passive radars basically use that, any frequency they are using to see.
First of all, no one here ever says stealth aircraft is invisible, so please stop making strawman argument. Lidar is laser used as radar, it is affected by atmospheric conditions such as fog, cloud, rains , smokes, snow.... the range is nowhere close to an actual radar.
Second of all, DSI being smooth does matter because it reduces the amount of surface scattering, it is the same reason the surface of stealth aircraft is far smoother than the surface of conventional aircraft. You can't pretend variable inlet are equally as stealthy as a DSI because they aren't.
Finally, it doesn't matter that your powerful radar can detect stealth aircraft because they can't detect stealth aircraft from as far as they can detect a normal aircraft, that what matters.
LM Aeronautics JSF Design Adopts DSI
The DSI concept was introduced into the JAST/JSF program as a trade study item in mid-1994. It was compared with a traditional "caret" style inlet. The trade studies involved additional CFD, testing, and weight and cost analyses. The new inlet earned its way into the JSF design after proving to be thirty percent lighter and showing lower production and maintenance costs over traditional inlets while still meeting all performance requirements.

https://www.codeonemagazine.com/article.html?item_id=58



System-level trade studies were performed to quantify the weight, cost, and benefits of the DSI, compared to more conventional inlets (e.g., F-22 and F/A-18E/F caret inlet systems). In these studies, a 30-percent inlet weight reduction was estimated for the DSI, relative to the reference caret inlet. The largest contributing factor was the elimination of the bleed and bypass systems. Studies performed by other ACIS contractors [25] indicated similar savings for diverter-less/bleed-less systems




The short test program, starting in 1996, proved highly successful with the modified F-16 tested at all points of the flight envelop up to Mach 2. The tests demonstrated comparable flying qualities to the standard F-16 at all angles of attack and sideslip. In-flight engine restarts and afterburner lights were achieved without failure. The DSI test flights validated the aerodynamic properties of the inlet, which were further proved in testing on the F-35.
To test their theoretical results, Lockheed Martin modified a Block 25 F-16, serial 83-1120, with what is called a “Diverterless” Supersonic Inlet or DSI. The short test program, starting in 1996, proved highly successful with the modified F-16 tested at all points of the flight envelop up to Mach 2. The tests demonstrated comparable flying qualities to the standard F-16 at all angles of attack and sideslip. In-flight engine restarts and afterburner lights were achieved without failure. The DSI test flights validated the aerodynamic properties of the inlet, which were further proved in testing on the F-35.

https://static.dvidshub.net/media/pubs/pdf_34264.pdf


This is a Master Thesis done at the Swedish Defence Research Agency with the purpose to design and investigate how different geometries of a compression surface integrated with an intake affects the performance such as distortion, boundary layer diversion, pressure recovery and deceleration of speed. A successful design, such as that on the Lockheed Martins F-35 Lightning II, shows that a Diverterless Supersonic Inlet (DSI) compared to a conventional intake can reduce the weight, and weight is the primary driver to reduce cost and increase performance of a fighter aircraft.


The diverter separates the inlet from the fuselage and the boundary layer, but it is a design feature causing the inlet weight and drag to increase and with higher maintenance requirements. It is also a negative factor when it comes to radar issues. Boundary layer bleed is a frequently used technique where the boundary layer is diverted by suction through small holes in the structure. Bleed systems can be fixed or movable. Although these techniques are fully functional in an aerodynamic sense, they are complex and add weight and cost into the system.
http://www.diva-portal.org/smash/get/diva2:221/FULLTEXT01.pdf


These three types of loss are illustrated in the inlet shown in figure 2.3: There is the frictional loss due to the thin attached boundary layer associated with on the internal surface of the cowl; the turbulent loss due to the presence of a separation bubble on the floor; and the shock-loss due to the shock which is required to decelerate the flow from a supersonic to subsonic velocities.

2.5.3 The need for multi-shock inlet designs
The way to reduce the large stagnation pressure losses associated with the Pitot inlet at high M1 is to introduce multiple shock waves into the inlet system (such as the inlets shown in figures 2.5b–d). The advantage of this approach is well illustrated in figure 2.8, which shows the variation of obtainable pressure recovery using a two and three shock system respectively. These results are based on simple planar shock theory (see Equations, tables and charts for compressible flow by Ames Research Sta↵). It can be seen that big improvements in pressure recovery are achievable using simple compression ramps upstream of the inlet cowl. For example, at Mach 2.5, with a Pitot inlet ( = 0) the recovery is 50%, with a single compression ramp this can be increased to 75%, and with two ramps this can be increased to 87%. The advantage of this multi-shock approach was first noted by Oswatitsch (1944).
https://core.ac.uk/download/pdf/42337454.pdf


The advent of supersonic aircraft powered by airbreathing engines opened up a new set of challenges for intake designers. A rule of thumb often used is that 1% pressure loss reduces thrust by 1%, but it became clear early on that the thrust loss caused by pressure losses in supersonic flight increases nonlinearly. For example, at a flight speed of Mach 2.2, a typical engine losing 8% of the freestream total pressure through the intake will suffer a reduction in thrust of 13% and a 5% increase in fuel consumption [9]. Since the mid-1950s, when this first became evident, a tremendous amount of research effort has gone into the study of supersonic intake pressure recovery and drag

Tradeoffs in Jet Inlet Design: A Historical Perspective András Sóbester∗ University of Southampton, Southampton, SO17 1BJ Hampshire, United Kingdom

4.1.1 Caret Inlet
The caret inlet technique has been understood as an academic concept for many years (Seddon and Goldsmith, 1985), but was not matured to a realistic engineering design until the 1980s. The primary trait of caret inlets is a pair of oblique compression ramps that generate a 2‐D flow field and co‐planar shock waves at the supersonic design point. Primary advantages of the caret inlet are efficient supersonic flow compression (as with the F‐14 or F‐15) and swept inlet edges that can be aligned with the aircraft planform. The challenge with the caret inlet lies at supersonic, off‐design conditions where the shocks generated by the two ramps are no longer co‐planar, resulting in shear layers and potential distortion and inlet instability. The caret inlet concept was adopted for both F‐22 and F/A‐18E/F. Design and development of the F/A‐18E/F inlet is discussed in Hall et al. 1993.
1572598075836.png

However, inlet characteristic airflow may be significantly greater than the demanded airflow. A bypass system provides a means to spill the excess airflow efficiently without impacting the inlet aerodynamic stability. Bleed and bypass systems typically exhaust the air on the upper surface of the vehicle in a location with a favorable local pressure. On occasion, diverter, bleed, or bypass airflow is utilized as a secondary air source for heat exchangers, ejector nozzles, or other such functions.

1572598268491.png
Various research efforts were undertaken to mature the bump inlet concept into a practical design, including a flight test effort on an F‐16 that lead to incorporation of such an inlet on the JSF X‐35 concept demonstrator aircraft and production F‐35 aircraft (see Hamstra, McCallum and McFarlan, 2003; and Hehs, 2000). This particular design, known as the diverterless supersonic inlet, integrated a highly three‐dimensional bump compression surface with a forward‐swept cowl. This combination produces a pressure gradient that diverts the majority of the boundary layer and provides a stable interaction between the inlet shocks and remaining boundary layer, eliminating the need for both boundary layer diverter and bleed systems. A diverterless inlet concept was also employed on the JSF X‐32 demonstrator.

1572598373415.png



https://onlinelibrary.wiley.com/doi/full/10.1002/9780470686652.eae490

Engine inlets for supersonic aircraft have complex aerodynamic requirements based on Mach number and other flight conditions. Fixed inlet geometries typically have highest efficiency at one specific Mach number and flight condition. Operation at other speeds or flight conditions results in degradation of the aerodynamic performance or efficiency of the inlet. To allow flight at varying Mach number, mechanical systems to adjust the capture area and ramp geometry of the inlet may be employed to increase efficiency. An existing solution to a variable ramps and variable capture inlet is the F-15 Eagle produced by The Boeing Company. This inlet system is highly efficient and is recognized as an optimized inlet design. However, later-generation fighters require unique shaping where the inlet aperture edges are highly swept. In such aircraft a caret-type inlet system is employed. Examples of aircraft employing such inlets are the F-18E/F Super Hornet produced by The Boeing Company and the F-22 Raptor produced by Lockheed Martin. These inlets are fixed geometry inlets and were designed for optimized operation at a particular flight Mach number. At off-design Mach numbers, a fixed-geometry inlet system may not provide the best shaping to maximize pressure recovery. In addition, because the inlet capture area is fixed, the inlet tends to capture more mass flow than the engine needs at lower speed than at the inlet sizing condition. As a result, the excess airflow will have to be spilled or dumped through a bypass; both of which will create additional inlet drag. Because the F-15 inlet system is not a caret-type inlet with the highly swept edges, it is not employed on current-generation fighter aircraft.

It is therefore desirable to provide a variable inlet which maximizes pressure recovery across the Mach envelope range to obtain higher pressure recovery at the engine face for maximizing thrust and fuel efficiency and to minimize inlet spill drag to maximize the propulsion system net propulsive force, thereby maximizing aircraft performance. It is also desirable that the variable inlet operate in an efficient manner without generating additional complexities such as opening gaps that will require more additional mechanisms or seals for closure.

http://www.freepatentsonline.com/9874144.html
 
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pegasus

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and RCS make a big difference whether your radar is powerful or not
View attachment 620993
Pt is a variable, basically it says will depend in the radar, σ = radar cross-section [m²] is another variable, it is not fixed thus the illustration you use will depend on the radar nothing is fixed

In theory, the RCS of some simple objects, such as a perfect sphere, can be
well defined. In practice, most targets are rather complex objects and their RCS
usually fluctuates considerably, as they move with respect to a radar
. In fact, the
monostatic or backscatter RCS depends on the following

Position of radar antenna relative to target
 Angular orientation of target relative to radar antenna

 Frequency of the electromagnetic energy
 Radar antenna polarization.


For the F-35, the approach was the construction of a l.o. aircraft, taking seriously
into account the cost parameter. Therefore, in the frame of cost reduction, some
capabilities were “sacrificed”: RCS is really low in the X-band (8 – 12 GHz) and in
the Ku-band (12 – 18 GHz), while it is not so low at lower frequency bands. The
scope is the break of the killing chain: even if the F-35 is detected by surveillance
radar, it will not be easy to be engaged by a fire control radar, which usually operate
in the X or Ku bands. On the other hand, the F-22 presents a lower RCS from all
aspects and at more frequency bands, of course at a considerably higher cost

The production F-35 is expected to present a higher RCS than the prototype

X-35, since more volume was required for the internal equipment and armament bays.
The curves of the redesigned fuselage will incur an RCS increase, from some certain
directions. It was calculated that the RCS will remain very low from the frontal sector
and more precisely from a sector of 29ο in front of the aircraft. However, the RCS will
not be so low from the lateral aspect and also from the rear aspect.
The whole
behavior deteriorates at lower frequency bands

Very low frequency band radars, for medium to high altitude
surveillance: as the frequency decreases, the wavelength increases and becomes
comparable with major parts of the aircraft. Thus, scattering enters the resonance
region, exhibiting a higher Radar Cross Section (RCS), at least momentarily.
Also, the
Radar-Absorbent Materials (RAM) are not very effective at lower frequencies. For
these reasons, radars operating, e.g., in the VHF band, are expected to see a l.o. target
at a longer distance with respect to “conventional”, higher frequency radars,
transmitting in the L or S-band.



https://www.researchgate.net/publication/259503614_Low_Observable_Principles_Stealth_Aircraft_and_Anti-Stealth_Technologies
 
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Fluff

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Please don't talk to me, im not here.
 

kaiserd

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Given above you do know that while the F-18E/F/G and F-22 don’t technically have DSI they do have fixed geometry inlets of a different design type?
Hence not really very relevant to discussion around DSI or variable geometry inlets. And you’ve certainly made no apparent attempt to make them relevant or relate them back to DSI or variable inlets. Or form any particular approaching-coherent argument or point.
Apart from vomiting almost completely irrelevant techno-babble at anyone who shows an interest.

The intrinsic “stealth” of any particular engine inlet approach is tied up with the overall integrated aircraft design (with the exception of the designs where you can see the fan straight down the inlet), the devil is in the detail.
DSI are not somehow flawed from that perspective and dependent on their detailed design may lose less in performance loss versus variable inlets than more traditional fixed inlets, especially if the variable inlets have to make their own compromises to be a integrated into a stealth design.
Variable inlets probably have a tougher time in regard to “stealth” integration but perhaps if combined with “inlet-blockers” like seen in the F-18E then some compromise can be met between maxing performance while successfully integrating into a “stealth” design.
Hence it’s not some great philosophical argument except for those who are trying to make it so.
 

quellish

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You can not prove the radar range formula say stealth means invisibility,
Actually, that is exactly what it says.
The radar range equation tells you the distance at which the target can be detected. When the target is farther than that, it is undetectable - invisible. It disappears into the noise. This is an important concept.

the only thing i said, is the only real limitation is the electricity an aircraft can provide to its radar,
No, there are as many limitations as there are variables in the radar range equation. Antenna efficiency is a big limiter. Increasing antenna efficiency has a higher payoff than increasing power. Decreasing the system noise would also help quite a bit, and increasing the power actually increases the noise significantly - effectively making the target harder to detect!

but ground radars do not have such limitations and aircraft work with
Ground radars are still limited by the laws of physics and what is practical to manufacture and operate. You can power your ground radar with a fusion reactor and pump more watts through it but you're going to start melting components long before the detection range is increased by any significant amount.

networks, to exemplify it, imaging you have a hall with many lamps, each light is helping you to see, passive radars basically use that, any frequency they are using to see.
And modern VLO aircraft are also optimized for bistatic and "networked" radars.
 

pegasus

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Actually, that is exactly what it says.
The radar range equation tells you the distance at which the target can be detected. When the target is farther than that, it is undetectable - invisible. It disappears into the noise. This is an important concept.



No, there are as many limitations as there are variables in the radar range equation. Antenna efficiency is a big limiter. Increasing antenna efficiency has a higher payoff than increasing power. Decreasing the system noise would also help quite a bit, and increasing the power actually increases the noise significantly - effectively making the target harder to detect!



Ground radars are still limited by the laws of physics and what is practical to manufacture and operate. You can power your ground radar with a fusion reactor and pump more watts through it but you're going to start melting components long before the detection range is increased by any significant amount.


And modern VLO aircraft are also optimized for bistatic and "networked" radars.
you know what, i do not believe you, the Sun show us there are not such limits,
1572638258819.png

In fact math too

1572639133593.png


this graph shows a tendency to growth to the infinite small to the infinite large


Second root graph

1572639230663.png

same to the second root graph, as long as you increase power density that graph will always go up, in fact fourth-root power function graph, grows slower but will go to infinity simple because X can run to infinity, Pt can run to infinity, thus Rmax can run to infinity

1572639623665.png


Thus you technical jargon pretty much is not proven by Math.


1572639560930.png

Pt can run to infinity, and as the wavelength gets longer the target RCS grows.

Now are real problems that limit radar technology? of course, but the radar equation does not limit the detection of stealth targets, RCS is not fixed First because aircraft have fixed sizes, a 20 meter F-22 or J-20 or whatever, has also fixed geometry, plus a detail you forget in your concept
their RCS
usually fluctuates considerably, as they move with respect to a radar. In fact, the
monostatic or backscatter RCS depends on the following

1-Position of radar antenna relative to target
2- Angular orientation of target relative to radar antenna




Now are there economic limitations to radar networks? yes, stealth makes the military budget more expensive, so Stealth can limit the radar network by over spending too much money, yes stealth is good to bankrupt militaries, but our friend the sun proves you are wrong
 
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quellish

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Pt can run to infinity, and as the wavelength gets longer the target RCS grows.
No, the RCS of the target does not grow as the wavelength gets longer. RCS is independent of the physical size of the object. The electrical size of the object and its impedance matters, but the physical size can be completely independent of that.

Now are real problems that limit radar technology? of course, but the radar equation does not limit the detection of stealth targets,
Yes, it does. That is exactly what it does - it is a model of how the detection range changes with a change to the variables of the equation. One of those variables is the RCS. The other variables are characteristics of the radar.

RCS is not fixed First because aircraft have fixed sizes, a 20 meter F-22 or J-20 or whatever, has also fixed geometry, plus a detail you forget in your concept
their RCS
usually fluctuates considerably, as they move with respect to a radar. In fact, the
monostatic or backscatter RCS depends on the following
If you were to look at an accurate polar plot of a very low observable object you would see that the RCS is very, very low through more than 99% of the plot. And in the other 1% there are "spikes" - which are still low when compared to an object not engineered for observables, and this 1% covers a very small percentage of the possible viewing angles.


but our friend the sun proves you are wrong
I do not understand what point you are trying to make by introducing the sun to a discussion of radar. Please elaborate.
 

kaiserd

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Unfortunately this is looking very much like trolling or lunacy (if it was ever anything better than that it has now devolved to this point).
Either way probably best we all now stop feeding “it”.
 

pegasus

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No, the RCS of the target does not grow as the wavelength gets longer. RCS is independent of the physical size of the object. The electrical size of the object and its impedance matters, but the physical size can be completely independent of that.

If you were to look at an accurate polar plot of a very low observable object you would see that the RCS is very, very low through more than 99% of the plot. And in the other 1% there are "spikes" - which are still low when compared to an object not engineered for observables, and this 1% covers a very small percentage of the possible viewing angles.




I do not understand what point you are trying to make by introducing the sun to a discussion of radar. Please elaborate.
Look, you have to be realistic, the equation does not limit detectability as you are saying, RCS does grow with the wavelength, it is called resonance, Ronny even posted that diagram many many times. in fact i posted an article that says that


Very low frequency band radars, for medium to high altitude
surveillance: as the frequency decreases, the wavelength increases and becomes
comparable with major parts of the aircraft. Thus, scattering enters the resonance
region, exhibiting a higher Radar Cross Section (RCS), at least momentarily.
Also, the
Radar-Absorbent Materials (RAM) are not very effective at lower frequencies. For
these reasons, radars operating, e.g., in the VHF band, are expected to see a l.o. target
at a longer distance with respect to “conventional”, higher frequency radars,
transmitting in the L or S-band.



https://www.researchgate.net/publication/259503614_Low_Observable_Principles_Stealth_Aircraft_and_Anti-Stealth_Technologies

The article is written by the greek military

So there you show you are wrong


Radars today use something similar to AESA but passive using different sources.

Experimental German radar 'tracked two U.S. F-35 stealth jet for 100 MILES' after lying in wait on a pony farm to catch them flying home from airshow
  • Radar is designed with sensors and processors capable of tracking F-35 jets
  • It works observing electromagnetic emissions in the atmosphere
  • Then it will read how signals are bouncing off airborne objects
  • German radar maker said the system tracked two US jets for nearly 100 mile
https://www.dailymail.co.uk/sciencetech/article-7522413/German-radar-tracked-two-U-S-F-35-stealth-jet-100-MILES-hiding-pony-farm.html

their RCS
usually fluctuates considerably, as they move with respect to a radar. In fact, the
monostatic or backscatter RCS depends on the following

1-Position of radar antenna relative to target
2- Angular orientation of target relative to radar antenna



in fact this means that if a radar is exactly bellow to F-22, its wings and aft tail will send a very strong signal to the radar, why? because fluctuates means RCS grows or reduces so you are totally wrong simply using concepts without really thinking what they really mean

1572652552376.png

1572652401940.png

right below the F-22 its wings act like the flat plate in the third place from top to bottom

or like the following illustration
1572652756586.png

So if the radar is below the F-22 its RCS will increase that is the reason F-22 has to plan its flight route
 
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Ronny

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LM Aeronautics JSF Design Adopts DSI
The DSI concept was introduced into the JAST/JSF program as a trade study item in mid-1994. It was compared with a traditional "caret" style inlet. The trade studies involved additional CFD, testing, and weight and cost analyses. The new inlet earned its way into the JSF design after proving to be thirty percent lighter and showing lower production and maintenance costs over traditional inlets while still meeting all performance requirements.
https://www.codeonemagazine.com/article.html?item_id=58

System-level trade studies were performed to quantify the weight, cost, and benefits of the DSI, compared to more conventional inlets (e.g., F-22 and F/A-18E/F caret inlet systems). In these studies, a 30-percent inlet weight reduction was estimated for the DSI, relative to the reference caret inlet. The largest contributing factor was the elimination of the bleed and bypass systems. Studies performed by other ACIS contractors [25] indicated similar savings for diverter-less/bleed-less systems

The short test program, starting in 1996, proved highly successful with the modified F-16 tested at all points of the flight envelop up to Mach 2. The tests demonstrated comparable flying qualities to the standard F-16 at all angles of attack and sideslip. In-flight engine restarts and afterburner lights were achieved without failure. The DSI test flights validated the aerodynamic properties of the inlet, which were further proved in testing on the F-35.
To test their theoretical results, Lockheed Martin modified a Block 25 F-16, serial 83-1120, with what is called a “Diverterless” Supersonic Inlet or DSI. The short test program, starting in 1996, proved highly successful with the modified F-16 tested at all points of the flight envelop up to Mach 2. The tests demonstrated comparable flying qualities to the standard F-16 at all angles of attack and sideslip. In-flight engine restarts and afterburner lights were achieved without failure. The DSI test flights validated the aerodynamic properties of the inlet, which were further proved in testing on the F-35.
https://static.dvidshub.net/media/pubs/pdf_34264.pdf
This is a Master Thesis done at the Swedish Defence Research Agency with the purpose to design and investigate how different geometries of a compression surface integrated with an intake affects the performance such as distortion, boundary layer diversion, pressure recovery and deceleration of speed. A successful design, such as that on the Lockheed Martins F-35 Lightning II, shows that a Diverterless Supersonic Inlet (DSI) compared to a conventional intake can reduce the weight, and weight is the primary driver to reduce cost and increase performance of a fighter aircraft.
The diverter separates the inlet from the fuselage and the boundary layer, but it is a design feature causing the inlet weight and drag to increase and with higher maintenance requirements. It is also a negative factor when it comes to radar issues. Boundary layer bleed is a frequently used technique where the boundary layer is diverted by suction through small holes in the structure. Bleed systems can be fixed or movable. Although these techniques are fully functional in an aerodynamic sense, they are complex and add weight and cost into the system.
http://www.diva-portal.org/smash/get/diva2:221/FULLTEXT01.pdf
These three types of loss are illustrated in the inlet shown in figure 2.3: There is the frictional loss due to the thin attached boundary layer associated with on the internal surface of the cowl; the turbulent loss due to the presence of a separation bubble on the floor; and the shock-loss due to the shock which is required to decelerate the flow from a supersonic to subsonic velocities.
2.5.3 The need for multi-shock inlet designs The way to reduce the large stagnation pressure losses associated with the Pitot inlet at high M1 is to introduce multiple shock waves into the inlet system (such as the inlets shown in figures 2.5b–d). The advantage of this approach is well illustrated in figure 2.8, which shows the variation of obtainable pressure recovery using a two and three shock system respectively. These results are based on simple planar shock theory (see Equations, tables and charts for compressible flow by Ames Research Sta↵). It can be seen that big improvements in pressure recovery are achievable using simple compression ramps upstream of the inlet cowl. For example, at Mach 2.5, with a Pitot inlet ( = 0) the recovery is 50%, with a single compression ramp this can be increased to 75%, and with two ramps this can be increased to 87%. The advantage of this multi-shock approach was first noted by Oswatitsch (1944).
https://core.ac.uk/download/pdf/42337454.pdf

The advent of supersonic aircraft powered by airbreathing engines opened up a new set of challenges for intake designers. A rule of thumb often used is that 1% pressure loss reduces thrust by 1%, but it became clear early on that the thrust loss caused by pressure losses in supersonic flight increases nonlinearly. For example, at a flight speed of Mach 2.2, a typical engine losing 8% of the freestream total pressure through the intake will suffer a reduction in thrust of 13% and a 5% increase in fuel consumption [9]. Since the mid-1950s, when this first became evident, a tremendous amount of research effort has gone into the study of supersonic intake pressure recovery and drag

Tradeoffs in Jet Inlet Design: A Historical Perspective András Sóbester∗ University of Southampton, Southampton, SO17 1BJ Hampshire, United Kingdom
4.1.1 Caret Inlet
The caret inlet technique has been understood as an academic concept for many years (Seddon and Goldsmith, 1985), but was not matured to a realistic engineering design until the 1980s. The primary trait of caret inlets is a pair of oblique compression ramps that generate a 2‐D flow field and co‐planar shock waves at the supersonic design point. Primary advantages of the caret inlet are efficient supersonic flow compression (as with the F‐14 or F‐15) and swept inlet edges that can be aligned with the aircraft planform. The challenge with the caret inlet lies at supersonic, off‐design conditions where the shocks generated by the two ramps are no longer co‐planar, resulting in shear layers and potential distortion and inlet instability. The caret inlet concept was adopted for both F‐22 and F/A‐18E/F. Design and development of the F/A‐18E/F inlet is discussed in Hall et al. 1993.
However, inlet characteristic airflow may be significantly greater than the demanded airflow. A bypass system provides a means to spill the excess airflow efficiently without impacting the inlet aerodynamic stability. Bleed and bypass systems typically exhaust the air on the upper surface of the vehicle in a location with a favorable local pressure. On occasion, diverter, bleed, or bypass airflow is utilized as a secondary air source for heat exchangers, ejector nozzles, or other such functions.
Various research efforts were undertaken to mature the bump inlet concept into a practical design, including a flight test effort on an F‐16 that lead to incorporation of such an inlet on the JSF X‐35 concept demonstrator aircraft and production F‐35 aircraft (see Hamstra, McCallum and McFarlan, 2003; and Hehs, 2000). This particular design, known as the diverterless supersonic inlet, integrated a highly three‐dimensional bump compression surface with a forward‐swept cowl. This combination produces a pressure gradient that diverts the majority of the boundary layer and provides a stable interaction between the inlet shocks and remaining boundary layer, eliminating the need for both boundary layer diverter and bleed systems. A diverterless inlet concept was also employed on the JSF X‐32 demonstrator.
https://onlinelibrary.wiley.com/doi/full/10.1002/9780470686652.eae490
Engine inlets for supersonic aircraft have complex aerodynamic requirements based on Mach number and other flight conditions. Fixed inlet geometries typically have highest efficiency at one specific Mach number and flight condition. Operation at other speeds or flight conditions results in degradation of the aerodynamic performance or efficiency of the inlet. To allow flight at varying Mach number, mechanical systems to adjust the capture area and ramp geometry of the inlet may be employed to increase efficiency. An existing solution to a variable ramps and variable capture inlet is the F-15 Eagle produced by The Boeing Company. This inlet system is highly efficient and is recognized as an optimized inlet design. However, later-generation fighters require unique shaping where the inlet aperture edges are highly swept. In such aircraft a caret-type inlet system is employed. Examples of aircraft employing such inlets are the F-18E/F Super Hornet produced by The Boeing Company and the F-22 Raptor produced by Lockheed Martin. These inlets are fixed geometry inlets and were designed for optimized operation at a particular flight Mach number. At off-design Mach numbers, a fixed-geometry inlet system may not provide the best shaping to maximize pressure recovery. In addition, because the inlet capture area is fixed, the inlet tends to capture more mass flow than the engine needs at lower speed than at the inlet sizing condition. As a result, the excess airflow will have to be spilled or dumped through a bypass; both of which will create additional inlet drag. Because the F-15 inlet system is not a caret-type inlet with the highly swept edges, it is not employed on current-generation fighter aircraft.
It is therefore desirable to provide a variable inlet which maximizes pressure recovery across the Mach envelope range to obtain higher pressure recovery at the engine face for maximizing thrust and fuel efficiency and to minimize inlet spill drag to maximize the propulsion system net propulsive force, thereby maximizing aircraft performance. It is also desirable that the variable inlet operate in an efficient manner without generating additional complexities such as opening gaps that will require more additional mechanisms or seals for closure.
http://www.freepatentsonline.com/9874144.html
Persus, just because DSI is lighter, easier to maintain and cheaper to produce than others kind of inlet, doesn't mean it can't also have lower RCS compared to other kind of inlet. Those advantages are not mutually exclusive
1.PNG


The DSI structure complexity is greatly reduced by the removal of moving parts, a boundary layer diverter and a bleed or bypass system thus decreasing the aircraft’s empty weight, production cost, and requirements of maintenance-supporting equipment. Furthermore, by eliminating the surface discontinuity of the diverter, the forward sweep cowl lips and the S-shaped duct, which house the mental blades within the engine’s compressor, the bump can efficiently decrease the RCS. The DSI has been the focus of renewed research after initial NASA work in the 1950s. Simon et al studied an external bump inlet in a direct comparison with a traditional two-dimensional compression ramp. It was determined that the bump inlet outperformed the ramp inlet over a range of Mach numbers from 1.5 to 2, with both surfaces employing boundary layer bleed.
.....
This design is called Diverterless Supersonic Inlet (DSI). The pressure field in the vicinity of the bump compression surface shows positive pressure gradients away from the bump, which effectively blow the upstream boundary layer away from the inlet.

This design has several advantages compared to the diverter. It decreases the inlet weight, since the structure becomes less complex and it has no moving parts therefore requiring less maintenance. This further reduces the cost of the aircraft and is better concerning radar cross-section.

This pattern is originally in Chinese so may be slightly harder to understand
DSI inlet (also known as non-layer separated supersonic inlet channel, English name DiverterlessSupersonic Inlet, abbreviated as DSI inlet) are raising in popularity in recent years . Because it eliminates the conventional supersonic inlet boundary layer remover, but instead rely on a pressure inlet port lateral compression gradient driven type front surface boundary layer to the outer edge of the overflow inlet port technical solution, so that supersonic inlet while maintaining the total pressure recovery coefficient of performance parameters of intake prerequisite substantially constant, simplifying the structure, reducing the weight, reducing manufacturing and maintenance cost; and because there is no attachment surface with strong RCS signal source across the inlet, it greatly improved supersonic inlet RCS stealth performance. For these reasons, DSI are ideal intake port means for hypersonic vehicles aspirated engine powered device. On the F35, and JlO modifications and other new aircraft it has been applied widely
https://patents.google.com/patent/CN204755085U/en
 

Ronny

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Pt is a variable, basically it says will depend in the radar, σ = radar cross-section [m²] is another variable, it is not fixed thus the illustration you use will depend on the radar nothing is fixed
You know what is fixed? the ratio.
You can make your radar more powerful, but your enemy can also make their jammer more powerful. However the detection range always depends on the signal/noise ratio, which stealth aircraft always have a remarkable advantage over any conventional aircraft.
B0z34eN.jpg

In theory, the RCS of some simple objects, such as a perfect sphere, can be
well defined. In practice, most targets are rather complex objects and their RCS
usually fluctuates considerably, as they move with respect to a radar. In fact, the
monostatic or backscatter RCS depends on the following

Position of radar antenna relative to target
 Angular orientation of target relative to radar antenna
 Frequency of the electromagnetic energy
 Radar antenna polarization.
Of course aircraft RCS change with aspect, their shapes are not spherical, how could you only figure that out just now?



For the F-35, the approach was the construction of a l.o. aircraft, taking seriously
into account the cost parameter. Therefore, in the frame of cost reduction, some
capabilities were “sacrificed”: RCS is really low in the X-band (8 – 12 GHz) and in
the Ku-band (12 – 18 GHz), while it is not so low at lower frequency bands. The
scope is the break of the killing chain: even if the F-35 is detected by surveillance
radar, it will not be easy to be engaged by a fire control radar, which usually operate
in the X or Ku bands. On the other hand, t
he F-22 presents a lower RCS from all
aspects and at more frequency bands, of course at a considerably higher cost

The production F-35 is expected to present a higher RCS than the prototype
X-35, since more volume was required for the internal equipment and armament bays.
The curves of the redesigned fuselage will incur an RCS increase, from some certain
directions. It was calculated that the RCS will remain very low from the frontal sector
and more precisely from a sector of 29ο in front of the aircraft. However, the RCS will
not be so low from the lateral aspect and also from the rear aspect. The whole
behavior deteriorates at lower frequency bands

Very low frequency band radars, for medium to high altitude
surveillance: as the frequency decreases, the wavelength increases and becomes
comparable with major parts of the aircraft. Thus, scattering enters the resonance
region, exhibiting a higher Radar Cross Section (RCS), at least momentarily. Also, the
Radar-Absorbent Materials (RAM) are not very effective at lower frequencies. For
these reasons, radars operating, e.g., in the VHF band, are expected to see a l.o. target
at a longer distance with respect to “conventional”, higher frequency radars,
transmitting in the L or S-band.

https://www.researchgate.net/publication/259503614_Low_Observable_Principles_Stealth_Aircraft_and_Anti-Stealth_Technologies
That paragraph is word by word copy from Carlo Kopp in APA with his infamous anti F-35 and F-22 lobby, unfortunately, it is full of crap
F-35 has lower RCS than F-22 has been confirmed by official authorities
The F-35 doesn’t have the altitude, doesn’t have the speed [of the F-22], but it can beat the F-22 in stealth.

2.PNG

1-2.png
 
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Ronny

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you know what, i do not believe you, the Sun show us there are not such limits,
View attachment 621016
In fact math too
View attachment 621017
this graph shows a tendency to growth to the infinite small to the infinite large. Second root graph
same to the second root graph, as long as you increase power density that graph will always go up, in fact fourth-root power function graph, grows slower but will go to infinity simple because X can run to infinity, Pt can run to infinity, thus Rmax can run to infinity

Thus you technical jargon pretty much is not proven by Math.
Pt can run to infinity, and as the wavelength gets longer the target RCS grows.
Now are real problems that limit radar technology? of course, but the radar equation does not limit the detection of stealth targets, RCS is not fixed First because aircraft have fixed sizes, a 20 meter F-22 or J-20 or whatever, has also fixed geometry, plus a detail you forget in your concept
their RCS
usually fluctuates considerably, as they move with respect to a radar. In fact, the
monostatic or backscatter RCS depends on the following

1-Position of radar antenna relative to target
2- Angular orientation of target relative to radar antenna
Now are there economic limitations to radar networks? yes, stealth makes the military budget more expensive, so Stealth can limit the radar network by over spending too much money, yes stealth is good to bankrupt militaries, but our friend the sun proves you are wrong
How far can you see a mosquito on a bright day? How far can you see an oil tanker on a bright day? Can you see both of them equally as far? That the point of stealth technology.
Your argument that because the graph can go infinite big, therefore you can detect stealth at an infinite distance because Pt can go to infinity is just utterly ridiculous. By that logic, because RCS is a variable, they can make it 0 or just infinite small to counter your infinite powerful radar. Or they can also make their jammer infinitely powerful so that your radar is useless. There are cost going along with increasing the power . The cost could be size of your radar, overheating, mobility, probably of intercept ..etc like the Sea base -X band, it is as maneuver as an oil tanker, the point is you can't just generate more and more and more power at no cost. If you can practically increase Pt to infinity then why stop at detection? why don't you design an HPW to fry your enemy from the horizon?

Look, you have to be realistic, the equation does not limit detectability as you are saying, RCS does grow with the wavelength, it is called resonance, Ronny even posted that diagram many many times. in fact i posted an article that says that
Very low frequency band radars, for medium to high altitude
surveillance: as the frequency decreases, the wavelength increases and becomes
comparable with major parts of the aircraft. Thus, scattering enters the resonance
region, exhibiting a higher Radar Cross Section (RCS), at least momentarily. Also, the
Radar-Absorbent Materials (RAM) are not very effective at lower frequencies. For
these reasons, radars operating, e.g., in the VHF band, are expected to see a l.o. target
at a longer distance with respect to “conventional”, higher frequency radars,
transmitting in the L or S-band.

https://www.researchgate.net/publication/259503614_Low_Observable_Principles_Stealth_Aircraft_and_Anti-Stealth_Technologies
The article is written by the greek military
So there you show you are wrong
RCS doesn't always grow with wavelength, pass the Mie region into the Rayleigh region, RCS will decrease with wavelength
hf-frequency.pngRCS2.PNG
 
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pegasus

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Persus, just because DSI is lighter, easier to maintain and cheaper to produce than others kind of inlet, doesn't mean it can't also have lower RCS compared to other kind of inlet. Those advantages are not mutually exclusive


This pattern is originally in Chinese so may be slightly harder to understand
DSI inlet (also known as non-layer separated supersonic inlet channel, English name DiverterlessSupersonic Inlet, abbreviated as DSI inlet) are raising in popularity in recent years . Because it eliminates the conventional supersonic inlet boundary layer remover, but instead rely on a pressure inlet port lateral compression gradient driven type front surface boundary layer to the outer edge of the overflow inlet port technical solution, so that supersonic inlet while maintaining the total pressure recovery coefficient of performance parameters of intake prerequisite substantially constant, simplifying the structure, reducing the weight, reducing manufacturing and maintenance cost; and because there is no attachment surface with strong RCS signal source across the inlet, it greatly improved supersonic inlet RCS stealth performance. For these reasons, DSI are ideal intake port means for hypersonic vehicles aspirated engine powered device. On the F35, and JlO modifications and other new aircraft it has been applied widely
https://patents.google.com/patent/CN204755085U/en
tell me is F-35 stealthier than F-22, first which aircraft has better RCS frontally, later laterally, and later from the rear and why?
 
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pegasus

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That paragraph is word by word copy from Carlo Kopp in APA with his infamous anti F-35 and F-22 lobby, unfortunately, it is full of crap
F-35 has lower RCS than F-22 has been confirmed by official authorities
You do not believe that simply F-22 is not for sale, and by the way, from rear views F-22 is stealthier why?
 

pegasus

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How far can you see a mosquito on a bright day? How far can you see an oil tanker on a bright day? Can you see both of them equally as far? That the point of stealth technology.
Your argument that because the graph can go infinite big, therefore you can detect stealth at an infinite distance because Pt can go to infinity is just utterly ridiculous. By that logic, because RCS is a variable, they can make it 0 or just infinite small to counter your infinite powerful radar. Or they can also make their jammer infinitely powerful so that your radar is useless. There are cost going along with increasing the power . The cost could be size of your radar, overheating, mobility, probably of intercept ..etc like the Sea base -X band, it is as maneuver as an oil tanker, the point is you can't just generate more and more and more power at no cost. If you can practically increase Pt to infinity then why stop at detection? why don't you design an HPW to fry your enemy from the horizon?
As shown in Fig. 14, when the aircraft is flying right towards the radar from 200 km away, the detection probabilities are very low when R is beyond about 120 km, for all 3 types of variable-sweep wing aircrafts. When the distance decreases to within 100 km, the aircraft with a sweep angle of χ = 54º performs best and the aircraft with a sweep angle of χ = 15º performs worst. When the distance decreases to within 40 km, all 3 types of variable-sweep wing aircrafts perform almost the same.

CONCLUSION

This paper utilizes the physical optics and the equivalent currents methods to study the RCS characteristics of the variable-sweep wing aircraft. Based on the numerical simulations of the aircraft, the following conclusions can be obtained:

The aircraft's RCS forward peak value decreases non-linearly with the sweep angle χ.

The sweep angle of the variable-sweep wing aircraft and the azimuth angle corresponding to one of the RCS peak values are identical.

When χ = 33º, σt ±30º = -0.7 dBm2. After unit conversion, σt ±30º of the aircraft when χ = 33º is 0.644% of that when χ = 0º.

The larger the sweep angle of the variable-sweep wing aircraft is, the lower the aircraft's detection probability will be.

We hope that the conclusions of this paper provide some reference and technical support for stealth aircraft's demonstration and designing


http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2175-91462015000200170

explain me this and apply that to F-35 and F-22
 

quellish

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Look, you have to be realistic, the equation does not limit detectability as you are saying, RCS does grow with the wavelength, it is called resonance, Ronny even posted that diagram many many times. in fact i posted an article that says that
As someone who has written validated scattering simulation software I can very confidently say you are incorrect.

The article is written by the greek military

So there you show you are wrong
I am not even going to touch that one.

Radars today use something similar to AESA but passive using different sources.
You are attempting to describe bistatic radars. "Radars today" are still predominantly monostatic. And stealth aircraft can still be stealthy against bistatic radars.

Your "experimental german radar" tracked an F-35 flying with a radar reflector installed.

so you are totally wrong simply using concepts without really thinking what they really mean
Not going to touch that one either.

Again, how does the sun factor into a discussion of radar? Can you elaborate on that?
 

pegasus

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Not going to touch that one either.

Again, how does the sun factor into a discussion of radar? Can you elaborate on that?
the Sun is the largest emitting electromagnetic wave source we have , use Pt with the Sun, you will not change the equations, the equation does not limit detectability, my eyes see F-22 pretty visible, in fact optical devices will help me to see it, many aircraft have electro optical and Infrared devices nothing is stealth, stealth is a commercial ploy to sell aircraft, but is far cheaper to build radars and SAMs, the german radar maker says for 170 km they detected F-35, so i believe them, sorry your credentials are not the only ones radar makers from Russia, China, Germany do also claim to detect stealth aircraft, in fact ask yourself if radar is so limited why they say they discover black holes with radio telescopes? you discover black holes but you can not find F-35? go figure it
 
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quellish

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the Sun is the largest emitting electromagnetic wave source we have , use Pt with the Sun, you will not change the equations, the equation does not limit detectability,
The sun is not a radar. Not even conceptually similar.

stealth is a commercial ploy to sell aircraft,
OK....

radar makers from Russia, China, Germany do also claim to detect stealth aircraft
Might that be a ploy to sell radars?

in fact ask yourself if radar is so limited why they say they discover black holes with radio telescopes? you discover black holes but you can not find F-35? go figure it
I do not see how radio telescopes, black holes, radar, and "finding" an F-35 are at all related. Can you explain?

Radio telescopes receive transmissions from radio sources very, very far away. They do not transmit.
Radars transmit signals which reflect from an object back to the radar where they are received. This makes them pretty useless for observing stars (or black holes).

You may be onto something here though. Black holes suck up everything - including radar signals. A black hole may be the ultimate stealth device! Oh wait, your radar has unlimited power to transmit, that could be a problem. Of course, only a fraction of "unlimited" can make it back to the radar, so...
 

pegasus

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The sun is not a radar. Not even conceptually similar.
No? what type of waves allow you to see?


if you answer electromagnetic waves, you are right, so then what makes your eyes to be? passive radars are not they?

AESA radars use an array of transmitters and receivers are not they? if you have in a hall many lamps do not they act the same way to your eyes?

Hey let me see, if there are multiple sources of electromagnetic waves is not possible use use them and build a radar , a passive radar that uses those arrays to detect stealth aircraft? yes the germans did it and they detected F-35 for 100 miles around 170 km wow so you do not need a single radar you can use a network of radars ah I see the Russians did the same wow, yes the sun and our eyes do act like a radar do you see?
 
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In_A_Dream

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I would be interested to hear about what kind of real world scenario where you would find the F-35 & F-22 squaring up against a formidable IADS (that's not a pop-up) on its own, to justify the lengthy discussions you are having with everyone Pegasus about F-22/F-35 stealth.

In reality, whether you're on a SEAD mission or what have you, you're going to have jamming support. Nevermind the fact that there's a whole arsenal of classified capabilities available to the US military to minimize the effectiveness of an enemy's air defense systems.
 

pegasus

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I would be interested to hear about what kind of real world scenario where you would find the F-35 & F-22 squaring up against a formidable IADS (that's not a pop-up) on its own, to justify the lengthy discussions you are having with everyone Pegasus about F-22/F-35 stealth.

In reality, whether you're on a SEAD mission or what have you, you're going to have jamming support. Nevermind the fact that there's a whole arsenal of classified capabilities available to the US military to minimize the effectiveness of an enemy's air defense systems.
I will say first I am not an expert, I am just an Engineer in Environmental sciences with some diplomas in software use for Computer Aided Design and other basic programs.


However I am a big fan of aviation, when i say fan i say that is what I am, I usually read a lot about basic technical papers that any one can find published on the internet.

So you can see I am not an expert, but I am not a stupid fan, in that well i am proud, the information on the internet on open sources and general aviation tells you DSI intakes have design limits, they have Design Mach numbers, F-35 for example has a DSI intake good for 0 km/h to Mach 1.6 ideal operation, probably it can go further, but it will lose thrust and spend more fuel so the F-35 is limited to Mach 1.6 speed, with the best pressure recovery at around Mach 1.


Now you have fans who will say to you J-20 will be a super fast aircraft of Mach 2.0 plus operation, ultra stealthy DSI, better than F-22 or Su-57, however if you read published speeds of F-35, J-10B or JF-17 or even papers published on the internet, the Mach 1.6-1.8 limit is pretty obvious


1572723453184.png


The same type of fans think the caret Intake is less stealthy and J-20 will be faster.


Now if you are honest, DSI require less RAM due to the lack of boundary layer diverter, thus they have a plus over caret intakes, but the Bump is not the stealthiest feature, frontally is okay, frontal RCS of DSI is okay but there is diffraction so there are some imperfections of DSI as well, so both have advantages and disadvantages, caret intakes require more RAM but they adjust better to the aircraft need for planform alignment for stealth, so F-22 will be more expensive to achieve similar radar signature than F-35 but its Chines will have more armony with the caret intake in general planform alignment than F-35.

On Su-57 performance will be better, why? its pressure recovery will be at Mach 2 around 95% while DSI intakes gets around 87%-89% due to the similarities in performance to F-14 intakes, it will require more RAM too like F-22, but in planform alignment will be better.


To summarize without fan feelings both intakes are good, F-35 and F-22 exemplify it, but if you want higher speeds Su-57 has the ideal intake, if you want lower speeds below Mach 2 then DSI intakes go well.


are they invisible to radar? yes they are if they are far enough, yes they are invisible to radar, but their RCS depends in several factors, if they are facing modern defences both types of intakes will be detected, however we are talking about different aircraft so the general RCS of each aircraft will differ, F-22 is not Su-57 or F-35 is not J-20 or J-31, we do not need to fall into fan like competitions, stealth aircraft are not infallible machines nor defenceless ones, the conversation has been basically about the advantages and disadvantages and originally about the potential mesh J-20 has as boundary layer bleed and bypass.

Just looking at the boundary layer bleed porous holes on JF-17s bump and cowl, which still is a Mach 1.6-Mach aircraft you still can conjecture J-20 is a Mach 1.8 type aircraft at the most with a potential Mach 2 but losing lot of fuel and pressure recovery.

So even with WS-15 will not perform better than Su-57 at speeds beyond Mach 2, with Al-31 or WS-10 well it is unlikely can out perform F-22 or even Su-57 with 117 type engines.

However my last lines infuriate J-20 fans, but DSI intakes have limits they do not want to see;).

1572727405347.png
Production
Pakistan Aeronautical Complex (PAC) holds the exclusive rights of 58% of JF-17 airframe co-production work. A comprehensive infrastructure comprising state of the art machines and required skilled human resource has very quickly been developed at the Complex. The final assembly and flight testing of the aircraft was the first JF-17 co-production activity to start at PAC. The first PAC produced aircraft was handed over to Pakistan Air Force in November 2009. Since then, aircraft are being produced regularly to meet the required schedule. The co-production of sub assemblies and structural parts has also commenced and is sequentially attaining the sustained production status. Besides upgrading the production system, PAC has also upgraded its quality, technology and archive management systems to meet the production and management standards of a 3rd generation fighter aircraft.
Specifications
Physical Parameters
Length49 ft
Height15.5 ft
Wingspan31 ft
Empty Weight14,520 lb
Performance Parameters
Maximum Take Off Weight
27,300 lb​
Max Mach No
1.6​
Maximum Speed
700 Knots IAS​
Service Ceiling
55,500 ft​
Thrust to Weight Ratio
0.95​
Maximum Engine Thrust
19,000 lb​
G Limit
+8,-3​
Ferry Range
1,880 NM​
Armament
No of Stations
07​
Total Load Capacity
3400 l​
https://www.pac.org.pk/jf-17
 
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Jemiba

CLEARANCE: Above Top Secret
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This discussion is going round in circles now. We should stop here with the old say
"I agree to disagree" .
 

overscan

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Agreed. Reading some articles does not make one an expert, and analogies are not always helpful beyond the most superficial level of understanding of a topic. Posting huge swathes of text and pictures with only vague relevance to one's argument is just annoying.
 
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