why pakfa trumps rafale heavily............
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IND151
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F 35 has more stealthy belly and just compare belly of F-22 and Pak Fa.
Also having flatter belly will increase the volume available in weapons bays.
sancho
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No it hasn't as I already showed it the pic, the F35 has a lot of rounded areas at the belly as well, while the only rounded area at the T50 is the engine covering in the rear, which is likely to be changed in the serial production versions with the new engine (at least for India). All other areas are shaped to not have any right angles (check the angles between weapon bay and the air intake for example. Same goes for the missilebays, only because they are not integrated into the belly doesn't mean they wouldn't distract radar waves, btw did you checked how they housed the guns on the F35? Compare that to these missilebays wrt to stealthiness.
Wrt the volume, don't forget that the air ducts are housed above the weapon bays, while the air intakes of the T50, ot Y23 are seperated, which gives actually more room. The F35 btw has no missile bays for SR missiles at all, that's why it has only space for 2 MR missiles in strike config, so much for volume.
gambit
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This will both clear up some misconceptions and create new ones, depending on the individual reader...
In radar detection, every body is a finite body, meaning there are clearly defined physical borders. In the classroom, exercises are often with something like 'perfect electrical conducting' (PEC) or edges with infinite length. This is not to mislead the student/trainee but to force focus on a particular mode of radiation. And there are many modes.
For the sharp (left) cube, we have several modes and pathways for radiation to have radar detection. The six plates (sides) are for specular reflection. That is one mode. If the plate gets more horizontal, as if we are rotating the cube, then eventually the plate will produce some measure of surface wave mechanism. That is another mode. The sharp edges produces edge diffraction, the calculations of which made the Russian mathematician Ufimtsev famous and falsely attributed as the 'father of stealth', a label that he continually denied.
For the right (rounded) cube, we still have specular reflection but since the edges are severely rounded (curvatures), the dominant radiation mode will be surface wave mechanisms and far far far far less for edge diffraction.
If we place multiple receivers around each cube and sum their received signals, we would find total energy to be the same. But then why would the rounded cube have a lower RCS if both are set into something as simple as rotating in place?
Because the vast majority of radar operation are mono-static, meaning a single antenna does both jobs of transmission and reception and because it is a single antenna, it receives only one perspective of each cube.
Remember...The radar cross section (RCS) value is absolutely dependent upon calculation of RECEIVED radiation, not from radiation from all perspectives as in multiple receivers looking at multiple perspectives. So each receiver will have a different RCS value based upon the amount of radiation it received from the perspective it is looking at.
The rounded cube would have far less edge diffraction as a CONTRIBUTOR to the RCS value that a single receiver calculated. Surface wave radiation usually are away from the receiver and as long as the surface continues to exists, aka the electrical path as it is called, eventually most of this radiation will be denied from the seeking radar, while edge diffraction radiation is an abrupt severance of this electrical path and will radiate into free space in all directions.
A good example of this is here...
Principles of Remote Sensing - Centre for Remote Imaging, Sensing and Processing, CRISP
Rough surfaces are never good for RCS control methods and tactics in designing a low radar observable body precisely because of edge diffraction radiation.
Whatever happens at the microscopic level usually translate into the same at the macroscopic level.
So there are three top rules in starting out designing a 'stealth' body:
Control:
1- The QUANTITY of radiation pathways.
2- The MECHANISM of radiation pathways.
3- The ARRAY of radiation pathways.
These three top rules are necessary because we are working with finite bodies that do not have perfectly conducting materials and have finite dimensions.
The vertical stabilators common on most aircrafts belongs to the first rule, so the B-2 eliminated them in compliant to that rule. If protrusions are unavoidable, then inducing curvatures is in compliance with the second rule. If the quantity of radiators cannot be controlled because of aerodynamic necessities, then canting them to avoid creating the dreaded 'corner reflector' structure is in compliance with the third rule.
Sophistication in how to obey these three rules give us the many variations of 'stealthiness' or RCS variations out there from aircraft to aircraft. The greater the sophistication on how to obey these rules, aided by computers, the lower the received radiation by any seeking radar at any viewing perspective.
- Prediction
- Modeling
- Measurement
With computers, Prediction and Modeling can swap places, but Measurement have the final word.
This is why in designing a 'stealth' aircraft, aerodynamicists must work closely with sensor specialists (me) in trying to meet customer's demands. The aerodynamicist proposes a certain configuration and the sensor specialist provide, at least via simulations, on how the configuration would 'look like' to a seeking radar. Aerodynamics must take priority, of course, because the aircraft must be able to take flight, and this is the source of many misconceptions on these bumps and flat expanses on these aircrafts.
True, that we should obey the first rule as much as possible, but if the design of the aircraft produces these bumps, how sophisticated are we in obeying the second and third rules? Prediction and Measurement are done and that is what have. But what does Measurement say about these bumps? If Measurement have the contributorships of these bumps below a certain threshold that are accepted as 'stealthy', then for most of the mono-static radars out there, these bumps are meaningless.
In radar detection, every body is a finite body, meaning there are clearly defined physical borders. In the classroom, exercises are often with something like 'perfect electrical conducting' (PEC) or edges with infinite length. This is not to mislead the student/trainee but to force focus on a particular mode of radiation. And there are many modes.
For the sharp (left) cube, we have several modes and pathways for radiation to have radar detection. The six plates (sides) are for specular reflection. That is one mode. If the plate gets more horizontal, as if we are rotating the cube, then eventually the plate will produce some measure of surface wave mechanism. That is another mode. The sharp edges produces edge diffraction, the calculations of which made the Russian mathematician Ufimtsev famous and falsely attributed as the 'father of stealth', a label that he continually denied.
For the right (rounded) cube, we still have specular reflection but since the edges are severely rounded (curvatures), the dominant radiation mode will be surface wave mechanisms and far far far far less for edge diffraction.
If we place multiple receivers around each cube and sum their received signals, we would find total energy to be the same. But then why would the rounded cube have a lower RCS if both are set into something as simple as rotating in place?
Because the vast majority of radar operation are mono-static, meaning a single antenna does both jobs of transmission and reception and because it is a single antenna, it receives only one perspective of each cube.
Remember...The radar cross section (RCS) value is absolutely dependent upon calculation of RECEIVED radiation, not from radiation from all perspectives as in multiple receivers looking at multiple perspectives. So each receiver will have a different RCS value based upon the amount of radiation it received from the perspective it is looking at.
The rounded cube would have far less edge diffraction as a CONTRIBUTOR to the RCS value that a single receiver calculated. Surface wave radiation usually are away from the receiver and as long as the surface continues to exists, aka the electrical path as it is called, eventually most of this radiation will be denied from the seeking radar, while edge diffraction radiation is an abrupt severance of this electrical path and will radiate into free space in all directions.
A good example of this is here...
Principles of Remote Sensing - Centre for Remote Imaging, Sensing and Processing, CRISP
Rough surfaces are never good for RCS control methods and tactics in designing a low radar observable body precisely because of edge diffraction radiation.
Whatever happens at the microscopic level usually translate into the same at the macroscopic level.
So there are three top rules in starting out designing a 'stealth' body:
Control:
1- The QUANTITY of radiation pathways.
2- The MECHANISM of radiation pathways.
3- The ARRAY of radiation pathways.
These three top rules are necessary because we are working with finite bodies that do not have perfectly conducting materials and have finite dimensions.
The vertical stabilators common on most aircrafts belongs to the first rule, so the B-2 eliminated them in compliant to that rule. If protrusions are unavoidable, then inducing curvatures is in compliance with the second rule. If the quantity of radiators cannot be controlled because of aerodynamic necessities, then canting them to avoid creating the dreaded 'corner reflector' structure is in compliance with the third rule.
Sophistication in how to obey these three rules give us the many variations of 'stealthiness' or RCS variations out there from aircraft to aircraft. The greater the sophistication on how to obey these rules, aided by computers, the lower the received radiation by any seeking radar at any viewing perspective.
- Prediction
- Modeling
- Measurement
With computers, Prediction and Modeling can swap places, but Measurement have the final word.
This is why in designing a 'stealth' aircraft, aerodynamicists must work closely with sensor specialists (me) in trying to meet customer's demands. The aerodynamicist proposes a certain configuration and the sensor specialist provide, at least via simulations, on how the configuration would 'look like' to a seeking radar. Aerodynamics must take priority, of course, because the aircraft must be able to take flight, and this is the source of many misconceptions on these bumps and flat expanses on these aircrafts.
True, that we should obey the first rule as much as possible, but if the design of the aircraft produces these bumps, how sophisticated are we in obeying the second and third rules? Prediction and Measurement are done and that is what have. But what does Measurement say about these bumps? If Measurement have the contributorships of these bumps below a certain threshold that are accepted as 'stealthy', then for most of the mono-static radars out there, these bumps are meaningless.
IND151
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No it hasn't as I already showed it the pic, the F35 has a lot of rounded areas at the belly as well, while the only rounded area at the T50 is the engine covering in the rear, which is likely to be changed in the serial production versions with the new engine (at least for India). All other areas are shaped to not have any right angles (check the angles between weapon bay and the air intake for example. Same goes for the missilebays, only because they are not integrated into the belly doesn't mean they wouldn't distract radar waves, btw did you checked how they housed the guns on the F35? Compare that to these missilebays wrt to stealthiness.
Wrt the volume, don't forget that the air ducts are housed above the weapon bays, while the air intakes of the T50, ot Y23 are seperated, which gives actually more room. The F35 btw has no missile bays for SR missiles at all, that's why it has only space for 2 MR missiles in strike config, so much for volume.
No yo think the RAM coating is not necessary to be applied on under fuselage of Pak Fa
Rectangular nozzles?
kurup
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Yeah , flat nozzles . Something like this .
Russians already have the technology for flat nozzles .
sancho
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Of course it's necessary, my point was only that the F35t belly is not flat and that a shaped belly / airframe is the key not if the belly alone is flat or not.
Quit possible, we know the Russian had such developments and also patents for Pak Fa with such nozzles, it mainly depends on if they can compromise to 2D TVC.
OT but this might be interesting for you:
http://defenseissues.wordpress.com/2013/10/19/how-stealthy-is-the-f-35/
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