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External Load RCS …is it that bad? Why?

Tempest II

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We discuss aircraft radar cross sections and say the Gripen, Eurofighter, Rafale, etc have radar cross sections below one. We then discuss the “fact” (???) that putting any external loads on these planes suddenly increases the radar cross section several times fold. Considering that the ordinance and EFT are much smaller physically, would it not be cheaper for the air-force to ask the ordinance manufacturers to work on RCS reduction of ordinance?

• We say wings and vertical stabilisers are bad for RCS. There is very little of these of ordinance.
• We talk for jet fan blades. These rarely are there of ordinance.
• Exhaust heat signature – only on missiles after being fired and only for the time the motor is burning.

Unless if we are missing something big, I find it hard to understand why four missiles on a JF-17 will contribute more to radar return that the bulk of the plane itself.

I want to think part of the answer is that with RCS, 2 + 2 ≠ 4

Please lets discuss LIKE ADULTS!
 

Jango

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good question youknow, one to which i have no idea as to why the manufacturers dont do it, maybe because it isnt just feasible, the missiles are already very compact, and they need to be very aerodynamic with a small motor to get the best range for tail chase, so no room there really.
 

Arsalan

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We discuss aircraft radar cross sections and say the Gripen, Eurofighter, Rafale, etc have radar cross sections below one. We then discuss the “fact” (???) that putting any external loads on these planes suddenly increases the radar cross section several times fold. Considering that the ordinance and EFT are much smaller physically, would it not be cheaper for the air-force to ask the ordinance manufacturers to work on RCS reduction of ordinance?

• We say wings and vertical stabilisers are bad for RCS. There is very little of these of ordinance.
• We talk for jet fan blades. These rarely are there of ordinance.
• Exhaust heat signature – only on missiles after being fired and only for the time the motor is burning.

Unless if we are missing something big, I find it hard to understand why four missiles on a JF-17 will contribute more to radar return that the bulk of the plane itself.

I want to think part of the answer is that with RCS, 2 + 2 ≠ 4

Please lets discuss LIKE ADULTS!
the external weapons surely introduce drag and increased RCS.
its not like total RCS is something like
RCS for plane = 3
RCS for external misiles = 2
RCS for external fuel tank = 2

so totla RCS is 7, no its not like that!

if you have noticed, the stealth aircrafts have special aerodynamic features, the angled vertical stablizers and DSI intakes, properly desidned nose and etc.
this means that using external payload disturbes the overall RCS of the aircraft and it is inclreased.

i hope i have made my point clear, someone with more technical knowledge may help!

regards!
Arsalan Aslam
 

SQ8

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For starters..(read this somewhere)
External stores add to an RCS, but not more than the RCS of the platform itself.
So for a frontal aspect, say with 5m2.. adding a missile like the sidewinder.. may take it to 5.20 m2.
so if the platform was to be detected at 100km.. then it'll be picked up at a 130km.
its simply a case of the bigger fish.. compared to the missile, the aircraft is the larger object.
NOW.
If you had a stealth platform, like the J-20, with a frontal RCS of assuming .005m2.. and you hang a store off it like a PL-9. The RCS jumps to .5m2, simply because the unstealthy accessory adds through a factor to the target RCS.

Taking the above and applying it on the JF..
Assuming an RCS of 5m2(to make sure trolls dont jump in and a cleanup job is needed ;) ).
four SD-10's and two PL-9's would take the RCS to 6m2 at the front in a worst case scenario.
The effect on the RCS viewed from an angle, or the ground would be a lot more extreme.
 

Mani2020

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A couple of design guidelines should be followed in order to achieve this goal. One of them is the geometric optimization of the vehicle shape. Much of the literature on this subject is classified; moreover, the computing burden to tackle such a design is quite demanding. In this work, a conventional PC running a commercial electromagnetic code based on a modified Method of Moments is used to analyze four different simplified missile models. Design rules are established in view of reducing the monostatic radar cross section (RCS) scattered signal.

Simulations of the radar cross section of a heat- seeking air-to-air missile model were performed using the CADRCS software. In these simulations at a frequency of 10 GHz, the surface of the missile was considered to be a perfect conductor and to be coated with a radar absorbing material (RAM). The comparison of results from the simulations shows how different parts of the missile contribute to the radar cross section (RCS). Also, it is shown how the RCS of the missile is reduced with the use of RAM.
 

Jango

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A couple of design guidelines should be followed in order to achieve this goal. One of them is the geometric optimization of the vehicle shape. Much of the literature on this subject is classified; moreover, the computing burden to tackle such a design is quite demanding. In this work, a conventional PC running a commercial electromagnetic code based on a modified Method of Moments is used to analyze four different simplified missile models. Design rules are established in view of reducing the monostatic radar cross section (RCS) scattered signal.

Simulations of the radar cross section of a heat- seeking air-to-air missile model were performed using the CADRCS software. In these simulations at a frequency of 10 GHz, the surface of the missile was considered to be a perfect conductor and to be coated with a radar absorbing material (RAM). The comparison of results from the simulations shows how different parts of the missile contribute to the radar cross section (RCS). Also, it is shown how the RCS of the missile is reduced with the use of RAM.
in english please!:what:..you an engineer or something.
 

Mani2020

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The study is being carried out to reduce the aircraft's external load RCS.For it to happen cocoon techniques are used.The cocoon concept is based on placing pylon-mounted stores inside radar absorbent or deflective casings that would be shed before weapon engagement. The casing would ideally blend the weapon with the aircraft wing to eliminate radar cross-section returns generated by the pylon.
 

Manticore

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i posted a picture of typhoon and tornado , in which half of the diameter of the weapons were indented within the fuselage of the fighter - forget what its called
 

kingdurgaking

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One of the main reason why the ordiance is not concentrated for stealth is the ordiance gets destroyed when the mission is completed or the life experies unlike the aircraft.. so the cost for destroying a target will be more that the target itself.. which is a loss to the country.... so the simplest solution is put them inside the belly.... secondly RCS of the missile or drop tanks varies extremely based on the design... based on the load under the wing... for EFT like of load .. it is more when they are loaded as compared to the clean config.. Clean config are mostly used for recon in case of heavy radar defence area...
 

Luftwaffe

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Before discussing external RCS if it is bad and why, we need to understand RCS, this will help to understand.

Typical radar cross sections are as follows: Missile 0.5 sq m; Tactical Jet 5 to 100 sq m; Bomber 10 to 1000 sq m; and ships 3,000 to 1,000,000 sq m. RCS can also be expressed in decibels referenced to a square meter (dBsm) which equals
10 log (RCS in m2).

Pylons/external munitions also affect RCS

This is logical. Pylons increase the reflective surface area. So do external munitions/fuel tanks. However, this is greater at the sides than the front. A2A missiles have smaller frontal surface area but large bombs have greater surface area. That’s why a weapons bay is a pre-requisite with lower RCS fighters.

The wings and tails contribute to RCS too, Those contribute to RCS too. The point about new designs such as the F-22 and F-35 is that their wings and tails although looking flat are not really flat but slightly curved. That’s probably why the F-15SE has a proposed canted tail. The current F-15 tail (like the F-18) is ~90 deg perpendicular to the side which increases its RCS. So are its wings in relation to the top.

http://www.tscm.com/rcs.pdf

I've found this to be very interesting written by an Iranian
http://www.jpier.org/PIER/pier57/15.0508011.Mallahzadeh.SR.pdf

Some more..
http://www.mar-it.de/Radar/RCS/RCS_xx.pdf
 

shehbazi2001

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External load is a big factor for RCS after the airframe itself but when air superiority has been achieved over a specific theatre or when enemy air defences have been suppressed, then its not bothersome to use externally-loaded armaments.

RCS is increased by antennas and even insect/bird excrement on the airframe. F-117 retracts all its antennas during wartime mission. Only in the training missions can it deploy its antennas.

The internal weapons bay does not open when the F-117 is being painted by radar because internal weapons bay is not stealth. Then the Nighthawk's autopilot does not allow "any turn" in wartime mission. All turns are designed/programmed to minimise radar returns.

During the Gulf war, ground crews started finding dead bats around the tails of F-117 in the hangors. Sound waves of the bats could not return to them and they used to collide with the airframe, a proof of its stealth skin.

Reference: F-117A Stealth Fighter by JON LAKE
 

gambit

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We discuss aircraft radar cross sections and say the Gripen, Eurofighter, Rafale, etc have radar cross sections below one. We then discuss the “fact” (???) that putting any external loads on these planes suddenly increases the radar cross section several times fold. Considering that the ordinance and EFT are much smaller physically, would it not be cheaper for the air-force to ask the ordinance manufacturers to work on RCS reduction of ordinance?

• We say wings and vertical stabilisers are bad for RCS. There is very little of these of ordinance.
• We talk for jet fan blades. These rarely are there of ordinance.
• Exhaust heat signature – only on missiles after being fired and only for the time the motor is burning.

Unless if we are missing something big, I find it hard to understand why four missiles on a JF-17 will contribute more to radar return that the bulk of the plane itself.

I want to think part of the answer is that with RCS, 2 + 2 ≠ 4

Please lets discuss LIKE ADULTS!
Here is the FIRST thing you should understand about radar cross section (RCS): That EVERYTHING is a contributor to the final RCS value. Meaning every individual component, from a surface scratch that you can barely feel with the most sensitive skin area -- your palm -- to those large flight control surfaces, each item has its own RCS value.

The second thing you should understand is that an aircraft is a complex body. In radar detection, the only simple body in existence is the sphere. We can eliminate the sphere from our discussion.

The third thing you should understand is that in a complex body, reflected and diffracted signals interact with each other in ways that we have only barely begun to model and predict. When I say 'barely' I mean post F-117. In many ways, the F-117 has more fortune working for its low RCS than the B-2, F-22, and F-35.

Here is the simplest example of those interactions...



A 90deg corner as produced by the above example is a serious no-no when the goal is to reduce RCS. It is called 'target corner reflector' or simply 'corner reflector'. This configuration can be created by any material, even paper, and metal is the worst. This structure GUARANTEE that of all complex arrangements on a complex body, most (not all) of whatever amount of radar signal power hitting that structure will be reflected back to source direction.



The above is a 'macro' view of this complex body we call an 'aircraft'.

Here is the 'micro' view...



Since no surface is ever perfect, we can see that those microscopic corner reflectors are very much contributors to the final RCS value. The interactions between these reflected and diffracted signals in a complext body give us 'constructive' and 'destructive' interference and it is they that we have the most problems modeling and predicting. Obviously we do not want constructive interference but aerodynamic necessities may not give us all the destructive interference we would like to create.

Now all you have to do is look FOR these contributors on every missiles, bombs, pylons, and fuel tanks that we can hang under the wings and see why from a radar detection perspective, pre-F-117 aircrafts are quite 'messy' or 'noisy'. No one who value his freedom will tell you how much these 'doodads' contribute to the final RCS value of a fully loaded for combat aircraft but all we have to do is look at the current generation of 'stealth' designs with their emphasis on hiding these 'doodads' to make an educated guess on how much they contribute. It is very very considerable and the JF-17 is no exception no matter how much anyone wish otherwise. DO NOT be misled by individual RCS values. Item three as I stated above can CUMULATIVELY make all the missiles, the bombs, the external fuel tanks, and the pylons that carries them as large an RCS value as the aircraft itself. Perhaps even greater.

Since the debut of the F-117, manufacturers are busy trying (with little success) to reduce the contributorships of externally carried stores. The problem lies with the second item I said above. The more protrusions you create, the more the complex the body and the greater the third item.

the external weapons surely introduce drag and increased RCS.
its not like total RCS is something like
RCS for plane = 3
RCS for external misiles = 2
RCS for external fuel tank = 2

so totla RCS is 7, no its not like that!
Actually...It is very much like that. We effectively sum up all the individual RCS and perform full scale model radar testing. Sometimes the results surprised us because of unexpected destructive interference that give us a lower final RCS value than anticipated. Sometimes the results are greater so then it is back to the proverbial drawing board we go. Some designs may not give us the option of re-doing our work because any changes could catastrophically compromise aerodynamic necessities. Like it or not, aerodynamics comes first.

The study is being carried out to reduce the aircraft's external load RCS.For it to happen cocoon techniques are used.The cocoon concept is based on placing pylon-mounted stores inside radar absorbent or deflective casings that would be shed before weapon engagement. The casing would ideally blend the weapon with the aircraft wing to eliminate radar cross-section returns generated by the pylon.
The mechanical complexities of the weapons system itself would increase dramatically. We now have to install another safety in that we do not want to launch a missile unless the 'stealth' pod is completely discarded. We have to design that discard mechanism to be %99.999 reliable. Not impossible, just very difficult to engineer and deploy.
 

nightcrawler

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The mechanical complexities of the weapons system itself would increase dramatically. We now have to install another safety in that we do not want to launch a missile unless the 'stealth' pod is completely discarded. We have to design that discard mechanism to be %99.999 reliable. Not impossible, just very difficult to engineer and deploy.
I think such 'coverings' also known as cocoons will deploy spring mounted pneumatic legs for missiles (such were also employes in TU-95 & MiG-31 for R-33/37 missile) to push the missile away from the fuselage & then turn on rocket moor; such technique will hardly interfere with missile shapes & isn't complex; also semi-recessed missile bays also reduce RCS
 

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