weasel1962
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BVR Missile question
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As previously, there are reasons why the B-2, F-117 and F-22 don't have large, circular Con/Di nozzles.
Blockers, serrated edges and lossy materials (as well as cooling air) can only do so much to reduce the observables - after all, the JSF nozzle is a BIG cavity. Check the physics!
AMRAAM v F-22 Detection Range
@rjmaz1
I agree with your assumptions and calculations on the likely detection range of the AMRAAM missile against an F-22.
Apart from the difference in power the other important factor is the size of the radar aperture. All other things being equal this can be determined by the relative size of the antennae.
The external diameter of the AMRAAM is 7inches allowing for a 160mm diameter antenna. The APG-77 Antenna is not round but roughly elliptical, close to 1000mm across and 800mm high, giving an equivalent area to an antenna 800mm – 900mm in diameter. The area increases in proportion to the square of the diameter and because this affects the performance of the radar on the outward and return path causes the performance by the fourth power of the diameter of the antenna. This compensates for the fourth power relationship between transmitted power and range. Hence as the AMRAAM seeker is about 5 times smaller than the APG-77 antenna it will have 5 times less range. (Some small account should be given for the different wavelengths, but it is lost in the noise, due to the very broad assumptions of transmitted power etc).
So the estimated detection range of an AMRAAM against an F-22 is given as follows: - Detection range of F-22 (22 to 25nm) divided by (the 4th root of the ratio of the transmitted power of the APG-77 (22-25kw) and the transmitted power of the AMRAAM) divided by the ration of the diameter of the APG-77 (800 – 900mm) and the diameter of the AMRAAM seeker head (160mm).
This works out at 1.6 – 2.2 nm, allowing a little extra for the different wavelengths around 2nm plus/minus 10%.
The AMRAAM has a two or three stage rocket motor, during the terminal stage it will still be travelling at very high speed. Assuming a head-on aspect with the F-22 flying at 600kts and the missile down to 1,200kts, flying on a parallel track to the aircraft with a two nm separation. The missile would have to execute an immediate 180 turn with a radius of 1 nm, requiring the missile to pull about 48g. At higher closing speeds the situation would be much worse. If the missile were flying at 1,200knt it would have to pull 84g. Where the cross-track error is less the amount of steering required is less and the g forces are reduced dramatically.
In most scenarios the time from acquisition to impact would only be a handful of seconds and the missile will have to manoeuvre very quickly and is likely to pull very high g resulting in a rapid reduction in speed and a very low probability of a kill.
A missile equipped with a mixed mode seeker with radar, optical & IR sensors may achieve better results.
Chris
@rjmaz1
I agree with your assumptions and calculations on the likely detection range of the AMRAAM missile against an F-22.
Apart from the difference in power the other important factor is the size of the radar aperture. All other things being equal this can be determined by the relative size of the antennae.
The external diameter of the AMRAAM is 7inches allowing for a 160mm diameter antenna. The APG-77 Antenna is not round but roughly elliptical, close to 1000mm across and 800mm high, giving an equivalent area to an antenna 800mm – 900mm in diameter. The area increases in proportion to the square of the diameter and because this affects the performance of the radar on the outward and return path causes the performance by the fourth power of the diameter of the antenna. This compensates for the fourth power relationship between transmitted power and range. Hence as the AMRAAM seeker is about 5 times smaller than the APG-77 antenna it will have 5 times less range. (Some small account should be given for the different wavelengths, but it is lost in the noise, due to the very broad assumptions of transmitted power etc).
So the estimated detection range of an AMRAAM against an F-22 is given as follows: - Detection range of F-22 (22 to 25nm) divided by (the 4th root of the ratio of the transmitted power of the APG-77 (22-25kw) and the transmitted power of the AMRAAM) divided by the ration of the diameter of the APG-77 (800 – 900mm) and the diameter of the AMRAAM seeker head (160mm).
This works out at 1.6 – 2.2 nm, allowing a little extra for the different wavelengths around 2nm plus/minus 10%.
The AMRAAM has a two or three stage rocket motor, during the terminal stage it will still be travelling at very high speed. Assuming a head-on aspect with the F-22 flying at 600kts and the missile down to 1,200kts, flying on a parallel track to the aircraft with a two nm separation. The missile would have to execute an immediate 180 turn with a radius of 1 nm, requiring the missile to pull about 48g. At higher closing speeds the situation would be much worse. If the missile were flying at 1,200knt it would have to pull 84g. Where the cross-track error is less the amount of steering required is less and the g forces are reduced dramatically.
In most scenarios the time from acquisition to impact would only be a handful of seconds and the missile will have to manoeuvre very quickly and is likely to pull very high g resulting in a rapid reduction in speed and a very low probability of a kill.
A missile equipped with a mixed mode seeker with radar, optical & IR sensors may achieve better results.
Chris
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- #24
cheers Chris,thats the sort of common sense answer ive been looking for. I assume that the JSF,s RCS would be similer or smaller than F22,s? The surviveability of any air to air fighter must surely be greatly enhanced by this tech. I am a firm believer that the RAAF should be patient and get the JSF,maybe just 24 Super Hornets on lease to cover the gap from F111,s....but thats a different thread!
No the F-22 has a much smaller radar cross section. Less than half of the JSF with some reports indicating a radar cross section a quarter of the JSF from the front. The description to the public is that the F-22 is marbal size and the JSF is golf ball size. So thats 2 to 4 times the radar cross section.
From the rear the JSF has very little stealth compared to the F-22. So the F-22 is atleast 10 times smaller, could even be upwards of 100 times smaller from the back.
Most of the firm believers of the JSF think that its radar cross section and speed is relatively close to that of the F-22, when in fact its not even in the same ball park.
The JSF will still be a good aircraft but it will be no where near as capable as some people wish/think it will be.
Given the F-22 is full spherical, broad band VLO (-40 to -30 dBSM), this would make the JSF, at best, LO (-30 to 0 dBSM). But as some folks say, what's one letter on a briefing slide between friends.
See page 48 on http://www.aph.gov.au/hansard/joint/commttee/J9128.pdf
I suppose it's when it is between adversaries that it starts to count.
Now, before the thought police start getting their nickers in a knot, these figures have been in the public domain for years, even before the classification shutters came down on 'stealth' back in the late 1970s/early 80s.
For anyone interested in getting a better handle on LO technologies, see the link at Post # 11 for one of the better primers, called 'The Radar Game'.
Thanks for that very interesting read.
Dr Kopp and his evolved F-111
Completely off topic but..
I cant believe such uneducated people are making the decisions for us. The JSF is two thirds the size of the F-22 yet has the same amount of internal fuel and one engine instead of two. This alone means the JSF will have similar if not greater range and have much greater endurance than the F-22... yet they claim the F-22 has more legs.
Crazy and idiotic stuff. In my opinion no one will take Kopp and Goon seriously until they drop the evolved F-111 idea.
I should write a proposal to the government about my A-10 idea in a high-low combat mix
nfloorl:Ozzy Blizzard
New Member
This is really off topic and i'm sure it'll be in another thread but is the F35 really going to be practical as an air superiority fighter? i ask this with one point in mind. The JSF can only cary 4 or maybe 6 (4 on double rails) AAM's internaly, which isn't much of an AA armement, and if you want more you loose LO. And without LO the F35 isn't super special. Kinda light for an Air superiority fighter. And for CAS too, weapons would have to be stored on external hardpoints. Doesn't sound to great as a Air Superiority fighter or a LO CAS platform to me? Is it really the best choice?
JSF RCS & Speed Comparison
The F-35 will have a larger RCS than the F-22.
Although we do not have the exact figures I have taken the following RCS estimates from the same source.
F-22 0.0002m2
F-35 0.0015m2
F-18E 0.1m2 * Roughly the same for Euro Canards.
F-16C 1.8m2 * Roughly the same for older generation e.g. F-18A/B etc
Using the F-22, as the basis, the F-35 RCS is 7.5 times larger and taken the fourth root would be detected at 1.7 times the detection range of the F-22. Similarly for the F-18E, 500 times larger and 4.7 times the detection range of the F-22. And the F-16C, 900times larger and 9.7 times the detection range of the F-22.
As discussed yesterday this would give an estimate for the detection range on an AMRAAM at 2nm for F-22, 3.3nm for F-35, 9.5nm for F-18E and 19.5nm for the F-16C.
Due to other limitations I recall that the maximum sensor range is 10 – 20nm depending on the model.
As mentioned elsewhere these are the RCS for the front aspect only, similar figures for the rear aspect would be very much greater particularly in the case of the F-35. For the dead astern position looking straight up the jet-pipe could result in an increase in the RCS by a factor of 1000, increasing the detection range by a further factor of 5.6. (It pays not to run away late in such engagements).
With regards to maximum speed, again we do not have the exact figures, but these estimates were taken from the same source and are good enough for the purpose of comparison.
F-22 M2.4+
F-35 M1.6+
F-18E M1.8+
EF M2.0+
F-16 M2.0+
The F-22 & F-35 were designed for very different roles so it is not surprising that there are differences in performance.
Chris
The F-35 will have a larger RCS than the F-22.
Although we do not have the exact figures I have taken the following RCS estimates from the same source.
F-22 0.0002m2
F-35 0.0015m2
F-18E 0.1m2 * Roughly the same for Euro Canards.
F-16C 1.8m2 * Roughly the same for older generation e.g. F-18A/B etc
Using the F-22, as the basis, the F-35 RCS is 7.5 times larger and taken the fourth root would be detected at 1.7 times the detection range of the F-22. Similarly for the F-18E, 500 times larger and 4.7 times the detection range of the F-22. And the F-16C, 900times larger and 9.7 times the detection range of the F-22.
As discussed yesterday this would give an estimate for the detection range on an AMRAAM at 2nm for F-22, 3.3nm for F-35, 9.5nm for F-18E and 19.5nm for the F-16C.
Due to other limitations I recall that the maximum sensor range is 10 – 20nm depending on the model.
As mentioned elsewhere these are the RCS for the front aspect only, similar figures for the rear aspect would be very much greater particularly in the case of the F-35. For the dead astern position looking straight up the jet-pipe could result in an increase in the RCS by a factor of 1000, increasing the detection range by a further factor of 5.6. (It pays not to run away late in such engagements).
With regards to maximum speed, again we do not have the exact figures, but these estimates were taken from the same source and are good enough for the purpose of comparison.
F-22 M2.4+
F-35 M1.6+
F-18E M1.8+
EF M2.0+
F-16 M2.0+
The F-22 & F-35 were designed for very different roles so it is not surprising that there are differences in performance.
Chris
The potential enemy countries are starting to move away from the large quantity of cheaper aircraft to fewer but more advanced aircraft.
China for instance used to have thousands of very basic aircraft, so our aircraft would need alot of missiles as they may encounter 10 aircraft at once. However those days are gone. The US will be facing an enemy with equal numbers or at the very worst twice as many enemy aircraft. So 4 missiles will be fine and 6 missile is more than enough.
When the JSF is on a strike mission it will be carrying two AMRAAMs with its bomb load. If in paired up with another aircraft thats 4 AMRAAMs more than enough to allow them to escort themselves in a small regional conflict.
AMRAAM is much more accurate than the old sparrow, so the chance of needed two missiles per aircraft is much less.
Trouble is, when you're travelling at Mach 0.9 and 35,000 feet, you realistically need to budget two missiles per kill. But from M1.8 and 50K+ in a VLO fighter with LPI sensors, one missile will usually do the trick! This is where the fighter argument swings across in favour of the F-22, and is where my own opinions on which way to go sometimes waver.
Magoo
Magoo,
You have introduced or rather lifted the lid on one of the most important points in this whole fighter debate which has been overlooked by most.
The F-22's capabilities have and will continue to re-write the tactics manual - a point not lost on those who understand such things, including Mr Sukhoi et al and their proponents, operators and licensed technologists in the region.
Thankfully, the more experienced operators in ACG have cottoned on to this fact - something that will be reinforced, at least at their level, by the recently approved exchange posting onto the F-22.
Here's hoping this will now become apparent up at the citadel level of the grey sponge (where it should have been in the first place) before it is all too late.
By the way, have you seen any JSF scenarios that are not multi ship flights (usually around four) ?
Multi ship flights with their requisite entourage (AWACS, Tankers et al) means the Air Commander would be denied the ability to and the benefits of surprise.
- Thread Starter Thread Starter
- #33
another question in regards to stealth vs payload. Is or will there be a weopons pylon that can be jetissoned after the weopons have been released?(JSF) or would this be rediculously expensive....just a thought that JSOW os JSSM could be delivered then the JSF take on a CAP or fighter role...without compromising its stealthy advantage.
Disposible weopons pylons...(after thought!)
Disposible weopons pylons...(after thought!)
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This was discussed on another forum after the release of pictures showing external fuel tanks being jettisoned complete with pylons.
Am I allowed to post the link to the other forum on this forum?
http://img213.imageshack.us/img213/4846/04e0130006qm0.jpg
The following was my response to the picture.
A very clean separation.
I agree with DL that the ability to jettison external stores is an essential requirement for the F-22 & F-35 in order to be able to switch back to stealth mode.
Having the pylon still attached to the tank maybe a better option than jettisoning the tank then the pylon. Obviously just one operation rather than two, but also potentially more stable. The shape of the pylon is similar to a wing and if it gets out of line with the airflow, providing an angle of attack, the lift generated could result in the pylon hitting the aircraft. A pylon released alone would have less roll stability, which could allow the pylon to roll same that the direct of lift is towards the aircraft. Releasing the pylon and the tank together is less likely to allow a roll component to develop and hence result in a safer release. As usual the forward mounting point is released first generating an initial pitch down motion.
Jettisoning pylons used for external weapons, after the weapons have been released, may be more problematic.
Other aircraft have used this method of jettisoning fuel tanks, I think the F-4 dropped the large Sgt Fletcher wing tanks with the pylons.
Most aircraft fitted with pylons have the ability to jettison the pylons as well as the external stores.
At some stage during the flight trial program, the carriage and release of asymmetric loads will be undertaken, and then things can get really interesting. The second of a symmetric pair is the difficult drop; often the aircraft is flying slightly sideways due to asymmetric drag. If released when the pylon is not exactly aligned with the airflow, lift can be generated and the pylon can go anywhere. With modern FCS it may be possible for the jettison release system to advise the FCS, so that the airflow can be aligned, before the pylon is ejected from the aircraft. Similar advanced warnings could be used when dropping weapons. After the store has been released the FCS will catch-up, but making corrections just prior to release could make for a better separation. (A little like correcting for drift when landing in a cross-wind).
Disposable weapons pylons, you bet, these will be an essential to the operation of the F-22 & F-35, allowing the aircraft to have the benefits of external weapons and fuel and the capability to go to stealth mode.
As you say the introduction of the F-22 & F-35 will require new tactical thinking.
Chris
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- #35
cheers Chris,
was thinking that for JSF, the only pylons would be fuel, Bomb or ASM pylons. Not sure if smart pylons "talk to their munitions" or not, could be costly!
was thinking that for JSF, the only pylons would be fuel, Bomb or ASM pylons. Not sure if smart pylons "talk to their munitions" or not, could be costly!
contedicavour
New Member
Guys what about the Russian Vympel missiles AA10 & AA12 ?
How do they compare with AIM120B, Meteor or Mica when it comes to engaging F35s or Typhoons or F22s ?
Btw, are all the MIG29, -31 and SU27/30 in Russian service capable of using these Amraam-type missiles or some still rely on old semi-active missiles ?
cheers
How do they compare with AIM120B, Meteor or Mica when it comes to engaging F35s or Typhoons or F22s ?
Btw, are all the MIG29, -31 and SU27/30 in Russian service capable of using these Amraam-type missiles or some still rely on old semi-active missiles ?
cheers
RubiconNZ
The Wanderer
Not to hijack the above questions, but additionally, why is the Air Launched Sparrow still in service with the USN and USAF, is it a question of production not meeting demand, the sparrows used to suffer hugely from reliability and accuracy issues, I know upgrades apparently fixed these but...
They are mainly held in reserve as "war stock" and are fired off for practice.
The RAF uses the Skyflash (Sparrow derivative), in the same fashion.
Chris
Not really. You have to account for the array gain, shape of the beam, duration of the pulse, the frequency itself, the strength of the emitter, time interval of the sweep. Also the AMRAAM seeker is working on a continious wave illumination while the fighter rader is working on the pulse doppler principle.
The emitter of one being run by nickel hydride batteries not much different from your cellphone is not going to match the output from emitters whose combined power is being fed from a generator.
It has been said before. Most BVRAAMs take a lofted profile. So they would be attacking their targets from high up, not directly faceward. Thus the target is not presenting to the missile the aspect where its RCS reduction is most effective. I would doubt that the F-22 has the same RCS when you're looking at it downward than faceward.
IR sensors don't work very well on the F-22 frontward as well because the F-22 has special systems (probably running fuel in the front edges of the wing) to cool the hot surfaces, which makes it difficult for an all aspect IR missile to lock on from a frontal aspect. You're back to attacking the F-22 from any other aspect but the front.
Of course with radar you have to take into account all the things you mentioned; however I was making a comparison, taking into account the relative power transmitted by the fighter radar and the missile, and the size of the antenna.
There are other factors, but they are likely to result in similar affects on both systems (i.e. losses between the antenna, transmitter and receiver). Beam shape is important but is a function of the size of the antenna, (these days the number of T/R Modules), and the frequency of operation. If you know exactly where to look it is possible to focus the beam to a very fine angle to search for a target, but the fighter radar has this ability to a greater degree than the missile radar. There are differences because the fighter and missile use different techniques. Strictly these days not a Pulse Doppler (PD) radar, or even an Interrupted CW (ICW) radar). Modern radars transmit pulses of varying length and change the transmitted frequency on a pulse to pulse basis (sometime even during the pulse). The computer then resolves the range and velocity ambiguities and generates track files for each potential target. Using these tricks the fighter radar can effectively improve the sensitivity of the receiver given a specific size of antenna and available transmitter power.
The missile radar has a few tricks as well that can effectively improve receiver sensitivity, but not as good as the fighter radar.
(The available power in the missile and fighter is a factor in determining the maximum power of the transmitter).
For the purposes of the original argument I assumed that the receiver sensitivity (including the processing tricks) were the same so that the comparative performance could be determined on the basis of antenna size and transmitter power.
Scan rates etc do come into play when determining the probability of detection, but apply to both fighter and missile radars. It helps to know where to look, the missile has the advantage that the fight can tell the missile on route where the target is (mid-course correction), but the fighter is also usually advised by AWAC where to look for targets.
The point about the missile flight path is valid, a lofted flight would present a slightly different aspect angle and likely an increased RCS, but not by very much and again the inverse fourth power law comes into play.
I think your suggestion about IR management on the wing leading edges using fuel is logical; it has been used on the SR-71 and on Concorde. It might be easier to use another more efficient primary cooling fluid, combined with a heater exchanger cooled by the fuel.
Combined sensor seekers are being developed, because it is very difficult to be stealthy in all wavebands, for all aspects all of the time.
The bottom line is that to hit an F-22 with an AMRAAM the missile must come very close to the fighter and very nearly aiming at it to get a hit. To achieve this result the attacking fighter’s radar must be able to see the target and provide mid-course steering information.
Also this won’t be one sided, the target F-22 will be advised by the missile warning system that a missile is approaching and will take avoiding action, with such a small RCS missile the no escape basket is very small and the F-22 would not have to move very far evade the missile: not to mention deploying other counter-measures.
IMHO using the current version of AMRAAM, in a F-22 against F-22 engagement it would be difficult for either fight to shoot down the opponent.
Chris