lukosFor ground targets that is certainly true, air targets not so much.
lukosyou sure about that?
Yes. Only laser and radar can measure this accurately, although you could theoretically do it using triangulation between two aircraft but I can only find limited testing results using passive targeting, the first involving a shot at 7.8nm and a second involving a shot that used laser for ranging at 10nm and two aircraft. So far it’s only been demonstrated at very close ranges in testing.
lukoswhy the early ARM aim at the side lobe but not the main lobe or the back lobe ? if the radar rotating wasnt it still the same because you still got radiating signal from the radar all the time ? why cant the missiles just home on it ?
This basically covers it:
http://ausairpower.net/alarm-armat.html
Conventional ARMs home primarily upon the mainlobe and horizontal sidelobe and backlobe emissions of the target, attacking the target in a shallow dive trajectory. Modern radars with very low sidelobe antennas will thus present a “blinking” target to an approaching ARM, which must estimate the real position of the target from the intervals of active emission, when the antenna is radiating in the direction of the inbound missile. In the terminal phase of the ARM’s flight, a slowly rotating antenna on the target may be pointing away from the missile, which will therefore have to follow an inertially steered trajectory based upon previous measurements of the radar’s position. As a result the missile will more than often not hit the target directly, but pass within several metres of the target, using its proximity fuse to set off the warhead. This imposes the need for a larger warhead to achieve acceptable lethality.
The vertical attack ALARM is designed from the outset to home in on the vertical sidelobes of the threat emitter. Since most air defence radars are designed for high bearing accuracy, they tend to have good horizontal but poor vertical sidelobe antenna performance. The ALARM exploits this, as no matter what direction the main beam is pointing in, the ALARM sees a steady albeit fluctuating microwave emission leaking upward from the target’s antenna. This allows the ALARM to home in precisely, indeed the missile is designed to select an aimpoint about 1 metre away from the target antenna/electronics enclosure. The intelligent seeker knows what type of radar it is attacking, and therefore also knows what the elevation of the antenna is above the ground. This information is then used to select the most suitable altitude for warhead firing, typically when the missile is directly abeam the antenna or electronics enclosure. This scheme was specifically designed to defeat mast mounted antennas, which have become a very popular means of improving the low altitude coverage of ground based air defence radars. Needless to say a smaller warhead can achieve similar or greater lethality if fired very close to the target, compared to a larger warhead set off at a greater distance.
what is interferometry ?
Explained 5-8.8:
http://www.phys.hawaii.edu/~anita/new/papers/militaryHandbook/sig-sort.pdf
btw how about find the elevation of enemy aircraft by IRST and find their altitude that way ? (you now the angle between your aircraft and enemy by IRST , you know your own altitude => know their altitude by triangulation )
IRST doesn’t give range very accurately either, and without range altitude can’t be determined, only bearing (azimuth and elevation angle). The only way you accurate get range and hence altitude is radar or laser.
lukosI think we will find that one cap does indeed fit all.
Nope.
Given that electronic scanning is done by manipulating the phase of the signals created by the individual Tx/Rx modules, it seems most unlikely that any current AESA will differ from this practice. Just how could you control the relative phase of two signals that are different frequencies? Invoking the Great God of Signal Processing (a common response by forum members who ascribe near-magical qualities to AESA arrays) is not good enough.
You get a coherent composite beam with several frequency components.
If each module could use its own frequency, this would be a huge EW advantage over PESA arrays, but such a claim is not made by Stimson, it is not made in Skolnik, and has never been made at any radar presentation that I have sat through. Nor have I seen it made in any technical presentation by a reputable authority in the field. I have only seen it in non-professional texts, and at least one non-technical piece by an academic. The idea of a major breakthrough has been made achieved, but no-one in the radar industry ever bothers to mention it is hardly a credible one.
Halloweene just mentioned it.
The only mention I have seen of getting a simultaneous second or third frequency out of an AESA postulated creating dedicated sub-arrays as part of the main array. Were any module to be able to operate at any frequency in the manner that you believe, there would be no need for such sub-arrays.
Yes you would have several sub-arrays working at different frequencies, the size of which will adjust the amplitude of that particular frequency component. By varying the amplitude of each frequency component or changing the frequency components over time you get a unique time-varying fingerprint that could also be made to alter when the presence of jamming is detected, or when an enemy is detected, or a different fingerprint could be used to paint each target.
lukosWasn’t it the beginning of that discussion? That missiles with small wings are unlikely to maneuver well at high alt? Otherwise your entire discussion is pointless, with 3,4 m2 wing area and 490 kg weight right off the rail, R-33 has 144 kg/m2 wing loading which less than half of any aircraft flying. BTW, I’ve also calculated the wing areas of AIM-120A and R-27RE. Their wing loadings are 176 and 159 kg/m2 respectively. With their propellent expanded, and weight reduced to half, these numbers should be halved also.
Nope, we were actually discussing whether missile performance deteriorates more than aircraft performance at high altitude due to having smaller wings. My position is that it doesn’t. The discussion is far from pointless, it just isn’t the one you seemed to think we were having.
I believe the current discussion came from this:
http://forum.keypublishing.com/showthread.php?131688-Best-Russian-heavy-weight-fighter&p=2165534#post2165534
However there was originally a note on this:
http://forum.keypublishing.com/showthread.php?131688-Best-Russian-heavy-weight-fighter&p=2164267#post2164267
My only intention here was to convey that intercept performance and g-limits weren’t entirely dependent on wing-size but also on velocity. I guess the point you’ve also introduced in response to obligatory’s original remark is that not all long range missiles have high wing loading either, which seems a fair point if your analysis is correct.
I wasn’t talking about two aircraft firing their missiles on each other, but that was my point. PS, not necessarily higher peak speed as in case of R-33, It can have longer burn time so it reaches similar peak speed, but maintain much better average speed.
I’d be interested to know what kind of motor the R-33 actually has. The problem with quoted speed, is that it isn’t always straight forward and sometimes a pseudo average is quoted rather than a peak. I can’t claim them to be realistic but on simulators I have fired R-33s and found them to reach much higher speeds than that quoted on wikipedia when fired at 60,000ft, and the same can be said of the AIM-54. The peak speed was much higher than that for an AIM-120C. I in fact put two aircraft in firing range of each other (MiG-31 and F-15C) at the same altitude and speed about 100km apart at >60,000ft and Mach 2.5, and the R-33 hit the F-15C before I think the AIM-120C even got into seeker range. Jamming isn’t really modelled in the simulator because it can’t be, since nobody knows enough. Again, I can’t claim this as fact, but beware of taking a quoted speed for two missiles and assuming it means the same thing.
That is why I called its about optimization. What you also need to consider is altitude; greater wing area will clearly lessen low altitude maneuverability of the missile.
There is clearly an optimisation process but would larger wings reduce manoeuvrability at low altitude, or just limit range, hence reducing manoeuvrability after a given range from launch?
What is more interesting is AIM-120A (with greater wing area than AIM-120D) has 9,95 deg/s turn rate and 5946 m turn radius at M3.5, but R-33 missile has 10,4 deg/s turn rate and smaller turn radius of 4846m at M3.0; So even if arrives much slower, it should have better Pk than AIM-120D for the above discussion.
I would be careful when comparing tighter turn circles at lower speeds with larger turn circles at higher speeds. Higher speeds always mean larger turn circles and lower deg/s at equal g load. And when accounting for speed, you need to consider how much the target can turn in the elapsed time too. A faster missile gives the target less time to move, even though its deg/s might be lower. A missile at Mach 1000 ten miles away likely wouldn’t need to manoeuvre at all and lead would be negligible, with a 60kg proximity-fused warhead, it could just point straight at a subsonic target and do the job just fine.
For a target at 24000m (as in MiG-31) G ability of those missiles at same airspeeds as follows:
R-33S: 2,8G; 4,3G; 6,3G; 8,58G
R-27RE: 2,52G; 3,9G; 5,7G; 7,77G
AIM-120A; 2,29G; 3,5G; 5,1G; 7.0GEven at overly optimistic terminal speed of M3.5; those missiles have following turn rates, and their turn rate covers following distance difference at 1km, 5km and 10km respectively:
R-33S: 4,6 deg/s; 80m/s; 401m/s; 802m/s
R-27RE: 4,16 deg/s; 72m/s; 362m/s; 724m/s
AIM-120A: 3,74 deg/s; 65m/s; 326m/s; 652m/sEven if those missiles plot an intercept course, just a 80 meter change from expected course in a second at 1 km distance will prevent missile from hitting it, as it will lack to turn rate to compensate afterwards. Aircraft will simply fly faster and into the turn radius of the missile. MiG-31 at 24000 meters at M2.5 flies at 744 m/s airspeed just for the comparison.
Accepted but the missile speeds at 24,000m will be higher than at 18,000m for a given intercept, and significantly higher than at 10,000m because of the reduced air density.
I’d be interested to see how an AIM-54C compares.
lukosThe Kh-31P uses one of three alternative seekers designated L-111, L-112, L-113. There are reported to allow attacks against the Nike Hercules, HAWK, Patriot, and Aegis. The follow-on K-31PM uses the new multiband L-130, developed by the Avtomatika CKBA.
What we don’t know is how any of these seekers are integrated into the INS, and whether this integration allows the sort of capability I described the latest HARM variants as having.
As regards AESA, I know that studies have been conducted on how an array could perform several tasks simultaneously instead of relying on mode interleaving, but to date there is no US requirement and no funding. You would have to throw a significant amount of money at the problem, I understand.
The company in question was only asked whether each pulse from an AESA was generated by all the modules transmitting on a single frequency, or by modules that each transmit on its own frequency. So the reply could well be little more than a simple yes or no. No-one at the company is likely to sit down and write a detailed technical report in response to such a basic question, although it would be useful if they could cite an existing published document that we could all see.
But a custom-written detailed reply is most unlikely. When I first set up business, a number of early commissions were to visit a facility, talk to a designer, go away and write an account of what I’d been told, then swap the finished manuscript for a cheque. The first time this happened, I asked why they did not do such a basic job in-house. The reply was something like:
“You must be joking. First we would need a cost code for the work, and approval of the spending. Then we would need one or more meetings to draw up a specification for the required document, and devise a formal review and approval process for the finished product.”
I doubt whether much has changed since then.
Be sure to find out what particular AESA radar they’re answering for too. One cap doesn’t fit all.
They may already have a suitable reference they can refer you to, without doing any work.
lukosHowever on this I have to disagree, in part. AIM-120D has 200+ km rated range. R-33S is also said to have 200+ km range. Looking at this by pure kinematics, (ignoring seeker performance etc), how would they perform if they were fired at at a high flying (not necessairly too high, lets sat 30k feet) maneuverable target at 160 km away? IMHO much lower wing loading would matter, and with bigger warhead I would put all my money to R-33.
BTW This discussion is not relevant at all; Lets make it more relevant by saying;
R-27RE max range = ~120 km. R-33S max range = ~200 km. I say,
a)R-33S fired at 100 km againist Su-35, has significantly higher Pk than a R-27RE fired at MiG-31BM at same range.
b)R-33S has much better terminal maneuverability than R-27RE at high altitudes, after both flies 100km distance.Reasoning: R-33S has better sustainer, lower wing loading, better warhead, and its more or less at middle of its launch envelope.
Lots of bones to pick with this one.
TBH, you’ve changed the subject entirely because we’re not comparing missiles, we’re talking about altitude affects on missile and aircraft wrt wing loading differences between the two, which this post has no bearing on. However, at a highly theoretical level, yes, if a missile has the same range but a lower wing loading, that subsequently implies that it likely has more drag, so to achieve the same range, it has to reach a higher peak speed, hence it’s average speed is higher and it likely gets there first. There’s a multitude of effects to consider. If it gets there a lot sooner, e.g. R-37 vs AIM-120D, then the other aircraft may be forced to break lock and go evasive, in which case the slower missile is left without the necessary mid-course guidance. If it arrives at the same speed or faster, then yes it will turn better and suffer less drag as it does.
However a more interesting and pertinent question is what happens if you put bigger fins on the same missile. Wing loading reduces but drag increases, meaning speed and range is reduced. At a given speed it has more manoeuvrability but in any given intercept it is going slower at any point. The missile with the lower wing loading has better manoeuvrability at any point in time up until the missile with smaller wings exceeds its velocity by a factor equal to the square root of the wing loading ratio. E.g. for a 1.5:1 wing loading difference, when the smaller finned missile’s velocity hits 1.225 times that of the larger finned missile, then it will have better lift. Exactly when this happens depends on burn time but it should happen after burn time unless the burn continues until T=D, which it may do with a sustainer. The narrower finned missile also reaches the target sooner. Swings and roundabouts.
lukosIf I had substituted ‘frictional forces’ for ‘drag’ then he still would be complaining.
Well that’s the issue here in a nutshell. The rocket thrust remains uniform so the speed will increase such as to reach roughly the same drag relative to that thrust (depending on burn time) and consequently lift, which is a nigh on identical equation in its parameters, increases in proportion to that drag, such that at Vmax drag and lift remain about the same for a missile at altitude because of the increase in Vmax.
It’s at low altitude that the missile is disadvantaged the most because it doesn’t reach as high a speed in the first place and doesn’t travel as far under propulsion and because initial deceleration will be about the same (since drag at Vmax is about the same) it dies quicker. E.g. if I start at 1600m/s and I lose 400m/s in time x seconds, V^2 only reduces by 43.75%. If I start at 800m/s and lose 400m/s in the same time, V^2 falls by 75%. So I lose lift faster at low altitude after propulsion stops.
lukosA rather silly way of dodging the fact that what “we” wanted or must have was in practice only an expression of what you personally would like.
Well I’m sure a lot of people will find an explained technical report more informative than a yes/no.
It takes a lifetime, if one wants to say at the cutting edge of one’s chosen subject.
To help you with the learning process, I’d recommend Skolnik’s ‘Radar Handbook’, preferably the 2008 edition, which has a long chapter on electronically-scanned phased arrays.
If that is too much like tough going, there is always the latest edition of Stimson’s ‘Introduction to Airborne Radar’. But you might be puzzled by the fact that when he lists the advantages that AESA has over PESA, he does not mention anything about the Tx/Rx modules being able to operate at different frequencies, rather than all at a single frequency. Perhaps Mr Stimson is someone else who has some catching up to do, making it negligent of a major radar manufacturer to have commissioned him to tackle the book.
I’ve read several books. There are different generations of AESA, just as there are different generations of earlier radar types.
The problem in jumping straight into a radar book is that you skip the RF basics and books on systems generally assume that they are known. Because of this it’s actually best to cover RF fundamentals first. They will cover an awful lot about more general RF beamforming and signal processing that will provide a better foundation for understanding the radar books.
If the ARM can detect the signal from an AESA, and home on it, why can’t a jammer detect the same signal and react to it? You can’t have it both ways, Lukos.
Well that’s the problem, detection and effective reaction are two different things. And in all honesty, effective jamming historically needs to be proactive not reactive, although there is an initial reaction period where the signal is learnt before it becomes proactive. Passive ARM homing only needs to be reactive (although I guess there could be a proactive guidance element if the target is moving). I can certainly detect AESA RF power by integrating signal strength wrt time and frequency and get a direction from that but that doesn’t mean that I know what frequency it’s going to use at any given time and therein lies the difference. Detection and prevention are two different things. If they weren’t then journalists, police and the military would be doing the same job.
lukos– @ Lukos- as speed increases so does drag and lift on a missile, at mach 4 the missile has exponentially more drag and lift than it does at subsonic speeds (though parasitic drag lower). Madrat is saying that a missile lofts while in powered flight trading kinetic energy for height then diving on a target at an optimal intercept point. Not sure why you are arguing this?
BTW- we are wayyyy OT- missile forum anyone?
Ah I see.
yes, about time to conclude it
lukos: stop your train of thought for a while, look at the extremes,
in a high density this missile will turn so hard it will shatter,
while in space it will not even get close to speed of light yet still cant pull a single G.
Speed ultimately will not create enough friction to compensate for the loss of density.
Now when you know how it pans out you can calculate a couple of examples to confirm it
Kind of irrelevant, since it isn’t in space. While in the air, lift will increase with speed and a missile can increase speed at high altitude more so than a plane because thrust remains constant. If you look at the drag and lift equations, you’ll find that on a rough theoretical level, speed exactly overcomes the loss of density.
V = sqrt(2D/Density.Cd.A)
L = 0.5 x Cl x Density x A x V^2 = 0.5 x Cl x Density x A x (2D/Density.Cd.A) = Cl x (D/Cd)
Hence density cancels (as does area). Lift depends on drag. At lower density V increases such that overall drag remains the same, hence so does lift. Obviously making assumptions about burn time, thrust and acceleration, but you get the picture.
Sadly for an aircraft, thrust is not constant because air breathing engines don’t work well with thin air and as speed increases, in theory more air should get into the engine, however the intense heating effect as the air is slowed from high speed means less and less combustion heat can be added at high speed in order to prevent the HP turbine melting/warping.
As a pure exercise in theoretical mathematics looking at your extreme. In space, if there was sufficient rocket fuel (you’ll note I mentioned assumptions about burn time) then the missile speed would be infinite, since there is no drag. Obviously this can’t be the case because it’s not possible to break the speed of light, but then as you approach the speed of light your mass will increase, which will slow time and compress space. What is infinity times zero? Answer = Anything. It should also be noted that even space isn’t a complete perfect vacuum.
lukosThe drag index calculated are wrong: (as I made the mistake with 600 gallon tanks which are not supersonic, nor used by USAF, in calculating drag, you also made a mistake by not adding the drag of the wingtip aim-9 or aim-120 which are calculated at a 7/6 as a baseline airframe drag ) Certain stores- are limited by airspeed. You are not figuring in the weight of the load or airspeed limitations of the configuration.
I used the 370gal tanks. I’m not really used to using these graphs, so I didn’t factor in weight since it only has a minor impact on drag/speed in level flight.
What do you mean about the wingtip missiles? I understood they had zero drag. Happy to see another calculation.
There’s a worked example on page A1-2/3 for 2 AIM-9s and 2 Mk-84s and 2 370gal tanks. Comes out at DI=149 including 7 for aircraft. I note I did forget that 7 in my calculations not that it makes much difference, I worked with 100 for the escort aircraft and 200 for the ground attack aircraft.
CAT I, II, and III are dependent on the load out. The 370 gallon drop tanks underwing put you automatically in CAT II. The pilot can only select I and III, so the pilot has to know CAT II limitations.
Where does it show these in relation to speed? B8 only seems to show them affecting turning unless I’m reading it wrong.
lukoswhat i was trying to say is if side lobe and back lobes radiate that my then why system like tor-m1 spinning their radar to evade ARM ? isnt that kind of useless ?
Not sure what you mean. Earlier ARMs guided by looking at the side-lobes to aim themselves but with rotating radar, this was problematic. ALARM tried to counter this by coming down from directly above.
i was trying to ask if the radar homming seeker on Agm-88 and alarm , KH-31 could home on an AESA radar ?
Whether the passive homing system can might be what you are asking??? I would imagine yes because, despite being LPI, over the accumulation of time, an AESA radar will still put out more energy than background, so it will home on that directly. However, for AGM-88E this is kind of irrelevant because once the launch aircraft detects the SAM radar, it calculates a geolocation and sends that into the missile and the missile is fitted with ARH and MWR terminal homing to finish job, irrelevant of SAM radar emissions.
if you know your own altitude + elevation of target isnt it really easy to determine their altitude too ?
still dont understand why enemy aircraft moving make it hard to determine range , wasnt the computer can do it in like a fraction of a second ?
Not if it’s an aircraft because you don’t know range accurately enough and so far bearing accuracy of RWR is an order of magnitude or so lower than for radar even for the best systems*, so it doesn’t provide useful targeting parameters. You don’t know the altitude of an aircraft and you don’t know range. You know the altitude of a SAM radar, because it’s on the ground, which gives you range via triangulation with ground, and after firing it probably won’t move, so even if it shuts down terminal homing will work. And aircraft radar could shut down, and it could move and you don’t have accurate targeting parameters in the first place because of the range/altitude issue, so there’s a lot more guess work.
*I’m even assuming that interferometry works against AESA here.
lukosYou also realize the big extension in range is due to ballistic flight where energy from thrust is traded for altitude and drag only impedes it gaining altitude. The orientation of the missile will be path of least resistance. During terminal dive the missile will use drag to steer itself to target and the nose of the missile will have a slight angle of attack off the boresight determined by the missile logic. If the missile was perfectly perpendicular to the target it would lose all benefit of its tubular shape. Missiles do not fly typically linear paths, they do generally fly a ballistic path with a variable roll rate. The missile logic’s job is path of least resistance to the terminal phase where it converts potential energy of an object in motion into kinetic energy for a change of said motion as necessary.
I think these basics escapes some of the people posting.
1) Actually gravity impedes it gaining altitude. Drag reduces at increased altitude, hence why speed increases, keeping lift good for missiles, and also increasing range.
2) The missile uses lift force to steer itself, not drag LOL.
3) Hence why diving at the same time as turning increases path length.
lukos“A quick scan shows he hasn’t allowed for the affect of reduced drag and therefore increased missile speed at high altitude.”
….and the exact same reduced drag reduced lift….
One counteracts the other though, which it doesn’t for aircraft because the thrust of gas turbines is also reduced as air density lowers. Rocket motors not affected though.
lukosno, the high wing load of the missile puts it at a disadvantage at high alt,
here’s an example by andraxxus
http://forum.keypublishing.com/showthread.php?128826-Su-27-s-family-is-the-most-maneuverable-aircraft-in-the-world&p=2114362#post2114362
A quick scan shows he hasn’t allowed for the affect of reduced drag and therefore increased missile speed at high altitude. The same Cl will give more lift at lower density if the speed is higher. You will note that effective range actually increases at high altitude due to this very effect. Lack of energy stops missiles making a kill before manoeuvrability ever does.
If density reduces 17.4% such that 1/density increases by a factor of 1.21, then velocity will increase by approximately 10% (lot’s of assumptions here but you get my drift). If V increases by 10% and density reduces by 17.4%, lift remains the same and there’s no reason this effect shouldn’t be observed, since rocket thrust remains constant regardless of air density, whereas gas turbine thrust doesn’t.
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