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View Full Version : Why does a fighter plane need a target lock?


Whack-a-Mole
05-30-2005, 07:57 PM
While watching some shows on fighter planes today I wondered why the planes need a target lock for some missiles to fire (or at least fire accurately)? More to the point, why does a target lock have to be something the pilot has to work to achieve? I would think a heat seeking missile should be able to look forward and see the only hot spot in the sky and pretty much know right away that it should track on that target. A radar seeking missile I would think would do the same. If there is more than one target to choose from the pilot should be able to easily enough designate which target s/he wants to engage. Instead though the missile seems to take some time to track in and "lock" on the target. Looking at the head's-up display (HUD) in the cockpit they show that the HUD draws a box around the plane the pilot has (mostly) in their sights so it seems something in the plane's avionics is pretty clear on what it is looking at while at the same time the missile is still struggling for a target lock.

So what is the deal with this?

silenus
05-30-2005, 08:27 PM
Fairly self-explanatory. The missle seeker head takes time to spool up, detect and lock onto a target. The targeting area is quite small...it has to be, or else you'll have missles heading for the sun. Heat-seekers need to be pointed at a target or they will just zip aimlessly across the sky. Ditto self-guided radar missles. The only missles that don't need a "lock" are those that are guided by the fighters on-board radar. These have the problem of requiring the engaging fighter to give away its postion with the radar, and remain fixed on the target until it is destroyed. This is not a good thing in a furball.

Padeye
05-30-2005, 08:44 PM
AQ2 (aviation fire control tech second class) Padeye checking in here. I've been out of this game for a while but I remember a little bit of what it takes to shoot down bad guys. Acquiring and locking onto targets is much more difficult in real life than in movies. Distances are measured in miles and even big airplanes make extremely tiny apparent targets.

Also fire control radar doesn't work like a camera seeing a blip in the middle of a big field. The sensitive lobe of the antenna is very narrow in order to give precision information on the location of a target. The planar array scans side to side and up and down in order to find a target. Once a target is found it has to gather information on the velocity and range in order for the track to be useful. This information needs to be passed to the weapon so it can find the target.

Radar doesn't see like we do with a picture, the return is a spectrum of energy from target reflection, ground reflection and any other noise in the sky at the time. If I paint a target and it's coming toward me the reflected signal will be a higher frequency than what I transmitted because of doppler shift. How does the radar know the return signal is the right one or some othe unrelated signal?

Radar missles for the most part work in conjuction with the firing aircraft's radar as they recieve signals transmitted from the airplane that bounce back from the target. Some missles like the AIM-54 have a fully active mode where they can be totally independant of the firing aircraft but only within a specified range. Because of the way radar guided missles are mounted most cannot "see" forward until they are launched so they must get target information from the fire control system so that once they are ejected from the aircraft they know where to look to acquire the target.

Infrared missles are mounted out on wing pylons so the seekerhead can see forward unlike radar guided missles. The AIM-9 has SEAM, Sidewinder Expanded Acquisition Mode, where its seekerhead can be slaved to the fire control radar antenna. When the missle has acquired the target it makes a growling tone in the pilot's headset. The Sidewinder is totally passive so it does not depend on the firing aircraft once it has launched.

Padeye
05-30-2005, 08:50 PM
The only missles that don't need a "lock" are those that are guided by the fighters on-board radar. This is incorrect. In virtually all cases both the launching aircraft's radar and the missle must be locked on target. The only exception to this I know of is when multiple AIM-54 missles are fired at once. The launching aircraft scans in a way similar to a search pattern and uses interpolation to track targets by computer. This is extremely dicy if the targets do any evasive manuevering and AFAIK has never been done other than in controlled tests.

Whack-a-Mole
05-30-2005, 10:54 PM
Thanks for the excellent answers. Note I am continuing this not to argue against what has been said but just to understand better. Clearly this requires the target lock and if there was a better, easier, faster way to go about it they'd do it.

What I do not get is watching the video out the cockpit window and the HUD has a targetting circle that I assume is where the pilot has to aim to shoot his cannon and properly lead the plane so bullet meets plane. Additionally that targetting circle has a line from the center of the circle to a little way out of the circle that always points at the plane the pilot is chasing. No matter how the two planes move that line points to the target. Add to that the targetted plane has a box overlayed on it in the HUD that seems glued to it regardless of how the two planes move.

What I get from this is something on the plane knows there is a target in front of it and is able to display various info about it. If the plane knows that much I am missing why it cannot tell the missle that there is a target there rather than the missile farting around going for a target lock. I mean, it seems the target already is locked in some fashion.

HMS Irruncible
05-30-2005, 11:06 PM
So is it fair to say that the meaning of "lock" is the weapon having acquired a range, velocity, and heat signature of the target?

Also, is a lock really a "lock?" Can a missile lose an acquired "lock"?

In the movies (yeah, I know), you often see the targeted aircraft with some sort of alarm warning them that they've been locked, but as it's been described here, I don't see how that could be possible.

Whack-a-Mole
05-30-2005, 11:29 PM
In the movies (yeah, I know), you often see the targeted aircraft with some sort of alarm warning them that they've been locked, but as it's been described here, I don't see how that could be possible.

I've always wondered this too. I assume that the attacking plane switches into a different radar mode when it gets a lock (i.e. switches from an occasional sweep of the environment to a steady, focused beam at the target...kinda like sweeping a room with a flashlight till you see someone standing in the corner and then leave the light on them). That said I wondered if a heat seeking missile would set off alarms in the targetted aircraft. Certainly the missile is passively reading the environment so I cannot see how the targetted plane could be aware of it unless whatever launched it had to use some kind of target acquisition radar before firing that would tip off the target.

Just guesses...interested to see what Padeye or others have to say about it.

wevets
05-31-2005, 12:12 AM
Certainly the missile is passively reading the environment so I cannot see how the targetted plane could be aware of it unless whatever launched it had to use some kind of target acquisition radar before firing that would tip off the target.

I don't know a lot about this, but I believe if you're using a passively guided missile (e.g. Sidewinder or other heat-seeker) the target will get no warning. Movies, of course, usually make sure the good guys get the warning bells & sirens going off in their cockpits whether it's realistic or not.

Padeye
05-31-2005, 12:53 AM
I don't ever recall seeing a movie with accurate representation of HUD sybology. They are typically much more complex than is shown in movies and I haven't seen one that was multi color. The MATS page has a pretty good explination of the HUD but not of the A-A or A-G symbols are shown.

Whack-a-Mole you pretty accurately describe the HUD's ASE, allowable steering error, circle and steering vector. If the target was outside the circle that means it is too far off axis to take a shot. The ASE will vary in size depending on range and other factors, usually getting smaller at close range. Often it will turn into a breakaway X at close range indicating that if the target is hit the pursuing plane will probably be hit by debris. The flashlight analogy is a pretty good one too and quite accurate.

Totally passive missles like the AIM-9 Sidewinder cannot be detected as seen in the movies as there is nothing being transmitted from the seekerhead. Some models of the AIM-9 have proximity fuses with laser emitters and detectors on the sides of the warhead but by the time you detect those you're pretty much toast. Something to note is that the AIM-9's seeker is designed to miss the target but just slightly. The ideal shot is when it is alongside the aircraft. The warhead is quite small so it leverages whiat power it has with an expanding rod warhead that opens up into zigzag circle. A few rods into the engine can cause the engine to come apart so hot turbine blades bursting through the fuel tanks do all the work.

ECM, electronic countermeasures was not my specialty but here are a few basics. It's very easy to detect a radar set painting you directly and some devices are little more than a glorified Fuzzbuster that runs on 28 volt aircraft power. More sophisticated units can detect the kind of radar, search or fire control tracking, give a vector to the source signal and in some cases send back signals that could fool the opponents radar into tracking away from the target and losing lock.

It shouldn't be suprising that Hollywood often doesn't reflect reality. Depiting air combat too accurately might be kind of dry to watch for all but the the most hardcore aviation enthusiasts. Air to air missles don't go zig zagging through the sky. Most have a very short motor burn which means lots of maneuvering eats up kinetic energy it needs to get to the target. In any event most missles can make tighter turns than a human pilot could survive.

Whack-a-Mole
05-31-2005, 08:10 AM
In any event most missles can make tighter turns than a human pilot could survive.

On the show I watched they said the Sidewinder got its name from its vectored exhaust nozzles that allow a Sidewinder to make 90 degree turns. That would certainly seem better than any plane can do.

On the flip side I understand that the AIM-54 Phoenix has an interesting intercept mode. Rather than fly straight to its target the AIM-54 flies very high and then plunges down on its target from above. In this case (if I am remembering right) the missile only has one shot at the target. If it misses on the way down it cannot turn around and come back like a Sidewinder could (as long as the Sidewinder is under power).

butler1850
05-31-2005, 08:54 AM
On the show I watched they said the Sidewinder got its name from its vectored exhaust nozzles that allow a Sidewinder to make 90 degree turns. That would certainly seem better than any plane can do.

On the flip side I understand that the AIM-54 Phoenix has an interesting intercept mode. Rather than fly straight to its target the AIM-54 flies very high and then plunges down on its target from above. In this case (if I am remembering right) the missile only has one shot at the target. If it misses on the way down it cannot turn around and come back like a Sidewinder could (as long as the Sidewinder is under power).

The AIM-9 missile's heat seeking system was developed, in part, by studying the heat receptor anatomy on sidewinder snakes. Though the current version may have thrust vectoring, the original was a fixed nozzle, with movable control surfaces. Early model AIM-9 missiles could only attack other aircraft from the rear (they needed to see the engines exhaust heat), new ones can be used from any angle, but work best looking 'up the tailpipes'.

Missiles have the capacity to 'out turn' manned aircraft due to a few things; size, weight, lack of 'biological cargo' (and it's squishy factors, which limit the 'G' loads of aircraft, not the materials), HUGE control surfaces (fins) in comparison to the above mentioned factors.

If a missile misses the target, it doesn't 'turn around for another try'... it's gone, the speeds of seperation would insure that the missile wouldn't be able to catch up before the fuel runs out. You'd need another missile, or perhaps the manuvering of your enemy would have allowed you to close into a guns solution.

Now to answer a couple of other lines above, which I'm not going to spend the time to quote and pull out...

The circle on the HUD, with the line pointing to the target indicates the direction the pilot should look to find the target, if it is not visible in the HUD. If it is in the HUD, it would have a 'box' around it. The actual circle is often the 'flight path indicator, which points to the spot in space (when viewed through the hud) that the aircraft is heading. This is based on speed/lift/control inputs, and may not be where the aircraft is currently 'pointing'.

Aircraft radars, and heat seekers scan (or view) the area in a 'cone' shape, and you can 'break lock' by moving out of your opponent's 'cone'. Modern US aircraft can move the direction of this cone away from where their aircraft is pointing by rotating the antenna on a pivot, this is obviously limited though.

Modern aircraft (military) have what's known as a 'Threat warning system', which reports to the pilot on what radars are being detected. They filter these by signal strength, and type, reporting back as a variety of tones. In general search radars use one frequency, of a longer wavelenght, as this aids in long distance, wide area searches. Fire control radars, use a shorter wavelength, which can be more 'focused'. When an opponent shifts from search, to fire control, the tone (frequency, volume, beat) changes, letting the pilot know he has to begin to earn his paycheck.

In general all ACM (Air Combat Manuvering) comes down to getting into a 'cone of vulnerability' behind your opponent. You then follow him to get into the 'optimal' firing location. This location is one that provides your opponent the least number of options to avoid your attack. There is too much involved in this to attempt to explain it here, by myself.... Here (http://www.ao.net/~chuck/atf/acmsycho.htm) is a site that explains a few of these maneuvers.

A quicky explanation of a basic HUD (http://www.meriweather.com/16/center/hud.html) can be found at this link.

More (http://www.fas.org/man/dod-101/sys/missile/aim-9.htm) than you probably want to know about the AIM-9 Sidewinder missile, and it's history can be found in this one.

There is a whole world of military simulator buffs out there, I'm sure if you google the terms you're looking for, you can even find better stuff than I've posted.

I've been interested in this stuff for years, and it's amazing that I've still not got a good handle on all of it... but if the USAF would like me to head over for pilot training, I'd be happy to report. :D

Hope this helps!

-Butler

David Simmons
05-31-2005, 09:49 AM
On the show I watched they said the Sidewinder got its name from its vectored exhaust nozzles that allow a Sidewinder to make 90 degree turns. That would certainly seem better than any plane can do.

On the flip side I understand that the AIM-54 Phoenix has an interesting intercept mode. Rather than fly straight to its target the AIM-54 flies very high and then plunges down on its target from above. In this case (if I am remembering right) the missile only has one shot at the target. If it misses on the way down it cannot turn around and come back like a Sidewinder could (as long as the Sidewinder is under power).Sidewinder uses aerodynamic control and not thrust vectoring.

The name resulted from the method of navigation. Sidewinder, like all air to air missiles, uses lead-pursuit navigation. The missile first points more or less at the target. Since that isn't a correct course for intercept of a moving target an error soon develops. The error causes the missile to maneuver so as to take a lead on the target and fly toward a predicted intercept point. The result is that the missile flies with the seeker head looking at the target pointed off to one side. That feature, combined with the prevalence of the small, desert rattlesnake, the sidewinder, in the area where the missile originated made the name a natural.

Whack-a-Mole
05-31-2005, 10:01 AM
Sidewinder uses aerodynamic control and not thrust vectoring.


Ok...I looked it up and it seems the show had it wrong that thrust vectoring is where the missile got its name (or I misheard) but the latest variant does indeed use thrust vectoring.

Now entering service is the AIM-9X, a new variant with an imaging infrared focal plane array seeker with claimed 90 off-boresight capability, compatibility with helmet-mounted sights (the new U.S. JHMCS, Joint Helmet-Mounted Cueing System), and a totally new thrust-vectoring system replacing the traditional control surfaces. It retains the same motor and warhead of the "Mike," but its lower drag gives it improved range and speed.

SOURCE: http://www.answers.com/topic/aim-9-sidewinder-1

David Simmons
05-31-2005, 10:38 AM
Ok...I looked it up and it seems the show had it wrong that thrust vectoring is where the missile got its name (or I misheard) but the latest variant does indeed use thrust vectoring.OK. I've been out of the Sidewinder game for quite a while. Going to thrust control seems like a natural and a good idea. All aerodynamically controlled missiles have some real difficulties at extremely high altitudes and thrust vectoring has been in development long enough now to be pretty reliable.

Padeye
05-31-2005, 10:45 AM
On the flip side I understand that the AIM-54 Phoenix has an interesting intercept mode. Rather than fly straight to its target the AIM-54 flies very high and then plunges down on its target from above.This isn't unique to the AIM-54 but any medium to long range air to air missle. The rocket motors don't have a long burn, I found a reference of 2.8 seconds for the AIM-7, so most of the flight is ballistic so lots of manuevering bleeds off kinetic energy rapidly. This is probably why short range missles are often more effective than long range ones. A Phoenix can go 100 miles but at that range it has little ability to follow an evading target. When I went to missle school in the early 80s we were told that in the jet age variants of the AIM-9 had gotten more kills for the US than guns and all other A-A missles combined.

Padeye
05-31-2005, 10:48 AM
Oh, the thrust vectoring thing about the 'Winder is pretty cool I was about to chime and tell you that you were wrong before I saw your reference. The regular AIM-9 and AIM-7 missles are steered by the forward canard fins with the rear fins being fixed. You may have notices metallic tips on the back corner of the AIM-9 back fins, these are gyroscopic stabilization devices. Each is hinged at a 45 angle and has a wheel that looks like a milling cutter that spins from airflow over the edge of the fin.

Dob
05-31-2005, 11:07 AM
Consider ignorance fought here today! I never knew so much about missles. Good stuff. After checking out the DoD page butler gave I am also suprised at the small amount of missles listed. I was always under the impression we had hundreds and hundreds of missle types. Again, ignorance defated :)