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Detecting Stealth Planes

Zurk writes " Newsweek said China's new Passive Coherent Location (PCL) system tracked the signals of civilian radio and television broadcasts and picked up aircraft by analysing the minute turbulence their flight caused in the commercial wavelengths. cool huh ? " They hope to use it to detect the F-117A and potentially the F-22. Very cool use of technology to fix a problem.

4 of 409 comments (clear)

  1. Re:Stealth Tecnology by TurkishGeek · · Score: 5

    Both the F-117 and B-2 fly with special fittings when they are not in combat duty. In the F-117 this is in the form of small rectangular boxes over the wings. These fittings increase the radar cross-section of the airplane and make it equal to an ordinary civilian plane; to make friendly skies safer to fly by allowing the planes to be tracked by air traffic control, just like every other plane.

    Plus, you don't want everyone on the fair grounds to learn about the capabilities of the plane. If you're interested in the topic, just compare the cockpit photos of the Mig-29 demonstrated to the West in 1989, and Mig-29s in actual service with the Russian Air Force. You will be amazed to see how they dumbed down the cockpit layout so that the first Western smart-ass to see the photos would say "Gee, Russians are using 1950s technology in these."

    It is amazing how this little known security feature causes people to downplay the capabilities of these aircraft. I remember back when a bunch of F-117s came to Turkey; the armed forces and civilian air traffic control boasted how they could easily detect the so-called "stealth" fighters. As the Iraqi and Serbian can tell, it is not that easy without the fittings.
    --

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    A site for everything Bluetooth. Coming in January 2000.

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  2. Logistics by hagar� · · Score: 5

    An invasion could be undertaken on the US. It would have problems though.

    First you send in infiltrators, who set up airstrips in remote locations, and purchase ammunition. They purchase vehicles and fuel. You then take about two dozen chartered commercial jet airlines, you load them with troops and land them at US airports all friendly like, most likely the east coast. It doesnt take long for 500 or so armed troops to capture an airport, and then fortify their position quickly. The 747's can carry anti-tank/heavy weaponary, and plenty of ammunition. No food, cause that isnt neccessary. These troops are the first wave and will only be the front line for a short period. 10-20 minutes behind these 747's, are standard long range cargo planes, carrying light armor vehicles and more troops, these land at the commercial airports and at the private airstrips you have set up.

    Your troops take the LAU's and go like hell towards your assigned targets. Airbases, Army Bases, Naval Bases, Police Stations, Gun Stores.
    The trick is to move fast and capture quickly. A night attack on a weekend would be best, as you would capture quite afew bases relatively lightly manned and vulnerable, you might even bring pilots/tankers/sailors with you to take the captured vechiles and add to the chaos. You continue to bring in troops from china by air and land them at your secured areas.

    At this stage it gets sticky. Your main mode of transport of large armor and troops is by sea. Getting by SOSUS is quite hard, and you have to deal with naval assests in the pacific. Hopefully you would attack at a time when a carrier isnt present close by in the pacific. You have to get your tanks in, so one way would be by using normal car carriers, who are on scheduled runs to make landfall on the same day as your attack to deliver vehicles. If you were serious about your plan, you might even nuke pearl/guam in the first 24 hours of your attack, to make it easier to move more heavy units from china to the US. This would also allow you to move a chinese carrier closer to the US to provide air support for the grunts and eventually transferring all aircraft to captured US runways.

    You have to link up your heavy armor, light armor and infantry to push inland, obviously after securing your captured cities. You then utilise these cities, and the railroads to supply food and munitions to your front lines as they spread inland. Time elapsed is about 48-72 hours, more then enough time for the US army to mobilise and to present a good front line, possibly near the rockies.

    Attack of the US is not an easy task, and requires exquisite timing of delivery of assets. It requires china to send troops a huge distance, and to get past pearl with ships. It would obviously be easier to attack with an allie close by, say from cuba or south america, to attack other borders at the same time. This draws units away from your main assault.

    Now this is a possible scenario, if, china had the logistical assets to do this. The Chinese army is much like the soviet army used to be. A large club to bludgeon your opponent to death with numbers, aslong as he is relatively close. China has never had to move huge amounts of troops over an entire ocean to attack an enemy so far from home. It isnt easy logistically. But possible. To make it more interesting, an enemy may even release chemical/biological weapons before he attacks. He may poison water supplies. He may release anthrax or similar diseases. He may sabotage power stations, he may cause an increase in terrorism before hand.

    There are alot of things in warfares bag-o-dirty tricks.

    As for disabling the US nuclear counter attack, that is a tough nut to crack, and would require unconventional techniques im sure. For example purchasing properties near known ICBM silos, buying a few hundred stingers and praying you can cripple a few missles before they hit your country. Perhaps small backpack nukes could be used to crack the silos at close range, but thats debatable, as those silos are hardened and quite well built. Maybe wait till they open up to launch? Who knows.

    Naval nukes are even harder to disable apart from an intense naval campaign by your forces to kill the subs, even then, they can launch from almost anywhere, and damn but their quiet.

    Carrier based nukes are also a concern. It is unlikely you would attack the US without first developing a good ABM defence.

    So in answer to your comment
    'It would be exceedingly difficult to come anywhere near the US shore with any kind of sizable force.'
    True, but not impossible. Give war a chance!:)

    --
    Insert something insightful here, or I'll insert something painful there.
  3. Typhoon class boats (OT) by zantispam · · Score: 5
    Right and wrong.

    "the typhoon is huge"

    Right. The largest military sub to see active duty.

    "it is nuclear powered rather than desal (sp) powered"

    Wrong. The Typhoon boats are nuclear, diesel, and battery powered. Why do you think they were so darned big? The reactor put out enough juice for a city. If that failed, there were two mammoth diesel engines. By mammoth, I mean 12'x10'x6', 10,000+ hp, and enough tourque to drive the boat through the water at 20 knots. Should those fail, there were two large banks of dry cell batteries on either bow. The batteries served three purposes:
    • Means of electrical power.
    • Additional trim control. Since the reactor and the diesels were aft and the missles midships, there was a lack of weight up front. Solution? Several tons of batteries added a degree or two of down angle to the centerline. Voila; a controllable boat!
    • Armor. Considering how much explosive was in a NATO torp (618lb for the mark 48), and considering that one could be fatal to a smaller boat, and considering that one Typhoon carried 20 ICBMs, any tactical advantage that one could get was worthwhile. Since the Typhoon's designers felt that most torps would hit the bow (standard sub tactics says to turn into a torp; makes for a smaller sonar return), having a boat that could take several hits and still fight (or stay alive long enough to launch her missles) made good tactical sense.


    "I don't think the largest sub in the world is more silent than the water around it."

    Wrong. Here's an example: Let's say that there is a skyscraper in the middle of a field (just follow me on this). Now let's say that the wind is blowing out of the North. Let's also say that you are blind, and walking past the south side of the building (going East to West). There will be a point when the building will start to block out the wind. Logic will tell you that it's no longer windy, and it's also very quiet. You may then deduce that there is a building to your right. Here's a diagram:

    **********************
    **********************
    .........--------*****
    .........||||||||*****
    .........||||||||*****
    ....o....||||||||*****
    .........||||||||*****
    .........||||||||*****
    .........--------*****
    **********************
    **********************

    Legend:
    * = wind;
    -,| = building;
    o = you;
    . = calm air;

    Now, relate that to being in a sub. Since there is always ambient noise in the ocean, the trick is to find someplace where there isn't enough noise. That'll be a Typhoon (or maybe a Charlie) with her plant cut way back. If you know where you are and how fast you're going, you can figure a bearing on the Typhoon. Once you have that, you can use basic trig to figure out range, speed, and mark, in that order. After that, it's simple to sneak up and fire your torps and get back out.

    zantispam (who gets waaaaaaaay to into this stuff)

    Jedi Hacker (Apprentice) and Code Poet
    --

    censorship is a form of noise, which actively seeks to drown out content with silence - Crash Culligan
    1. Re:Typhoon class boats (OT) by zantispam · · Score: 5
      Ok. This reply is going to cover the three replies I've received so far. I apologize in advance for the long post. And to anyone thinking of dropping out of High School, stay it, if only for the math (you'll see why later). Bear with me.

      craw wrote: "What are the sources of ambient noise in the oceans?...I'm going to assume that you are talking about high frequency sources, given that you allude to blockage."

      Actually, I was referring to flow noise. Flow noise occurs because, well, water flows. When trillions of molecules of water move and tumble and collide, they make noise. Depending on water speed, depth, and temperature, water can have all three frequency ranges...

      craw wrote: "However, the propagation paths will be complicated due to the vertical sound speed structure and the variablity of this function. Note that rain and breaking wave sources will be broadly distributed (including those close to the sensor)."

      Correct. This is complicated further by the position of the thermoclyne(sp?).

      When water is of two contrasting temperatures, the cold water will sink and slow down. It forms a fairly flat `layer'. On top of this is the warmer water. Water on top of the layer tends to move faster and have more variety of currents. Therefore, detecting sound below the layer from above the layer is more difficult than detecting sound above the layer from below the layer. Since the layer sits at between 200 and 600 feet, it's easy to stay underneath it.

      Now, if I'm 100 feet below the layer, and the Typhoon is 100 feet above the layer, and the chop is about 20 feet (think mid-Atlantic in fall), I will probably have a difficult time hearing her.

      If the chop is closer to 5 feet, however, and all other factors are equal, I should be able to hear the Typhoon if I'm +- 3 degrees to either side of her (like this: /\).

      Below the layer, these factors are mitigated.

      craw wrote: "If you are talking about low frequency signals, then the dominant source is shipping, earthquakes, and whales."

      And flow noise (below the layer). Remember that the currents under the layer run at about 3 to 6 knots. These currents are not nearly as fickle as the currents above the layer, therefore, we can depend on them (a bit more).

      craw wrote: "If natural fluctuation occur, then how do you differentiate betweeen natural fluctuations and the "silence" of a sub?"

      If the current is coming from the East, and there's a Typhoon to my East, then depending upon the difference between our respective `altitude' (can't remamber the proper word) and distance between us, I may be able to detect her, either from an absence of flow noise, or because of a variance in what I'm expecting to hear. The point is that I should hear x amount of y different types of noise. If x is ever more than a standard deviation off, I have cause to investigate. More on this later.

      Ozwald wrote: "When moving air hits a round object (or an object boing through air), it tries to go around and continue on its original path."

      But is does not do this perfectly. See below...

      Ozwald wrote: "Ever drive down a highway at 100 km/hour behind a truck/trailer? Being directly behind one causes your car to bounce side to side from the truck's turbulance until you finally get atleast beside the cab of the truck."

      You have proven one of my points for me. (Keep in mind that Typhoons can't (and wouldn't) go 100 kph) Ok, when you're behind that semi, everything concerning the air is totally different than it would be if you were not behind that semi. Because it is there, and because it is causing a disturbance several meters behind itself (you don't tailgate, right ;-), you notice that it's there. That's one thing to look for.

      Another point: have you ever sat in the back of a pickup? If it's going slow, the air is calmer right next to the cab than it is by the tailgate (it's much easier to light a cigarette there). If you're looking for a sub that's going reeeeeealy slow (as boomers are want to do), they will leave `holes' in the water at those speeds. How big a hole is a function of the speed of the boat (I wish I could remember my trig - all two weeks of it before I dropped out. Thought I forgot, didn't you?).

      Diagram:

      ***************************
      ***************************
      ************.**************
      **********...**************
      *******...../\*************
      ******.....|T |************
      ******.....|Y |************
      ******.....|P |************
      ******.....|H |************
      ******.....|O |************
      ******.....|O |************
      ******.....|N |************
      ******.....|__|************
      ******.........************
      ********......*************
      **********..***************
      ***************************

      Legend:
      * = Flow Noise
      . = Hole in the Water (quiet water)


      Because of this hole in the water, the noise that reaches the sonar will be different for roughly that shape (as in the diagram above) for a certain distance at a certain speed yadda yadda ad nauseum.

      Ozwald wrote: "A aerodynamic object like a plane, submarine, trout, etc. are designed not to cause turbulance from movement alone,"

      Number one: They may not be designed to, but they do. Remeber that air is a liquid too, for the purpose of this exercise. Liquids have this nasty property called adhesion. Because all of the molecules of (water|air) are togeter in a finite space, moving one molecule will case it's neighbors to move. This is called drag. For a better explination of why this is a problem and possible solutions (for aircraft, anyway), look up the Laminar Flow wing here and here).

      Ozwald wrote: "but it is impossible not to if it is maintaining a speed or accelerating."

      Subs have to move. Kinda like sharks. Well, they dont have to, but they need to. Why? Three reasons (off the top of my head):
      • To prevent broaching. Subs are designed to be a tiny bit boyant. That's why when they move normally at a constant depth the diving planes are at a slight down angle (usually a degree or two). If the sub stops moving, she can no longer totally control her depth. That's a Bad Thing ©
      • Steerage. Almost the same problem as above. Any good skipper will try to go no slower than 2 or 3 knots. That way, the boat will still be responsive to steering input. Why? beacause...
      • Sonar equipment only works in cones or echelons. Problem: you cannot cover the entire 360 degrees around a boat with one passive sonar. Solution: have multiple passive sonars. Most boats have a front array, lateral array, and some (I know the Los Angeles boats do) have towed arrays. For those to work, the boat needs to be able to move the arrays around (purposes of triangulation and all).


      Therefore: Subs will never not move. Boomers will usually hold a really slow speed, but it's constant. Laminar flow problems and adhesion cause disturbances in the water, especially under the layer. And a really good sonarman can detect these disturbances.

      *whew* I'm done now...


      Jedi Hacker (Apprentice) and Code Poet
      --

      censorship is a form of noise, which actively seeks to drown out content with silence - Crash Culligan