J-20 5th Gen Fighter Thread VI

Discussion in 'Air Force' started by siegecrossbow, Sep 4, 2017.

  1. Inst
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    Inst Senior Member

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    The issue is that a gun system has a maximum range of 2-4km, and when fired while the platform is supersonic, the aircraft can actually hit itself with its own ammunition. A modern BVR AAM, on the other hand, can travel 8 km before its motor runs out of fuel. A WVR AAM can travel at least 4 km before its motor runs out of fuel, and has a NEZ of at least 15 km.

    Having a gun port available as a failsafe is a good idea, but dropping the gun isn't such a bad plan.
     
  2. ougoah
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    ougoah Senior Member
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    This isn't correct. A round from the gun will leave the muzzle with its nominal velocity plus that of the J-20. A round will not be hitting the plane firing the round. It'll just have a greater speed. Missile ranges and kill probability vary WILDLY depending on situation. There is no such thing as concrete NEZ, max range, and kill probability. There may be charts that can give pilots an idea but these things are extremely difficult to anticipate which is why narrow AI is so useful for fighters. They will actually do a much better job calculating when and how to launch certain missiles at certain targets and when to not bother.

    A fighter has fuel advantage on the missile chasing it. Pulling tight turns and burning fuel can result in survival well within a theoretical NEZ. Most AAMs are solid fuel single pulse motored rockets where once the fuel is burned out, it is essentially in ballistic mode where trajectory is constantly adjusted according to its own seeker data or fed target from a plane. At the extremes of this theoretical NEZ, a missile has very little energy to spare on tight turns and a couple of well timed turns from a fighter can easily dodge the missile. This is partly why PLAAF is upgrading PL-12 to PL-15 for most frontline fighters. PL-15 has dual pulse motors.
     
    #4482 ougoah, Jan 6, 2019
    Last edited: Jan 6, 2019
  3. Inst
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    Inst Senior Member

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    @ougoah :

    https://www.popularmechanics.com/military/aviation/a27967/the-fighter-plane-that-shot-itself-down/

    Problem is, a missile can reach 45 or 60 G turn rate and Mach 4 speeds. Dogfight missiles also tend to be optimized for agility and lethality at very short ranges.

    I'll also point out that the maximum stated range of the AIM-9X2 is 38+ km. If NEZ is calculated as half max range, it comes out to 19+ km. If NEZ is calculated as a third of max range, it comes out to 12+ km, which both exceed the max gun range. AIM-9X3 was supposed to have a 60% range increase, or roughly reach the 60 km rumored range of the PL-10ASR, implying a NEZ of at least 20 km.

    ===

    Dogfight capability in 5th gen aircraft are usually insurance, barring the Su-57, where the Russians come to win WVR. That is to say, if you somehow manage to get into a dogfight with an enemy 4th gen, as long as they don't have HOBS and IR capability, you can still dogfight your way out. But in general, you don't want to dogfight, because you don't want to fight attritional combat with HOBS. In practice, agility in 5th gen aircraft matters more insofar as it reduces the effective range of enemy missiles, but does not counter them.
     
  4. latenlazy
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    latenlazy Colonel

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    45-60G for how long, and with how much energy burn? How much PE is left in the missile after one of those maneuvers, and does the missile lose speed when it does these maneuvers? What were the assumptions and parameters of those NEZ calculations? When you’re 19 km apart it matters a whole lot whether the missile has sufficient energy to hit an evading target, and that will vary by differences in altitude (is the missile trying to hit a target above it or below it?), position, speed, and direction of both the target and attacker, and how quickly either can accelerate or change their vectors.

    I am an awful example of following my own advice, but don’t bother with Inst. I tried having this same discussion with him at CDF, raised the same points, and it flew over his head like a 4th grader being taught the finer points of quantum mechanics. All he keeps doing is clinging to sourced statements without any effort or thought to analytically break down and examine how the conclusions from those statements were drawn. Bet he’s never done a kinematic force diagram problem in his life.
     
    #4484 latenlazy, Jan 6, 2019
    Last edited: Jan 6, 2019
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  5. ZeEa5KPul
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    ZeEa5KPul Junior Member
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    Since you brought up CDF, do you know what problem they have with gmail? I can't register with it. Do you know what email service they accept? Sorry about the OT, I'd send you a PM about this but I don't think I can. This forum's software is antediluvian.
     
  6. AndrewS
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    AndrewS Captain
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    On a (large) ship, the weight and space of a CIWS is really negligible yes.
    On a (small) fighter jet, the M61A1 is listed with a combat weight of 375kg, which is actually significant.

    And for the next 5 years at least, J-20 doctrine will be to never get into a WVR range, and to disengage immediately after launching BVR missiles.
    There are just too few J-20s to risk, and they don't have the engine thrust available for a dogfight.

    But once there are larger numbers of J-20 with better engines available, they will likely revise that doctrine and require a gun system to be fitted into the allocated space.
    And by then, it is possible that guided 30mm rounds may be available.
    Or even lasers or EM gun rounds.
     
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  7. latenlazy
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    latenlazy Colonel

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    I don’t think guided rounds work the way you think they do...
     
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  8. Inst
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    Inst Senior Member

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    Missiles generally maintain energy until the motor is shut off. The point of bringing up motor burn is to point out how long the missile can function at max energy, and in practice, a missile can exceed a gun's effective range.

    The other part is that missiles typically need 5 times the G of a maneuvering target to hit it, which is why long-range missiles are always ripple-fired; the first forces the target to maneuver, bleeding off its energy, the second is actually to hit the target. When your missile is around 45G, as with AMRAAMs or R-77s, this is necessary. With short-range missiles, however, the ability to hit 60G means that your target needs to maneuver at 12G, beyond any stated aircraft maximum G, to avoid the hit.

    It is possible that the Su-57, given its extreme maneuverability, could be nearly immune to long-range missile shots with 11 max G. However, the problem with this is that it's easier to upgrade a missile than it is to upgrade an airframe and keep the pilot alive at max G; the Su-57's 11G might be able to defeat AMRAAMs today, but its successor could get 60G or above at similar ranges.
     
  9. Deino
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    Deino Lieutenant General
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    Guys ... not again arguing with phantasy figures for the Su-57, no endless discussions on general warfare issues like gun vs. no gun or the g-forces of different missiles ... ! Stay on topic please.
     
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  10. Inst
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    Inst Senior Member

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    We are on topic, we're discussing whether it's a good thing that the J-20's gun port is empty. The core discussion is whether or not the J-20 should be a dogfighter, or whether aiming at more interceptor-like qualities (high speed, ability to hit and run) is better for the PLAAF.
     
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