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Amiga500

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Viewing 15 posts - 796 through 810 (of 2,151 total)
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  • in reply to: PAK-FA thread about information, pics, debate ⅩⅩⅢ #2233139
    Amiga500
    Participant

    Calculation of the book “Design of aircraft,” Jaeger. 1983.

    Lift dependent drag only forms a small fraction of the total drag at ~ Mach 2. [by small, I mean less than 10%]

    Thus, using thrust:weight as a means of determining max velocities is… questionable.

    I don’t have (and have never heard of) that book; could you check the equations to see if they are using aircraft mass as their basis for calculation?

    in reply to: PAKFA and Silent Eagle comparison #2233296
    Amiga500
    Participant

    All the prototypes are “hand made” and a series production for most items is not possible for some time.

    ugh.

    If the entire series run is, say, 400 aircraft over 10 years – you don’t need massive production lines.

    This is not the JSF.

    in reply to: PAKFA and Silent Eagle comparison #2233299
    Amiga500
    Participant

    The question we must ask is, does adding missiles to a plane add to radar signature? Certainly from the front due to more surface area added. From the side there is no addition because the missile’s body would block radar waves from hitting the side of the plane. If the missiles are air to air missiles, we know the side shape of the missiles which are round would reflect radar waves better than the slabbish side of a plane, and should therefore reduce the radar signature from the side. From the front there would be a minor addition of radar signature.

    Hence why the galactic empire designed the TIE fighter with two big sides – it blocks any radar wave from reaching the body and deflects it back instead.

    http://www.oocities.org/imperial_military/pictures/navy/tie0.jpg

    The emperor knew a thing or two about evading radar waves.

    in reply to: PAKFA and Silent Eagle comparison #2233302
    Amiga500
    Participant

    No, but I’m sure conformal fuel tanks increases radar signature from the front and rear.

    I suppose that would depend if they conform to what they are told… and sit there and be quiet instead of replying when the radar starts calling for them.

    They don’t always conform… Cheeky little ******s.

    in reply to: PAKFA and Silent Eagle comparison #2233863
    Amiga500
    Participant

    conformal fuel tanks :applause:

    Tanks?

    Do these tanks conform to the mathematics of being lighter outside the aircraft than inside the aircraft too? If g is a constant, I’m not sure that would be the case.

    in reply to: PAK-FA thread about information, pics, debate ⅩⅩⅢ #2233915
    Amiga500
    Participant

    Technically, propulsive efficiency tends to a maxima when the exhaust velocity approaches the freestream velocity.

    Utterly impractical yes, as you then are required to accelerate inordinately large amounts of massflow by this small amount… but still, it is what it is.

    Anyhoo – in relation to your point about exhaust velocity being the principle factor in high speed propulsion – its really the inlet aerodynamics that are king*. Nozzles actually produce drag.

    Here is the classic diagram, courtesy of Rolls-Royce.
    [ATTACH=CONFIG]221165[/ATTACH]

    *So why is the turbojet the bees-knees when it comes to high speed flight? ‘Cos there is less massflow rate required by the turbojet at highspeed, the inlet nozzles are more easily optimised and all of this (reduced relative to a turbofan) airflow is passed through the compressor, where it generates more thrust per unit massflow than if it were sent through a fan alone. Its not the nozzle that generates the thrust, its the fan/compressor.

    in reply to: PAKFA and Silent Eagle comparison #2233925
    Amiga500
    Participant

    Mathematically, one can show that, putting missiles on the outside of a plane reduces the plane’s overall radar signature.

    Absolutely correct*…

    Same as when you put fuel on the outside of the aircraft, it is lighter than when you put fuel on the inside… :dev2:

    *Its signature will tend to zero after a short time in the air too…

    in reply to: PAK-FA thread about information, pics, debate ⅩⅩⅢ #2233929
    Amiga500
    Participant

    F-15E powered by F100-229 would not be a whole lot less powerful in dry thrust than an Su-35 or T-50 with their present engines. The F-15 probably is not much less aerodynamically than either Sukhois at supersonic speeds (has anyone any idea?)? No one has ever suggested that the F-15E could supercruise at Mach 2?

    The F-22 is more powerful than the Blackbird. Yet it doesn’t go near Mach 3.

    Its all about aerodynamics and engine inlet design. [well, not all, but you get the drift]

    in reply to: PAK-FA thread about information, pics, debate ⅩⅩⅢ #2234179
    Amiga500
    Participant

    M2.4/M2.0=1.2
    1.2^2=1.44

    Product 30 thrust figures: 107 kN dry, 176 kN wet
    176/107=1.64

    Does not compute…

    I can’t remember the old numbers off the top of my head… but they are about somewhere.

    in reply to: PAK-FA thread about information, pics, debate ⅩⅩⅢ #2234371
    Amiga500
    Participant

    Berkut is right, i’m speculating that neither T-50 or Su-35 makes over M1.2 dry on current engines, (f-22 kpp 1.5, performance 1.75)
    pak-fa was always meant as a predator

    IIRC, tidbits of data (dry:wet thrust ratios along with the top speed claimed to be attained in testing and some working out based on supersonic drag equations) that exist currently would suggest a supercruising speed of ~ Mach 2 and a top speed of ~ Mach 2.4.

    Its in one of the PAK-FA threads somewhere. Go dig it up.

    Amiga500
    Participant

    Are you David Isby, or just using his name as your username?

    [Read the book – throughly enjoyed it]

    in reply to: Dassault Rafale, News & Discussion (XV) #2236208
    Amiga500
    Participant

    The doctrine and war never goes exactly according to plan.

    Exactly.

    All this “one-two punch”… Load of complete bullsh!t.

    But, when they throw in a few buzz words, sprinkle it with a bunch of acronyms and leave to simmer for a half-hour on a powerpoint slide… then it becomes irresistible to some!

    In Vietnam, the highly experienced air-chiefs as you pay homage to didn’t expect to find their much vaunted F-4s and AIM-7s not exactly work as advertised. But it happened.

    In GW1, they didn’t expect their hyped precision guided munitions to actually turn out to be… well… not precisely precise 100% of the time. Or even close.

    In Kosovo… they’d learned their mistakes, early editions of Powerpoint said so. That old AIM-7 had been replaced with the bestest missile ever, the AIM-120. The sun is lucky AMRAAMs don’t shoot it down from the sky. Oh, erm. Wait a minute. Ended up they’d more misses than kills.

    Note: YES, VLO has the potential to be a big advantage, YES, the SDB has the potential to be a very useful item to have. But, and this is the thing you continually disregard, potential does not always be realised* – particularly when the fog of war settles in.

    *see the F-4/AIM-7, the F-117/LGB, the F-15/AIM-120. None performed as advertised (despite the latter two not paying any penalty bar the fuel/munition/airframe maintenance cost of repeat sorties – which disguises the munition effectiveness).

    Amiga500
    Participant

    Are regulators actually expecting a 3rd Western wide-body engine OEM to emerge and compete against RR and GE?

    Pratt are the third competitor.

    I think there were articles about 6-12 months ago on them developing GTF for widebody.

    in reply to: Dassault Rafale, News & Discussion (XV) #2236320
    Amiga500
    Participant

    [QUOTE=bring_it_on;2067043[B]The shock effect of this B-2/F-22 “one-two” punch will be unprecedented. In the first 24 hours of Desert Storm, after six months of buildup, the US launched 1,223 strike sorties, hitting 203 targets. Stealth assets accounted for 40 sorties and 61 targets. With GSTF, four B-2s and 48 F-22s carrying miniature munitions can strike 380 targets in only 52 sorties.
    [/QUOTE]

    The shock effect of that one-two powerpoint punch has had an unprecedented effect on your rationality dude!!

    Assuming those 1223 sorties in desert storm launched only 1 missile each… they managed to hit only 203 targets. A weapon Pk of 0.17. Being realistic, no doubt multiple weapons were released on the targets, with weapon Pk being so much lower. [2x weapons per sortie = 0.083, 4x = 0.041]

    Now… 4 B-2s carrying 80x SDBs/JDAMs (its rack space limited) each and 48 F-22s carrying SDBs (4x? 8x? each) gives a total number of deployable munitions of 512 (realistically, the F-22s will not sacrifice AMRAAM capacity completely so will carry 4x SDB each + 2/4 AMRAAM). Thus all up, you’ve 380 hits for 704 weapons = Pk 0.74

    So you are expecting a ~4x improvement of weapon Pk (based on the absolutely most pessimistic values for desert storm) from desert storm.

    Double the weapons released per sortie in Desert storm and you are expecting a ~9x jump in Pk from desert storm.

    If 4 weapons were released per sortie in Desert storm, the weapon Pk jump is now ~18x from desert storm.

    I know my skepticism of weapon Pks is well known – but those numbers really are highly speculative. Kosovo was nearly 10 years on from desert storm. All the wonder weapons of the day didn’t exactly distinguish themselves very well did they? So, despite the bluster of the powerpoint wizards of the weapons companies, the historical trend really would have to have changed significantly for their numbers to even approach stacking up.

    in reply to: USAF – Back to the 1950s! #2236350
    Amiga500
    Participant

    Yeah… but

    “full-spectrum operations”
    and
    “highly contested environments”

    Look mighty good on a powerpoint slide. You can even have them whoosh in from the side with an accompanying sound. How can experience, reason and logic fight that? :dev2:

Viewing 15 posts - 796 through 810 (of 2,151 total)