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Tiger-II

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  1. It has been said before and I'll say it again... there is something alluring about the EN1 voice when she says "Missile! Missile!". Being shot at will never be the same...
  2. I thought we were discussing it from the pilot perspective rather than an engineering perspective, but you are correct. The end result for a pilot, is that an unstable aircraft is always trying to end up out of control, and we do not experience this in the sim because the models are stable. It's not hard so much as the fact the average desktop computer lacks the processing power required to do so in real time, which we require for any usable flight simulation. Super-computers can about manage it, but anything of any real use is not capable of being computed in real-time. It's easy to defeat AoA protections of even something like an F-16 - point the nose at ~45 degrees nose-high, wings-level attitude at idle power. By the time the aircraft bleeds off speed, even if the aircraft starts to pitch nose down, gravity will take over and AoA will far exceed 60 degrees AoA. It should settle quite nicely into a pretty interesting situation. The F-16 as modelled right now doesn't seem to do this. It just kind of falls out of low speed flight and re-gains speed without any problem (i.e., as if it never stalled). PS: 60 degrees AoA isn't a random figure... My point still stands that the flight models are stable. It's easy to model instability in the aerodynamic sense - you add something that approximates neutral or negative stability, then create a second layer on top (e.g. FBW sim) that corrects it. The point is though, without doing that, and in the absence of real-time calculations for airflow (turbulent or otherwise) the models themselves will not inherently create this behavior. Inadvertent spin is another side-effect of stability of flight modelling. A spin is due to increasing yaw rate, created by stalling a wing (e.g. slow flight in an un-coordinated turn). One wing will have a higher AoA than the other, causing it to stall. Beyond the stall AoA it creates an increased amount of drag. This drag causes the yaw moment to increase, increasing yaw rate to that side. As the other wing accelerates it generates more lift, and causes the aircraft to roll over (until it, too, stalls - this is why aircraft sometimes enter inverted spins from an upright entry). The yaw rate becomes such that instead of the aircraft continuing to turn, conservation of momentum means that the aircraft stops turning/flying and starts rotating around the yaw axis (linear momentum becomes angular momentum). At this point it has departed controlled flight and unless the pilot does something, will continue into a fully developed spin where the aircraft is no longer flying, but rotating as it falls like a sycamore leaf to the ground. We do not see this in simulators why? Because the flight models don't or can't compute it. The only way we can get them to spin (usually) is by inputting certain inputs, and only if certain pre-determined conditions are met, will the flight model act like it is spinning. The equations used for normal forward flight are not capable of developing to a spin without additional help. This seems to be the point that is being missed when the word "stable" is used. It applies not only to situations like the above, but stability in the aerodynamic sense. Some aircraft have interesting roll stability characteristics. The 747, at roll angles less than 32 degrees, demonstrates positive spiral stability (that means the pilot must hold in some aileron to maintain a constant bank angle). At 32 degrees of roll it will hold the roll angle with neutral aileron input. Beyond 32 degrees of roll, it has negative stability, and will roll tighter into the turn unless you hold some opposite aileron input to prevent the roll angle increasing further. A simple model of dihedral will not model this particular behavior. It will always be positively stable at all roll angles. It must be augmented by additional calculations to determine the strength and limits of positive, neutral, and negative stability. Just look at what happens when you get the F-5 into a high AoA situation and add rudder. It yaws, but the reality is the aircraft should roll! Even this is not correct. This is because the calculations being made even in this "simple" situation of high AoA are not adequate. If the flight models were more sophisticated and modelled the more noticeable effects accurately, we wouldn't even be having this discussion. 7.22 makes for interesting reading for those who are still unconvinced that flight modelling is quite inaccurate. The flight models are failing at smaller (yet significant) details, so why is everyone so convinced they're right on the more important details? Just because something "hits the numbers" doesn't mean a whole lot for how the calculations were made to get there. https://www.f4phantom.com/docs/F4_Phantom_Guide.pdf
  3. LOL. Do they? Really?? Do you even know what instability actually is? Two aircraft you really should be discussing didn't even get a mention, which is very telling indeed. I have nearly every DCS module going, and I can tell you that at the edges of the flight envelope, several of them are quite seriously deficient. They don't perform as the real aircraft would (because the flight models are inherently stable). MiG-15: if flying at high altitude/high Mach and you get into an accelerated stall, it should get into an aggressive, unrecoverable spin. F-5: If you do a loop at too low an airspeed, the aircraft should want to pitch NOSE DOWN and enter an inverted spin. It does not. High alpha flight is also too stable, and in fact doesn't remotely reflect the difficulty of its handling. You can roll with ailerons without any care. The real thing would kill you. F-86 is hard to spin, but the real thing wasn't. MiG-19 last time I flew it (2020?) had some strange behaviors and didn't behave as reality. It could also climb far above its service ceiling. F-14: it used to spin well (initial release) but because of "balance" or whatever the justification was, they dumbed down the flight model so now you need to work to spin it (not realistic at all). It was far better at release. The real thing was very prone to spins if mis-handled, especially at low speed. The two aircraft you didn't mention which should be top of the list, are the F-18 and F-16. These aircraft were designed to be unstable and can't fly without FBW. Did you explore the flight envelopes of either of these? Again: too stable. Don't get me started on the F-16 handling in pitch. It improved recently, but still has a long way to go. The F-16 also doesn't seem to understand what a stall is. It just mushes. All these problems are the result of the inherent stability of flight models. Instability must be added. Equations are insufficient to capture the instability of their designs as the airflow itself can't be modelled to sufficient detail to do so. It's a combination of aerodynamics and turbulent airflow around them that causes these handling difficulties. Add on top of that the fact that some aspects of the flight models are seriously lacking in fidelity (the LEF of the F-5 for example). Aside from adding a bit of drag and lift, they don't seem to affect the handling of the aircraft at all. The magic words that hardly any simmer ever has to utter is: "I did a dumb thing and the aircraft departed controlled flight". Inadvertent spins are non-existent in any sim I can name, yet they kill many aviators in real life on an annual basis. The reason is: stability.
  4. Take an empty jet and 50% fuel load, and as you approach 180 kts, pull the power off so it slowly accelerates through 180 kts, then you'll see it in operation. The tires only burst if you abuse the aircraft or exceed absolute tires speed limits (200 kts IIRC). Tires really do have such low safety margins. I wish the pitch problem would be addressed as a matter of priority. It flew really well and now is busted.
  5. Sims are too stable (flight models do not suffer the instability of real aircraft or model the minor perturbations you get from flying through real air), so I'd say it is a non-issue if you are relatively smooth to begin with (a major problem sim pilots suffer is they are not smooth). If you can refuel the F-18, you should be able to refuel the F-4 (in the sim).
  6. Ahh! That's the part I missed! Thanks for the procedures. Very useful!
  7. Regardless of where the trim is, the shift of the center of pressure will require you ease back-stick pressure through lift-off. I'm just pointing out that speed vs. trim isn't the only thing affecting the change of trim condition.
  8. How do you place objects to pick up? Add static items?
  9. Swept wing causes a pitch up at the stall, but during takeoff you are above the stall and accelerating. As the aircraft leaves ground effect, the center of pressure moves forward, causing a pitch-up moment. This, and the fact you're accelerating above trim speed, require that you trim nose down after lift-off.
  10. That's insane! Re-framing the question: why do people doubt the veracity of the claim? 50 years ago makes it the 1970s, and by then they understood lifting bodies, so I would doubt it is ignorance of the physics? Is it a East vs. West thing, or were people within Russia also debating it? I think we were experimenting with wings on helicopters, but AFAIK in the 1970s we weren't flying anything with "wings". Pylons, yes. I'm also thinking about helicopters such as the Sikorskis that have the protruding landing gear wells, and others such as the SH-3 and derivatives that had long, shaped nacelles either side of the fuselage, such as the CH-3 and later MH-53.
  11. You were clear! I wondered if the wings offset the right rolling force, but as you point out, with the tail rotor being above the CoG it could be enough to do this on its own (and an effect I hadn't actually considered). I don't understand why people would think it is over-modelled? If you're flying with virtually flat pitch on the main rotor in high speed flight, sure, but I don't see that in any of the videos I've seen. The collective is far from "at the bottom".
  12. Are the left and right wings symmetrical? Is the rolling tendency offset by the right wing producing slightly more lift than the left? i.e. not symmetrical? The thrust due to the tail rotor is diminished at high forward speed, so seems a reasonable assumption that it would help cancel out the rolling force. Why would this be in doubt? The wing area is not insignificant, and clearly forms an aerodynamic surface.
  13. It ca't be that dubious - I've recently seen Western military helicopters sporting something similar.
  14. My other post was just talking about informational sources and how there are reports of JF-17 making a couple of kills. I have previously linked articles in older threads from a year or two ago when this was discussed. Sky Dragon SD-10A SAM: http://chinesemilitaryreview.blogspot.com/2013/09/chinese-sd-10a-sky-dragon-medium-range.html
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