SgtPappy Posted June 26, 2015 Posted June 26, 2015 (edited) I have come to believe that the DCS MiG-15bis ITR is too high, based on some tests I evaluated against real data. The full post is here in a different thread, but I thought I should bring this up in the bugs sub-forum so that BST can see it: http://forums.eagle.ru/showpost.php?p=2421737&postcount=74 Essentially, I found that the MiG-15's 7G corner speed is the same as the Sabre's in-game, although John Boy'd real-world tests plotted on an EM chart state that the Sabre should have a significant advantage in that category; able to hit 7G @ 5000' at a speed 52 knots lower than the MiG. Unless of course, Boyd's plot is wrong, but I cannot find a more reputable source. I have also heard from some that MiG's sustained turn rate might be too low, but I'll have to test that next weekend. My aim is not to nerf the MiG. I love flying it very much, but I certainly do not enjoy flying it as much (or flying against it) now knowing that its turn performance is too high and inaccurate. Please BST, take a look at this at least for the sake of accuracy. Thanks. Edited June 26, 2015 by SgtPappy Fixed link
Hummingbird Posted June 26, 2015 Posted June 26, 2015 (edited) When I do some of these tests I get some pretty wild deviations in G forces (it spikes quite abit), but I am always able to pull a higher G at ~310 knts in the F-86 than in the MiG-15bis. As for Boyd's chart, it's probably taking into account things such as stick forces etc., whilst ingame you might very well be able to pull slightly harder than what'ever average pilot strength figure Boyd arrived at. Stick force is a significant factor where even a small change can have a big impact due to the steep nature of the ITR curve. Also note that the MiG-15bis features about the same stall speed as the F-30 Sabre, and as a result its ITR curve starts at pretty much the same spot, thus a higher pilot strength figure will also yield a more similar ITR curve until a certain speed. That having been said Boyd's chart also shows a rather significant 3 deg/sec advantage in STR for the MiG-15bis, which I have to say I really don't feel like it has ingame at all - basically you have to use the vertical to win a STR fight against a well flown Sabre ingame. Edited June 26, 2015 by Hummingbird
Foul Ole Ron Posted June 26, 2015 Posted June 26, 2015 I think we'll have to wait for DCS 2.0 at this point as they've made some adjustments to the Mig to better match Soviet data. I think we have what we have for now.
SgtPappy Posted June 27, 2015 Author Posted June 27, 2015 (edited) When I do some of these tests I get some pretty wild deviations in G forces (it spikes quite abit), but I am always able to pull a higher G at ~310 knts in the F-86 than in the MiG-15bis. As for Boyd's chart, it's probably taking into account things such as stick forces etc., whilst ingame you might very well be able to pull slightly harder than what'ever average pilot strength figure Boyd arrived at. Stick force is a significant factor where even a small change can have a big impact due to the steep nature of the ITR curve. Also note that the MiG-15bis features about the same stall speed as the F-30 Sabre, and as a result its ITR curve starts at pretty much the same spot, thus a higher pilot strength figure will also yield a more similar ITR curve until a certain speed. That having been said Boyd's chart also shows a rather significant 3 deg/sec advantage in STR for the MiG-15bis, which I have to say I really don't feel like it has ingame at all - basically you have to use the vertical to win a STR fight against a well flown Sabre ingame. The stall line is the stall line. I also posted the MiG-15bis VN diagram here: http://airspot.ru/book/file/1108/MIG15bis.pdf. Page 42 in the pdf (real page 73, 74). Doesn't matter how strong you are, you are not going to be able to pull G past the point when your wing stalls. But I'm not too sure how stick force into account so I can't comment much on that. Either way, the MiG's VN diagram yields the same results when compared to the Sabre's. Huge difference in corner speed. I'm not sure if the stick force can account for that difference. Comparing these, the MiG is still turning too well at too low of a speed. It's as simple as it's simply not supposed to turn at 7.0Gs at the speeds it can right now according to every publication so far, Soviet or American. Edited June 27, 2015 by SgtPappy
Hummingbird Posted June 27, 2015 Posted June 27, 2015 (edited) The stall line is the stall line. I also posted the MiG-15bis VN diagram here: http://airspot.ru/book/file/1108/MIG15bis.pdf. Page 42 in the pdf (real page 73, 74). Doesn't matter how strong you are, you are not going to be able to pull G past the point when your wing stalls. But I'm not too sure how stick force into account so I can't comment much on that. Either way, the MiG's VN diagram yields the same results when compared to the Sabre's. Huge difference in corner speed. I'm not sure if the stick force can account for that difference. Comparing these, the MiG is still turning too well at too low of a speed. It's as simple as it's simply not supposed to turn at 7.0Gs at the speeds it can right now according to every publication so far, Soviet or American. No it's not the stall line unless you have powered control surfaces so that you can always pull full deflection no matter the speed, hence why pilot strength matters :) In the MiG pulling full elevator deflection becomes harder and harder with increases in speed because of the lack of powered control surfaces, which in turn will effect the max attainable ITR. The fact that both aircraft start out being able to pull the same ITR however tells us that airframe wise they should have the same ITR at most speeds, however as mentioned the MiG's ITR becomes limited with increases in speed whilst the Sabre's doesn't due to its powered controls. If the MiG had been equipped with powered controls however, then it most likely would've featured the same ITR as the Sabre at most speeds. Edited June 27, 2015 by Hummingbird
SgtPappy Posted June 27, 2015 Author Posted June 27, 2015 No it's not the stall line unless you have powered control surfaces so that you can always pull full deflection no matter the speed, hence why pilot strength matters :) In the MiG pulling full elevator deflection becomes harder and harder with increases in speed because of the lack of powered control surfaces, which in turn will effect the max attainable ITR. The fact that both aircraft start out being able to pull the same ITR however tells us that airframe wise they should have the same ITR at most speeds, however as mentioned the MiG's ITR becomes limited with increases in speed whilst the Sabre's doesn't due to its powered controls. If the MiG had been equipped with powered controls however, then it most likely would've featured the same ITR as the Sabre at most speeds. Ohhh I see what yo mean lol forgive my mistake :) But then it technically wouldn't be the stall line right? Because they would know they're not stalling. They won't get enough deflection to stall and no buffet would occur, or am I missing something? Also, at low speeds, that's no excuse because they should be able to get full deflection and then at higher speeds, there would be something of a discontinuity in the curve, i.e. it wouldn't be modeled by that consistent spline that we see. I hope I'm not sounding too aggressive. Still trying to figure this issue out.
Hummingbird Posted June 28, 2015 Posted June 28, 2015 (edited) Ohhh I see what yo mean lol forgive my mistake :) But then it technically wouldn't be the stall line right? Because they would know they're not stalling. They won't get enough deflection to stall and no buffet would occur, or am I missing something? Also, at low speeds, that's no excuse because they should be able to get full deflection and then at higher speeds, there would be something of a discontinuity in the curve, i.e. it wouldn't be modeled by that consistent spline that we see. I hope I'm not sounding too aggressive. Still trying to figure this issue out. As the forces on the control surfaces gradually increase the amount of control surface deflection the pilot is able to pull gradually decreases as well, hence why we see the MiG's ITR line gradually bend more and more (noticably more than the F-86's ITR line), and eventually intersect with the STR line at Mach ~0.45. That's the effect of high control forces limiting the ITR. However the fact that both aircraft start out with the same ITR at low airspeeds proves that the MiG15bis features about the same lift to weight ratio as the F-30 Sabre, thus if given powered controls it would've featured a very similar ITR graph. - and the ITR & STR lines wouldn't intersect at max STR. But again let's remember that the above graph likely wasn't done by Boyd and that it seems to originate from an early sim, thus we need to take it with a grain of salt. Edited June 28, 2015 by Hummingbird small typo
SgtPappy Posted June 28, 2015 Author Posted June 28, 2015 Well what I'm saying is that even though we see the ITR limit as it is, it would be known that the aircraft isn't flying near stall, but is hard on the controls. Also I'm pretty sure that just because the aircraft have a similar stall speed doesn't prove it will have the same ITR. Other EM diagram comparisons (like the Su-27 vs F-15) do not have a huge disparity at the lower left of the plots but they have very different turn characteristics. But yes, let's forget about the supposed Boyd diagram because we don't really know its conditions. Let's just look at the Soviet TO and the F-86 flight manual. Both have VN diagrams that are not suspect and we can see ITR but in G's instead. From what Curly said, these plots are using CL values and likely have nothing to do with pilot strength. They both show the disparity between the Sabre and MiG 7G corner speeds so I really don't think surface deflection is a factor. I'd still like to find more VN diagrams of the MiG though to make sure.
Hummingbird Posted June 28, 2015 Posted June 28, 2015 (edited) Well what I'm saying is that even though we see the ITR limit as it is, it would be known that the aircraft isn't flying near stall, but is hard on the controls. Also I'm pretty sure that just because the aircraft have a similar stall speed doesn't prove it will have the same ITR. Other EM diagram comparisons (like the Su-27 vs F-15) do not have a huge disparity at the lower left of the plots but they have very different turn characteristics. Well that depends on what measurements you're using, G measurements are the most accurate as they are what the rate figures are based on, and if we look at the sustained & instantanous G measurements there's a pretty noticable difference between the Su27 and F-15. Also let's keep in mind that the curves will be noticably different due to the fact that the Su27 features leading edge flaps that alter the camber of the wing, where'as the F-15 does not. But in general two aircraft with the same stall speed will also have a similar ITR providing they both feature the same control effectiveness of course. But yes, let's forget about the supposed Boyd diagram because we don't really know its conditions. Let's just look at the Soviet TO and the F-86 flight manual. Both have VN diagrams that are not suspect and we can see ITR but in G's instead. From what Curly said, these plots are using CL values and likely have nothing to do with pilot strength. They both show the disparity between the Sabre and MiG 7G corner speeds so I really don't think surface deflection is a factor. I'd still like to find more VN diagrams of the MiG though to make sure. Don't you trust the Russian VN diagrams? AFAIK the Russian figures are based on flight tests with all sorts of measuring equipment (incl. accelerometers), just like the US tests. Thus pilot strength/control forces were always a factor. Edited June 28, 2015 by Hummingbird
SgtPappy Posted June 29, 2015 Author Posted June 29, 2015 (edited) Don't you trust the Russian VN diagrams? AFAIK the Russian figures are based on flight tests with all sorts of measuring equipment (incl. accelerometers), just like the US tests. Thus pilot strength/control forces were always a factor. No no, I do! I was just confused because the first one doesn't really agree with the second one in terms of Mach number at 7G, and Curly was postulating that they might be calculated, not taken from flight tests. If they actually are from flight tests, well that works moreso to prove my point concerning the disparity between the real and DCS MiG-15 so I'd rather use the Soviet VN diagrams as fact. Let's not forget that we do have control effectiveness modeled though, to an extent. A MiG-15bis at 0.78-0.82 Mach will barely pull any G's due to the heavy control forces needed. But you can and will physically stall if you pull G's under corner speed. So I understand your point but I'm not convinced that it would be recorded as the stall line on the VN diagram since the plane isn't actually stalling. Edited June 29, 2015 by SgtPappy
Hummingbird Posted June 29, 2015 Posted June 29, 2015 I am quite confident that said VN diagram is based on flight tests, anything else would make little sense in my mind. Also I don't really like calling the ITR curve the stall line seeing as said curve will be greatly affected by control forces on aircraft without powered control surfaces - and looking at the MiGs ITR curve it shows very clear signs of control force limitations.
SgtPappy Posted June 29, 2015 Author Posted June 29, 2015 I am quite confident that said VN diagram is based on flight tests, anything else would make little sense in my mind. Also I don't really like calling the ITR curve the stall line seeing as said curve will be greatly affected by control forces on aircraft without powered control surfaces - and looking at the MiGs ITR curve it shows very clear signs of control force limitations. The thing is on a VN diagram, it defines the aircraft's capabilities to load itself. Anything beyond that is subject to endless discussion. I think the VN curve in the Soviet diagrams should therefore really define what G's our MiG can pull at a given speed.
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