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38Deg AoA Wobble at 600+kph IAS. Thoughts ?


LupinYonder

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Hi all, I've been messing around since the few small flight model changes.

 

I'd been noticing that at high AoA you encounter a very sudden and repeatable snap into horizontal wobble. After more testing, I've discovered that it happens exactly as the AoA needle hits 38. After futher testing, I've discovered this only happens when you hit 38deg at speeds lower than around 700-600kph. If you hit 38 at higher speeds then you can hold the turn even as your speed drops below 500kph with no wobble.

Any thoughts on this ?

 

Personally, it feels a bit suspect and scripted. An obvious caveat is that I am no pilot or Mig 21 expert. Track included

High AoA wobble .trk

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Hi, after updating the flight model the acceleration dynamics became noticeably worse, also there is not enough thrust in the corners.

Wish list:

-> MiG-3, MiG-9, MiG-17F, MiG-21F-13, MiG-23MLD, MiG-27K, MiG-25PD, MiG-29K, MiG-31, Su-17M4, Su-24M, Su-27SM3, Su-30SM, Su-34, Su-35S, Yak-3, La-7

-> Me.262, F-4D/E Phantom II, F-100 Super Sabre, F-104 Starfighter, Mirage III, Mirage F1, Saab 35 Draken, Saab JAS 39 Gripen, IAI Kfir

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I've forwarded all the feedback but with my own research, I did not find a single document describing aileron control loss at high AoA. Manuals and Flying Characteristics documentation describes very well aileron authority at speeds up to 200 km/h as the aircraft maintains roll rate of about 85 deg at that speed. Document states that this is for level flight at 5.000 m, which raises eyebrows since reducing speed to 200 km/h without increasing AoA at such altitude in MiG-21 is unlikely.

I think this is where pilots experience (Dolphins) will be crucial.

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That is very interesting and counter intuitive. In my mind, loss of aileron authority just kind of always happens. It could be that in the mig-21 it somehow occurs at speeds lower than a reasonable stall speed, hence the behaviour we're seeing.

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Guys this thread went totally off topic. I was not discussing roll authority directly or low speed control. I was discussing specific and strange behaviour at 38deg AoA at certain speeds and not others. I even included a track.

 

Please have another read.

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I have not seen the track yet Lupin, but are you describing an accelerated stall? I’ve noticed a tendency to see the nose drop when yanking and banking at slower speeds (like you indicated) and figured it seemed appropriate accelerated stall behavior, even if it wasnt there before. Ive also noticed the occasional wing drop during stalls, which I dont think was there before, but is a nice believable touch regardless. Whether the real mig actually demonstrates this behavior, I can’t say.

 

That said, this new flight model feels weird. I’m still trying to figure out the best way to describe it. The plane acts sloppily along the longitudinal axis, and tends to have a one-two oscilation after any size pitch input, at any speed. Increasing airspeed doesnt seem to “firm things up” as I would expect higher dynamic pressures would. The rotation behavior is also very different, as if the center of gravity is too far back. Very easy to over-rotate now. I used to rotate with 4 sec of up trim, and now with 0 it’s too much. It also seems to need to lift off at higher speeds if you want a more controlled takeoff. I used to touch down at around 300, but now the sloppiness in pitch makes it too unpredictable. Unfortunately, touching down at higher airspeeds such as 375is causes it to easily jump back in the air.

 

It just has a very different character now. Look at how the g meter moves now in flight in response to control input. Even that seems to reveal a certain softness that wasnt there before. Yes, the mig could feel sloppy before in some slow flight regimes, but now it feels like that during all speeds and loadings. I wish I could put this in a track, but it’s more of a “feel” thing if that makes sense.

 

I will say that I welcome improvements in FM to better simulate the real thing. Having no time in a Mig, the previous flight model was the only thing I could reference. The very different feeling FM we currently have begs the question, was the previous flight model that far off, or is the new FM the one that is “off”

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Dolphin informed me that new FM is WIP and will be further tweaked so current issues are taken into consideration.

AMD Ryzen 5900X @ 4.95 Ghz / Asus Crosshair VII X470 / 32 GB DDR4 3600 Mhz Cl16 / Radeon 6800XT / Samsung 960 EVO M.2 SSD / Creative SoundBlaster AE-9 / HP Reverb G2 / VIRPIL T-50CM /
Thrustmaster TPR Pendular Rudder Pedals / Audio Technica ATH-MSR7

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The rotation behavior is also very different, as if the center of gravity is too far back. Very easy to over-rotate now. I used to rotate with 4 sec of up trim, and now with 0 it’s too much. It also seems to need to lift off at higher speeds if you want a more controlled takeoff. I used to touch down at around 300, but now the sloppiness in pitch makes it too unpredictable. Unfortunately, touching down at higher airspeeds such as 375is causes it to easily jump back in the air.

 

At least some of the takeoff behaviour seems to be due to the stiffer suspension rather than the flight dynamics, by 250+ you're already bouncing quite hard and it doesn't take much to cause the nose to bounce right off the ground.

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Don't pull. Trim until the neutral light goes out, then trim the same amount again. It should either rotate by itself or require only a feather-light touch to the stick to bring it off, be ready to counter with a gentle nose-down push if it bounces too hard and comes up too quickly.

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Don't pull. Trim until the neutral light goes out, then trim the same amount again. It should either rotate by itself or require only a feather-light touch to the stick to bring it off, be ready to counter with a gentle nose-down push if it bounces too hard and comes up too quickly.

 

That is a complete deviation from the aircraft manual though. I would not start learning doing things the wrong way due to a flight model currently being worked on.

[sIGPIC][/sIGPIC]

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That is a complete deviation from the aircraft manual though. I would not start learning doing things the wrong way due to a flight model currently being worked on.

 

Agreed, the real mig appears to need substantial stick back to get the nose up. There are youtube vids where you can see the pilots pull back and hold the stick about 3/4s back once they start rolling. Then they ease off the stick to control rotation rate as the nose eventually starts to rise. It was possible for me to model that procedure exactly when using the previous FM.

 

In the previous FM I would usually use 3 to 4 sec of back trim, and once off the runway, I would need to maintain some back pressure until it finally flew through the trim speed a good 10 to 15 sec after takeoff, when I could finally relax stick pressure.

 

I flew some more last night, and I think I like the high AoA snap-stall behavior. Qualitatively, it fits with the raw nature of the Mig21. But I have to look closer at AoA readings when it is at higher speed. If there isnt accelerated stall behavior at higher speeds, then it should not be possible to reach the 38 degrees of AoA Lupin was referencing. Because theoretically, wouldn’t 38 degrees define where stalls occur (regardless of speed)? Isnt the point of having the gauge red-zone to warn you of imminent stall?

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Indeed the correct technique according to the manual should be hold the stick at 3/4 of travel, ease a bit when the aircraft rotates and let it fly off by itself. Now the aircraft is quite unstable after rotation and impossible to keep steady. It was also quite difficult previously and I thought that with the new patch it will be a bit more stable, but the opposite has happened. This also applies to landing, now it is very hard to keep the aicraft on main landing gear after touchdown. So in my opinion this change was for the worse :(

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I took up the mig to check on the accelerated stall characteristics at higher airspeed. Most of the time at speeds above 900 i could not reach 38 degrees AoA and stall before blacking out or bleeding speed low enough, which is what I would have expected. So in my opinion, the acc stall behavior seems realistic on theoretical grounds. In real life, manufacturers guarantee you a maneuvering speed below which an accelerated stall will always happen under high AoA. But if you maneuver above that speed, the wing will continue to fly with as much wing load as you put on it including until the point of complete structural failure (or human failure). Of course, modern fighter jets eliminate structural failure possibility by digitally limiting the amount of AoA/ G’s that you can pull.


Edited by Cgjunk2
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It is basically beyond to be useable and to be fun. Every take-off landing is big gamble now.

 

 

You are overreacting a big way, I was able to takeoff just fine within parameters described in pilot manual and landing was absolutely fine,

 

direction control was no problem with a little crosswind and my VS during touchdown was less than 1m/s at about 300km/h, so very controlable, didnt even had to use chute.

 

 

This was great update to MiG-21 (appart from that 38° AOA problem), it feels lively if somewhat under powered.

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As I've said, FM is going to see more tuning so we will work on all this issues guys!

AMD Ryzen 5900X @ 4.95 Ghz / Asus Crosshair VII X470 / 32 GB DDR4 3600 Mhz Cl16 / Radeon 6800XT / Samsung 960 EVO M.2 SSD / Creative SoundBlaster AE-9 / HP Reverb G2 / VIRPIL T-50CM /
Thrustmaster TPR Pendular Rudder Pedals / Audio Technica ATH-MSR7

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That is very interesting and counter intuitive. In my mind, loss of aileron authority just kind of always happens. It could be that in the mig-21 it somehow occurs at speeds lower than a reasonable stall speed, hence the behaviour we're seeing.

 

NOT AN ENGINEER but from what I understand, there are ways to mitigate it through design and certain aircraft do retain usable roll authority even well into the stall. That said, I don't think the 21 has any of the usual design features that cause this, and it also lacks roll from the stabs (as correctly modelled visually, and as far as I can tell reflected in the FM - I think old problems of retaining roll auth without ailerons was a DM problem where it thought they were still there).

 

Thankfully, whether it's accurate or still needs tweaking, it shouldn't really make too big an impact on gameplay as putting yourself into that state during a fight is 100% going to result in death, you're a standing target and will take forever to regain your speed.

 

As for T/O and landing... landing doesn't feel much different to me other than the aircraft is slightly more prone to wandering. The bounce induced by the suspension stiffness is what's messing with me most, including for T/O. I fly by feel and not any manuals, so maybe doing a by-the-book landing is complicated now, but my usual standby of coming in at 380-400 and then dropping to 280-320 over the fence hasn't been causing any issues at all.


Edited by rossmum
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Anyone think some of this behavior is tip stalls and single wing wings stalls which also causes huge adverse yaw? I remember it always used to stall both wigs at the time if you pulled, but no it tip stalls with enough encouragement. Am I imagining this? Sure it might need to betuned, but I really like it

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