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Stall + High AoA behaviour...


Robin885

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On 6/19/2022 at 4:27 PM, Kobymaru said:

OK so I want to believe that high AoA situations lead to wing rock and unstable roll/yaw axis due to stalls.

But the current implementation just feels really silly. I do not own a Mig-21 IRL, so I can not check, but does Magnitude really want to tell me that it departs in the exactly same way, every single time? In a left hand turn, at exactly 16° AoA (DCS, not indicator), the plane rolls right, yaws left and then in the opposite direction. Right hand turn exact opposite.

It doesn't even lose any lift during this "wing rock", because the g-load stays pretty constant. If it's a form of stall, should it not decrease somehow?

To me it looks less like an aerodynamic phenomenon and more like Dolphin jumped into my cockpit and started to wiggle my controls to mess with me for fun 😉

Have been complaining abou this for many years now. My outtake is M3 is just unable to properly tune the FM, so they added a "digital spike" stall that is scripted. Not holding my breath to see it changed... 


Edited by bkthunder
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The Magnitude 3 MiG 21 sometimes behaves like a playful young goat that jumps and defies the laws of physics. There is no inertia in its motion so it looks more like a bouncing ping-pong ball than an 8-ton aircraft.

Take a look at these shots of flight parameters and flight dynamics. If you manage to bring the flight model partially closer to the one in the videos, we will be very grateful!

I'm sorry but I use google english!

 

 

 

 

 


Edited by yufighter
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  • 6 months later...

There is no way separation will result in an instantaneous change of yaw rate. It makes absolutely no physical sense, and to hear it was intentionally designed this way from an operations manual is not a good point of defense.

What you should expect is an immediate effect of wing drag and possibly turbulence across the tail during separation producing a yaw moment, not an instantaneous yaw rate. Furthermore, it will be a weak one because of how small the aspect ratio is vs its yaw inertia.

Here is an example step by step of the expectation:

  1. High Angle of Attack
  2. A wing separates, let's say the left wing
  3. Left wing loses lift so it begins to roll left
  4. At the same time, a small left yaw moment is introduced, but it is weak because the ratio of AR to INy is very small.
  5. By the time it rolls 90 degrees, almost all of its original angle of attack is now sideslip, but some sideslip was lost because of the yaw moment.
  6. Now there is a strong yaw moment due to sideslip.
  7. it begins to yaw more strongly until it reaches peak yaw rate at zero side slip
  8. If allowed, yaw will oscillate and stabilize, but intervention can either allow early correction, or even greater difficulty regaining control.

In the FM I saw:

  1. High Angle of Attack
  2. Instantaneous yaw rate that makes no physical sense and would probably kill a pilot if it really happened.

Clearly there is a major conceptual error there, as if this reaction was scripted.

This was almost the first module I ever bought, but I skipped it for this reason alone. Actually, it was the defense of it that struck me down. Of all the things that have killed Mig-21 pilots, can you guess what none of them ever died from? There were over 11,000 of these aircraft built. Should be easy to find one video of this happening IRL. 

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Yes, fix it ASAP, it's unacceptable!!! Don't tell me that the pilot wouldn't black out or throw up from such negative G...

 

 


Edited by D4n
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  • 4 weeks later...
On 1/24/2023 at 6:48 AM, NineLine said:

Track?

Just hop in Mig-21, fly around 600 km/h and pull on the stick until exceeding AoA limit. Not sure how a track is supposed to help against an abandoned module though.


Edited by Kobymaru
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  • 3 weeks later...
On 2/19/2023 at 5:23 PM, Ala13_ManOWar said:

Funny how an "abandoned module" gets updates almost every patch. One needs to read changelogs to notice, though 🤣 .

Since you're so good at reading, could you help me find the part of the changelog where they talk about fixing 8 year old bugs?

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39 minutes ago, Kobymaru said:

Since you're so good at reading, could you help me find the part of the changelog where they talk about fixing 8 year old bugs?

It's where devs already said after Corsair release there'll be a MiG-21 v2.0 😜 .

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"I went into the British Army believing that if you want peace you must prepare for war. I believe now that if you prepare for war, you get war."

-- Major-General Frederick B. Maurice

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I can't believe the MiG 21 is so unstable when you try to keep the nose up 10 degrees of AoA during take off and landing! It's just awful, it's not a MiG-21. I use a long stick and straight curves but I'm always in a strange when I'm holding my nose. I regret buying this module


Edited by Red_Pilot
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8 hours ago, Red_Pilot said:

I can't believe the MiG 21 is so unstable when you try to keep the nose up 10 degrees of AoA during take off and landing! It's just awful, it's not a MiG-21. I use a long stick and straight curves but I'm always in a strange when I'm holding my nose. I regret buying this module

...But it's not unstable at 10 degrees indicated AoA?

What weight are you landing at? Loadout? Are you cutting the throttle below 80% N1 before the main wheels are on the ground?

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Even using a long stick (25cm here) without proper curves it's not that easy to fly mate. Try some proper curves and test the difference. It wasn't unstable at those situations you mention last time I flew it.


Edited by Ala13_ManOWar

"I went into the British Army believing that if you want peace you must prepare for war. I believe now that if you prepare for war, you get war."

-- Major-General Frederick B. Maurice

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In another section of the forum, there were guys who claimed that the wrong cooling system of the spitfire is great, until the devs improved it. I will say one thing: I have no problems with other plane or helicopter. Including with MiG 29 and MiG15. Only in MiG21 some special skills are needed to hold the nose. In fact, there have been many issuses on behavior at high angle of attack. 


Edited by Red_Pilot
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4 часа назад, Ala13_ManOWar сказал:

Even using a long stick (25cm here) without proper curves it's not that easy to fly mate. Try some proper curves and test the difference. It wasn't unstable at those situations you mention last time I flew it.

 

Thanks for the advice. You're right. I really could try other curves, but after a series of tests on a long runway, when I kept the speed for nose up, I was not satisfied with the flight model

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I have yet to see a single case of someone complaining about the 21's landing characteristics, where they were finally persuaded to provide a trackfile, only for it not to become immediately apparent that the problem was shockingly bad technique (usually because they were "inspired" by another player's genius "lifehack"). Of all the problems the FM has, landing characteristics are not one of them, and takeoff issues mainly come down to how much the jet rocks on its suspension combined with too lengthy of a takeoff run compared to the real jet. Almost all bad takeoffs I've seen (as well as my own messy ones) are from holding the stick back and lifting too early, versus holding the stick back until the nose attains the correct attitude and then holding the nose there.

You can make comparisons to the Spitfire's cooling all you want, it doesn't change the facts of the matter: the only reason people complain about landing the 21 in DCS comes down to terrible technique every single time.


Edited by rossmum
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40 minutes ago, Red_Pilot said:

terrible technique? nose rising  terrible technique... lol

It's really easy mate, show a track where that bad behaviour you meant happens and we can see it 🤷‍♂️ .

"I went into the British Army believing that if you want peace you must prepare for war. I believe now that if you prepare for war, you get war."

-- Major-General Frederick B. Maurice

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On 10/26/2020 at 1:38 AM, Robin885 said:

I was expecting this kind of answer... But no, none of these two points are realistic, and it is a bug. It's not about the way the plane stalls, it's that it simply doesn't stall. The manual states that after 33° AoA, the plane reaches it's critical AoA and won't go further. This limit does not exist in game today.

And about the wing rock, I'm not talking about stability. Just watch it by yourself:

It just looks like the plane reaches an area where the FM is not even "coded" anymore

I have to disappoint you, but everything what @m4ti140 wrote is true. In my university we made a experiment in Wind tunnel with the delta wing (well... I know Re < 300 000) Vortex kept stable up to 90°. What is missing in MiG-21 DCS however, is gyroscopic moment from engine during low speed stall. Every source I found mention about it (during stall and by loosing stability in level flight by V > 1300KIAS Gyroscopic moment playes in MiG-21 significant role). It was confirmed by many sources. If you're interested in Vortex you may find many interesting articles and even movies about these fenomenon.

My best regards
Kermit


Edited by 303_Kermit
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At speeds from 250 to 300 km/h, I tried to keep the stick in one position to raise the nose. Every time there was a tendency to raise the nose even more, I tried to push the stick forward, i was forced to fluctuate within 5-6 degrees. So, I have already pushed the stick forward, and the plane still continues to lift its nose. The next stick position is much farther than what was needed to hold 10 degrees. But the nose is still moving up and don't move down.

So I had to push the stick even harder and this resulted in constant wobble and inability to accurately control holding the 10 degree angle of attack. You are constantly forced to fluctuate within 5-6 degrees

MiG_21_take_of.trk

MiG_21_takeof_2.trk

 

In short, you need more force to lift the nose wheel off the concrete than to keep the nose wheel up. But further, at the same speed, the plane continues to raise its nose

I have no problem taking off and landing safely. It's not a problem for me! But I don't like this behavior


Edited by Red_Pilot
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  • 1 month later...

 

Here is a very good demonstration of what I wrote about. In DCS, when you can lift your nose, you take off almost immediately. If you can't take off, you can't hold your nose properly. In the second case, you are getting a permanent wobbling. As if the speed is not enough, even though you already have 260 - 280 km/h. But the video clearly shows that the IRL can first lift its nose, continue to roll and take off when you have got enough speed for this


Edited by Red_Pilot
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It's a problem affecting both takeoff and landing. Difficult to get the front wheel smoothly off the ground (contrary to notes in real life flight manual), and difficult to keep it from slamming down at touchdown. Almost as if there was too much weight on it, or stabilators were not producing enough lift in these transitional phases.

It's always been like that, however, since module release 9 years ago, and countless posts were written about it. No point in beating a dead horse. I don't expect it to be ever changed, but truth to be told it's not a critical problem either.


Edited by Art-J

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It is tricky I admit. And I have never been able to hold 10° aoa on takeoff like the DCS manual says. I kinda wobble around 12-15°. I imagine this is easier in a real plane since you can feel movement instead of having only visual feedback.

Here's me taking off in Caucasus if you're interested.

takeoff.png

takeoff.trk

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