Unrealistic Flight Model Mig-21

[KThax]

I think that the flight model of this aircraft is very unrealistic when performing high AoA turns at low speed. It should be possible to get out of turns or stalls at full throttle without having to let go of the stick (depending on your loadout)
I was testing the dog fight capabilities of this aircraft the other day and I was not impressed by it.
I am not an expert in aviation so I am not sure if the aircraft actually behaves like this IRL or its just been POORLY designed that way (in which case this aircraft has to be sold at $10 for this issue alone)

Please do take a look at what happened in that dog fight I mentioned just now:
https://www.youtube.com/watch?v=1dzqIfZCr2g

EDIT: I AM NOT ASKING FOR TIPS TO GET OUT OF A STALL, IF YOU ARE NEW AND DONT WANT TO READ THE SUBSEQUENT COMMENTS TO GET UPTO SPEED THEN KINDLY HAVE A LOOK AT THIS LINK, IT SUMMARIZES WHAT I'M TRYING TO GET ACCROSS. THANK YOU.
https://imgur.com/a/lOIMf

[KThax]

Originally posted by startrekmike:

I have watched your video a few times in the event that perhaps there is something that we are all missing but when I look at the gauges and I look at sequence of events as you describe them, it is rather obvious that the aircraft is indeed in a stall due to excessive angle of attack. You make the problem worse by continually holding the nose of the plane in a level position and thus maintaining aerodynamic load on the wing.

In this case, your pressure on the stick is just pushing the plane further and further into a stall as the angle of attack is simply too high for the aircraft to do much of anything else.

The solution in that scenario is to release the stick and let the nose fall. This will reduce the angle of attack almost immediately and would allow you to pull up normally.

The MiG-21 is not a perfect module and does have a few issues here and there but its flight behavior is rather solid and your example is (to be blunt) rather obvious pilot error. You stalled the plane and it crashed, it would have happened that way in the real plane because of the basic physics of flight.

As for its dogfighting ability not "impressing" you. The MiG-21 is a high speed, high altitude interceptor at its core and while those delta wings do help with speed, they are a liability in a close-in dogfight. The plane can still hold its own but you will need to study up on how to use it properly. It is not going to perform like a MiG-29, F-16, or Su-27. It is just not that kind of airframe.

No no, I'm not asking for tips on how to get out of a stall. I held the stick back all the time just to demonstrate what I had previously observed.

What I'm trying to say is that the aircraft is capable of pulling itself out from the stall during that brief level flight simply because it is light and has a comparatively powerful engine for its weight, but this has not happened.
The mirage does it beautifully at much lower speeds, granted it has a slightly higer power to weight ratio.

[Delta Dagger]

I keep putting a fork in the toaster and I keep getting electrocuted. What's up with that?

[startrekmike]

So, in a effort to ensure that I know what you are asking. You put the aircraft into stall speed, pull the stick back enough to put your AOA incredibly high, turn your plane into a giant airbrake/brick and wonder why the engine on its own can't push the plane into forward flight?

What happened is not a unreasonable result. In cases like that, there is no scenario where using the afterburner will suddenly take a MiG-21 out of a stall and back into normal forward flight. The ONLY solution is to release the aerodynamic load on the plane by releasing the stick, let the nose drop, gain airspeed, and then pull out of the dive.

[Delta Dagger]

In addition, what you labeled level flight wasn't at all what is considered level flight. Level flight isn't just where the nose is oriented, but rather how the aircraft is oriented relative to its flight path.

[Vilab]

You may read the "landing part" of the manual of the Mig-21 manual.

the Mig-21 isn't meant to fly at less than 320km/h, landing at less than that is already a death trap, the engine can not overcome the drag due to the high AoA, pulling the nose will just increase your AoA while it will kill any velocity, and the plane will just fall to the ground.

Mirage-2000 is a much more modern plane, you may compare with the Mirage-3 which suffered from the exact same problem.
Mirage-3 needed military power to not lose altitude at 370km/h, only the use of afterburner or a decrease of the AoA could prevent the plane from falling like a rock at 350km/h.

in your video, you are not trying to land, you don t apply small corections with your control surface while you keep high AoA, you are completely pulling the stick back with extremely high AoA, it is expected that your your plane fall from the sky.

[Patton]

You didn't recover correctly, that's not the fault of the FM, that's pilot error.

And it seems plenty of people have already given you the pointers on how to fix that issue.

[KThax]

Originally posted by startrekmike:

So, in a effort to ensure that I know what you are asking. You put the aircraft into stall speed, pull the stick back enough to put your AOA incredibly high, turn your plane into a giant airbrake/brick and wonder why the engine on its own can't push the plane into forward flight?

Yes, since the power to weight ratio is ~ 1, it is capable to get out of the stall using engine power alone. Thats what I'm trying to get across.

Originally posted by startrekmike:

What happened is not a unreasonable result. In cases like that, there is no scenario where using the afterburner will suddenly take a MiG-21 out of a stall and back into normal forward flight. The ONLY solution is to release the aerodynamic load on the plane by releasing the stick, let the nose drop, gain airspeed, and then pull out of the dive.

I did not say that I was expecting it to "suddenly" take it out of the stall, what I was saying is there was no increase in the forward momentum, there should be nothing to prevent its forward velocity vector to increase and still the aircraft did not do that.

https://imgur.com/a/lOIMf

This is what I'm talking about.

[KThax]

Originally posted by MiG-21bis Fishbed-L:

In addition, what you labeled level flight wasn't at all what is considered level flight. Level flight isn't just where the nose is oriented, but rather how the aircraft is oriented relative to its flight path.

I've labelled it in those previous comments as a referrence to the horizon

[KThax]

Originally posted by Vilab:

You may read the "landing part" of the manual of the Mig-21 manual.

the Mig-21 isn't meant to fly at less than 320km/h, landing at less than that is already a death trap, the engine can not overcome the drag due to the high AoA, pulling the nose will just increase your AoA while it will kill any velocity, and the plane will just fall to the ground.

Mirage-2000 is a much more modern plane, you may compare with the Mirage-3 which suffered from the exact same problem.
Mirage-3 needed military power to not lose altitude at 370km/h, only the use of afterburner or a decrease of the AoA could prevent the plane from falling like a rock at 350km/h.

in your video, you are not trying to land, you don t apply small corections with your control surface while you keep high AoA, you are completely pulling the stick back with extremely high AoA, it is expected that your your plane fall from the sky.

Ok,
1. I'm not trying to maintain a glide slope
2. Please look at the grapgh I've posted in the imgur link that I've included 2 comments above.
3.Modern or not, it shares a lot of features with the mig such as the delta shaped wings, the only difference would be the slats at the leading edges of the mirage and its comparatively more powerful engine.

4. I am not asking people to give me tips on how to fly nor am I asking people to tell me how to get out of a stall, I wouldnt still be playing this if I didnt know these basic things

[KThax]

Originally posted by Patton:

You didn't recover correctly, that's not the fault of the FM, that's pilot error.

And it seems plenty of people have already given you the pointers on how to fix that issue.

Hhhh....it was an intentional stall, the video exists to demonstrate the limitations of the FM of the mig 21, I am not asking people to tell me how to get out of the stall. Kindly look at the imgur link I've included 3 comments above. It summarizes what I want to say.

[Emperor of The Great Unknown]

I think I know what the OP is getting at.

Basically when you draw the force diagram on the aircraft and split it into it's x and y components with respect to the ground. (postive x lets say forward direction level flight and negative y points torwards the ground.

If we assume the aircraft is not accelerating i.e. is failing at constant velocity, then we know that the magnitude of the thrust has to equal the magnitude of the drag force in the x direction, and the magnitude of the weight has to equal the magnitude of the drag in the y direction. (since this is a stall we ignore lift.)

The problem seems to come in is that the drag in the x direction is so great that even full afterburner provides no acceleration at relatively low speeds. (even if stall the continues you would still expect acceleration in the forward direction unless the plane is at max speed.)

And we also know the plane is failing and drag forces act antiparrallel to the velocity vector, so most the drag forces have to be in the vertical direction in this case. (which is probably realistic)

I would like to see you reproduce this scenario however, and post of video of you letting go of the controls and see how it behaves. That way we can see the effect of the control surfaces on the areodynamic forces of the aircraft.

On a second note I am also surprised that you can hold that position in a stall like that. I would expect there to be a torque on the aircraft, that either results in a spin or the nose to fall forward. The tail section would induce a lot more drag falling vertically like that than the nose, therefore pushing the nose down, regardless of the elevator/stabliator's position.

[Emperor of The Great Unknown]

In other news in the bug section for the Mig 21 in the ED forum is there serious disscusion on the PFM that is quite concerning.

https://forums.eagle.ru/showthread.php?t=179681&page=8

https://forums.eagle.ru/showthread.php?t=194892

https://forums.eagle.ru/showthread.php?t=146550


"Another and much greater issue is that when reaching 90 deg. of AoA, which can only be reached through stall spins (which is absolutely normal for such a highly stable aircraft), after reducing the yaw rate to 0 the aircraft trims itself to 90 deg. of AoA like if it's statically relaxed there and won't budge in pitch whatever you'd try. This is also abnormal..., normally the higher the AoA (after the stall occurs) the higher the stability margin and therefore the higher the stabilizing moment should be towards reducing the angle of attack, but it seems that at 90 deg. there is no more stability margin left at all."

[KThax]

Ah finally! Thank you for the reply

Originally posted by Emperor of The Great Unknown:

I think I know what the OP is getting at.
The problem seems to come in is that the drag in the x direction is so great that even full afterburner provides no acceleration at relatively low speeds. (even if stall the continues you would still expect acceleration in the forward direction unless the plane is at max speed.)

In this statement, you mention that drag is being exerted in the x axis, what is causing this drag? This is the part that I dont get. Since the aircraft is falling down (along -ve y axis) the drag exerted on the aircraft is in the direction of +ve y axis which in LEVEL FLIGHT (wrt to horizon) is LIFT.
Where does the drag along x axis come from when the resultant vector of the aircraft is pointing ~80° towards the ground?

Originally posted by Emperor of The Great Unknown:

I would like to see you reproduce this scenario however, and post of video of you letting go of the controls and see how it behaves. That way we can see the effect of the control surfaces on the areodynamic forces of the aircraft.

I'd be happy to do the video for you, but if you want to, I can describe it as I've already experimented the same thing.

What happens when you let go at that speed is as you have described it in the next paragraph, a torque acts on the aircraft resulting it to spin (almost whip lash) around the axis of its center of gravity and into the direction of the resultant vector (this applies to any point after the moment of exit from the loop as long as the aircraft is in stall speeds)

Originally posted by Emperor of The Great Unknown:

The tail section would induce a lot more drag falling vertically like that than the nose, therefore pushing the nose down, regardless of the elevator/stabliator's position.

The elevators are pointing along (almost) the resultant vector during that brief level flight. It should result in producing a small bit of lift along the x axis of the aircraft IMO

[KThax]

Originally posted by Emperor of The Great Unknown:

"Another and much greater issue is that when reaching 90 deg. of AoA, which can only be reached through stall spins (which is absolutely normal for such a highly stable aircraft), after reducing the yaw rate to 0 the aircraft trims itself to 90 deg. of AoA like if it's statically relaxed there and won't budge in pitch whatever you'd try. This is also abnormal..., normally the higher the AoA (after the stall occurs) the higher the stability margin and therefore the higher the stabilizing moment should be towards reducing the angle of attack, but it seems that at 90 deg. there is no more stability margin left at all."

I dont understand this, I'm pretty new to this aircraft so I'm having a hard time visualising this.
But thank you for showing it to me, i'll go check it out!

[Emperor of The Great Unknown]

Originally posted by KThax:

Since the aircraft is falling down (along -ve y axis) the drag exerted on the aircraft is in the direction of +ve y axis which in LEVEL FLIGHT (wrt to horizon) is LIFT.

Drag and lift are not the same thing. Lift is caused by an exchange of momentum when air passes over a wing. In a stall there is no airflow over the wing and therefore there is no lift. What you experience in the video is falling at terminal velocity where the vertical componment of the drag force is exactly equal to the weight of the aircraft.

I would really like to see a video so we have info of air speed, AoA, and so forth.