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The critical angle of attack is wrong, and its not because the F2 view shows the pitch angle.


KenobiOrder

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The explanation given at few years ago as to why the Mig is showing a different angle of attack than in the F2 view is as follows:

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As per the above, the flight model is using the angle of attack shown by the cockpit instruments. But the angle shown in the cockpit is about double the actual angle of attack. 

Here is proof the angle of attack in F2 is correct and the AoA in Mig-21 is wrong, and therefore the stall/wingrock part of the flight model is wrong rather severely and causing the plane to be uncontrollable at about half the realistic angle of attack:

 

First, so everyone is on the same page here is what Dolphin means by pitch angle and AoA

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The following screenshots show the F-18 angle of attack, and confirm that the long axis and the flight path indication are the same as the AoA readout. Which is also the F2 readout. This followed by mig-21 and tacview comparison. 

 

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You don't even need to go that far to conclude the AOA indicator is very wrong.

WQwe6K0.png

 

The most... "sane" (huge strech on that word)... explanation I read for that was that the soviets intentionaly made the indicator give higher values just so it would scare pilots and force them to better follow "by the books" procedures (????). But if the FM realy takes that value as the "true AoA", them from what I understand, the plane will never be able to achieve those 25°+ of AoA both soviet and american sources claim to achieve. Not only that, but it would greatly affect how drag is calculated, messing up low speed characteristics, which is another problem recurrently brought up by players.

 

As I'm no expert on any of this. I can just hope after the Corsair launch M3 will go back to research and iron out all the 21's FM weirdness, or at least give reasonable explanation on why it is the way it is.


Edited by Skuva
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The scare explanation is quite strange but the problem is more strange itself. It's quite normal on earlier aircrafts that AOA indicator shows not in degree but they are not claimed as degree. Just see the F-14 and F-5E and the AoA indicator is in "unit", a totally arbitrary stated "unit". They just adjust the unit to fit some integer critical point, 15, 20, 25 unit for approach or for stall. It's reasonable that the indicator on MiG21 was made also in arbitrary unit but strangely M3 and the English manual(maybe from Poland or somewhere else) both said 25 "degrees".

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Those screenshots of you two in external views can't be exactly "right" either. Real AoA isn't the angle between wing chord and a horizontal line, or even the free flow incoming, you can fly descending with that attitude shown, still be flying, and AoA wouldn't be what you think you're visually seeing as is obvious. That's why a external pic showing whatever isn't actual AoA whatsoever.

AoA is meant to be the difference between a high pressure spot below leading edge (which is not just the wing foremost spot), and the incoming airflow which is not either just the free air current, but the corrected flow angle because a wing moving through a dense fluid pushes air downwards even before it reaches the wing. Because of that, actual AoA can be either lower or higher than what you visually think you're seeing. Now, the delta wing as you know in fact needs AoA to fly, without any AoA there is no lift at all (you could run the whole Groom Lake 7Km runway and still the plane wouldn't take off without AoA no matter how fast and wheelless you get), which is true for almost any wing profile but specially true in delta wings, so it makes perfect sense I can get a variometer showing 0 (next time BTW show also airspeed in the screenshot), KPP showing 5º nose attitude which is not AoA, while actual AoA reading (measured with a couple of small pieces on the nose to get them out of wing or any disturbing influence) can be 10º and those 10º are the ones making you fly. But, in the F2 screenshot view shows AoA to be 4.9º which is what your KPP nose attitude reads (so not that bad), and as per devs explanation it wouldn't match AoAmeter and that's normal.

By the way, even in the Hornet screenshots there are inconsistencies, the HUD showing 10ºAoA but your velocity vector isn't 100% over the horizon, following your logic that means actual AoA should read 10'somethingº but it doesn't? No, it means velocity vector isn't the free flow either so it's no exact reference to eyeball an AoA. If AoA actually matches at some point nose high attitude in the Hornet it's because it's designed like that, meaning nothing to the MiG-21.

Also, bear in mind anyway a Hornet isn't delta wing either, you should try to compare at least with something comparable, another delta wing plane at the least (M2000 is the only available in DCS, I believe), even though different wings with different profiles and designs aren't exactly comparable either, but at least it would be closer to start with.

 

Edit: Funnily enough OP title says "critical AoA" which is a whole different thing either 😅.


Edited by Ala13_ManOWar

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According to manual the indicator shows the exact angle of attack (in degrees) measured by the vane (idk if it's the one in the fuselage or the one on the pitot).

I understand such measurements are deviated from the real value due to the airflow being influenced by the surfaces, but I don't understand how wing characteristics could influence a device in the front of the plane.

But I still doubt it's just a matter of taking the real AoA and applying a 2x factor (as it seems to be in the case of the mig-21). No other redfor aircraft have such a drastic deviation, the worst of them have about 5° extra at high AoA (and at 10° less it's almost margin of error). In fact all of them can pull higher AoA (measured by the game) than the 21 (which can only do 16° before the sudden stall).

So at the end I don't know how some sources claim the 21 is capable of achieving AoA's comparable to "modern" fighter jets. While the one in the game can't even do better than a su-25.

Just out of curiosity I took some close screenshots of both pitot and fuselage vane at high AoA. The fuselage one has an extra 5° (which don't add up to the 20° on the indicator, considering near 10° pitch). I'm pretty sure the pitot one should be very well aligned with the horizon, but all of it could be just a 3d model oversight.

68FxPxh.png


Edited by Skuva
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Air bunches up. The pressure wave from a leading edge of a wing can influence areas farther forward just like a wave in front of a ship's bow. The actual CL graph can be extracted from DCS by experiment and compared to known CL curves from the real life aerofoil.

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7 hours ago, Ala13_ManOWar said:

Those screenshots of you two in external views can't be exactly "right" either. Real AoA isn't the angle between wing chord and a horizontal line, or even the free flow incoming, you can fly descending with that attitude shown, still be flying, and AoA wouldn't be what you think you're visually seeing as is obvious. That's why a external pic showing whatever isn't actual AoA whatsoever.

 I have no clue what your blabbering about...
lOQkxha.png

7 hours ago, Ala13_ManOWar said:

AoA is meant to be the difference between a high pressure spot below leading edge (which is not just the wing foremost spot), and the incoming airflow which is not either just the free air current,

??????? wut

7 hours ago, Ala13_ManOWar said:

but the corrected flow angle because a wing moving through a dense fluid pushes air downwards even before it reaches the wing. Because of that, actual AoA can be either lower or higher than what you visually think you're seeing.

Not quite... and this is downwash angle and only matters for the surfaces behind the main wing.

7 hours ago, Ala13_ManOWar said:

Now, the delta wing as you know in fact needs AoA to fly, without any AoA there is no lift at all

No, if the airfoil is non symmetric you get lift even at 0deg AOA:

image.png

7 hours ago, Ala13_ManOWar said:

(you could run the whole Groom Lake 7Km runway and still the plane wouldn't take off without AoA no matter how fast and wheelless you get),

Assuming the wing isn't canted on the aircraft maybe.

7 hours ago, Ala13_ManOWar said:

which is true for almost any wing profile but specially true in delta wings,

lol wut

7 hours ago, Ala13_ManOWar said:

so it makes perfect sense I can get a variometer showing 0 (next time BTW show also airspeed in the screenshot), KPP showing 5º nose attitude which is not AoA, while actual AoA reading (measured with a couple of small pieces on the nose to get them out of wing or any disturbing influence) can be 10º and those 10º are the ones making you fly. But, in the F2 screenshot view shows AoA to be 4.9º which is what your KPP nose attitude reads (so not that bad), and as per devs explanation it wouldn't match AoAmeter and that's normal.

No, lets assume here wings camber is in line with the nose angle, that would mean that the flight path vector is 5deg below the horizon which by definition means you cannot be in level flight.
 

7 hours ago, Ala13_ManOWar said:

By the way, even in the Hornet screenshots there are inconsistencies, the HUD showing 10ºAoA but your velocity vector isn't 100% over the horizon, following your logic that means actual AoA should read 10'somethingº but it doesn't? No, it means velocity vector isn't the free flow either so it's no exact reference to eyeball an AoA. If AoA actually matches at some point nose high attitude in the Hornet it's because it's designed like that, meaning nothing to the MiG-21.

By definition the velocity vector is the direction your flying, and is equivalent to the angle of the oncoming flow.

7 hours ago, Ala13_ManOWar said:

Also, bear in mind anyway a Hornet isn't delta wing either, you should try to compare at least with something comparable, another delta wing plane at the least (M2000 is the only available in DCS, I believe), even though different wings with different profiles and designs aren't exactly comparable either, but at least it would be closer to start with.

I fail to see how this at all relevant here.

7 hours ago, Ala13_ManOWar said:

Edit: Funnily enough OP title says "critical AoA" which is a whole different thing either 😅.

I suggest you re-read the OP it really seems like you didn't actually read it.


Edited by nighthawk2174
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On 5/21/2022 at 1:02 AM, Skuva said:

As I'm no expert on any of this.

Clearly.

The reason the AoA is not a direct relationship (and also why the fuselage vane - which is the one UUA uses, the others on the probe are for the gunsight) is because the airflow over the vane is already disturbed by the aircraft. This is also why older American aircraft use "units" of AoA, not degrees, with "units" being an arbitrary measure that takes this effect into account. If you make the assumption pitch angle = AoA, you're very quickly going to come unstuck when dealing with a lot of aircraft, not only because they lack flight computers that can run the equation to get true AoA from the local AoA, but also because not everything has a 0 degree angle of incidence wing.

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It seems most people here have a misconception about what angle of attack is and how it's measured.

The angle of attack of the aircraft is defined as an angle between free-stream flow vector projected to the vertical reference plane (usually the plane of symmetry) and the longitudinal axis of the aircraft. This axis can be technically arbitrary and is up to the designers of the aircraft to define, but usually it's often (but not always - and in fact it's up to devs how it's gonna be defined in DCS and shown on the info panel) either parallel to chord line at some point along the wingspan (which one is, again, arbitrary but usually it will be the root chord or mean aerodynamic chord) or defined in such a way that the lift coefficient at 0° AoA is 0 (this is called a "zero-lift axis").

In order to measure aircraft's angle of attack, you have to measure the component of free stream vector parallel to symmetry plane. Problem is, that IRL it's impossible to obtain directly it in flight. Unless you use optical methods (which are only practical in wind tunnels) the very presence of the instrument (the aoa vane) as well as the aircraft itself will deflect the flow not just around the aircraft but even some distance in front of it. This is why the DUAS probe is mounted where it is, as it attempts to obtain AoA and sideslip as close to free stream as possible. But that's not what the UUA uses. UUA uses the AoA vane to the left of the inlet - well within the "disturbed" airflow. And it's the only indication available to the pilot, which is why most documentation that is easily, publicly accessible for the MiG-21bis uses UUA indications as reference, unless stated otherwise (or unless it's wind tunnel testing - which I'm yet to find for the 21bis), and not the "real" AoA.

So yes, the info panel AoA is the more accurate AoA measurement, because it's taken directly from the simulated state vector. Problem is that it's useless. And any characteristics you will find for the aircraft use the "wrong" AoA as reference because IRL the pilot can't press F2 and/or ctrl-y to see the info bar.

As to why F-18 shows you "real" AoA - it's because there's usually an approximate mathematical relationship between measured and real AoA that can be obtained for each aircraft, and the computer can calculate it for you. The UUA on the other hand shows you the angle of deflection of the AoA vane rather than your angle of attack, it's not an electronic system. Think of its indications in same categories as the AoA indicator in the F-14. There's in fact a formula somewhere in MiG-21 manual (or flight characteristics, can't remember) that tells you how to calculate your approximate "real" AoA from the UUA indication.

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2 hours ago, rossmum said:

Clearly.

There is no need to be salty.

I'm not advocating on anything here. Just trying to understand how things work (and if something doesn't work, express my concern, as I paid for it).

I get even more concerned when looking at many other similar threads (there are dozens of them at this point), because they all go the same way. Someone asks something about the 21, then a bunch of "experts" come and give the wildest explanations for it (not getting near a consensus), then a dev might or might not come, talk some pr stuff along the lines of "it is what it is". And there we have another thread without a proper answer to the question, not getting anywhere or getting anything done, wasting everyone's time.

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The explanation myself, Torbernite, and Frederf gave are hardly wild - they're exactly what you'll find if you read the aircraft's flight manual, or for that matter any aircraft's flight or technical manuals from that era, or if you ask mechanics, or aerodynamicists. You are trying to derive angle of attack of the wing from the aircraft's pitch angle which makes absolutely no sense, even before considering the position of the AoA vane and the effect of the airflow off the aircraft itself.

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I think you are all missing the point. The developer has already stated that the AoA on the UUA is the true AoA and is what the flight model is using. The point is that they claimed the F2 view is the pitch angle, and not the AoA, which was supposed to be the reason we stall when the F2 view is about half what the UUA indicates. But clearly the F2 view is in fact the AoA, as the game sees it, and not the pitch angle. So the Mig-21 is using the wrong data point as its AoA measurement and that is resulting is us exceeding the critical aoa at a much lower actual AoA because the flight model of the Mig-21 is seeing a completely different number. 

unknown.png

 

As per actual documents, and the behavior of Delta wings in general, we should be stalling at about 28-33 degrees and not 15-16 like the flight model does right now. 


Edited by KenobiOrder
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19 minutes ago, Skuva said:

There is no need to be salty.

I'm not advocating on anything here. Just trying to understand how things work (and if something doesn't work, express my concern, as I paid for it).

I get even more concerned when looking at many other similar threads (there are dozens of them at this point), because they all go the same way. Someone asks something about the 21, then a bunch of "experts" come and give the wildest explanations for it (not getting near a consensus), then a dev might or might not come, talk some pr stuff along the lines of "it is what it is". And there we have another thread without a proper answer to the question, not getting anywhere or getting anything done, wasting everyone's time.

Go read an aerodynamics handbook, you'll see for yourself. Or learn Russian and read the original 21 manuals. I've explained to you how an AoA vane works and what the UUA-1 displays. That's what Dolphin referred to as "local angle of attack" - it's the angle of attack relative to airstream at the point it was measured, not in the free stream. If you think I'm lying, go read the original sources.

You're saying "you're not advocating on anything" but your accusatory tone suggests otherwise.


Edited by m4ti140
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11 minutes ago, KenobiOrder said:

I think you are all missing the point. The developer has already stated that the AoA on the UUA is the true AoA and is what the flight model is using. The point is that they claimed the F2 view is the pitch angle, and not the AoA, which was supposed to be the reason we stall when the F2 view is about half what the UUA indicates. But clearly the F2 view is in fact the AoA, as the game sees it, and not the pitch angle. So the Mig-21 is using the wrong data point as its AoA measurement and that is resulting is us exceeding the critical aoa at a much lower actual AoA because the flight model of the Mig-21 is seeing a completely different number. 

He didn't say it's "true" AoA, he called it "local" AoA. That's exactly what it is.

By "relative pitch angle" he means that the angle shown in F2 view is arbitrary based on how body axes are defined in DCS, with no direct correspondence to how they're defined in documentation for the real aircraft. I don't know how he coded the FM but from what he says, he isn't using that value as reference for calculations.

Note the he's not a native English speaker.

The documents for MiG-21 you're referring to use UUA indications as reference, not the real AoA. They explicitly say it's in reference to UUA. And you have all those critical angles marked on UUA-1 gauge itself.

Just because delta wing aircraft can technically go to higher AoA doesn't mean one of the first delta wing designs will be able to go there. Mirage 2000 is limtted to ~30 IIRC despite having vortex generators to delay wing rock. 21 has other issues with it aerodynamics that limit usable AoA.


Edited by m4ti140
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16 minutes ago, m4ti140 said:

This is literally Flat Earth approach...

Go read an aerodynamics handbook, you'll see for yourself. Or learn Russian and read the original 21 manuals. I've explained to you how an AoA vane works and what the UUA-1 displays. That's what Dolphin referred to as "local angle of attack" - it's the angle of attack relative to airstream at the point it was measured, not in the free stream. If you think I'm lying, go read the original sources.

You're saying "you're not advocating on anything" but your accusatory tone suggests otherwise.

 

Can you recommend a good book/article that teaches this sort of stuff? That preferably touches the topic here.

I'm not accusing anyone to be wrong, sorry if it sounded like it, I'm genuinely in doubt, I'm reading what to me looks like very different answers to the same question, and they mostly disagree with what makes sense to me.


Edited by Skuva
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15 minutes ago, m4ti140 said:

He didn't say it's "true" AoA, he called it "local" AoA. That's exactly what it is.

By "relative pitch angle" he means that the angle shown in F2 view is arbitrary based on how body axes are defined in DCS, with no direct correspondence to how they're defined in documentation for the real aircraft. I don't know how he coded the FM but from what he says, he isn't using that value as reference for calculations.

Note the he's not a native English speaker.

The documents for MiG-21 you're referring to use UUA indications as reference, not the real AoA. They explicitly say it's in reference to UUA. And you have all those critical angles marked on UUA-1 gauge itself.

 

He referred to it that way because he was making a distinction between the pitch angle and the AoA, as per the image in my first post. He also states that the UUA readout is the local AoA and that is what is implemented in the FM code. The discrepancy is that he thinks the F2 view and tacview arent showing AoA, but pitch angle, which is not correct. Whatever angle he has coded is erroneous and is resulting in us stalling at about half the approximate value we should be. 

Regardless of what the Mig-21 base their angle on, deltas do not stall out at 15-16 degrees angle of attack like it is in game right now. Deltas have a lower slope than say a straight wing like a ww2 plane, but they generate a slightly lower Cl Max at a much higher max AoA. Whatever the true value of the AoA, our current stall is far too shallow. 


Edited by KenobiOrder
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9 hours ago, nighthawk2174 said:

 I have no clue what your blabbering about...

Saw it coming, sorry I couldn't explain myself better. I'll tell you a secret. Even in PPL they tell you AoA is just "free flow current against wing chord", that's the theory and what they expect you to answer in tests. BUT, then again if you happen to have a curious enough instructor/teacher, they tell you, "but even that isn't exactly true if you go CPL/ATPL, the real deal is that other thing". And that thing is there's a low pressure spot below leading edge (zero pressure indeed) in any given wing, and AoA is measured against that spot, not actual foremost leading edge spot. PLUS, as I said, and m4ti140 also explained, free airflow isn't just straight line in front of you since an object submerged in a dense fluid while moving actually displaces the fluid even before you reach the place where fluid has already been displaced, you displace fluid ahead of you even though you haven't reached the physical place. Hence, "free flow" isn't either that straight line just in front of the wing. Actual AoA is the difference between low pressure spot and the already "curved" flow in front of you.

My point being, if you understood any of it, that's why one can't just press F2 and eyeball the angle one thinks to be seeing between the direction one thinks aircraft moves and actual aircraft seen and say that's "real" AoA. Even less one can take a screenshot from a different aircraft, since delta wings are quite a special profile kind, and directly compare. Just that 🤷‍♂️.


Edited by Ala13_ManOWar
typo

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-- Major-General Frederick B. Maurice

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36 minutes ago, KenobiOrder said:

As per actual documents, and the behavior of Delta wings in general, we should be stalling at about 28-33 degrees and not 15-16 like the flight model does right now.

The "actual documents" you mean are, I'm going to guess, the original flight manuals - which explicitly state 28 and 33 degrees as indicated by the UUA-1, which is the AoA gauge, which tells you what the DUA sensor reads, which is on the side of the fuselage and not in clean air. Every single chart I have seen for the 21 across flight manuals and memoranda references the UUA. I have never seen one that references true AoA, as that would be absolutely useless to the pilot as he has no point of reference except UUA-1. What it says is law as far as he is concerned.

Where do you guys think the Americans got all those AoA values from when they test flew the aircraft? Magic? A bolted-on F/A-18 air data computer reconfigured to derive true AoA from the UUA reading? No, they referenced the gauge in the aircraft, just like US manuals reference units of AoA rather than true angles. The pilot has no use for units of measurement he doesn't have access to in flight.

I already know which paper you guys have read, which is somehow leading you to draw the conclusion that our 21 has been unfairly treated and should be able to turn with modern fighters. You should not read too much into a single paper, especially when it leads you to conclusions that fly directly in the face of documented Soviet and American flight testing.

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Actually, while I'm here - if you want to see some of the magical nose authority you guys want, make a hard, sharp pull at reasonably low speed and full power or afterburner. Make sure the aircraft is wings level and the slip ball centred, or if you're in a turn, that you have it perfectly balanced. The aircraft will either rock its wings briefly and then stabilise, or it will not even wing rock at all, and will enter an extremely stable state where it's basically hanging in the air on its thrust. Maybe that approaches what you're expecting, but it's debatable if the aircraft should even do it, considering that at such a high AoA the wing is fully shadowing the vertical tail surface and the ventral strake is no longer enough to maintain directional stability. Now perhaps you've got a better idea of why the MiG-21 departs where it does. It's not a Mirage 2000 with vortex generators, dogtoothed leading edge slats, and fly by wire... it's a 1950s aircraft. You cannot expect modern performance out of it just because a single academic paper told you (with a bunch of qualifiers, I should add) that the 21 still has some relevance in the modern age due to manoeuvring potential.

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14 minutes ago, rossmum said:

The "actual documents" you mean are, I'm going to guess, the original flight manuals - which explicitly state 28 and 33 degrees as indicated by the UUA-1, which is the AoA gauge, which tells you what the DUA sensor reads, which is on the side of the fuselage and not in clean air. Every single chart I have seen for the 21 across flight manuals and memoranda references the UUA. I have never seen one that references true AoA, as that would be absolutely useless to the pilot as he has no point of reference except UUA-1. What it says is law as far as he is concerned.

Where do you guys think the Americans got all those AoA values from when they test flew the aircraft? Magic? A bolted-on F/A-18 air data computer reconfigured to derive true AoA from the UUA reading? No, they referenced the gauge in the aircraft, just like US manuals reference units of AoA rather than true angles. The pilot has no use for units of measurement he doesn't have access to in flight.

I already know which paper you guys have read, which is somehow leading you to draw the conclusion that our 21 has been unfairly treated and should be able to turn with modern fighters. You should not read too much into a single paper, especially when it leads you to conclusions that fly directly in the face of documented Soviet and American flight testing.

Right so you have no idea where I am coming from. I am pretty sure you think I have read that bull<profanity> paper regarding the supposed magical agility of the Mig-21 written by two guys whose names I cannot pronounce or remember. 

Except I am not. I don't think the jet should turn with modern planes, far from it. The 21 cannot even turn with the IRL F4, much less a F-16.  Not sure where you got that from either aside from making wild irrational assumptions about my goal here. 

Making the jet stall at the correct critical AoA would not result in a magical turn fighter. It would only mean that we wouldn't get artificially stuck faffing about at 15 degrees of AoA when doing an unsustained turn. The Mig-21 doesnt have the thrust necessary, so while we would get to the proper AoA the sustained turn performance would still be worse than the current in game max sustained turn performance which is about 12-14 degrees a second. 

In game right now if you get below 400kph the wing rock magically goes away for some reason, and you can pull over 30 degrees of AoA as per the F2 view. But even with Emergency Burner, you are not going anywhere. Your stuck waffling about at 300kph, which is fine. 

The problem is we cannot generate reasonable levels of instantaneous turn performance due to the incorrect amount of AoA we pull. 

The mig-21 we have in game right now is stalling in a manner that is consistent with straight winged world war two prop planes, not a Delta wing. 


Edited by KenobiOrder
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1 hour ago, Ala13_ManOWar said:

Saw it coming, sorry I couldn't explain myself better. I'll tell you a secret. Even in PPL they tell you AoA is just "free flow current against wing chord", that's the theory and what they expect you to answer in tests. BUT, then again if you happen to have a curious enough instructor/teacher, they tell you, "but even that isn't exactly true if you go CPL/ATPL, the real deal is that other thing". And that thing is there's a low pressure spot below leading edge (zero pressure indeed) in any given wing, and AoA is measured against that spot, not actual foremost leading edge spot.

This doesn't make sense, yes across the lower surface you will have a point where CP=0 (infact depending on the wing shape multiple points may exist).  But I see no way to derive the angle of attack from the position of these points.

1 hour ago, Ala13_ManOWar said:

PLUS, as I said, and m4ti140 also explained, free airflow isn't just straight line in front of you since an object submerged in a dense fluid while moving actually displaces the fluid even before you reach the place where fluid has already been displaced

Yes although the range of this effect is rather quite limited.

1 hour ago, Ala13_ManOWar said:

 Actual AoA is the difference between low pressure spot and the already "curved" flow in front of you.

I have no clue what your talking about.

1 hour ago, Ala13_ManOWar said:

My point being, if you understood any of it, that's why one can't just press F2 and eyeball the angle one thinks to be seeing between the direction one thinks aircraft moves and actual aircraft seen and say that's "real" AoA. Even less one can take a screenshot from a different aircraft, since delta wings are quite a special profile kind, and directly compare. Just that 🤷‍♂️.

 

The downwash will just reduce your total effective lift requiring a small increase in aoa to compensate. The effect is a local effect impacting the area near the wingtip, hence the effect drops off with higher aspect ratio wings, or with wings that include a small twist into the wing.

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Just telling mate, whatever you want to understand out of that (and I acknowledge my explanation here is probably not quite good without the specific technical terminology and me being no English native, not to mention I have no intention here of digging a PhD about the subject just to please a few ones' unsupported suspicions) is up to you.

Still, you can't just F2 and say "this is true AoA because my guesswork is good enough for designing high performance fighter jets" 🤷‍♂️.

"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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12 minutes ago, Ala13_ManOWar said:

Just telling mate, whatever you want to understand out of that (and I acknowledge my explanation here is probably not quite good without the specific technical terminology and me being no English native, not to mention I have no intention here of digging a PhD about the subject just to please a few ones' unsupported suspicions) is up to you.

Still, you can't just F2 and say "this is true AoA because my guesswork is good enough for designing high performance fighter jets" 🤷‍♂️.

I think the OP is right though delta's stall near 30deg that is their typical critical angle of attack.   Its one of the features of this wing design.  However in game this is not the case, the aoa where you stall out is half of what is typical for delta's which is a major discrepancy.  The ingame value listed in F2 is angle of attack and its showing a value half that of the guage.  And as said by the devs the AOA being used by the FM is this value.

 

On 5/20/2022 at 9:02 AM, Skuva said:

You don't even need to go that far to conclude the AOA indicator is very wrong.

WQwe6K0.png

 

The most... "sane" (huge strech on that word)... explanation I read for that was that the soviets intentionaly made the indicator give higher values just so it would scare pilots and force them to better follow "by the books" procedures (????). But if the FM realy takes that value as the "true AoA", them from what I understand, the plane will never be able to achieve those 25°+ of AoA both soviet and american sources claim to achieve. Not only that, but it would greatly affect how drag is calculated, messing up low speed characteristics, which is another problem recurrently brought up by players.

 

As I'm no expert on any of this. I can just hope after the Corsair launch M3 will go back to research and iron out all the 21's FM weirdness, or at least give reasonable explanation on why it is the way it is.

 

I doubt that the indicator is actually off by 100% irl, this would be extremely weird.  Delta's just by their inherent design have higher stall angles then conventional wings. The gauge even shows this with the red stall region being near 30deg.   In game our wing is entering the stall regime at the same point as conventional wings.    Would there be some small errors sure, but it has an aoa sensor well away from any disturbance.  I think you are correct in being suspicious.

 

3 hours ago, Skuva said:

Can you recommend a good book/article that teaches this sort of stuff? That preferably touches the topic here.

I'm not accusing anyone to be wrong, sorry if it sounded like it, I'm genuinely in doubt, I'm reading what to me looks like very different answers to the same question, and they mostly disagree with what makes sense to me.

 

Aerodynamics for naval aviators is a amazing place to start.  It has some of the best-better explanations of aerodynamic concepts i've seen.  It is freely available on the internet.

 

3 hours ago, rossmum said:

The "actual documents" you mean are, I'm going to guess, the original flight manuals - which explicitly state 28 and 33 degrees as indicated by the UUA-1, which is the AoA gauge, which tells you what the DUA sensor reads, which is on the side of the fuselage and not in clean air. Every single chart I have seen for the 21 across flight manuals and memoranda references the UUA. I have never seen one that references true AoA, as that would be absolutely useless to the pilot as he has no point of reference except UUA-1. What it says is law as far as he is concerned.

Where do you guys think the Americans got all those AoA values from when they test flew the aircraft? Magic? A bolted-on F/A-18 air data computer reconfigured to derive true AoA from the UUA reading? No, they referenced the gauge in the aircraft, just like US manuals reference units of AoA rather than true angles. The pilot has no use for units of measurement he doesn't have access to in flight.

I already know which paper you guys have read, which is somehow leading you to draw the conclusion that our 21 has been unfairly treated and should be able to turn with modern fighters. You should not read too much into a single paper, especially when it leads you to conclusions that fly directly in the face of documented Soviet and American flight testing.

I don't think that's the case that the OP is making in the slightest, I think he's right about this.  Plus small disturbances near the airframe CANNOT explain a value double the actual AOA value. 

 

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The MiG-21 has historically not had the DUA sensor on the fuselage. That was added at some point I think slightly before the bis variant. I'm gathering the assertion is that UUA-1 is in degrees wherein a "20" on the gauge indicates a rotation of the fuselage vane of 20/360ths of a circle, yes?

Limit of UUA-1 is not wing lift but controllability. If curious I did experiment to find UUA/true AOA relationship in... 2016.

MiG-21LocalTrueAOA.gif

Correlation was high confidence. It's not 0=0 and 2x the slope simply.

If you expect higher CL from more AOA then you will be disappointed. Maybe AOA/UUA-1 relationship is wrong but CL relationship is not that far off. Performance won't change but body angle would.

Fig6 CyM Russian 2.gif

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