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The new critical angle of attack might be too low!


Maverick Su-35S

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  • 1 month later...
Few quick answers:

 

- UUA shows local angle of attack (note local)

- F2 view in human module will show you relative pitch angle although it says AoA

- local angle of attack is greater than relative pitch angle about 2 times

- exact local AoA calculation is implemented in the code

 

The only correct information about local AoA is what UUA shows.

 

So why is the drag at ~5° (= ~2.5° actual) so excessive that the MiG bleeds of speed so much even in a slight turn? I flew it a few times now after it stood in the hangar for years. Without using the afterburners, this plane feels like a total brick that is in dire need of an engine. Completely different to what it was like to fly when it came out. Back then, I was able to take off with 90% N1/N2 with 2 UB-32 and 2 UB-16 plus a small tank with ease. And it went over 1000 IAS on max mil and around 750-800-ish at 90% after dropping the bag. Now the max I get out of her is around 750 on full mil with those pods.

Was possible to do some ground attacks and do the turnaround by pulling up to 60° gently (like 10° max on the "clock"), then flip her around and pull hard for 180° until she points 60° down in the direction where the targets are, then ease off the stick to lower AoA and gain speed quickly, coming in at the targets again at 800+. Try this now. It's impossible even at full mil, and even without the pods, she still struggles a lot if not at full mil at least. I always have been wondering what it is with all that fuzz about the FM, but now I see it. Also, on takeoff with that load, it's possible to get off the ground with full mil, but not with 90% anymore. But then, as soon as I'm airborne, she just can't pick up speed at all until I kick in the burners or drop stuff.

Also, on landing finals, I used to run her at ~80-85%, now I even struggle to keep speed up high enough at 90%+.

At any flight condition, pulling back the throttle to less than 90% feels like deploying airbrakes... also, when running at M2, just reducing the AB level will result in a rapid speed loss, switching it off completely is almost like opening the drogue chute. Do that in the Hornet or any other supersonic module and she'll take ages do drop her speed off to ~M 1.

 

I can't put in the hard facts, but just tell what I noticed. There definately is something way off at the moment.

 

PS: Just another thing... she still wiggles around prior to rotating and lifting off so very excessively at 250+ that I'm totally frightened the plane just flips over and lawndarts itself. I can't even imagine how that could be explained with physics... and I don't remember it being that excessive some years ago although it definately has been there since the beginning.

 

PPS: FFB trim is fixed which is great, but it still has some "jump to center position" weirdness happening while actuating the trim.

 

Still a great module and fun to fly nevertheless salute.png

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The bricks are the UB rocket launchers. Lot of drag. Keep in mind that the MiG-21 was designed to be an interceptor, not a multirole aircraft. The wing loading is very high and the shape is optimized for supersonic conditions. Delta wings are notorious to bleed energy a lot in maneuvers.

 

The deceleration without thrust is greater when the aircraft weight is lower. It's the only parameter that changes (inertia) while the external forces on aircraft are the same when compared with larger aircraft types.

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- local angle of attack is greater than relative pitch angle about 2 times

 

"About two times" is a very wide and unprecise definition, in Polish AF this value was 1,7 what means that stall angle is ~19,5 deg. ( 33 deg. UUA-1 ). Even if 2 is true number this gives us about 16,5 deg, now in game we have 14 deg. Every 2-3 deg. is a big difference.

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There are different measures of lift: true AOA, local AOA, Coefficient of Lift

 

 

C-L maximum for MiG-21bis seems pretty believable and correct at least to "legal limits" of UUA indication. Otherwise instant turn authority would not match. What I do significantly doubt is the accuracy of the C-L curve in shape if not maximum value. We might be very happy with C-L is 0.9 or 1.0 or 1.1 or 1.2 at peak lift AOA but what angle is it when it drops to 80% of its peak? I estimate that this angle should be much greater than we see currently. C-L should be higher into the 20s and 30s of true body angle.

 

 

 

True AOA or especially indicated AOA might be well off though. Currently the wing stalls (peak C-L) at exactly the same indicated AOA at all Mach. And this simply isn't so by real documents. For a narrow range near M0.9 33 indicated is C-Lmax and stall. But below this range C-Lmax occurs much above 33 indicated. It's right there in the real documents.

 

 

But both of these might be off in opposite directions in a way that balances the errors. For example down at M0.4 the stall units of indicated AOA are much much higher than 33. But the C-Lmax we achieve there is about what the DCS module provides. And we can't be sure of the true AOA at all since there isn't a good record (that I have) how true AOA relates to any of these other values over the Mach range.

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  • 2 weeks later...

There is defenitly a lot wrong with the Mig21 as it is now: it's slow and underpowered and stalls all the time even when going vertical. I used to be able to beat the F-4 quiet easily in the "instant actions" missions, but now it's just impossible. The max. AOA is way too low now, which cuases it to stall in a dogfight all the time.........................My favorite plane is totally ****ed up now :-(

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There is defenitly a lot wrong with the Mig21 as it is now: it's slow and underpowered and stalls all the time even when going vertical. I used to be able to beat the F-4 quiet easily in the "instant actions" missions, but now it's just impossible. The max. AOA is way too low now, which cuases it to stall in a dogfight all the time.........................My favorite plane is totally ****ed up now :-(

 

I just tried to dogfight an AI mig 21 in a mig 21 and it was running circles around me even at the same speed range, it just sustains way more aoa and accelerates faster, in the same dive at the same speed he pulled up climbed, managed a split s and got back on my tail all in the same time i had just got out of an aoa stall.

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so you're saying that we have to have two different styles to fight the same aircraft? how does that make any sense, surely you want this to be uniform as ED strives for a realistic simulator.

 

Imho, if DCS would do for AI all those calculations, which is doing for human plane, game would be to much CPU demanding...


Edited by blokovchan
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so you're saying that we have to have two different styles to fight the same aircraft? how does that make any sense, surely you want this to be uniform as ED strives for a realistic simulator.

 

Well, that's how it is. A lot of sims do this to save CPU time, this isn't new.

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Imho, if DCS would do for AI all those calculations, which is doing for human plane, game would be to much CPU demanding...

It is all in the programming (not an expert but) coding the AI to use the same stick forces and stick movement as a human pilot would solve all of this repeating AI maneuvers, plus skill level should relate to how the AI is "learning" as you fight and responds to the BFM. But That is for another thread..

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It is all in the programming (not an expert but) coding the AI to use the same stick forces and stick movement as a human pilot would solve all of this repeating AI maneuvers, plus skill level should relate to how the AI is "learning" as you fight and responds to the BFM. But That is for another thread..

 

I was referring to flight model, as you say AI behaiour is another topic, and it should be addressed also... :)

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  • 1 year later...

Ability to achieve with MiGs delta wing as much as 20 degree according to real pilots, not possible. Maximum is around 15 degree which is even less than F-5 without delta.

We want this fixed more than any other bugs or external 3d model or textures.

Edit: Delete this post, found how to achieve such high AoA without big problems.


Edited by GumidekCZ
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  • 1 month later...
Ability to achieve with MiGs delta wing as much as 20 degree according to real pilots, not possible. Maximum is around 15 degree which is even less than F-5 without delta.

We want this fixed more than any other bugs or external 3d model or textures.

Edit: Delete this post, found how to achieve such high AoA without big problems.

 

Were you able to keep the DCS MIG-21 at around 20 AoA without having it's wings stalled (losing lift)?

 

Again, I say this from a MIG-21's pilot experience (not me) who used the pitch attiutude and vertical speed indicator (held very close to zero) during the plane's wing stall. It was around +20 AoA. 15 AoA is what a Cessna 172's wing has as critical. A low aspect, high sweep delta which also generates some small intensity vortexes near the fuselage and which gradually dissipate along the leading edge, yet a bit useful to keep the flow attached closer to the fuselage, is a wing that has more than just 15 AoA as a stall limit. It's more than common sense for those who know some aerodynamics. All of these characteristics give the 21's delta wing a critical AoA of around 20-21. Take the M-2000's wings for example which are just close enough in terms of planform shape and still have a critical AoA going over 30. Don't imagine (without knowing anything) that the M-2000's wing or any other modern aircraft wing has some wonder making effects and the older wings didn't have. The general shape of the wing's planform is what gives more than 70-80% of it's overall performances, while only 20 to maximum 30% would be the airfoils designs that affect performances. The M-2000's wing can go a bit beyond 30 AoA before a pitch departure will occur, but it's limited by FBW to only 28..29 to avoid the departure. And no, it's not increasing from a 15 AoA (as you might believe or as LLC's mistake wants you to believe) to more than 30 just due to the leading edge droops or due to those small vortex generators on the inlets, which are not even ahead of the wing to affect it considerably and which were actually put there to increase the directional stability at higher AoAs. The most performant leading edge droops usually increase your AoA by no more than 6, while most help the wing with around 4..5 critical AoA increase. Compared to the MIG-21, the M-2000 can go slightly over 30 real AoA before the complete wing stall occurs due to both the effects of slightly lower aspect ratio and higher sweep as well as the LE droops + some benefit from the inlet strakes. So as I say again, that's no leap from just 15AoA, but from rather at least 20 as described.

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I think you've misunderstood him. He was stating that he was unable to pass 15 and that real pilots attest to 20, but Czech syntax and English syntax are a bit different and so the word order appears reversed.

 

e/ reading is hard. Looks like most questions have been answered here so my input beyond the above is not really adding anything.


Edited by rossmum
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On the Mirage 2000 comparison, you speak of advantage it must have to reach higher AOA. Well I’m sure one of those is higher Reynolds numbers, with a larger wing air molecules are proportionally smaller so with similar characteristics such as sweep it can still have better characteristics. It also had leading edge slats, and strakes above the wing rather then 21 where they are below the wing.

 

Just saying those slats, higher Reynolds number, not to mention how thick it is could all help it have that high critical angle. And I don’t even know if it has washout like most tailless deltas, I’m sure it does. I believe the 21 has a wing with no washout or wash in, perfectly flat. So that would also hurt it when it comes to critical AOA, but a wing with no washout also has less drag and better speed characteristics, so it makes sense that Mikoyan would make that decision to keep it flat.

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