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The new critical angle of attack might be too low!


Maverick Su-35S

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I heard original installation of AP-155 autopilot (predecessor to SAU-ESN) did not connect to AOA sensor at all but I guess SAU does.

 

The side-vane was MiG-21PFSM which was a little before an autopilot? Were they thinking ahead?

 

Yeah booms bend and bounce. The bending is probably not such a big problem but oscillation when connected to an autopilot sounds like real bad news.

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The earliest manual for the equipment I have access is mig21m... and as you can see on the picture DUA3 is part of the AP155 system.

 

Regarding your question, I can only speculate regarding earlier birds... all I know is that retrofitting could be done.. also export 21 could be lacking some features from Soviet's at given time period...

ap155.thumb.jpg.76401bd14b289d77ee63e645a9107485.jpg

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Returning to the topic: Why had Leatherneck brought down the critical AoA from 20+ to about 15? The landing speed as well as the minimum speed at which the plane still has 1G at critical AoA (so called stall speed) isn't different, which proves that the lift/AoA slope is steeper now, so this needs to questioned and answered. I consider the older flight model's AoA more true than this. Although some aspects were made better within the flight model, some have been made worse, so it still needs tweaking to make it right!

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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So I'd say we have all of this reasonably well figured out, now we just need to wait until LN is done busting their asses finishing the Viggen....

 

I hope they won't forget about the MIG-21's flight model and let it go on like this, because there are very important things regarding the simulation of the real plane's performance (which for now is too high in terms of lifting forces alone) and the ability to simulate an authentic dogfight with another jet. There's another thread regarding the MIG-21 flying at quite negative AoA in supersonic. Not even the in-game tested F-15 or Su-27 can do such thing, planes which have a lower wing loading than the MIG-21.

 

There's still quite a lot of work from LN to get the MIG-21's FM reach ED's standards, from my point of view and I can only wish them what is best in order to finally achieve it.

 

I don't want to look impatient, but I suppose that what anyone else wouldn't like to see, is that unfinished stuff would remain unfinished or get forgotten!

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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Yep, I also feel the FM sort of degraded nowadays. Especially the mentioned high AOA handling and behavior.

"See, to me that's a stupid instrument. It tells what your angle of attack is. If you don't know you shouldn't be flying." - Chuck Yeager, from the back seat of F-15D at age 89.

=RvE=

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Think like the AOA is getting a lot worse in OB today. I will have a better day maneuvering with the frogfoot.

 

EDIT: Had a quick check the su-25 will go above 15-16 AOA (F2 Indicated) at 500 km/h, M2k will pass easily 18-20 AOA same speed, Mig21 will never pass 15 AOA before stall, then AOA will go 28-30.

 

Hope this will be adressed to the dev's and will not make it to stable.


Edited by BadHabit

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Literally I've been getting back into this bird. But I get a huge wing wobble at times, something just doesn't seem right.

 

I'm going to hold off on my tutorial studies with the Bis. I'll stick with the MiG-15, Sabre, and the WWII stuff for now. I'll lurk (and learn) from you guys, and then jump back in at some point...

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Gents, there were some test values left in the release bins. Hopefully the next update will fix it back.

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Hey Rudel, did the bin fixes make it in to DCS 1.5.6.1648 Update 2017-02-03 ?

 

Something must have happened as performance has changed again. Things seem to be much better. I was initially way fast on all of my approaches since the MiG-21 holds onto speed better than before (doesn't require full mil-thrust to maintain speed in the approach config any longer). Also, I can't sustain flight with pegged AOA any longer (not for long that is), the aircraft bleeds off speed or the engine flames out.

 

The overall feel sort of reminds of the MiG-21 in early 2016, but with more inertia (roll inertia feels good) and much better departure characteristics.

 

Anyone else tried her out yet?

 

-Nick

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Think like the AOA is getting a lot worse in OB today. I will have a better day maneuvering with the frogfoot.

 

EDIT: Had a quick check the su-25 will go above 15-16 AOA (F2 Indicated) at 500 km/h, M2k will pass easily 18-20 AOA same speed, Mig21 will never pass 15 AOA before stall, then AOA will go 28-30.

 

Hope this will be adressed to the dev's and will not make it to stable.

 

You're right, the real AoA isn't going beyond 15 deg. for the MIG-21 which is not realistic, as even straight winged aircraft like the A-10 or Su-25 or L-39 can reach between 16 to 18 deg of critical AoA (before stall). The mig-21 should get decently to around 20 deg AoA before aerodynamics stall, but the devs must re-tweak it for that to happen.

 

The 28-30 AoA indicated in the cockpit now corresponds to only 15 real AoA, but should correspond to 20+.

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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Something must have happened as performance has changed again. Things seem to be much better. I was initially way fast on all of my approaches since the MiG-21 holds onto speed better than before (doesn't require full mil-thrust to maintain speed in the approach config any longer). Also, I can't sustain flight with pegged AOA any longer (not for long that is), the aircraft bleeds off speed or the engine flames out.

 

The overall feel sort of reminds of the MiG-21 in early 2016, but with more inertia (roll inertia feels good) and much better departure characteristics.

 

Anyone else tried her out yet?

 

-Nick

 

The rolling inertia seems quite high in relation to the aerodynamic forces which generate rolling moments for a given AoA, IAS and ailerons deflection. From my perspective, the rolling response time seems like almost twice higher than the real one. Why do you find it feeling good? You maybe like it, but it's far from real. Just visually compare (it's roughly enough anyway) the rolling response and rolling acceleration due t inertia of the MIG-21 flown by a real pilot in similar conditions as in DCS, and you'll understand that either the rolling moment of inertia of the MIG-21 in DCS is too high or simply the variation of lifting forces between the wings as the ailerons are deflected, is too low, because in DCS the 21 is too sluggish in roll response even at low AoA for a comparably high airspeed.

 

Next are some real life videos that can give you a clue of how long it takes for the MIG-21 to reach full roll rate from zero. It takes at least twice as much time for the MIG-21 in DCS to get from zero to maximum roll rate for the same flying conditions.

 

https://www.youtube.com/watch?v=0-cEdwgYdAw

 

https://www.youtube.com/watch?v=tgkfSefPAjE

 

I believe that the relation/ratio between rolling moment of inertia and rolling aerodynamic moments at a given IAS still isn't correct and still needs improvement, next to other issues this plane has at the moment.

 

I don't want to sound bad or full of criticism, but almost always the truth hurts and I simply won't feel satisfied until it's finally done well (at least 90-95% of the real jet, 5-10% error).

 

About the engine stalls at high AoA, I find it exaggerated as well! The real aircraft which was secretly tested by the Americans at Nevada never had an engine stall and they tried the best they could to make the engine flame out like their fighters at the time were encountering, but the MIG's engine simply didn't..., and that was not the BIS but an older variant of MIG-21, so how can the BIS in DCS flame out such easily if it's not intended just to make it look interesting? I don't find it right, but exaggerated to make some people think it's realistic.


Edited by Maverick Su-35S
corrected 2nd youtube link

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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About the engine stalls at high AoA, I find it exaggerated as well! The real aircraft which was secretly tested by the Americans at Nevada never had an engine stall and they tried the best they could to make the engine flame out like their fighters at the time were encountering, but the MIG's engine simply didn't..., and that was not the BIS but an older variant of MIG-21, so how can the BIS in DCS flame out such easily if it's not intended just to make it look interesting? I don't find it right, but exaggerated to make some people think it's realistic.

 

 

Indeed, the FM is still very disappointing 2 years down the line. Hopefully now the viggen is released LN can put some resources back to finishing the 21.

 

I also have the same feeling about the engine stalls having read the report you refer to, and remembering back to 1.2 version when LN erroneously interpreted the real world stores maximum G safety guidelines as absolute mechanical failure figures, leading to the pylons falling off the plane nearly every flight.

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The rolling inertia seems quite high in relation to the aerodynamic forces which generate rolling moments for a given AoA, IAS and ailerons deflection. From my perspective, the rolling response time seems like almost twice higher than the real one. Why do you find it feeling good? You maybe like it, but it's far from real. Just visually compare (it's roughly enough anyway) the rolling response and rolling acceleration due t inertia of the MIG-21 flown by a real pilot in similar conditions as in DCS, and you'll understand that either the rolling moment of inertia of the MIG-21 in DCS is too high or simply the variation of lifting forces between the wings as the ailerons are deflected, is too low, because in DCS the 21 is too sluggish in roll response even at low AoA for a comparably high airspeed.

 

Just to confirm - you're flying the 1.5.6 OpenBeta with the silent update from 2/3/17 - correct?

 

About the engine stalls at high AoA, I find it exaggerated as well! The real aircraft which was secretly tested by the Americans at Nevada never had an engine stall and they tried the best they could to make the engine flame out like their fighters at the time were encountering, but the MIG's engine simply didn't..., and that was not the BIS but an older variant of MIG-21, so how can the BIS in DCS flame out such easily if it's not intended just to make it look interesting? I don't find it right, but exaggerated to make some people think it's realistic.

 

The engine isn't stalling at high AOA, it's stalling due to low airspeed (which has been present since I started flying the MiG-21 in early 2015). The difference is that at full burner and pegged AOA, the previous MiG-21 FM could maintain speed and even climb. With the update, it cannot. Airspeed is steadily lost and the engine flames out.

 

The roll rate of that lancer doesn't seem too different from what I'm seeing IMHO. I need to use coordinated rudder and neutralize AOA, but under those conditions with airspeed above 600 km/h indicated the roll seems very reasonable.

 

Just my 2 cents,

 

Nick

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...

The engine isn't stalling at high AOA, it's stalling due to low airspeed (which has been present since I started flying the MiG-21 in early 2015). The difference is that at full burner and pegged AOA, the previous MiG-21 FM could maintain speed and even climb. With the update, it cannot. Airspeed is steadily lost and the engine flames out.

...

 

Ok but you said "OR", which led to the conclusion that it's either the speed or the AoA which causes flameout: "I can't sustain flight with pegged AOA any longer (not for long that is), the aircraft bleeds off speed or the engine flames out." For a bit of moment I was confused and I forgot that I also couldn't make it flameout due to high AoA only, but sorry, I got mislead to think that the engine also stalls due to high AoA when I replied. Indeed it doesn't flameout in the sim for any other reason than just the IAS going below a given value, but there's still a problem though! Why would it flameout when the IAS goes below "X" value when in midair, no matter the AoA (be it high or close to zero), if on the ground it doesn't flameout even at 0 IAS? What's the difference? If you know the reason why this happens, we would appreciate to know!

 

The roll rate of that lancer doesn't seem too different from what I'm seeing IMHO. I need to use coordinated rudder and neutralize AOA, but under those conditions with airspeed above 600 km/h indicated the roll seems very reasonable.

 

Even with coordinated rudder to control your AoA the way you like can't beat the crude relationship between inertia and the aerodynamic reactive forces which cause the problem I refer to. The plane is still too sluggish in roll response, period.

 

Over 600km/h? Well yes, the faster you go the less the difference between reality and the sim will get, that's very logic as the aerodynamic rolling forces/moments would be much greater than the rolling inertia, but that's not the correct way to determine the difference, right? Or are you just turning away from the facts that make you see the truth.

 

That Lancer you saw doing that takeoff roll was done at no more than 500 km/h, 450 I'd say if you'd take into account that at 400 it lifts off and the pilot didn't allow it to accelerate quite much as he immediately pulled some good AoA climbing just prior to the roll, so he wasn't even at 500 km/h yet, but the rolling inertia is clearly very low in comparison to the aerodynamic rolling moment generated with full aileron deflection. The Lancer reacted quite similar to an F-16 in roll response. But our MIG-21 in DCS at 450 or 500km/h is nowhere near that. It accelerates in roll very slowly which proves that it either has too high moments of inertia in roll or simply the simulated aerodynamic rolling moment isn't high enough to be realistic. Also the maximum roll rate of the MIG-21 in DCS isn't as high as it possibly should, but maybe let's say the aileron's deflection is limited on the BIS at higher speed if that would be the case, cause if not it would mean that the variation of aerodynamic lifting forces between the wings due to aileron deflection isn't within an acceptable margin of realism.

 

Sadly, the DCS's recorded track replays tell a whole different story and don't match what you've actually done during gameplay, so I can't provide an authentic track file here where a correct roll response comparison can take place between DCS's MIG-21 and reality's MIG-21 to make it more clear that the difference is huge, but if someone tries to replicate in the sim what is in the video can see the difference for himself with no further arguments needed.

 

All the best!


Edited by Maverick Su-35S

When you can't prove something with words, let the maths do the talking.

I have an insatiable passion for helping simulated aircraft fly realistically!

Sincerely, your correct flight model simulation advisor!

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I feel like the ailerons move too slowly. Unless the stick in the real aircraft has some VERY serious eddy current dampers, I think it should move a bit quicker when the pilot wrenches it over. Or it could be that the ailerons move at the correct speed and the stick is just moving in unison with them.

DCS modules are built up to a spec, not down to a schedule.

 

In order to utilize a system to your advantage, you must know how it works.

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Does the engine flameout because of low IAS? I've never got that impression, to be honest. At low IAS and during stalls it always was the question of getting to around-zero G, which, as we know, is more flamout inducing than negative G.

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Low IAS with full power AB and a high AOA will give you compressor stalls normally in every aircraft form my very little knowledge, as airflow in a high AOA is not enough for the engine to run. F-5 for instance atm has no compressor stalls implemented as it should.

I had never experience engine stalls because I was to slow. Rather than what Art-J describes or what I described above.

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Gents, there were some test values left in the release bins. Hopefully the next update will fix it back.

 

Hi Rudel. Quick question, is N. Đ. A.K.A. Dolphin887 still at Leatherneck? We haven't heard from him in a while.


Edited by OnlyforDCS

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