Removed

The landing AoA is known = 14 degrees.

But the SLATs are retracted when landing gear is out.

So then we would have to guess how much the slats would be extended and the effect in such conditions.

And I think there is a good reason why you dont find such data in open source :music_whistling:

Then then parameters below 100kt and at 30 degrees AoA aren't what would help to compare to F-15...

Just for the record: that doesn't bother me ;)

 

You, yes, obviously. Me, not so much (perhaps even not at all). Jojo, I can't tell, he speaks for himself.

 

Regards :)

Az'

I see, because you love it being overpowered in both lift and engine thrust as it is right now! Pure French nationalism, no problem, but at least be true with yourself and aware that this aircraft right now needs some more attention, if the goal is to have it perform as the real Mirage 2000C which I enjoy as an aircraft, so let's start working on it. From how I see the discussions atmosphere evolve with you guys the Mirage 2000C's FM will probably stay the way it is right now. At least this is the general impression! So be it, I'm not the one losing anything here, you do and sadly this airplane!

I gave you a lot of useful clues from many directions which point out that this plane has a too low stall speed which is directly linked to the very high lifting capability and the engine performance is overrated. If you guys find anything wrong with my effort to have this plane respect the real life performance, please give me an example, but don't treat me this way and let's be pro-active.

Regards!

The landing AoA is known = 14 degrees.

But the SLATs are retracted when landing gear is out.

Perfect my friend;). I have a good input now, 14 degrees slats retracted.

So then we would have to guess how much the slats would be extended and the effect in such conditions.

For this wing's AR and sweep, at 14 degrees AoA (about 9 lower than critical), the lift slope is still in the linear region so the slats won't have any effect on the CL. Indeed, by lowering the slats, the local AoA is also reduced a bit (if the AoA indicator in the cockpit remains the same), which overall reduces the CL a bit, but this is not the case now if you say they are retracted in this config.

And I think there is a good reason why you dont find such data in open source :music_whistling:

Hmm, I don't find this info (landing AoA and high lift devices employment) a need for secrecy. Idk, but I may not find something useful as a secret in this area.

Then then parameters below 100kt and at 30 degrees AoA aren't what would help to compare to F-15...

What? Please let me know where did I compare the 100kias at 30 alpha with the F-15's performance? The F-15's wings provide more lift than the Mirage's at that alpha anyway (lower AR, high wing camber, relatively good high energy vortexes generated between the inlets on the fuselage which create a huge fuselage lift) and the F-15 has it's supercritical AoA (vortex breakdown) above 35.

Regards!

Hmm, I don't find this info (landing AoA and high lift devices employment) a need for secrecy. Idk, but I may not find something useful as a secret in this area.

I meant the Cz values you are trying to guess :music_whistling:

I see, because you love it being overpowered in both lift and engine thrust as it is right now! Pure French nationalism, no problem, but at least be true with yourself (...)

:megalol::megalol::megalol:

You're overreacting. Quite a lot.

I don't, and I keep my nationalism under control, and I'm...

aware that this aircraft right now needs some more attention

... and I also agree with this:

the goal is to have it perform as the real Mirage 2000C which I enjoy as an aircraft

so let's start working on it.

Oh, I didn't wait for your magnificience to shine light upon me, Sir.

I'm actually doing something about it, outside this forums ;)

From how I see the discussions atmosphere evolve with you guys the Mirage 2000C's FM will probably stay the way it is right now. At least this is the general impression! So be it, I'm not the one losing anything here, you do and sadly this airplane!

Seriously: your impression gives you the wrong idea :)

I gave you a lot of useful clues from many directions which point out that this plane has a too low stall speed which is directly linked to the very high lifting capability and the engine performance is overrated. If you guys find anything wrong with my effort to have this plane respect the real life performance, please give me an example, but don't treat me this way and let's be pro-active.

I already answered both sentences, but let's do again:

- There may indeed be an issue on this (I see it as a light one and concerning only a seldomly used "corner" of the flight enveloppe. I may be mistaken about this, but this is why it doesn't go as far as "bothering" me as much as it does for you) ;)

- I gave you a specific example of where you were wrong (assessing strakes max % effect of lift addition); I certainly didn't (and still don't) reject all you say; quite the contrary :)

Regards,

Az'

...

- There may indeed be an issue on this (I see it as a light one and concerning only a seldomly used "corner" of the flight enveloppe. I may be mistaken about this, but this is why it doesn't go as far as "bothering" me as much as it does for you) ;)

Jojo helpfully said that during landing the Mirage settles around 14 AoA. He didn't give me an IAS and actual plane weight for that, but it's a good start so far to see if we're on the right track to reality.

...I certainly didn't (and still don't) reject all you say; quite the contrary :)

 

Regards,

Az'

Then what was the reason for saying: "...Jojo, I can't tell, he speaks for himself"?

Anyway, if we are indeed looking for a realistically performing aircraft, let's just try reviewing the thrust versus speed and altitude and aero data tables a bit. One step at a time we should reveal what's true from what's far from true.

Kind regards!

The landing AoA is known = 14 degrees.

But the SLATs are retracted when landing gear is out.

 

So then we would have to guess how much the slats would be extended and the effect in such conditions.

 

And I think there is a good reason why you dont find such data in open source :music_whistling:

 

Then then parameters below 100kt and at 30 degrees AoA aren't what would help to compare to F-15...

So, Jojo, can you please also give a corresponding IAS and actual plane weight (or better said fuel status and loadout config) for a landing M2000C as it approaches at 14 alpha? Thanks! Step by step we can help solidify the actual's plane performance or help get what's right out of it;).

Cheers and regards!

After quite some play around with the aircraft trying all kind of crazy stuff, I found that our plane exhibits some out of line pitching moments or alpha trims way beyond stall AoA. All known aircraft (even the Flanker which does cobras) exhibit a CP (center of pressure or lift) shift with alpha. As the alpha increases towards positive or negative lift, the CP always moves towards the leading edge (which becomes trailing edge for negative airspeed components) as the alpha approaches stall. Once the stall AoA has been reached, the CP will see a more rapid forward movement with increasing AoA until the airflow separation reaches the leading edge. Once the separation has reached the leading edge, the CP normally and rapidly moves backwards now to about 40.45% of chord length (anyway, not beyond 50%) or at a % of chord length were it was (the CP) at an AoA slightly above or below null lift. This effect of CP travel fore (below and upon reaching the critical AoA) and aft with AoA is least pronounced for straight and high AR (aspect ratio) wings and gets more pronounced for lower AR higher sweep wingsI might've put too many details in it, but for short, once the stall AoA has been passed by 1..2 degrees, the CP should rapidly move back to around 40..45% of MAC. Although the Flanker, with the use of LERX finds about the highest forward CP travel with alpha among modern fighter planes (which helps it do a cobra through pitch inertia), it's position will rapidly come towards the rear as the AoA goes past 40..50 AoA, thus a pitch down moments starts to develop above this angle.

Somehow on our plane, the CP continues to move even further towards the leading edge as the alpha goes well beyond stall and even 90, leaving the aircraft settle somewhere around 150 to 170 AoA if there is no gyroscopic effect due to spin (which reduces it by some amount).

Here's a quick video showing this behavior:

https://youtu.be/GRzq6PK5MnY

You should at least specify that you messed up with FBW (probs ly the CDVE GAINS switch ?).

[Edit] or not the last version of the FM

Why don't you code your own FM ?

Yep the Mirage land at 14 AoA, and guess what: speed depends on weight :D

Then what was the reason for saying: "...Jojo, I can't tell, he speaks for himself"?

I honestly don't know what you mean with this question, so sorry I can't answer it.

Anyway, it's not the core of the topic, so let's drop it.

Here's a quick video showing this behavior:

 

https://youtu.be/GRzq6PK5MnY

Indeed but... your video is made with a FM that has now been re-worked, specifically on that point I may say (not only on that, but still). ;)

You're using 1.5.8 (stable release I presume). Last FM isn't yet available on this, but will be soon (it's a matter of days, 1-2 weeks at most is my best guess).

See what you may do now (last FM, DCS 2.5 OB):

https://forums.eagle.ru/showthread.php?p=3374712#post3374712

++

Az'

You should at least specify that you messed up with FBW (probs ly the CDVE GAINS switch ?).

[Edit] or not the last version of the FM

 

Why don't you code your own FM ?

 

Yep the Mirage land at 14 AoA, and guess what: speed depends on weight :D

What is unclear to you?

Why should I specify that I touched the FBW if I haven't? By what you clearly saw and from what you can test as many times as you like and from what you answer proves that you don't get the problem! Do you have basic flight dynamics knowledge, or should I stop wasting my time?

What would the FBW ON or OFF have to do with that high angle of attack (150 AoA O.o) trimming? Unless there is some gyroscopic effects of the yaw rate which forces the AoA to decrease to about 100..110 (as in the video), the plane would fall forever on it's tail (presuming it flies backwards in a limitless fluid) at around 150..170 AoA!

Does this look abnormal to anyone here?

I already gave the complete explanation of the CP travel phenomena and pinpointed exactly what is wrong with our plane. Why do you even go thinking about FBW ON or OFF as it doesn't affect the pitching moment anymore (at least not much) on above 40..50 AoA? What magic could you believe the FBW does other than commanding the elevons? It's the same as commanding them manually up or down, and above that alpha, it makes no difference! And as you can clearly see it was ON due to the elevons deflection which had no effect anyway, because once again, the CP position simulation isn't where it should be and instead of moving drastically to around 40..45% of MAC, it stays somewhere around 0% or probably below 0% (forward of MAC's position on X axis).

The problem's solution is very simple. Tweak the pitching moment with AoA as to go towards negative once the supercritical AoA has been overshoot.

No plane in the world behaves like that in mid air if it managed to takeoff and fly steadily (if there is still a positive longitudinal static stability margin left) and of course if the structure didn't suffer any catastrophic changes.

I honestly don't know what you mean with this question, so sorry I can't answer it.

 

"...Jojo, I can't tell, he speaks for himself"?"

These were your own words, so I'd like to ask you the same: What do you want to mean by this banter as I'm here to help you guys?

Indeed but... your video is made with a FM that has now been re-worked, specifically on that point I may say (not only on that, but still). ;)

You're using 1.5.8 (stable release I presume). Last FM isn't yet available on this, but will be soon (it's a matter of days, 1-2 weeks at most is my best guess).

True, I'm only using the stable release 1.5.8, I never tried the beta and perhaps I should from now on, but, as long as the 1.5.8 is what most of us use and it's the default, this is what concerns us.

See what you may do now (last FM, DCS 2.5 OB):

https://forums.eagle.ru/showthread.php?p=3374712#post3374712

 

++

Az'

Good looking picture but it tells me nothing if I can't clearly see how the plane behaves from start to finish. I mean how the alpha accelerates (due to generated pitching moments) towards "+" or "-" depending on elevon deflection (so it doesn't matter FBW is ON or OFF) and actual alpha.

Unless I have a track (or maybe I should test it myself) or video of how the plane behaves this can't tell if something got fixed.

Regards!

...and guess what: speed depends on weight :D

Man..., are you trying a mockery or are you serious? I clearly asked if you could please find out at what weight and IAS the plane comes to land for that alpha.

These were your own words, so I'd like to ask you the same: What do you want to mean by this banter as I'm here to help you guys?

Well, it wasn't intended to be a banter. Only a statement: I won't presume to write in place of someone else (jojo in the present situation). Nothing more. ;)

True, I'm only using the stable release 1.5.8, I never tried the beta and perhaps I should from now on

OK :)

I don't think you need to switch to the beta. I do think, however, that you should wait for 2.5.0 (or ultimate 1.5.8) to be released, then check again: as the part of the flight enveloppe that you are concerned about (low speeds, high alphas and even post-stall) has been specifically updated...

but, as long as the 1.5.8 is what most of us use and it's the default, this is what concerns us.

Not anymore, from a developper's point of view (which I'm not, just trying to explain). And as it's a matter of a few days...

Good looking picture but it tells me nothing if I can't clearly see how the plane behaves from start to finish.

It's only meant to tell that what isn't possible in the 1.5.8 version you use, is now possible in more recent (still in OB) versions. Specifically: getting out of the "stuck" post-stall behaviour that the video you posted earlier showed.

(so it doesn't matter FBW is ON or OFF)

FBW is never Off on this aircraft (or the aircraft isn't controllable anymore). There isn't a non-FBW back-up option.

++

Az'

FBW is never Off on this aircraft (or the aircraft isn't controllable anymore). There isn't a non-FBW back-up option.

++

Az'

I see, lol! I didn't know how the button which allows higher alpha is called.

Yes, in 2.5 the nose indeed eventually drops from very high alpha to below stalls, but there is another problem that must be worked out now. Beyond 35.40 AoA, the plane starts a slow roll to either right or left until it almost flies sideways at around 40 degrees (as alpha transferred to beta). Once the vortex created by the strakes fades away, the directional and lateral stability should drop, therefore the wings should begin to rock left-right at "some" frequency, not roll to either right or left until the AoA is almost completely converted to beta (sideslip angle) in order to start rolling the other way again. The rolling oscillation tables (or how the FM is made) above supercritical AoA also need a refreshment.

Cheers!

Hi

Beyond 35.40 AoA

... is out of the aircraft "normal" flight enveloppe.

I have a feeling we may differ here, but I'm simulating a fighter pilot most of the time. And not being so enthusiast about simulating a test pilot in the long term.

Moreover, as the aircraft is still "young", so are the skills of the pilots. Mine anyway. So I tend to stay away from emergency buttons... unless I have an emergency.

And I like to imagine that the FM coding process follows the same path: get the "normal enveloppe" done & perfect, then eventually (and potentially optionnally), do fundamental research or advanced modelling of ~ uncharted territories.

That being said, you're probably right about wing "rocking". But what about the zero-roll situation? The one intended by demo pilots when doing the figure I shown a few posts back on my screenshot? You may want to say "a lucky guy" and that may apply to me indeed. But not to real French demo pilots: Luck, I'm told, isn't something they like to rely upon. :joystick:

Sometimes I'd like to invite persons to go to a flight school which have a proper FNPTII, pay a few hours (~130€/h) and than come back to DCS. Or go back and install Jane's FA18 or Microprose Gunship...

... But what about the zero-roll situation? The one intended by demo pilots when doing the figure I shown a few posts back on my screenshot? You may want to say "a lucky guy" and that may apply to me indeed. But not to real French demo pilots: Luck, I'm told, isn't something they like to rely upon. :joystick:

What is it about zero G rolls regarding the Mirage? I don't know, tell me! If it has to make the plane depart in pitch or yaw as I know the F-18 does, that would only have to do with inertial coupling as the CG isn't lying on the true axis about which the plane rolls (it's not always the X axis of the plane). Don't know, I'll test that later too for curiosity.

Yes, I agree with you that you normally wouldn't have to touch the emergency buttons of the FCS, but all I'm focusing on is how the plane behaves around all AoA and beta angles which can be reached in different ways and so we want the plane to respond realistically. For instance if you go into the vertical against a bandit and your IAS drops significantly so you won't have anymore control to keep the AoA and/or beta to a wanted value and let's say you fall on one wing, high beta (let's say 90) and very low AoA (but let's say it's enough negative to produce negative lift)..., what should be the plane's response? The plane's leading wing should find a higher negative lift than the lagging one (general rule whenever there is a beta) so there should be a rolling moment which gradually accelerates the plane in roll in the correct direction and not reach a low constant roll rate (zero rolling acceleration) as it does at the moment and keep that constant roll rate until the beta angle turns almost to the same value (but with opposite sign) of about 90 in order to have the roll stop. This is what I'm saying.

Here's a short track which clarifies what it does:

Wing rocking and high beta effects.trk

Good day!

...

 

 

I have a feeling we may differ here, but I'm simulating a fighter pilot most of the time. And not being so enthusiast about simulating a test pilot in the long term.

 

Moreover, as the aircraft is still "young", so are the skills of the pilots. Mine anyway. So I tend to stay away from emergency buttons... unless I have an emergency.

 

And I like to imagine that the FM coding process follows the same path: get the "normal enveloppe" done & perfect, then eventually (and potentially optionnally), do fundamental research or advanced modelling of ~ uncharted territories.:joystick:

Hello again man,

Sorry I couldn't be here for a while due to a long story of computer faults, although I imagine you're not terribly yearning for long (yet useful I hope) talks with me.:doh:

I agree with you that on the short term a "young" simulation product will have to have accurate data on the mostly used area, such as flying performances between the critical angles of attack (positive and negative) and not yet above what we call "operational envelope", but..., modern day simulators (including DCS) should be able to simulate how the aerodynamic forces occur all around the envelope (inside-out) between +180 AoA to -180 AoA combined with +180 beta to -180 beta + their variations with the Mach number which is highly important.

That's what a mature and professional flight simulator is capable of and yes, there are already simulators out here (I'm not going to give names, but many might know them already) which do just that and also get into areas, which possibly, are not yet accessible in a DCS simulation, such as local CFD algorithms that occur during an actual plane's flight simulation and calculate how the airflow is affected in the wake behind the plane. This is the only reason why I'm addressing the issues that I personally find here and because they regard performance issues, such as engine thrust tables and lift coefficients that still need refinement! Otherwise I could just say goodbye to DCS and every module in it no matter how much I've spent on them and that would be it, but I'm only asking for things to improve, nothing else.

Cheers/regards!

Are they looking at the issue where bombs are released when you pull the trigger in INS offset bombing?

Hello again,

RAZBAM, good job! I'm at least happy that the thing with the lift is not totally in the wrong direction.

After re-testing the maximum lift coefficient it turned out that only at very low speeds the CZ max tends to grow wildly (can't yet logically find out why). The lower the IAS, the greater the CL grows for a given AoA. The maximum lift coefficient when flying at or above low dogfight speeds is around 1.3. Remarkably as I've concluded in my own analysis and said it over and over. Only after latest tests I've found that it was already simulated to be at that value (my congrats and good remarks are back), yet again, only above stall speeds (at and below stall speeds, for some weirdo reason, the CL rises to 1.9+).

On the other hand, the thrust tables still haven't been corrected it seems. The Mirage 2000C is climbing like a rocket and still has the same outstanding acceleration (better than F-15) at very high altitudes (above FL360). Hopefully this will get fixed.

As I've talked to GGTharos on a thread regarding the F-15's ability to accelerate in the vertical, I understood that the engine ratings that we have from wikipedia are for the best conditions only (marketing stuff) and are usually obtained only on test benches using a huge bellmouth air intake which essentially drastically reduces the non-uniform airflow and airflow disturbances that occur in the real inlet ducts of the aircraft. As GGTharos said (and I take his word on this one), relatively 80% of the maximum engine thrust that is obtained on a bench test at full afterburner is achievable when mounted on the aircraft. The 20% losses are due to intake design which is a compromise for better performance (reduced wave drag) at higher speeds, so it's detrimental to the engine's performance at lower speeds and lower altitudes.

Thus, if RAZBAM would consider multiplying all the thrust tables by 0.8 (as a momentary hotfix), the aircraft's forward acceleration performances would get closer to that of it's real counterpart. Right now, the Mirage accelerates in vertical climb from sea level and low speed just with a thrust/weight ratio which proves that the highest thrust rating is somewhat similar to the values quickly found on the internet. I believe that a quick multiplying of the actual thrust tables by 0.8-0.85 would bring the resultant thrust a big step closer to realistic values.

Regards!

How arbitrary is this.... That's not how you do stuff...

No, here we go again....

« the aircraft's forward acceleration performances would get closer to that of it's real counterpart »

The lads who used to work in Bretigny’s CEV must be laughing their a$$es off.

How arbitrary is this.... That's not how you do stuff...

Then how do you do stuff actually to make it realistic? Simply copy-paste data without corrections? Cause that's exactly what it looks like you're doing to make an FM by how the plane actually flies! Use some CFD tool, and whatever results it gives, you blindly input them into the FM and expect it to be realistic? You need some knowledge in order to know the range within which the results are correct and from where on they are going very wrong and what to do to correct them, not simply take them for granted. For that, you first of all need some experience with those numbers to not allow absurd results take over! What I'm saying now is especially regarding how the CL (lift coefficient) and CD (drag coefficient) are being simulated according to AoA and IAS. Although I have found that the maximum CL is realistically around 1.3 (which I have told long before it should be close to), that only happens above certain speed at almost 30 AoA, but below a certain speed it goes wild to about 1.9 (that's very wrong) close to 30 AoA and also the drag becomes dramatically high towards 90 AoA (the plane falls very slow near 90 AoA). Remember, that for any 3D flat plate (no matter the area), at 90 AoA, the drag coefficient is about 1.15. Yous is well above 2 (even higher than for 2D flow). This proves that whatever your CFD analysis resulted with these weird aerodynamic slopes/functions, you took them without any knowledge based corrections and directly inputted them into the aero tables that the game uses for simulation.

I don't know how you have obtained the engine thrust tables, yet I believe that you did it in a similar way as with the aero data, starting from the given thrust value on wikipedia, maximum thrust value which has resulted on a bench test (in the best conditions possible), value which ISN'T the actual maximum thrust value of the engine that operates on an aircraft. Yes, 0.85 times the wikipedia's FULL AB thrust is a very good approximation. Don't tell me that you're using some sort of very high complexity math analysis methods determining the thrust tables (even if you would, the results are wrong...). You either have been given these tables from Dassault, which are only the tables of the engine on a test bench (only where it can have the greatest possible performance) or you have some rather simplified equations which start from a known thrust function and extrapolate the results. For both cases, if you multiply those tables by 0.85, our DCS Mirage's engine will develop a much more realistic thrust and also allow the plane to accelerate horizontally and vertically (especially vertically) more appropriate.

So, you tell me that being arbitrary for estimating corrections is more wrong than using crude/uncorrected data resulted from CFD (the actual simulation proving it)?

[...]

Nice 8 month necro.

Do you think I work for Razbam ?

I don't care of your wall of text. RB is currently working with the French Air Force to improve the M-2000C.

I don't think they need the help of someone who have no knowledge of the air-frame and that is throwing random numbers in the air. I don't ever know were to start on how many problems the "multiply those tables by 0.85" would cause in the rest of the FM.

Anyway, with the name you made yourself in this forum, I don't have any interests with this conversation anymore.

Have a nice day.