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Degraded Su-27 aerodynamic lift


Maverick Su-35S

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Fair.

 

I'm not saying the Flanker is inferior to the Eagle in BFM, what I am saying is that the way we discuss BFM is inferior to ... actual BFM.

...

Thus naturally, the Flanker does have a lot of WVR advantages, but it's not utterly superior like we all used to assume. The Eagle has things going for it that you can't ignore, and some of this stuff is due to the silly way that people do these comparisons. You can confidently over-g a 30% fueled Eagle to 10-11g at the assumed speeds at low altitude and get a higher average turn rate than the Flanker because you just can't do it with that huge air-frame.

 

Does that mean that you can 'easily' out-turn a Flanker? No. But it does mean you can easily out-turn every lay-man out there who's either hauling butt at 500-600kts in the merge or doing the stick-to-the-gut maneuver and running themselves so low on airspeed that even a mildly patient and knowledgeable Eagle pilot can out-rate by keeping better maneuvering speed that he can bleed for a shot or just cut up the TC in the vertical. All this means that you need to pure more thought into your BFM than just the belief that a Flanker is utterly superior in WVR. It's not.

...

It's funny how opinions on the web are just repetitions of themselves without any thought or science put behind them, right?

 

Ok, you are looking at the fact that the Eagle has a higher ITR than the Flanker due to higher G-load at a given IAS (also lower radius as a result) as it happens now in DCS, and let's say it is real and the Eagle has higher ITR than the Flanker at any speed beyond and below 9G as it goes now in DCS (which I strongly doubt for speeds below 9G, and the aerodynamics of the planes are there to support me). Now put some science in and how about testing to see both planes STR also? Constant similar G-load, full AB and let the speed trim where it likes. Result? The Eagle has higher STR at all speed regimes between lowest and highest G-load (below 9) at AoAs comparable to the Flanker. How could this be? It turns the aerodynamics laws upside down, seriously!

 

So once more, if people believe that Eagles can't out-turn Flankers, there are bridges to be sold and I'm charging a fair price :D

 

How much for the cheapest bridge?

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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You're right, yet I personally couldn't get access to a Su-27's Cy (CL) vs AoA at any flight regime, so I had to improvise right now by rather comparing the Su-27 to the F-16, which I'm pretty sure is a good comparison, aerodynamically speaking.

 

And neither of us will get those docs - as far as I'm aware, those who have them are not allowed to share.

 

Comparing to the F-16 isn't valid.

 

For reference, here's a page with a graph - ignore the eagle and viper data, it's (over and under) estimated.

 

Flanker configuration is 50% fuel, 2xR-73, 2xR-27R. No other configuration is valid for this comparison.

 

Atmospheric data unknown, but might just be ISA - 15C/standard day.

0045.thumb.jpg.90c4ee88931807ea4fb8650f79961820.jpg

0036.jpg.da23bf7183c6de995a05e0ea0e8b703e.jpg


Edited by GGTharos

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Actually, the eagle does not have higher ITR but it might be able to achieve a higher average ITR in practice. More importantly, it might be able to hang onto a higher turn rate for longer.

 

Ok, you are looking at the fact that the Eagle has a higher ITR than the Flanker due to higher G-load at a given IAS (also lower radius as a result) as it happens now in DCS, and let's say it is real and the Eagle has higher ITR than the Flanker at any speed beyond and below 9G as it goes now in DCS (which I strongly doubt for speeds below 9G, and the aerodynamics of the planes are there to support me). Now put some science in and how about testing to see both planes STR also? Constant similar G-load, full AB and let the speed trim where it likes. Result? The Eagle has higher STR at all speed regimes between lowest and highest G-load (below 9) at AoAs comparable to the Flanker. How could this be? It turns the aerodynamics laws upside down, seriously!

 

 

 

How much for the cheapest bridge?

 

Again, quit quoting 'aerodynamics laws'. This is literally non-sense - my kite could out-turn both of those birds ... so what? The ONLY valid comparison to the aircraft's own data. Nothing else is valid.

 

Comparisons of the type 'but it out-turns my flanker' are not acceptable. I am telling you straight up, I don't believe for a second that ED's aerodynamicist will accept your arguments because you are trying to analyze something based purely on a small set of circumstances which do not describe the entire situation.

 

Further, because it bears repeating, arguments of the 'but it out-turns my plane' type are not acceptable. Only comparison to own data is. I've given you some in the post above.


Edited by GGTharos

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That is fairly difficult to believe. Because while I dream that Su-27 is a highly maneuverable aircraft and better than anything that F- series offers, just by claims like these:
Although that is about Mig-29, but still. https://dunsfoldairfield.org/john-farley-afc-obe/ As I still believe that F/A-18C will outmaneuver Su-27 or Mig-29 in optimal setups for both, but still needs to run for its money.

 

Yeah, I also doubt that the Flanker can have a higher STR than the Eagle if the speed won't drop when the Eagle is in FULL AB and the Flanker only using 100% MIL power.

 

 

One thing that as well interest me, is that isn't it unfair to use a percentage of fuel capacity, instead use the fuel that would give the same range in specific altitude or altitude+time?

 

Like how much fuel it would be required for a fighter to fly 300km, loiter 5min and then fly back? And then perform the flight maneuvering tests at that begin of the loiter?

 

As I find it just wrong that it is used like 30% or 50% of fuel capacity for both, when other can fly 1500km with that and other just 600km? As if one wants to get the best maneuvering, shouldn't it just be then used almost empty regardless that no one would be in real combat situation with such setup?

 

I don't know what are you trying to point out because, indeed the fighters takeoff with full fuel and also tanks (who has them), but if they get involved in a dogfight, their actual fuel might be well below 60% left, that's why such comparisons of performance are mostly looked at for lower fuel quantities, not because you want to be low on fuel and not make it home, but because it's likely your fuel would be around half and below during a dogfight.

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

Sincerely, your correct flight model simulation advisor!

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...it was 'Su-27 bug because F-15 out-turns it'. There's only one way to show bugs, and that's to show that the specific aircrafts don't behave as they ought to, NOT that one out-turns the other. That's just proof that one fares better than the other under x/y circumstances.

 

No one said this is a bug. A bug is usually a writing error in a programming line, which isn't the case here. The case here is aerodynamic data which affects our planes turning performance in an apparently abnormal way.

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No, it's not. Had you pulled thru the AoA limiter (modeled as the "Y" key) you would have been in the 30°/sec range just before that.

 

Speaking of 30°/sec, that video you linked has me puzzled. It seems to suggest that the Flanker in question turned 360° in 12 seconds. If that's actually the case, then it somehow held its max instantaneous turn rate for the entire turn which seems to be a contradiction.

 

Correct. It seems to be in contradiction to DCS, in which you said you were just able to achieve 30 deg/s as ITR (that is maximum capable for a split of a second at very low fuel, no loadout and rapid AoA onset), which in reality is the average turn rate, below the highest ITR (at corner speed where it started turning) and above the lowest ITR (where the turn ends).

 

Guess for yourself which is wrong, reality or...? The video is untouched in terms of frames/second or timing and it's not the only video proving the same qualities of the Flanker's turning performance.

 

Regards.


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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Why the heck do I have to log into YT to view that video?

 

In any case, it isn't possible to hold the 32dps all the way around. This is IMHO misinterpreting a high AoA as a full turn.

 

Or, it's just not the flanker we're talking about.

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If they have data, i really hope they do, then why fligh model changes from time to time? I can understand structural modelling or damage model being hidden or hard to evaluate but flight performance margins should be clearly known and clearly immitated if ed guys have them.

...

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Good point man, exactly! And as I've tested the PFM Su-27 as it initially appeared (as PFM), the Flanker's turning capability matched perfectly with those in the video, which was 12 seconds needed for 360 turn. Now it takes almost 16 seconds for the same conditions, so apparently, the changes made it worse.


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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Given up on that fight right now - a warm-up will buy you a bit more g-tolerance.

 

As for the -g, the representation is fair. The reason is that severe -g is not something combat pilots train for, and it absolutely ruins their ability to continue fighting (mental faculties), as well as their +g tolerance for the rest of the fight. IIRC from studies.

 

Just.don't.do.-g. :)

 

For the roll, that's a symptom of something else ... use +g and/or turn off the black-out simulation, do a severe loaded roll and watch the g on the external g-meter.

 

Right, fighter pilots may not necessarily be trained to withstand 12G for 16 seconds, although some do train for just that, like this guy:

 

Although at 2:14 he had enough (got tired probably), he still withstood 2 seconds more at 12 Gs (7 seconds) than our "virtual pilot" in DCS can stand at 9G before passing, which is just 5 seconds.

 

F-16 fighter pilots are grounded if they can't hold 9G for at least 15 seconds. The higher the G-load the exponentially lower the time available till blackout, so if the guy who held 12 G for 16 seconds, he can very easily hold 9 for at least 30 seconds, that's how curved the function is. In DCS right now, you can stand forever at 8G (even if you can't see much on your monitor) but blackout at 9 in just 5 seconds, so the G load to blackout time curve is incredibly exponential/logarithmic (depending on graph interpretation).

 

About negative G-load redout in DCS, the function behaves the same as for positive Gs.

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!

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Not to derail this conversation... but F-15>Flanker.

 

But it doesn't matter, once the Hornet comes out we'll be toasting you with that. :joystick: haha

 

Sorry, but I don't get your arguments. F-15>Flanker O.o. In reality or game? and if in reality, in which area? On the other hand I can't wait for the Hornet to come out and if you guys want to toast me, I'll toast you too...!:D Cheers!:thumbup: The Hornet has better ITR than the Flanker and better STR only in diving spirals, otherwise it's dead meat in the vertical against the Su-27, in reality I mean, no matter how will it "show up" in DCS!

 

I understand you figured me out the wrong way buddy! I love all airplanes the same and I'm not pro or con for one plane against another...! ALL I WANT IS REALISM and perhaps you don't know what it is!

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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And neither of us will get those docs - as far as I'm aware, those who have them are not allowed to share.

 

Comparing to the F-16 isn't valid.

 

For reference, here's a page with a graph - ignore the eagle and viper data, it's (over and under) estimated.

 

Flanker configuration is 50% fuel, 2xR-73, 2xR-27R. No other configuration is valid for this comparison.

 

Atmospheric data unknown, but might just be ISA - 15C/standard day.

 

Thank you Tharos, very interesting charts, but something's weird, even though the planes are A-A combat loaded! How come the F-16 is so much worse at STR than the F-15 and Su-27? What is this, F-16A with downrated engine? It's strange! Besides the F-16's performance, even here we can see how the Su-27 should have better STR below 700km/h IAS, so..., how come in DCS the F-15 has better STR at all speeds between full aft stick to 9G (over 9G, of course it has much higher STR and ITR).?

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!

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...

arguments of the 'but it out-turns my plane' type are not acceptable. Only comparison to own data is. I've given you some in the post above.

 

It's not my plane or someone's plane, it's reality's plane and yes, the real data should validate each aircraft's (helo or plane) performance in DCS also, but only through thorough testing... and here the turn rates, axial and normal accelerations according to various conditions are key to know if something's not right.

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Why the heck do I have to log into YT to view that video?

 

In any case, it isn't possible to hold the 32dps all the way around. This is IMHO misinterpreting a high AoA as a full turn.

 

Or, it's just not the flanker we're talking about.

 

Idk what's going on with that link, I've re-copied it now.

 

Well, yes it's not 32dps as STR, I guess we both agree, but the mean dps is around 30 (12 seconds for a 360 turn). The deg/s is one thing, the AoA is another and hopefully no one mistaken dps for AoA. At least this was the flanker on which these manoeuvres at Farnborough and Woodford were done in the 1990s.

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

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...you were just able to achieve 30 deg/s as ITR (that is maximum capable for a split of a second at very low fuel, no loadout and rapid AoA onset)...

No...not rapid AoA onset. It's accomplished moving from the max sustained turn rate toward the max instantaneous turn rate in order to make your tighest, fastest turn. Doing that, you can get down to around 14°/sec averaged for the 360.

 

 

...which in reality is the average turn rate, below the highest ITR (at corner speed where it started turning) and above the lowest ITR (where the turn ends)...

No...that is precisely backwards. The lower turn rate is where the turn begins because you enter it with the highest sustained turn rate airspeed and pull toward the highest instananeous turn rate. The highest instantaneous rate is at the lowest speed that can generate maximum G and that is below the sustained turn rate speed. To do it in reverse leave you with an extremely slow turn. Oh, it'll be tight all right. But it'll also be anything but fast.

 

And every chart I've seen for the SU-27 puts the max instantaeous rate at around 30°.

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No...not rapid AoA onset. It's accomplished moving from the max sustained turn rate toward the max instantaneous turn rate in order to make your tighest, fastest turn. Doing that, you can get down to around 14°/sec averaged for the 360.

 

What would the 14 deg/s mean! ITR? STR, and in which condition of weight and height? You don't start with sustained turn rate if you pull full stick at a speed for which you can achieve G-limit at critical AoA. That is instantaneous turn rate that you generate. What would you understand by sustained turn rate? I understand a constant rate of turn of my plane's velocity vector at a constant alpha, altitude and weight which will trim my speed and G-load to a constant value. By instantaneous turn rate I understand a momentary turn rate of my velocity vector for a given alpha (which may be constant or variable), weight, altitude according to a G-load which varies with speed. If you want to enter an ITR situation from a STR that's fine, but if you pull the stick in a way of making the airspeed (and thus G-load) vary, you conduct an ITR scenario. Please correct me if I'm wrong!

 

No...that is precisely backwards. The lower turn rate is where the turn begins because you enter it with the highest sustained turn rate airspeed...

 

Well, if it's the highest sustained turn rate airspeed (as you say), how can it be the lowest turn rate at the same time? The highest turn rate possible that you can achieve (and is always ITR and not STR) corresponds to the highest G-load at a given speed, so I don't know about what we're talking here.

 

The lower turn rate is where the turn begins because you enter it with the highest sustained turn rate airspeed and pull toward the highest instananeous turn rate. The highest instantaneous rate is at the lowest speed that can generate maximum G and that is below the sustained turn rate speed.

 

So you are saying that the STR is for a speed which is initially well beyond the one for maximum G-limit, so you fly at a low alpha, right? What would that help you with unless it's the one corresponding to the highest STR? If the speed is higher than for your highest STR (which is lower than the highest ITR anyways), you are only doing a big circle turn at a relatively low rate and wait for the drag to reduce the speed to a value below which upon reaching critical alpha the G eventually starts to drop and where you have touched the maximum possible ITR.

 

I believe that what I've said was right. After pulling the stick to reach the critical AoA while flying at the exact speed needed to reach exactly the G-limit you have rapidly achieved the highest ITR and lowest turn radius possible, not passing through any STR or anything and as your speed drops (usually the T/D ratio is well below 1 at critical alpha), so does your ITR drops. A STR is only corresponding to a constant speed and G-load.

 

By trying to review what you've said another way:

 

...The highest instantaneous rate is at the lowest speed that can generate maximum G...

 

Correct!

 

...and that is below the sustained turn rate speed...

 

Sorry, but wrong! How can you have the highest ITR lower than STR (even if it's the highest STR)?

 

To do it in reverse leave you with an extremely slow turn. Oh, it'll be tight all right. But it'll also be anything but fast.

You mean about the lowest ITR which eventually turn into the lowest STR? Right, it won't be fast, because the drag will keep both your airspeed and G-load (thus STR) low for the given thrust you have.

 

And every chart I've seen for the SU-27 puts the max instantaeous rate at around 30°.

 

Perhaps the charts you have seen have a loaded and heavy plane, not with less than 40% fuel with no loadout.

 

 

Regards!

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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This track shows that our Flanker in DCS can't do the benchmark 360 turn in less than 15 seconds even after pushing the frame to 10G:

 

DCS Su-27's maximum turn rate capability.trk

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 just watched the video. It isn't a 12 second turn, it's more - he cuts it too early. The second turn is 13s+.

 

And since we are cutting up the seconds ... that entire film is a bit fishy parts of it appear sped up - where's the info on the fuel load? I mean, where does it come from?

 

Anyway, there are the charts. It either matches the charts, or it doesn't.

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Did is in 13-14 sec. I could probably improve my technique a bit and slice off a half second or a whole one, but I don't feel like working on it right now.

 

As I thought, releasing the AoA limiter is one key, the next is to control the AoA or the turn. If you max out AoA you will never make the time.

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Sorry, but wrong! How can you have the highest ITR lower than STR (even if it's the highest STR)?

 

You should read more carefully. Ironhand was talking aboutairspeed not turn rate.

 

 

Max sustained turn happens at a given airspeed for the aircraft mass.

 

Max instantaneous turn happens at a lower airspeed for the same plane with the same mass.

 

 

You start the turn with a limited budget of energy, if you start at max sustained turn and carefully pull through bleeding energy to get to max instantaneous turn near the end it uses that energy budget wisely and gets you the fastest 360 turn.

 

If you pull straight to ITR at the start you waste a lot of energy, and as you bleed airspeed in the turn you fall below the airspeed needed for a decent turn rate. It gives a very tight radius, but takes a long time to do a 360 compared to a turn where the pilot does good energy management. This, I believe, was the point Ironhand was trying to make.

 

 

Perhaps the charts you have seen have a loaded and heavy plane, not with less than 40% fuel with no loadout.

 

The charts are made for pilots that are expected to take the aircraft into combat. How interested are they going to be in the performance of an aircraft with little fuel and no weapons?

 

I'm poking a bit of fun at you here, but in general performance charts for airshow configurations are less available or non-available compared to combat configurations. Though if you can find some airshow configuration performance charts I'm sure people would be happy to see them.

 

 

 

 

Also a few other notes.

 

 

When people were complaining about your fuel percentages:

 

A fully fueled Su-27 only has about a ton less fuel than an F-15E with full internal and CFTs.

 

So unless your F-15C was 30% internal plus one full external tank (or equivalent fuel mass internally), it wouldn't really be a good comparison.

 

Relatively speaking, an F-15 with just 30% internal is a smaller proportion of its max takeoff weight than an Su-27 at 30% internal fuel is of its max takeoff weight. The Su-27 has a lot more internal fuel capacity for its size.

 

 

 

 

Finally, 30 deg/sec is awfully high as a sustained turn rate for aircraft of that generation in a combat configuration. If you're basing on similar aircraft, a range of roughly 15 deg/sec to 20 deg/sec would be expected, with some of the more maneuverable ones getting to the mid-twenties in light configurations. The F-22 is supposed to be in the vicinity of 28 deg/sec or so.

 

For ITR, then 30 deg/sec is well within the realm of possibility. For thrust vectoring variants it might even go into realm of 60+ deg/sec. The problem is that if you pull that sort of maneuver, unless in the process you killed your last opponent you'll be in serious trouble due to lack of airspeed after having bled so much energy that you're slower than an A-10.

 

 

The maximum possible turn rate is irrelevant except maybe in airshows, the maximum practical turn rate is what matters.

 

 

 

Looking at your initial post's charts what I see is the F-15 getting to an ITR of around 29 deg/sec, and then bleeding a huge amount of airspeed. A very reasonable result.

 

For the Su-27 I see it pulling to 20 deg/sec, and then running into the limiter which keeps the foolishness of a full stick aft turn from hemorrhaging energy quite as badly as happened in the F-15. Using the override (wheelbrake keybind) you likely could have gained ITR and bled energy much like the F-15.

 

 

Your comparison isn't a turn rate comparison or a max lift comparison, it's an energy bleed comparison, and the only reason the Eagle won is because of user error in the Su-27. If you want to see how impressive the Su-27 is at bleeding energy all you have to do is correctly perform a Pugachev's Cobra maneuver. ;)

 

 

Jokes aside, in your test you didn't correctly fly either aircraft for a maximum average turn rate and the results are about what would be expected based on publicly available information.

 

 

Edit: I just looked through the slide show you linked and the performance stats it cites are:

 

F-15

 

STR: 19 deg/sec

ITR: 26.4 deg/sec

 

Su-27 SK

STR: 19.4 deg/sec

ITR: 28 deg/sec

 

Doesn't say for what loadouts those are though.

 

If you're after evidence that the average turn rate for an Su-27 through a 360 deg turn is above 30 deg/sec you might not want to link sources saying that the max ITR is only 28 deg/sec. ;)

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I did the flanker test last night.

 

Technique and setup:

 

15C standard day

Flanker fueled to 20% and locked

Arrive low over kobuleti (~100agl) lined up with the runway.

Light AB at 600kph, roll, disengage AoA limiter (paddle brake) and pull max deflection when I reach 700 kph.

Moderate the AoA as required so we don't blow all the airspeed in one pull (this is CRITICAL - stick-in-the-gut will get you a lower average ITR)

Stop the turn when aligned with the runway again (obviously parallel to the runway) or slightly past it.

 

Analysis done in Tacview, with results as follows:

 

360 turn time is ~13-14 sec and I bet I can shave that down a bit. It all depends on when you want to start measuring.

 

Peak ITR is 30 deg, dropping gradually and maintaining at mid-20's for a while or slightly lower.

 

Because my technique wasn't perfect I bunted the nose and bit and probably lost a few fractions of a second to this.

 

PS: After watching the video again a couple of times, I can definitely say that the 360 is not performed in 12 seconds. It is 13+, and in both cases the clocked demo cuts out before full completion of the 360.

I am satisfied that my test demonstrates the same performance as in the video.


Edited by GGTharos

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Did is in 13-14 sec. I could probably improve my technique a bit and slice off a half second or a whole one, but I don't feel like working on it right now.

 

As I thought, releasing the AoA limiter is one key, the next is to control the AoA or the turn. If you max out AoA you will never make the time.

 

Ok, so you say you managed to do a horizontal 360 in 13-14 (rather said more than 13.5?) seconds, at what fuel? 1%? About the real planes, I say again, they takeoff for airshows at around 50% or maybe less, so by the time they start doing that turn they have quite spent a lot of fuel, that's why I say they have a maximum of 30% left at that moment, maybe 20%, but not less either otherwise they can't continue the show for so much longer.

 

And about the video, again, you can find the originals on youtube, so they are the same, unaltered! I had no meaning to cut seconds from the moment the turn started until it ended. I want to seek the truth only!

 

What are you looking for as a reference for the 360 turning time? Time needed between the moment the nose or heading started to change until it came back to the same position or time needed between the moment the velocity vector started moving acceptably (although we don't see it on a HUD it has a bit of lagging behind the actual heading change) and the time the velocity vector passes through the initial (unchanged) heading? I used the second mode as a reference, because what I find important is how fast the CG (or velocity vector) changes over time, not the actual heading (which is affected by alpha changes). In the video when the nose pointed the initial heading only 11 seconds have passed, so I took care of that to not falsify anything and by actual heading prediction on turn rate I allowed the timer to go for more than 1 second more before calling a count. That's how it terminated in 12.33 seconds (12.10 frames, where 30 frames are 1 second).

 

Even if it may be +1 second more (13+ seconds), it still turns with at least 2 seconds better than what we can get in our simulator for 25% fuel left (infinite fuel used for this purpose), this is what the problem is all about, cause no matter how much someone tries to manage the AoA increment rate (different AoA onsets) during the turn (indeed not sharply pulling 30AoA by disabling the limiter) he can't do a horizontal turn below 13.5 seconds even at 1% fuel load or below 15 seconds at 25% fuel.

 

Here is another track proving this last paragraph. 1% fuel loaded:

 

[ATTACH]179238[/ATTACH]

 

Maybe the devs believe this won't need a change because the difference doesn't seem great, but it is. 2 seconds difference means our plane in DCS turns at least 15% worse than real.

 

About that turning diagram that you linked to us:

 

And neither of us will get those docs - as far as I'm aware, those who have them are not allowed to share.

 

Comparing to the F-16 isn't valid.

 

For reference, here's a page with a graph - ignore the eagle and viper data, it's (over and under) estimated.

 

Flanker configuration is 50% fuel, 2xR-73, 2xR-27R. No other configuration is valid for this comparison.

 

Atmospheric data unknown, but might just be ISA - 15C/standard day.

 

I have tried to see if our plane matches those max STR values for the different altitudes and airspeeds in there and it turns worse than in the chart! The real graph clearly shows a max STR of 20 dps at 200 meters while carring 2xR73 + 2xR27R as you said. You can't reach that STR even with no loadout at 50% fuel. And by the way, as the resulted graphs from my test clearly show there is no difference between a loaded configuration with the 4 mentioned missiles and a clean loadout another problem emerges, which is that the Flanker doesn't get a G-load reduction (lower lift to weight ratio) while loaded with missiles and also the needed AoA for trimmed speed remains the same, which means the drag increment isn't present/simulated!? The missiles cannot create lift while being carried on wings because the local AoA on each missile is close to null, but should create drag otherwise. The test shows that the plane doesn't get a resultant G-load reduction for the same speed (hence turn rate) and doesn't get a higher drag either (hance the constant AoA is the same). The truth is straight in front of us, so why do we ignore it?

 

Here is the plane's STR while flying at 12 AoA at 200m MSL, full AB, ISA conditions (15 Celsius), 50% fuel, NO loadout, having the speed trimmed at 650km/h IAS:

 

2058781091_Su-27STRatIAS650kmh200mhalffuelclean.thumb.jpg.3658fef53687203612921d2eae7e929b.jpg

 

Here it is under the same conditions (slightly lower AoA, around 11.2) but at 3000m MSL:

 

857449142_Su-27STRatIAS650kmh3000mhalffuelclean.thumb.jpg.cb221c0b185662925083dbed65b66c1a.jpg

 

Here is the plane's STR while flying at the same 12 AoA (surprisingly and abnormal) at 200m MSL, full AB, ISA conditions (15 Celsius), 50% fuel, loaded with 2xR-73 and 2xR-27R, having the speed trimmed at 650km/h IAS:

 

1433466926_Su-27STRatIAS650kmh200mhalffuel2xR73amp2xR27R.thumb.jpg.1117063654868d524be0bc084a49ffa8.jpg

 

Please verify that you obtain similar results!

 

Regards!

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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Max sustained turn happens at a given airspeed for the aircraft mass.

 

Max instantaneous turn happens at a lower airspeed for the same plane with the same mass.

 

You should read more carefully. Ironhand was talking aboutairspeed not turn rate.

...

 

You start the turn with a limited budget of energy, if you start at max sustained turn and carefully pull through bleeding energy to get to max instantaneous turn near the end it uses that energy budget wisely and gets you the fastest 360 turn.

 

That is what I'm trying to say as well, but you formulated it in another way! So you also agree that the maximum STR can't be higher than the maximum ITR, as Ironhand suggested!

 

If you pull straight to ITR at the start you waste a lot of energy, and as you bleed airspeed in the turn you fall below the airspeed needed for a decent turn rate. It gives a very tight radius, but takes a long time to do a 360 compared to a turn where the pilot does good energy management. This, I believe, was the point Ironhand was trying to make.

 

Yes, that's what he said and I understood that, but at some point (other sentence) it seemed to me that he contradict with himself by making it look like the max STR becomes greater than max ITR which sounded absurd, or maybe I mistook it for a lower speed ITR (if that's what he meant) which indeed may become lower than the highest possible STR (which of course corresponds to just one speed value).

 

The charts are made for pilots that are expected to take the aircraft into combat. How interested are they going to be in the performance of an aircraft with little fuel and no weapons?

 

Perhaps very interested if they get into that situation. About the weapons, maybe in less occasions as they usually score a hit before remaining with clean loadout, but about the fuel, in more occasions during dogfight.

 

I'm poking a bit of fun at you here, but in general performance charts for airshow configurations are less available or non-available compared to combat configurations. Though if you can find some airshow configuration performance charts I'm sure people would be happy to see them.

 

Ok, and could you give us an example of what would be so different? Do you want to say that the airshow plane misses a lot of weight compared to a combat ready one? How much weight can that be if it's true?

 

When people were complaining about your fuel percentages:

 

A fully fueled Su-27 only has about a ton less fuel than an F-15E with full internal and CFTs.

 

So unless your F-15C was 30% internal plus one full external tank (or equivalent fuel mass internally), it wouldn't really be a good comparison.

 

Relatively speaking, an F-15 with just 30% internal is a smaller proportion of its max takeoff weight than an Su-27 at 30% internal fuel is of its max takeoff weight. The Su-27 has a lot more internal fuel capacity for its size.

 

First of all, you might confuse me with people who like role playing games, I don't. I don't care about "balance" and stuff like that. I want each plane to fly like the real plane flies, regardless of people's liking.

 

Yes, as compared to it's MTOW, the Su-27's internal fuel covers a higher percentage than the F-15 does, but again, when I've said between 20 to 30% of fuel left when performing the quickest 360 turn I estimated the amount of fuel left if the airshow plane (F-15 or Su-27) would takeoff with 50% and until starting to do that turn it burned fuel until remaining with about 20..30% (25% let's say). So my comparison was strictly to related to each plane's turn rate abilities at airshows and hopefully in combat if there are no differences in actual weights for the same fuel, not about how a DCS F-15 vs Su-27 1vs1 guns only balance (for counterstrike lovers) would develop, cause again this is not what I seek.

 

 

Finally, 30 deg/sec is awfully high as a sustained turn rate for aircraft of that generation in a combat configuration. If you're basing on similar aircraft, a range of roughly 15 deg/sec to 20 deg/sec would be expected, with some of the more maneuverable ones getting to the mid-twenties in light configurations. The F-22 is supposed to be in the vicinity of 28 deg/sec or so.

 

For ITR, then 30 deg/sec is well within the realm of possibility. For thrust vectoring variants it might even go into realm of 60+ deg/sec. The problem is that if you pull that sort of maneuver, unless in the process you killed your last opponent you'll be in serious trouble due to lack of airspeed after having bled so much energy that you're slower than an A-10.

 

I know that very well, but this was not the point again, the only point is the comparison to the 30deg/sec AVERAGE (can't predict precisely the ITR from the video and there is no STR because the speed is dropping) throughout the whole turn.

 

The maximum possible turn rate is irrelevant except maybe in airshows, the maximum practical turn rate is what matters.

 

Couldn't be more correct, this is what I'm trying to merge into and as GGTharos gave us those golden Su-27 armed charts we have a good start for exactly that, and from my last post you can see how far our DCS Su-27 strings from those values.

 

 

Looking at your initial post's charts what I see is the F-15 getting to an ITR of around 29 deg/sec, and then bleeding a huge amount of airspeed. A very reasonable result.

 

For the Su-27 I see it pulling to 20 deg/sec, and then running into the limiter which keeps the foolishness of a full stick aft turn from hemorrhaging energy quite as badly as happened in the F-15. Using the override (wheelbrake keybind) you likely could have gained ITR and bled energy much like the F-15.

 

Even without the limiter turned off, the Su-27 didn't get more than a second faster through the turn, what do you say about that?

 

Your comparison isn't a turn rate comparison or a max lift comparison, it's an energy bleed comparison, and the only reason the Eagle won is because of user error in the Su-27. If you want to see how impressive the Su-27 is at bleeding energy all you have to do is correctly perform a Pugachev's Cobra maneuver. ;)

 

Looks like you don't see the big picture and start going off-topic. What I'm trying to prove is that no matter how well one would manage the turn by the AoA (hence stick), the F-15 completes the turn in less time than the Su-27, and I'm not talking about heading/nose pointing, but about speed/velocity vector carrying through the turn versus time. Even if for the tiniest split second the Su-27 would have a better ITR through a turn than the Eagle, it's dead, because the Eagle finishes the turn faster. So once again, either with a lower or higher Su-27 ITR compared to the Eagle, the Eagle carries it's mass (hence velocity vector) through the circle quicker. At least for any STR according to a constant speed range between 300km/h and above, the Eagle beats the Flanker, which is utterly opposed to the chart GGTharos just provided. Where is the truth?

 

Jokes aside, in your test you didn't correctly fly either aircraft for a maximum average turn rate and the results are about what would be expected based on publicly available information.

 

Yeah? Ok, then please be honest and do a test yourself trying to achieve the highest average turn rate with each aircraft (so be fair) and show us the results so we can see.

 

 

Edit: I just looked through the slide show you linked and the performance stats it cites are:

 

F-15

 

STR: 19 deg/sec

ITR: 26.4 deg/sec

 

Su-27 SK

STR: 19.4 deg/sec

ITR: 28 deg/sec

 

Doesn't say for what loadouts those are though.

 

"Combat ceiling, 4 AAM", it says. Probably, exactly the configuration told by GGTharos which corresponds to the diagram he provided.

 

If you're after evidence that the average turn rate for an Su-27 through a 360 deg turn is above 30 deg/sec you might not want to link sources saying that the max ITR is only 28 deg/sec. ;)

 

Yes it's a bit intriguing, so you might be right then and the airshow plane is much lighter, otherwise there's no explanation why in 2 authentic videos the airshow planes turn within 12 to 13 seconds.

 

If you hopefully didn't want to play blind on the other side, let's look at the Eagle for the same source of info. What do you read there? Max ITR = 26.4. AhAA! So now the Eagle in DCS is an airshow configuration for reaching almost 30 deg/s?

 

Regards7!


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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Ok, so you say you managed to do a horizontal 360 in 13-14 (rather said more than 13.5?) seconds, at what fuel? 1%? About the real planes, I say again, they takeoff for airshows at around 50% or maybe less, so by the time they start doing that turn they have quite spent a lot of fuel, that's why I say they have a maximum of 30% left at that moment, maybe 20%, but not less either otherwise they can't continue the show for so much longer.

 

Locked to 20%.

 

And about the video, again, you can find the originals on youtube, so they are the same, unaltered! I had no meaning to cut seconds from the moment the turn started until it ended. I want to seek the truth only!

 

I'm not accusing you of changing the videos; they're simply cut in a way that prevents good review.

 

What are you looking for as a reference for the 360 turning time? Time needed between the moment the nose or heading started to change until it came back to the same position or time needed between the moment the velocity vector started moving acceptably (although we don't see it on a HUD it has a bit of lagging behind the actual heading change) and the time the velocity vector passes through the initial (unchanged) heading? I used the second mode as a reference, because what I find important is how fast the CG (or velocity vector) changes over time, not the actual heading (which is affected by alpha changes). In the video when the nose pointed the initial heading only 11 seconds have passed, so I took care of that to not falsify anything and by actual heading prediction on turn rate I allowed the timer to go for more than 1 second more before calling a count. That's how it terminated in 12.33 seconds (12.10 frames, where 30 frames are 1 second).

 

Again I'm not accusing you of falsifying anything :D I'm accusing the videos of being cut in a way that makes them inaccurate for our purpose.

 

Regarding reference: I start counting from the stick is pulled on my end, until the heading is restored or even slightly past - it doesn't make a huge difference because I am controlling the AoA and I can roll out on-heading without delay. Of course, that's all up for debate.

 

Even if it may be +1 second more (13+ seconds), it still turns with at least 2 seconds better than what we can get in our simulator for 25% fuel left (infinite fuel used for this purpose), this is what the problem is all about, cause no matter how much someone tries to manage the AoA increment rate (different AoA onsets) during the turn (indeed not sharply pulling 30AoA by disabling the limiter) he can't do a horizontal turn below 13.5 seconds even at 1% fuel load or below 15 seconds at 25% fuel.

 

I'll redo my test.

 

Maybe the devs believe this won't need a change because the difference doesn't seem great, but it is. 2 seconds difference means our plane in DCS turns at least 15% worse than real.

 

First of all, doing the turn is 12 seconds is physically impossible. You can deduce as much from the graph that I supplied to you. It would require an average of 30deg/s, where that is a peak that you can only transition through.

 

I have tried to see if our plane matches those max STR values for the different altitudes and airspeeds in there and it turns worse than in the chart! The real graph clearly shows a max STR of 20 dps at 200 meters while carring 2xR73 + 2xR27R as you said. You can't reach that STR even with no loadout at 50% fuel.

 

Sure, I'll have a look. FMs aren't perfect, they can have a small percentage of error. I believe it's within 3% for the flanker. It could be a difference in drag (base or induced) or in thrust or everything together! But there's a limit to how tightly they'll tune this stuff - getting this close is already a lot of work. Losing 2+ deg/s though is certainly significant. I don't know the actual test conditions for the Russian chart, I assumed ISA. I'll go ask and see if my assumption was correct. Maybe it wasn't :)

 

And by the way, as the resulted graphs from my test clearly show there is no difference between a loaded configuration with the 4 mentioned missiles and a clean loadout another problem emerges, which is that the Flanker doesn't get a G-load reduction (lower lift to weight ratio) while loaded with missiles and also the needed AoA for trimmed speed remains the same, which means the drag increment isn't present/simulated!? The missiles cannot create lift while being carried on wings because the local AoA on each missile is close to null, but should create drag otherwise. The test shows that the plane doesn't get a resultant G-load reduction for the same speed (hence turn rate) and doesn't get a higher drag either (hance the constant AoA is the same). The truth is straight in front of us, so why do we ignore it?

 

Missiles add drag. I have no idea what you're talking about now. Is the STR with missiles lower than the one without? Did you add fuel weight equal to the missiles to a clean flanker to perform a weight-equivalent test?

Also, the pylons themselves are reasonably draggy. We don't know the pylon configuration of the graph, though I would assume it would be all aboard.

 

PS: I just looked at your charts - I won't have time to run my own tests until later, however - you've lost about 0.5deg/s when you put the weapons on. Looks ok to me. Missiles will indeed add drag, but you've already have so many many pylons hanging off the thing that their contribution is reasonably negligible.


Edited by GGTharos

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