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Old 02-13-2018, 01:33 AM   #61
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Quote:
Originally Posted by GGTharos View Post
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).?
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Old 02-13-2018, 01:39 AM   #62
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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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Old 02-13-2018, 01:39 AM   #63
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Like I said, IGNORE the F-15 and F-16 data.
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Old 02-13-2018, 01:51 AM   #64
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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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Old 02-13-2018, 02:30 AM   #65
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Quote:
Originally Posted by Maverick Su-35S View Post
...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.


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...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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Old 02-13-2018, 03:58 AM   #66
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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!

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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.

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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:

Quote:
Originally Posted by Ironhand View Post
...The highest instantaneous rate is at the lowest speed that can generate maximum G...
Correct!

Quote:
Originally Posted by Ironhand View Post
...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)?

Quote:
Originally Posted by Ironhand View Post
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.

Quote:
Originally Posted by Ironhand View Post
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!
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Old 02-13-2018, 04:01 AM   #67
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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
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Old 02-13-2018, 04:41 AM   #68
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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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Old 02-13-2018, 04:58 AM   #69
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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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Old 02-13-2018, 05:50 PM   #70
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Quote:
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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.


Quote:
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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