Degraded Su-27 aerodynamic lift

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

 

Very good man, but now try to fly the plane and match the very valuable chart you linked, the one with the 2xR27R and 2xR73 loaded Su-27 and make the comparison again. I have made mine and the differences are quite big.

 

Fly a constant horizontal turn at 200msl at 600 or 700km/h IAS or as you wish (I did at 650km/h IAS), at 50% fuel, FULL AB (of course) and use Tacview again to see the turn rate, or pause the game when you consider you hold the AoA so that the speed and altitude won't vary, use the illustrated G-load (but substract 0.1 from it, because for some reason during play the outside view G-meter always shows a higher value by 0.1 or so (tested)) and actual speed on the circular pattern (actual IAS) and determine the constant turn rate. Formula is ω = G/V, where V is IAS and G is G-load. But using Tacview is more accurate anyway.

 

Regards!

Like I said, I will check it. There's no need for this much math here. Do a sustained 360 and you'll get a good average. And like you mentioned, tacview works great :)

 

Very good man, but now try to fly the plane and match the very valuable chart you linked, the one with the 2xR27R and 2xR73 loaded Su-27 and make the comparison again. I have made mine and the differences are quite big.

 

Fly a constant horizontal turn at 200msl at 600 or 700km/h IAS or as you wish (I did at 650km/h IAS), at 50% fuel, FULL AB (of course) and use Tacview again to see the turn rate, or pause the game when you consider you hold the AoA so that the speed and altitude won't vary, use the illustrated G-load (but substract 0.1 from it, because for some reason during play the outside view G-meter always shows a higher value by 0.1 or so (tested)) and actual speed on the circular pattern (actual IAS) and determine the constant turn rate. Formula is ω = G/V, where V is IAS and G is G-load. But using Tacview is more accurate anyway.

 

Regards!

So I checked with Yo-Yo and the answer was very surprising to me! :)

 

The 50% 'internal fuel' is considered to be 50% of internal tanks, wing tanks are considered external.

 

That means that the actual fuel weight for this graph is about 30% of total. Try running your test with that.

So I checked with Yo-Yo and the answer was very surprising to me! :)

 

The 50% 'internal fuel' is considered to be 50% of internal tanks, wing tanks are considered external.

 

That means that the actual fuel weight for this graph is about 30% of total. Try running your test with that.

My apologies for disappearing from this conversation. This week has not been kind.

 

Well, isn't that just the cat's"meow". I had decided to try sustained turns with 50% fuel and 4 AAMs this morning and didn't like the results. So I reduced fuel to 30% with 2xR-72 and 2xR27R. Came here to post the results and saw your post.

 

Here is what I get for sustained turns at 900, 800, 700, 600 (TACVIEW files are attached):

 

 

 

 

 

Pretty good at the higher TAS levels. There's a bit more dropoff compared to the chart at 600 & 700. Also the G's for the 600 & 700 a definitely less than on the chart which, I suppose follows.

 

And a turn pulling to max ITR. It was nice to see that 30°/sec spike on the graph:

 

 

 

 

 

 

 

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.

 

 

 

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!

That was absolutely not what I was suggesting. Just the opposite.

 

...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).

That was my point. You have to enter the turn at a higher speed required for max STR and pull toward the lower speed required for the ITR in that turn.

 

Originally Posted by Ironhand

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?...

 

I guess that's what I got that day for posting, when I'm rushed. I conflated the two ways to conceptualize it. Read that as either "26°/sec averaged to complete the 360" or "14 seconds to complete the 360". Either reflects what I was thinking.

Tacview.zip

Edited February 17, 2018 by Ironhand

So if I read this right, you got the best STR at 900 km/h, 21°/sec ?

So if I read this right, you got the best STR at 900 km/h, 21°/sec ?

Unfortunately, yes. :) According to the chart, I should only be getting about 19.5°/sec @ 9Gs The 800 km/hr STR is the one that matches most closely. The Gs are correct and the rate is a very close match. The 700 & 600 tests were a bit under for both compared to the chart.

Edited February 17, 2018 by Ironhand

Depends on what you're trying to accomplish. Yes, the turn rate is the highest at this point, but your turn circle size and required g is also something to consider.

 

So if I read this right, you got the best STR at 900 km/h, 21°/sec ?

There are 2 problems at the moment. One regards the Su-27 which falls under that true chart (talking about STR of course), the other problem is the Eagle (after later tests prove) in DCS which outturns the Su-27 by 2 seconds in a 360 turn.

 

There is one thing when talking about a 360 turn in which it seems that some people don't understand how to obtain the smallest amount of time needed and rather think of how the ITR varies with speed (which affects the average turn rate). They talk about managing the AoA as to not get it too high too soon (thus smoothing out the ITR increment as speed drops). That would indeed be useful if you want to obtain the highest average turn rate for more than one circle of turn, but if you want to obtain the highest average turn rate for just a 360 turn which was the only subject here, pulling full aft stick regardless of how the AoA and drag (thus airspeed drop) evolve, will always get you the lowest amount of time required, of course, unless you want longer turns (because you have indeed already wasted most of the energy).

 

Here's another track which is proof that after some update (don't know which) the F-15C has "found" a greatly exaggerated lifting to drag performance (mostly lift increment as it seems the deceleration rate through the turn is the same as it was when PFM came out) which translates to an abnormally high turn rate for this plane in particular.

 

DCS F-15C's exaggerated lifting performance.trk

 

Both planes loaded with just 1% fuel (infinite). The Su-27 can't do a 360 i less than 13.8 seconds. The F-15 however does it in 12 seconds flat.

 

How come the DCS Eagle outturns the Flanker in all areas (STR and average turn rates)?

 

Let's not forget key facts regarding the F-15C.

 

1.The F-15 has no slats, thus a lower critical AoA before the wing stalls (about 6-7 degrees lower), not to be confused with the fuselage which stalls later due to the vortexes generated between the inlets. Another problem although seems to show up which is that above 20% AoA (where the wings stall for the real F-15C), the lift continues to increase O.o. Yes, those little vortexes between the inlets keep the fuselage (or the area they wash) from stalling until some 10 or more degrees of AoA (about 30+), but the lift should find a smooth decrease from 20 to supercritical AoA (at vortex breakdown). What we see is a constant lift increment above 20% which is nothing but wrong.

 

2.The F-15 has no LERX. Huge amounts of lift slope, maximum lift and higher directional stability and also very much higher critical AoA is achieved through this. Still in DCS it behaves like it has LERX, not like it hasn't.

 

3.The F-15's wing has an AR (aspect ratio which mostly influences lift slope, maximum lift, drag slopes and thus L/D ratio) of 3.0 which is lower than that of the Su-27 (AR = 3.5), so just from start, the F-15 finds an overall lower maximum lift coefficient (could be 10 to 15% lower) and lower lift to drag ratio (so it loses speed faster at a given G-load), thus irrefutably it's turn rates should suffer (both ITR and STR) even against a fighter with similar wing loading and thrust to drag ratio. The F-15 was mostly designed for interception, not to be an excellent dogfighter..., but in DCS it even outturns a real F-16.

 

Take this as a reference: F-16 better than F-15 in terms of maximum lift and lower L/D and also better turning performance. Su-27 very close to the F-16 in this domain. This is reality, so in no way we should see the opposite in DCS, right?

 

Here's a video of the best F-16 (equipped with the most powerful engine for it, the GE F-110) in which you can clearly learn that the fighter which always wins against the F-15C at turn rate, when having just around 2000lb of fuel left (around 25..30% left) takes at least 14 seconds to complete a 360 turn:

 

So how in the world does the F-15C in DCS do it in less than 13 in comparable circumstances?

 

Regards!

There are 2 problems at the moment. One regards the Su-27 which falls under that true chart (talking about STR of course), the other problem is the Eagle (after later tests prove) in DCS which outturns the Su-27 by 2 seconds in a 360 turn.

 

That 'problem' exists only in your mind. In other words, that the F-15 turns faster than a flanker isn't a problem. The only problem that can exist is an eagle turning faster than an eagle.

 

Both planes loaded with just 1% fuel (infinite). The Su-27 can't do a 360 i less than 13.8 seconds. The F-15 however does it in 12 seconds flat.

0/10 completely unrealistic scenario. Flanker is a heavy airframe.

 

How come the DCS Eagle outturns the Flanker in all areas (STR and average turn rates)?

Who cares? Does an eagle out-turn an eagle?

 

Let's not forget key facts regarding the F-15C.

Yes, let's not forget that there are charts to test to. Everything else you said has no value in view of actual data :)

 

I hate to break it to you, but the F-15 FM is very well validated. And yes, it was designed to be an excellent dogfighter.

When you load a plane with unrealistic fuel load you get unrealistic performance. Is there a problem when you have a realistic fuel load? F-15 wing seems to be optimized for low AoA so it performs well when fast or light when you don't need high AoA for turning.

 

Full aft stick pull is optimal for only about 90-180 degrees in typical combat load, depending on starting speed so you do need to manage AoA in order to make a good 360 turn. From corner speed you only get about 90 degrees. If you fly with empty fuel tanks you can get unrealistic UFO behavior but is that contructive way to asses flight model?

 

We don't care if you feel like Su-27 doesn't turn good enough compared to F-15 as it's not scientific way to get correct performance. F-15C has moving intake ramps that can act as leading edge flaps for the fuselage which both Su-27 or F-16 doesn't have. F-15 also has relatively light but strong contruction because of simple wing structure. Which feature is better and how much and in what condition? Comparing planes using their outer appearance is fallacy anyways unless done using wind tunnel or CFD. Professional designers don't simply slap on aerodynamic features because "slats give 15% more turn rate" but actually use wind tunnels, CFD and test flights to get desired performance from their design. More stuff means more weight and weight means less performance so you need to balance weight and stuff. Why would we do any better as amateurs? There are performance graphs from real planes to asses sim performance.

I must suck at flying this eagle, I can't get it to turn around in under 14 sec.

 

PS: Actually I can make it happen in about 13 in the eagle with an insane 500kt start and a near 12g turn.

 

I can get the flanker started at 850kph and do it in about 12 sec with similar insanity. So, does the flanker turn better? Yep!

 

It's all good if your pilot survives. Generally speaking you'll run yourself out of AoA must sooner in the eagle than you will in the flanker so, while the flanker's still turning, you'll be stuck trying to get your nose around 90 deg before him.

 

That's if you have g simulation on and you try to make a sensible ITR turn.

 

1% fuel, too.

Edited February 19, 2018 by GGTharos

Quite a bit of essential info missing in your comparison.

 

1. What are the airfoil differences between the F-15 and the Su-27?

2. What's the difference in washout?

3. The F-15 doesn't have slats but the Su-27 doesn't have slats either.

4. Do you mean 20° AoA? I don't know any airfoil on which flow stays attached at such a high AoA.

 

Su-27 doesn't have slats? :D

I thought slats were leading edge flaps... I need to look into that ! :)

I thought slats were leading edge flaps... I need to look into that ! :)

 

So did I. I will give you guys this - I love the discussion. Lots of information to digest.

The Su-27 certainly has slats....

And again, I don't think so. Of course I'm curious where you have got your info from? Do you have a link?

 

From the FC3 manual :

Ailerons and flaps were replaced with unified control devices -

flaperons, wing leading edges were fitted with slats (the T-10 had no leading edge high-lift devices),

the automatic adaptive deflection mode for the flaperons and leading edge slats was ensured

providing for the fighter's "polar curve envelope" flight concept.

 

Also on Wikipedia and so on.

Can you post serious links? Not from pc games and wikipedia?

 

Btw, the later T-10 version did have leading edge flaps.

Nope, sorry, I am in no way an expert. I was just answering to your question about where one could have read that information.

On that note, I'm out.

Leading Edge Flaps(LEFs) is the same thing as "slats" and yes the Su-27 has them :)

 

It doesn't have separate trailing edge flaps and ailerons - the functions of those are combined in single devices known as "flaperons".

 

Btw, the later T-10 version did have leading edge flaps.

 

The initial T-10 design you were referring to was never put into service - it was a pre-production design that was abandoned because it didn't meet the performance specifications set out for the aircraft. Subsequently the aircraft was completely re-designed and assigned the factory designation T-10S, under which it entered service as the Su-27 in 1983-84. This is also the reason why the "baseline" Su-27 got the NATO designation "FLANKER B"("FLANKER A" had been assigned to the abandoned initial design).

 

The "baseline" Su-27 was produced in two sub-variants; the Su-27P for the PVO(air defence forces) and the Su-27S for the VVS(airforce) - the designation suffixes are rarely used though and the difference between them basically boils down to the former having no air-to-ground capability.

 

So the Su-27 version in DCS is the Su-27S(T-10S).

Macerick explained the difference well. F15 is energy fighter and flanker better in close combat. Thats fundamental difference and RL fact. Yenkee knows it, Commies knows it. DCS is wrong.

 

 

Sent from my iPhone using Tapatalk

No slat gap...

We call that Kruger Flap .

No hinge rib or driven rib. Only flap on articulated hinge with actuators . Less eficient than slats for sure.

And then what is your opinion ?

Thèse are kruger flaps adapted To su27

Edited February 20, 2018 by =THRUST=

Not really. Kruger flaps are as well noticable different compared to LE flaps.

Perhaps. But if the function of a slat is to allow air to flow from below the leading edge to the top of the wing to increase allowable AoA, no gap means it would function similarly to a Kruger flap, wouldn't it. Different name but similar effect.

The function of the gap is To create an air mouvement coming from intrados To stick the stream more eficiently on the top skin or extrados. You cant do it with kruger