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SU-27 and J-11 slower to regain airspeed after maneuvering..


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It seems that the su-27 and the j-11 have had the thrust levels changed ?.. they used to recover airspeed quickly during a turning fight especially if you lowered the nose. Now it seems they are no longer recovering that airspeed even in full AB with 10 to 20 degrees of nose low.... anyone else notice this?

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They are both very heavy aircraft, and getting slow is not the best thing in the world - the advantage of small light fighters is that they can get out of this hole faster - but it doesn't mean that this isn't a bug (or deliberate change!).  Do you have any tacviews or anything else that might show the discrepancy?  When did this start happening?

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36 minutes ago, GGTharos said:

They are both very heavy aircraft, and getting slow is not the best thing in the world - the advantage of small light fighters is that they can get out of this hole faster - but it doesn't mean that this isn't a bug (or deliberate change!)...

Weight should not be a factor, but rather thrust-to-weight ratio. If a heavier airplane has more thrust to its relative weight then a lighter one, it will accelerate quicker.
 

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4 minutes ago, Cmptohocah said:

Weight should not be a factor, but rather thrust-to-weight ratio. If a heavier airplane has more thrust to its relative weight then a lighter one, it will accelerate quicker.

 

You're right about TWR, but as you see from its name weight is a huge factor; when slow you've got inertia and induced drag vs. reduced thrust (thrust generally decreases for turbofans if the speed is too low or too high).

 

And thus why I'm asking if there's a comparison, because there are a lot of things one can run into that will cause an apparent difference:  Maybe there's more fuel, maybe technique has regressed a bit and even though the nose is being pointed down, the pilot is still keeping the aircraft loaded etc.

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On 12/20/2020 at 6:40 PM, chucknellie said:

I fly the SU-27 and J-11 ALOT. It just seems much more sluggish. It may have started at this last update a few days ago. Seemed fine until then. Might just be me......

For me the Su-27 always accelerated like a truck, so I can't really tell if it's more or less sluggish than before.

But personal impression is not really a valid argument :D.

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On 12/20/2020 at 9:14 AM, chucknellie said:

It seems that the su-27 and the j-11 have had the thrust levels changed ?.. they used to recover airspeed quickly during a turning fight especially if you lowered the nose. Now it seems they are no longer recovering that airspeed even in full AB with 10 to 20 degrees of nose low.... anyone else notice this?

Just tested the Su-27. Flew in an older version of Release (2.5.6.55960). Saved the TRK and played it through the latest Beta (just finished downloading yesterday). End speeds were identical. So no difference as far as the Flanker is concerned.

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The perception of sluggish acceleration is probably due to fuel carried. Max fuel for the Su-27 is 9,400Kg (possibly with another 500Kg in the cache tank). Put in to perspective, fully fuelling an Su-27 adds more weight than strapping an empty F-16C to it would. Fully fuelled and fully laden with A-A or A-G stores the Flanker does behave like a beached whale. Take it down to 30% fuel with 4 x missiles and it's a very, very different machine.

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14 hours ago, DarkFire said:

The perception of sluggish acceleration is probably due to fuel carried. Max fuel for the Su-27 is 9,400Kg (possibly with another 500Kg in the cache tank). Put in to perspective, fully fuelling an Su-27 adds more weight than strapping an empty F-16C to it would. Fully fuelled and fully laden with A-A or A-G stores the Flanker does behave like a beached whale. Take it down to 30% fuel with 4 x missiles and it's a very, very different machine.

I think it mostly comes from the drag of the R-27 missiles. If you put same fuel, let's say 75%, and two Su-27s one with 4xR-27 and one with 6x, the latter one will be significantly more sluggish. Now if you consider, what garbage the R-27 missile family is, we come to the conclusion that one should strap on as many as one can. Hence, the sluggish feel.

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It's not just drag - the weight of an R-27E is 350kg, 250kg without the E.   Flankers don't load all of the stations when on patrol, but I expect the ideas is that even if they do, a lot will be expended BVR.

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  • 2 weeks later...

Because it is a flying airbrake, like all aircraft.  You're not pitching that much AoA during a landing roll-out and after the aerobraking if you don't hit the brakes, the tyre friction is all you got for a braking force ... not sure why you'd even ask such a question.

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The SU-27 has always lacked some thrust in DCS after it got its PFM. I personally did not notice any difference lately and i find the actual acceleration to be quite realistic in the low subsonic range. Its problem is in the transonic regime. If you've ever tried to do some time to climb tests I am sure you've noticed that too. At the moment a low fuel, clean Flanker needs about 60% more time to reach Mach 1.6 than the Eagle from a standing start, and that's ridiculous... (it seemingly needs an infinite amount of time to get over mach 1.2) but you don't notice this problem in a dogfight because its performance in the subsonic range is totally believable and most likely correct as i already stated. An official figure we have is the 15 seconds needed to go from 600 to 1100 km/h at sea level with 2000 kg of fuel,  and in the game we can match that result. In conclusion, if there's anything to fix, it's not the slow speed range.

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3 hours ago, TaxDollarsAtWork said:

Is there a graph with that trans sonic acceleration somewhere?

Do you mean a graph of the transonic acceleration in DCS or in real life? We should be able to produce a graph from DCS quite easily, while for the real acceleration charts that's a different thing, I don't have them and I really don't think they're available anywhere. All we have is some talking from flanker pilots in the russian section of this forum and common sense that tells you that there's clearly something wrong about it, given the huge disparity between its behaviour and that of all the other fighters with movable intake ramps of the game. Also at higher speeds, around mach 1.6, the flanker starts accelerating as much as the eagle. It's really an odd behaviour, I don't know why it isn't addressed more often

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21 hours ago, stefasaki said:

If you've ever tried to do some time to climb tests I am sure you've noticed that too. At the moment a low fuel, clean Flanker needs about 60% more time to reach Mach 1.6 than the Eagle from a standing start...

I’m a bit confused. You start by talking about time to climb and end by talking about acceleration to M 1.6.

 

Awhile ago, I did some max mil climbs according to the book and was shocked at how little time it took to reach 11,000 meters. I’ve never bothered with the afterburner regimen but perhaps I should.

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On 1/10/2021 at 3:45 PM, Ironhand said:

I’m a bit confused. You start by talking about time to climb and end by talking about acceleration to M 1.6.

 

Awhile ago, I did some max mil climbs according to the book and was shocked at how little time it took to reach 11,000 meters. I’ve never bothered with the afterburner regimen but perhaps I should.

I should have worded that differently. A common test is a mixed time to climb and time to speed. It’s relevant for scramble scenarios. Time to 11000 m and mach 1.6 is a common test for interceptors, as it gives you an idea of both climbing and acceleration. The su-27 suffers particularly on this aspect in DCS


Edited by stefasaki

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1 hour ago, stefasaki said:

I should have worded that differently. A common test is a mixed time to climb and time to speed. It’s relevant for scramble scenarios. Time to 11000 m and mach 1.6 is a common test for interceptors, as it gives you an idea of both climbing and acceleration. The su-27 suffers particularly on this aspect in DCS

 

What should the Su-27’s time be out of curiosity.

 

Edit: Also want to know the specified fuel quantity. I’m assuming 4 AAM’s. Correct?


Edited by Ironhand

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1 hour ago, stefasaki said:

I should have worded that differently. A common test is a mixed time to climb and time to speed. It’s relevant for scramble scenarios. Time to 11000 m and mach 1.6 is a common test for interceptors, as it gives you an idea of both climbing and acceleration. The su-27 suffers particularly on this aspect in DCS

 

Sure, you test it according to the time-to-climb procedure for the specific aircraft usually found in the aircraft's manual, along with the time-to-speed.   I'd like to know what those are for the flanker.

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23 hours ago, GGTharos said:

 

Sure, you test it according to the time-to-climb procedure for the specific aircraft usually found in the aircraft's manual, along with the time-to-speed.   I'd like to know what those are for the flanker.

The climb schedule is similar for most fighter jets. The SEP is highest at around Mach 0.9 and a climb should be performed at around that speed. Both the f-15 and the su-27SK manuals that are available online confirm this: for the f-15 we have the full max SEP graph on its performance appendix that shows you that the eagle follows that, while for the incomplete su-27sk manual there's just written that a maximum climb to 11000 m should be performed at around Mach 0.9. Also, changes in climb schedule have a lower order of magnitude effect on the overall time to mach 1.6  (you can test this yourself in DCS) compared to the 60% difference  that we currently have between the two aircrafts. The eagle should have the advantage but, in particular for a clean aircraft, this should be very slim. 

 

The gap increases between the two aircrafts if they carry missiles, but that's understandable. The problem is the base value.

 

 

My personal estimate, coming from experience with various aircrafts manuals and a degree in aeronautical engineering, is that the difference between a flanker and an eagle at low fuel and in a clean configuration should not be more than 5~10% (and closer to 5)

 


Edited by stefasaki
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I haven’t been in the F-15’s cockpit for years. Just flew a profile and was shocked at how quickly it got to altitude and speed compared to the Su-27.

 

I flew both aircraft clean with comparable (1.32% base gross weight) fuel loads. The F-15 was at 11000 m and 1.6M in 172 sec (2:52). It took the Su-27 258 sec (4:08) to achieve the same.

 

Quite an eye opener.


Edited by Ironhand

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On 1/12/2021 at 2:18 PM, Ironhand said:

What should the Su-27’s time be out of curiosity.

 

Edit: Also want to know the specified fuel quantity. I’m assuming 4 AAM’s. Correct?

 

Performance charts in the Su-27 manual are usually for a configuration with: 50% fuel, 2xR-27 and 2xR-73

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50% of fuel of the 'basic' configuration which is something like 2800kg IIRC.

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21 hours ago, Ironhand said:

I haven’t been in the F-15’s cockpit for years. Just flew a profile and was shocked at how quickly it got to altitude and speed compared to the Su-27.

 

I flew both aircraft clean with comparable (1.32% base gross weight) fuel loads. The F-15 was at 11000 m and 1.6M in 172 sec (2:52). It took the Su-27 258 sec (4:08) to achieve the same.

 

Quite an eye opener.

 

That's pretty much what I mean. You found exactly a 50% difference, which is not realistic at all (my disparity was slightly larger because my time with the eagle was slightly lower). Should we post this as a different thread? This risks to go unnoticed otherwise (as it did for 3 or so years)

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