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Degraded Su-27 aerodynamic lift


Maverick Su-35S

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Apparently certain tanks (wing tanks for sure) are not considered 'internal fuel'. I didn't get a more detailed explanation unfortunately and I can't read the manual :/

Manual says there are 3 options of refueling the plane.. full (forward, center, back & wings), basic (center & wings), partial (center).

So the graphs for example state.. 50% remaining of normal fueling, which could been interpreted as 50% of basic option.

 

tank forward - 3180 kg

tank center - 4160 kg

tank wings - 1060 kg

tank back - 1000 kg


Edited by Vatikus
added fuel tank volumes
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Apparently certain tanks (wing tanks for sure) are not considered 'internal fuel'. I didn't get a more detailed explanation unfortunately and I can't read the manual :/

 

Someone once said that "the Su-27 carries its external fuel internally" :) .

JJ

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^

Hwasp, could you post anything that you believe is relevant? I think you have a more complete manual than I do.

 

Sorry but I only have my phone and tablet until saturday, and I can not upload anything from those for some reason.

 

The pages I have found interesting are 13/269 14/269 (limitations) 20/269 (flight envelope) and 51/269. Please have a look at those.

 

I think chapter 1 (limitation) and chapter 4 (maneuvers?) are the most relevant for us here, so if parts of it could be translated, it would be great :)

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Now, (a bit absurd one will find it), the F-15 turns better than the Flanker at both low (full aft stick full AB) and high speeds (around the best turn corner). For short, with both planes fueled the same (30% fuel), the F-15 completes the fastest (full aft stick from around corner speed) 360 turn in about 14.4 seconds, while the Flanker in no less than 15.8. How did this happen?

 

 

I'm not sure if this has been pointed out... and I'm otherwise not getting involved in a debate about flight models..

 

But the Flanker's fuel is measured in tonnes. Full capacity is 9.4 tonnes, or 18800 lbs.

 

F-15C's internal fuel capacity is measured in lbs and maxes at something like 13,400 lbs or 13, 800 lbs.

 

Hopping in both aircraft and fueling them both up to 30% is not "fueled the same".

 

Flanker is carrying 5,640lbs of fuel.

 

F-15c is carrying 4,140lbs of fuel. How much this would effect your "testing" I won't go as far to assume.. but there's 1500lbs difference in fuel weight there. Seeing as we're talking about the accuracy of an FM.. perhaps it'd be worth running your test with accurate fuel measurements.


Edited by Headwarp
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We're good now, Vatikus provided exactly the information required.

 

Basic fueling would be 5220kg, which would result in a 50% fuel weight of 2610kg or 5700lbs, or 28% of total fuel.

The implications on maneuverability here are fairly big.

 

Sorry but I only have my phone and tablet until saturday, and I can not upload anything from those for some reason.

 

The pages I have found interesting are 13/269 14/269 (limitations) 20/269 (flight envelope) and 51/269. Please have a look at those.

 

I think chapter 1 (limitation) and chapter 4 (maneuvers?) are the most relevant for us here, so if parts of it could be translated, it would be great :)

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In this case, where we have the charts of the two aircraft, the only valid measurements are that of DCS FM vs. the aircraft's data.

 

From there on, any comparisons between the two aircraft have value in DACT knowledge, not in the judging of one aircraft's performance based of that of another.

 

So the comparisons can be made for any desired purpose OTHER than making claims that one or both FMs are somehow wrong.

 

F-15c is carrying 4,140lbs of fuel. How much this would effect your "testing" I won't go as far to assume.. but there's 1500lbs difference in fuel weight there. Seeing as we're talking about the accuracy of an FM.. perhaps it'd be worth running your test with accurate fuel measurements.

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In this case, where we have the charts of the two aircraft, the only valid measurements are that of DCS FM vs. the aircraft's data.

 

From there on, any comparisons between the two aircraft have value in DACT knowledge, not in the judging of one aircraft's performance based of that of another.

 

So the comparisons can be made for any desired purpose OTHER than making claims that one or both FMs are somehow wrong.

 

Personally, again I'm not here to debate FM. But perhaps anyone that is here to provide input on FM or even just comparison data, along with required documentation, can at least use simple math if wanting to test by fuel weight to actually make the fuel weight equal as "fueled the same" would imply.

 

Also making such an argument based on their own testing, might want to provide video evidence with instrument flight as empirical proof that one can perform an 100% coordinated turn in both aircraft, under the same atmospheric conditions.

 

But more or less was just pointing out that claiming 30% of two different values is equal pretty much skews any test results that turned this into a 21 page thread.


Edited by Headwarp
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You are right about that. Some have suggested that aircraft should be fueled to 'same endurance' for testing.

 

Personally I think none of that should be done, and instead do the charts for each aircraft at different weights etc, then overlay them. Then you'll have data for any circumstances.

 

In any case, this thread was all about FM and who out-turns who. In the end, the flanker turns just fine - it's quite deadly when flying it in order to do what it was meant to do, instead of lab tests :)

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That certainly calls for a in soviet russia joke :D

 

Heh yeah - it sounds contradictory, but there is some truth to it and, as per Yo-yo's remark, it also sounds like thats exactly how it is regarded :) .

JJ

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I'm not sure if this has been pointed out... and I'm otherwise not getting involved in a debate about flight models..

 

But the Flanker's fuel is measured in tonnes. Full capacity is 9.4 tonnes, or 18800 lbs.

 

F-15C's internal fuel capacity is measured in lbs and maxes at something like 13,400 lbs or 13, 800 lbs.

 

Hopping in both aircraft and fueling them both up to 30% is not "fueled the same".

 

Thats true and, as mentioned, the large internal capacity of the Su-27 is in part down to a design decision not to employ external drop tanks, but...

 

Flanker is carrying 5,640lbs of fuel.

 

F-15c is carrying 4,140lbs of fuel. How much this would effect your "testing" I won't go as far to assume.. but there's 1500lbs difference in fuel weight there. Seeing as we're talking about the accuracy of an FM.. perhaps it'd be worth running your test with accurate fuel measurements.

 

...you would normally also try to scale the fuel capacity to engine consumption. The Su-27 has more engine power than the F-15C and thus likely a higher consumption rate, so it might actually need that extra fuel to achieve the same endurance.

 

But for trying to evaluate the accuracy of the FM against official performance charts, it is of course necessary to assign the exact fuel state used in these.

JJ

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Thats true and, as mentioned, the large internal capacity of the Su-27 is in part down to a design decision not to employ external drop tanks, but...

 

 

 

...you would normally also try to scale the fuel capacity to engine consumption. The Su-27 has more engine power than the F-15C and thus likely a higher consumption rate, so it might actually need that extra fuel to achieve the same endurance.

 

But for trying to evaluate the accuracy of the FM against official performance charts, it is of course necessary to assign the exact fuel state used in these.

 

Regardless of consumption, I would assume if you wanted to compare the turning performance of the airframes from Aircraft A, and Aircraft B, any fuel added is an addition to the airframe. To give one more weight in fuel than the other is certainly going to effect its flight characteristics.

 

It's not the same as comparing flight longevity, and then that's not even considering whether or not there is a desire to compare aircraft using a set gross weight and what it would take to achieve equal numbers there.

 

That being said.. I'm not an aeronautical engineer or anything. So I'll not argue further, but since the subject was the turning speed of two aircraft and not the amount of time either is spending in the air.. seems to me equal amounts of fuel would only be fair. 1500lbs isn't exactly light. Think 3 gbu-12's and how a plane is effected dropping just one of them...minus the drag they would induce.

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Lets get back to the point please!

 

So according to the data in the manual, I would expect the plane to reach 8 g at 740 kmh indicated at 1000 m with the previously mentioned 28% fuel with stick pulled back to the limiter.

 

740 kmh roughly means 0,6 Mach at that alt. meaning 23 deg AOA commanded by the limiter. This corresponds to about 22 deg\second turn rate, which is about max sustained.

 

Question is: Does it fly like that or not? If not, why?

 

Also from the same table, max g at 600 kmh should be roughly 6g with AOA limited to 24 deg (Mach 0.5)

Is 6g available at 600 kmh in DCS?

 

Next there is a flight envelope figure in the book that shows 8g at 550 kmh (roughly) at a weight of 21400 kg. I would assume that this figure is with the stick pulled back as far as it goes. Limiter override or direct control.

 

This would correspond to a max instantenous turn performance of 29,5 degrees per second. Does the plane achieve that with the stick limiter override or not?

 

Please test the following data! (I can't because I'm away from home until saturday)

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If my memory serves me right, the Su-27 limiter in game does not let you pull beyond 22 degrees of AoA as the speed decreases below M 0,7 and that makes the plane perform worse than expected in the 600 kmh region, where it should have the upper hand against other fighters.

 

So the main question again: can you pull 6g with the limiter on at 600 kmh or not?

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If my memory serves me right, the Su-27 limiter in game does not let you pull beyond 22 degrees of AoA as the speed decreases below M 0,7 and that makes the plane perform worse than expected in the 600 kmh region, where it should have the upper hand against other fighters.

 

So the main question again: can you pull 6g with the limiter on at 600 kmh or not?

Unfortunately, like you, I'm not where I can run a new test at 1000m altitude. I had done a previous test awhile back at 200 m based on the chart that GG posted and got these results:

 

attachment.php?attachmentid=180151&d=1519911630

 

So I'm thinking that you might not quite be able to. Fuel at the time was 30%, though. And this is only attainable by pulling thru the limiter (holding down the Y-key).


Edited by Ironhand

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Press the Y key, I think you have to hold it down.

 

I understand the function of the limiter override and use it frequently. I also use the direct control mode during dogfights.

 

In direct control the plane is capable of 8 gs at that speed at low weights

 

I think the values in the manual are without overriding the limiter, since it is not a normal procedure to do so (except the flight envelope chart, that seems to show the raw aerodynamic capabilities)

 

Also in the limitations section there are different AoA limits for different speeds. In my opinion that means the limiter should set itself to those values.

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Overriding the AoA limiter in RL is pulling through the force imposed by the mechanism - there's no button like we have, so I basically disagree with your statement :)

 

I have seen different G limitations based on speed, but not AoA. Where is that?

 

I wouldn't be against concluding that limiter override doesn't give you quite enough authority for whatever reason.

 

I think the values in the manual are without overriding the limiter, since it is not a normal procedure to do so (except the flight envelope chart, that seems to show the raw aerodynamic capabilities)

 

Also in the limitations section there are different AoA limits for different speeds. In my opinion that means the limiter should set itself to those values.

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I´m not sure about your last statement.

 

There is a switch to disengage the AoA-G limiter ¡n the cockpit.

 

KonFkzM.jpg

 

Maybe i´m wrong but if this is not a switch to turn off the AoA-G limiter, what is the function of the switch?

 

In the Su-27SK manual also there are a explicit reference about "Turning Off the limiter during acrobatic maneuvers doesnt give any apreciable gain in maneuvrability and is possible to make the plane stall or exceed the load limits"


Edited by Esac_mirmidon

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Overriding the AoA limiter in RL is pulling through the force imposed by the mechanism - there's no button like we have, so I basically disagree with your statement :)

 

I have seen different G limitations based on speed, but not AoA. Where is that?

 

I wouldn't be against concluding that limiter override doesn't give you quite enough authority for whatever reason.

There's a section in the manual dealing with various aircraft limitations that states acceptable AoA limits for various Mach #s beyond with you might lose control of the aircraft. I believe that's what he's referencing.

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I think if there is a switch in the real cckpit for turning off the AoA-G limiter is because it has a real function.

 

Because people in DCS are mapping the AoA-G limiter On-Off in the stick for comodity doesnt mean that in the real cockpit you must move a switch in the left console, not in the stick. And that switch, as far as i know disables the extra weight moving the stick needed when you are passing the AoA -G limit. But i´m not 100% sure.

 

I´ve read a document in russian where describes the AoA-G limiter and, with a rude online translation thats the conclusion for me. The extra weight and the opposite movement to the center is turned off with the limiter off. But maybe i´m wrong, im not sure. But the manuals says very clear that the limiter can be turned off.


Edited by Esac_mirmidon

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