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Did someone test the Su-27's acceleration in horizontal and/or vertical plane?

 

Probably not too many bothered with it!

 

The Su-27's engines AL-31 are rated at 27560lbf in full AB on test beds. I had an interesting discussion with GGTharos (a guy with a relatively respectful knowledge) about the F-15's ability to accelerate into the vertical. And yes, by the maths, in DCS and certainly in reality it is possible, but at a considerably low fuel % status at no loadouts and only at low altitudes <3000m. "Tharos" gave a rather useful ratio between the maximum available jet engine thrust (full AB) on the aircraft and the maximum achieved engine thrust on bench tests. This ratio, as he said, would be found about 0.8-0.85. So around 80 to 85% of the maximum jet engine thrust that we may find on the internet regarding a jet engine may probably be the maximum available on the aircraft. The engines tested on test beds are fed with air through a bellmouth intake (https://i.ytimg.com/vi/SIjBU9tI-Go/hqdefault.jpg) which makes sure that the tested engine provides the best performance possible, no matter how will it degrade on the mounted aircraft. On the aircraft however, the airflow qualities decay more or less due to the intakes designs and flight regimes (ones are better for low speed & altitude, some for higher speed & altitude.

 

That 80-85% maximum jet thrust of the one found on fighter jet engine data documentations is confirmed in DCS with the F-15, F-18 and other aircraft (except the Mirage 2000 which has 100% or probably more the value found on wikipedia). Simply take the F-15, put some 18400kg of fuel, no loadout and see how the plane can stand on it's tail at very low airspeed (to eliminate drag from the equation as much as possible) into the vertical near sea level. This results that the F-15's engines in DCS develop about 84.6% of the maximum engine thrust of 24000lbf which is told by the manufacturer. The DCS F-18, at 38% fuel with no loadout proves a T/W = 1 at sea level, thus it's engines also provide exactly 85% of the maximum available thrust found on wikipedia for example. Also the Viggen proves 84.7% engine thrust of that found in online documentations. If DCS is correct for the engine thrust tables of F-15, F-18, Viggen, Harrier, F-5 and other (except for DCS Mirage 2000 which has it's engine's thrust overrated) then what "Tharos" said is relatively accurate.

 

Here's a track:

F-15 at 18400kgf for a unitary T to W.trk

 

Now watch out what happened to the Flanker (of course, after many FM modifications throughout FC1, FC2 and also FC3). At only 2% fuel with no loadout, weighing 17800kgf, the Su-27 is barely holding a 1G (barely stands on it's tail) along the longitudinal axis at sea level in full AB. This results that the simulated maximum jet engine thrust for the AL-31 of the Su-27 only develop some 71% of the known 27560lbf. I'm not pro one aircraft and against other aircraft and stuff like that! My only goal is to see them respect real data. From my point of view, the thrust ratings on the Su-27 and 33 are kind of much lower than expected. Just 71% of the maximum achieved on test beds is just way lower than expected and may even be unacceptable on a real Su-27. I believe that the drag tables should be slightly increase for higher speed regimes only (the deceleration at high and low AoAs looks natural for lower speeds) on the Su-27 besides increasing the thrust data values in order to maintain the aircraft's maximum speed where it has to be, because as it is, the full AB engine thrust seems too low to be true.

 

Here's the one for Su-27:

Su-27 at 17800kgf for a unitary T to W.trk

 

 

Regards!


Edited by Maverick Su-35S
Mirage's engine thrust

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 do wonder if the effect of temperature on the AL-31F might be slightly over done. I wonder if this is related.

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I do wonder if the effect of temperature on the AL-31F might be slightly over done. I wonder if this is related.

 

 

Is the AL-31F such an alien engine to have so drastically different thrust characteristics from other engines? If you completely read it all, every other aircraft has it's engines maximum thrust output in AB at around 85% of the value found on the internet (ex: wipiedia). How come only the Su-27 has 71%? Indeed temperatures affect density, thus thrust, but common, this is common sense! You might be right and indeed the temperature data might be overrated in the simulation, thus we get this inexplicable thrust decrease, but this can only be corrected by the "experts" who made the Su-27's FM.

 

 

Kind 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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...the F-15's engines in DCS develop about 84.6% of the maximum engine thrust of 24000lbf which is told by the manufacturer....

 

...the thrust ratings on the Su-27 and 33 are kind of much lower than expected. Just 71% of the maximum achieved on test beds...

I don't imagine that you bothered to pull any data from the tracks you posted, did you? Because I'd love to see the data upon which you are basing your conclusions.

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Yeah, his test methodology appears to be standing it on its tail and seeing at what throttle setting it climbs. Less than precise, to say the least. He doesn't appear to have recognised the flaw in his approach the previous time, like

 

Air quotes around 'experts' (attitude)

And conjecture based testing, ie lack of hard data


Edited by zhukov032186

Де вороги, знайдуться козаки їх перемогти.

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Yeah, his test methodology appears to be standing it on its tail and seeing at what throttle setting it climbs. Less than precise, to say the least. He doesn't appear to have recognised the flaw in his approach the previous time, like

 

Air quotes around 'experts' (attitude)

And conjecture based testing, ie lack of hard data

 

I didn’t check his throttle settings but it was my impression that the changes in thrust were due to fuel starvation caused by pushing negative Gs. That certainly seemed to be the case in the Flanker.

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I don't imagine that you bothered to pull any data from the tracks you posted, did you? Because I'd love to see the data upon which you are basing your conclusions.

 

 

Hi Ironhand,

 

 

Perhaps you don't imagine, but although I didn't use any software for charts drawings which might've made things clear much quicker than I try to explain, I've done simple investigations (exactly as I detailed them) using simple math to determine the ratio between the simulated AB output thrust of each plane's engine and the AB output thrust told by wikipedia (I believe it's enough accurate from there). I've simply used the plane's weight force and true airspeed variation to determine when the thrust force equaled the weight one. The ratio is remarkably similar to all the mentioned fighters, around 0.85, except for the Mirage which has it 1 (so it's a bit abnormal) or possibly higher and for the Su-27/33 which has it at only 0.71. Test it for yourself, cause no one has to take my word for granted, but test please. And if you have the time and patience (I've lost it and Ill leave it like that), please draw the results.

 

 

Kind 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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Yeah, his test methodology appears to be standing it on its tail and seeing at what throttle setting it climbs. Less than precise, to say the least. He doesn't appear to have recognised the flaw in his approach the previous time, like

 

Air quotes around 'experts' (attitude)

And conjecture based testing, ie lack of hard data

 

 

You guys truly are amazing! How come you guys don't understand anything? Really? Did you correctly watch the track and correctly interpret what you saw there?

 

 

1. I didn't check to "see" at what throttle the plane stands on it's tail. This proves you understood nothing! I start losing my patience again! Man, this test is to see at what plane's weight force and at full AB throttle, thus maximum engine output thrust, the plane has 1G along it's X axis (constant speed) and I tried to reduce the speed after climbing from sea level (where the thrust is maximum) in order to not let the drag interfere, because I only wanted to determine the engine's maximum thrust force through the plane's weight. At what weight force the plane's speed won't vary at full AB, that's the thrust force produced by the engine! If this is so hard to understand..., then everything else makes a lot of sense!

 

 

2. I never had flaws in my approaches to testing techniques. Never! This gives the feeling that I'm probably much too smart for you guys to understand either what I'm doing or trying to suggest and in your conclusions you self-lead yourselves into a confusion which you eventually also believe to be correct. Fascinating! I feel like losing my time here and also with those who believe DCS's simulation but are blind to see what's wrong and also don't even want to listen to those who found what's wrong, simply because they accept things as they are and don't give a s@$t if it's wrong because they only want to fly! Honestly, this joke is not for me!

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 didn’t check his throttle settings but it was my impression that the changes in thrust were due to fuel starvation caused by pushing negative Gs. That certainly seemed to be the case in the Flanker.

 

 

Where did you see fuel starvation? Didn't you see that I was throttling back on purpose just to not let the speed build up (which creates drag) and climb (which reduces the air density and available thrust) and then slam at full AB and see how the speed varies while the plane is still at 90 deg. of elevation? I'm out of words...!

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'm out of words...!

 

I seriously doubt that =)

 

No, I didn't watch your tracks, I read your description. You then redescribed it just now, and confirmed my interpretation, that you are standing it on its tail and estimating thrust via climb rate (or lack thereof). I understand perfectly what you're saying.

 

No one has said you are incorrect necessarily, only that your methodology for filing complaints is less than ideal, and that you have a tendency to assume you're smarter than everyone else. I do it too sometimes, however I don't act surprised when they respond negatively =)

 

-edit

Acfually, rereading what you said, I think I misunderstood initially. Regardless, keep clutchin' that podium =)


Edited by zhukov032186

Де вороги, знайдуться козаки їх перемогти.

5800x3d * 3090 * 64gb * Reverb G2

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Where did you see fuel starvation? Didn't you see that I was throttling back on purpose just to not let the speed build up (which creates drag) and climb (which reduces the air density and available thrust) and then slam at full AB and see how the speed varies while the plane is still at 90 deg. of elevation? I'm out of words...!

:) Ooppps.

 

...

 

1. I didn't check to "see" at what throttle the plane stands on it's tail. This proves you understood nothing!...This gives the feeling that I'm probably much too smart for you guys...

You probably are. I am a simple farmer trying to raise his chickens and cows and enjoy a flight sim in his spare time. I will leave you to your work.

YouTube Channel: https://www.youtube.com/channel/UCU1...CR6IZ7crfdZxDg

 

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It isn't alien, it's just different. Yes, installed thrust is less than bench thrust. The .8 is just some average/rule of thumb, nothing is stopping a specific engine installation from deviating from this.

 

You will get more than bench thrust as well, as soon as you get up to speed - therefore accelerating straight up is a feat best performed at high speed. Of course you'll need to measure true airspeed and you should find that it is increasing up until certain altitude.

 

Check the Streak eagle data and you'll see what's going on there. Now having said that, there's no production aircraft right now that performs like the streak - the streak, like the P-42, were both special.

 

Again ... I'll come back to this: Compare against any actual published/official Su-27 data for acceleration. I'm sure there are some charts floating around.

 

As to WHY the thrust is this or that, that's an engineering matter that I could guess at, but it's over my head - any number of things can contribute, including the intake ramp schedules.

 

Is the AL-31F such an alien engine to have so drastically different thrust characteristics from other engines? If you completely read it all, every other aircraft has it's engines maximum thrust output in AB at around 85% of the value found on the internet (ex: wipiedia). How come only the Su-27 has 71%? Indeed temperatures affect density, thus thrust, but common, this is common sense! You might be right and indeed the temperature data might be overrated in the simulation, thus we get this inexplicable thrust decrease, but this can only be corrected by the "experts" who made the Su-27's FM.

 

 

Kind regards!

[sIGPIC][/sIGPIC]

Reminder: SAM = Speed Bump :D

I used to play flight sims like you, but then I took a slammer to the knee - Yoda

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Congratulations on authoring the most arrogant comment I've ever read in my years here. You hold on to that feeling.

giphy.gif

 

Reminds me of an official white house twitter account :angel:

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[sIGPIC][/sIGPIC]

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Some real information, or as close to real as we're likely to see in publicly available sources:

 

A TsAGI report apparently states that the base line Su-27(S?) accelerates from 600km/h to 1,100km/h in 15 seconds, at 1,000m altitude, at an all-up starting mass of 18,920kg, and this equates to an average acceleration of 9.25m/s^2.

 

I can't find an actual acceleration graph or the TsAGI report mentioned in the source, so the above should all be taken with a pinch of salt until it can be verified with actual documents. Obviously due to non-linear drag variation & other factors adjusting the figures for different altitudes & different speeds is far from simple, and since it's been 17 years since I last solved a differential equation I'm not about to try ;) or do the integration to find the theoretical thrust value for that matter.


Edited by DarkFire

System Spec: Cooler Master Cosmos C700P Black Edition case. | AMD 5950X CPU | MSI RTX-3090 GPU | 32GB HyperX Predator PC4000 RAM | | TM Warthog stick & throttle | TrackIR 5 | Samsung 980 Pro NVMe 4 SSD 1TB (boot) | Samsung 870 QVO SSD 4TB (games) | Windows 10 Pro 64-bit.

 

Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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I respectfully disagree with GGTharos about the loss of thrust with an installed engine. I have no numbers for the Su-27 and F-15 specifically, but looking at other airframes this number is less 20-15% percent. For example, the F-14 approaches 13% of a difference between installed and uninstalled thrust. SR-71 with 4.5%, A-10 with 1.8%. But all these numbers are pointless since they are different airframes.

 

But I don't think the loss of thrust is that intense. I wouldn't use those numbers as reference, you need to find out the exact difference (installed and uninstalled thrust values), and then use that to prove your point. A general rule of thumb isn't going to help you here. Measuring the thrust in the game is nearly impossible due to the lack of tools.

 

Also what was your speed when testing this out? Forward speed (in this case vertical speed) affects thrust too.

 

I haven't checked the tracks yet, I'll take a look at them later.

 

Discussing this kind of topic is really difficult though, as I said, due to the lack of proper tools to measure thrust, drag and other things. We simply don't know the thrust and drag values. So that's why I believe that flying the aircraft vertically (obtaining altitude and forward speed, which affect thrust dramatically) isn't a good way to find out the installed thrust of the DCS Su-27. And saying you're smarter than everybody here isn't going to help either, that's quite rude, to say the least... Again, I think your posts lack evidence, documents, and real proofs. Not one cares about thinks, guesses or whatever.

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I seriously doubt that =)

 

No, I didn't watch your tracks, I read your description. You then redescribed it just now, and confirmed my interpretation, that you are standing it on its tail and estimating thrust via climb rate (or lack thereof). I understand perfectly what you're saying.

 

You prove for the second time you do not understand...! Man..., from where do you get the idea that I'm "estimating thrust via climb rate"? From climb rate? Sorry man, but you seem to lack general knowledge of physics and I have to waste my time here with you to answer. If you can prove how you estimate a force through speed, you're even smarter than those who invented quantum mechanics!

 

I hope everyone else can see what you wrote before commenting on this subject.

 

No one has said you are incorrect necessarily, only that your methodology for filing complaints is less than ideal, and that you have a tendency to assume you're smarter than everyone else. I do it too sometimes, however I don't act surprised when they respond negatively =)

 

I didn't use elaborate charts with graphs (I don't want to buy Tacview yet) and no longer have the patience for DCS (maybe just for other sims that worth it, but not for DCS anymore), yet why do you find my methodology to not be useful, neglecting the possible errors which I personally consider very small or which rather affect the output result by a small enough amount for the result to be accurate.

 

Yes, in this example of trying to estimate the engine's maximum output thrust as a ratio to that given by wikipedia (or other source) by knowing the weight force which affects the plane's X axis acceleration, I have 2 rapid options:

 

1. Try to find at what weight (which is a force) the plane's engines maximum thrust would deliver a 1G longitudinal acceleration, thus trying to find at what weight the plane will eventually stand on it's tail in Full AB is an option, or...

 

2. Simply use the Newton's second law and find out the delivered engine thrust force by knowing the plane's mass (which can be any) and the dV/dT derivative (acceleration).

 

I used the first method (although I passionately had to do more tests to find the 1G weight) as it can be a "harder proof" and quicker to understand by most and uses almost no math (just a thrust ratio). I would've personally used the 2nd method (more engineering oriented), but as I see that the message I tried to address is so difficult, I don't know what did I do wrong with to come here and even post these problems...!

 

-edit

Acfually, rereading what you said, I think I misunderstood initially. Regardless, keep clutchin' that podium =)

 

I appreciate you for being honest, yet I no longer believe I can change my reputation anymore and become more patient in the future because through all the talks I have here on this forum I feel like "fighting with a wind" which only "likes" to blow a wrong direction, to say it as a metaphor. Btw, I'm not looking towards being appreciated, but only f#@&ing taken into consideration by testing what I say as I'm not trying to steer anyone in a wrong direction or "my direction", but just to have a look at what I found...! But seeing that even what I found isn't understood, then..., what a heck am I doing here?

 

I don't know how..., seems like a miracle to me, although it shouldn't normally be so if everyone wouldn't be so ignorant and born for denial without any tests to prove otherwise..., only Ironhand actually took the time, and I can only start appreciating him for this as he can "think out of the box" and has proved that I was right when I was freaking trying to point out in a dozen replies that the Su-27's CG shifts back and forth, back and forth as the fuel gradually depletes, instead of constantly shifting towards 1 direction. He was the only one in there to notice that I was right. I'm not looking for any kind of reward, not even a "thank you", but to see all of those who only start by not accepting that DCS is wrongly simulated here and there, without even testing what me and others are saying..., ohhh..., that makes me just sick and makes me hate DCS more and more everyday!

 

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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You probably are. I am a simple farmer trying to raise his chickens and cows and enjoy a flight sim in his spare time. I will leave you to your work.

 

Look...! I feel sorry now for that arrogant reply there, but I just don't know to stimulate the thinking of some people here and that one wasn't addressed to you, it was my way of discharging my anger to see how badly understood a relatively (as I see it) easy test is.

 

I wonder...! If I would've used my second method (but I forgot to try it and it's a much easier method for me) to determine the maximum engine output thrust which uses F=m*a (Newton's second law) form the start, perhaps everything would've been clearly understood, but now I wonder if anything out of it would've been understood at all if even the simplest test was interpreted in the way the earlier replies prove!

 

You seem to be among the few around here to try and test what every "stupid" like myself talks about.

 

Really..., I respect you and don't consider you a farmer, yet even if you might be, you're a lot better than most "wanna know aviation", to say so!

 

Cheers!


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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Congratulations on authoring the most arrogant comment I've ever read in my years here. You hold on to that feeling.

giphy.gif

 

Well, I felt I had to "considering the company here, eh?" -from Top Gun-

 

Joking! Smartness and foolishness are relative to some reference! If you move the reference, you can have both ends of the domain lie in the same bucket, but the difference remains unchanged.

 

I may have a great personal habit of making my statements look or become complicated that the message addressed is blurred or creates confusion (at least this is what I believe it happens to those not understanding what I say, but I sometimes truly start to believe that no matter how much I try to simplify, it's still too much to be comprehended, so instead of losing it I'd rather try joking, nothing more.

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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Looks like someone got their posting privileges back... now let’s see how many threads it takes to lose them again :)

 

Maybe it's already lost, who knows..., it's not up to me to be understood anymore and I don't even care anymore! I feel like I've done my duty to point out what's wrong here and there inside out and yes..., I will have my rights revoked again for telling the truth in a mix of "losing the filter" and through arguments which seem to attack those who have the power to rule this forum (moderators, devs, etc.) regardless of what's actually true.

 

How would you personally feel about having a fist put to your mouth and being made look like s$it after all that you worked on to point out (with good intentions, in this case for DCS) which eventually is not just disrespected, but also modified to turn you into a foul, by lying about the facts or hiding the truth about those facts. Changing a thread's name to: "NO BUG", just by brute force, by someone who has it, without any real proof and/or agreement with the one who initially created that thread, again with the purpose of discussion and truth emerge, but only with a few people who anyway are on the same side with those who control it all, is what creates the big and not funny picture (yes, not funny at all) about DCS...! I've got what's it all about and why I'm seeing the replies that I usually see (very rarely I see someone who shares my opinion and looks for hard evidence) and why threads names that regard simulation are modified into the well known and wonderful "NO BUG". It's all about money! Some may laugh, yet some may not...! I am pro DCS, but I am against this mockery here and the great disrespect which is oriented to otherwise loyal clients...!

 

I know, the perspectives of what I say are shared, some are with me some are very infuriated, but I'm not the problem..., the problem actually is the problem and it's getting bigger by ignoring it.


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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I wonder...! If I would've used my second method (but I forgot to try it and it's a much easier method for me) to determine the maximum engine output thrust which uses F=m*a (Newton's second law) form the start...

Cheers!

 

That would not give an accurate figure since the mass constantly changes due to fuel usage. It would be something like F = (Ms - dm/dt) * a where Ms is the starting mass and dm/dt is the change in mass due to fuel drain. The calculation is also altitude, humidity and temperature dependant.


Edited by DarkFire

System Spec: Cooler Master Cosmos C700P Black Edition case. | AMD 5950X CPU | MSI RTX-3090 GPU | 32GB HyperX Predator PC4000 RAM | | TM Warthog stick & throttle | TrackIR 5 | Samsung 980 Pro NVMe 4 SSD 1TB (boot) | Samsung 870 QVO SSD 4TB (games) | Windows 10 Pro 64-bit.

 

Personal wish list: DCS: Su-27SM & DCS: Avro Vulcan.

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