Maverick Su-35S

It's nice to meet you then if you provide accurate data for Eagle Dynamics and sorry I had to divert from arguing about the seemingly lower Su-27 turning performance. I didn't know that of the plane seen in the 1990's demo flights had a lighter airframe than the one used now so I now agree that the Su-27 is correctly simulated as performance! Maybe I should have started a new thread now regarding the Eagle all alone and not discuss facts about 2 planes performance on a thread which initially regarded just one which I consider solved in this area, so, yes I'm sorry I have done this, but then give me an advice on how to discuss about the F-15's aerodynamic lift performances (instead of making another thread) which I find quite important if DCS is to be respected as a true simulator and not just graphics and visual effects oriented. I don't want to go too much into the DCS F-15C discussion on this thread because it's off topic and neither like to waste so many hours writing so much, but what I saw (resulted performance values) during simulation that seem intriguing compared to what real life footage provide which I trust mostly as it is an undeniable fact of one plane's real performances. I want to find out the truth for my own curiosity (if it's different than what I know) about the F-15C now. One thing is what I knew for years and what still confirms in demo flights of the F-15 and another (totally different story) is what you guys who work at ED are telling me here. From what I believe someone's not saying the truth, so it's either the life footage of the F-15C's performances or the data you implemented in DCS. I may only trust genuine wind tunnel test data or mid air performance testing of the aircraft, otherwise what I see "in-game" I regard as "off-track". If NASA gave you such illustration of lift coefficient versus AoA, I believe they didn't give you the accurate and true tables. Based on my experience in aerodynamics only, the maximum lift coefficient of the F-15 (global CL) as 1.6 is way too high. If it gets above 1.3 at 40 AoA at Mach 0.3 it's a big deal. There's no way it can be that high even if the plane would have a relaxed static pitch stability, while the normal F-15 has tremendous static stability margin so the needed elevators deflection to hold 38 AoA greatly degrades the resultant global lift coef. On the other hand no F-15 wing reaches the tremendous AoA of 38, unstalled. The in game ailerons responsiveness becomes lost (aileron stall) only above 27, regardless of beta angles (driven by rudder inputs which can be override), proves that in game the ailerons are still not stalled where they should (around 20 or below) as they still give good lift differentials between the wings up until 27 AoA is reached! The way this plane was flying when PFM F-15 just came out was very realistic and better reflected the real aircraft's performances, but someone didn't like it that way and wanted to make it fly as he desired, thus ruining it's authenticity. From my own determinations (CFD & personalized algorithms) the CL max of the whole F-15 at Mach 0.2 at 20 true AoA is found at about 1.1 which means it's 70% (0.70 times) that of the F-16 which has 1.57 at 26 AoA for the same Mach. Also the lift slope of the F-15C would be about 3.065 (CL per radians) or 96% that of the F-16's, which is 3.21. Have a short look here: How much it takes for the F-15 to complete the circle in both examples? Yes, a staggering 20+ seconds. Much "wow" compared to 13..14 seconds in DCS at similar weight! Also note in the 2nd video how after pulling towards initiating the turn, the pilot quickly reduces the AoA and settles it at some lower value (thus degrading the G-load and turn rate) until almost finishing the turn (where he pulled a bit more again), which tells that this plane suffers from bleeding airspeed quickly if the pilot would keep the AoA a bit higher. This is non-comparable to the DCS's F-15C's which seems to bleed speed slower (because you can hold a higher AoA and turn rate for longer). What I found during actual in game testing of the DCS F-15: Weighing exactly 16 tons force (38% internal fuel, clean), the plane flies at 226km/h IAS while gliding (engines idle to not affect lift) at 20 AoA at nearly 1G which results in a lift coefficient of 1.15. This shows a rather correct lift slope up to this alpha (and thus lift coef.), but..., at AoA 38 it can hold nearly 1G at 190km/h IAS (engines idle) which results in a maximum lift coefficient of 1.63, which proves a rather too high and incorrect lift slope simulation from the point (20AoA) where both wings are already stalled to the point (35-40AoA) where normally the generated vortexes also brake up (supercritical AoA). This proves that the lift slope decays to only 75% of the initial one between 20 and 38 AoA which is incredibly high. It normally should find a very low positive value and only increase the CL to a maximum of about 1.28, let's say roughly 1.3, but never 1.6. So this one problem (the other is probably the drag function) why the F-15 finds such a tremendous turning rate, because every time you pull above 20 AoA (30 indicated on the cockpit indexer) the wings keep providing an unrealistically high lift and not high enough drag which make the plane turn incredibly quick, which is incomparable to the real plane, the real plane can't turn any better (just barely noticeable until the speed drastically bleeds off) above 30 on the AoA indexer and real F-15 pilots should normally confirm this! A good correction for the F-15's aerodynamic lift performance is simple and requires nothing else than to revert to how it was when PFM F-15 first came out which I'm pretty sure it was more correctly simulated than how it does now (including lateral control also which is also exaggerated now), by flattening out the lift slope above 20 (just slight lift increase above wing stall) up to the AoA (that you determined, probably 40) where the vortexes between the engine inlets break up and from there on (higher AoA) the lift slope should become negative and drop to almost half some 5..8 degrees of AoA more, I'd say at 45. That would bring a correct simulation of the lift to AoA function. At this moment it seems that only these products worth it: -Belsimtek - All their products (the best flight simulation developers); -Heatblur - JAS-37; -RAZBAM - Harrier only; -ED's - All their products (greatest team with Belsimtek), except for the F-15C in FC3. ... which can be called authentic simulations of each aircraft's flight dynamics, aerodynamics and engine data which replicate rather correct in flight performances. The rest of them: -Polychop - Gazelle -Magnitude 3 LLC - MIG-21 -RAZBAM - Mirage 2000 -ED's F-15C ...should still be a WIP until more correctly replicating the real planes performances, which should normally not be a concern in the hands of people with good knowledge. It's even worthless mentioning AVIODEV's and VEAO's products which I regret that I own. I just feel like I bought a simulation of cockpit systems, not flight simulation which is the only reason why I buy something in DCS because I want to analyze and feel it's flight, nothing else, and it's least to say that for me it became a disappointment now. Regards!

So far, this remains the truth: https://youtu.be/DMEdbwS4Fhs?t=1389 This is one of the reasons I disagree that the real F-15 proves better turning performance (clean or guns only weight) than the Su-27 and why I don't trust DCS, anymore!

Ok, but is this extracted from DCS's FM or is a NASA result? Regards!

I only wish you were right, but I can't agree that the DCS F-15C respects the real plane's wing lift performance cause in the end this is what mostly affects a plane's turning ability (besides T to Drag ratio and wing loading). Why not? I'm forced to use other references such as the F-16C if I haven't seen a chart of the F-15's performance from ED which matches our plane in DCS and which totally differs from what I see on the internet (the charts that we can find). The best F-16C (GE powered) can't do a 360 in less than 14 seconds, but our Eagle with no LE devices, no lerx is much better than the best, by doing it about +13 at 25% fuel. I trust the true F-15C's performance only so far, not what I see in DCS at the moment, which I find deliberately exaggerated and I believe that someone at ED wanted/liked it this way. I was talking about roll rate? There is a basic knowledge problem here if you say that weight affects roll rate. The Flanker doesn't have ARI? The Flanker has even bigger rudders if this is what you're looking at, but that's not what matters for a rolling acceleration and rate to gain a specific value. What matters is the ratio between the resultant aerodynamic moment to rolling inertia moment. At the moment, I do not trust that the way it was tuned reflects the same values found by NASA as I do not believe that what I see in DCS reflects the real plane, sorry! Again, I was talking about roll rates, not moments and yes, the wing span and the relative aileron area to that of the wing, the relative aileron span to that of the wing and it's position along the wing affect the resultant roll rate, but the general sense tells that if the F-15 has very much lower aileron span and area to wing ratios than that of the Su-27 and if the Su-27's flight controls and aerodynamics are correctly modeled in this area, the F-15's achievable rolling rate should by logic be lower for the same AoA not higher.

The droops don't increase the critical AoA...! You are very none sense my friend! Sorry, but that graph is correct! The droops reduce your effective AoA (thus the null AoA lift drops or becomes negative) and increase the critical one. Exactly what you told me (regarding aerodynamics knowledge) matches you in fact...!

Then tell ED to implement it! In DCS the F-15 finds a constant CL increase up to 35 AoA. How is that compared to the very low critical AoA you suggest? Like I said, you only know 2D aerodynamics! I guess you are the one who's limited in aerodynamics knowledge by what you wrote all along, and I'm not the only one contradicting you on things. I do have a background for more than 10 years in this domain and I didn't waste time on just one direction, you only have words so far and regarding the leading edge flaps, I have never head of (although it wouldn't matter much) anything else than kruegers. The droops are normally not regarded as leading edge flaps, but non-slotted slats if I may call them this way (because slats are of only one type = with gap). For me it's not time consuming as long as good things can also come up. Regards!

I don't know what was the reason for this reply as I was saying the same thing. I admit I didn't also tell that the effective AoA decreases (defined by the affected chord line), thus lift coefficient decreases, so I only focused on it's primary role: increasing the critical AoA only (not moving the slope as flaps do) and logically, of course (maybe this I also forgot to say) the maximum lift by prolonging the lift slope. But..., for what reason do you guys still like or want to call the droops as flaps? Because they act like plain flaps mounted on the leading edge? Seriously, it's not the first time when someone invents a new terminology which is not normally recognized and creates a lot of confusion and later contradictions. I know it's not you guys here who named the droops as leading edge flaps, but someone did that and it's wrong. There is only ONE leading edge device for which the name leading edge flaps came out... and those are the kruegers, nothing else. It's not a general rule where they are placed along the wing. They may be placed anywhere along the wing.

I see. So then, for a first turning shot, the Eagle driver would can that in his advantage! Nice things to learn.

You are right that I didn't test them at the same G-load, yet still, I've tried it at 9 (what the Flanker's flight controls limit it to) and guess what, the F-15C is still quicker than the Flanker. Here it is: F-15's 360 turning time still lower even for the same G.trk Anyway, even if in DCS the Flanker would finish the quickies 360 turn in less time than the Eagle (but not even this is provable so far), the Eagle has a higher STR than the Flanker at any airspeed for similar fuel percentage, which is utterly wrong and this is what I'm trying to point out more than everything, even more than the fact that the Eagle's ITR is also higher. At speeds below 600km/h, the Flanker should have a better STR (constant airspeed and G-load turn), period! Then something really is wrong with the Flanker's performance simulation, yet I believe it's more with the Eagle although both suffer. How can the F-15 with no lerx, no droops (not slats) have such a great roll control even at 25 to 30 AoA, while the Flanker's roll control (which should be enhanced in comparison to the Eagle) is badly degraded above 17..18 AoA for the same amount of beta (sideslip angle). For me, it's case not closed until the truth wins! Regards!

Well, then you talk without knowing what's going on in DCS atm. Test, then come back! Again, re-check and use numbers, not feelings or beliefs. Things have changed very much. You are talking just from what you experience in DCS! In reality, the Flanker puts it's nose and keeps it (although it flies slower) on the Eagle right near the end of the first circle after a face to face merge. The real F-15 pilot won't pull 11..12G constantly (although he normally can even for at least 10 seconds) and will mostly stay at 9. Don't really know if the latest CAS (control augmentation system) on the F-15 still allows the pilot to pull as many Gs as he likes. Regards!

Sorry, you are right, but..., I sometimes don't know how to say it all in just a few words, so I spread into details very quick;(. Regards!

You are right, the slot does help the lower pressure (usually upper surface) area's flow separate at a higher angle of attack than droops (again, not leading edge flaps) do, but in that illustration there were no numbers given, so you can only look at what the picture wants to say. Again, the leading edge flaps (Kruegers only, cause there is no other type of leading edge flap) also slightly increase the critical AoA besides improving the zero AoA lift. The droops also increase the critical AoA (which is in fact their only purpose). You messed things up again!:( Then why are the A-380's droops used at landing if they do such trouble? The nose (leading edge) of the droops is quite thick, right? Regards!

The other way around friend. Some folks here found some wrong stuff on the internet and it spreads real quick, lol! That's what those leading edge devices on the Su-27 (or F-16 or F-18 ) called droops (not flaps or sealed slats or whatever one might re-invent now) are used for..., to increase the critical AoA, so you guessed it right. It's pretty simple in the end how the masters who built airplanes named these devices based mostly on their general effect. Flaps -> for primarily increasing lift. Slats -> for primarily increasing the critical alpha (AoA). Droops -> for increasing AoA only and are used when selected by designers in order to reduce mechanical weight and to avoid various structural problems. So the droops aren't as good as slats for critical AoA increment, but are a better compromise for designing. Regards!

Someone, somewhere, just used the wrong definition for droops by calling them leading edge flaps and now look what happened...! It's so hard now to clean this mess!

The man said it just right, sadly you are the one who entangles these devices definitions and functions!

You are among those few who understood them right.

Sorry, but their effects are quite different as their names too. You were perfectly right about their description, but their effects differ, one improving the AoA mostly, the other improving the zero AoA lift mostly. https://www.theairlinepilots.com/forumarchive/principlesofflight/flapcurve.jpg Regards;)!

The slat by definition allows the airflow from one side of it to mix with the airflow of the other side of the edge it leads. It's incorrectly said: slats without gaps (or sealed slats as someone invented this term). Again, those that you refer to are: droops only.

This confirms you confuse things and the T-10 never had leading edge devices afterall. That was already the Su-27 that had LE droops!

Was I wrong based on what you described? Buffeting on the F-15C's wings at 8 AoA? Here we're talking about the F-15C right, or are have you only been referring to the T-10 (Su-27 prototype) all along? Buffeting is a partial flow separation indeed. If for some reason (usually low Reynolds and very high to infinte AR) you have a buffeting at 8 AoA, there are just a couple more degrees of AoA until complete separation, 12..13 AoA or so, but for our subject which is the F-15's wing and it's critical AoA (which takes place at a quite high Reynolds), regardless of what separately happens over the fuselage, for the AR it has (about 3) a buffeting wouldn't probably (can't know for sure) occur before 14..16 AoA has been reached. I haven't contradicted myself anywhere! Check here: https://surjeetyadav.files.wordpress.com/2014/02/staj-7.png http://cfile219.uf.daum.net/image/115856534DE23F29347E44 https://ultralightdesign.files.wordpress.com/2017/10/flaps-fig31.jpg?w=660 https://www.theairlinepilots.com/forumarchive/principlesofflight/flapcurve.jpg The 4th link shows exactly what I am saying about leading edge flaps (which are not droops as you most probably believe) and for your knowledge they have a slot too, yet very small compared to slats, while the droops have no gap. Now you provide the difference in effects for each of them if you have better info!

Sorry, but one of us isn't true here, and I'm not the one. I've just provided a track, did you check it? How can it be that in my test, the Eagle did a 360 in 12.00 seconds at 1% fuel starting from 200meters MSL and 450 KIAS and you can't get it below 14, while for the same conditions but starting the fastest turn from 750km/h IAS, the Su-27 can't do it in less than 13.8? Again, I use the other reference, the F-16C. How can our DCS F-15C have a better STR than the F-16C? Somewhere, there's a nonsense, period!

For point 3, was too quick on that word "slats"! Yes, droops, not slats, but even so the critical AoA increment advantage should be there and in reality it is great as compared to F-15C. 1. How much of a difference in output performance do you believe would occur if one would have a symmetrical airfoil while the other has the most highly cambered airfoil ever used for high lift? You confuse what happens in 2D with what happens in 3D. In 2D, yes, the differences are high in CL0 (zero AoA lift coefficient), CL vs AoA (lift slope) and critical AoA (which decreases for the more cambered foil), but in 3D (and I understand you don't know) the differences exponentially decrease (can't tell an exponent but it's at least 2) as the AR (aspect ratio) decreases. So to answer your question, taking into consideration what I've just said and the fact that the airfoil differences for these aircraft aren't great (when the Flanker's droops are retracted), there can't be any advantage for the F-15 in this area, but rather a disadvantage when the Flanker's droops fully extend (which increase the camber at a position very close to the leading edge). 2. What does a washout help you with if you mentioned? In this domain, the F-15 has a disadvantage rather than an advantage. 4. Same as for point 1, you only seem to have 2D airflow knowledge. For infinite span or AR, the critical AoA won't usually go beyond 13..15 AoA (depends on camber). For 3D (limited span and AR), the critical AoA exponentially increases (can't tell an exponent, but the function is non-linear for sure) as the AR decreases. From my knowledge, the F-15's wings only (not vortex washed fuselage) stall above 20. This is the truth and it was perfectly simulated when the F-15C just came out as PFM. So above 20 AoA, you can't have any more aileron effectiveness on a real F-15 and have to use beta angles (obtained by rudder) in order to command a roll and the lift coefficient normally remains flat (lift vs AoA slope becomes null) up to a couple of degrees of AoA more and then find a shallow decrease (negative lift to AoA slope) up to around 30+ AoA. Above 30+ AoA the small energy vortex created between the Eagle's engine inlets starts to break away and by the time the AoA reaches 35, the lift slope starts dropping fast. Kind regards!

Which happens only in DCS and is not only in my mind. As you provided the Su-27's chart which already contains the Eagle and I doubt that the F-15C's performance in that chart are wrong, can you provide a more real chart for the F-15 then? We'd appreciate it. Well validated? Beating even the better powered F-16 in constant turn rate at any airspeed? And about being an excellent dogfighter, sorry, but that can't be more wrong! If you already know to build a plane which excels in aerodynamic lifting performance (F-5 which has LERX and droops or F-14 and F4 which have slats), who would you make a clean wing and with low AR (draggy in turns as compared to the provided lift). Again, even an F-16C powered with the worst engine variant (F100-PW-220) always outturns the Eagle (F-15A and C) in constant turning at all speed ranges, but in DCS the F-15 turns better even than the best F-16. I trust real data only and not what I see now in DCS flight models. Sorry, but I kind of start to lose my trust in how DCS planes performances are being dictated. It's not a problem for me if a plane outperforms another in reality in any way, it's a problem for me because I only wanted to fly a simulator which respects real life data, but what I find is way off...!

Wrong! The leading edge flaps are one type of LE devices. The slats are another type of LE devices and finally droops are another type of LE devices. In terms of aerodynamics only, disregarding their structural disadvantages / advantages, they are all quite different in performance output. The LE flaps only slightly increase maximum CL, with little effect on critical AoA (only move the lift slope upwards due to higher CL0 with small AoA increment). The droops (non-slotted LE devices) increase the critical AoA not affecting the lift slope (as a result the maximum CL also increases). The slats (slotted LE devices) re-energize the boundary layer by rapidly increasing the airflow on the appropriate region (usually the upper surface of an affected airfoil) and provide the highest amount of critical AoA and maximum CL increment. The presence of LERX induced vortexes increase the critical AoA, thus the maximum CL, with low effect on lift slope. Who talked about flaperons? Regards!

So you say we shouldn't care if things are wrong in this simulator (being an internet game).?!