DarkFire

Looks like an aircraft model corruption issue. Try running the DCS repair tool & see if that helps. Are you running any aircraft mods that alter the aircraft? If so, try disabling them.

You're right of course, though G will be proportional to AOA up to the critical limit. No they're not. In fact both the Su-27 (and -33) and the MiG-29 were all deliberately designed not to have care free handling.

Yes. At an all-up weight of ≤ 21,400 Kg no matter what you do, no matter what crazy stuff you command the aircraft to do, if the ACS is operational it'll make sure that you'll never exceed the structural limits. At any all-up weight > 21,400Kg you have to take the max G in to account via the calculation as stated in the manual. Of course switching the ACS to manual using the Button Of Death is an entirely different matter :music_whistling: ShuRugal: I don't think the damage model does take aircraft attitude in to account. Maximum structural G load is a hard limit and I think that exceeding it by any means results in airframe destruction.

I think you're probably right. It's a shame that nobody makes high-end force feedback flight sticks, otherwise I think that would probably be the way to go for hard-core flight sims like DCS. It's also a shame that FFB is more or less broken in DCS at the moment. Hmm. I might start flying with the controller position display always on & keep half an eye on the soft limiter during high speed engagements. I wonder what happens if the ACS is turned off at high mach numbers. Insta-death probably. Might give that a try just to test it...

Apparently this actually happened during flight testing. Described in this documentary just after the 53:30 mark, the test pilot was conducting strength testing when he lost the outboard section of his port wing. Unfortunately it doesn't go in to great detail.

Well said. :thumbup: I guess a lot can be explained by the basic design philosophies that produced the Su-27. Sure it has supersonic capabilities and a nice long range, but Russian design philosophy has always believed strongly in WVR maneuverability, hence the corner velocity, the speed produced by cruise throttle setting, the G-load settings programmed in to Betty; it's clearly all designed for fighter combat at fairly high subsonic speeds, probably with a high altitude, high-speed interception mission as a secondary design objective.

I'm guessing that neither the MiG-29 nor the Su-27 actually have multi-position flaps, hence the mechanical devices indicator shows them as either up or down.

No, you're absolutely right - it does still happen no matter what curvature is applied. Tried it at 0, 10, 15 and 20 curvature values. All nearly identical to the 8th screen shot you posted. I think it might be a little less pronounced with higher curvature values, but that might just be because the soft limiter effectively has a little more time to catch up with the commanded input. So, I guess the question then is whether the observed behaviour is: Accurate to the ACS system in the real Su-27 An artefact of the way in which the game modells the ACS. A coding bug. I wish I could read Russian or Spanish to see if the actual Su-27 technical manual has anything to say on the subject. In any case I guess the take home is that conducting high-G manoeuvres at anything over ~0.9M is inherently very dangerous.

I hadn't noticed but having viewed it again you're right. Interesting. So, if we posit a sharp control input, possibly caused by not having input curves, the soft limiter chases the commanded input up to it's maximum value as opposed to it's value at that particular time, caused by the soft limiter laging slightly behind the true value. Could easily cause the observed behaviour.

Track 1: During the descent you briefly went just over 8G --> airframe was fatigued. At the moment the wings broke the G meter spiked to over 9. Mach was about 1.1 --> well within the 'mach notch' on the safe G diagram. Track 2: Just before the wing broke the stick input maxed out in positive pitch. Seconds later the G meter hit >9 which was again the reason for the airframe destruction. Speed was again over the Mach which puts it within the mach notch on the G safety margins diagram. Track 3: Just after rolling inverted the G meter spiked to 8, at I think around 1.25M --> airframe was already weakened. When you pulled up the G meter spiked past 9G --> destruction of airframe. Speed was again well over 1.1M putting it in the danger zone of the G chart. Track 4: Again just after you rolled inverted & began the descent the G meter spiked to 8. Couldn't see the mach meter but by the IAS it looked like it could have been in the region of 1.1M. During the pull up at ~1.25M the G meter spiked to 9 --> destruction of airframe. Track 5: Again just after you rolled & pulled the G meter spiked at 8, at 1.2M. When you pulled up at just over 1.3M the G meter spiked at 9 and the wings broke at about 8.5. Again completely as expected. Track 6: G meter didn't go in to the danger zone, hence no broken wings. OK, let's try to fix this for you. I think I see what the problem is. From watching the stick input v the in-game control column movement at 1/4 speed, I'm guessing that you don't use control axis curves? You need to start using them. In DCS the liner 1:1 input, with no curvature, is calibrated to the real aircraft. Thing is the real aircraft has a control column that's probably some 50cm long, whereas most of the joysticks we use don't, they're obviously much shorter. Because of this short, sharp stick inputs result in disproportionately large excursions of the control surfaces, which in turn produces the large G spikes that are causing your wings to break. Try using curvature values of between 15 & 25 for both roll and pitch. This will produce much smoother inputs for you. Slow is smooth, smooth is fast. I'm sure you also noticed the 'swaying' that happened at high speed with short, sharp roll inputs? That's also a product of not using input curvature. Personally I think the cross-talk between yaw and roll channels of the ACS is much too high, but that's really nothing more than a personal opinion. This will also go away if you start using curvature for your roll input. Last thing, I didn't see any rudder movement but if you are using rudders, feet off! The one and only time you need them flying the Su-27 is for cross-wind landings. At any rate, the in-game aircraft is behaving exactly as per spec. Try using input curves for pitch & roll and see if it helps. I think it'll solve the problem for you.

Agree. Irrespective of stick movement (reduction in G is probably due to loss of wing surfaces) the pictures clarify nicely what the cause of the accident was: Screen shot 4: At that speed 7.5G is deep in to the danger zone. Screen shot 6: 8G. Aircraft is doomed. Clear case of over-G resulting from too much pitch control input. Edited to add: The problem, and destruction of the wings, is easily reproducible - see the attached track files. In attempts 1-4 the wings broke at nearly identical G values: between 8.5 & 9. It is not however possible to break the wings without a continued pull once the nose has fallen through the horizon. Increasing the Gs via stick input is the only way to break the wings. With stick neutral the maximum observed G during the dive was 1.3 - 1.7. Keeping the G at a maximum of not more than 8.0 makes the inverted dive & pull through survivable as shown in track 5. Again, cause of crash: deliberate pilot input resulting in over-G condition. Further edited to add: The observed conditions at the point of failure agree completely with the contents of the actual Sukhoi Su-27S manual, together with the 1.3-1.5 x safety margin that the design engineers appear to have built in, as shown in Ironhand's tests for another thread. Conclusion: nothing wrong with the aircraft and the DCS Su-27 is empirically accurate to the real one. /thread.

The stress / strain graph for high tensile steel and high-tensile aluminium alloys doesn't look like that. There's barely any plastic deformation before failure occurs. Insta-breaking wings is materially accurate.

I'd always assumed the shaking was due to turbulence from the weapons as opposed to mach buffet.

It does, but only for the Su-25T and the Su-27.

^ This. The civilian traffic is mostly just decoration. Military units that you place & control with the mission editor will behave in the way you want, but not the civ traffic, unless they physically can't proceed, e.g. the destroyed bridge scenario. That being said, you have to be careful with military units: some, like tanks, will try to drive around obstacles and can go off-road to avoid things.

Most don't have any commentary. Maybe training missions is the wrong description. Practice missions would be a better description, but most are still very valuable tools for skill improvement.

The only FC3 aircraft that have interactive training modules are the Su-25T and the Su-27, though some of the training missions for the Su-27 can be applied to other Russian aircraft, e.g. the SPO-15 training mission. There are also purchasable training mini-campaigns for some DCS aircraft. The Su-27 is one, not sure if there's one for the F-15C. There are also community-created training missions in the user files section of the DCS web site: https://www.digitalcombatsimulator.com/en/files/

The patches you've designed (very nice by the way): are they colour on a white background or are they colour on a transparent background? If the background is white, try making it transparent & see if that works.

Early Su-27S aircraft had fixed Nadia settings that were set for a gross weight of 21,400 Kg. The system did not (does not) take in to account variations in weight or configuration. Nadia systems that take weight & other factors in to account were only available in much later Su-27 variants such as the S-30Mki, Su-35 etc. It's interesting to consider what this might mean in terms of the intended purpose for the Su-27. 21,400 Kg. equates almost exactly with an Su-27 that has 2 x R-73 & 2 x R-27ER with 35% fuel, or a 4 x R-73 with 55% fuel configuration. These could reasonably be considered to be consistent with either an airfield defence interceptor profile or that of a longer range interceptor where WVR combat is assumed to take place after a lengthy flight and some BVR combat. It might therefore be reasonable to conclude that the original Nadia settings were designed for PVO and not VVS typical mission profiles. I think it is possible to export telemetry data - isn't that exactly how Tacview creates ACMI files, via Lua export of telemetry?

Can't comment on the rest, but the above section is nicely consistent with the in-game observed onset of vibration at around 18-20° AOA with a clean configuration.

The Su-27 has anti-collision lights (RCtrl-L) but doesn't have the electroluminescent formation strips that the F-15 and A-10C have.

Always good to get back in to the swing of things. I'm saving up for a Warthog so this could come in handy, thanks for posting it :)

You will be able to. Gradually you get used to listening to the air turbulence sound at a given combination of G & air speed. I agree completely about the broken wings: makes it much more interesting to fly. Harder to learn but more rewarding. Having flown and loved the current PFM Su-27, going back to the SFM Su-33 feels neutered and totally on-rails. I'd never go back now :)

To be honest this isn't as landing technique that I use often at all, so it could well be the case that a bit of extra pitch will cancel out the rotation moment produced by deploying the chute. I don't think the DCS Su-27 models the ABS brakes unfortunately, though again in fairness I tend to land with higher than average speed - I tend to come over the runway threshold at ~300 and touch down at anything between 280 and 240 depending on weight. The Flanker PFM is supposed to be pretty accurate. Apparently it's been tested and 'signed off' by actual Flanker pilots, so it should be pretty close. Having said that, the Su-27 flight model does get changed sometimes without it being mentioned in the patch notes. For example, I'm pretty sure that the engine thrust profile was changed again in a patch 2 weeks ago without it being mentioned.

21,400 Kg according to the manual, but yes. By "pure coincidence", an Su-27 with 30% fuel, 2 x R-27ER, 2 x R-73, full expendables and a full gunpad weighs in at 21,414 Kg. Or, an Su-27 with 4 x R-73, full expendables and full gunpad with 56% fuel weighs in at 23,396 Kg. Looks like the early PVO Su-27s had their Nadia tuned for some sort of short range interception or airfield defence mission in mind.