DarkFire

That's WAY too fast. Even with a full fuel load and taking off using only 100% dry thrust you should rotate at roughly 260-270 and should be wheels up and climbing by 350 Km/h. Retract flaps at 420 Km/h, re-trim and away you go.

Ah, well there we go, thanks for posting that. Wish there was an English translation of the actual Su-27 flight manual available...

Landing procedure: Landing in the Su-27 requires a 3-degree glide slope, with 5 m/s vertical velocity sink rate. When you have the 'landing' navigation mode active, any airfield that has a Russian ILS system will display the director and offset circules on the HUD. Fly so that the smaller circle is lined up with the larger circle on the HUD. The HUD will also display a desired IAS and altitude. Nearly always the desired IAS will be 240 Km/h and the desired altitude at the point at which you intercept the glide slope will be 1,000m altitude or thereabouts. Note that for the altitude reading to be accurate, you must calibrate your pressure altimeter to the QFE setting given to you by approach traffic control at your destination airfield. Ignore what the HUD says about desired speed. In the real Su-27, landings above 23,000 Kg all-up weight are not permitted and pilots have to dump fuel to get to or below this weight limit. Since the fuel dump command in our Su-27 doesn't work, we have to compensate for higher weights. Note that the 23,000Kg weight limit assumes no weapons and roughly 2,000Kg of fuel remaining. For a safe landing you must maintain the 3-degree glide slope and 5 m/s sink rate. What can therefore be varied is your IAS on the final approach. Personally I tend to intercept the glide slope at anything up to 400 Km/h. On finals I have the flaps, gear and airbrake extended. My speed over the runway threshold is usually about 280-310 depending on weight, with heavier weight --> faster final approach. Flare so that at touchdown your sink rate is no more than 2-3 m/s, again the heavier you are the lower your sink rate should be at touchdown. There are a couple of schools of thought with regards to chute usage, with none really being any more valid than any other. Most of the runways we have in DCS World (Caucasus or NTTR) are long enough that you won't need the chute: simply hold the nose in the air (but not above 14 degrees or you'll drag the tail on the ground) until it drops then when your speed is below ~100 Km/h gently apply the brakes as necessary. Alternatively, for short field use, as soon as you've touched down drop the nose and pop the chute. Stay off the brakes until your speed drops to 80 Km/h (the minimum that can be calculated by the flight system) then drop the chute and use brakes as necessary. A few final points: 1. Don't be afraid to use the brakes. The Su-27 has a nice wide, stable track and very tough tyres. If you need to use the brakes turn 'em on and use them. 2. Be cautious about using the chute in strong cross-wind conditions, it can cause the aircraft to weathervane strongly following touchdown and can make things worse than using the brakes on their own. Hope this helps...

Ah OK, so while the "level to horizon" button is an emergency recovery option, it looks like the ACS is supposed to then activate barometric altitude hold once the aircraft is wings level and to the horizon. So it's the latter feature that isn't quite working correctly.

Yep, works as per spec. I tried this to see if it's modelled, and indeed it is. I tried flying low altitude (~300m) circuits at between 20 and 25 degrees AOA at around 240 Km/h - essentially balancing the aircraft on the engine thrust together with a little bit of lift from the wings. Using only the flapperons I maintained 45 degree bank turns around the circuit. Several times with no additional command input the roll increased quickly to 60 degrees and beyond, always in to the direction of the turn. At the time I was wondering what was happening and it only occurred to me later that the 'inside' or lower wing was probably stalling due to the high AOA combined with low airspeed and use of the flapperons. PFM in action. Yoyo did an amazing job with the Su-27 :thumbup:

I was always under the impression that the "level to horizon" button was more or less an emergency feature to recover to level flight in the case of pilot near-incapacitation or disorientation, and isn't meant to be used beyond the actual recovery phase.

Yep, roll authority using ailerons alone at AOA >20 degrees is roughly 25% of level flight full roll authority. Using rudders adds roughly another 25 - 30% at high AOA so the total feels like a bit over half, maybe 55-60%.

Yes there's significantly less roll rate now at high AOA, but only if you're using the stick for roll. The cross-coupling between the rudder & flapperons has been significantly reduced. Roll at high AOA is much more effectively generated by the rudders than the flappersons, hence with reduced cross-coupling we now have reduced roll effectiveness when using only the flappersons to command the roll. At high AOA if you add in manual rudder it rolls just fine, though at very high AOA (>25) you need to have a very steady touch on the controls.

Yep, I've tested this again and you're exactly right: anything over about a 1.2M difference between the speed at which the AP is engaged and the final speed produces the pitch oscillations, so I'd say that the maximum trim difference that the AP can cope with corresponds to about a 1.2M speed difference.

Well, yes and no. Before the PFM update it was perfectly possible to engage the autopilot at ~1040 Km/h TAS and it would be rock steady all the way from there up to 2770 Km/h TAS which is the maximum possible speed I've ever seen. It never generated such a huge pitch oscillation around 2.3M. What you may be thinking of was the issue whereby if the AP was engaged beneath 560 Km/h IAS it would generate a yaw oscillation.

Yes, I gather that the F-15C (used to?) reach 2.606M and the Su-27 would amusingly go all the way up to 2.62M, though it now tops out at about 2.54M.

The MiG-29 has a very slight advantage in terms of sustained turn rate and T/W ratio, compared at "combat weight". That's only a small part of the comparison though, since the MiG-29 has only 43% of the fuel capacity of the Su-27 and only 6 missile hard points versus 10 for the Su-27. The MiG-29 also has a shorter range radar and no head-down-display so all other things being equal it's harder to achieve decent SA in the MiG than it is in the Su. Apart from the slightly better STR & P/W ratios, other advantages enjoyed by the MiG-29S are that it can carry the R-77 and that it sort-of has a search-while-track radar mode. To give you an idea, Russia reportedly has a total of 50 MiG-29s of various types in service, whereas they reportedly have 359 Su-27s of various types in service. Ultimately, late-series MiG-29s are probably amongst the best point defence & FEBA-CAP aircraft available anywhere, but as a general fighter aircraft capable of other missions such as escort, long range interception as well as PD and FEBA CAP the Su-27 series is superior.

Yep, the only time I ever sit there at 12,000m accelerating to M2.5 is for a max altitude run. Otherwise it's fairly pointless. Not a bad idea. If the speed were to be limited to M2.35 (or is it 2.32?) I don't think anyone would really notice. Plus as you said anything except an SR-71 or a MiG-25/31 travelling at that sort of speed is going to start melting anyway.

Indeed it does. Re-tried it a couple of times and found the same thing. So what we have is a 'trim out of range' anomaly rather than an absolute trim issue. This is pure speculation on my part, but I wonder if this sort of anomaly and a few other minor quirks were produced as a result of adjustments made to the modelling of the ACS when it was improved in the patch a few weeks ago? Have to admit, given a choice between the ACS working perfectly at speeds down to ~320 Km/h, with a better AOA / G limiter and all the rest of the improvements we now have; and a funky autopilot at Mach 2.5, I'd take the other improvements any day. Realistically, in pretty much any combat mission in the Su-27, how often do we really need to cruise around at M2.5 at 40K feet? :)

This is by far one of the most outstanding threads I've seen on this site in a long time, thanks very much Renhanxue for posting that extremely detailed description of the missile & how it works :thumbup:

This is an excellent point. It's been my experience (sometimes at great cost in parachute rides) that the SPO-15 prioritizes threats for good reason, whatever type has been prioritized.

I think that represents the typical lock distance of the radar in question. Frostie: Thanks very much for posting these, very useful. :thumbup:

True, but as far as I know the "Speed above Mach 2, not more than 5 minutes" comment from the manual is due to friction heating of the canopy and elements of the airframe. Aerodynamically it's quite capable of flying at faster speeds. I could understand if, maybe due to limits on computing power available to the ACS, the system begins to lose stability above certain speed as the system struggles to cope with increasingly extreme data inputs. I could also imagine that the ACS system increasingly fails to compute proper outputs given 'edge of envelope' inputs. All that being said, the sudden onset of the pitch oscillation at quite a precise speed and it's harmonic oscillation characteristics, despite the fact that the ACS is supposed to be a deterministic system, is more suggestive of an anomaly of the in-game ACS programming as opposed to an accurate simulation of the real system. To be a bit more concise: I can imagine that the real Su-27 ACS system suffers from decreasing stability as flight approaches the edges of the envelope due to the limitations of the system, but what we have hear I think is probably an anomaly of how the game programming works rather than a simulation of real limitations.

Since DCS has such a diverse player base having the option to turn them on and off would be ideal, but I didn't think that DCS supported that, so defaulted to the "yes" option.

He he not many people would know what that means :lol: Yes, the usefulness of the comm guy is that he can be placed some distance away from the chap with the launcher. Placing the comm soldier a few Km away along the expected route of approaching enemy aircraft can provide them with a nasty surprise... Edited to add: Just realised how old the original posts were!

TEST CONDITIONS: Standard DCS day. No wind. No clouds. No precipitation. FLIGHT CONDITIONS: Flying at 12,000m Accelerating using maximum afterburner. Altitude held using ACS "H" mode. OBSERVED PROBLEM: With "H" mode engaged, when speed reaches between Mach 2.25 and 2.30 an abrupt pitch oscillation sets in, initially as high as ±25 m/s vertical velocity. As speed increases to M2.55 the oscillation gradually damps down to ~±6 m/s vertical velocity. Switching off the altitude hold mode stops the oscillation but on re-engaging the autopilot the oscillation reappears. Attaches is a track and my DCS log file. A small request: please, please, I beg, for the love of ($belief system) can the trim reset be made to work on the roll channel? :cry_2:

There can be problems with the speed and altitude references shown on the HUD: SPEED: The speed reference shown on the HUD is calibrated for an expected maximum landing weight. If your aircraft is heavier than the expected weight then to maintain a usable AOA you'll need a higher than expected air speed. I'm not sure what the expected maximum landing weight is for the MiG-29, but for most Russian aircraft it seems to be the empty weight, with no weapons, and about 20% fuel. Any higher than that and you'll need to be faster to compensate. ALTITUDE: The expected altitude can some times be inaccurate, especially if the weather at the airfield is very different from the standard DCS day. This isn't often a problem for single player missions but in multiplayer servers with dynamic weather the 'expected altitude' on the HUD can be so inaccurate that you have to fly a purely visual approach. For this reason, it's very important to contact the ATC at the airfield and tell them you're inbound so that they'll tell you the QFE pressure setting for that airfield. Calibrating your pressure altimeter before you approach helps a lot to make the expected altitude value more accurate. If you do find yourself having to fly a purely visual approach, keep the runway threshold in the lower 1/3rd of your HUD and fly a standard 5 m/s sink rate approach. It won't be perfect but it should get you down safely.

Not bad, and almost there, but you were much too high when you intercepted the glide slope and also too fast. You also didn't perform an adequate flare before touchdown so the combination of excessive sink rate with excessive speed either collapsed your gear and destroyed the aircraft or the tail hit the runway which, combined with too high a sink rate caused the aircraft to be destroyed. During final approach you should have a sink rate of no more than 5 m/s and at the point where you intercept the glide slope (usually around 12-15Km from the runway) you should be at 1000 + airfeld altitude in metres. 3 degree glides slope + 5 m/s sink rate until you flare. Your speed, depending on weight, should be no more than around 280 Km/h coming over the runway threshold. Chop the throttle as you flare and touch down with 1-2 m/s sink rate. Lower the nose and open the drag chute.

Yep, pretty much what I find myself doing. If I'm just wandering around looking at the scenery on the VA server I'll try to keep things precise, but if I'm in a furball with the limiter off or god forbid in direct mode there are more pressing things to be worrying about :)

Agreed. Personally I find that for AOA above say 23-25 degrees the rudders produce much more roll than the flapperons do. As a bit of an aside, I'm quite looking forwards to what the Su-33 will bring to the table once it gets its PFM. Low speed, high-AOA jinking & jiving should get a little more interesting. Maybe not in terms of roll rate but I'm thinking that in the pitch plane high-AOA stuff should be a little more stable than with the -27.