LJQCN101

Press the pause key first.

80~90 deg. And yes, you'll enter an inverted deep stall whatever you'd try. (Just tried minutes ago) BTW I've uploaded a trk in which you can clearly see the aircraft departs from a normal slice turn at high speeds and Direct Control Mode is off: http://forums.eagle.ru/showthread.php?t=134140

Here's my methods of recovery from an inverted departure, mainly based on the pitch-rock technique used by F-16 in deep stall situations. My move is to create large amounts of adverse yaw momentum (hence side-slip & rolling motions) by full deflection of flaperons and rudder during pitch-rocking to rotate the aircraft out of inverted situations. EDIT: Seems that in DCS 1.2.12, tracks of previous versions are not supported anymore. Fortunately I've recorded the whole situation of entering into a inverted departure during mutiplayer under 1.2.12. Same technique used in 1.2.11: ${1} Su-27 pitch departure recover 1.trk

Nice read Esac_mirmidon. As a rule of thumb, if you see or expect rapid pitch-down movements, pull the stick all the way back and use Direct Control Mode to override FCS pitch-up control authority if possible. Then inverted departures can be well avoided. :thumbup: Ref Su-27SK manual (some kind of translated-by-robot version):

Once for a moment in Multiplayer, I'm at 500kph in a level flight and then pulled into the vertical. The aircraft just overshoots 28° AOA and pitch departure occurs at a speed as fast as 300kph. EDIT: Sometimes it does, sometimes doesn't. Tried to replicate that but failed.

For more specific situations, maybe you can take a look at this: http://forums.eagle.ru/showthread.php?t=133922

Enter the chart with mach number or kph, proceed vertically to desired Ps curve (Ps=0 means sustained turn. The green curve of Su-27 is also a Ps=0 curve.) or the dashed curve which means g-load. And then proceed horizontally to read turn rate. Here you go.;)

Hello guys. Here I present the flight test data of the aircraft's sustained turn performance. Although I did pay a lot attention while testing the bird to ensure the accuracy of the data, don't take it too seriously.;) DATA BASIS: FLIGHT TEST Time of test: Nov. 15, 2014 DCSW version: 1.2.11.33921 CONFIGURATION: 34% internal fuel, clean aircraft, test conducted below 50m (BARO), MAX AB, standard day (QNH: 760mm HG; Temp: 15° C). Actually I took off with 70% internal fuel and then adjust the aircraft for a stable & constant-speed turn below 50m. Upon reaching 34% fuel, I took a read of the current g-load. One test each for a single number. BTW I used the F-16C Block50 E-M chart as a basis chart to draw the curve. Source: T.O.GR1F-16CJ-1-1.

IMO this quote is referring to the FBW system without airspeed trimming law which uses normal acceleration feedback (and g command signal) to provide the aircraft with neutral speed stability. The neutral speed stability is characterized by no pitch changes with speed increase or decrease (stick fixed). An airspeed trimming law is added to Su-27 to imitate how a conventional speed stable aircraft will behave with speed changes. That control law changes the speed stability of the aircraft from neutral to positive, which means it has a pitch-up tendency at high speeds and a pitch-down tendency at low speeds. All that pitch up/down characteristics is artificially made by the airspeed trimming law of FCS.

From the beta manual: http://forums.eagle.ru/showthread.php?t=133669

For now, when a departure occurs, the Su-27 can easily enter into an inverted deep stall with constant AOA and no yaw rate. (Yeah, below 300kph.) Some says that it is irrecoverable. Haven't tried the pitch rock technique like in F-16. Maybe it will work I bet.

Yeah I thought the same as you. An aircraft with positive speed stability will go pitch-up when accelerating and pitch-down when decelerating (with FIXED stick) as I stated before. Maybe my problem is the comprehension of the phrase "leading edge up" and "stabilizers deflection nose down". I was thinking: Hence nose down.:doh:

And the last sentence of the Longitudinal Channel section: When accelerating, the FCS commands the aircraft to go pitch-down according to the airspeed trimming law. So in order to keep the aircraft level, shouldn't the pilot trim nose up instead of nose down as the airspeed increases? EDIT: When accelerating, the FCS commands the aircraft to go pitch-up (not pitch-down). No problem in this quote either.

Secondly, the manual also states that: According to what a neutral speed stable aircraft behaves, the angle of attack does increase when decelerating. But with the airspeed trimming law incorporated into the FCS, the nose will go up when decelerating hence more angle of attack?:huh: EDIT: Now I got it right. The diagram actually means that the nose will go down when decelerating. No mistake in this quote.

Well then, the manual seems quite confusing when it comes to the airspeed trimming law part. First it said: My comprehension is that, according to the control logic diagram given below, the aircraft do change pitch attitude when accelerating or decelerating. Without this control law, the Su-27 would be an aircraft with neutral speed stability. But I don't think it is imitating the airspeed stability of a conventional aircraft for the reason that an aircraft with positive speed stability will go pitch-up when accelerating and pitch-down when decelerating. Totally the opposite. EDIT: 1. "Stabilizers deflection nose down" doesn't actually mean the nose will go down. It means "stabilizer's leading edge down", hence nose up. See post #13. 2. There's also a mistake in the diagram. "leading edge up" is wrong, should be "leading edge down".

Sure, good to be polite. :book:

That is absolutely normal. The FCS incorporates a Roll-Yaw crossfeed system that operates in accordance with side stick inputs which is helpful in eliminating adverse sideslip induced by roll.

And here's another question if you don't mind.;) Let consider the longitudinal FCS in TAKEOFF-LANDING mode. There's not much mentioned in the manual and I maybe wrong but does it suppose to use pitch-rate feedback to hold a zero pitch rate if the stick is in neutral position? If that so, a change in CG position or the extend of flaps or speed brakes won't change the pitch attitude. If not, then I'm glad to accept any info from you guys. I made a guess like this because it reminds me of F-16 whose TAKEOFF & LANDING gains of the longitudinal FLCS operates as a pitch-rate command system which means when no input is requested, the system commands zero pitch-rate (until 10° AOA). Just trying to find the similarities.:book:

Wow thanks for clarifying. So the Longitudinal FCS operates as a Ny-command system and uses normal acceleration feedback to maintain neutral speed stability while the airspeed trimming law only imitates conventional plane stability (which is positive speed stability). Is that correct?

I don't know much about the FCS control laws of SU-27 but when FCS is in TAKEOFF-LANDING mode, does it suppose to hold a zero pitch rate if the stick is in neutral position? Or in other words, does it operate as a pitch rate command system?

The airspeed trimming law seems quite charming in the manual which is said to be responsible for adjusting the stick longitudinal deflection according to ram air pressure in order to provide a neutral speed stability. (Most of the FBW aircrafts provide apparent neutral-speed stability.) However in game I can still notice a high positive-speed stability of the aircraft. I don't know if the Su-27 still retains some kind of conventional trim "feel", but when I manually trim the aircraft to level flight and gradually increase speed, it feels like the airspeed trimming doesn't work at all and the aircraft pitches up from level flight and keeps pitching up. Therefore I wonder how well does the airspeed trimming law work in RL. To what extent will it hold the set flight path for the pilot if the stick remains in the same position? ;)

Well that's really funny. Hope ED can give us a good reason.:D

True in FC3. The Course Arrow is automatically set according to the currently selected waypoint and the corresponding course (in NAV Mode). While IRL you have to manually rotate the Course Arrow by simply turning the Course Set Knob to set a required course in NAV Mode, a certain radial in TCN Mode, or a localizer course in NAV/ILS and TCN/ILS Mode.

Guess you mean the Course Arrow. Well actually it doesn't show the current course you are flying, but still the manually selected course set by the Course Set Knob. In DCS F-15C, it is automatically set by game, and is better illustrated in DCS A-10C.;)

No I'm not. I'm talking about the number indicated in the window at the upper right corner, which should be 045 according to where the Course Arrow points at. I'm wondering why it shows 289. Edit: The window is called "Course Selector Window", ref. T.O.1F-15A-1. Just a note for my side.