Su-27 Flight Model Discussion

Could some of the more experienced SU-27 pilots please take a look at the attached track? I tried the first mission in the new campaign. OK, I burst both main tyres on taxi, but I know how to deal with that.

As soon as I took off I was experiencing wild gyrations around the pitch axis which required constant stick inputs to correct. No matter what attitude, airspeed & altitude I was at I just couldn't get it to settle. Trimming made no difference whatsoever.

Eventually I was able to get the damned thing semi-stable at the desired altitude & speed then out of the blue severe nose-over & the dreaded inverted departure set in. Unrecoverable.

Seriously? Is the real aircraft this f***ing twitchy? I used to be able to fly the -27 very smoothly. Ever since the new FM appeared it's been one long huge pile of fail.

What am I doing wrong? This is getting damned frustrating, to the point where I'm seriously thinking of ditching the -27 and concentrating on the Su-25T which does not behave in the same erratic manner at all! :mad: :mad: :mad: :mad: :mad:

You cannot 'invert' depart with ASC Direct Control disabled. You should never touch the magic button unless you're ready for a specific maneuver. The 27 is still in the early stages of development, the PFM is excellent however systems to tame its instability such as its flight computers and autopilot need attention. Give it time to develop.

I will check your track out now :P

...first mission in the new campaign...

Now I get it. :) Sorry I can't watch the track, but trimming must be the key...

OK..

First of all I can't believe you made me buy the campaign to view your track, you must be a sales agent for ED.

Second I apologize, looks like you can invert depart even with ASC disabled however I had to abuse the aircraft to do so and is most apparent at high altitudes.

Third - Ok I tested this, with similar loadout and full fuel I went further to 10k ASL then 13k ASL and the aircraft trimmed out perfect, auto pilot also worked fine when I tested it. Note that I only engaged auto pilot at above ~500km/h ish speed to prevent oscillation.

Check out my test track for reference, what is your settup ? - joystick, throttle, pedals. Might be a control issue or tune that is causing you so much grief.

AltTest.trk

Well this is severely embarrassing. Particular apologies to you OB1 for encouraging you to purchase the campaign... Though it is actually a fun campaign :thumbup:

This literally just came to me: while I was taxiing to the runway... I first thought that "S" was the wheel brakes key as opposed to "W" which of course it actually is.

I therefore... wait for it... flew that entire track with the ASC-DC turned off :music_whistling:

No wonder the damned thing departed on me, I'm amazed it didn't do it sooner!!!

Sincere apologies all, I'm off to hide in a corner... :(

Well this is severely embarrassing. Particular apologies to you OB1 for encouraging you to purchase the campaign... Though it is actually a fun campaign :thumbup:

 

This literally just came to me: while I was taxiing to the runway... I first thought that "S" was the wheel brakes key as opposed to "W" which of course it actually is.

 

I therefore... wait for it... flew that entire track with the ASC-DC turned off :music_whistling:

 

No wonder the damned thing departed on me, I'm amazed it didn't do it sooner!!!

 

Sincere apologies all, I'm off to hide in a corner... :(

LOL, not a problem, and I don't mind donating my money to ED, probably the only game developer that deserves it.

I therefore... wait for it... flew that entire track with the ASC-DC turned off :music_whistling:

Ahahahahahaha sorry i I can't help it this just made my day :))))))

On a serious note, learn to fly it like that in a dogfight! It's twitchy, but it performs better if you're accurate with it. You just have to actively fly the plane, not vice versa (yeah i know it's a Soviet plane but still..:D)

What's ASC-DC? And isn't the S-key "sound on/off". At least according to the keyboard map?

What's ASC-DC? And isn't the S-key "sound on/off". At least according to the keyboard map?

I think he means ACS, not ASC--Automatic Control System or the system primarily involved in the various autopilot routines.

DC, I assume, is Direct Control which, in the sim, is switched on/off with the "S" key. (Sound is the "S" key with one of the modifiers (Ctrl, Shift, etc)). When you have direct control of the aircraft, the Flight Control System is turned off and you have, well, direct control of the aircraft's inherent instability. FWIW, I posted a short video tutorial on YouTube this morning that talks about it's use in performing the cobra.

Rich

Ah, yes, my typo, I meant ACS in direct control mode, i.e. how to guarantee an inverted departure :D

So ACS = autopilot? Thanks! My head is getting overloaded with all these abbreviations! I'll think I stick to the good old AP...

One more thing, what's this "inverted departure" everybodys talkin bout? You put the gear in reverse and take off?

And thanks DarkFire for a truly hilarious story, made my day too! :-)

So ACS = autopilot? Thanks! My head is getting overloaded with all these abbreviations! I'll think I stick to the good old AP...

 

 

One more thing, what's this "inverted departure" everybodys talkin bout? You put the gear in reverse and take off?

 

And thanks DarkFire for a truly hilarious story, made my day too! :-)

One more acronym for you: FCS. Flight Control System otherwise known as Fly-by-Wire. That's the system that you turn off with a flip of the Direct Control switch.

Inverted Departure: The Su-27 has a strong pitch down tendency and the greater your airspeed, the greater the effect. The FCS more or less keeps this under control unless...you turn it off with the Direct Control switch. Then it's entirely up to you to keep it under control.

If you're not ready for it, you are immediately on your back flying backwards (inverted departure). Sort of a cobra with the fun left out. Usually it goes like this. Let me flip the switch. There's an instant shift of the horizon and the lights go out...permanently.

It's perfectly flyble even with the FCS turned off.. as long as you keep in mind that it has a (big) tendancy to dive imediately as you pressed the "S" key.if you constantly pull the stick (more as the speed increases) you will find the Su27 being very flyble.

Though it seems to me that pulling >20Gs should break some systems apart but it doesn't which means the damage models is not in place atm.. Other than that, you'll need practice and after that some more practice.. you know the drill..

:) Got up early this morning so I'd have time before work and flew from Anapa down to Kutaisi with dynamic weather set so that there were changing wind directions and speeds on the flight down (I had set turbulence as well but that seems not to be working). Took direct control right after takeoff and, after cleaning up the aircraft, made the entire flight down, including the landing, in that mode. It's certainly not as relaxed a flight as it would have been otherwise but...

Experimented with different airspeeds, etc. The best time to take direct control is at slower speeds for the obvious reasons. It also seems that, as the manual states, short, quick stick inputs are better than long, slower ones for changing direction, etc. It's also interesting that this mode seems far less "quirky", when you are actually maneuvering as if in combat. That's my impression, anyway.

I flew my first test flight in SU-27 the other day. If you mean "upside-down shuttlecock of death", then yes; managed that on first flight.

Interestingly, it took me a little while to work out what was going on. After a few attempts at standard anti-spin inputs, the aircraft appeared to respond positively for a moment. Alas, I was no more than 2K aloft by this point, so crashed nonetheless.

That experience, however, suggests that it's not an impossible mode of flight (ha!) to recover from.

Baker

Edit: The anti-spin attempts were performed from an external view, since I was completely and permanently G-LOC in the cockpit view.

...

 

Edit: The anti-spin attempts were performed from an external view, since I was completely and permanently G-LOC in the cockpit view.

And your inputs had an effect? It used to be that, if you were G-LOC, none of your inputs worked because, well, you were unconscious and unable to influence the aircraft.

EDIT:

After a few attempts at standard anti-spin inputs, the aircraft appeared to respond positively for a moment.

I wonder if, had you stayed in the cockpit, that positive response from the aircraft would have coincided with the return of consciousness.

Rich

I haven't flown in a week or two, but to what I recall activating ACS only wildly pitched down on me when my trim was not neutral.

Other than that I've also noticed a reduced "black out" effect (red out really) in a way, yes I would black out if it wildly pitched down, but also recover a lot quicker, allowing for possible recovery at reasonable altitudes.

Seems the g-load can not kill you anymore :) if it ever could *whistle* 55g maneuvers everywhere.

I haven't flown in a week or two, but to what I recall activating ACS only wildly pitched down on me when my trim was not neutral.

That would seem to be correct. That's would be why the effect is less pronounced at slow speeds. OTOH, if you set neutral trim at high speeds, you'll be pushing hard on the stick to keep level flight when you "flip the switch". For that matter, you'd probably still be eyes down in the cockpit as well in the real aircraft.

...

Seems the g-load can not kill you anymore :) if it ever could *whistle* 55g maneuvers everywhere.

I haven't gotten back into the sim until fairly recently myself. So I don't know what was in V3.0 when it was released. It certainly isn't there presently in 3.1. It'll be an entirely new ballgame when damage modeling, etc catches up with the PFM.

I wonder if, had you stayed in the cockpit, that positive response from the aircraft would have coincided with the return of consciousness.

Rich

You're probably correct, along with the control input at that time reintroducing G-LOC immediately. I've flown /lots/ of sims prior to DCS, yet this is the first where near-instant and self-induced death is just around every corner. EVERY CORNER.

That said, it is becoming increasingly clear why 5th gen aircraft such as the Typhoon make a big deal of the fly-by-wire righting the aircraft when the systems therein "perceive" that they've lost the pilot.

"Hi Dave. Can you hear me, Dave? I really need to talk to you, Dave..."

"Bugger this."

*some seconds pass*

"Right! Now that I have your attention..."

You're probably correct, along with the control input at that time reintroducing G-LOC immediately. I've flown /lots/ of sims prior to DCS, yet this is the first where near-instant and self-induced death is just around every corner. EVERY CORNER.

That hasn't happened to me in quite awhile--long enough that I can't recall is I was using FBW or was in direct control at the time. I wonder if its frequency has something to do with how any particular flightstick is set up in the sim (dead zones, curves, etc).

...

 

"Hi Dave. Can you hear me, Dave? I really need to talk to you, Dave..."

"Bugger this."

*some seconds pass*

"Right! Now that I have your attention..."

:megalol: It certainly does grab your attention, when it happens.

Rich

I flew my first test flight in SU-27 the other day. If you mean "upside-down shuttlecock of death", then yes; managed that on first flight.

 

Interestingly, it took me a little while to work out what was going on. After a few attempts at standard anti-spin inputs, the aircraft appeared to respond positively for a moment. Alas, I was no more than 2K aloft by this point, so crashed nonetheless.

 

That experience, however, suggests that it's not an impossible mode of flight (ha!) to recover from.

 

Baker

 

Edit: The anti-spin attempts were performed from an external view, since I was completely and permanently G-LOC in the cockpit view.

Interesting you should say that. The last time I experienced the inverted departure I thought I was getting somewhere by 'rocking' the plane in pitch. Unfortunately exactly as in your example by the time I thought I was getting somewhere I was passing 1500m and in the wrong direction, inverted, so I decided it was time to eject.

I wonder if taking the thing up very high (~15,000m) and trying a recovery might work. Still, if it's necessary to be that far up to recover it's a bit academic for most combat situations :(

Can I ask you folks a favor? The next few times you find yourselves in inverted spins with no exit, would you save the tracks and send them to me? I'd like to take a look at your examples.

Thanks.

Rich

Funny you should ask! I just took the 27 up for a spin to see if I could deliberately cause it to depart with the intention of trying to recover given plenty of altitude.

Starting conditions: 75% fuel load, no ammunition (as I later reminded myself the hard way when I tried strafing an airfield :megalol:), no weapons, standard meteorological conditions.

Test conditions: Took the bird to just over 15,000m, military thrust, level flight. Disengaged the ACS at what I think was about neutral trim.

Result: Aircraft failed to depart. This amazed me. I even tried a hard nose-over at nearly full stick forwards deflection. This caused every warning buzzer mounted in the cockpit to go off, and I lost altitude VERY quickly to about 1000m but I just couldn't replicate the inverted departure.

Having failed in the intended task I flew around for a bit, landed, took off and landed again. I'm really starting to love the new FM for the -27, this thing really is a joy to fly once you've got the controls (axis curve etc.) sorted out.

From remembering the conditions under which I last experienced the departure, I'm wondering whether having a war load, nearly 100% fuel and specifically rudder deflection might exacerbate the propensity to depart.

Track attached. Apologies if the track IR makes things a bit difficult to follow but hopefully it'll be fairly obvious what I'm concentrating on.

Funny you should ask! I just took the 27 up for a spin to see if I could deliberately cause it to depart with the intention of trying to recover given plenty of altitude.

 

Starting conditions: 75% fuel load, no ammunition (as I later reminded myself the hard way when I tried strafing an airfield :megalol:), no weapons, standard meteorological conditions.

 

Test conditions: Took the bird to just over 15,000m, military thrust, level flight. Disengaged the ACS at what I think was about neutral trim.

 

Result: Aircraft failed to depart. This amazed me. I even tried a hard nose-over at nearly full stick forwards deflection. This caused every warning buzzer mounted in the cockpit to go off, and I lost altitude VERY quickly to about 1000m but I just couldn't replicate the inverted departure.

 

Having failed in the intended task I flew around for a bit, landed, took off and landed again. I'm really starting to love the new FM for the -27, this thing really is a joy to fly once you've got the controls (axis curve etc.) sorted out.

 

From remembering the conditions under which I last experienced the departure, I'm wondering whether having a war load, nearly 100% fuel and specifically rudder deflection might exacerbate the propensity to depart.

 

Track attached. Apologies if the track IR makes things a bit difficult to follow but hopefully it'll be fairly obvious what I'm concentrating on.

:) That's one reason I was asking for some tracks showing it. I was interested in how folks were getting themselves into the situation. It's been a long, long time since I was last able to do it. I can induce an inverted departure but it's tough. And, when I do, it's easily recoverable.

I've tried it with a fully loaded aircraft and was immediately reminded that the aircraft flies like a brick loaded up that way but, even then, an inverted departure was hard to come by and easily (though less so) recoverable when it did. Maybe I'm just not pushing the envelope hard enough.

I probably won't have time to review the track until morning. It should be fun to watch.

EDIT: I know that the more I fly her, more I enjoy her. The thing that taught me how to handle her was working up the Radom air show routine. In practicing that, I really learned her capabilities and a number of her nuances. (I also learned why certain routine transitions are performed in the sequence they are.) Now accidental departures are far less frequent and, when they do occur, they're no longer a cause for panic...unless I'm very low and very departed. :)

Thanks.

Random air show routines? That sounds like a very useful training tool, where is it to be found?