Weird physics when negative Gs?

[chnapo]

Hey guys. I just bought SU33 and after takeoff, I just wanted to level myself, I pushed my joystick a little forward and airplane made aerodynamically nonsense movement - it started drastically rotating forward and in 1-2 seconds it rotated 90 degrees - nose pointing down. On some other ocasions, it will rotate even more, like 180 degrees and engines will point in the direction of the flight. This movement seems aerodynamically nonsense - there is no way that such a large surface as wings would allow something like 90 degree AOA (just negative). Also engines will go off during this "maneuver".

 

Why it is a huge issue? When you exceed 400-500 km/h in SU33, it will (similarly to Mig 29) keep rotating its nose up. So you have to push joystick forward to keep the nose down basically all the time. And there is just veeery tiny difference between keeping a level flight and completely destroying your jet. Also, by some miracle, wings won´t rip off but if this happens bellow 1000m, jet is not going to recover from it no matter what you do.

[AeriaGloria]

Happens to all Flankers, and acording to documents I’ve seen referenced here it appears to known limitation for Flankers, however in real life is usually a non-issue becuase you feel those negative G really hard and wouldn’t ever willingly push that far

[chnapo]

Happens to all Flankers, and acording to documents I’ve seen referenced here it appears to known limitation for Flankers, however in real life is usually a non-issue becuase you feel those negative G really hard and wouldn’t ever willingly push that far

 

 

That makes sense, but this is way too sensitive and way too extreme, I don´t believe this could happen IRL - from aeordynamic pow it makes no sense.

[Airhunter]

Doesnt happen IRL, like, ever. Thats what the FBW is for. And even when you end up on your back recovery is very easy. If thid behabiour was the case the world famous taislide and cobra would not be possible.

[Fri13]

This movement seems aerodynamically nonsense - there is no way that such a large surface as wings would allow something like 90 degree AOA (just negative). Also engines will go off during this "maneuver".

 

 

After seeing that first time in west, how one can say "aerodynamically nonsense"?

 

 

For some the cobra is just a joke or unusable feature, because all they see is their limitations to understand what possibilities and capabilities it represents.

[draconus]

When you exceed 400-500 km/h in SU33, it will (similarly to Mig 29) keep rotating its nose up. So you have to push joystick forward to keep the nose down basically all the time. And there is just veeery tiny difference between keeping a level flight and completely destroying your jet.

You have to constantly trim the pitch due to changing air speed. And you just don't push the stick forward in a jet fighter apart from gentle correcting motion.

[BBCRF]

You have to constantly trim the pitch due to changing air speed. And you just don't push the stick forward in a jet fighter apart from gentle correcting motion.

 

[GGTharos]

That makes sense, but this is way too sensitive and way too extreme, I don´t believe this could happen IRL - from aeordynamic pow it makes no sense.

 

IRL the controls have a lot more travel and require more force to move, so ham-fisting the aircraft is simply harder to do.

 

If you realize you've ham-fisted some negative pitch, immediately counter with positive pitch and if you're timely with it you'll be fine.

 

You can also change the curves so that negative pitch inputs are gentler (beyond what you would do symmetrically for the positive pitch as well), but I don't believe this to a be a good solution.

[draconus]

Which moment you wanted to show?

[grafspee]

Every modern jet will act like this. Airframe is extreme sensitive in pitch, to that extent thet once you initiate pitching up momentum you have to apply opposite elevator deflection to stop increasing AOA. Modern jets are almost impossible to be flown by human with direct control, only via computer aid for the pilot.

Edited July 2, 2020 by grafspee

[chnapo]

Guys, I understand BUT. This is much more extreme. Nothing even remotely similar happens in the cobra or any positive G pitch. I will try to take a video of what happens and show you.

[Mars Exulte]

I think the Sukhois have a negative G limit of -1 to -1.5 under most conditions. Exceeding that limit is inadvisable and can include results up to and including structural failure. Whether you ''think'' that's right or not is irrelevant.

 

The Cobra is not a negative G maneuver. It's a high AoA maneuver at very low speed (ie very low G generally). Postive G maneuvers and behavior have literally nothing to do with any of this.

 

RTFM

 

Also, use trim, every aircraft naturally climbs as it accelerates. That's what trim is for. Establish a stable speed, then trim, then forget about it. If you are constantly climbing, it means you are constantly changing speed. IE bad piloting.

 

I have flown the flankers before, and not had issue with losing control or self destructing in level flight, so I am fairly confident in saying you're being too aggressive with your movements somehow.

Edited July 2, 2020 by zhukov032186

[GGTharos]

Guys, I understand BUT. This is much more extreme. Nothing even remotely similar happens in the cobra or any positive G pitch. I will try to take a video of what happens and show you.

 

No, it isn't. We've all flown it, we've all brought it up with ED. There are entire virtual flanker squadrons and they're controlling the aircraft just fine.

 

You could be ham-fisting, your controls may be spiking etc. In this case it's you, not the aircraft as far as we know.

[Airhunter]

Trust me, it's not him, it's the f-ed up FC3 flight model bs.

 

Here's a cockpit view of said maneuver showing proper control inputs.

 

 

Timestamp: 1:18:59

Edited July 2, 2020 by Airhunter

[Mars Exulte]

Trust me, it's not him, it's the f-ed up FC3 flight model bs.

 

Here's a cockpit view of said maneuver showing proper control inputs.

 

Timestamp: 1:18:59

 

 

Airhunter said ''trust me'' and posted a non-functional YouTube video. All the evidence we need, right guys?

[AeriaGloria]

As GG said, outside of being delicate with the stick the secret is to constantly trim down as speed increases just like is taught in real life for positive stable aircraft.

 

As Zhukov said, not only is -1-1.5 G the absolute limit of down pitch acceleration, your FBW doesn’t limit you in G in ANY condition. It gives you an alarm at max positive G that depends on speed. In real life you would not ever go close to that -1-1.5 G limit because you FEEL that negative G like crazy. I’ve heard here that the Soviet flying philosophy more so then western ones taught to never go negative G with maneuvers, that doing a roll over and split S is preferable to any negative G maneuver.

 

So likely the real pilots would use their butt or G meter to not go past zero, but for us as long as we watch G meter and are aware of limits we will be fine. You will become good at noticing the tendencies and giving stick at the right time and amount

[GGTharos]

Trust me, it's not him, it's the f-ed up FC3 flight model bs.

 

Why would I trust a blatantly uninformed opinion?

 

It's funny how some people still want to badmouth FC3's FMs (which are on the same level as 'full fidelity' modules at minimum these days) while not knowing a thing about them.

[Coxy_99]

Do you even trim bro :smilewink:

[Airhunter]

 

Airhunter said ''trust me'' and posted a non-functional YouTube video. All the evidence we need, right guys?

 

The video literally shows the control inputs during the famous cobra maneuver Have you even watched it? You HAVE to push the nose over quite forcefully to break the alpha. And no, the plane won't ever nose over and enter an inverted, unrecoverable stall where, for some reason, you lose all elevator authority even though it's not masked by the airframe. This is indeed a flaw in the FC3 flight model in that particular regime. You can believe me or not, that is completely up to you. I've talked to a couple active duty Flanker pilots and they both have tried DCS (from pre 1.5 and up). The FM and FCS have serious flaws and there isn't a flight regime that would cause losing control of the aircraft - that was literally the primary goal and design of the Flanker's FBW system - ease of control for your everage russian, low hour pilot.

 

How people can belive that DCS and especially the arcady FC3 level aircraft resemble their real counterparts accurately and are the pinacle of flight modelling is beyong me. It's a videogame, slightly more on the simulator spectrum. If people point out inaccuracies in various modules that are blatantly wrong then it's kind of up to the developer whether they want to adress this or not. Some contantly tweak their FM's and flight envelope models, because they really care, some simply don't, because they don't care.

 

Point being, it's a game, enjoy it for what it is, even the PFM's have flaws if done poorly. That doesn't mean however that one can't adress and fix the obvious game breaking stuff. As a sidenote, in the ral thin you never ever want to disengage the FCS, ever. Cobra is performed in normal law with all sytems operational. If you turned the system off any external or internal impulse could render the aircraft unflyable and uncontrolable.

[Mars Exulte]

I repeat : Cobra is NOT a high-G (either positive or negative) maneuver. It is a high AoA, low speed post-stall maneuver. You can move the stick as much as you want at that point, you're not going to overstress the airframe.

 

OP was talking about ''pushing forward'' during level flight, after takeoff, etc, which will not damage the aircraft ingame unless you're doing something really weird. He then referenced the Cobra which has exactly zero relevance to G stress, if you're performing it properly anyway. If you try to do one too fast, overriding the FCS yes, it'll probably self destruct since nothing is there to stop you doing so. Performed at a proper low speed regime, it's fine, but again has nothing to do with G stresses.

 

And no, I can't watch your video because it does not work. I also don't consider your claims of expertise really relevant.

[Ironhand]

...

 

Airhunter said ''trust me'' and posted a non-functional YouTube video. All the evidence we need, right guys?

 

You just have to select the “watch it on YouTube” link toward the middle of the image. The video simply shows two different cobra maneuvers. The first begins in the pit with the stick being pulled full back. It then switches to an external view and remains there.

 

EDIT: Actually I hadn’t quite watched to the indicated time stamp. It does show the cockpit view. Full back on stick, full forward, neutral or a bit back. It’s been a few years since I last performed the maneuver. IIRC, in the sim you flip the switch to take direct control, pull back full on the stick, push it to neutral, pull back a bit to hold the nose, flip the switch back to FBW. If I’m remembering correctly, then the middle stick positions are different.

Edited July 3, 2020 by Ironhand

[BBCRF]

Which moment you wanted to show?

 

4:06

[draconus]

4:06

..and then? I saw a cobra before.