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Is their any way to recover from an inverted spin?


marchand73

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Since the FCS attempts to adjust the control surfaces to achieve a certain # of Gs or a specified rate of roll, being in an inverted stall (where neither is possible to achieve) would only confuse the FCS.

 

That would be true if we were talking about the F-15 but the FCS of the SU-27 doesn't work like that.

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There's no reason for the FCS to NOT know that it's in a spin.

 

Since the FCS attempts to adjust the control surfaces to achieve a certain # of Gs or a specified rate of roll, being in an inverted stall (where neither is possible to achieve) would only confuse the FCS.

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FWIW, in the track that Stuge posted in this thread, recovery is as easy as it usually is. Nothing special involved. I take control right after the external view. Make sure your throttles are at idle and start with controls neutral. Trim to neutral as well. Then rock the nose as few times and it'll drop and you'll be sunny side up.

 

Take notice that, once I was right side up, I tried to force the nose down and remained in a stall. You don't do that. If you do, it'll be harder to exit the stall. Controls to neutral, the nose will drop on its own, and you're flying again.

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That would be true if we were talking about the F-15 but the FCS of the SU-27 doesn't work like that.

 

According to several posts in the Flight Model Discussion thread, that's almost exactly how it works. It just also has a trimming law added that pitches the nose up with speed increase.

 

There's no reason for the FCS to NOT know that it's in a spin.

 

True, but is there any reason for it TO know? Does the SU-27 FCS have programming to tell it it that it has departed the normal flight envelope, and thus the normal control laws will not produce the desired results?

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True, but is there any reason for it TO know?

 

Yep. The sensor (yaw rate) is there.

 

Does the SU-27 FCS have programming to tell it it that it has departed the normal flight envelope, and thus the normal control laws will not produce the desired results?

 

I'm sure Yo-Yo knows. I'd be somewhat surprised if this wasn't the case. The F-15's CAS knows and it's not exactly using anything more sophisticated AFAIK.

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Yep. The sensor (yaw rate) is there.

 

 

 

I'm sure Yo-Yo knows. I'd be somewhat surprised if this wasn't the case. The F-15's CAS knows and it's not exactly using anything more sophisticated AFAIK.

 

Fair enough from a technological capability standpoint. I would, however, expect the Russian design-team logic to be more along the lines of "why put time and money into adding complex and potentially troublesome additional modes to the FCS for unusual situations when we can have the pilot disable the FCS and manually fly the plane out of those conditions?"

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FWIW, in the track that Stuge posted in this thread, recovery is as easy as it usually is. Nothing special involved. I take control right after the external view. Make sure your throttles are at idle and start with controls neutral. Trim to neutral as well. Then rock the nose as few times and it'll drop and you'll be sunny side up.

 

Take notice that, once I was right side up, I tried to force the nose down and remained in a stall. You don't do that. If you do, it'll be harder to exit the stall. Controls to neutral, the nose will drop on its own, and you're flying again.

 

Ok Ironhand, your recovery was easy because you started it significantly higher than me, at a point where there were still significant oscillations (it hadn't stabilized so much yet)

 

Please bear with me, try again, watch my track, and take control at 3000m altitude, not higher.

 

If you can do that as easy and post it here, then my earlier post is officially wrong :)

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Doesn't that just put you in an impossible situation for the mere sake of it? Why wait until the point of no return, when you can recover it earlier?

 

It seems to me that you are just trying to prove a point with no regard to what is or isn't practical or possible!

 

Altitude simply cannot be used as when deciding it is impossible to recover from a particular flight attitude if being higher remedies the situation easily. Put any plane below it's stall recovery height and stall it, and you're going to die! That has nothing to do with the flight modelling.

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Doesn't that just put you in an impossible situation for the mere sake of it? Why wait until the point of no return, when you can recover it earlier?

 

It seems to me that you are just trying to prove a point with no regard to what is or isn't practical or possible!

 

Altitude simply cannot be used as when deciding it is impossible to recover from a particular flight attitude if being higher remedies the situation easily. Put any plane below it's stall recovery height and stall it, and you're going to die! That has nothing to do with the flight modelling.

 

In my track, the stall is more stable/deeper when the plane reaches 3000m.

 

The point is not to force the plane too low to recover, but force the plane in a deep enough inverted stall so that there aren't initial oscillations that make recovery easier.

 

With the technique I presented earlier, recovery ideally occurs after three up/down oscillations.

If someone can do it with two or less, please post it also :)

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You got 2 engines so maybe it would be a good idea to utilize just one of them to compensate the spin ?

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And in order for a deeper stall to occur you have to wait until the oscillations cease?

 

Again, the answer is simply not to allow things to deteriorate to that degree if it is therefore more difficult to recover.

 

Or is the entire point to push things beyond the limit purely to make the flight model seem poor?

 

I'd just add a first line to the step by step guide on how to recover effectively:

 

1. Act quickly to recover the situation BEFORE it deteriorates to a point that means recovery is no longer possible.

 

Please don't take this the wrong way, but surely, if delaying recovery makes the stall unrecoverable, then the very simple approach would be not to allow it to go that far?

 

As an academic exercise, I can certainly see your point, I cannot deny it is a very valid one too, and I understand what you are doing. Obviously, if the stall is allowed to deepen to that degree, then recovery might be impossible, and probably correctly so.

 

There lays the solution too. Don't delay recovery, or you may have no choice but to eject.

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You got 2 engines so maybe it would be a good idea to utilize just one of them to compensate the spin ?

 

Spin compensation is not really the biggest issue of recovery, that can be done with rudder, but sure good idea if you got separate thrust controls ;)

 

To NeilWillis: my point is that recovery IS possible. When the stall is entered accidentally, there may be very little altitude, and it may settle straight into that non-oscillatory position.

 

Thus, knowing the most effective recovery technique is certainly very valuable.

 

With the logic that such conditions should be avoided, the same argument could be used to say don't fly at all then you'll never crash (a very life-threatening condition.. in a sim) :)

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With the logic that such conditions should be avoided, the same argument could be used to say don't fly at all then you'll never crash (a very life-threatening condition.. in a sim) :)

 

Now this is just getting silly. I also don't hold a gun to my head and pull the trigger, because I know it is dangerous. Nor do I smoke!

 

However, you are right. You should have the ability to recover effectively, should you find yourself up a creek in Niagara minus a means of propulsion.. I just wouldn't personally take a canoe up that particular waterway without a spare paddle!

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Spin compensation is not really the biggest issue of recovery, that can be done with rudder, but sure good idea if you got separate thrust controls ;)

 

To NeilWillis: my point is that recovery IS possible. When the stall is entered accidentally, there may be very little altitude, and it may settle straight into that non-oscillatory position.

 

Thus, knowing the most effective recovery technique is certainly very valuable.

 

With the logic that such conditions should be avoided, the same argument could be used to say don't fly at all then you'll never crash (a very life-threatening condition.. in a sim) :)

:) A couple of things I find interesting. 1) In both your original track and mine (where I take over from your track), it takes us both about 1400 meters to get sunny side up. That's not meant as proof of anything. It's merely an observation. 2) When I take over your original track after you've engaged ASC direct control (and started the oscillation) I still can't get sunny side up in time.

 

As a matter of fact, I find that Direct Control actually makes recovery more, rather than less, difficult for me. See the attached track. You'll have to watch the controls indicator in the lower right corner to see when I take direct control and when I turn the system back on. It isn't until I turn it back on at around 2900 meters, that I'm able to regain control. It might just be that my timing is off. I don't know. But I've never found that taking direct control improves the situation.

 

Since the FCS attempts to adjust the control surfaces to achieve a certain # of Gs or a specified rate of roll, being in an inverted stall (where neither is possible to achieve) would only confuse the FCS.

I don't think so. If you watch the horizontal stabilizer in external view, it is trying to move your nose in the right direction throughout the procedure. You get full deflection with the stick in your lap and only partial deflection when you have it full forward. Never does it try to push your nose up. It's always trying to pull you through to a greater or lesser degree depending on your stick position.

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It isn't until I turn it back on at around 2900 meters, that I'm able to regain control. It might just be that my timing is off. I don't know. But I've never found that taking direct control improves the situation.

 

So you actually managed to recover from 2900 like that? Impressive, I'll definitely take a look, i couldn't do it the way you describe..

 

I'm moving today, so not possible to test til tomorrow, but will look at your track and see and test more :)

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So you actually managed to recover from 2900 like that? Impressive, I'll definitely take a look, i couldn't do it the way you describe..

 

I'm moving today, so not possible to test til tomorrow, but will look at your track and see and test more :)

Yes and no. I did it in this track but only after having taken direct control first and, when that wasn't working, said: "Screw it. I'm turning ASC back on." As soon as it came back on, I was able to initiate a recovery.

 

More to the point, if I take direct control (turn ASC off with the "S" key) and mimic how the ASC normally interprets my stick movements, I am also able to recover. (In other words, full back on the stick to initiate nose down, roughly 2/3 of the way back toward neutral (instead of pushing stick full forward) to rock the nose up, full back on the stick followed by 2/3 of the distance back to neutral, etc.) Using the full forward stick deflection that direct control allows just makes recovery more difficult for me.

 

EDIT: When you test, see what happens if you have your stick in a neutral position prior to taking direct control. IIRC, you had been pushing the stick full forward the entire time to dampen the nose--up to and including the point where you took direct control. Unfortunately, I can't double check right now. But that was my impression.


Edited by Ironhand

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According to several posts in the Flight Model Discussion thread, that's almost exactly how it works. It just also has a trimming law added that pitches the nose up with speed increase.

 

AFAIK the only G management the FCS does is try to prevent the pilot from over G'ing by pushing the stick forward and it will limit the amount of lateral input the pilot can make in high AoA situations and some rudder work with lateral input.

The FCS is basically a damper system that also serves the purpose of making the airframe act as though it has positive stability.

It will limit the travel of the elevator with speed but the it's not the same as, like the F-15, providing an amount of G for an amount of stick deflection and as far as my experience it's not doing that either.

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  • 3 years later...

 

Mods should I be posting in this thread or making my own? I just wanted to talk about this particular type of stall which is deceptively easy to fall into in the Su-33 and I have a video of exactly what happened, what I did to fall into it and what I tried to do to get out.

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My instinct was that people who play games online tend to get hyper sensitive and angry whenever they die in a way that they perceive to be not their own fault.

 

My area of study in university was philosophy and I can't help but be reminded of what are generally accepted as the progressive stages of moral reasoning - ostensibly one progresses from one to the next but in reality of the six stages only a small minority of people reach the sixth stage, which would entail less caring for your own treatment, less concern with what's fair than what's right and the cognitive dissolution of a firm connection between legality and morality among other things.

 

My point being, I find that the internet is rife with people who never really advance past the second stage - wanting to be seen as good, pleasure in deriding those you're allowed to (allowed to because they have done something to be seen as bad and an overiding concern with fairness (that's not fair that I am being punished for breaking this rule, so and so is a worse person than me and they weren't punished) At this stage the entire purpose of being 'good' is to avoid punishment, and goodness is defined as doing what you believe you're being asked to.

 

When people at this stage find that they are dying, or having their attempts thwarted in a game, they instinctively tend to believe that they are being treated unfairly. Combine this with the Dunnen-Kreuger effect (the effect by which a person with no training in a complex skill perceives that their knowledge is roughly equivalent or sufficient to field strong opinions on said task and even in contradiction of experts)

 

This is, I believe, why when faced with a stall and falling to their death as a result of unskilled operation of an incredibly complex military machine - even with a more logical part of themselves saying that it was likely their lack of experience that caused it, you have people who just picked up their first flight sim questioning the wisdom of more experienced people and the competency of the work of people whose livelihoods and well being literally depend upon having created an accurate depiction of the flight model and who create these flight models daily and for a living.

 

And all because at that early stage of morality one only perceives bad results happening to them to be the result of more powerful forces, while not choosing against the idea of personal responsibility but literally not ever considering it as the idea is so alien and contrary to their operating paradigm. It's nearly as instinctively unnatural a concept to such a person as taking emotional needs of others into account is for someone born into the high functioning end of the autism spectrum.

 

Anyway yeah I came here knowing it was my fault, and I had that on my mind after I read the first few pages on this thread and people so obviously new to it, to the man, suspected that such behavior was not at all realistic.

 

A friend of mine in aerospace engineering said that the particular stall is known and famously deadly, and made a quick simulation for me to explain what happened.

 

(the design philosophy of the Flanker line is based on hyper-instability combined with the canards in a patch down position while the aircraft itself is level, which creates an extreme pressure differential between the center of mass and the center of lift while also actually just plain blocking airflow to the primary wing which causes lift to stall along side said pressure differential and said instability also translates into the aircrafts inertia easily translating into spinning on its own axis - which further removes longitudinal speed from an already slow and stalling aircraft, he said the canards almost act as two ridiculously effective (proportionally) air brakes in that situation.

 

His final conclusion was that it was nearly impossible sans the grace of god, to escape in the video I posted, like I'd literally need a strong wind to come by that I could gain purchase on for some pitch authority haha Also suggested that the earlier the intervention the better the chance of escape, to definitely NOT try to let go of the controls to stabilize it and that the higher altitude you are the more likely that stall is to happen but also the more likely you'll be to escape from it.

 

So more altitude + less speed + aggressively pitching down while the body of the jet is in stable horizontal flight = a great way to destroy a flanker, and reproduce this spin if anyone is interested.

 

You can avoid it in the first place by maintaining at least 400+ IAS at all times, and at higher altitudes like 30,000 feet or more, at least 600 IAS. And if you're not, the next best thing is to be gentler on the stick, and rather than pitch directly down, instead consider rolling inverted and pulling on the stick to maintain stability without the risk of the stall.

 

Then again maybe we've interpreted it all wrong, but it seemed to follow and make sense to me.

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