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Lord_Flashheart

Il2's very odd pitching stability behavior

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Posted (edited)

This has been bothering me since the beginning of il2, but until now we didnt have exact analogues to compare to in other games. In il2 the stability of the aircraft in pitch seems....incorrect. I have not seen this behavior in any other sim, or in real life. Mainly the il2 planes appear to be rooted to some fixed point in the sky, and they react to pitching moments in a manner that suggests  a lack of interaction with the surrounding air.

 

Two main things happen:

 

1) the airplane will oscillate around an axis with next to no up or down movement from the pitch inputs. Its like the airplane is fixed in space and just moves forward unless the pitch is maintained for a long time. It is extremely wobbly.

 

2)A relaxing of the stick does not cause near-immediate cessation of the commanded control, instead, the nose of the plane will rubber band back and forth as though it is on some kind of elastic trapeize.

 

 

Conditions: no wind, 1000m, 50% fuel, combat power. In the il2 video i just rock the stick back and forth. In the DCS video the plane refued to pitch back down without a very long hold of down stick. the second set of movements in the dcs video is what happens if i just rock it back and forth as fast as i did in the il2 video. 

Edited by Fumes

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Posted (edited)

Fumes,

 

I know , and I agree - it's a long debated subject...

 

But the "problem" is more related to how static pitch stability appears to be modeled.

 

The Spitfire(s) since they tried to mimmic their neutral pitch stability, tend to exhibit a more "expected" kind of response.

 

IRL there's naturaly always a response due to static and dynamic pitch stability ( assuming the aircraft is not unstable ) which tends to return it to the trimmed AoA, but in IL-2 it has always been too abrupt ( ? )

 

 

Some users with FFB controllers have reported that the behavior is different. I really can't say because I have a T.16000.

Edited by cagari-cagarou
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Posted (edited)

My old buddy who did fly old il2 said same thing when he tried BOS some years ago. I remember it exactly because he use same analogy about  elastic trapeize :) No FM is perfect and all can be made better but if this can be changed I think we need to wait for next iteration of physics engine. Which in current tasks in progress and  scheduled work that need to be done, I doubt that it can be look  at in 2019, without saying yet when done if needed.

Edited by 307_Tomcat
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Why on earth would anyone think that a video shot from a fixed position relative to an aircraft can be used to demonstrate "next to no up or down movement"? It self-evidently cannot, since the camera moves up and down with the aircraft. To prove the existence of such movement (or in this case a claimed lack of movement), it would be necessary to record the video from a fixed camera, or use other means (i.e. Tacview) to measure the movement. In relation to another rather silly claim, I have amply demonstrated to myself that the aircraft in question (in that case a Bf-109) did in fact move up and down with considerable amplitude. I'd provide the evidence here, if I thought it worth bothering, but given the obvious lack of common sense exhibited here, I can't be bothered.

 

A little logical thought in this forum would go a long way towards eliminating much of the vacuous fluff that goes into discussions of FM issues, and perhaps leave a bit more room for constructive, evidence-based, discussions.

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25 minutes ago, AndyJWest said:

Why on earth would anyone think that a video shot from a fixed position relative to an aircraft can be used to demonstrate "next to no up or down movement"? It self-evidently cannot, since the camera moves up and down with the aircraft. To prove the existence of such movement (or in this case a claimed lack of movement), it would be necessary to record the video from a fixed camera, or use other means (i.e. Tacview) to measure the movement. In relation to another rather silly claim, I have amply demonstrated to myself that the aircraft in question (in that case a Bf-109) did in fact move up and down with considerable amplitude. I'd provide the evidence here, if I thought it worth bothering, but given the obvious lack of common sense exhibited here, I can't be bothered.

 

A little logical thought in this forum would go a long way towards eliminating much of the vacuous fluff that goes into discussions of FM issues, and perhaps leave a bit more room for constructive, evidence-based, discussions.

I know, a little logical thought right? Now, could you yourself please try demonstrating some?

 

You can tell the plane is gaining or losing altitude in my video in both games when it does. If there is anything "self evident," its what you can see with your own eyeballs.

 

 

Its even more obvious here, the plane is losing altitude. In none of these videos does the camera position prevent you from telling if the plane is moving up and down relative to its velocity vector due the contols. They dont, except in the DCS bit where its fairly obvious (although apparently you are blind and cant see it I suppose) that changes in the velocity vector result in the plane moving with them.

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Since you clearly don't understand perspective, and are too pig-headed to actually do a proper test yourself (which will amply demonstrate that the aircraft is moving up and down - I know because I have done exactly that), I am adding you to my ignore list. 

 

Enjoy your vacuous time-wasting threads. I'm quite sure that if the developers look at them at all, it will be for their comedy value.

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Well, I must confess I didn't quite understand, after all, the idea expressed on the OP.

 

I thought the OP was referring to the long discussed "wobbling effect" that most aircraft, with the Spitfire(s) being an exception due to the modeling of neutral pitch stability, exhibit.

 

Instead I now believe he was referring to a completely different aspect, the fact that in the video the aircraft appears to be pivoting around a "fixed" in altitude point that moves along with it - it's center of rotation. Well, if that's it, then I must say that my observation of the original video puts DCS and IL2 in the exact same situation - I actually see no differences, and as Andy put's it, it would be very difficult to judge because it depends strongly on how the reference for the cameras is defined in the sim views.

 

What I do find quite different between DCS and IL.2, in similar aircraft modeled on both sims - Spitfire IX, Me 109 K-4, Fw 190 D-9, is that the way they model the static response to pitch perturbations from a trimmed state is more close to real, IMO and from my 38+ years of real flight experience, better modeled in DCS overall.

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20 minutes ago, cagari-cagarou said:

...very difficult to judge...

 

The thing is, you don't need to 'judge' anything. Tacview provides raw data which is quite sufficient to demonstrate that the aircraft in such conditions are in fact moving upwards and downwards quite considerably in response to pitch changes. Evidently though, some people would rather fill the forum with repetitive threads about things they think they can see in videos than actually do a little objective testing to find out whether the data backs them up.

 

As for pitch response to perturbations, I'm not a pilot myself, but nothing I've seen so far suggests that either short-period or long-period (phugoid) responses that IL-2 GB models in such circumstances are far from what might be expected, though the real-world data on this is often lacking for the specific aircraft in question. If there is a difference between how IL-2 GB models such things and how DCS does it, we'd probably have to find the relevant data to determine which is right, and it may not even exist. With most aircraft (i.e. those not having fly-by-wire stability augmentation) short-period oscillation is expected to be heavily damped, which I'd say was true of IL-2 GB. Long-period phugoid oscillations are more difficult to test, and the relevant data is even less likely to be available, since unless it is divergent, such oscillation is rarely an issue, being readily corrected by the pilot. This is of course my opinion, not backed up by data, but since I'm not claiming any specific fault with the FM, the burden of proof lies with those that are. 

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Posted (edited)

To OP:

odd compared to what?

Edited by LF_Gallahad
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The plane movement in the first two videos appear...nearly identical to me. Down to the oscillations of the too-rich mixture trail behind the planes. What are we supposed to be looking for? 

Here's an anecdotal experience for this though: I was attacking a FW-190A-8 a few nights back, got some hits on him, and he started doing plane movements as shown in the video to throw me off - just flopping around violently in almost the exact same way. He didn't appear to be moving through the air all that much, so I decided to just fire a stream of bullets to hit him and hold it steady while he flopped around in what appeared to be one spot. He flew back and forth through and around the tracers as he flopped, i.e. he moved through the air relative to the stream of bullets). If he had been staying in the same position while simply 'oscillating around an axis', my bullets would either all have missed him or all hit him as he wouldn't be moving. As it was I just got a few hits when he moved up and down through the bullet stream.

Now, this isn't 'evidence' but just goes to show that just because something doesn't look like its moving, without a good reference point how can you be sure? Altitude data is critical here to get something measurable and repeatable.
 

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this is referring to the wobbling effect, although i think there is alot more to the stability issues in pitch than just the wobble.  quite frankly, i am finding it rather baffling that some of you cant tell the difference....

 

The 190 in il2 oscillates absurdly from positive to negative pitch like it is attached to a pintle mount or something. It behaves like its flying connected to rubber bands and not air. The DCS plane oscilates.....significantly less. And it does not act like its on a fixed point. The DCS plane pitches up, but I had to hold the stick for several seconds to reverse the pitch below 0 into the negative. The second half of the DCS video shows what happens if a just stir the stick forward and back like in il2. there you can see that the DCS plane barely moves at all because the short pitching moments arent enough to actually move the plane much, at least till it starts to climb a bit. 

 

Basically the il2 aircraft acts alot like its pitch control is separate, to a point, from the other forces affecting the plane. You can also reference this in the way the 109 behaves in the second video from the other person. 

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Posted (edited)

Yes,

 

It's in fact a "tensor-like" phenomena 🙂

 

It can be due to the limitations imposed by our controllers, by there being in my case no feedback modeled, or any other factors, but IRL, unless your CoG is way fwd of the acceptable range, if we're flying S&L trimmed for a given speed / AoA, and we perturb the pitch axis by pushing or pulling aggressively in the stick / yoke and then releasing it back to it's neutral ( stick free or stick fixed ) position, the aircraft "nose" will not suddenly / abruptly ( like in IL.2 GB ) move towards the trimmed "pitch"... This return, on a stable aircraft will begin slooooowly....

 

That's one of my major "negative" observations in IL.2 GB's  FDM.

Edited by cagari-cagarou
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