Space plane tilting downwards when using warp

[aidyn89]

Hi,

I have had this bug for month, even back in the early access on Steam. Whenever I try to fly a space plan in the atmosphere and use the time warp, the plane will start tilting down every few seconds. If I am not using the time warp, it simply never happens (flew for over 30 minutes without warp, the plane never tilted), while when using warp, it will happen at different intervals (higher warp factor means it reoccurs more often).

The drop caused by the tilt is quite significant, and seems to increase as the warp factor increases. It usually is a 5 to 15 degrees drop. If used in warp factor 4, an upwards angle of 30 degrees can change to a descent at 30 degree in a matter of seconds.

I am always flying using SAS, as it is nearly impossible to fly a plane in the atmosphere in warp without it.

This seems to be affecting smaller space planes the most. Larger ones seems to have less of those tilts, and they don't seems as frequent.

Also, although I couldn't try it again recently, I do remember trying to fly a plane in higher altitudes (25km+), and it was affected by this bug, but it seemed to be working both ways, meaning that after a certain number of drops, the plane would start tilting up, doing the exact opposite, and going back to the height it was before starting to go down again. Problem is, the difference between the high point and low point could be of more than 15km, so this would render the use of warp for missions that require to fly below a certain altitude too dangerous.

I have tried to install and use MechJeb to work around this, as it has more accurate control on the craft, but the issue is the same in this case.

Build ID is 00861, but as stated, this is happening since the Alpha on steam.

DX diag: https://www.dropbox.com/s/ykiu79oxlao368l/DxDiag.txt?dl=0

I have not included screenshots, as in this case it would be pointless (showing a plane that is pointing lower than the previous screenshot), but I could make a video to show the bug, but I do not have any video software at the moment

[aidyn89]

I did some more tests, and it seems that this drop is caused by the space plane rapidly rolling left and right, for a short period of time. Those, altough small, are enough to make the nose of the plane drop a lot. So it seems the problem is with the SAS control while in warp.

[Gaarst]

Can you please tell what is computer specs are ?

In atmosphere, time warp is actually physics warp: the physics calculations are still done (unlike when warping x5, x10... when in space) but due to the fact they are done faster (from x2 to x4) they lose accuracy the faster you go. On lower-end machines, these calculations will be inaccurate and your craft may behave abnormally.

When you're warping, does the time displayed top left of your screen turns red ?

[aidyn89]

Hi,

I do know that the warp in atmosphere is basically just the game calculating everything 2x, 3x or 4x faster, hence why there can be inaccuracies. I do not believe I saw the timer change color as you mentioned, but I can try again to see. As for the specs of my computer, they are (as far as I know) above the recommended spec. I did send a link to my DX diag above, but here is the summary:

Windows: Windows 7 Ultimate 64-bit

Processor: Intel Core i7 (12 CPUs)

RAM: 16GB

Graphic card: NVIDIA GeForce GTX 670

DirectX 11

Hard drive is SSD

EDIT: I did verify, and yes the timer does change color (yellow or red), but only for a fraction of second at a time while using warp, and due to the fact that it was so quick, I couldn't be 100% sure of the color.

EDIT 2: As I was sure that this would be the first thing to try, I tried to lower the graphic options of the game so everything is at minimum, and the problem persist. Also, timer really seems to be switching to yellow, not red, for maybe 0,1 second.

Edited September 3, 2015 by aidyn89
More details

[sal_vager]

I think the best thing you can do is to post the craft in question, and describe your flight profile.

[Hagen von Tronje]

Hi,

In my experience, if you want craft that operate well with physics warp, especially x3 or x4, you pretty much have to design and test it around that wish, and it may just not work the way you want it to. For the reasons given above, any time you warp you are playing with fire. When I design rovers, I often want them to operate safely at x2 or x4 warp so I bugtest it around that, which is counterintuitive and not much fun and sometimes compromises designs, but you pick your poison. Keep in mind my rovers are typically built for circumnavigation...

If your timer is flickering, you're getting physics inaccuracies, which is of course the root of your woes. You can lower your part count or try different configurations but in the end atmosphere or other physics considerations may already be enough to make for your problem.

[aidyn89]

Well, that's the thing: it happens no matter how I build the space plane, no matter how I fly it. I can (and this is what I use for testing at the moment) just put a cockpit, followed by a few fuel tanks, add just enough wings for take off and the problem occurs. I can also build an extremely complex plane, with 3-4 engines, tons of fuel, etc, and it still happens.

As for the flight profile, there again it doesn't matter: I can simply take off, climb to 500m and use warp, it happens. Just like I can climb up to 30km, fly around, do barrel rolls, do a vertical drop and recover just in time, and it still happens.

- - - Updated - - -

Also, I can hardly lower the part count, as I am below 30 (no point in upgrading the space plane hangar if I can barely use them).

[sal_vager]

Is SAS on? Thing is it shouldn't be bouncing like you describe so I'm having difficulty figuring out what's going on.

[aidyn89]

Yes SAS is on, and that is the root of the problem, along with the warp. Due to the increase in calculation when using warp 2x to 4x, SAS seems to have trouble to realize that the plane is *already* stable, and tries to adjust its angle by rolling left and right a few times really quickly. In fact, in 4x I did see one of my space planes getting torn apart due to SAS not stopping this "adjustment".

[aidyn89]

I have to just tried to do a new install, so I uninstalled the game from steam, re-downloaded, then I created a new game, and the same issue happens again.

[Claw]

I have seen this and I know what you are talking about. Some planes I have that fly under phys warp also behave like someone kicks the wing every so often. I haven't yet figured out where those behaviors come from, but it probably is some sort of inaccuracy buildup with the increased time steps. Perhaps another way to test that would be to increase the physics timestep in the settings menu.

[aidyn89]

I have just tried to modify the "Max Physics Delta-Time per frame", which I assume is what you meant (it was the closest I could find), but increasing or decreasing this bar doesn't seem to make any difference.

[aidyn89]

Anyone has any other idea of how to resolve this?

[sal_vager]

Sorry no, maybe if you uploaded the craft I could have a go at tweaking them.

[aidyn89]

Uploaded ship to drop box, it's an autosave. https://www.dropbox.com/s/iw92kx2kaxn5961/Auto-Saved%20Ship.craft?dl=0

Also sent my save file: https://www.dropbox.com/s/0ku5tw9ldh0jgaz/persistent.sfs?dl=0

Just reuploaded, as original upload was with my mods on. Those are without mods, in sandbox mode.

Edited September 8, 2015 by aidyn89
Re-uploaded files, was using mods.

[aidyn89]

So, has anyone been able to test it, and see if the issue occurs on their end? Or have any other idea?

[sal_vager]

I can't prevent this, but I can reduce it to manageable levels.

Every few moments a control input is being sent to the vessel, you can see this on the pitch gauge in the bottom left, and you can see this in a twitching of the control surfaces.

It's much more pronounced on your craft as it only has canards and your center of mass is a long way in front of your center of lift, the slightest movement of the canards has a large effect on the vessels stability and their movement is greater because of the difference between CoM and CoL, this wouldn't be as severe if you used regular elevators instead and brought your mass and lift closer together.

So to fix your craft I inverted your main wings to bring the CoL forwards and added elevators to balance control between the front and rear of the vessel, I also tweaked the landing gear to reduce the chance of tailstrikes.

It still has the full fuel load for those long distance survey contracts, and while the twitching is still present the craft is stable enough that it won't be a problem.

You can download the craft here [LINK]

[aidyn89]

Well, I started by understanding what you were saying, and then it turned into complete gibberish for me... So I went and tried the plane you provided, and yeah, that did it. I lift off at a 15 degree angle, immediately put myself in 4x, and by the time the plane reached 8000m (at which point it was having trouble maintaining altitude because it was too slow), I only lost a fraction of a degree, instead of the usual 5 degrees every few seconds at best. So, simply putting the wings more to the front resolved it... I have been playing this game since the early alpha stages, and I never could figure this one out. Thanks.

[xtoro]

You can also try strutting the wing tips to the fuselage. I find physics warp bends the wings causing unwanted behavior. Strutting worked for me but they do add drag... Perhaps KJR would also fix this.

[cantab]

Physics warp makes the craft more flexible. That in turn affects the aerodynamic trim which can make the plane want to climb or descend when you go from 1x to 2x, 2x or 1x, or any other change of speed. SAS doesn't do a very good job of compensating for this effect.

The best solution I have is to try something better than the stock SAS. Mechjeb's SmartASS might help, or else use an autopilot and program your desired flight in it.