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Autopilot Oscillation In FSX Acceleration

Posted: Wed Jun 18, 2008 1:15 am
by KDTWflyer
Alright this is extremely annoying.. I have FSX with the acceleration add on and when flying ANY jet on autopilot with a time compression level of 8X or greater the airplane will porpoise i:e ocscilate up and down and will not hold altitude correctly. Seems especially bad with POSKY planes. Anyone have a fix aside from reinstall/ removal of FSX: accleration >>?

RE: Autopilot Oscillation In FSX Acceleration

Posted: Wed Jun 18, 2008 3:29 am
by khelmDTW
I have heard that flying planes above 16X, causes the autopilot to become less stable. I don't know why, but it seems to autopilot has a limit on how fast it can react, even at 128X.

My suggestion, don't fly faster than 4X.

RE: Autopilot Oscillation In FSX Acceleration

Posted: Wed Jun 18, 2008 4:20 am
by StarAC17


Quoting KhelmDTW (Reply 1):
I have heard that flying planes above 16X, causes the autopilot to become less stable. I don't know why, but it seems to autopilot has a limit on how fast it can react, even at 128X.

My suggestion, don't fly faster than 4X.

You cannot fly faster than 16X with the autopilot enabled even if not using autothrottle. The ossilations that occur I have noticed as well with Posky planes as well as some others, the v4 posky planes are better but it still happens now and then

I have attributed it to the fact that this would happen at a lower sim rate but wouldn't be noticable, or the fact that I often climb to cruising altitude with a full tank which isn't done in reality. Also it doesn't cause a overstess or cause the ATC to yell at you for not holding your altitiude so its really minor.

RE: Autopilot Oscillation In FSX Acceleration

Posted: Wed Jun 18, 2008 9:42 pm
by 9VSIO
I'm pretty sure it has something to do with the way the aircraft is trimmed out via the FS autopilot. No quick fix that I can think of at the moment

RE: Autopilot Oscillation In FSX Acceleration

Posted: Thu Jun 19, 2008 2:49 pm
by David L
I think it's more to do with the fact that the simulator isn't actually running faster, it's just omitting chunks of "real" time. For argument's sake, let's assume the sim state is evaluated and adjusted ten time per second at normal speed. If you go to 8x, each tenth of a second represents eight times as long so any deviation is allowed to continue eight times longer, in "real" terms, before it's corrected and the sim isn't optimised to make the correct adjustments eight times faster.

Quoting StarAC17 (Reply 2):
I have attributed it to the fact that this would happen at a lower sim rate but wouldn't be noticable

 checkmark  I'd go further and say that, at normal speed, it would be nipped in the bud before it became noticeable.

Quoting KhelmDTW (Reply 1):
My suggestion, don't fly faster than 4X.

 checkmark  Many add-on aircraft warn you not to use go any faster than 4x with autopilot.

RE: Autopilot Oscillation In FSX Acceleration

Posted: Sat Jun 21, 2008 10:41 pm
by KDTWflyer
Yeah but this "porpoising" oscillation never used to happen prior to installing FSX acceleration addition, which leads me to believe it is a problem with the acceleration expansion pack.

RE: Autopilot Oscillation In FSX Acceleration

Posted: Sun Jun 22, 2008 10:13 am
by David L


Quoting KDTWFlyer (Reply 5):
Yeah but this "porpoising" oscillation never used to happen prior to installing FSX acceleration addition, which leads me to believe it is a problem with the acceleration expansion pack.

Fair point. Perhaps there's just more data to process with the expansion - I don't know. In any case, since FS 98 I never trusted any speed greater than 4x and you certainly shouldn't exceed that with the PMDG 744 that I use these days.

RE: Autopilot Oscillation In FSX Acceleration

Posted: Thu Jun 26, 2008 6:26 pm
by yegspotter
There is no fix to this problem. I've posted on forums on other sites to see if there is a solution, but it appears to be a glitch that was introduced in SP2. Prior to SP2, I could fly at 16x time acceleration and the only time I would see oscillations was when the wind speed and direction changed abruptly - other than that, everything was smooth as silk. Once I installed Acceleration/SP2, I could not go any higher than 4x time acceleration without the consistent oscillations taking place, throughout the entire flight - even when no winds were present. I also had a colleague test this on his computer, and he encountered the same problem - AFTER installing SP2. Since Microsoft/ACES has said that there will be no more service packs, we are stuck with this glitch, unless we go back to SP1. (kinda sucks if you enjoy some of the Acceleration add-ons.....)


cheers

RE: Autopilot Oscillation In FSX Acceleration

Posted: Wed Jul 02, 2008 10:51 pm
by misterdsdan
It sounds like you're suffering from phugoid oscillation:

http://en.wikipedia.org/wiki/Phugoid

That might help your understanding of what's going on and why.

Dan

RE: Autopilot Oscillation In FSX Acceleration

Posted: Tue Jul 08, 2008 6:31 pm
by yegspotter


Quoting Misterdsdan (Reply 8):
It sounds like you're suffering from phugoid oscillation:

If it was phugoid oscillation, then it would be perceptible and any simulation rate, 1x through 16x or higher. Of course, the oscillations would not be as obvious at lower simulation rates, as they are at 8x and higher, but they would be noticeable, especially since the aircraft in FSX seem to pitch up and down at least 30 feet. The flights are generally perfectly smooth, other than turbulence effects, until autopilot is activated and the simulation rate is taken over 4x. This was not a problem prior to SP2 so my conclusion is that it's a glitch, and not something that replicates a real world situation.


cheers

RE: Autopilot Oscillation In FSX Acceleration

Posted: Fri Oct 09, 2009 9:12 pm
by KDTWflyer
Has anyone come across this problem?