ILS APPROACH (large movements from side to side)

[SYSCD7000]

Whenever I do a standard ILS approach in your A2A 172 CEESNA, at the last 500-0 feet the aircraft really moves about from side to side.
In fact so much so that I find it very hard to land the plane on the runaway because it tends to be too far right or too far left.

I do not have the same problem with any of my default and other add on aircraft. They go straight for the runaway and land down very easily.

Please tell me why this is the case?

[Nick - A2A]

Hello and welcome to the A2A forums.

It sounds a bit like you're trying to use the ILS and the autopilot in the 172 as a kind of 'auto-land' facility. This isn't what the KAP 140 autopilot installation is intended to do.

However, it should be pretty stable, so if you're seeing very large excursions when under autopilot control, it might just be worth checking to see that your framerates in the sim are at least a stable 24-25 or so.

Also, please make sure your 172 installation is fully updated. If you can let us know which host simulator you're using, we can provide more info on how to do this.

Thanks,
Nick

[Adam_NZ]

However, it should be pretty stable, so if you're seeing very large excursions when under autopilot control, it might just be worth checking to see that your framerates in the sim are at least a stable 24-25 or so.

The framerate was the key for me. When messing around in hi-res "screenshotting mode" I found that AP drifting left/right exactly as described - a kind of exaggerated (and delayed) oscillation.

However - as soon as I knocked the detail settings back to regain a decent "flyable" framerate, the AP behaved itself.

Adam.

[SYSCD7000]

I am using P3D version 4 ,Thanks

[Nick - A2A]

If you're using P3Dv4 and purchased the 172 in the last two years, you should have the latest installer and be good in terms of updates.

However, please can you let us know roughly how many frames per second you're seeing when flying the 172 as mentioned above?

Thanks,
Nick

[SYSCD7000]

This is my reading:-

FRAMES/SEC = 60. (UNLIMITED) +1.0Gs

I purchased A2A CEESNA 172 about a week ago.

P3D v4 or P3D v4.5 about two months ago.

[SYSCD7000]

Alright, thanks for your replies.

I know now how to show the top left, red Coordinates/frame rate (cycle), its SHIFT+Z.

How do I reduce the frame rates down from 60, which is what mine is showing?

[Nick - A2A]

Just to be clear, if your frame rate is 60 it's not a problem. It's low FPS such as in the teens which can cause issues.

Please could you take a screenshot showing the cockpit when this behaviour start to happen, with the FPS readout visible at top left. Then if you can attach it to a forum post here, it'll help us to understand the issue.

Thanks,
Nick

[SYSCD7000]

This 30 second video shows three screenshots. Pictures last for 10 seconds each:




This all part of the same ILS landing at 08R Gatwick, UK

[SYSCD7000]

not sure how to upload attachments

[SYSCD7000]

or try this link:

https://www.youtube.com/watch?v=t-rAn-RPhVw

[MarcE]

or try this link:

https://www.youtube.com/watch?v=t-rAn-RPhVw

This is not a Boeing or Airbus. Its autopilot is by far not as precise as a sophisticated airliner that uses double nav receivers, GPS and/or IRS, flight directors and redundant servos to achieve an autoland procedure. The KAP140 flies towards a VOR station and follows a localizer but it's absolutely not meant to do so that close to the origin of the localizer beam. If you get close to any VOR station you'll see these left and right turn too. The same happens here. The closer you get towards the emitter the more sensitive the localizer receiver reacts and the more the autopilot thinks it has to compensate. It's meant to fly you there, not to hit the runway. You have to do that yourself. The A2A autopilots are still very precise, much better than I have dealed with in reality. I wouldn't trust a KAP140 working together with a simple analogue baro altimeter and radio compass for a second that close to the ground if I was in instrument meteorological conditions. It's just there to help you on long flights or when you have to do some planning stuff.

[SYSCD7000]

True, but I ONLY fly light general aviation planes. With all my other planes (OF THE SAME SIZE and or similaiar AIRFRAME) they do not have the same Ocillation problem on ILS appraches.

It is a poblem unique to the A2A plane and no other.

However, I do understand needles become more sensitive the closer you fly to their source, VOR etc.

[MarcE]

Well, honestly I'd call it a "problem" with the planes that actually let you do it. This behaviour of the A2A fleet is pretty much what you would see in reality too. It's just not designed to do what you try to do. The autopilot I have in the Skyvan I use to fly can bring me to a VOR too.. but I'm better if I use the Heading bug to do it manually or even better fly hands on and do it myself. It's just a very simple logic "needle right of center --> turn right. more or less. And it will not fly a stright course if there is just a little wind And it doesn't even have a GS or APR mode

[flapman]

or try this link:

https://www.youtube.com/watch?v=t-rAn-RPhVw

I just looked up the ILS 08R Gatwick. The DA (Decision Altitude) is 396ft MSL. Assuming your altimeter is set correctly, the very first screenshot in your video is at DA, and all subsequent ones are below it.
Somebody else can crack open a C-172 POH if they want, but I'm 99.99% confident that a KAP-140 cannot be engaged below DA on an ILS. Thus at the very start it's highly likely you are operating the autopilot outside of it's limits.