SU-25T Autopilot BUG

Level hold autopilot and all altitude AP channels in Su-25T are bugged, if sea level pressure is different from 760. The AP always thinks that SL pressure is 760 and therefore thinks you are higher than the actual altitude if the pressure is lower and vice versa.

I am sending a track illustrating this behavior. Weather tab setting 730 HG SL pressure. Aircraft setting - 3000 metres ALT.

1. At beginning of the mission altitude shows 3270 m

2. Correct altitude meter by setting sea level pressure to 730 -> Altitude meter shows correct 3000 meter altitude

3. Engage Baro alt hold AP

4. Baro alt AP descends to 2730 meters (it thinks I was flying at 3270 and commanded descent to 3000)

5. Engage level flight mode AP at 2730 meters -> AP will descend another 270 meters

6. Engage baro alt hold -> AP descends again.

AP basically operates correctly only when SL pressure is 760. This affects also landing channel and in dynamic weather AP is completely unusable and therefore problematic for many people. Track illustrating this behavior is attached. I hope it gets finally corrected.

Su-25T_AP_BUG.trk

Yeah, I almost crashed to the ground yesterday when executing a low profile attack run.

Thanks to a handy autopilot invalidation mapped to the C button of my X52 I could avoid ground and continue mission.

Are you adjusting your barometric altimeter to the airfield elevation as part of your startup ( RSHIFT + - / RSHIFT + = )?

Are you adjusting your barometric altimeter to the airfield elevation as part of your startup ( RSHIFT + - / RSHIFT + = )?

It happens regardless adjustment or lack of.

Edit: Do you mean QFE? I adjust it to QNH.

Edit2: I am using release, nor betas neither alphas.

AP baro alt hold, as well as level hold does not work if QNH on the map is different than 760 and you adjust for it. If you don't adjust and leave it at the default 760, it works, however you fly at incorrect altitudes. I think it is a simple bug, where the feedback to the autopilot is not from the on-board altimeter with the player's QNH setting, but some "virtual" altimeter with fixed QNH setting at 760. This problem comes from the prehistoric era when Su-25T didn't have the altimeter with pressure correction.

bug still present.

Not related to the original poster's bug but my Su-25T goes crazy when I turn on the electrical system when performing a cold start. The aircraft registers an high angle of attack warning while it is not moving.

I don't think anybody reads this forum, as major and minor bugs alike have been completely ignored.

This is crazy because depending on the mission the autopiliot will just fly you into a mountain, you can't even use "level flight" because it drops down. Particularly noticeable on the "Command post strike" mission because it starts you with an altimeter set to the local airports.

I've been setting my alt for waypoints to around 350 feet AGL then use the radar altitude hold and route follow and it seems to work reasonably well as long as there are no large mountains in the way then you may have to help it over them a little bit. I've been doing some SEAD testing, low alt in the mountains making some missions for the viggen, (its a lot like the viggen as far as tactics) after I learn it better.:D the su-25 is a good plane to do SEAD and it seems to be fixed after the 1.5.6 open beta update yesterday as far as anti-radiation missiles go, but I see what everyone has been talking about about the auto-pilot though,it crashed me twice before I figured out to set the alt to 350 AGL

After successfully completed a "Gun Training Mission", I engaged autopilot in RTN mode, and aircraft started to a steep dive and crashed into a hill! :O

It was so dark, no any rescue team could find me... :P

This bug has gone unfixed for years. :(

And that's why I don't use autopilot....

lol using auto-suicide in su25t is hilarious

On the subject of altimeters, I noticed last night that, if I left the default 760 mmHg in the Mission Planner, what showed up in the Su-25T's cockpit depended on whether or not the mission started with the engines running. A ramp hot start or runway takeoff setting yielded 734 mmHg in the Baro Altimeter window. A cold ramp start, OTOH, displayed 760 mmHg in the window.

Something else I've noticed is that Baro Altitmeter Hold seems to work perfectly, regardless of the setting, if you are nearly perfectly trimmed. Otherwise you take an unwanted dive.

EDIT: Just had a thought. I always place the aircraft, etc and subsequently deal with the weather, when creating missions. Has anyone tried changing the mission QNH setting prior to placing aircraft to see if that makes a difference?