Autopilot levels off early on descent

[Peter8]

I did a few searches and could not find an answer to this one. If someone knows of a thread or post to answer it, feel free to just point me at it.

This is something that works properly with FSUIPC 3.4.11 but not 3.51 or 3.53, hence I am posting the question here first. It may have nothing to do with FSUIPC, but it is the most obvious possibility at this stage.

The setup is MSFS 9.1 using metric controls (altimieter etc in metres, not feet). The only addon is FS Flight Keeper, which was also present with the older FSUIPC. If I use the autopilot to descend to say 600m, the descent stops at about 2000m, which coincidentally is the metre to foot ratio (2000ft is 609m). It's almost as though the altimeter is being converted to metres regardless of what is actually used. I get a similar result for other altitudes. I doesn't happen on an ascent, as I usually level off myself using the autopilot vertical speed (VS) control. If I get time, I'll test this on an ascent sometime.

Any ideas?

[Pete Dowson]

This is something that works properly with FSUIPC 3.4.11 but not 3.51 or 3.53

Actually that's wrongwith the same option settings it cannot work with any Version 3's at all, nor even version 2's. In fact you've found a bug that has been there since the "Enable A/P Altitude Fix" option was first provided! Well done. ;-)

Any ideas?

Yes, for the time being go to the Technical options page and turn off "enable A/P altitude fix". That is reading the altimeter value from FS and assuming it is in feet. That's the trouble. I'm amazed that no one's discovered this for what must be around the five years it has been this way, but the fix is quite easy and the next interim version, up in the Announcements in this Forum, will include the fix. Have a look over the next few days.

Thanks,

Pete

[Peter8]

Hmmm, I was sure it used to work properly :) Maybe something had automagically done the work for me.

Thanks very much for the workaround, and I'll keep my eye open for the announcement.

[Peter8]

While you are at it, I have another metric related possible bug for you. Under the modified autopilot of FSUIPC, the V/S is flipped in sign if you try to go "the wrong way", except under metric it changes from +50 to -61 (which is 200 ft/s, the nearest round imperial number). Not a huge issue, but untidy :)

[Pete Dowson]

While you are at it, I have another metric related possible bug for you. Under the modified autopilot of FSUIPC, the V/S is flipped in sign if you try to go "the wrong way", except under metric it changes from +50 to -61 (which is 200 ft/s, the nearest round imperial number). Not a huge issue, but untidy :)

That is very strange. According to all the documentation, the autopilot V/S supplied to me by FS is in feet/minute. I didn't think that was ever different. I simply change the sign, I do no conversion whatsoever, but for FS2002 and above I have to send it back to FS, which of course assumes fpm still.

Upon checking, I find that FS does still provide the value internally in feet even in metric altitude mode. For instance an indicated AP VS of 300 (metres) is read internally as 984.

If I change the sign I would send -984 back to FS. I do not round it to 100's of feet, or 50's or anything. I do no changes to it whatsoever except for the sign.

So it seems it is FS -- possibly only the gauge display? -- which is doing the rounding.

Sorry, I cannot change the innards of FS to operate in 50 metre increments instead of the usual 50 feet.

Regards,

Pete

[Pete Dowson]

While you are at it, I have another metric related possible bug for you. Under the modified autopilot of FSUIPC, the V/S is flipped in sign if you try to go "the wrong way", except under metric it changes from +50 to -61 (which is 200 ft/s, the nearest round imperial number). Not a huge issue, but untidy :)

Hi again.

Okay, I managed to find a way around this anomaly. There are two controls FS offsets to set the V/S in the A/P:

AP_VS_VAR_SET_METRIC and

AP_VS_VAR_SET_ENGLISH

Now I always thought that the first uses Metres/Min and the other Feet/min. But that isn't true!

They BOTH use feet! The difference between the two is only in whether they round to 50 metre or 50 feet intervals!

Duh!

So I will use the METRIC one when the altimeter is working in metres. I've changed it here and it works. Look for it in the interim version I shall release over the weekend or so, maybe Monday.

Regards,

Pete

[Peter8]

I have just tried 3.553 and these two situations now work correctly. Thank you for fixing them.

[Peter8]

New probably metric one. It may not be FSUIPC, but I'll ask here anyway.

I decided to try the Project Fokker F100. Nice plane, but when I switch the autopilot altitude hold on the set altitude divided by 3. I try to adjust it up again, and as I try it gets divided by 3 every second or so.

I tried using V/S instead, and it's settings are unusual numbers (converted multiples of 100 - 30, 61, 91 etc), not multiples of 50.

--

Edit - this only happens when autothrottle is engaged.

[Pete Dowson]

New probably metric one. It may not be FSUIPC, but I'll ask here anyway.

If it only happens with that aircraft, it cannot be FSUIPC, as FSUIPC makes no distinction between aircraft. In any case, it does not interfere between gauges and FS -- unless the writers of that aircraft use FSUIPC as their source for such information instead of FS as others would. What does it do if FSUIPC isn't even present?

Pete

[Peter8]

Good. I did think that myself, but felt it was worth the question here.

I did email the Project Fokker team about it at the same time, I'll see what they come up with.

Thank you again for your time.