Cessna 172 Steam Gauge - Autopilot problems

[Immunol 10]

I've searched the forum and viewed several YT videos and I can't get certain aspects of the autopilot to function. Setting it to ROL, HDG and NAV functions work fine, but the vertical functions don't want to obey. The plane won't increase or decrease altitude after pressing ALT and then dialing in the fpm in VS. Most of the time it ignores the inputs, whereas other times it will start to ascend or descend but will wildly overshoot what was dialed in.

Holding a heading is great using the autopilot, but I may be doing something wrong with the vertical functions. A search of the forum indicates that most people who are flying GA aircraft seem to be pretty happy with the autopilot.

Any ideas to remedy this situation?  Thanks in advance.

Tim  

[Jetman67 517]

Are you dialling in the desired altitude, that works for me, then I hit vs and select rate

[Immunol 10]

Great question Jetman. I do dial in the altitude before setting VS. I see that I left that step out of my original post.

It just seems like all the vertical data that is entered is, essentially, ignored.

[N7470 26]

It's tricky, I usually have to play with it a couple of times before it works.   Set Altitude, then set vs works.

[GAJ52 54]

I'm getting the same problem after the last update.  The C172 analogue version is my main GA aircraft in MS2020 as I don't like the G1000, so I've flown it a lot.  Since the last update I'm having trouble setting the rate of climb and descent as the OP describes.  If I'm lucky I can get the altitude increase to work but not descent, so now I just hand fly it to the required altitude and press ALT.

I've also noticed when I select the Autopilot the nose dips down quite violently before stabilising.

[vbazillio 2,404]

29 minutes ago, GAJ52 said:

I've also noticed when I select the Autopilot the nose dips down quite violently before stabilising

Same here. -+700 ft/min is the only default value that the MSFS KAP140 knows ;(

[Ixoye 1,841]

Press Alt and set desired altitude, then press Alt again to get in VS mode, press up or down buttons to desired VS.

[Old_As_Dirt 160]

If you are flying with anything other than standard barometric pressure (29.92), the autopilot and the altimeter do not agree on the steam gauge C-172.  With the pressure set on the altimeter at 30.30 (for instance) and the same set in the autopilot, you will usually overshoot the set altitude by about 500 feet.  This results in ATC telling you to get down to the right altitude, even though everything looks good (at first glance).  I have sent a description to Zendesk and received a nice note back from them, but we shall see what happens.  As stated earlier, if you are at 29.92, things seem to stay on track.  That is usually the case if you just pick clear skies rather than live.

[ronh99 14]

Remember that you have to set the throttle.  Just setting the alt/vs etc. is not enough.  Climb - then add power, descend - then reduce power

[Republic3D 1,232]

This is how I do it:

Set your desired altitude, then press VS and dial the preffered rate up or down. When it reaches the altitude you want it goes into ALT by itself.

Don't press ALT. If you press ALT it will set the current altitude. And then if you press VS it has no goal. 

At least this works for me on the steam gauge version.

[Ixoye 1,841]

5 hours ago, Republic3D said:

This is how I do it:

Set your desired altitude, then press VS and dial the preffered rate up or down. When it reaches the altitude you want it goes into ALT by itself.

Don't press ALT. If you press ALT it will set the current altitude. And then if you press VS it has no goal. 

At least this works for me on the steam gauge version.

There is no VS button in the steam gauge version, at least not in mine, I have to press Alt to switch to VS mode after I have set desired altitude.

Edited November 10, 2020 by Ixoye

[Republic3D 1,232]

55 minutes ago, Ixoye said:

There is no VS button in the steam gauge version, at least not in mine, I have to press Alt to switch to VS mode after I have set desired altitude.

Hmm, maybe I'm thinking of the Mooney. 

[fppilot 4,407]

1 hour ago, Ixoye said:

There is no VS button in the steam gauge version, at least not in mine, I have to press Alt to switch to VS mode after I have set desired altitude.

This is the correct solution to this issue.  First and foremost the AP is not fully modeled, so if you identify the AP model and then read the user manual for the real world AP, it will confuse the issue further.

Ixoye said: Set the desired altitude.  When airborne, activate the AP.  Click the Alt button.  It should present you with a zero value.  At that point click the AP's up button.  Each click should result in 100 of climb rate after the airplane settles into a climb. 

If you do not preselect an altitude, pressing the Alt button will result in the AP locking in the current altitude.

Old_as_Dirt was correct in his report that the Baron AP takes you to an altitude based on 29.92 pressure.  That sim behavior is wrong and should be fixed for flights below 18,000 ft.  This issue has an aircraft  flying at 5,000 based on the real world pressure setting.  But the altimeter gauge is reporting the altitude at 5,300+ ft. as if the real world pressure below was 29.92, which is standard, or average sea level pressure. At altitudes below 18,000 the altimeter should be set to the actual pressure reported by ATC or by ATIS/AWOS recordings along the route. 

 As most pilots and experienced sim pilots clearly know, when climbing above a 18,000 ft altitude the altimeter is required to be set to the standard pressure of 29.92. This keeps all aircraft at the same flight level as they pass through different ATC control sectors.  The atmospheric pressure does change along the route. But the altimeter setting does not until a descent takes the aircraft to below 18,000.

Add or vote at Zendesk for this issue to be fixed.

Edited November 10, 2020 by fppilot

[RaptyrOne 1,457]

3 hours ago, fppilot said:

the Baron AP takes you to an altitude based on 29.92 pressure.  That sim behavior is wrong and should be fixed for flights below 18,000 ft.

I have noticed that behaviour on other aircraft too. There is incorrect logic in the altimeter settings for the AP in general across the sim. If you don’t set the altimeter correctly, the AP will still level off at the assigned altitude as if you had selected it correctly. So while you may have set, say 8000 ft on the AP, you might see the altimeter showing 8,200 ft. By then adjusting the altimeter to the correct setting (mb/QNH), it indicates 8000ft. That is wrong. Regardless of what setting you have for mb/QNH, the needles should settle to the altitude selected. If your mb/QNH is set wrong, you will be at an incorrect altitude (and ATC should moan) but the altimeter would show you are on the numbers.

[Immunol 10]

23 hours ago, fppilot said:

Ixoye said: Set the desired altitude.  When airborne, activate the AP.  Click the Alt button.  It should present you with a zero value.  At that point click the AP's up button.  Each click should result in 100 of climb rate after the airplane settles into a climb. 

Tried this and it did get me a fairly stable climb at 500 fpm, but I only clicked the "up" button once and the plane didn't level out at the altitude that I selected. A step in the right direction though.....