C172 Autopilot

[b1bmsgt 207]

Well, I installed the update with a clean Community folder, and took the C172 G1000 out for a spin to try the autopilot to see if they fixed anything. Set it up on the runway to climb to 4000 feet at 700fpm at runway heading. Took off and engaged the AP at 1000 feet in a 600 foot climb. FPM went to the set value OK, but the aircraft started to porpoise a little. I then set the heading to about 20 degrees to the left and clicked the HDG button. The aircraft showed HDG on the PFD and started to turn for a split second then went right back to ROL. Tried several times with the same results. A few seconds later the AP warning tone went off, the AP disconnected, and the aircraft went into a violent pitchover towrd the ground, actually tucking under and going past a 90 degree dive and crashing.

 

 

Not exactly realistic behavior I dare say...

 

Wonder if anything actually did get fixed?

 

Guess I'll keep flying hand flown VFR until the next update, which is actually OK with me. If I want to fly something on AP, X-Plane still works perfectly...

 

 

[LarryD 132]

3 minutes ago, b1bmsgt said:

Wonder if anything actually did get fixed?

And that's the odd part, because I was flying the C172 G1000 after todays patch, and have flown it many times since launch, and the PFD autopilot always works perfectly for me.  Now the MFD doesn't work as expected, but for now, most of us know that.

Why some folks have problems and some don't certainly is perplexing, making it all that more difficult to resolve.

[Little Jenny 317]

Oh boy, I'll have to try a flight tomorrow morning.  The G1000 172 is my go to plane right now, so hopefully the AP doesn't return to it's plot to kill me (it's been playing nice for the past 60 or so flight hours).

[b1bmsgt 207]

I should have said that this is the same behavior that I have experienced since launch. I was an Alpha tester and it worked better back then...

[Ixoye 1,847]

I have experience this issue a couple of times since launch, something that seems to help is to move the elevator trim and rudder axis to its full extent before take off.

[Bert Pieke 7,594]

15 minutes ago, Ixoye said:

I have experience this issue a couple of times since launch, something that seems to help is to move the elevator trim and rudder axis to its full extent before take off.

Move the elevator trim all the way up and down??

Or move the elevators up and down?

[b1bmsgt 207]

1 hour ago, Ixoye said:

I have experience this issue a couple of times since launch, something that seems to help is to move the elevator trim and rudder axis to its full extent before take off.

May be, but one shouldn't have to do that...

[marsman2020 1,310]

Robert Young mentioned that when developing the Bonanzo Turbo mode he saw weirdness with coupling between the trim and the elevators if the control axes had not been deflected through the full extent prior to taking off.

I've seen some similar oddness as well, where things behaved oddly on the Bush Trip flights with the Savage Cub until I had deflected controls through the full range.

I also saw some comment somewhere about the sim doing its own built-in joystick calibration beyond the Windows calibration.

Just as in a real aircraft, it seems like it might be good to check that the control are free and clear through the whole range prior to takeoff.  I like to watch from the external view.

[dlm9000 10]

I flew C172 G1000 today and autopilot worked great.   I used ALT hold and VS and the the plane behaved well (no fighter jet climbs or oscillations. Used APR, captured the glide slope and took me down to minimums.  I flew a second flight for a big loop around Klagenfurt valley using only the VOR and DME to mark the turns and again captured the ILS.  In fact, the AP had the plane trimmed so well on final, that after disengaging, I only made minor adjustments to the throttle until flaring.  I am not saying that you do not have a problem, I just can't imagine how people are getting such different experiences. 

[RaptyrOne 1,463]

No AP issues for me in either the G1000 or steam C172 after the patch. No sign of porpoising either. Those and the G36 Bonanza (for now, no mods at all and that includes liveries) seem to be behaving with both manual and AP flight. 

Edited October 14, 2020 by RaptyrOne

[Will Fly For Cheese 1,710]

2 hours ago, b1bmsgt said:

May be, but one shouldn't have to do that...

Why not?

You move the control surfaces to full deflection whilst eye-balling them in the real thing as part of your before takeoff checks.

[sd_flyer 6,108]

5 hours ago, b1bmsgt said:

Well, I installed the update with a clean Community folder, and took the C172 G1000 out for a spin to try the autopilot to see if they fixed anything. Set it up on the runway to climb to 4000 feet at 700fpm at runway heading. Took off and engaged the AP at 1000 feet in a 600 foot climb. FPM went to the set value OK, but the aircraft started to porpoise a little. I then set the heading to about 20 degrees to the left and clicked the HDG button. The aircraft showed HDG on the PFD and started to turn for a split second then went right back to ROL. Tried several times with the same results. A few seconds later the AP warning tone went off, the AP disconnected, and the aircraft went into a violent pitchover towrd the ground, actually tucking under and going past a 90 degree dive and crashing.

 

 

Not exactly realistic behavior I dare say...

 

Wonder if anything actually did get fixed?

 

Guess I'll keep flying hand flown VFR until the next update, which is actually OK with me. If I want to fly something on AP, X-Plane still works perfectly...

 

 

Basically it seems like your autopilot preset getting you in stall.  There are two major factors to consider: density altitude and weight. 172 doesn't have solid reserve of power (thrust available vs thrust required) to be comfortable relying on steady AP VS climb . The proper way to do it is to use indicated airspeed instead! In particular for 172S best rate of climb  (Vy) which is around 74 kts or cruise climb which is around 80 kts to keep engine cooler if anyone cares. But that are numbers at sea level because Vy gradually decreases with altitude, but we are not going to depth  of that.

IRL particular  vertical speed is used when  departure procedure dictates minimum climb gradient. In this case we use Vx or higher airspeed to meet obstacle clearance requirements. 

But it either IAS or VS climb case autopilot shouldn't be relied on! I would recommend manual climb, pitch for airspeed, and set autopilot after leveling off. After all C-172 is not airbus with alpha floor protection and auto thrust, so autopilot there is pretty basic there.

 By the way I remember similar situation  IRL many years ago a newly trained owner of King Air crashed  while departing KCRQ in IMC. Obviously he wasn't comfortable flying Beechcraft by hand in instrument conditions, so he turned autopilot on right after take off and set VS climb. Autopilot couldn't maintain VS climb and pitched until critical angle of attack. Sadly pilot didn't catch it in time and perished with airplane at very low altitude.

172 is one of few airplanes in MSFS that modeled decently in my opinion. 

[Ixoye 1,847]

3 hours ago, b1bmsgt said:

May be, but one shouldn't have to do that...

It is a simulator after all, and to check that all moving parts work ok should be included in the preparations 😁

[Sterzenbach 1]

The same to me. Porpoising of C172 Analog cockpit using autopilot is not fixed after last update. Setting climb rate higher as 200ft/min ends in Jo Jo after a while.

Bernie

[b1bmsgt 207]

6 hours ago, Will Fly For Cheese said:

Why not?

You move the control surfaces to full deflection whilst eye-balling them in the real thing as part of your before takeoff checks.

Flight controls yes, trim no...