Autopilot

[NeilC 3]

Spent about 50 hours in the last couple of weeks flying this beautiful bird.

I am suffering with some autopilot problems.  This mostly occurs in turbulence (or should I say it is more accentuated).

When I run the final checks (just before establishing) I get a huge pitch up sometimes up to 30 degrees.  It seems to be worse when the aircraft is in a turn.  I will do more checking, but it seems to be around the time the gear is dropped.  At the time the aircraft is in altitude hold mode.

Also, the Approach mode doesn't seem to work.  It doesn't intercept the glide at all.  Sometimes it does pitch down, but nowhere near enough to follow the glide.  I don't mind this too much, after all, who wants an autopilot flying in CAT1 conditions when you can hone your own skills further by doing it yourself!

[randomTOTEN 13]

Sounds like you're letting it get too slow.

Robert Toten

[randomTOTEN 13]

Just completed flight check. Autopilot performs as expected for this vintage.

Autopilot has no problem adjusting to gear and flap extension, kept normal pitch values throughout. Turns had minor pitch deviations but nothing unusual. Appears to successfully track a localizer provided you capture it with the turn knob first (struggles with a 26kt direct crosswind 🙂). Glideslope coupling requires disengagement of altitude hold.

I highly suspect you had insufficient speed thus the pitch up as it tried to maintain altitude.

 

Robert Toten

[NeilC 3]

Speed was about 160 when it pitched up, Tried a few more tests.  It seems to be weather related.

I still can't get the Approach mode to work though.  I establish on the LOC, disengage the altitude hold and switch to Approach mode before the GS bar comes down, but nothing happens at first, the bar goes down and then it tries to react but never manages.

One thing I did notice, is if you then go back to LOC mode, the pitch is no longer controlled by the Autopilot, you can fly it with the yoke and trim.

[BlueStar 323]

On ‎2‎/‎2‎/‎2019 at 7:47 AM, NeilC said:

This mostly occurs in turbulence (or should I say it is more accentuated).

The autopilots of this vintage tend to struggle in turbulence and are not very intuitive when it comes to the approach mode.  Although there is a LOC and APPROACH mode the autopilots of this generation were not capable and designed to fly precision approaches (my opinion).    When I fly the DC-6 I hand fly all departures and arrivals and only use the autopilot enroute.  

Grace and Peace, 

[downscc 1,327]

4 hours ago, Bluestar said:

The autopilots of this vintage tend to struggle in turbulence and are not very intuitive when it comes to the approach mode.  Although there is a LOC and APPROACH mode the autopilots of this generation were not capable and designed to fly precision approaches (my opinion).    When I fly the DC-6 I hand fly all departures and arrivals and only use the autopilot enroute.  

Grace and Peace, 

However Wilhelm, the Sperry that is modeled in the DC-6 by PMDG is a very good autopilot.  We went through a lot of testing and tweaking during the P3D beta that I think resulted in a solid product.  This autopilot is the state of the 1950s art, sure it is full of tubes and transformers but just because an operational amplifier in a PID loop is a tube instead of a piece of silicon doesn't detract from it's capabilities.  Those engineers created a real work of art.

As for the complaint that GS is not being captured, I've been quiet because I haven't seen enough of an explanation of the problem to understand why it isn't working for the OP but I'm sure the problem is procedural.  I haven't flown the DC6 recently and when i do I also hand fly most of the time because it's fun (not because I need too), but last time I flew a coupled ILS she did exactly what was expected of her.

Edited February 3, 2019 by downscc

[randomTOTEN 13]

2 hours ago, Bluestar said:

Although there is a LOC and APPROACH mode the autopilots of this generation were not capable and designed to fly precision approaches (my opinion).

It'll get you down to 200', wouldn't surprise me to learn it's CAT 1.

The other problem you might have Neil is that the autopilot has a maximum control authority of 18 degrees pitch below the horizon. If the combination weight/weather/speed/configuration requires more than 18 degrees nose down to follow a 3 degree slope then the airplane is going to fly high. If you work within it's limitations (and you PMDG guys did a fantastic job on this AP which I have never explored until now 😎) it'll achieve the required performance.

Neil try these conditions: 88,000 LBS, 2400 RPM, 24" minimum MAP, Gear DOWN, Flaps 30, 130 KIAS, Cowl Flaps 2, AUTO RICH. Remember that this AP cannot "capture" a GS, as soon as you command APPR and deselect ALT HLD it pitches for a GS wherever it is. Also it's a little slow (gives a smooth ride?), give it a chance to do it's thing.

 

Robert Toten

Edited February 3, 2019 by randomTOTEN

[philfab2 3]

DC-6 COUPLED APPROACH

I have never been able to do an autopilot coupled approach to minimums.  I have no trouble with the localizer, but when the aircraft descends through maybe 1000 ft, it decides to level off, or maybe even climb.  My actions are as follows: Flying along with autopilot, and altitude hold engaged.  Turn knob to select a heading approx. 30degs to the LLZ and positioned about four miles to glideslope capture.  Disconnect altitude hold and arm LOCALIZER.  When captured, engage APPROACH mode.  Aircraft tracking LLZ as glideslope needle starts to move down.  Glideslope captured and approach is exactly as it should be.  As mentioned before, it will continue like this until out of the blue it decides to level off or even climb.  Thankfully in my entire career as an airline pilot, I have never come across an aeroplane that does this.  What am I doing wrong?  PHIL MCCONNELL

[randomTOTEN 13]

Phil,

what IAS are you capturing the glideslope at?

 

Robert Toten

[philfab2 3]

Around 130k - which seems to work, but it flies down from 3000 ft to about 1500 ft and then just levels off or climbs.  The model seems to have a very slippery grip of glideslope whilst localizer is perfect. I flew the DC-4 for four years, so I would like this to work.  Thanks,

Phil McConnell 

[MikeTheAviator 0]

Hi,

 

I have been having problems with pmdg s dc6 autopilot. I am flying VOR to VOR, without gps (bendix radios only). I set the VOR frequency and turn on localizer mode to intercept the radial. Problem is that the airplane does not follow the radial in straight line, it banks  left and right, although banking is very small but it does not seem to be right...has anyone had this problem or is this normal?

 

Thank you very much

 

Edited June 11, 2019 by MikeTheAviator
Mispeling

[scandinavian13 5,192]

4 hours ago, MikeTheAviator said:

has anyone had this problem or is this normal?

Using a weather add-on?

Also: keep in mind that the Sperry A-12 is from the days when autopilots were still novelties...like TVs at home.

[MikeTheAviator 0]

8 minutes ago, scandinavian13 said:

Using a weather add-on?

Also: keep in mind that the Sperry A-12 is from the days when autopilots were still novelties...like TVs at home.

I use fsuipc, the aicraft is flying an S shaped route, like always chasing the radial, flying over it, overshooting, and turning on to it again 

Edited June 12, 2019 by MikeTheAviator

[MikeTheAviator 0]

Scandinavian13 sorri for the mistake for wx add on i use opus fsi

[randomTOTEN 13]

Mike that sounds like normal behavior for VOR tracking.

 

Robert Toten