Trouble engaging AP

[Ecosse_821 24]

Hello.  I haven't had any issues with the autopilot until my last 10 or so flights.   I usually want to engage the AP fairly soon after take-off, because there is so much else to do to get cleaned up and set power, props, etc.

 

So lately it is just refusing to engage until I'm been climbing for almost a minute.  I am trimmed well and holding the speed that the FD cue is giving me.   Before Takeoff I have the FD set to GA, HDG hold, and ALT Sel engaged.

 

I don't know what criteria I am not fulfilling at this point to get it to come on when I need it.   I retract gear, retract flaps, set props to 98.0, set climb power, all of that while I'm waiting for the AP to agree to engage.  

 

I've searched the forums and manuals, not seeing the missing clue here.

 

 

[downscc 1,327]

The AP cannot engage because it does not have a VNAV capability..., simply setting ALT Sel only ensures that it will enter altitude hold when you arrive. You must fly up to there.... my technique is to hand fly until I stabilized in a 170 KIAS climb (per POH) then engage AP in IAS mode to hold 170.  It is a good idea to preset the TAS speed to 170 before engaging.

 

Basically, you will either use V/S or IAS mode for climbs/descents.  Stay away from V/S mode for climbs because there is no speed protection. 

[Ecosse_821 24]

Dan, thanks for the reply.   I've tried what you are talking about.  I'm having to hand fly the aircraft up to about 2500 AGL before it will come on, regardless of which vertical mode I have selected.  

Even without a vertical mode selected, should it not hold the pitch when engaged?   That is how it worked for my first 75 flights.   I had no problem engaging the AP  after 500 feet AGL, as long as I was trimmed and in stable flight.   Of course , immediately upon seeing it engage, I would then hit IAS and dial up 170 kias right away.

 

No, something else is going on here.   I must be doing something differently, but not pre-selecting a vertical mode isn't it.   I might have to try re-installing the plane, because this is not consistent with what's in the manuals.   It should engage after 500 feet AGL.

[Ecosse_821 24]

I just re-installed the aircraft, now the AP is engaging fine at 500 feet AGL or above.   No vertical mode is pre-selected in the FD until after enaging the AP with HDG and Alt Sel selected (and GA, of course).

 

Weird!

[ckyliu 1,749]

How odd, glad you fixed it. Yeah the AP doesn't need any modes engaged when you switch it on, it just defaults to wings level and pitch hold until you select something else (which in my case is usually bashing IAS as we hit 180 kias)

[Ecosse_821 24]

Spoke too soon.   After working properly just the one time after re-install, it started doing the same thing--it won't engage until 2500 feet AGL.   Tried re-installing again, same deal.  

I'm not sure what else could be wrong here.  I turned off all weather and made sure I was perfectly trimmed (no hands on yoke), flying exactly on the FD cue, etc, etc.  

Frustrating.

[Ecosse_821 24]

Is there a time-out that needs to elapse after getting locked out from engaging the AP?   Because right now I am trying to engage every 5 or 6 seconds with failure after failure. 

 

I know that this is not likely to be a bug.   That just doesn't usually happen with PMDG stuff.    I just think I need to figure out what is different between the times it works nominally, and the times where it balks and won't engage.

[downscc 1,327]

I suggest you start looking at your controller, maybe there are control spikes from a dirty pot or maybe a control assignment conflict. At least rule it out.

[Ecosse_821 24]

Thanks Dan.  I had thought that that could be the issue.  The thing is, it is a brand-new CH Yoke that I just got in December, and I also have the payware FSUIPC with the three spike elimination boxes checked.   I have made sure that it is calibrated, and I don't seem to have spike/noise problems in any other context.

But who knows.  Right now, continuing testing has it working 1 time, them failing 3 or 4 times, then working properly again the next time.  

I've also tried it with no wind or weather, and at different airports and such.   No clue.