Jump to content

Light Sport Auto Pilot Strategy


Ed Cesnalis

Recommended Posts

My big complaint about my auto pilot is that it makes too many correcting turns to maintain course.  I do sometimes fly in conditions where my AP maintains course without anoying turns but most of the time I end up turning it off and hand flying to minimize all the corrections. 

 

Thinking about it en-route I figured out that the mode type had something to do with how many correcting turns.

 

With my AP these modes are all track oriented.

  • Course (bug)
  • GPS (flight plan)
  • VOR
  • ILS
  • Virtual VOR

And this mode is heading oriented

  • Heading (bug)

Algorithms might differ but my AP does 1 turn in heading mode to correct and 2 turns in course mode to correct.  Here's how it works:

  • Heading mode: 1 turn from current heading rolling out on new heading.
  • Course mode: 1 turn from current heading rolling out on new heading to intercept course lost due to drift or not yet acquired then a 2nd turn to intercept the course rolling out on new heading intended to track the course.

 In the horizontal axis course modes are more annoying because they do twice as many turns and are more prone to rolling out on a heading that might be wrong because it might not track the course and in that case the turns continue.  Heading mode is less annoying but will drift off course every time the cross wind component changes.  Heading mode has the advantage of deviations for terrain or airspace that aren't in the flight plan so a little more work moving the heading bug gives me a more pleasant trip than using a course mode.

 

Vertical mode in cruise is annoying but that's the fault of the thermals not the AP.  In my light sport the pitch changes can be dramatic and if the horizontal mode is active too the attitudes can be entertaining but annoying and even disturbing.

 

If I'm not happy with the result often I will use 1 axis at a time.

 

Minimizing my gain settings makes the AP easier for me to live with.  I mostly hand fly but lately I'm getting along with the AP a little better.

 

What are your tips?

 

PS my AP is fully aerobatic, it has no pitch or bank limitations.  The most fun can be had by accidentally reversing the aileron mode in a moderate gain setting.  As soon as I activate the bank happens in the wrong direction and the moderate gain setting makes it happen in a faction of a second.  The fun comes if you are a little slow hitting disengage because the CT roll rate is pretty good.  If you are slow to disengage your next best option becomes a split S maneuver (altitude dependent.)

Link to comment
Share on other sites

My AP does not seem to have this problem. It can waggle about in bumpy air, but generally no worse than I am. But in smooth air it's rock steady. Is your gain set too high? Which AP do you have?

 

My main problem is that if the air is hot and there are a lot of thermals, the AP will try to maintain altitude through the up drafts and down drafts and ends up changing pitch enough that I have to work the throttle quite a bit to keep the rpm and speed where it needs to be.

Link to comment
Share on other sites

I have recently gone from 40 to 35 on aileron gain.

 

post-6-0-69815400-1465944718_thumb.jpg

 

What setting would you try? 35 seems very gentle.  

 

You guys say yours are 'rock solid'  what does that mean exactly?  I'm complaining about the number of correcting turns not that it doesn't do as commanded.

 

Edit:  I guess its right there in the instructions that I posted, I turned the gain down when I should have went up.  Meaning not quite so much like an RV instead move in the direction of a COZY.  Another way to say it is the RV probably has a better initial roll rate than a CT but the CT has a good rate so try a setting close to the RV but for slower roll rate not faster.   

Link to comment
Share on other sites

I have normally used my Garmin 696 as the source. I update the direct to and it turns to the line. One turn.

 

That would be 1 turn for me as well. Direct to creates a new course that your old course crosses.  

 

After you turn, if and when you drift of course due to change(s) in the crosswind component you have to 1st turn to intersect the original course and then turn again to track it. Even if your AP is not annoying and even if you don't notice it takes 2 turns for a new Direct To unless you were already pointed at the new waypoint.

Link to comment
Share on other sites

The AP in both the Dynon and the Cirrus react pretty much the same.  The Dynon AP will turn to heading in heading mode with no deviation.  When intercepting a GPS course line it will overfly the target a bit then turn back and align.  I can't us the Dynon AP at all when the air gets rough because it will break loose.

 

The Garmin AP in the Cirrus has a Yaw Damper so all turns are well behaved.  It will react the same as the Dynon AP when intercepting a GPS course line.  But it is more robust and will fly in any conditions rough air or smooth.  It will act a little like a boat in water in a strong headwind slightly rising.descending a few feet then correcting back down/up to ALT altitude.  On "Direct To" it will behave like the HDG mode...immediately banking in a standard rate turn to course if a turn is required.

Link to comment
Share on other sites

... It will act a little like a boat in water in a strong headwind slightly rising a few feet then correcting back down/up to ALT altitude.

 

thanks for the feedback.  I think a better way to say what's in the above quote would be "when encountering positive wind shear (headwind increase) it will act like a boat in water, rising a few feet then correcting back down ...'  In a steady state strong headwind there would be no need for a correction but when the headwind component increases and lift increases you rise until the AP detects and corrects or the airframe's stability corrects.

Link to comment
Share on other sites

thanks for the feedback.  I think a better way to say what's in the above quote would be "when encountering positive wind shear (headwind increase) it will act like a boat in water, rising a few feet then correcting back down ...'  In a steady state strong headwind there would be no need for a correction but when the headwind component increases and lift increases you rise until the AP detects and corrects or the airframe's stability corrects.

 

okay, I'll buy that.  The wind is usually not right on the nose....the last time I saw it pronounced it was flying back from Duluth over Wyoming and Utah and back to Nevada.  Over part of the Rockies I saw the effect and the winds were severe, about 30 to 40 kts.

Link to comment
Share on other sites

By "rock solid" I mean that the airplane *seems* very stable in roll.  Obviously it's making many changes per second, but they are precise and smooth enough that the airplane feels like it's pretty much staying level.  It doesn't wander around the course line, it stays right on it.  

 

That's in smooth air, once the bumps start all bets are off and the AP does whatever is necessary within its limits to hold heading and altitude.  Sometimes it flies better than me, sometimes it's Mr. Toad's Wild Ride.

 

I don't think my airplane has a mode where it will just work the roll servo and disconnect the pitch servo; that would be handy in the thermal situation as I could just work the stick back and forth to keep relatively stable pitch and let the AP fly the course line.

Link to comment
Share on other sites

Yes 1 axis at a time is a feature you should request, in light sport APs obviously have limitations and 1 axis only allows them to be still useful when 2 axis isn't.

 

I'm going to take the 'inner tennis' approach and find both too low and too high gain settings so I can then find the middle.

Link to comment
Share on other sites

I have a TruTrak APIII. On my last XC I was within the boundaries of a frontal change. Flying south with a SW wind. Direction and speed changed to north then back to the SW. During this period the AP was hunting to stay on the course line. I hand flew for approx. 5 minutes then turned AP on again and it was fine. I'll chalk that up to wind speed and directional changes as this never happened before.

 

At the onset, hitting direct to, activate didn't stop the hunting. Wind direction and speed were noted on the 796.

Link to comment
Share on other sites

 

I'm going to take the 'inner tennis' approach and find both too low and too high gain settings so I can then find the middle.

 

That sounds like the best bet.  If you can get it down to not "hunting" the course line in smooth air, it should be pretty well dialed in.  RVs are heavier than the CTs, so even your 35 setting might be too much gain.  It might need 30 or even 25.

Link to comment
Share on other sites

That sounds like the best bet.  If you can get it down to not "hunting" the course line in smooth air, it should be pretty well dialed in.  RVs are heavier than the CTs, so even your 35 setting might be too much gain.  It might need 30 or even 25.

 

After posting the instructions I finally read them. I don't 'search' for the course in smooth constant state air, but when its not tracking it is wandering (too little gain) too much gain should mean quick pulses and I don't get that.  RVs might be heavier but its initial roll response that gain is the inverse of.  I went from 40 to 35 (wrong direction) so I'm tempted to next try 48.  

 

We are having a week long wind event plus the airport is all torn up and I just got busted taxiing through the construction so now I'm banished to a tie down till next week. :(

Link to comment
Share on other sites

I added gain and have precise steering without wandering, except when it starts wandering...  symptom still means too little gain so I'm going to add in smaller increments until its perfect or until I get the 'too much gain' symptom and then I'l back off to best compromise.

 

gain settings.

 

1st ten years 40  often wanders

recent new setting 35:  wanders more

today's setting 48  works with precision but also lost it once and oscillated till I reset it.

 

I'll probably try 55 tomorrow.  I'm happy

Link to comment
Share on other sites

  • 2 weeks later...

Trutrack two axis here, and I prefer running in heading mode. Keeps my head in the game better. When the thermals get too annoying I flip off the altitude hold and let her drift up and down a bit to smooth the ride. WF

Link to comment
Share on other sites

Trutrack two axis here, and I prefer running in heading mode. Keeps my head in the game better. When the thermals get too annoying I flip off the altitude hold and let her drift up and down a bit to smooth the ride. WF

 

Heading hold mode is pretty useful.  I will often fine-tune a course by making small changes in heading mode, then flip back to Nav mode if I have a course set up in the 496.  Sometimes I just want to take a break from the controls and don't have the 496 set up, and the heading mode is great for that.

 

I really just wish we could get a constant speed prop on these things -- then I wouldn't have to be constantly playing with the throttle lever to stay on my chosen RPM as the AP makes changes. 

Link to comment
Share on other sites

Archived

This topic is now archived and is closed to further replies.

×
×
  • Create New...