Autolanding failure. Tip stall? on turn to final causing uncommanded roll to 80 deg.

Today's autolanding attempt with my Skywalker 1880 was a failure. I attempted to insert some Do_Change_Speed commands to incrementally slow down from cruise speed to landing speed. On the base to final turn the plane continued its roll to 80 degrees. I suspect I got too slow and the inside wing tip stalled. However it appears the airspeed was adequate at that point, although it dropped way below stall speed during to recovery. Perhaps there is a lag time in the data? Could this be an accelerated stall? Is there any way to see how many G's I was pulling?

The graph below shows a large divergence between Servo_Roll and Nav_Roll & Roll. I need help understanding this.

Roll shows an 80 deg left bank, that's obvious.

Nav_Roll shows the identical thing, we would this be exactly the same?

Servo_Roll, I presume is showing what the servos were trying to do to correct the excessive bank angle, which probably stalled the wing tip more.

Roll_Sensor is the pink line that is very hard to see. I have no idea what this is telling me.

 

Here is a short video http://youtu.be/p6kayKtrg9I

 tomorrow.

Here is my flight plan:

 

Here is a Google Earth view, I just figured out how to display the "Planes", that is so cool!

 

Here is the .log file, sorry my computer crashed so no tlog.

2013-10-07%2013-59%203.log

 

There were some other odd things you'll see if you watch the video. The plane really dived hard to get down to 175ft at WP20 where it was to do 2 turns in Loiter but the profile was too steep and it crossed the point too high at about 220ft and too fast. Why at this point does the APM add 50%+ throttle in the turn?

 

 

 

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Can't help you but gotta ask how you got the aircraft icon to display in GE.

Well at least 1 person read my post.
To find the little plane icons go into the log .kmz folders listed on the left pane in Google Earth. Expand the folder tree until you see a folder called Planes. Inside you will will find an item for every recording point in the log. This part is a pain b/c there are far too many to easily find the ones you want. Every item you check the box on will open up a little airplane icon that is in the exact attitude that the log recorded at that moment. Very cool, but too cumbersome with so much data. Let me know if my description was inadequate and I'll get you some screen shots.

Thanks. Will try it out. The Views count above says over 100.

What is your min pitch angle parameter.  Your WPs call for a steep descent as you approach your landing site.  Your plane is diving to reach the next WP and reaching 55 mph - which is probably entering the danger zone for a SW if it tries to abruptly pull up.  From WP19 to WP20, MP is predicting a -90% grade (-42° descent angle).

Bring up the Elevation Graph in MP.  I am not 100% sure I know what APM does with the Do_Speed_Change commands, but I'd be curious to see what MP shows in the Elevation Graph.

You have the Google Earth track.  Pull up the elevation profile and compare to the Elevation Graph in MP.  I would like to see what you find.

In general, I think your approach flight path is too steep, with a final turn that is too sharp.  I try to err on the side of very shallow descents and shallow bank angles.  Are you able to play back the log on the Flight Data screen with the flight path overlaid on the waypoints?  What I do for autoland is design the approach such that the path roughly matches the glideslope of my SW.  This makes for a very long, but uneventful approach.  I should admit that I had flaps under manual control on my SW1680 to really scrub off speed on final.

Trung,

I really appreciate your post, but I think your math is wrong and you are like the rest of us still not understanding what Grads means. WP19 to WP20 is 825'. The descent was from 400' to 175' = 225'. The rise/run = .27 or 27% grade = 15 degrees. I agree that is too steep, but not as severe as you suggest. This is close to the limit of my Skywalker, but the tailwind made it worse. I understand all this, except why the APM added throttle when it was high. The max pitch is set to -20, perhaps too much for the skywalker. I'll change it to -15. My max speed is set to 19m/s (43mph). My TECS Max Sink is set to 5m/s (980ft/min). I think that is a bit too high also.

Back to the real question, the approach:

I need to keep the approach fairly tight and steep due to those power lines. I would love to have a gradual descent path like you, but at this field I need to be more aggressive. I'm not sure how to make my turn to final less sharp.  I could add waypoints to make a traffic pattern that isn't the standard rectangle. I could open up the WP Radius, but I need that tight for the photo missions I am doing.  I have had success with this approach before, but the plane landed at cruise speed and it should slow down before ground contact, that is why I added all those speed changes. I wish I had flaps, not as easy on the 1880 wing.

 

Post your WP19 coordinates.

21.403912 

-157.764337

@400'

See my post in your other thread about the "Grad" column.

iskess, I think that the altitudes in your flight plan are measured in metres , not feet, check waypoints 20 to 22.

distance between them is 237 metres change in altitude 175m to 80m ie 95 metres

grad = 95 x 100/237 = 40 as shown in the grad column.

works for waypoints 19 to 20, 400m -175m gives 225m, distance between is 250m,

grad = 225x100/250 = 90 too. :)

might explain your tip stall too.

iskess, having just read Trung's reply to your post in the mission planner category, maybe your altitudes are in ft after all.

It seems that Mission Planner treats altitude like they were measured in meters, even when you've set alt to show feet, when it makes the Grad calculation.

I'm now confused too!

Yes, its a bug. Good find. I posted it on github: https://github.com/diydrones/MissionPlanner/issues/193

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