Plane won't fly grid survey set up in Mission Planner

I set up a grid survey yesterday with my Skywalker X8 quadplane running 3.8 but it would only fly to the first waypoint and then circle. Mission planner announced that it was heading for the next waypoint but it just kept circling until I initiated a RTL. I was playing around with different waypoint radius sizes to see if I could get it to turn faster but other than that I don’t think I set up the mission any differently than I have many times before. Here are links to two flights where it failed to fly the grid and just circled at the first waypoint. If anyone can figure out what caused this and how to correct it I would really appreciate the help.

Hi,I found two parameter in your log file Q_WP_RADIUS 200 (unit centimeter) and WP_RADIUS 60(unit meter), In my opinion may be the radius is so small, the drone will judge that it has not reached the target waypoint, so the drone going to keep circling to go to the target wp! you can try to make the radius bigger, and try this WPs again.

There is something badly wrong with your elevons. The plane just could not turn right. It had the elevons hard over for a right turn but would not go past a 20 degree left bank. Similarly for pitch - it wanted to pitch up, but just didn’t have the control authority.
Some possibilities:

  • the elevon servos are not moving freely
  • the elevons are bending
  • the wing is badly twisted
  • there is a large weight on the left wing
  • the elevon trims are way off
  • airflow over the elevons is disrupted
    I’m sure there are other possibilities

I don’t think any of those possibilities are likely for various reasons that I won’t take up time with. Here’s a log from a long flight I did earlier that day where it was doing a clockwise circuit for some time making only right turns. I’m using the wings from the old SkyWalker that was doing grid surveys for Jack and I just fine. But I have wrapped them in vinyl since then.

In general the plane looked like it was flying much better than the previous test as I made the two changes you suggested, extending the range of the elevon servo throws by 200 pwm and changing the COG. The only thing that looks odd to me is the alignment of the forward motor.

I’d sure like to get to the bottom of this. I’ll bring the plane down to CMAC next weekend and we can have a look at it together.

that flight log looks totally different from the later one. In the later log the elevons are not able to produce a right turn, whereas it has no problem in 29.bin.
I’m sure there is a hardware issue with the elevons of some sort. I just can’t tell you what it is.

Two different sets of wings, same issue. Doesn’t make sense. I’ll bring both sets of wings when I come down. Thanks.

I discovered that the motor mount I used was quite bent so I’ve fixed that. As far as the left turning goes, I set the plane up level and put it in Manual mode. The elevons were perfectly straight. I then flipped it in to FBWA mode and the left elevon raised up quite a bit. I did the leveling routine in the configuration and the elevon went to the neutral position. Hopefully, these two adjustments will take care of the issue. Cheers.