Saturday, August 15, 2015

Flight Session #37 - Flying to 120 meters - Poor Landing

Same field and not very cloudy, but hdop could only achieve 1.8 . Later found out it might have been geomagnetic storms (poor KP-Index).

Battery #1 - Manual flying in various modes. Practiced landings. A little FPV flying. Battery very hot after landing.

Battery #2 - Took it up to 120 meters (393 feet) in Loiter. Quad did great and seemed to hold a fixed position. Never been this high before (about 90 meters was old max). Tower/DP3 warnings sounded as I got close to 400 foot limit. At apogee, I slowly did a 360 to take-in the view.

I started my way down. At about 60 meters, LowVoltageAlarm starts to sound even though I was only about 6 minutes into flight, so I slightly accelerated my descent. At about 30 meters, the quad started to wobble. Apparently I was descending too fast and the Nova had entered a Vortex Ring State (VRS). I gave it more power but the VRS seemed to be affecting the thrust and it was falling too fast. The Tower/DP3 "Imminent Ground Collision Warning" was going off now even though I had the throttle at max now.

The Nova bounced off the ground pretty hard. The gimbal and Mobius got slammed into the ground. I could see part of the landing gear had broken off (laying on ground) but quad was still flying, gimbal was still working, and camera still recording. I flew it a few more seconds to get my bearings and landed it (remember, LVA was going off this whole time).

Edit: After flight analysis reveals I made at least 2 piloting mistakes.
1. Descending too quickly (for a quad with this payload and so little net thrust).
2. After entering VRS, I continued to descend straight down.

So far, it looks like the damage is just:
- Broken landing gear.
- Gimbal lower aluminum plate bent at 45-degree angle. Not sure how gimbal is still working and board didn't short-out.
- Quick MP check (getting logs) reveals Nova's accel/gyro calib. is now way off (severely lilted).

Not really a crash, but 2nd most damage done in an afternoon.

1 comment:

  1. Looking online, a good way to descend a multirotor is to go down and sideways (pitch or roll) at the same time. Therefore youre able to move into fresh air volume rather than into your own downwash. I have found this to allow faster descents with minimal WOD. (unfortunately my last crash had nothing to do with WOD... clicked into stabilise while on an Auto Mission as my throttle position was at minimum... silly me... no damage fortunately)


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