Air crash investigation – 2

[biggestRCEfan]

Had a nasty crash on my V3 this morning. No recording available, unfortunately. I report to get comment and for awareness.

Context: V3 with RC timer motors, DYS 30 amp escs, and RC timer 9×5 CF props. Betaflight 2.1.6. 4s 3300 mAh. Flying FPV acro mode, second battery, doing climb, then, from hover about 40m high, I would reduce power, go into a dive, start pull out and increase power, then go around for another. Was trying to see if I can feel Air mode differences.

Event: on the third dive, when I started pulling out of the dive, I could hear the screeching/rattling sound of a prop not well attached and I lost control. Damage three broken arms, right side panel of mini conversion canopy cracked. Interesting is that I found two props close to the wreck. One of them had its prop nut close to it. The third was about 2m away from the wreck with nut close to it. After some searching I found the third prop nut about 10m from the wreck.

Conclusion: One of the prop nuts became undone and the screeching/rattling noise was the shaft spinning in the prop hub. Loss of control and crash. Lesson: regularly check tightness of prop nuts.

[Jarno]

Hi, was the rotation direction of these motors right? The nuts should be self tightening if the rotation is right.

[biggestRCEfan]

@Jarno, left motor CW, right motor CCW and aft motor CCW. These RC Timer motors have nuts that tighten when turning the prop in the normal sense of rotation, i.e. when I turn the left prop CW, then the nut would tighten, and the opposite for the other two. I guess this is what is meant by self-tightening. But if the prop would contact grass during a dodgy landing the torque is in the loosening sense, explaining why the props with tip damage (two of them) came off upon impact.

I guess one of the props may have slightly lost torque during a previous incident that went unnoticed.

[Terje]

Are your ESCs calibrated with active braking/dampend light? If the propellers have enough mass they could come undone when the motors are braking.

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