Manned multicopter / multirotor build PART 8
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Manned multicopter build part 8
So here’s the crash story: One of the eight motors underperformed from the very first day compared to the other seven. It was good enough for participating in keeping a 100kg octocopter in the air but would struggle with 125kg. This resulted several teardowns followed by several re-assembling sessions in order to find out what the problem was. During the most resent re-assembly I accidentally misalign a carburetor spacer plate 180 degrees, cutting off the pressure transferee tube between the crankcases with its fluctuating pressure and the carburetors fuel pump, which is driven by the fluctuating pressure present in the crankcase when the motor is running. This mistake was disguised by two circumstances: 1, The normally relatively high static fuel pressure head resulting from a full fuel tank in combination with 2, the relatively relaxed flight conditions with the multicopter not carrying the full intended payload. These circumstances quite effectively compensated for the absent properly working carburetor fuel pump. So the fuel systems static pressure was enough to provide the incorrectly assembled motor with the fuel needed as long as the octo was flying fully fueled up with reduced payload. In the flight where the octo crashes, the defect motor is working harder due to heavier load, thus requiring more fuel. To make matters worse I, as a safety precaution ironically, only fueled up the octo to a ¼-tank lessening the static fuel pressure further. The net result was that the faulty motor started working intermittent a short time in to the flight revving up and down according to momentarily changes in the carburetor fuel pressure. When one motor drops in rpm the multicopter starts jawing. Being an inexperienced pilot I quickly lost orientation and control and crash into nearby trees.