PeteGould
lvl.4
United States
Offline
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I've been offline for awhile so am just seeing this.
In simple terms, remember that GPS tells the bird where it IS, but not which direction it's FACING. For the Inspire to remain predictably facing in a specific direction - whether in GPS OR ATTI MODE - it needs the compass. And to fly level, it needs valid IMU data. Without accurate and predictable compass input, air currents will cause unintended changes in heading/direction. Presumably the flight logic computer will battle this issue and try to correct for it as it gets updated GPS input, but if you lose GPS and switch into Atti mode AND have bad compass data AND have bad IMU data, now you're in an unbelievably bad mess: the bad IMU data means the bird won't fly level, the fact that it's not flying level will cause both drift AND rotation, further exacerbated by whatever the air currents and eddies happen to be, the lack of valid compass data means the bird has no idea that it's rotating and won't do a thing about it, and the pilot suddenly has to compensate for all of it at the same time, quite possibly while too far away to clearly see the rotation or tilt clearly. Only a genuinely amazing, HIGHLY experienced pilot would have a prayer of recovering from that, and I'm not even sure they could. I suspect, without knowing, that a lot of poorly configured Inspires fly more-or-less okay as long as they have GPS input, because the computer keeps correcting for the other errors, but when GPS is lost, those other errors come to the fore and sandbag the pilot. Conversely a well-tuned system, inclined to fly straight and level without help, can enter Atti mode unexpectedly and will remain stable.
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