>I want to know how this makes a safe unpowered descent.
the wings seems to be enough for reasonable unpowered gliding. The canard design naturally helps prevent stall. And i'd be surprised if the engines on production models aren't split into 2 completely independent groups (given their number - 3 per/wing - on that prototype i think they aren't split) with completely separate power, controllers, etc, so even relatively serious failure would still leave you with half the engines - that would allow while uncomfortable, yet still controlled even vertical landing from lower hover which i'd suppose would be the worst situation to lose engines.
the wings seems to be enough for reasonable unpowered gliding. The canard design naturally helps prevent stall. And i'd be surprised if the engines on production models aren't split into 2 completely independent groups (given their number - 3 per/wing - on that prototype i think they aren't split) with completely separate power, controllers, etc, so even relatively serious failure would still leave you with half the engines - that would allow while uncomfortable, yet still controlled even vertical landing from lower hover which i'd suppose would be the worst situation to lose engines.