I don't think ground effect while hovering involves wingtip vortices at all. His 'flying' figures are only speculation, and all he's proven is that he can hover.
His 'official' specifications: "Hover (out of ground effect) – >10,000ft (estimated)"
"Assuming mass moved is constant then a helicopter hovering in free air will be required to produce a force equivalent to V2 (speed after passing through the rotor) - V1 (starting speed of air) where V1 is some value above 0 given that the air is already moving downwards before reaching the rotor.
When close to the surface (generally considered 1/3-2/3 of the rotor diameter), air forced downwards through the rotor disc is restricted in its flow by the ground. This produces an area of high pressure below the disc and in turn, reduces the duct effect and hence the downwards velocity of the air above the disc. This reduces V1 while V2 remains relatively static, so the value of V2 - V1 increases. From the equation F = M x A we can see that the 'lift' of the rotor disc is greater when in ground effect."
Wingtip vortices are a major cause of induced drag,
which refers to any drag created as a side effect of
generating lift.
Less drag -> more efficiency -> less power required to maintain altitude. I don't know how much of a factor this would be compared to the cushion, though, so we'll just have to wait and see. Given that he's already bought and engine and molded a nice, shiny shell, my guess is that he has plenty of power.
