Graviman
Check your math,
I think it should be power 3 and not power 1/3. The result is also not intuitive: you don't need 53 BHP to drive 50!!
So the difference with the glider will be less...
Using power 3 will also be too optimistic for scaling down to zero, some lower harmonics will come into play (linear frictions etc)
Cheers, d3