>It's also unstable because of the high center of gravity. the high center of gravity is just one aspect. I'd suggest glancing over this: http://www.hiller.or

>It's also unstable because of the high center of gravity. the high center of gravity is just one aspect. I'd suggest glancing over this: http://www.hiller.org/flying-platform.shtml http://www.hiller.org/flying-platform.shtml >Also did you notice the Hiller's lip around the top edge? the primary purpose of [relatively wide] lips of ducted fans is this: "Utilizing the Bernoulli principle, 40% of the vehicle's lift was generated by air moving over the ducted fan's leading edge. The remaining 60% of lift was generated by thrust from the counter rotating propellers."