High-Speed VTOL -- DARPA Tries ... Again

High-Speed VTOL -- DARPA Tries ... Again:
DARPA does not want bidders for its new VTOL X-Plane program to "just revisit old concepts" for vertical take-off and landing that combine the high-speed performance of fixed-wing aircraft with the low-speed agility of helicopters.
A look at the American Helicopter Society's wonderful V/STOL Wheel (of fortune or of shame, take your pick) shows how hard that could be, as it lists no fewer than 45 different concepts that have been tried, of which only three can be considered successes -- the Hawker Harrier, Yakovlev Yak-38 and Bell Boeing V-22 (four if you include the Lockheed Martin F-35, but I won't go there).

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