Sunday Fail : Rockwell XFV-12

The Harrier is, to date, the only successful V/STOL jet fighter in the west. The US adopted the Harrier themselves but in the 1970s they tried to produce a superior and supersonic fighter to replace it. This was the Rockwell XFV-12 which was fine except it couldn't actually take off.

The XFV-12 had a thrust augmented wing, engine thrust was diverted through slots in the wing to produce vertical thrust. The XFV-12 had 2 sets of wings more or less as it's canards providing almost half of the available wing area. So why did it fail?

The problem was simple. The thrust available, even with an uprated engine, was not enough to get the plane off the ground. Too much engine thrust was being lost through the exhaust ducting. It probably could have worked, if the aircraft weighed 25% less. A major drawback with the thrust augmented wing scheme by the way was that the wings could not be used to carry weapons which meant that the only place to carry weapons was under the fuselage.

This proved rather academic in any event as the project was canceled by the end of the 1970s due to cost... and being useless.