Weapon Fail : Rockwell XFV-12

The Hawker Siddeley Harrier Jump Jet is, to date, the only successful V/STOL jet fighter in the west (and the way the JSF is going that may well remain so). The US adopted the Harrier themselves but in the 1970s they tried to produce a superior supersonic fighter to replace it. This was the Rockwell XFV-12 which was fine looking and futuristic but had one slight snag... 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 provided almost half of the available wing area. So why did the plane 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 lost through the exhaust ducting. It probably could have worked, if the aircraft weighed 25% less. Another major drawback with the thrust augmented wing scheme 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.