I consider myself to be a bit of a connoisseur of weird airplanes. So when something comes along that even I've never heard of, you know it's going to be crazy.
I just learned of this one today: The Cornelius XFG-1
What the hell is the XFG-1? Apparently in 1944 the USAAF had an idea for transporting fuel: a dedicated glider towed behind a bomber. The problem is most gliders can't fly very quickly without tearing apart, so they tasked George Cornelius, who had previously experimented with unusual airplanes such as the Mallard shown here, to develop a fast glider.
The idea behind the XFG-1 was initially to carry 677 gallons of airplane fuel in a gas tank in the fuselage of the plane, tow it to its destination behind a bomber, and then fly it to land to provide fuel to a base. Er, at least that's best I can come up with since resources about it are sparse at best. Apparently there was also a proposal for an unmanned version to be towed behind B-29s and provide extra fuel to the bomber to extend the bomber's range. Only two words can describe this idea: Batshit Crazy!
What makes the XFG-1 so weird beyond the craziness of its mission is its configuration. It's a true monoplane - it only has one lifting surface. There's no horizontal tail, just a forward swept wing. It's almost like a flying wing, except it actually has a fuselage and a vertical tail. It's truly unique and strange, and not really the brightest idea.
It flew alright, but one of the two prototypes entered into an irrecoverable spin, killing the pilot. Not really surprising given the difficulties of keeping a forward swept wing with no horizontal tail or canard stable...
Eventually the USAAF wised up and stopped investigating the XFG-1, and after WWII the advancement of aerial refueling technology made the idea of a fuel carrying glider obsolete. Ultimately though, that's the bizarre beauty of wartime technology: it's only crazy if it doesn't work, and the only way to know if it won't is to build it and fly it.