Alexander Lippisch's Aerodyne

To look at Alexander Lippisch's Aerodyne is to be baffled at how engineers managed to get such a crazy thing off the ground. And it's far from alone in the gallery of bizarrely shaped aircraft we've seen over the years. From balance-driven helicopters to inflatable airplanes, even a cursory tour through the history of aviation reveals some strange beasts that look little like the jet shape we're all accustomed to.

You have to wonder, why do aircraft designers keep building such far-out flying machines? We asked Dan Hagedorn, the curator of Seattle's Museum of Flight, who provided more than a few reasons. Over the last 100 years, unconventional aircraft have let researchers probe the still-murky principles of aerodynamics, test novel aircraft design features and technologies, and much more. "The military has also driven a lot of the development," Hagedorn says, and some strange looking machines "were simply built in order to confront genuine or perceived needs," such as refueling in the air, escaping radar detection, or ferrying odd-shaped or heavy cargo. And in a few, rare cases, some odd flying creations help us discover entirely new methods of flight.