Ionic Wind

A team at MIT has successfully built and flown a model of an absolutely silent airplane with no moving propulsion parts. Basically, it uses high voltage electricity to create its own wind. Impractical for anything larger than a model, (you'd need hundreds of millions of volts to fly even a modest-sized real airplane), and based on an old theory from the 1960s, it is nonetheless a fascinating proof-of-concept which may yield smaller-scale applications.