I would argue that using your logic, we 'fly' submarines under the water.

Small aerodynamic models are often tested in moving water because of the Reynolds number. A vacuum doesn't work.

There is a submarine that "flies down" in the water instead of using ballast.

http://www.cnn.com/2009/TECH/03/06/eod.luxury.submarines/index.html

I would argue that using your logic, we 'fly' submarines under the water.

Small aerodynamic model are often tested in moving water because of the Reynolds number. A vacuum doesn't work.

There is a submarine that "flies down" in the water instead of using ballast.

http://www.cnn.com/2009/TECH/03/06/eod.luxury.submarines/index.html