Tucked away in the Mojave desert lies the Armstrong Flight Research Center, where NASA engineers imagine, design, and test the future of flight in aircraft that carry the designation "X."

That single letter has since the dawn of the jet age meant "leading edge" and appeared on some truly historic planes. In 1947, the X-1 became the first aircraft to break the sound barrier in level flight. Just four year later, the X-5 proved that moving, swept wings work. The X-24 program of the 1960s and '70s led to the development of the "lifting body" design that brought the space shuttle back to Earth.

After 70 years, NASA and the US Air Force still build X planes in pursuit of breakthroughs. The latest is the X-57, an all-electric aircraft with 14 propellers. Crazy as it looks (and sounds), NASA engineers say the narrow wings will reduce drag and increase efficiency. But first, they must figure out how it will handle, and how pilots will control it.

We went into the California lab where engineers and other experts run the simulations needed to do that. We even got a peek at the leading contender for the next X designation—a 21st century take on supersonic flight that could revive the age of Concorde. Take a look in the video above.