Materials technology Pen. That's always the roadblock that holds something of this nature back.

However, I am certain that issue has been long since solved. Electric propulsion was recognized long before the 1920's. Tesla was the first person to propose it, sometime right before the end of the 19th Century. So it has been around for quite some time. In fact Tesla released a paper with the complete description of how an electrically powered, Jetson's style world wide transportation system would work around 1903, or thereabouts. I'm confident that there are much more viable, Lifter style aircraft flying today. Our right to know would have been found lacking in this type of case. I have suspected for a long time that this was one of the things they were after when they inspected Tesla's papers, immediately after his death. But the primary reason was undoubtedly to prevent that death ray from becoming a common device. After all, why put two nightmare defense technologies out there at the same time?

Tim