Whenever I see an anti gravity aircraft, it seems to have some kind of spinning gyro or other, undetermined spinning force to repel gravity. If you think of gravity as a weak force try jumping off a high building. One jump may convince you otherwise. These spacecraft defy gravity using artificial gravity.
How they can hover in mid air motionless is still a mystery. Maybe the military has figured it out, and has built their own version of these craft, wherever they come from. My theory is that gravity is an opposite force to magnetism. If you believe otherwise, then read Keely's book, "Universal Laws". It is the most brilliant book I have ever read. He was the first FE researcher and scientist. I think all his laws can be proven factual. If gravity is the opposite of magnetism, then it should be feasible to build a gravity motor using magnetism to reset the falling weight. Good Luck. Stealth