While traveling east on Arizona highway 389 about 20 miles west of Fredinia Arizona my Wife and I traveling in separate vehicles observed three airplanes that were a very dark grey in color without any markings. They were large four engine planes with approximately 100' wingspans. What was most unusual was that they were flying at about 40mph and were less than 100' off of the ground. I was certain the first one I saw was going to crash because it seemed impossible for such a large Craft to stay airborn at such a slow speed. The second plane came towards me at about the same speed but was tilting the wings about 80 degrees as it flew over a power line nearly hitting the line with its wing. These Craft seemed to be without weight. The strangest part was they made no sound of any kind. Two of them flew directly over my vehicle at less than 40' of altitude. I opened my window a little and there was no wind or exhaust from the large jet engines and absolutely no sound. I was in a moving van with my Wife following in her car and she observed the very same things. There were another 3 or 4 cars that must have seen them too. They seemed to be almost playing as they swung back and fourth tilting there wings at angles that should have stalled any aircraft I know of. I have not been able to identify the planes. The outer 10-15 feet of the wings sloped down about 5 degrees. I called 911 and was told that US military planes often practiced in that area. These planes must have had anti-gravity and a different type of propulsion than forced air through jet turbines. I have asked around my town in Southern Utah and others claim to have seen the same planes. They were in sight for quite a while. I was traveling 60mph eastbound and they were flying westbound at extremely slow speeds. The one that banked 80 degrees over the Power lines must have slowed to 20mph or less. It almost seemed to hover at that steep angle. The things they did were not possible by conventional Craft. Again there was no sound or wind of any kind. I'm certain they were ours but not anything I can find on any sight. I could clearly see the cockpit windows but because of glare could not see inside. These were very large planes.