Nazi Flying Saucers From Outer Space! Also, Hitler!
The story of the Flugelrad (German for "wing wheel") is one of the stranger conspiracy theories to emerge out of World War II-era Nazi mythos, but what makes it interesting is that it is fairly grounded in physics, avionics, and plausibility.
The SS had been ordered by Adolf Hitler to research ways of saving fuel (a constant stumbling block in many of the Nazi's war plans.) They began investigating ways of using standard block engines as VTO (vertical take-off) instruments for possible helicopters (still called autogyros back then!) This in turn led to BMW, the famed German auto and airplane manufacturer, to develop the Flugelrad (nicknamed "Dora").
A flying saucer.
It had a central pod to hold its pilot. Twelve rotor blade discs extended three meters out in a spoke-like fashion. An axial-flow turbojet was attached to the bottom. Its exhaust was used to spin the rotor blades up to 2,000 rpm. Then a set of 4 deflection blades would be engaged and, with careful maneuvering, the Flugelrad's rotor disc would pitch forward slightly. The combination of the deflected exhaust and the pitched rotor would cause the whole vehicle (which weighed some 3,000 kilograms) into the air from a standing position.
After six months of research and engineering, the Flugelrad 1 saw the light of day. It took off from a small field in Prague in September of 1943. It flew about 500 yards and landed roughly, snapping off one of its wheels.
That's the end of the official record of the Flugelrad. But let us now speculate ...
Records of dubious authenticity indicate that research into the Flugelrad continued into 1944, resulting in a second prototype. This (again, all allegedly) added room for a second pilot, replaced the fixed landing gear with a variable suspension, and added a rudder. It failed to do more than hop a few yards at a time and was scrapped.
At the same time, however, time became of the essence, and a third prototype, the Flugelrad 3, was developed which included bomb armament capabilities and mounted machine guns for offensive use. It would have two cockpits capable of holding up to 8 crew members, retractable landing gear, and two turbojets to separate the tasks of generating rotation and generating lift.
By 1944, of course, the Russians were in Czechoslovakia and nearing Prague. The Flugelrad plans were scrapped, all traces of the project destroyed, and all knowledge of it disavowed.
Because of this lack of official documentation, conspiracy theorists believe that while the work in Prague may have ceased, work on the Flugelrad did not. They believe that the famed "flying saucer" came to fruition, and was used by many top Nazis (including our favorite Fuhrer) to escape the clutches of the advancing Allies. Flugelrads have occasionally reappeared in pop culture, most prominently in the silly loose sci-fi of Robert Rankin.
And the UFOs spotted today?
You guessed it.