Can "Unidentified" Flying Objects be man made? Yes, they can be.
There are six main propulsion types of UFO craft:
1) Air powered: Some of the oldest patents are air foil discs and giant blowers.
2) Electrogravitic: Large voltages of electricity pulsed into the proper receiver materials cause movement on a scale previously unimagined.
3) Plasma Propulsion: Think of thrusters that blast off by lightning.
4) Magnetohydrodynamic craft: These are the ‘glowing balls of light’ people see. Ionization of atmospheric gases cause the craft to be enveloped by plasma.
5) Fusion propulsion: A catch all category for fusion, fission, and antimatter drives.
6) Inertial craft: Craft flying by generated internal momentum, gyroscopic activity, centrifugal and/or centripetal force... No propellers, wings, or thrusters.
How did I discover all this evidence?
I found it at the patent office.
117 years of records of such flying craft.
The free E-book explains in greater detail, and introduces the more important inventors you should know about to understand UFO's and their propulsion systems.
More info / Meer info: ufohowto.com