Deltas are man-made IMO: TR3B, and similar.
My opinion at this time is that many saucers are man-made of German origin, later us origin.
Good run down on German hoax/myth/reality:
http://greyfalcon.us/German%20UFOs.htm
Very good investigative research:
http://www.americanantigravity.com/d...-Interview.pdf
In my opinion, some of the early pictures of saucers are quite crude in design. These MUST be man made, if I were to guess. As the decades progressed, the designs have become sleeker. Is this not interesting how it coincides with man's progression in industry?
This is NOT to say that there have not been landings of aliens, or even the tech was gotten from them. There seem to be plenty of examples.
One of the most interesting is the 1994 Zimbabwe incident involving school children. Why would they lie? (pysops?) It would be interesting to discuss with them now.
http://www.ufoevidence.org/cases/case127.htm