Let us use a little bit of common sense. If aliens had indeed visited
the Earth with vastly superior technology, how likely is it that a
spacecraft would crash in the terrestrial environment? Any terrestrial
craft would be safer even than todays airliners.

What hapenned in area 51 cannot therefore have been an alien spacecraft
crashing, it was much more likely to have been some sort of craft of
purely terrestrial origin. We know that the US after WW2 had 2
different objectives. Ostensably Nazis and Japanese were brought to
trial at Nurenburg and Tokio. Unofficially if you had anythiong to
offer by the way of technology you got away with things. Dan, US Air
Force, retired says that v Braum should have been hanged, however offer
the Moon (literally) and you can get away with anything.

I believe that German aircraft were test flon in area 51 with a number
of mishaps. Basically the disc aircraft could indeed take off
vertically using the Coanda effect (no antigravity or metric
engineering just Bernoullis equation), but was unstable and needed
constant activity on the joystick. This would not be a problem today
but was then.

The Pentagon was in a bit a quandry and chose to float the alien
theory, a decision which it may well have subsequently regretted. It
tried unsuccessfully to debunk the alien hypothesis. The only problem -
There were in fact real aircraft even though they were NOT alien. It is
difficult to do a convincing debunking job under those circumstances.

Just one point for Google. I tried to reply to Jack Scarfetti but was
not a member of the Space forum. Could Google look at permissions for
multiple posting.