Today I picked up the most recent issue of Popular Mechanics due to the three big letters on the cover that said "UFO". Not only did I find one of the worst attempts at debunking the Stephenville UFO ever, but in the same article they had a picture of one of Lockheed's most recent Skunk Works projects: The P-791 Airship.
This is one weird looking bugger, and huge! It's a hybrid airship, or simply a blimp that combines both traits of lighter then air craft and fixed wing aircraft or helicopters. From the side, it appears to be a normal blimp, but it's when you see it head on that it gets funky, and you see how large it is. Heck, I could even see people looking at this thing from the bottom mistaking it for an extra-terrestrial spaceship, however that does not mean that it accounts for all UFO sightings by the way, just that it would be one to anyone unaware of it's existence.
Speaking of being unaware of the existence of aircraft, there are rumors floating around the UFO and conspiracy communities that the military has some black projects using similar airships. These airships are a possible explanation for some of the commonly seen black triangle UFOs which have been reported over the last couple of decades.
As for the debunking of the Stephenville UFO, well the article tried to convince the reader that despite the fact that FAA radar data showed a large unknown object (capable of accelerating from about 49-60 miles per hour to 500 plus mph in under 30 seconds. I doubt even that fancy airship above can do that.), the sighting was nothing, but people mistaking military aircraft lights for a large unknown object. And the whole large object on radar? Radar error, or so the article tried claiming (no back up other then what the was read in a radar study down in 1997)...yeah and my name is Buddy Holly...
Sources and Further Reading:
P-791 - Wikipedia
Lockheed Martin's Secretly Build Airship Makes First Flight - Aviation Week
Patton, Phil. "Something in the Sky." Popular Mechanics March 2009: 54-66.