I think this was a trilogy. An alien spacecraft crashes on a farm on Earth and the guy who lives there figures out how to get inside. He finds that the ship is controlled by the pilot's thoughts via a kind of electronic headband, and the craft is fueled by water. For quite a long time no one notices it on the property because the guy finds that he can shrink it so it appears to be just a small statue of a spacecraft. It has powerful antigravity, anyone standing directly beneath the craft when it powers up to take off gets crushed and at some point in the book(s) this is used to kill baddies (not sure if they are aliens or earth people). I seem to recall a plot by a rich evil guy to establish a base on the moon and take over...something...Earth? and the crashed spaceship becomes instrumental in foiling the plot. The book titles are very short and the words "spaceship" or "starship" don't appear to be part of the titles.
Could this be Saucer by Stephen Coonts? The copyright entry on one of the title pages mentions 2002, so how does that fit in with when you read your book?
From the back cover of the paperback version (well, the UK version that I have read a few times):
When Rip Cantrell, a seismic surveyor in the Sahara spots a glint of reflected light in the distance he is intrigued. A piece of metal is apparently entombed in the sandstone and Rip uncovers a vessel that has been resting there for 140,000 years.
Now, that may not sound much like your book, but Rip C. does get inside, control it via a headband, and it is fuelled by water.
I don't remember anything about shrinking the craft to small size to hide its presence, but it does use the power of gravity underneath the ship to kill 'baddies'. It is hidden on a farm at some point, and some rich Australian dude is trying to buy or acquire the ship. Finally, as far as I can tell, this particular book wasn't a trilogy.
Well, maybe some additional info, but it's been at least 5 years since I re-read the book, and I've read quite a lot of others since then, so my memory may not be too accurate ...
I seem to remember that the hatch to the interior of the craft was underneath, and only found when Rip C excavated underneath to make some shade so he could rest.
With reference to the farm (in the original question), Rip C brings the craft back to the USA and takes it straight to his uncle's farm where it is hidden in a barn. I remember the Uncle as being called 'Uncle Egg', because he was fat/overweight fellow, and always seemed to be wearing blue dungarees.
At some point the 'baddies' from the Government (it's always them!) come to try to take the craft away, or, it may be the henchmen from the Australian dude. The craft is hidden in a lake, and during a stand-off it raises out of the water and hovers over a baddie and/or his car, and the 'anti-gravity propulsion' system squishes the car.
Egg is a bit of an inventor, and between them both they manage to discover most of the working of the craft; Egg is also quite smart in legal matters, so towards the end of the book the craft is bequeathed to all humanity and is placed in the Smithsonian.
The authors web-page about the book is at Saucer.
And, apparently, it was a trilogy ... Saucer #1, #2 and #3