It would be a shame if all you saw in Oregon was the Spruce Goose in McMinnville! The museum is in the heart of Oregon wine country with dozens of wineries that you may visit and sample. Really lovely. Wonderful dining opportunities available.
www.willamettewines.com
www.yamhillvalley.org
www.sprucegoose.org
You will be only a short distance from the coast. Again, beautiful scenery around every turn. Highway 101 is a wonderful, yet curvey drive down the coast. In Tillamook, Oregon is a large air museum in an old World War Two blimp hanger with over 30 war planes exhibited among other things.
www.tillamookair.com
On the northern part of the coast near Astoria in Warrenton is Ft. Stevens State Park which was a military installation for over 100 years and is very well preserved with underground bunkers and the like. This was the only spot in the continental US to be fired on by the Japanese. Astoria has The Columbia River Maritme Museum and is an interesting Victorian era town founded by John Jacob Astor.
www.visitftstevens.com
www.crmm.org
None of these things would be more than a two , MAYBE two and a half hour drive from the airport.
Another attraction an hour away to the east from Portland is the Columbia River Gorge. Again beautiful scenery, with major waterfalls. More wine country on the Washington side of the river. This is a major windsurfing destination and watching these guys from the shore is a thrill.
www.crgva.org
And don't forget Washington State right across the river. A short flight from PDX or about a two and a half to three hour drive depending on the traffic will take you to Seattle and the Museum of Flight. They have a retired Aireforce One plane there that you can actually board and a retired Concorde, as well as a Blue Angel simulator and much much more. Anyone interested in avation would love this.
www.museumoffllight.org
If you drove you might want to check out Mt. St. Helens on the way up. Another interesting and worth while stop.
www.mtsthelens.com
Hope this might inspire you to do more than a day trip to the northwest!
Gayle