Smithsoinian "Flying saucer"

Ok. This is a bit odd.  
Many years ago I visited the Silverhill aircraft restoation center of the Smithsonian institute.  It is sort of the aviation attic of America.
In the one hangar lying on the floor just in front of the then unrestored B-29 'The Enola Gay', was a craft called a 'flying saucer'   It was a one man round craft about 25 feet in diameter.   It had US Air Force written on both sides of the cockpit.  It was NOT the de havilin ground effects craft nor the navy's 'Flying Flapjack'.  
The Ideal Toy Corporation made a model of the thing back in the fifties.  I reciently wrote the Smithsonian, asking for info on the craft so i could build a model of it.   Apperently it was never there. 
I find it hard to belive the Smithonian lost an aircraft?   I cannot find ANY information on either the aircraft or the model.  I've never seen it refered to in any UFO programs or books on test aircraft!  I know it was there.  I touched the darn thing.   I even have a picture of it if I could find it.  
Do you know anything of it?
Witness indicates that the date of the incident is approximate.  We do not know about the aircraft/object, but invite anyone to comment.  PD