VZ-9-AV Avrocar: Jack Frost's Flying Jeep (1958)

Wikipedia has a fascinating section devoted to the maverick engineer "Jack" Frost's "proof-of-concept" test vehicle he called the Avrocar. Funded by the US army who were undertaking several experiments on smaller VTOL aircraft that would act as a "flying Jeep", 2 units were built and later abandoned due to stability issues.