I was at EAA Rockford (the predecessor of Oshkosh) in the mid 60s when he gave a series of talks and I caught most of them. At that stage he was in his 70's and had a reverse delta homebuilt that had a very low take off and landing speed because the wing shape created an air cushion. A most interesting speaker and very much mentally ahead of most of us who listened to him.
Like with this video he always started slow and then sped up. Several others who listened thought he suffered stage fright until he got going.