He was a M.D, an expert in deceleration. His study was important since he had shown that human could withstand at least 45 g. He tested it himself, and hold that record. However, his test was not on a jet-plane, but on a railway and mounted on rocket sled. The highest survived involuntary g experience is 179.8 on a formula-one car crash. In both cases, the g forces that both subjects experienced only a very short period of time, in milliseconds range.

As for fighter pilots, the record in 1995 was 12 g for 15 sec. This is from the air force factsheet.