Sikorsky first performed this photographic feat on an S-51 rotor system mounted in a whirl stand at the old South Avenue plant. This was in the very late 1940s (around 1949) or the early 1950s. Two things were accomplished in the test. The traveling wave or snake action (undulating) of the blade was discovered and they also found that the advancing blade would lead and the retreating blade would lag. Up until that time the opposite view was held.
When this movie was shown to helicopter pilots many of them refused to fly any more.
