It is posed that angular air-hammer self-excited vibration and half frequency wobble self-excited vibration are two reasons for resulting angular wobble self-excited vibration for gas film face seals.

But that changes the instant you set eyes on some of the items set to go under the hammer next month as part of a sale of the contents from the Bel Air home that Michael was renting.

This paper collects the typical structure of air hammer, understands the principle, determines the design principles and methods.