Improved mechanical efficiency is a driving advantage for the application of gas hybrid bearings to oil free turbomachinery. Characterizing the transient response of rotors supported on gas bearings during high friction contact at start up and shut down is essential to improving system reliability and performance. Further experimental results obtained in a test rig consisting of a rotor/motor supported on simple hybrid gas bearings are reported. The experiments of startup transient rotor responses aim to reveal the rotor lift off speed and time for full film gas bearing support. Exact determination of rotor lift off conditions from the time domain data is highly subjective. Ensemble overlapped FFTs of the rotor displacement response reveal the synchronous response and excitation of the rotor-gas bearing natural frequency at lift off. The analysis of the test transient responses also determines the lowest feed pressure for sustained operation at low speeds. Identifying the rotor-bearing system time constant and comparing lift-off speeds and times for uncoated and coated rotors shows the beneficial effect of an inexpensive low-friction solid lubricant (PTFE based coating) applied to the test rotor at room temperature.

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