The oil-film interferometric skin friction technique is described and applied to an isolated full-scale XV-15 rotor in hover. This is the first time that this technique has been applied to a rotary wing. The chordwise component of skin friction is presented for both low and high thrust cases. The technique is shown to be capable of revealing the presence of natural transition, leading edge laminar separation followed by turbulent reattachment, and the presence of reversed flow.
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