A brief account of some unrecorded techniques for flow visualization in flight for locating (a) boundary layer transition at altitude, (b) shock-wave position

Abstract

Flow visualization techniques, which have been successfully used in flight tests, are described. One indicates boundary-layer transition on a wing with a "china clay" coating, that is wetted at high altitude with a liquid of suitable volatility emitted by another aircraft; the result is photographed at altitude. The second shows the shock-wave position by the differential rippling of a viscous oil coating on the wing; it also reveals laminar flow areas by unrippled oil, at the same time. It relies on direct sunlight but is not over-sensitive to the direction of this, within quite wide limits. Comparative shock-wave results are given using an earlier direct sun-shadowgraph method which requires precise sun alignment and has been little used.