Simple Shielded Total‐Pressure Probes: Details of Small Probes with Results of Tests on their Performance

Design features and characteristics of conventional, modified and shielded total‐pressure probes are briefly discussed, and compared with new shielded instruments of simple construction which combine smallness of size with adequately fast response to pressure changes. Tests at air speeds up to 280 ft./sec. showed that a probe featuring a total‐traversing cylinder with single orifice inside a tubular shield will register total pressure to within 1 per cent of the dynamic pressure up to inclinations of the flow of ±28 deg., the error in the range ±22 deg. being less than 0.5 per cent. The response time of the instrument under a suddenly applied air pressure of 500 mm. W.G. was less than 60 seconds when linked to a Betz projection manometer. If the inner cylinder is replaced by a central sting, the range of insensitivity to flow inclinations is increased to ±45 deg., the error being less than 0·5 per cent of the dynamic pressure. The response time of this probe under 500 mm. W.G. air pressure was approximately 100 seconds. Still simpler versions of the instruments described are under development.