The aerodynamics of a circular jet emerging normally from a wall into a cross flow is critically assessed. Some general trends are obtained when viscous effects are neglected. But viscous effects dominate the real flow behaviour. Attempts to predict these real effects are reviewed and their anomalies highlighted. The importance of understanding and specifying the jet exit conditions is stressed, which is relevant to complete numerical solutions.

The paper describes the air-injection method of fixing transition in wind-tunnel tests on a two-dimensional aerofoil and a swept panel at high subsonic free-stream speeds. The method is shown to provide a repeatable level of disturbance which, for a given flow condition, may be generated without interrupting the test and which appears not to cause a significant excess drag. Examples are given illustrating the effectiveness of the technique in demonstrating scale-sensitive features of flows, and a correlation is presented which allows the minimum value of air-injection mass flow needed to fix transition to be estimated from a knowledge of the behaviour of natural laminar flow on the wing.

An investigation of the four-bladed Dowty Rotol R212 propeller (NACA 16 sections) has been made at l/5th scale (0·7 metre diameter) in the RAE 1·5 metre acoustic tunnel. Propeller power absorption and thrust have been measured over a range of rotational speeds up to 8000 rev/min at mainstream speeds from 15 m/s to 60 m/s for a range of blade settings. Slipstream wake surveys show outward movement of the position of the peak pressure as propeller loading is increased.

Noise analysis demonstrates the predominance of multiple tones whose number and intensity increase with helical-tip Mach number. An empirical formula shows that the fundamental tone SPL varies with tip speed and power loading in an identical manner to that observed on a modern ARA-D section propeller.