Wind Tunnel Tests on a Streamlined Fan-Lift Nacelle Part I. Tests on Nacelle Alone and with Wings or Underfins Fitted Part II. The effect of Forward Speed on the Lift Produced by a Lifting Fan and its Inlet

Abstract

Part I describes tests on a streamlined body with a lifting fan mounted normally to its axis. Most of the tests were made in the 5 ft x 4 ft windtunnel at Imperial College, and others in the No. 1 11½ ft x 8½ ft tunnel at R.A.E. Farnborough. Comments are made on model design and engineering. Three component balance measurements and flow visualization were carried out over a range of ± 20 deg. incidence at speeds from 15 to 65 per cent of the jet velocity, keeping fan r.p.m, constant. Comparison between tunnels showed important differences at high incidences and high forward speeds (18 deg. and V/Vs = 0.6) but 2 to 3 per cent or less at lower speeds and incidences. Part II analyses in more general terms the way in which forward speed changes affect the lifting unit and the forces on it and examines the properties of hypothetical lifting units which have constant pressure and constant volume characteristics. The former is found to have some desirable features. The analysis is then applied to the experimental results from Part I, showing that, at a typical transition speed, a 5 per cent lift loss due to fan-mainstream interaction is less significant than, say, the addition of underfins which influence the efflux-mainstream interaction.