In this paper, the aerodynamic performance of the telescopic blade wind turbine concept has been analysed experimentally and computationally. A model-scale wind turbine with two-stage telescopic blades, having a chord ratio of 0.6, was studied in the wind tunnel for different blade extensions (i.e. different lengths of the second section, ranging 0-40% of the first section). The experimental setup allowed the measurement of rotor speed, shaft torque, and thrust, under varying wind speeds. It has been established that the effect of a step change in blade chord is significant for the range of blade extensions studied. In particular, the power coefficient C-p of the wind turbine was found to decrease with extension, with 25% decrease in maximum C-p obtained for a 20% blade extension. This is attributed to additional losses arising from the step change in chord. Correlations proposed to quantify losses arising from the step change in the chord of a telescopic blade are found to be in good agreement with experimental data. In spite of the detrimental effects of a step change in blade chord, the power output of a telescopic blade wind turbine is found to increase for all blade extensions considered in this study. (C) 2013 Elsevier Ltd. All rights reserved.