This paper describes the design of four different specific speed microhydro propeller turbines operating at heads between 4 m and 9 m, and their application to a wider range of heads and outputs by scaling. The features are specifically tailored for ease of manufacture and uniquely resistant to debris blockage. Test machines are described and test results given; hydraulic efficiencies of over 68% have been achieved in all test models despite the fact that these turbines' blades are planar, further simplifying manufacture. Theoretical models show how closely these flat blades can be made to approach the ideal blade shapes. Outline drawings are given with key dimensions for each reference model, along with the equations for scaling to arbitrary sites. These turbines are the axial flow members of a family of turbines developed to cover the microhydro range from 2 m to about 40 m of head. (c) 2008 Elsevier Ltd. All rights reserved.