INTRODUCTION

BACKGROUND

Spirals, screws, and windmills have a long history of use for speed measurement. Robert Hook proposed a small windmill in 1681 for measuring air velocity and later one for use as a ship's log (distance meter). A Captain Phipps, in 1773, created a ship's log, using the principle that a spiral, in turning, moves through the length of one turn of the spiral. Many centuries earlier, it appears that a Roman architect, Vitruvius, suggested a more basic form of this device.

In 1870 Reinhard Woltmann developed a multibladed fan to measure river flows (Medlock 1986). The device was a forerunner of the long helical screw-type meter still called after him and used widely for pipe flows in the water industry. The first modern meters, of the type with which we are mainly concerned, were developed in the United States in 1938 (Watson and Furness 1977; cf. Furness 1982). These were attractive for fuel flow measurement in airborne applications. They consisted of a helically bladed rotor and simple bearings. Improved sleeve bearings were developed for longer life with hardened thrust balls or endstones to withstand the axial load. An alternative, developed over several years and patented by Potter (1961), was to profile the hub of the rotor so that the pressure balance across the rotor, rather than the thrust on the bearings, held it against the axial drag forces. This allowed the rotor to run on a single journal bearing.