Editing Windpump (section)

==Fundamental problems of multi-bladed windpumps==

===Inefficient rotor===
[[File:Derelict windpump with water tank in the foreground next to the Boorowa railway in Galong NSW Australia.JPG|thumb|Derelict water tank with windmill in the background]]
The main design feature of a multi-bladed rotor is "high starting torque", which is necessary for cranking a piston pump operation. Once started a multi-bladed rotor runs at too high a tipspeed ratio at less than its best efficiency of 30%.<ref name="Hau 2005, page 101">Hau, Erich "Wind Turbines", 2005, page 101, Fig.5-10</ref> On the other hand, modern wind rotors can operate at an aerodynamic efficiency of more than 40% at higher tipspeed ratio for a smaller swirl added and wasted to the wind.<ref name="Hau 2005, page 101"/> But they would need a highly variable stroke mechanism rather than just a crank to piston pump.{{citation needed|date=June 2023}}

===Poor load matching===

A multi-bladed windmill is a mechanical device with a piston pump. Because a piston pump has a fixed stroke, the energy demand of this type of pump is proportional to pump speed only. On the other hand, the energy supply of a wind rotor is proportional to the cube of wind speed. Because of that, a wind rotor runs at over speed (more speed than needed), yielding a loss of aerodynamic efficiency.

A variable stroke would match the rotor speed according to wind speed, functioning like a "variable-speed generator". The flow rate of variable stroke windpump can be increased two times, compared to fixed stroke windpumps at the same wind speed.<ref name="ena.com.tr">[https://web.archive.org/web/20161223052210/http://www.ena.com.tr/Wind90.pdf Clark, Nolan "Variable Stroke Pumping for Mechanical Windmills", 1990, AWEA Proceedings]</ref>

===Cyclic torque variation===

A piston pump has a very light suction phase, but the upstroke is heavy and puts a big backtorque on a starting rotor when the crank is horizontal and ascending. A counterweight on the crank up in the tower and yawing with the wind direction can at least spread the torque to the crank descent.{{citation needed|date=June 2023}}