Evolution by Trial and Error

It has been said that when you encounter a native from Holland he will talk about windmills within five minutes. So, what else is there for me to do in the seven minutes I am given by the chairman? The windmill I visited last year had a large rigid rotor of about 100 feet diameter and was built in 1648. its four blades incorporated nonlinear twist and a thin droopsnoot airfoil near the blade tip (see Fig. 1). The mast angle could he adjusted to relieve the hub moments and to prevent overspeeding. (This was done manually, although techniques were available to do it automatically with a tail rotor.) Flutter was avoided in the wide-chord blades (solidity .2) by locating the main spar and the blade c.g. at the quarter-chord point. The development of this rotor system had taken a little while – in fact, about 400 years – by evolution through the process of trial and error.