overall: 11 1/2 in x 9 3/4 in x 11 7/8 in; 29.21 cm x 24.765 cm x 30.1625 cm
patent model, windmill
United States: Illinois
United States: Illinois, Good Hope
This model was filed with the application to the U.S. Patent Office for Patent Number 208,208 issued to Elijah H. Smith on September 17, 1878. His invention was an improved design for a windmill with folding sails. The concept of the folding sail windmill was not new. In fact Mr. Smith had received an earlier patent for such a windmill. Folding sails allowed the windmill to automatically regulate its speed in varying wind strengths. As the wind increased the individual arms and sails would progressively fold up to present less area to the wind, thus acting as a governor. Once completely folded the windmill had little more cross section to the wind than would a windmill with a single arm and two sails. In Smith’s first folding sail design the maximum angle between its eight sails was limited by leather straps interconnecting each sail arm. Speed was then controlled by an auxiliary sail attached to the sails on the inner most sail arm. This auxiliary sail was loosely held down onto its host sail by a spring. As the wheel speed became greater the spring was overcome and the auxiliary sail would open to an angle of 90 degrees to the plane of the primary sail. This caused the inner arm and sails to slow until it was behind the next outer arm and sails, and this was repeated for the rest of the arms and sails until the wheel was folded. At that point little more than two sails face the wind and the speed of the wheel would be at a minimum. Smith included a braking wheel on the hub of the inner most arm and sail set. A wooden lever was pivoted at the front of the cross-head and could be pulled down by a rope led to the base of the windmill, thus making the lever contact the brake wheel and stop the windmill. There were two new elements in Smith’s 1878 patent. The first was to replace the function of the leather straps that controlled arm and sail spacing with a new design for the hubs at the center of each arm. Each hub had metal projections on its circumference that limited the motion of the next arm to an angle of 30 degrees to it. The outer-most arm was secured in place with a set screw on the shaft. This allowed the six arms to be evenly spaced around the wheel when fully extended. Folding of the wheel in heavy wind was controlled as in the earlier patent. The second new element was a modification of the braking mechanism. The tail-board beam was pivoted at the rear of the cross-head. This allowed the front of the beam to move upward to contact the brake wheel, and the weight of the tail-board was sufficient to apply friction and stop the windmill. A rod attached to the front of the brake lever was led to the base of the windmill and could be drawn down and pinned to disable the brake for normal operation.
The patent model is constructed of wood and metal and is mounted on a wooden base. The model illustrates the main elements of the patent including the hubs controlling the spacing of the arms when extended and the braking mechanism. The model also includes a thread representing the rope extending to the base of the windmill tower used to engage the braking mechanism. Not represented on the model is the auxiliary sail used to fold the windmill to govern speed in high winds.