MYSTERIES OF THE EQUILATERAL TRIANGLE - HIKARI Ltd

96 Applications
Application 25 (Square Hole Drill). In 1978, U. S. Patent 4,074,778 was
granted for a “Square Hole Drill” based upon the Reuleaux triangle (Figure
3.25) [242].
The resulting square has slightly rounded corners but achieves approximately
99% of the desired area. It was not the first such drill granted a
patent: the Watts drill received U. S. Patent 1,241,176 in 1917!
Figure 3.26: Wankel Engine [303]
Application 26 (Wankel Engine). The Wankel non-reciprocating engine
(Figure 3.26) is a rotary internal combustion engine which has the shape of a
Reuleaux triangle inscribed in a chamber, rather than the usual piston, cylinder
and mechanical valves [303].
This rotary engine, found in Mazda automobiles, has 40% fewer parts and
thus far less weight. Within the Wankel rotor, three chambers are formed by
the sides of the rotor and the wall of the housing. The shape, size, and position
of the chambers are constantly altered by the rotation of the rotor.
Application 27 (Equilateral Triangular Anemometer). Anemometers
are used to measure either wind speed or air pressure, depending on the style
of anemometer [186].
The most familiar form, the cup anemometer, was invented in 1846 by
J. T. R. Robinson and features four hemispherical cups arranged at 90 ◦ angles.
An anemometer’s ability to measure wind speed is limited by friction along
the axis of rotation and aerodynamic drag from the cups themselves. For
this reason, more accurate anemometers feature only three cups arranged in
an equilateral triangle. Modern ultrasonic anemometers, such as that shown