By far the most popular water pumping windmill of the 20th Century, the Chicago built self oiling Aermotor mills have been called the Cadillac of the windmills because of their outstanding design and quality of workmanship.  Even today, old reconditioned 702 Model mills command prices almost as high as those of factory fresh mills.

Although there are some variation among the four models, the basic operation of the self oiling Aermotor mills is the same.  The motion of the turning wind wheel is carried by a main shaft to two pinion gears at the opposite end.  The cogs on these mesh with teeth on two large crank gears running on their own shaft parallel with the main shaft.
The bearings on the first three models of self oiling Aermotor mills are babbitt, with those on the other two models being poured into the castings and those on the 702 being interchangeable.  From the two crank gears two cast iron pitmans extend up to a crosshead moving on a roller between the two round steel uprights of an inverted U-shaped guide.  The crosshead supports a steel pump rod which is suspended downward through a protected opening in the main casting to a swivel, where it is fastened to a pump rod inside the tower.  A mechanical difference between the earlier self oiling Aermotor mills and the later 702 and 802 mills is the placement of the rear bearing on the main shaft.  On the older mills the rear bearing is at the extreme end of the main shaft behind the pinion gear, while on the more recent models it  placed between the pinions.  In the self oiling Aermotor mills the main casting serves as its oil reservoir.  The crank gears carry lubricants to the rear main bearings, the crank gear bearings, and the lower pitman bearings.  Oil is deposited on the front main bearing by a special spout washer collecting oil from one of the pinion gears.  After lubricating the entire length of the forward main bearing, oil flows out the front end into the end of the hollow hub, where it is collected by a specially designed "oil collector" that returns it to the oil reservoir through a passage in the front bearing.  The upper pitman bearings and the crosshead are lubricated through the action a circular wire oil ring that is attached to the crosshead and carries oil up to these moving parts from one of the crank gears with each stroke of the mill.  The entire head of the mill is protected f rom dust and the element by a galvanized sheet steel hood.

The key to the Aermotor is its wind wheel.  Developed in the early 1880's by engineer  Thomas O. Perry and adopted by LaVerne Noyes, the founder of the Aermotor Company. This wheel consists of curved galvanized steel blades which are riveted to steel wheel clips which in turn are riveted to curved bar steel rims.    The wind wheel on the 502 and 602 Model mills remained the same as on the open back geared mills with the V-shaped straight arms are screwed directly into the wheel hub instead of being V-shaped.  This is one of the new distinguishing characteristics of the 702 Model that maybe seen from the ground.

The pumping Aermotor is governed through the action of a slightly off center wind wheel counterbalanced by a coiled governor spring.  As the wheel automatically turns away from increasing wind, because of its being off center, and slows its speed.  The increased tension on the spring causes the wheel to return into the wind when the wind decreases.  When the mill is turned off from the ground or when it is completely put out of the wind, a friction brake on the hub tightens, preventing the wheel from free-wheeling.

Self oiling Aermotor windmills were made in a full range of sizes including six, eight, ten, twelve, fourteen, and sixteen foot sizes.  From 1929 until 1966 a large 20' mill, weighing forty nine hundred pounds and having a five gallon oil reservoir, was manufactured for deep well pumping or for use in localities where large volumes of water was needed from shallow depths.  Most of these were seen in the desert Southwest.  All of the Aermotor mills were made by the Aermotor Company of Chicago until 1958, when the firm began the first of several changes in corporate ownership.  Among the firms producing the mills since that time have been:  Aermotor Division, Motor Products Corporation, Chicago, Aermotor Inc., Division of Nautec Corporation of Chicago, Aermotor Division, Braden Aermotor Corporation of Broken Arrow, Oklahoma: Braden Industries of Conway, Arkansas:  and Aermotor Division, Valley Corporation of Conway, Arkansas.  The manufacture of mills was shifted from Chicago to Broken Arrow in 1964, at which time the company began purchasing castings from foundries other than its own.

About that time the ring shaped outer hub of the wheel was redesigned into a solid spool shape.  By 1969, the company began purchasing castings from an Argentinean licensee, buying some casting in the United States, but by the next year all casting were coming from the South American producer.  Soon this policy changed to one of complete mills being made overseas and then being shipped to the Untied States for the domestic market.   These Argentina 702 Model mills, sold by the Aermotor in America until 1981, are easily identified in the field from their spool shaped hubs and the simple red "Aermotor" stenciled on their vanes.  In addition, Argentina made 702 Model mill marketed as the F.I.A.S.A. named for the initials of the Southern American manufacturer have been imported and sold in the US since 1980 by Essex Associated, Inc. of Dallas, Texas.

The Aermotor windmills, a tradition for over a century, and are still making history.  Following is a year by year history of the company.