90deg fan blade story

[clovermachine@sbcglobal.net]

When I was a kid my mom and I visited family in Detroit every couple years. We always took the train. At Chicago we had to transfer from the Santa Fe Super Chief or the El Capitan, or in later times the California Zephyr to the NYC from Chicago to Detroit. On the1959 trip we were about an hour or so out of Detroit returning to California. We were sharing a lunch table in the dining car with a man and his wife. The train stopped for passengers at a small town where the main street was parallel to the tracks. Stores, cafes, a bank; a nice clean middle American town. The man told me he was a retired mechanical engineer and worked his whole career at GM. He said 'see that main street?...I used to race up and down that street in the dark of night testing fan blades'. Right out of college he was hired by GM's testing department. He went on to say his first assignment in about 1920 was to find out why fan blades were flying apart. He and an assistant needed a place where they could drive flat out, be near a machine shop, rent a garage and a room. I guess GM didn't have a test track back then. He said one consideration was this town was close to Detroit and had only one cop; if anyone called in a complaint about their mid-night tests they'd be-holed up in their rented garage by the time the officer got dressed and left home. He said he was told by the boss to not come back till the problem was solved. The boss would probably have been Charles Kettering. He said fan blades had prior been made simply at 90 degrees but as engine RPM increased over the years the blades began to fly apart. He and his assistant came up with an angle for the blades to each other where harmonics and thus stress were minimized and solved the problem. My folks were gold and tungsten mining in the California, so as a kid I was always climbing around mechanical equipment and that story stuck in my mind. I should have asked why the tests could not be performed on a stationary test mounting. Anyway, it is to the best of my memory from 60 years ago. Bill Traill TC 5221 Santa Clara, California