the first a/c unit appeared in a home in the 1950s.
when did the first a/c unit appear in a home?
1950s
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d-d locomotives so far have fallen out of favor as nearly all of these have been twin-engined locomotives, which placed too much horsepower in too few axles, thereby making these consists rather inflexible (each locomotive featured two prime movers, making each unit essentially a pair of high-powered b-b locomotives on a common frame as far as traction and power was concerned).





















































in fact, a usual consist of a d-d unit included a leading c-c unit and a trailing c-c unit, for a total of about 12,600 hp (with four total prime-movers).
aar wheel arrangement