These cards are from a series of 40 American Heritage Cards produced by the Milton Bradley Company in 1961.
The Lockheed Vega, first introduced in 1927, set a new standard for all purpose passenger carrying aircraft. In June 1931 Wiley Post and Harold Gatty lifted the "Winnie Mae" off the Roosevelt Field runway in New York to fly around the world. More info on Wikipedia.
The National Air Races, held annually from 1926 until 1939, provided an exciting stimulant to aviation development. Perhaps the most unique racers built for this competition were the "Gee-Bees" designed by Bob Hall. More info on Wikipedia.
In the 1920's the Ford Motor Company was the best known name in industry and when Henry Ford went into the aviation business the nation sat up and took notice. The Ford Tri-Motor affectionately known as the "Tin Goose," was one of the finest airplanes ever built in America. More info on Wikipedia.
One of the most graceful flying boats ever built. the Boeing 314 Clipper went into service for Pan American Airways in 1939. Only 12 of these ocean spanning giants were ever constructed by Boeing, but their fame was world wide. More info on Wikipedia.
The famous "DC line" of Douglas propeller driven transport planes, begun in the mid 1930's, reached its ultimate development with the DC-7. This comfortable, dependable plane, introduced in 1953, soon became the mainstay of airlines all over the world. More info on Wikipedia.