During the decade of the Great Depression, the streamlined form stood as an optimistic symbol of progress and efficiency. Streamlining was applied to cars, trains, ships, buildings, and even household appliances. This new idiom replaced the angular, art deco forms of the 1920s.
By the mid-1920s aircraft construction was in need of a new design approach. With the availability of engines with 200 to 350 horsepower, aircraft were flying faster, but not in proportion to the increase in power. With all the higher turbulent flow being experienced at higher speeds due to common design practices of the time, a reduction in drag became important to improved performance.
So in the era between the middle 1920s and middle 1930s, streamlining came into its own in aircraft design.