The first controlled flight, the Wright Brothers' flyer, was 1903. The first mass-produced car, Model T, was 1908, just five years later. Neither paid any attention much to aerodynamics. The strut-and-wire construction would be pretty standard for airplanes into the 1920's, and automobiles would tend to derive most their style and design from wagons, coaches, locomotives at the same time...not airplanes.

Airplanes became more aerodynamic as aeronautical engineers, equipped with good wind tunnels, came to know more and more about airfoils and drag. It was realized that wings did not need to be extremely thin: thick ones could also lift quite well, and so it was no longer necessary to make a biplane wing box with struts and wires: a single wing could be structurally strong enough to hold a plane fuselage. As engines became lighter and more powerful, the engineers ( like B.Melville Jones) gradually identified how much drag all those struts and wires and exposed engine parts limited the top speed of a plane, and a high speed, it was learned, was where an ideal airplane would be the most efficient, consume the least fuel per mile. The Wrights could happily fly around at 40 mph, but at speeds over 100 mph real streamlining was needed. Most airplane designs wouldn't start to incorporate a lot of that information until after 1929, with some exceptions like the Lockheed Vega.

The first mass-produced streamlined automobile seems to have been the Chrysler Airflow , in 1934: so, five years after the concept took hold in the airplane industry. There were some early experiments with aerodynamic automobiles in Europe in the 1920's: but though I am unclear on all the details, they definitely were never mass-produced.

John D Anderson: A History of Aerodynamics

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