This is a heckuva story although most of it occurs after 1939. Click on the link to learn more.
“Chestien Wynn, a 70 year old retired attorney with an interest in lubrication chemistry, discovered a formula he named ‘Wynn’s Friction Proofing’ Oil. This surface treatment for metal actually changed the chemistry of the metal, making it softer and better able to withstand friction and wear.
“Chestien Wynn would mix a batch of his product in his one car garage workshop, fill and label glass bottles with it and sell them to the local service stations and garages. Motorists, who used the products once, wanted another bottle of it.”
“The lead-up to World War 2 for the United States saw a period of constant progression for its bomber force… [The B-23] prototype went airborne for the first time on July 27th, 1939 – just months ahead of the official start of World War 2 in Europe (September 1st). Serial production was begun that same month and ended in September of 1940 with all 38 aircraft completed.
“By the time of the American entry into the war [in 1941], the B-23 had already met its performance match as newer, better medium types were taken into USAAC service. As such, the B-23 was never seen as an active combat performer during the war but instead relegated for service use as a trainer, stateside maritime patrol, and transport.”
“The maiden flight of the B-23 took place from Clover Field at Santa Monica on July 27, 1939. After being evaluated by the Materiel Division at Wright Field in Ohio, the B-23 entered service with the 89th Reconnaissance Squadron based at March Field in California.”
On this date in 1939 Igor Sikorsky piloted the first successful helicopter which he also designed. While he was a pioneer in vertical flight he was not the inventor of the helicopter. However, his improvements of a single lift rotor and a tail rotor made the craft controllable. This prototype led to the first production helicopter.
Although this test occurred in Connecticut, it influenced flight around the world.
National Aviation Day, August 19, celebrates the development of aviation.
“The holiday was established in 1939 by Franklin Delano Roosevelt, who issued a presidential proclamation which designated the anniversary of Orville Wright’s birthday to be National Aviation Day (Mr. Wright, born in 1871, was still alive when the proclamation was first issued, and would live another nine years). The proclamation was codified (USC 36:I:A:1:118), and it allows the sitting US President to proclaim August 19 as National Aviation Day each year, if desired. Their proclamation may direct all federal buildings and installations to fly the US flag on that day, and may encourage citizens to observe the day with activities that promote interest in aviation.”
Excerpt from https://en.wikipedia.org/wiki/National_Aviation_Day .