France had one of the most advanced aircraft industries in the world, at the end of WWI. later, in the mid-1930s, they seem to have gotten into trouble-all of their designs were a good 50 MPH slower than similar British and German fighters. they seemed to have problems making high power aircraft engines-they even wound up buying British Mercury engines, or USA-built Pratt and Whitney engines. what went wrong-was it lack of R&D, investment in general? I had thought that france survived the Great Depression if failely good shape.
Usually it has to do with vision coupled with strategic planning, no one really knew what they needed until the spanish civil war, and not everyones industry could turn on a dime. Japanese zeros were faster than their american counter parts, the p40 and the F4F wildcat, but they had no armor.
As well German and English designs for the most part were okay in level flight, but had issues in the vertical regime, until the FW 190 and fuel injection.
But it comes down to what kind of war you want to fight, Russians were perfectly happy with being in the weeds with the p 39 which was an under performer for its time.
France’s air force in the late 1920s and up through the 1930s seemed a bit scatterbrained. They kept changing who was in charge, and couldn’t decide where their focus was. Until 1933, the air force was part of the army, and the army wanted the focus on close air support and reconnaissance. Then the air force was split off from the army, and it decided to focus on bombers. As different people were placed in charge, they had different ideas. A few year later, the focus was switched from bombers to fighters, but by then, France was already lagging significantly behind other nations, as you noted. They had put their resources elsewhere, leaving fighters development to lag due to lack of funds and lack of focus.
Their fighter production was just as scatterbrained. Instead of focusing on one or two planes, they made small orders to several manufacturers. This prevented them from taking advantage of economies of scale. They ended up with small numbers of numerous different models, and all of them mediocre at best.
For whatever reason, France also seemed to be stuck in a rut. They refused to put any emphasis at all on new technologies, so they had no radar, and they completely rejected the idea of the dive bomber with barely any research at all into it.
The French air force also did not coordinate its efforts with the other military branches very well. There was no overall cohesive plan on how the French military should fight.
Apparently some combination of nationalizing some aviation related companies in 1928, along with a lack of clear air warfare doctrine meant that French aviation development was rather shambolic in the 1930s.
Link (PDF article): Defense Technical Information Center article (page 4, 15-18)
Link (PDF article): Article on French doctrine & culture between the wars.