I've played as them a few times. I never have a decent air force as them until much later because the manpower is so low I'd rather us it to strengthen the land divisions. When you take control of the country in 1936, it's an absolute mess, there's not even enough manpower to fill the few divisions you have. In my current play through I had so many other things to do that I didn't have time to research any planes whatsoever. I had loads of reserved planes because I knew mine were weak and would need reserves, eventually just licensed German and British ones but that was only after sorting out manpower.