I'm (slowly) working on a semi sci-fi world, set in a WWII-ish tech level (Semi sci-fi being how they got to this world). Except in this world, aircraft have developed significantly later, and battleships still rule the seas.
In my research, I've seen that buoyancy is generally unaffected by gravity - The USS Iowa will still float on pretty much any body of liquid water, up to the point where high gravity causes structural issues or low gravity causes Weird Things to happen.
Aircraft, however, are affected by a multitude of things. My first thought at slowing their development was pushing the availability of large quantities of aluminium later, but history shows that once they got off the ground there's not much stopping them. I'm still keeping this, but it's a minor consideration. Beyond construction materials, there is design - Something that would be affected by differing gravity and differing atmospheric pressure. Higher gravity means an existing aircraft would have to fly faster or through more dense air, either way requiring more power to fly
The world I'm building has high-ish gravity, somewhere around 1.2G-1.3G. Not a lot, as I still want humans to be, well, humans. It also has lower atmospheric pressure than Earth, somewhere around 65-75%. This would mean a higher partial pressure of Oxygen to keep up with Earth biology, but again - I'd like humans to be human. As far as other components of the atmosphere go, I'm aiming for mostly earth-like composition, perhaps with a bit more yellow in the sky.
So, now that we have the setup of the world, I have two primary, related questions:
1 - How would a heavier-than-air aircraft on this High-G, lower-Atmosphere planet differ from Earth aircraft? I'm presuming they would need larger wings and more powerful engines than the early aircraft, but while I understand most of the basics of aircraft design and function, I'm not an aircraft engineer.
2 - How would flying critters develop on such a planet? Would flying critters develop? The place is somewhat intentionally designed to make flying more difficult, but would that make it impossible for things such as birds and bats to develop? What about smaller things like insects? And how would this affect plants - Since many Earth plants use insects for pollination, what would they have to rely on without this? Also note, I'm only using birds/bats/insects as analogues. Alien planets would, of course, develop some pretty strange critters that may not exactly be an insect or bird, but occupy a similar niche in the ecology.