# How would aircraft and air-life develop on High-G, Lower-Atmosphere planet?

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.

• I think that you have a credibility issue here. More gravity would create a denser atmosphere. Mar 9, 2017 at 8:09
• Not exactly. Gravity is not 100% related to atmosphere. Yes, if you took Earth and cranked up the gravity to 120-130%, you'd end up with a thicker atmosphere. That's not always the case, though - Titan has a similar gravity to the Moon, yet one has a super-thick atmosphere and the other does not. Similarly, Venus and Earth have highly different atmospheres. Mar 10, 2017 at 0:02
• if earth planes were steel pigeons, your planes would have to be paper albatrosses
– user23560
Mar 15, 2017 at 5:37
• Less air = less drag, which is a major defining aspect of wing size. A google image search for high-altitude plane gives you plenty of incredibly thin long wings, the shortest you may ever see, while low-altitude planes seem to have stubbier shorter wings. I don't have anything to create an answer with, but these real world examples seem to contract the logical idea of 'huge wings' Mar 16, 2017 at 18:31
• I asked a question similar to this one and received some great answers. If anyone is still wondering or someone in the future has a similar question, here is the link to mine so that both of these can be useful for posterity link Jan 16, 2018 at 21:47

$$L = (1/2) d v^2 s$$ this means: Lift (in newtons) = one half x density (air density in (kg/m^3) which is about 1.2 at earth sea level at 20 degrees Celsius and about 0.84 on your planet's sea level at the same level. The highest cruising altitude of a spitfire (an iconic WWII plane) is about 9.144 km, meaning that the air density would be about 0.4671 on earth and 0.3270 on your planet) x velocity (in km/h) squared (the average speed of a spitfire would be about 400 km/h) x reference area (area of wing in m^2 (a spitfire is about 22.48)) x something else we probably don't need to worry about so I left it out of the equation. We must always remember that Lift = Weight (the weight of a spitfire on earth is 29430 newtons on earth and 38259 on your planet.)

So there are number of ways you could create a spit-fire equivalent on your planet by changing around the variables. You could make it go really fast by using jet engines, you could simply make it much lighter or you could use huge wings. The most practical and effective design would be to use jets and make it lighter, thus making it more agile without long flimsy wings. The lack of atmospheric pressure means less drag and allows you to make more creative designs.

As for flying creatures, the wingspan of a gull in your world would may take the form of an albatross. Flying insects would be less like fat little flies and bees and more like dragonflies with long wings.

Just one quick note on flora: Trees in your world may be a tiny bit shorter than on Earth.

In conclusion: Planes are fast and light and living stuff has big wings.

It would have larger wings, and may have more powerful engines. Also for helicopters. And even baloons could work.

Some comparisons:

• The wings of a plane are quite small compared to their size. Make larger wings, you will have more elevating force, although also more drag. This will have to be compensated by stronger drive.
• Most passanger planes are flyng around 10km high. It is against the drag. On 10km, the atmospheric pressure is only around 25% of the sea level, despite that it is more cost effective as to fly on low altitude.
• The case is the same for helicopters.
• For baloons: there are already baloons went to 53km high, or even take people to 40km high.
• Baloons are definitely something that would be easier to make (Just look at history). I was thinking more along the lines of heavier-than-air aircraft, though, and will be editing the question to be more clear on the matter. Mar 9, 2017 at 4:00

I'm no expert but I believe that more gravity would result in faster compression of carbon substances (dead things) and therefor more oil and other fossil fuels would be produced. This would make up for the excess amount of fuel needed to power the much more powerful engines needed for flight in such a place. As for the question of flying creatures, yes, they will develop, but they would look strange to us as they will have had to adapt to the gravity there. They will probably be large winged and small bodied in order to make up for the mass to propellant ratio.

• More fuel means you have to have more power and more lift. It's not necessarily a good thing to have more fuel on a craft. Mar 14, 2017 at 2:49