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For practical purposes I think about something in line of Cessna 172. As it was the most produced aircraft, then it must have hit some sweet spot or be near it.

  • atmosphere with barely noticeably higher oxygen content, and much higher nitrogen
  • tech level similar to contemporary
  • rugged, simple, inexpensive aircraft that can serve well on sparsely populated planet

OK, so how to adjust it for such planet?

Assuming that I get physics correctly, in order to keep the same performance, it would need roughly the same engine, frame, but wings would need just 1/3 of surface area from Earth. So my first guess would be a Cessna clone, but with trimmed wings... ok with much smaller wings.

Honestly, does it make sense? Or maybe under such lift friendly condition this wing size reduction offers minimal gain and when having such leeway there would some clearly more tempting things to improve instead for an utilitarian bush aircraft? (Dunno minimum take off distance, load, whatever?)

Question: Is such wing surface reduction correct way of making rule of thumb aircraft adjustment for thicker atmosphere? Assuming "Yes", does it make much sense for its intended function?

EDIT: Extra food for thought: Does such aircraft actually need normal wings at all? Seriously. Under normal conditions small part of the lift comes from aircraft body. When the need for lifting surface is reduced, then the share of the lift provided anyway by the body would increase, but I'm not sure whether that would be significant enough to matter much in design.

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  • $\begingroup$ While things like the C172, C182, and C206-C210 are used as bushplanes, they aren't quite in the sweetspot for that specific role. Something like a DHC-2 or DHC-3 might make for better RL inspiration? $\endgroup$
    – Shalvenay
    Jul 13, 2019 at 17:11
  • $\begingroup$ If you have a barely higher oxygen content but a much higher nitrogen content, how exactly does this work? The Earth's atmosphere is already roughly 21% oxygen and 78% nitrogen.How would this be raised? $\endgroup$
    – Dawnfire
    Jul 13, 2019 at 18:41
  • $\begingroup$ Not really an answer, but might help: what-if.xkcd.com/30 $\endgroup$
    – elemtilas
    Jul 13, 2019 at 19:28
  • $\begingroup$ @Dawnfire Roughly: 9% oxygen, 90% nitrogen, 1% other. $\endgroup$
    – Shadow1024
    Jul 13, 2019 at 19:42
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    $\begingroup$ The same aerodynamic principles reducing your wing size would affect your propeller too, don't forget; Higher pressure means more force being applied by (and to) your propeller so you'd want shorter, stronger blades there as well I would think. $\endgroup$
    – Morris The Cat
    Jul 15, 2019 at 19:16

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TLDR: Your hunch is correct. Shorter wings.

You ask, "does such aircraft actually need normal wings at all?" The answer is an emphatic no. In fact, aircraft on Earth don't even need traditional wings. Check out the X-24.

Martin X-24A

You still need control surfaces, but in a high pressure environment you don't necessarily need wings. It would be helpful to find a vehicle that flies in a setting that has higher pressure than the surface of the Earth. Fortunately, we have just such a vehicle in the form of submarines. After all, you're talking about the pressure 100 feet/30 meters under water on Earth. On submarines, diving planes serve a somewhat similar function to airplane wings. Notice the two stubby sets of diving planes at the stern of the boat in the picture.

WWII submarine in drydock. Photo from Wikimedia.

This WWII crew manual describes the effect of planes on submarine maneuvering:

The bow planes are placed on ten degrees dive and rigged in automatically unless the conning officer gives other instructions. A report, "Bow planes rigged in," is made to the conning officer. Speed is increased to about 6 knots to give maximum lift. Due to the up-angle on the ship, the increased speed makes the inclined surface of the hull effective and the resultant lift raises the ship.

Beyond wings, other parts of airframes would need to be redesigned. For starters, there would be a stiffer penalty for drag, so I imagine aircraft would be more streamlined. I've flown a 172 and they're amazing, but they don't have the sleekest profile. You'd also have to change the engine to accommodate the different pressure and O2 concentration, and you'd have to use a different design/pitch on the prop.

With greater lift and drag, I imagine flying a small plane might look a lot like a STOL competition.

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    $\begingroup$ With this, it is also important to remember the density of the substance in question. A submarine is the right idea, but it needs far less lift to stay buoyant as it is moving through a liquid, not a solid. In the case of an actual flying plane, you need to have some kind of lift surface as well, or just more speed. Something similar to the X-24, which uses not wings, but the body to generate lift, may be the best answer here. $\endgroup$
    – Dawnfire
    Jul 15, 2019 at 18:05
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    $\begingroup$ Well... so we effectively achieved a planet of flying eggs. And it makes sense from logic perspective. $\endgroup$
    – Shadow1024
    Jul 15, 2019 at 18:54
  • $\begingroup$ If you take an Earth-optimised aircraft, then it would indeed behave as STOL at such planet. However, wouldn't making them STOL by default wouldn't limit their optimal speed too much? $\endgroup$
    – Shadow1024
    Jul 15, 2019 at 19:14
  • $\begingroup$ @Shadow1024 your question asked about a rugged plane. Rugged planes in a high-pressure environment would lend themselves to having short takeoff and landing distances. An alternative in this world would be planes that look like the SR-71; super sleek and aerodynamic. $\endgroup$
    – Andrew Brēza
    Jul 16, 2019 at 22:58
  • $\begingroup$ @Dawnfire well said! I totally agree. $\endgroup$
    – Andrew Brēza
    Jul 16, 2019 at 22:58
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Firstly, lift and drag are both linearly proportional to atmospheric density, so at 3 atm, to provide the same lift as a plane on earth you need 1/3 the wing surface area.

This can be a mixed blessing: while you wings are smaller and thus less draggy, to achieve a reasonable velocity during cruise the airfoils need to be thinner to reduce pressure drag. This means you have less space in the wing for reinforcement. The optimum point of how long and thin the wing should be before it's in danger of snapping is complicated and an exercise I leave to the reader. Now, because of the greater density, you control surfaces can be smaller, which will help with drag. Your body will also be as streamlined as possible, looking more like a racing airplane. The surface is also as smooth as possible. Internal deploy-able landing gear is a must.

Now, fun fact: higher density air means better engine cooling, so you might be able to forsake those pesky radiators altogether and use a simpler air-cooled engine which will be lighter.

Here's an example: enter image description here Short, thin wings for cutting through the thick air at speed, rudder flush with the tail, and staggered tandem wings for both lift generation and pitch control (allows you to eliminate the tail-plane and its attendant drag). Airscoop under the propeller nose for cooling the engine and feeding it air.

This is a fighter, so it's got a big bubble canopy, a bush plane will sacrifice visibility for a cockpit that's more flush with the hull to generate less drag.

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