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In my world, humanity was put on a Earth-like (but not Earth) planet thousands of years ago by an alien species for reasons. Before these aliens left, they created a field around this planet that causes anything manmade that flies by engine to stall and crash to the ground. This is a futuristic society that is roughly 400 years ahead of the present time on Earth.

With this in mind, how advanced could air power get without engines? Would they just use air balloons made out of very light, but strong materials?

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  • $\begingroup$ Define "engine" - Does is only cover combustion engines? What about electric engines? Or steam engines? (Probably too heavy for aircraft, but lets be clear on it anyway.) How about a large rubber band wound up to spin a propeller for a little while? $\endgroup$ Aug 18 at 16:50
  • $\begingroup$ @TheUndeadFish I would say it covers all of the engines you mentioned except the last, which I guess is just mechanical right? $\endgroup$
    – forgotenm
    Aug 18 at 16:52
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    $\begingroup$ Sure a rubber band is just mechanical. Though a steam engine is primarily mechanical (other than whatever means are used to heat water into steam in the first place). Perhaps this special field somehow inhibits chemical reactions above a certain distance from the surface? Though in that case I fear for any humans that get up there since they're powered by chemistry too. $\endgroup$ Aug 18 at 17:41
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    $\begingroup$ (Oops, accidentally submitted my comment before I finished my thoughts). The reason I'm picking at the details here is that your question could be rephrased as "how might people work around this arbitrary restriction regarding powered flight" - so to best answer that one has to have a good understanding of what is and isn't restricted. $\endgroup$ Aug 18 at 17:44
  • $\begingroup$ Is human power (pedals etc.) an option? $\endgroup$
    – Alexander
    Aug 18 at 17:59
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Heavier than air flight had gliding before engines. Modern sailplanes, given suitable weather conditions (wind to produce ridge lift, sunshine or other heat sources (calderas?) to produce thermal updrafts), are limited mainly by launching (tow or winch or roll down a steep slope); they can beat light planes for overland speed (despite having to search for lift along the way) and carry tens to hundreds of kilos of ballast to fly faster.

In our world, sailplanes have stayed limited to one or two seats for performance reasons, but if engine power weren't possible, there's no reason a sailplane couldn't be made larger -- four or even six seats (in pairs), a narrow cargo hold -- and travel routes arranged to take advantage of winds and landforms (ridge lift is far more reliable and stronger than thermals, absent thunderstorm formation).

Sure, there would be balloons, but if you need to go upwind, the fastest way to do so would be by sailplane.

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I guess that a liquid fuel rocket engine would count as an engine.

What about a solid fuel rocket?

If that doesn't count as an engine, a plane could take off with solid fuel rockets and then glide a great distance to its destination.

JATO (acronym for jet-assisted take-off), is a type of assisted take-off for helping overloaded aircraft into the air by providing additional thrust in the form of small rockets. The term JATO is used interchangeably with the (more specific) term RATO, for rocket-assisted take-off (or, in RAF parlance, RATOG, for rocket-assisted take-off gear).

https://en.wikipedia.org/wiki/JATO#:~:text=JATO%20%28%20acronym%20for%20jet-assisted%20take-off%20%29%2C%20is,for%20rocket-assisted%20take-off%20%28or%2C%20in%20RAF%20parlance%2C%20RATOG%2C

There has been speculation about intercontinental rocket powered bombers or passenger planes which would use rockets to boost them above most of the atmosphere and then use falling back into the atmosphere to skip like a stone on water and travel halfway around the world.

The Amerikabomber (English: America bomber) project was an initiative of the German Ministry of Aviation (Reichsluftfahrtministerium) to obtain a long-range strategic bomber for the Luftwaffe that would be capable of striking the United States (specifically New York City) from Germany, a round-trip distance of about 11,600 km (7,200 mi). The concept was raised as early as 1938, but advanced, cogent plans for such a long-range strategic bomber design did not begin to appear before Reichsmarschall Hermann Göring until early 1942. Various proposals were put forward, but these plans were all eventually abandoned as they were too expensive, too reliant on rapidly-diminishing materiel and production capacity, and/or technically unfeasible.

Other designs were rockets with wings. Perhaps the best-known of these today is Eugen Sänger's pre-war Silbervogel ("Silverbird") sub-orbital bomber. While the A4b rocket, winged version of the V-2 rocket and probably its successor A9 rocket were tested several times in late 1944/early 1945, the A9/A10 Amerika-Rakete, planned as a full 2-staged ICBM, remained a project.[14]

https://en.wikipedia.org/wiki/Amerikabomber#Winged_rockets

Silbervogel (German for "silver bird") was a design for a liquid-propellant rocket-powered sub-orbital bomber produced by Eugen Sänger and Irene Bredt in the late 1930s for The Third Reich/Nazi Germany. It is also known as the RaBo (Raketenbomber – "rocket bomber"). It was one of a number of designs considered for the Amerika Bomber mission, which started in the spring of 1942, being focused solely on trans-Atlantic-range piston-engined strategic bombers, like the Messerschmitt Me 264 and Junkers Ju 390, the only two airframe types actually built and flown for the competition. When Walter Dornberger attempted to create interest in military spaceplanes in the United States after World War II, he chose the more diplomatic term antipodal bomber.

https://en.wikipedia.org/wiki/Silbervogel

It was designed to be launched from a rocket sled on a track and then use its own rocket engine to reach the upper atmosphere and then bounce and skip off the stratosphere several times as it crossed the world. It was the first design of a space plane using a lifting body form, like the space shuttle used.

If solid fuel rockets doen't count as engines, such a space plane could be built using solid fuel rockets instead of liquid fuel rockets.

So if solid fuel rockets don't count as engines rocket launched gliders or space planes could be used for long distance air travel.

If solid fuel rockets do count as engines, i guess that biochemestry doesn't work on that planet and nothing can live there.

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As of today we know only two ways of flying: powered (propellers, jet, rocket) and un-powered ("lighter than air" and deltaplans).

With the first out of the picture, only the unpowered is left. They could probably evolve in the same fashion ships did, with the only difference that, lacking a keel, they would never manage to go against the wind.

This would make transoceanic travel somewhat troublesome, at least in one direction, because it would need to rely on existing winds giving the direction of travel.

If they would switch to helium or hydrogen depends on the economy of the situation: with those gases you save on fuel weight but you need to waste them for landing, and in cases of emergency landing taking off again might become impossible.

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