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Flying is hard. Most flying species can lift comparatively minuscule amounts of mass in the air beside themselves. Flying is also exhausting, there are only so many species that can soar in the sky for hours.

But our guys are sapient, and sapience grants you many cool things, like the ability to invent tools to overcome your own limitations. So are flight-assist machines that could enhance the flying capabilities (such as speed or carryable cargo weight) or endurance of the user possible, prior to the invention of an aircraft motor running off coal or gas? (After that point, it becomes sort of obvious that a motor is vastly superior to any organic wing) How could they function?

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – L.Dutch
    Aug 26, 2021 at 16:56
  • $\begingroup$ It's worth noting that flying on Earth is hard. How hard it is to fly is a function of (among other factors) gravity and atmospheric density. A world with weaker gravity but a thicker atmosphere (though those two don't normally go together) could be really easy to fly on. Thicker atmospheres make flying more like swimming, in which case the air equivalent of diving fins might be handy. $\endgroup$
    – Beejamin
    Aug 27, 2021 at 0:10

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No, that would be like an improved walking apparatus for us, not like a bicycle. Flying creatures are already evolved to pretty derive much optimum performance from their muscles for flying.

Note that a bike does not stand on its own. We can only use it because we have roads. (Also, evolving wheels is hard). We walk on legs because typical terrain is uneven and overgrown. Unless you can improve the air with a road analog, you won't improve on the natural mode of transportation, until you introduce artificial sources of power.

Gliders may have special uses but will generally be a pain in the butt to lug around if you want to get back up. A lighter than air balloon strapped to the back might be nice to relieve you from having to lift your body weight, but it will provide you with a lot of drag, and make rising and falling harder. It could be used for cargo transport, though. Trim it to neutral buoyancy, and let it be towed by a team of flyers.

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    $\begingroup$ There is sort of an inverse to the square-cube law that needs to be considered. Balloons do have a lot of drag, so it might be hard to move cargo up wind, but the lift increases by volume while drag increases by surface area. The force required to move something heavy would thus be more decreased the heavier the thing is, and small balloons might be unpractical. You might end up with something more akin to an oared ship than to a bike. $\endgroup$
    – EdvinW
    Aug 24, 2021 at 10:47
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    $\begingroup$ “We can only use [bicycles] because we have roads.” This is a bit of an overstatement — there are some kinds of natural terrain where bicycles work very well. In my own experience, mostly dry places with light vegetation and hard, reasonably even ground — e.g. some types of savannah, desert, semi-desert, and alpine landspaces — are suitable for “ordinary” bicycles. Similar places with softer ground — e.g. beaches or sandy deserts — aren’t good for ordinary road/mountain bikes, but are fine with suitably designed tyres, like the beach bikes popular in California. $\endgroup$ Aug 24, 2021 at 11:58
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    $\begingroup$ anyway, it takes special terrain. which doesn't apply to air. $\endgroup$
    – ths
    Aug 24, 2021 at 14:52
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    $\begingroup$ I think this is focusing too much on bicycles specifically, when the OP is asking a much broader question (increased speed, carrying capacity, or endurance). There were a lot of pre-bicycle technologies that were very much improved walking machines, e.g. wheelbarrow. Also, who says that the bird-bicycle would be powered by legs? Humans use legs going in a circular motion because that's useful for how our muscles work, but probably bird-bikes would be powered by some kind of wing flapping motion. $\endgroup$ Aug 24, 2021 at 22:00
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    $\begingroup$ In all fairness, there are differently optimised birds. Birds that are efficient long distance fliers. Birds that are highly manouverable. Birds with from-ground take off capability. Birds that can hover. You can imagine an intelligent bird species of one type sometimes wanting to convert itself to one of the other typed $\endgroup$ Aug 25, 2021 at 8:35
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It was mentioned, but in passing by and there seems to be no interest in.

Gliders

You'd basically want some kind of a wing prothesis, initially without a motor. The tricky part is:

  • to source light-weight construction materials (balsa wood, silk / artificial materials), look into early gliders. All this developed rapidly, a nice source of inspiration are pre-WW2 smaller planes, sans the engine;
  • to design the glider in a way to be usable and not to shadow own wings aerodynamically. The user would either need to be able to still use their wings or we would need some kind of a transmission and a propeller, which is more advanced.

I would imagine either some kind of a "nest" to hold onto, possibly only when curled in a ball, with wings – this is some kind of "let the own wings rest" thing. Or some kind of a thrust / endurance / wingspan extender. "You can fly further with this", like a bicycle, yes.

Also, because aerodynamics is hard (and they might not have the right engines yet), that initial designs obstruct the airflow and make it hard to impossible to use own wings when that thing is mounted on the user. Basically, initial designs might have the image of the (urban legend) winged tower jumpers of the 16th-18th century: the cranks that seldom survive the tests of their inventions.

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    $\begingroup$ This is the best answer IMO. I was going to post along these lines. If a regular glider can help a 100kg man fly for miles at a time, it can do better yet for a species that is already a natural flyer. In the very least that species would have their senses more attuned to this. Humans that glide usually need to watch birds for clues about where to find thermal currents. $\endgroup$ Aug 23, 2021 at 19:42
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    $\begingroup$ Like stilts, a gripper hands, or even a cane for us... simple enhancements to existing biological structures... basically wings that they put on like a backpack, lightweight, easy to lift... even fabric like a kite... easy to get airborne with, but once airborne they can provide steady lift while the biological wings steer and propel. Once that becomes the state of the art, propulsion and other advances are inevitable. $\endgroup$
    – OhkaBaka
    Aug 23, 2021 at 23:11
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    $\begingroup$ How about a paraglider? It attaches to the user by some kind of harness. The paraglider's wing is above the user, some distance away, so it doesn't shadow their own wings. The paraglider wing can handle all the lift, so the user only has to provide thrust and control. Plus it's lightweight and probably not that hard to invent if you're a flying species already. (Actually I'm going to post this as an answer.) $\endgroup$
    – N. Virgo
    Aug 24, 2021 at 7:51
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Paragliders

enter image description here

A few others have suggested gliders of one kind or another, but I think paragliders have a lot to recommend them. The wing is high above the user, so it won't interfere with the user's own wings. The paraglider wing can handle the lift, leaving the user free to provide thrust and control using their own wings, turning it into a powered paraglider, like the ones in the image.

As far as I know it doesn't need any high-tech materials, beyond strong-but-lightweight fabric and cables. This means it would probably be fairly easy to invent, for a flying species that already has those things.

There is a safety issue because the user might get their own wings caught in the cables, but bicycles have safety issues as well, and we can expect a safe design to emerge over time.

I can imagine this being particularly useful if your species evolved for fast flight but not for long-distance gliding. Then this will give them the ability to do that as well, saving a lot of energy on longer flights.

image GFDL, via Wikimedia Commons. Original Uploader was Mikefifield at 5 September 2007.

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    $\begingroup$ I like the idea, but I suspect you'd have problems with the airfoil collapsing when the cables lose tension as soon as the user starts flapping their own wings to gain altitude. $\endgroup$
    – Cyrus
    Aug 24, 2021 at 8:35
  • $\begingroup$ That sounds like a plausible issue, for sure. I'd imagine it's something that can be designed around, but I don't know enough to speculate how. $\endgroup$
    – N. Virgo
    Aug 24, 2021 at 8:45
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    $\begingroup$ @Nathaniel Use a hang-glider wing instead. Then the bird is more securely fixed to the artificial wing, allowing it to directly propel the whole contraption. Powered hang-gliders existed before paragliders - after all, that's all a weightshift microlight is. And even for normal foot-launched hang-gliders, people have been putting motorbike engines into rigid harnesses since the 1990s. The reason you don't see more of them is due to the general decline of hang-gliding (because they're heavy and inconvenient to store/transport), not because they don't work. $\endgroup$
    – Graham
    Aug 24, 2021 at 13:12
  • $\begingroup$ Yeah, I was going to suggest an offset to the user's body, making them into a kind of bi-plane style shape. I can see this as either a rigid or flexible system. $\endgroup$ Aug 24, 2021 at 19:43
  • $\begingroup$ @Cyrus, it would probably take a bit of training, as most things do, but I see the parachute being dragged a little bit, keeping the cables taut. With the correct rigging, the chute could probably be kept parallel to the body and provide lift when climbing, banking, or diving, until they want to slow down for landing and use it as a brake. $\endgroup$ Aug 24, 2021 at 19:48
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Wing Extenders/Artificial Feathers

Larger wings give more lift/speed, so if the species can increase the size of their wings, it will give more lift and/or speed (with probably some cost in the form of agility). If your species have wings like a bird, they may add some extra feathers (or perhaps replace their existing feathers with longer ones). Either (semi-)permanently or done just before taking flight. If they are more bat like, with leathery flaps between bones, you can think of a construct of light weight poles next to their pinkies or thumbs and some fabric increasing the effective size of their wings. If they have fixed wings like most (all?) insects, they may be able to clip on a light weight rigid piece.

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  • $\begingroup$ I like this. We humans can benefit greatly from a nice pair of running shoes. I can imagine a civilization of winged people would invest a great deal of research in augmenting their wings with shoe-like ideas. Something light-weight & wearable. $\endgroup$
    – Toddleson
    Aug 25, 2021 at 17:34
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Cycling is more efficient because it eliminates the principal inefficiency of bipedal locomotion, which is that we use energy from falling to propel ourselves forward, but don't recycle that energy. Much of the effort is spent constantly raising our center of mass, whereas wheels allow your center of mass to remain at a constant height, so you only need to replace energy lost to friction (on a level road).

(In nature, moving fast on a paved road is less important than controlling your movement on rough terrain, and legs are better for that; but you can still use the second-best option of regenerating energy with springs, and animals optimised for running may do that to some extent).

Winged flight doesn't have this fundamental inefficiency, so there wouldn't be a close analog to bicycles for birds. It takes a certain amount of wing-flapping energy to reach a given height, and no simple machine can make that more efficient; and when a bird isn't flapping it's just a ballistic projectile, which again can't be made any more efficient, other than with better aerodynamics (which evolution is already good at).

  • Several answers have suggested gliders as the answer, but many birds are already excellent gliders – in some places you can see birds of prey basically parked on updrafts for long periods of time, expending no more energy than it takes to keep their wings locked in place.

  • Some kind of lighter-than-air device would make it easier to gain and maintain altitude, and increase the load you could carry, but it wouldn't help with speed. That would be more analogous to a boat than a bicycle.

  • That leaves the question of whether a winged being could fly more efficiently by spreading its wings and using a pedal-powered propeller to generate forward speed. That would depend on several factors, but doesn't seem impossible. It certainly wouldn't approach the efficiency gains of cycling vs. running, though, because birds simply aren't that inefficient to begin with.

NB I am assuming that the question refers to sentient creatures that can already fly. If we're talking about human-powered flight, that is already a real thing and Wikipedia has details.

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    $\begingroup$ IIRC bigger wings are almost always more efficient. That's why you see solar-powered planes and human-powered planes having ridiculous aspect ratios (width/length ratios). They need to get the most lift out of their limited amount of thrust. $\endgroup$
    – user253751
    Aug 25, 2021 at 12:40
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    $\begingroup$ @user253751 These planes also fly at ridiculously slow speeds. It's a tradeoff: wingspan vs speed vs efficiency. $\endgroup$
    – ZOMVID-21
    Aug 25, 2021 at 17:15
  • $\begingroup$ bicycle-road systems are mind-bogglingly inefficient. it's a toss-up whether train-rail systems or bicycle-road systems are more inefficient. $\endgroup$
    – Fattie
    Aug 26, 2021 at 12:11
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    $\begingroup$ I may be missing the SF implication, but for IRL purposes trains are the most efficient form of land transport at scale, leaving my mind comfortably unboggled en.wikipedia.org/wiki/… $\endgroup$
    – bobtato
    Aug 26, 2021 at 12:38
  • $\begingroup$ Is the TLDR here that Bicycles are good because they allow 'coasting' (keeping your momentum), so Air Bicycles aren't very valuable because flying naturally allows coasting anyway? $\endgroup$
    – Beejamin
    Aug 27, 2021 at 0:48
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Foldable gliders

Let´s take the bycicle analogy:
A human takes the bycycle with the hands and takes if from its storage place, then walks a few steps with the bycycle until the place the human wants to start riding (could be just one step away or many steps to the street). Then climbs on the bycycle and starts the trip.
When the human arrives to the destination, stops the bycycle and must use the legs again to stand and descend.

Let´s imagine a set of very light foldable gliders that have both wings resting down in the sides by gravity, and deploy when you drop down the glider and remain locked this way.
The intelligent bird would walk/fly to the glider and will grab the glider with its legs, and will fly a few seconds carrying the glider to the place it wants to start gliding. When the bird has reached the desired altitude, it just stops flying and (still grabbing the glider) just lets gravity do the work: when falling, the wings of the glider will deploy and will be locked in position. The glider must (of course) have a piece in the upper part where the bird could firmly grab the piece and even move side to side to control the center of gravity and maneuver (I´m not an expert in gliding, but I know it can be done).
When arriving at the destination, the bird just releases the glider and must use its own wings in the last seconds of the trip, the same way the human must put the foot in the floor the last seconds of the trip.

And yes, birds can carry some decent weight. For example: A female harpy eagle can fly through the canopy and capture a 17-pound (7.7kg) monkey standing in a tree (info in this link):

https://storyteller.travel/harpy-eagle/

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Sure.

A human on a bicycle is just a less efficient runner, using a more efficient runner to assist it.
So too is a human riding a horse.

A less efficient flyer might use a more efficient(or less lazy) flyer as transport in the same way.

enter image description here

enter image description here

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Elevator

If I would be a sapient flying being, I would take off from the highest point possible and soar towards my destination. An alternative would be some kind of catapult (think aircraft carrier-style).

Cable

Just like with gliders, these flying beings can use a cable to provide forward motion while their natural wings provide the lift. They should be able to gain altitude rapidly without too much effort.

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    $\begingroup$ I can imagine one of the most useful things as a flying species would be artificially constructed up-drafts. Or a way to quickly launch yourself into the air. For a bird, taking off is definitely one of the most exhausting parts of flying. $\endgroup$
    – Toddleson
    Aug 25, 2021 at 17:30
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    $\begingroup$ Both elevators and cables are powered. No net energy savings for SELF-powered versions. However, a catapult is an idea that might have some advantage. Still it takes power to compress the catapult (net gain or loss?). Using landscaping to produce updrafts is a good idea. But neither is like a bicycle, in that there is no net efficiency gain. $\endgroup$
    – Mark G B
    Aug 25, 2021 at 19:08
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Using their legs

Since the species is already flying we can assume their natural flying ability is already pretty much as efficient as it can be due to evolution. If not, then some kind of augmented wing that recreates a more efficient design would be the obvious extension.

However, we are forgetting about the species' legs, whose muscles are unused when flying. They have invented a simple machine that consists of a harness connected to long frame at the back of which is a propeller. The propeller is turned by pedals, and gears are used to increase the speed once the user gets faster.

Given the aerodynamic profile of the species' body, once a certain speed is reached it actually becomes less efficient to flap their wings, and better to run solely on pedal power. The best "rapideurs" have been known to reach speeds 10 times that of normal flying.

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    $\begingroup$ Bird leg muscles are not only far weaker, but also far less efficient than their wing muscles. Try turning bicycle pedals with your hands. That's what it will be like for a bird. $\endgroup$
    – ZOMVID-21
    Aug 25, 2021 at 17:10
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Hang (Perch) Glider

enter image description here

Hang-gliders can support many times their own weight. Since bird people are smaller and lighter than humans, they can use much smaller gliders.

When using a glider the bird flies as near to vertically upwards as possible, carrying the glider by one wing tip to minimize air resistance. When they get high enough, they reorient the glider to perch in the normal place, and use their wings to steer.

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No. It would defeat the purpose.

What is the advantage of the bicycle? A man walking has to spend part of the energy to stand and part for the forward movement, when he runs also the attrition of the terrain comes into play. Sitting on a bicycle requires less energy than standing and thus most of the energy can be used for the forward movement, counting also the reduced attrition everything results in a great efficiency improvement.

Can a flying creature get a similar advantage in some way? After all a bird has to spend some energy to lift itself and some energy to move forward. So with a paraglider attached to his back, two cables attached to the feet control the angle of the paraglider, all the movement of the wings can be tuned for the optimal forward push. However the advantage would be cancelled out by the additional drag. What has to be taken into account is that a wing, a glider or a paraglider don't stand in the air by themselves, they need a forward movement to create lift or get some help from a thermal current which is not always there, so, we are back to square one, part of the energy is used to create lift and part of the energy is used to move forward and even if the extra wing is made of light weight material it will add some weight.

The alternative

If your creatures still don't have engines, but can create cool tools they could at least try to save some energy in some way and the most costly part of the flight is the beginning. Why not starting with a catapult?

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If your goal is

enhance the flying capabilities (such as speed or carryable cargo weight) or endurance of the user possible

forget about it.

The Gossamer Albatross is the first human powered airplane, and doesn't do that.

The Gossamer Albatross was constructed using a carbon fiber frame, with the ribs of the wings made with expanded polystyrene; the entire structure was then wrapped in a thin, transparent plastic (mylar PET film). The empty mass of the structure was only 71 lb (32 kg), although the gross mass for the Channel flight was almost 220 lb (100 kg). To maintain the craft in the air, it was designed with very long, tapering wings (high aspect ratio), like those of a glider, allowing the flight to be undertaken with a minimum of power. In still air, the required power was on the order of 300 W (0.40 hp), though even mild turbulence made this figure rise rapidly.

It's listed to have a useful load of just 66 kg, mostly water to keep the human hydrated.

Note that it's made with advanced material, not available before the invention of engines.

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    $\begingroup$ I'm confused - the Gossamer Albatross allows a terrestrial creature to fly. How does that not "enhance the flying capabilities of the user"? It's unclear how a machine that allows a non-flying creature to fly is evidence of the impossibility of a machine that allows a flying creature to fly more efficiently. I don't see the logic in the premise or conclusion. $\endgroup$ Aug 23, 2021 at 18:41
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    $\begingroup$ @NuclearHoagie, it doesn't allow the creature to fly pretty much anything else than itself. OP is asking for that. $\endgroup$
    – L.Dutch
    Aug 23, 2021 at 18:53
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    $\begingroup$ @Nuclear Hoagie it takes a lot for a creature to fly without engines and without using its own capabilities. The basics of a bike and those of an airplane are drastically different. $\endgroup$ Aug 23, 2021 at 19:07
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    $\begingroup$ "doesn't allow the creature to fly pretty much anything else than itself" // hmm, you mean he can work the 'bicycle' or his own wings but not both at same time? // how about an inflatable helium filled sausage he lies astride with a propeller in back allowing his own wings to flap while he peddles at the same time :) $\endgroup$
    – Pelinore
    Aug 23, 2021 at 19:28
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    $\begingroup$ @L.Dutch Right, but the baseline here is a human, which can't even come close to lifting itself. This apparatus increases a human's lift many times over. Why does that suggest you cannot improve the lift or efficiency for a creature that can already fly under its own power? $\endgroup$ Aug 23, 2021 at 19:42
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Almost all of this will require some very light building material.

The flapping of wings creates an inconsistent thrust - modern aircraft tend to have constant power, from a propellor or a turbine. You could rig up some mechanical contraption to attach to the wings that would allow them to power a turbine strapped to their chest. This would allow them to keep building up thrust between wing beats, rather than having to reset their wings each time.

They could also build lightweight wearable hulls that reduce air resistance. This is especially viable with the turbine - that way, you don't need air flowing over the wings to produce lift.

Finally, you can create a buoyant structure like a blimp. That allows the flyer to stop expending energy fighting gravity, so they can focus on fighting air resistance and moving forward.

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Gliders are not bicycle-like.

If the sapient species has the same basic design as birds, i.e. two wings and two feet, I think the most direct analog of a bicycle would be pedal-assisted mechanical wing extensions.

Imagine the bird creature's natural wings fitting into lightweight artificial wings attached to a harness designed such that the artificial wings respond to and mimic the shape of the natural wings but allow the bird creature to convert pedaling into additional flapping energy.

Basically the idea would be allowing the bird creature to use its feet to produce more lift than it could with its wings alone. Its natural wings would essentially be used for "steering".

It doesn't seem particularly far-fetched to me that such a device could work. Particularly on a planet with lower gravity than earth but with a dense atmosphere e.g. Saturn's moon Titan.

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I think everyone is looking up when we should look down. If you already have wings, you just need something to assist with propelling you along.

Then it is just a matter of hooking up the propeller to their wings or other limbs to make it spin.

enter image description here

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The bicycle provided mankind with a mode of transport that was more efficient than walking or running, almost right from the get-go. The first wooden velocipede was barely there, but it was there. Once past the velocipede stage, a man with a bicycle was already more efficient and capable than man and horse. What makes this efficiency possible is the wheel. In order for an avian species to realize a similar gain, or ANY gain, they would have to invent something that functioned, for flight, in the manner that a wheel does on the ground - by making moving through the air more energy-efficient. The proposition of machines or tools to enhance an avian's flight is mostly nonsensical, given the physics of our known world. However, there might be some exceptions. I'll return to the wheel later.

ALL human flying machines are LESS efficient than any avian's nature-given ability*. All flight involves 3 stages: ascending, traveling, and descending. Avian physiology is dictated by these requirements. Ascent requires the most significant energy expenditure. Gliding is traveling and descending. For flighted birds, the energy requirement for gliding is near zero. Adding a gliding device to the ascent would add weight to the ascent, and would require greater energy expenditure to attain altitude. Thus, the net gain would be negative for a single glide-slope.

Some avians use multiple glide-slopes by utilizing updrafts to ascend. You could offer improved glide characteristics for avians who are poor gliders, but such avians would likely not have the innate flight power required for ascent with the added weight (think turkeys). But gliders, or paragliders, are out, due to insufficient gains and too high an energy cost. **

Most avians have sufficient muscle power to provide lift. Musculature for other uses is reduced to optimize weight to lift ratios. Most avians would have to use their wings to power an avian-powered machine. Adding any device adds weight, with no consequent increase in power (or reduction in lift requirements or enhancement of the power to lift ratio). This would negate any gain. The only way an avian-powered machine could improve on the avian's flight capacity would be if the avian was flightless, like an ostrich, or an emu. A flight-capable avian species could not have enough muscle power in other muscle groups, due to weight restrictions required for lift and flight, to power some driving force, such as a propeller. So, you'd have to have a flightless avian species.

Now, when it comes to powered aircraft, it is conceivable that an avian species could invent such. Just like for earth-bound humans, the power source would have to be essentially free or low cost, but such a development arc is conceivable. After all, the development of mechanical engines came about because of ground-based needs. And, an avian species could have an ecology with similar needs, where, at some point in time; a mechanical engine provided greater efficiency and productivity than attainable without the device.

But an avian-powered flying machine would have to be more efficient than the avian or there's no point. The machine would have to have some way to act as a multiplier to the avian's innate efficiency. I could imagine that a sapient flying squirrel could invent something like a glider - to make them more efficient at gliding, and to able to use thermals to gain altitude. But a flying squirrel is not an avian. Flying is not its nature.

Returning to the wheel. Man's natural means of transportation, walking and running, are on the ground. These natural means of transportation were made more efficient by the invention of the wheel. The combination of wheels, in a relatively light and steerable human-powered device, rendered a huge increase in energy-efficiency. In order for an avian species to realize a similar gain, or ANY gain, they would have to invent something that functioned, for flight, in the manner that a wheel does on the ground - by making moving through the air more energy-efficient. The only thing I can think of that might fit would be some sort of small anti-gravity device (currently unknown technology). Balloons don't work to enhance flight due to wind resistance. Design a world where your avian species has anti-gravity devices, and those devices could improve flying efficiency.

I have, in comments, posited some possible exceptions to what I've argued here. Mankind has, to date, not invented anything (non-motorized) that would logically enhance a flighted bird's natural abilities to fly. You can't make an albatross out of a turkey, due to the physical limitations of each body. The turkey doesn't have the musculature to power the albatross's flight gear. The albatross can't walk on ground as well as the turkey. However, we are dealing with science fiction. If you posited materials development that was lighter, more flexible, more workable, and stronger than anything yet known to man, you might be able to design something that would work. Or, if you had anti-gravity capacity that was as small as the avian or smaller (small size required due to wind resistance problems). A bicycle works because a man's major muscle group is almost completely re-tasked to do something that was a relatively minor function. Legs no longer had to hold us upright. All of a sudden they were only devoted to moving us forward, and they could use all that "standing-up" energy to move forward.

*This is not entirely true, as an aircraft like the Gossamer Albatross is more energy efficient than some flighted creatures. But for the sake of simplicity, and not writing a book, that is the exception, not the rule.

**Because of the extended discussions involved in posting comments on this question, and editing this answer, I have realized that there might be one way, given known technology (and physics), for an intelligent avian species to enhance flight capacity, although in a limited way, and only for avians with limited flight capacity, or non-flighted. Lighter-than-air craft would not work to enhance flight, due to wind resistance. However, let us propose that our alien avian is like a turkey, with limited flight capacity, but intelligent. A lighter-than-air balloon could be used for ascent, carrying our avian and a gliding device. Thus, the balloon delivers the primary energy requirement for a flight. Once at altitude, the gliding device could then be deployed, and our avian has a net gain. This isn't precisely avian-powered, but it could be an enhancement.

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Many have mentioned that flying species are often very well engineered for flight. However, as @Goodies mentions, not all of them are. He mentions a few that don't fly at all anymore, but some, like chickens, can fly, but aren't very good at it, as evolution (and/or, in the case of chickens at least, breeding) have given them weighty muscles for walking as well.

For such flying species, I propose "kick-assisted flight": it consists of wing extenders to give extra lift (but making wings difficult to flap), together with cords between feet and wings and pulleys connected under the wings. As you raise your wing, you pull up and bunch your feet under you; as you flap you kick back and down, using your leg muscles to pull the cords to help you flap the extra-large wings.

It is hard to imagine that this mechanism would be very elegant, but it might help you gain altitude more quickly. Once you were up, the wing extenders could help you glide (or stoop, if you wanted). Thus, it might be a practical way to get a glider up to altitude.

Update

@geometrikal also proposes a way to use leg muscles in another answer. Here we envision simpler mechanism which presumably needs lower technology.

I should note that all of the answers assume that flying creatures are (perhaps with a few exceptions) highly optimized by evolution for flying. On a world like Ursula Le Guin's Rocannon's World, which has a dense atmosphere relative to gravitation, evolution might have had an easier time with flight per se, resulting in many creatures that can fly without necessarily being very good at it. (Maybe tool use & bearing burdens would have an easier time evolving among the avian, in return.) On such a world, assistive technology such as proposed here, or in other answers, would have a lower bar to be helpful.

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  • $\begingroup$ Yes, this extending of the wings may work for chicken ! It has to be intelligent to use the extensions.. gliding and gaining altitude by subtle movement is quite different from the natural fluttering, like chicken usually do. $\endgroup$
    – Goodies
    Aug 26, 2021 at 21:37
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Solutions for penguins and chicken

Flying species are manifold, most are quite effective, flying many 1000s of kms per year. An eagle will need only shoulder muscles to fly.

But there are lots of species that don't fly so well, or don't fly anymore.. A wing suit seems appropriate for adventurous pinguins. Glide. Same counts for hobby flyers like cats and squirrels, who may use wing suits or delta wings to extend their limbs. I guess most intelligent chicken will prefer balloons ?

Ostrich bicycle drone

Suppose the Ostrich would have evolved as an intelligent species, there could be a cultural urge to fly, among ostriches. When designing the means, I think they can make good use of their very strong legs, using a quadcopter-like vehicle to lift off the ground. A carbon bicycle belt can be attached to carbon wheels mounted on either side of the animal, driven by pedals, connected to the toes. The fast spinning wheels drive the propellors in some way. Can't think of a suitable transmission to do that, but probably these ostriches will be much smarter than me.

enter image description here

https://www.youtube.com/watch?v=j02CzMyf0DA

(this one is for lazy ostriches)

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  • $\begingroup$ The word "flying" in the question kinda suggests that it isn't concerned with species that can't fly. Because those would have to go more or less the same path humans did. $\endgroup$ Aug 25, 2021 at 19:03
  • $\begingroup$ Ostriches did fly once.. what if your intelligent flying animals would have lost their ability for flight, because they don't need it anymore ? The ostrich is one of the animals that could actually lift their own weight.. if only they would have the aircraft to do that.. $\endgroup$
    – Goodies
    Aug 25, 2021 at 21:39
  • $\begingroup$ I'll reiterate, the question is about flying species. Not species that will evolve flight in the future, not species that lost the ability to fly in the past, flying, present tense. $\endgroup$ Aug 25, 2021 at 22:00
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In real bio-physics, you can prolly count all the relevant examples here!

In Worldbuilding, what says the flyer can't use drugs - this isn't the Olympics, is it?

What says the flyer can't use prosthetics - can't an ordinary athlete get the same advantage from "blade" feet that paralympians see? Can't you translate that to wings?

What says the flyer can't use umpty psychic abilities?

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Yes, they could be both possible and practical

This is a very simple question being made over complicated by what limits HUMANS from flying. Humans can not do self powered flight because we are dense, slow moving, mammals with proportionally much weaker appendages than a bird's wings, but a bird could easily make use of mechanical advantages to improve both flight speeds and distances. In other words, we can not fly in a self-powered plane for the same reasons a turtle would be unable to stay upright on a bicycle.

Let's start with how a human bike works: Bobtato's answer so far has done the best job of nailing down what makes human bikes work. Basically locomotion by feet wastes a lot of energy that a bike recaptures and turns into forward motion... but he misses the fact that all the same basic principle apply to birds too. Like feet, wings only generate forward power with part of the flap as the wing pushes down and backwards against the air to create an equal and opposite reaction, but as it rises and comes forward, it actually pushes the bird in the wrong direction to get back to its starting position (just less so because the wing folds and angles into this motion).

SEE: https://www.pbh2.com/wordpress/wp-content/uploads/2014/03/how-a-bird-takes-off.gif

So, a lot of the power spent bringing the wings back up and forward is lost to inefficiency. However, if a bird were to just flap up and down, it would at no point push itself backwards, and if you attach its wings to a gear assembly, then that up and down motion could turn a propeller which would convert the full stroke of a flap into forward momentum, and none into backwards momentum.

But this only tells part of the story about what makes an air bike better. The main thing that makes bikes so good is gear ratios. To fly horizontally forward you must swing your wing faster than you are already moving to create additional speed. So, if you want to move at 50km/hr, and your wing speed maxes out at 40km/hr then your medium retreats away from your wing faster than you can push into it so you can't make yourself go any faster by pushing against the air once you pass 40km/hr. If you've ever run at full sprint, you've probably noticed something similar where at some point you stop feeling the resistance of pushing back against the ground and all your energy is being spent just keeping your legs moving and that you can not actually go any faster because your feet themselves can no long impart any more acceleration with the ground... this is more-or-less the same thing accept that a bird can at this point choose to glide to mostly maintain that speed.

But, like a bike, a propeller can use gear ratios to turn a slow strong biological action into a faster weaker one to make higher speeds more sustainable. So, once your bird reaches an air speed nearing its max, it can increase the gear ratio. So instead of a strong but mostly wasted 40km/hr push, you might get a weaker 120km/hr push out of your propeller, and this faster backwards push means you can either sustain your 40km/hr speed wasting much less of your power on inefficiency, or you can speed up to a higher maximum speed even through you have a lower torque following the same principle that allows your car to accelerate to and maintain interstate speeds at high gears with a relatively small strain on your motor.

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The value of a bicycle is that it holds one up; one can then expend one’s energy on moving forwards.

The air analogue is the airfoil.

An airfoil has to be moved forwards quickly to work, but this is workable, as the air pressure against the front (fighting forwards movement) is less than the air pressure under the airfoil (which does the lifting).

It is thus possible for a human being to fly, under their own power, using a machine whose main components are an airfoil [“wing”] for lift, and a small airfoil [“propeller”], powered by the user, for forward movement.

Unfortunately, I can not see how a flying creature might gain any advantage over its existing ability to fly, using such a device.  …But I would be happy to be shown to be wrong.

(There are devices — such as • hot air balloons, • gliders and • hang-gliders that enable a human being to fly, in some manner or other, without expending much energy… but each of those listed makes some compromise.)

Having said all that… there is one thing that possibly might qualify. It might be more viable with several “people” powering it. It is — added to a glider — a “self-propelled hydrofoil board” — adapted for air, of course; the idea is to “flap” up and down {a flexible airfoil shape}. Search the above, and see the following links to get the idea.

. Start the following at about 0:40.
https://www.youtube.com/watch?v=wuzWYqCm4T0

. Start the following at about 0:45.
https://www.youtube.com/watch?v=VyyMN5RzlTg

. The second is the YouTube video in the first.
https://www.mensjournal.com/adventure/kai-lenny-surfs-his-self-propelled-foil-board-on-open-ocean-swells-for-miles/
https://www.youtube.com/watch?v=h7XupqFOFSg

. Ditto.
https://www.surfertoday.com/surfing/one-ride-two-waves-kai-lenny-tests-a-self-propelled-hydrofoil-surfboard
https://www.youtube.com/watch?v=px88XsARHwc

. I am pretty sure this is the “mechanism”. (That is for water; I would expect an air one to be much more like a standard aircraft wing.)
https://www.thesurfboardwarehouse.com.au/products/takuma-lb1300-pro-foil?currency=AUD&variant=35282973098152&utm_medium=cpc&utm_source=google&utm_campaign=Google%20Shopping&gclid=CjwKCAjw1JeJBhB9EiwAV612y_tK1FmjHguPTBIUWo5sGW6K5r8ectHTBb5RG4dI-raDdv_RXN3DvRoCyloQAvD_BwE

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