Wikipedia:Reference desk/Archives/Science/2023 August 7

= August 7 =

Flying birds
Is the only reason birds don't use props, rotors and/or some sort of lung-powered air anus cause axles etc are so much more suited for engineers than mutation/biology or is flapping actually better at those Reynolds numbers and power-to-weight ratios? Sagittarian Milky Way (talk) 21:01, 7 August 2023 (UTC)
 * Rotating locomotion in living systems is relevant.- gadfium 21:18, 7 August 2023 (UTC)


 * Some mollusks use jetting. See Octopus and Squid, for examples. ←Baseball Bugs What's up, Doc? carrots→ 21:51, 7 August 2023 (UTC)
 * A lot easier when you don't weigh hundreds of times an equal volume of air and each liter of squirt has 800 times the momentum of air at the same speed. They used to spray water in some jet engines till just after takeoff for extra mass flow and thrust. Sagittarian Milky Way (talk) 22:05, 7 August 2023 (UTC)
 * Injecting water in a jet engine, which immediately turns into steam, increases the volume of the exhaust gasses and thereby exhaust speed and thrust (which is good), while keeping the temperature under control and preventing the turbine from melting (which would be bad). PiusImpavidus (talk) 10:42, 8 August 2023 (UTC)
 * I really want to see a flying squid now though. At first just jumping out of the water a little then becoming ever better at jumping then gliding like flying fish till it can squirt air out its jet for 300 yards with 10 flapping wings. Sagittarian Milky Way (talk) 22:12, 7 August 2023 (UTC)
 * See Todarodes, which are making efforts in this direction. The 30 metres achieved by the Japanese flying squid is not 300 yards (more like 33 yards, for the benefit of the mathematically challenged), but it's still impressive. {The poster formerly known as 87.81.230.195} 51.198.140.169 (talk) 11:11, 8 August 2023 (UTC)


 * As the article linked above mentions, flapping wings or tails is at those high Reynolds numbers indeed more efficient than spinning a screw propeller (not to mention paddle wheels). To get propulsion in a fluid it's best to move a large amount of fluid at a low speed, only slightly faster than your speed relative to the medium. The entire wing is much bigger than the propeller, so it can move more air. So why have human engineers failed to build an aeroplane with flapping wings? They have tried, but when you start with a crankshaft rotating at 2200 rpm and want to convert that to a flapping motion at 50 fpm (flaps per minute) and variable amplitude, you need a heavy and lossy transmission that will prove a maintenance nightmare. Alternatively, you could use a low frequency internal combustion engine, directly coupled to the wings with no rotating parts and variable amplitude (use an engine with opposing pistons), but those tend to be under-powered. PiusImpavidus (talk) 11:07, 8 August 2023 (UTC)
 * Sounds like a job for artificial muscles. Card Zero  (talk) 11:42, 8 August 2023 (UTC)


 * It could also be that the method of flapping wings (which is not limited to birds, but also mammals and dinosaurs, and arthropods), is that it works, whereas all of the other wild-ass methods your imagination came up with don't. -- Jayron 32 12:02, 8 August 2023 (UTC)
 * Of course propellers and rotors work at bird sizes, radio-controlled planes and copters use those methods. There are even radio-controlled jet propelled planes. They just might not work for evolved organisms (no animals have wheels instead of legs either, and the blood would need to go through the axle if the rotator needed nutrients from the body). Sagittarian Milky Way (talk) 16:14, 8 August 2023 (UTC)
 * Well, there you go then. You answered your own question.  Didn't even need to have been asked.  -- Jayron 32 16:22, 8 August 2023 (UTC)
 * But is flapping more efficient than props or rotors or jet-like air ducts at bird sizes? Since man-carrying flapping planes are so impractical at Holocene air densities and oxygen levels I had some doubt though realizing it could just be physics and/or engineering difficulties (the lack of flapping man-carrying airplanes) Sagittarian Milky Way (talk) 17:26, 8 August 2023 (UTC)
 * We're near the utmost depth of my understanding of fluid dynamics, so I may stand corrected by someone else here, but I'm fairly certain that relative ratios of efficiencies for generating lift from the amount of total force exerted are relatively similar at the two scales; or at least, certainly not orders of magnitude different. Let me reiterate for clarity, I'm talking about the ratios in efficiencies between the two types of systems as compared between the two scales, not the level of efficiency of a given system between the two scales.


 * Anyway, what I can tell you with more precision and authority is that the physical limitations (or biophysical as the case may be) are also as well understood in terms of the efficiencies of the systems necessary to generate the force in a particular way as they are about how you judge the amount of force to life as a closed system. Presuming for the moment that you could create a membreanous wing-like structure capable of replicating bird-like wing movements with an extreme level of precision, it would require significant energy consumption.


 * You can see extreme versions of this in the avian world with hummingbirds, most species of which exhibit such high caloric demands that individuals typically cannot go more than a few hours during daytime activity without feeding before they just begin to starve to metabolically shut down, while they must go into a deep torpor to conserve energy and survive the night. From this high demand, and the unique and more fully rotational functionality of their wing-to-shoulder joint articulation, they get a bevy of benefits, including, speed, maneuverability, and ability to aerodynamically hold position in space with a degree of subtlety that has only just recently been matched by our most recent drone technology. So, highly inefficient by certain very non-contextualized physical metrics, but fit for purpose and essential to the species' ecological niche, which requires accounting for a lot more factors than "how to I cover this much distance, with this much load with the least amount of newtons?"


 * Which brings me back around to your original and more broad inquiry. Too be perfectly honest, I'm not sure how much your tongue is in your cheek here, but the biggest reason that birds haven't adapted most of the more mechanically complex systems you allude to is that they can't physically do so or such changes wouldn't occur because they make little adaptive sense.  While human engineering has a means of pondering and then artificially replicating organic systems in the form of biomemmetics, there is no particular reason to expect a living system to converge in terms of form and function upon every efficient design created by even the simplest form of human engineering.


 * As alluded to above, there are two components to this: 1) systems which organic tissue is ill-fitted to replicate and/or which would require far too many other compromises to effectuate. Hence, no wheel and axle locomotion either. And to treat one of your own examples, a "lung-to-anus" system is physiologically (or rather, just straight anatomically) infeasible, as pulmonary system shares no contiguous chamber, cavity, or channel with the anus in any bird species. And those systems aren't adapted (in the high level, scale of epochs sense) for propulsion.  Forgive my picking the low hanging fruit, but in any such species those physiological elements have other crap to do--quite literally in the case of one system.


 * And 2), less obviously but just as relevant, the iterative nature of natural selection itself. Adaptations do not typically spring into existence fully formed, and something of the mechanical complexity of much of what your propose for alternative methods of bird propulsion are never going to result as the consequence of a single mutation; likewise, it's statistically beyond possible that a viable offspring evolving all of those vast and highly adaptive mutations at once would ever occur.  Rather you would need countless generations of slow, iterative advancements, and the costs to such a radical redesign of already highly adaptive set of systems would be so substantial, that it's unlikely the countless generations of necessary intermediaries would be competitively fit enough for the chain to survive throughout. SnowRise let's rap 21:20, 8 August 2023 (UTC)


 * "...evolution favours what is good at reproducing itself, not what is good". Why evolution is better than design. Alansplodge (talk) 10:39, 9 August 2023 (UTC)


 * Even more to the point, human imagination is not confined by reality. That has a flip side: Reality has no requirement to conform to one's imagination.  If you imagine some thing that you insist should work (and it may even actually work if you were to build it, i.e. a helicopter or a jet engine or a prop plane), actual biology is under no requirement to conform to your imagination.  When some one asks "Why didn't biology do what I imagined it could" the question is mostly meaningless, it just didn't.  We can recount what did actually happen, but to say why it didn't happen a different way is quite unanswerable.  Who knows.  It was your imagination, not reality itself, that thought it could.  Use your own imagination to answer your own imaginary question.  Reality is under no obligation to explain itself.  -- Jayron <b style="color:#090">32</b> 12:03, 9 August 2023 (UTC)
 * I asked if it was just the limitations of mutation and biology (in which case the paucity of working manned ornithopters is either the scale difference and/or what is suited for human engineering) or if it is also less efficient flapping at those scales. I did not say any of the common aircraft methods exist in natural life anywhere in the universe or are even evolvable. Sagittarian Milky Way (talk) 14:45, 9 August 2023 (UTC)
 * So here's the thing: it's difficult to generalize an answer to the second part of your question, because of 1) the vast array of tasks which winged organisms within Animalia use their wings, which generate lift with a number of different aeromechanical profiles, enabling behaviours particular and necessary to those species (that is, the kinematic description of a particular movement), and at different altitudes (and across time especially, in different atmospheric substrates); and 2) because the difference in scales between these species are comparable or even much greater than the difference in scale between the size of your average extant bird and the size of the aircraft you are describing, depending on what that scale is. Further, the mechanics for individual cases involve aerodynamic profiles which may be poorly qualified by existing empirical frameworks and are extremely difficult to extrapolate/generalize from the simple description of "the way animals (or even just birds)" fly.


 * In those terms, this source may or may not be a little dense depending on your familiarity with aerodynamics, but I think may be of particular interest to you, though it explores the scaling of insect insect varieties of wing morphologies, mechanics, and kinetics and is mostly more occupied with replicating them at smaller scales. Nevertheless, I think it might go a long way to expressing the complexities involved here and what can and cannot be generalized with regard to your inquiry. Here's another more concerned with biomimmicry of avian wing mechanics/aerodynamics, though it also does not answer your inquiry in and of itself. Here's some more in the same vein:, , , , , . From what I can tell, this is area of energetic inquiry right now, and you can find many more sources with fairly obvious search terms in both conventional and research database search engines.


 * On the other hand, the "biological limitations" as you frame it, while also presenting difficulties with over-generalizations, can nevertheless be easily and dependably validated as an empirically robust set of limiters. Thou I hasten to reiterate that we're not just talking about structures which may be outright infeasible for organisms using anything like the anatomy of existing birds (or animals generally), or even that factor combined with the constraints of feasible evolutionary development.  It's also a matter of these systems being less dynamic or less case-sensitive, making them non-adaptive and capable of saddling already quite graceful flyers with an inferior set of tools for taking to the sky, relative to the needs of such animals. <b style="color:#19a0fd;">S</b><b style="color:#66c0fd">n</b><b style="color:#99d5fe;">o</b><b style="color:#b2dffe;">w</b><b style="color:#B27EB2;">Rise</b><b style="color:#d4143a"> let's rap</b> 19:22, 9 August 2023 (UTC)
 * I never knew insect wings were that clever. To me bumblebee and Periplaneta americana wings always seemed undersized for hovering and fleeing me respectively (P. ams need hot muscles to fly) but that's probably the fittest compromise and they probably stop looking clumsy in shadowgrams of many frames per flap and pixels per body length. Hummingbirds on PBS did seem like graceful masters of the whole 3D position and motion thing. Sagittarian Milky Way (talk) 02:41, 10 August 2023 (UTC)
 * The section explains in its last subsection "Nutrient and waste transfer" that truly rotating wheels cannot be made up of living tissue because of the anatomical impossibility of delivering nutrients. So any damage to naturally grown wheels would be permanent, making them an iffy proposition for lifeforms not evolving on pothole-free highways. So the real barrier may be the lack of evolutionary advantage.  --Lambiam 15:56, 9 August 2023 (UTC)