Wikipedia:Reference desk/Archives/Science/2022 December 4

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December 4

is there a theoretical maximum size and weight for bird flight?

As I understand it, most of the largest flying birds are either predominantly gliders that can't sustain powered flight for long, or are bulky, mainly terrestrial chonkers that can fly just enough to get up into a tree and down again. With something like swans being the limit for sustained powered flight? Has anyone ever calculated a theoretical maxmum size and weight for flight? — Preceding unsigned comment added by 146.200.126.234 (talk) 00:56, 4 December 2022 (UTC)

If there is a theoretical maximum, the same theories would presumably apply to the pterosaurs, some of which were considerably larger than any flying bird. As for what the pterosaurs were capable of, see the discussion on the Quetzalcoatlus article: there seems to be considerable debate as to what this genus (the largest of the pterosaurs) were capable of. AndyTheGrump (talk) 01:58, 4 December 2022 (UTC)

I was under the impression that pterosaurs and pterodactyls used a different "design" when it came to flight? Also wasn't there more oxygen in the atmosphere in those days? 146.200.126.234 (talk) 02:24, 4 December 2022 (UTC)

It's a simple question of weight ratios. --Trovatore (talk) 04:00, 4 December 2022 (UTC)

If you simply scale up a flying creature, the required power to mass ratio increases with the square root of scale, which at some point must become a problem. Take-off speed also increases with the square root of scale. So as the bird gets bigger, the reserve power gets less, making the take-off run longer and reducing manoeuvrability until at some point it can no longer fly. Questions are, what drag coefficient can a bird reach? What power to mass ratio can a bird reach? What lift to drag ratio can a bird reach? Those numbers cannot be given very accurately, but it looks like swans and pelicans are close to the limit.

Pterosaurs had a more efficient design (reduced hind legs compared to birds reduced their mass, increasing power to mass ratio), so they could have been bigger than birds and still able to fly. A 20% increase in power to mass ratio already allows scaling up by 44%. But a lot about pterosaurs is unknown. We're not aware of entire groups of pterosaurs that had lost their wings, so presumably all species on the main branches of the pterosaur evolutionary tree could fly, but some, in particular large, species may have gone the way of the moa, developing island gigantism while loosing their ability to fly. Of most species, we haven't found complete wings, so it's hard to say if any particular species could fly. PiusImpavidus (talk) 11:21, 4 December 2022 (UTC)

See also Respiratory Evolution Facilitated the Origin of Pterosaur Flight and Aerial Gigantism (apparently pterosaurs were full of air). Alansplodge (talk) 12:07, 4 December 2022 (UTC)

Nature tends to push evolution to the limit. The largest flying birds today are the great albatrosses and the heaviest is the great bustard, so I think it's safe to assume those are the physical limits given the physiology of modern birds. Shantavira|^{feed me} 20:46, 4 December 2022 (UTC)

Moreover, it appears that in several families of large flying birds (albatrosses, bustards, swans, pelicans, vultures), the limit is always about 10–11 kg. That doesn't look like coincidence. PiusImpavidus (talk) 10:36, 5 December 2022 (UTC)

Perhaps heavier birds could exist if the atmosphere was denser. So for example if the Mediterranean Sea dried up, so that the there was air down to 4000 meters below sea level, a different constructed bird could be heavier. Graeme Bartlett (talk) 21:14, 4 December 2022 (UTC)

Assuming lift-to-drag ratio, power-to-mass ratio and drag coefficient stay the same, a simple calculation shows that the maximum scale is proportional to air density. Increase air density by 50% and we can have pelicans with 5.25 m wingspan and a mass of 35 kg, flying at the same speed as current pelicans. PiusImpavidus (talk) 10:36, 5 December 2022 (UTC)

Lift is proportional to wing area, which is proportional to the square of the length if the length to width remains the same. But, since birds have not evolved hollow wings, mass is proportional to the cube of length. Therefore, mass goes up faster than lift, so there must be a point where wing mass exceeds wing lift, and the bird cannot have a body and fly.

Man made airplanes are very large but the wing volume is mostly air. Dionne Court (talk) 03:29, 5 December 2022 (UTC)

Lift is also proportional to speed squared (until you hit the sound barrier), so the trick is to go faster. Man-made aeroplanes are much faster than birds. A Boeing 747-8 has a stall speed higher than the top speed of any bird in level flight. Power is speed times thrust and thrust is proportional to weight, so power-to-mass ratio matters. The Boeing 747-8 has a power-to-mass ratio during take-off of about 900 W/kg (190 W/kg effective power, as jet engines aren't very efficient at low speed), whereas few animals can get much above 12 W/kg for short bursts. Actually, it works out quite nicely. PiusImpavidus (talk) 10:36, 5 December 2022 (UTC)

This is also sort of interesting further reading:

Debunking the two-dimensional assumption on infinitely long wings, a 2018 conference paper at the Annual Meeting of the Fluid Dynamics division of the APS ...

More than once this year, I've engaged in fascinating discussions with very well-informed professionals on the topic of infinitely-long wings: if infinitely long wings are such a good idea - every extra meter of wingspan adds more lift than it weighs in structural mass - then, why not make airplane wings infinitely long? Well, the Boeing 777X already has wings that are sooooooooo looooooooong that the designers need to fold them to make room for the aircraft when it's at an airport.

It turns out that there are practical considerations - not the least of which relate to what to do with a very large wing while it's not flying.

Nimur (talk) 19:33, 5 December 2022 (UTC)

Radiation belts

Is there some kind of theory that explains which radius radiation belts occur at? Say about the Larmor radius? JoJo Eumerus mobile (main talk) 15:29, 4 December 2022 (UTC) JoJo Eumerus mobile (main talk) 15:29, 4 December 2022 (UTC)

Radiation belts are caused by the interaction of charged particles with a planet's magnetosphere. So the theory you're looking for is the overall theory of how planetary magnetic fields are generated and shaped. The Larmor radius refers to the shape of the orbit of a charged particle travelling in a uniform magnetic field, and on the scale of radiation belts, planetary magnetic fields are decidedly non-uniform. PianoDan (talk) 18:28, 4 December 2022 (UTC)

@PianoDan:I know how they originate, but what I wanted to know if there is some theory that says why a given belt occurs at a given distance. Jo-Jo Eumerus (talk) 17:16, 7 December 2022 (UTC)

Like I said - what you're looking for is the theory of how those magnetic fields are generated - the radiation belts are a direct causal result of the shape of the magnetic fields. So the general theory is magnetohydrodynamics, and with relation to the earth specifically, there's references in the article on the Earth's magnetic field. PianoDan (talk) 18:35, 9 December 2022 (UTC)

Hyracodonts from the Ergilin Dzo Formation

What kind of Hyracodonts coexisted with Embolotherium andrewsi and Hyaenodon gigas? and what size and appearance did they have? CuddleKing1993 (talk) 18:39, 4 December 2022 (UTC)