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I How much could heaviest flying animal weight?

  1. Oct 20, 2016 #1
    OK I'm not sure if I put this in right subforum.

    I remember once reading in some science book by Isaac Asimov that the heaviest any flying animal can be is 22 kg, but I read on Wikipedia that Quetzalcoatlus may weighted up to 250 kg. So how come there's such a great difference in that assumption just few decades ago?
     
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  3. Oct 20, 2016 #2

    boneh3ad

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    Well for one, Isaac Asimov was not an aerodynamicist, so I hardly believe he is the authoritative source on the matter. There is no theoretical maximum limit. We make airplanes that fly that weigh many tons, and they are less efficient than birds. The limit is how large the animal can be, because the heavier it becomes, the larger wings it needs (and the more it needs to eat to provide energy).
     
  4. Oct 20, 2016 #3

    davenn

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  5. Oct 20, 2016 #4

    A.T.

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    There is also the the issue for all big animals, that mass scales cubic, while area just quadratic.
     
  6. Oct 20, 2016 #5

    A.T.

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    Yes, but there are also debates on what kind of flight they did. Soaring in updrafts after taking off from an elevated position (like a hang-glider) is different from take off from level ground in still air. These different criteria might be the reason for the discrepancy.
     
    Last edited: Oct 20, 2016
  7. Oct 20, 2016 #6
    Less efficient then birds? Animals only have muscle power. So there is no weight limit to muscle power?
     
  8. Oct 20, 2016 #7

    Andy Resnick

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    There's a delightful discussion in Thompson's "On Growth and Form". We need to distinguish *gliding flight* from *active flight*. Larger birds (and pterodactyls) primarily rely on gliding.

    For active flying, the work required by a bird of length 'l' to fly varies as l3.5; an ostrich requires 5 times as much effort to fly than a sparrow. This is because the momentum of the bird scales as l3v and the momentum of air air deflected downwards is proportional to l2v2, where v is the speed of the bird. Setting them equal gives the scaling relationship above. Now, comparing the work expended on flying to the rate of power generation from muscles (which scales as l2v) probably gets to Asmiov's estimate

    Considering gliding flight is more difficult, because 1) it depends on the relative speed between bird and air and 2) depends on the details of the wing geometry, and wings are both movable and flexible. For aircraft, the minimum speed scales as the square root of the length- if we say the sparrow's minimum speed is 20 miles/hour, the ostrich must fly at 100 mph- and here again, birds (and flying insects) display a range of behavior, including swooping- a griffon vulture can swoop at speeds up to 180 mph. By contrast, terns have been observed to fly at 15 mph. Clearly, gliding flight accommodates masses greater than 22kg- consider hang-gliders. and sail-planes.
     
  9. Oct 20, 2016 #8
    I read 40 lb is the upper limit. The musculature to support more than 40 lb at takeoff would be cumbersome. I'm not sure of this as I have never considered the question in depth.
     
  10. Oct 20, 2016 #9

    David Lewis

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    True, but as scale goes up, wing loading can also go up: Cube loading = weight/(wing area)3/2
     
  11. Oct 20, 2016 #10

    Nugatory

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    Seems like a really big sparrow or a rather small ostrich to get just 5 times the effort out of that l3.5.
     
  12. Oct 20, 2016 #11

    boneh3ad

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    Sure there are some practical considerations, and at some point you'll definitely run into problems of energy consumption in order to fly, but since we are talking about the theoretical limit, and there is no theoretical reason why you couldn't have a 500 kg animal flying. It just probably would never evolve because of the energy/food requirements to sustain such a creature.
     
  13. Oct 21, 2016 #12
    Well there is the Kori Bustard of Africa, up to 40 pounds that can fly, but it spends most of its time walking around.
    https://en.wikipedia.org/wiki/Kori_bustard

    The 22 pounds seems to be a reference to the Albatros, which can sustain flight for days and travel 1000 of miles without doing a wing beat.
    Long wing span and use of soaring can keep it in the air with no more energy expenditure than if it was resting.
    https://en.wikipedia.org/wiki/Albatross
    http://www.dailymail.co.uk/sciencet...le-journey-WITHOUT-flapping-wings-solved.html
     
  14. Oct 21, 2016 #13

    A.T.

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    The OP states 22kg = 48.5 pounds, so the Kori Bustard is within that, and can even takeoff vertically:



    The Albatross is more optimized for long flights than quick escape, so it runs (ideally downhill) or uses the updraft at a cliff.

     
  15. Oct 21, 2016 #14

    Andy Resnick

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    It's a ratio. If the length doubles, the work increases by a factor of 23.5: 23, or 1.4:1. If the ratio of linear dimensions of an ostrich to sparrow is 25:1, the work increased by a ratio of 253.5: 253, or 57:56, or 5:1. And yes, that calculation seems to imply that ostrich flight is not much more difficult than sparrow flight- until you consider gliding.
     
  16. Oct 21, 2016 #15

    Nugatory

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    Got it - thx.
     
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