just suddenly struck by curiosity, i vaguely remember that big quadrupedal or hexapodal (if you count the wings) animals cant fly well basically. I dont remember why, but i think it was related to aerodynamics but correct me if i am wrong.

so i wonder: what if the limbs were retractable like a turtle's head or limbs, with either all 4 limbs or just the two front/back ones being retracted during flight (though honestly I'd prefer if only two limbs were retracted)

Is it a possible biological or anatomical solution, or would it still not fly well?

if it possible, would be helpful to include images of how it could look like or about the biomechanism.

and basically this is a monster so their size ranges from pteranodon to Quetzalcoatlus.

i imagine they'd run with the four limbs to gain leverage and then retract the limbs while flying.

Feel free to edit my grammar and the tag to the appropriate one, (though i appreciate it if this is not removed when you edit it, give others a chance to know that they are welcome to fix or edit this, if theres still some mistake left.

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    $\begingroup$ The main issue here is not just about aerodynamics, it's about weight. The bigger a creature the harder it is to fly due to them needing more lift, meaning more muscle, meaning more weight, and even more lift will be needed. That's why pterosaurs like those you mentioned have hollow bones and lost their beaks and teeth, to become lighter. To add extra limbs for ground locomotion means a large amount of extra weight, making powered flight a much harder job. The biggest limitation isn't about being aerodynamic, it's about having enough strength to support yourself in the air. $\endgroup$ – ProjectApex Apr 23 at 18:01
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    $\begingroup$ Is the flying monster on Earth? Lower gravity or higher air density would both make this a little more plausible. Another option would be a gliding monster that can flatten its body into a lifting-body type shape, perhaps also with some membranes like a flying squirrel. But powered flight on Earth for anything large would be really hard to explain. $\endgroup$ – Dan Hanson Apr 23 at 18:59
  • $\begingroup$ @DanHanson yeah Earth like with same gravity and atmosphere $\endgroup$ – Li Jun Apr 23 at 19:00
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    $\begingroup$ Insects have six legs and four wings and fly very well. $\endgroup$ – AlexP Apr 23 at 20:06
  • $\begingroup$ @DanHanson no gliding (just seeing your edited comment) $\endgroup$ – Li Jun Apr 24 at 4:07

Once the limbs are retracted, assuming they are retracted in a way that does not reduce the monster's aerodynamics, the what's more important is if its weight can be suppported in flight.

The Argentavis is the largest flying bird to ever exist, with a height of about a person (1.8m) and a wingspan of about 5-6 metres. According to its Wikipedia page,"The ability to fly is not a simple question of weight ratios, except in extreme cases; size and structure of the wing must also be taken into account. As a rule of thumb, a wing loading of 25 kg/m2 is considered the limit for avian flight."

Therefore, as the monster will be heavier due to the extra limbs, the wingspan must be larger. This is increased by the fact that the monster will most likely have non-hollow bones, especially if it is a big monster designed to do damage and withstand some force.

The way in which the limbs can retract is also an intresting point! Cavities that they retract in to is probably not possible if they are going to be running, so maybe there could be channels along its front/side that they could lie flat in?

Hoped this helped!

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In order to retract its limbs like a tortoise, it would need tortoise-like limbs, which would be unlikely to evolve into wings. However, it may actually be more plausible for a flying quadruped to have tortoise-like forelegs than to have regular forelegs, as the wings would be able to be where the forelimbs should be. Furthermore, a large flier would need to walk using its wings, as if it walked on just its non-wing legs, it would need more muscular legs to support the wing, whereas if it walked with its wings, then only the wings must be muscular. Also, pterosaurs had a system of air-sacs, which allowed them to become lighter and achieve their large size. This could most likely exist in your creature, as the foreleg's shoulder girdle would be directly beneath the wing's shoulder girdle, which would keep the creature balanced.

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