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I know it sounds kinda stupid, but I’m trying to create a really ominous figure that would always watch the player in this a hypothetical video game that I’m writing with my dad.

We both agreed that having a huge 3 headed mechanical bird with a dead city on its back would be pretty creepy. The hypothetical bird would have a wingspan of about 160 miles (which is the size of Vermont from north to south.), it's sorta like Vah Medoh from The Legend of Zelda: Breath of the Wild, but instead of using propellers, it would flap its huge wings.

My question is, would this thing even be able to fly? And if not, does the “rule of cool” kinda help suspend the player’s disbelief?

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    $\begingroup$ As a rule of thumb, if you want to make a physically realistic huge airship, your only real option is a lighter-than-air vehicle (because in that case, the square-cube law actually works in your favor). $\endgroup$ – Kevin May 10 at 16:09
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    $\begingroup$ Note that ultimately, the weight of a flapping creature will be transferred to the air and then the ground. A sealed box with a bird inside, for example, will weigh the same whether the bird is sitting on the bottom of the box, or flying midair and not even touching the walls - the wingbeats force air downward, which hit the bottom of the box with the same force as the weight of the bird. Being underneath this behemoth will likely be catastrophic for the local environment. $\endgroup$ – Nuclear Hoagie May 10 at 18:26
  • $\begingroup$ The "rule of cool" works fine if you're routinely using it to justify worldbuilding decisions in your game, i.e. nothing even has the pretence of trying to obey the laws of physics. If everything else in your story is science-based then it would be harder for people to ignore that this one thing is obviously physically impossible. $\endgroup$ – kaya3 May 10 at 19:31
  • $\begingroup$ @kaya3 Although, I've also seen stories told where everything is pretty realistic except one standout oddity that never gets an explanation. $\endgroup$ – Devsman May 12 at 15:19
  • $\begingroup$ @Devsman Sure, my point is just that if it's one thing then readers are more likely to think it's lacking an explanation, whereas if it's everything then they wouldn't expect one. $\endgroup$ – kaya3 May 12 at 16:19
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NO.

Not by flapping wings, that's for sure.

Problem the first:
Flyable air only goes up from the surface a short distance. Let's be extremely generous, and call this 10 miles.
Your bird has a wingspan of 160 miles.
If it flaps its wings more than 1/16th of their span, it slams them into the ground! 1/16th, that is barely a wiggle, not a flap.

Problem the second:
Wing lift is roughty proportional to the surface area of the wing, which scales as length * length.
Weight, which needs to be countered by this lift to be able to fly, scales as length * length * length.
It is the old square-cube scaling law that always comes in to bite larger creatures.

If your creature could fly close to the ground for ground-effect lift, and use not flapping but some system that moves air from above its wings to below them, you have a chance. In effect, you are then making a huge (really huge) hovercraft.
Unfortunately, the end effect will not be very bird-like! Rather it would appear as the dust-storm to end all existence, and will leave a trail of devastation behind it.

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    $\begingroup$ Problem the third: moving its wings fast enough to produce any noticeable lift would require the tips to move at speeds that would far exceed any reasonable material properties. $\endgroup$ – Matthew May 10 at 13:50
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    $\begingroup$ Note that ground effect is normally said to start taking effect when you are within one wingspan of the ground. I don't know if this rule holds up for massive wings like these, but if it does, then even flying 10 miles up would still make it a ground effect vehicle. $\endgroup$ – Charles Staats May 10 at 14:40
  • $\begingroup$ Your comment about the depth of the atmosphere reminds me of XKCD (as so many things do.) $\endgroup$ – Michael Seifert May 10 at 16:50
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    $\begingroup$ However, the square-cube law can be overridden if the bird is rude and mean enough. That's how Canada geese manage to fly. $\endgroup$ – Harper - Reinstate Monica May 10 at 19:42
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The lifting power of an airplane grows with the surface of its wings, so roughly with the square of its dimension.

The mass to be lifted instead grows with the volume of its body, thus with the cube of its dimension.

At a certain point, all the rest being the same, the mass will grow more than the surface providing lift.

The above, known as the square-cube law, already hints that it's unlikely such a thing can fly. Then you are topping it with

  • having to carry a city on its back (it disrupts air flow, thus wing lift, and adds weight)
  • having to constantly follow the player, who I suppose is walking (thus low fly speed, meaning low lift).

This thing sounds very implausible, unless you sprinkle generous amounts of magic all around.

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  • $\begingroup$ You could get around the square-cube law by having a very thin pancake-like bird. Basically a giant sky manta ray. You'd have to be careful if you want to make it imposing, rather than hilarious, though. $\endgroup$ – kaya3 May 10 at 19:25
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would this thing even be able to fly?

Yes, why not? It depends on what you mean by "flapping its wings". The useable atmosphere is not very thick, and it's actually way thinner than the wingspan.

Also, the wing beat has a relationship with lift and obviously with the maximum air flow - which is air speed - which needs to be infrasonic. And the sonic barrier is just around 340 m/s; irrelevant for even the largest birds, but very relevant for your behemoth.

To fly, the construct would have to flap the forward edge of its wings, creating an overpressure that would then be maintained by the rest of the wing, which would be stationary. It would then "float" over this air cushion. So, it's not a bird -- it's a hovercraft. And being beneath it wouldn't be an experience to recommend.

Another possibility would be if the wings are selectively permeable - and at that point they're not "wings" but more like drone-wings, just with flutterers instead of rotary propellers. They gulp air from above and eject it from below. Wing movement becomes largely irrelevant (it could be synced with the fluttering, so more of a ripple than a wingbeat).

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Maybe, if the lift isn't from flapping its wings.

While the square-cube law would likely prevent a naive scaling-up of bird wings, it might be possible for such a thing to fly if it has some other form of propulsion. While you have indicated that you don't want propellers (and presumably you wouldn't want similar methods of propulsion, such as jet engines), there is one possible method of propulsion that would take advantage of having a large wing area: electromagnetic thrusters.

Put simply, if the wings are electrically charged, it would be possible for them to ionize the air around them, and then thrust it downwards using magnetic fields to generate lift. Of course, lifting such a large structure into the air would consume a massive amount of electricity, so such a construct would require a very beefy power plant on board. Exactly how much energy it would require is beyond my ability to readily calculate, but perhaps a nuclear power plant would suffice.

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Since it's a mechanical bird, it doesn't have to be built or fly like a biological one. Instead, build it like a huge parade float in the form of a bird. The square-cube law works in your favour here, at that size, you don't even need helium, just warm air like in Buckminster Fuller's Cloud Nine.

Give it a back plate stable enough for a city, and slap on some propulsion (wing flapping won't really work at that scale for reasons explained in other answers, but part of the wings could maybe undulate); it won't be a surprise that the city is dead, though, since it will be far to high up to have a breathable atmosphere.

Also, it wouldn't so much "follow the player" as "completely darken the sky from horizon to horizon".

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