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NOTE: I previously asked the same question regarding wheels, because I thought that the answers would still help me and that wheels were more applicable to a wider audience than propellers. However, I deleted it after realizing it was a duplicate. I should've just asked my original question, since biological propellers have been my goal from the very beginning. After searching, this post is the closest thing to a duplicate I managed to find.

What the heck do you mean, Anatomically Correct Propellers??

So I've been playing around with the idea of biologically evolved propellers for a while now. I got the idea from the Peahat from the Legend of Zelda series of video games.

Is there a way for a biological creature to evolve in such a way that they have 'propellers' that allow them to fly around?

One problem would be that the spinning of the propellers would pull on muscles and ligaments until they tear. Think about what happens upon accidentally getting a wire or string caught in something that spins: it just pulls and pulls until the wire or string wraps around the mechanism completely, making it much harder to unravel. Sometimes it will even cause damage to the materials involved.

For this question, "propeller" can refer to any body part or body parts capable of moving in a circular fashion and that meet the requirements listed below:

  • Body parts must spin to achieve enough lift to fly (no vertical limb movements)
  • Must not damage the ligaments, muscles, or any body tissue. This includes damage from heat due to fast movements.
  • Back-and-forth movement is allowed, but it somehow must meet the above two conditions
  • The propeller should be biologically connected to and part of the organism.

Upon doing some basic research, I learned that the structure found in some single-celled organisms, the flagellum, is the closest thing we have to this. I'm looking for a large enough organism that could be seen without a microscope or magnifying glass. This range could be anywhere from small and bug-sized to the size of an elephant.

How might an organism evolve 'propeller-like' body parts that are capable of similar mechanical movements and allow flight?

My current idea involves having several flat "arms" at the top of the organism that can spin around for several revolutions. They tilt like helicopter blades to provide lift and boost upwards, and then straighten out to spin backwards and return to their original position to begin the process once again.

This is a new spin on the Anatomically Correct Series. Just roll with it, it's your turn now.

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    $\begingroup$ If you take out the 'biologically connected' component, it'd be easier. A full 360 revolution isn't easy. It'd be a lot easier if something that was formerly biological and not connected was used instead - something like an animal's horn, for instance. $\endgroup$
    – Halfthawed
    Oct 23, 2019 at 20:25
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    $\begingroup$ Surprisingly, is is easier to make a spinning propeller than a spinning wheel. In fact, it is quite easy to make a continuously spinning propeller. You can do it too! Put your arms in front of you as if your elbows were on a table, and the the forearms extend horizontally in front of you, with the hands palm down and their axes bent outwards. Now rotate your hands in a continuous motion, with the wrists still and the hands trying to move along the surface of a cone, with the right hand moving clockwise and the left hand counterclockwise. $\endgroup$
    – AlexP
    Oct 23, 2019 at 20:27
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    $\begingroup$ Imagine that you are in a corridor, facing along its axis. Extend your arms sideways at the height of your shoulders. Now begin to rotate your arms so that your hands move along the circumference of two big circles painted on the walls of the corridor. Hey look, you have two arms that spin! $\endgroup$
    – AlexP
    Oct 23, 2019 at 20:35
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    $\begingroup$ @AlexP The joints themselves are the not-easy part. They tend to be fragile compared to other joints, and the OP wants it to be capable of flight. Any circle I can describe with a body part can be done maybe a few times per second, and it starts hurting at that point. Flight capacity needs that to be higher. $\endgroup$
    – Halfthawed
    Oct 23, 2019 at 20:47
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    $\begingroup$ @AlexP the problem is that joint is not rotating 360 degrees, not even close, it spins about 180 degrees than has to counter rotate to keep from tearing all the ligaments and blood vessels off. That is not rotation, that is circumduction which is very different mechanically. Your not talking about a propeller, you are describing a poorly utilized tentacle/tail. $\endgroup$
    – John
    Oct 23, 2019 at 21:06

3 Answers 3

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Simple answer:

Two organisms in symbiosis.

Organism one serves as the body of a biotic airship. It would sprout one (or more) woody or bony protuberances the knobby ends of which serve as a universal joint for the biotic propeller.

Organism two serves as the propeller itself. It comprises a woody or bony "bowl" which grows over the protuberance of organism one. Its many limbs serve to support the propeller and also to drive it around its axis.

The joint space between the two organisms is composed primarily of water with mucus components. Robust mucus secreting pads keep the two organisms from chafing one another while allowing for a rapid spin velocity.

This solves the impossibility of a biological wheel being part of a single organism and also gives you true 360deg rotation without stressing or tearing the tissues.

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  • $\begingroup$ You have a rotary joint. Where is the motor? $\endgroup$
    – Vogon Poet
    Oct 23, 2019 at 21:43
  • $\begingroup$ @VogonPoet the shoulder is NOT a true rotary joint. I have extensive, and very painful personal experience with what happens when you try to put a shoulder through an actual 360 rotation. TLDR: It doesn't work. $\endgroup$
    – Morris The Cat
    Oct 23, 2019 at 22:04
  • $\begingroup$ Oh I do know this! Did I say shoulder? $\endgroup$
    – Vogon Poet
    Oct 23, 2019 at 22:08
  • $\begingroup$ @VogonPoet: The motor is also the propeller: It has May limbs it can use to ‘run’ in a circle. Energetically speaking I think it’s a bit on the ludicrous side, but at least the propeller spins! $\endgroup$
    – Joe Bloggs
    Oct 23, 2019 at 22:18
  • $\begingroup$ It all depends on how massive the organism is, energetically. Better have some lightweight bones! $\endgroup$
    – Vogon Poet
    Oct 23, 2019 at 22:20
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Nature has done this with the flagellum on some bacteria and archeae but your probably looking at an eukaryotic flagellum.

But at the scale of a macro-organism friction will make this impossible, as well as providing nutrients to connective tissue. The most practical design is a flailing jointed appendage. Think of Thor spinning his hammer to fly. It never rotates, just spins around. But even this will create quite a bit of friction, it happens to be the best option however.

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There are only two ways.

You can't have a contiguous cellular mass that freely fully rotate, so there is only two solutions it is not contiguous, which is covered quite well by Elemtilas's answer, or it is non cellular.

The propeller itself is an excreted acellular material like a pearl, they will need to be grown separately then moved into position on a shaft of some kind , something like a horn. Then you need something like a foot or series of feet that "walk" along the propeller, turning the propeller. The problem is this is breathtakingly inefficient.

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