## Saturday 22 November 2014

### The wrong farf (Tetropters VI)

I made a few animations especially for the Loncon3 convention, some of them concerning tetrop
ters (see here for the previous tetropter post). The reason was that I wanted show some of the 'flight platforms' that tetropters could conceivable evolve into. So far, there are the 'standard, 'rowing', 'helicopter' and 'farf' modes.

 Click to enlarge; copyright Gert van Dijk

These modes all have to do with the relative amount of movement in all the four ways a tetropter wing can move. The image above shows the idea: there is a general tetropter body, characterised by its vertical position, four jointed legs at the bottom and a head with sensors at the top (there is a head with smaller eyes and a mouth at the bottom end of the body, not visible here). The red, blue and green axes run through the attachment point of one wing and concern the movement of that wing. There are similar axes systems for the other wings, but these are not shown (the wings are, though, just). The arrows indicate the direction of rotation of each axes. A to and fro movement around the blue axis will result in a clockwise and anticlockwise movement. If you combine that with an up-and down movement around the red axis you get interesting patterns: the wing could describe a circle, but the most common pattern is a horizontal figure of eight. The wing moves clockwise and down, then at the end moves up quickly, so it can move down again while moving anticlockwise. That just leaves the green axis, which rotates the wing around its own longitudinal axis, allowing it to achieve the proper 'angle of attack'.

I said there are four ways to move a tetropter wing, and the fourth is not a rotation around an axis as are the first three, but warping the plane of the wing. Well, if you followed that an can envisage it, top of the class. Its more or less what you need to describe the movement of the wings of animals with hovering flight, so we are on common ground here.

I will probably come back to the other tetopter flight modes later, but let's talk about the farf mode. A farf is short for farfalla, the name the Furahan citizen-scientists gave to tetropters with a very long wing base. In fact, the image above has just such a wing membrane: you can see that the membrane lies against the vertical blue axis over its entire length. Actually, the wing membrane shown here would not be an actual one. It is just a rectangular placeholder, but is does show the principle of the thing nicely. This arrangement means that movement around the green axis cannot take place, and to get a good angle of attack the wing will have to warp considerably. If you think this scheme reminds you of a butterfly, you are right: butterflies also have wings with a broad long wing base. In fact, 'farfalla' is Italian for butterfly.

So here is an animation of a farf, made for this post, showing the placeholder wings. Not too bad, is it?

And this is the one I showed at Loncon3, with colours etc. Just about the day before I showed it, it dawned on me that I probably made a mistake in warping the wings. When the wings clap together, they have to be more or less flat, and then they should peel apart, first at the top, and then downwards towards the bottom. Well, that bit worked, but for some reasons I had also warped the wings in such a way that the distal end of the wings –that is the bit farthest away from the body- leans into the movement, so it moves before the part near the body. But the wings would encounter resistance from the air, and so the tip of the wings should probably lag behind the proximal part instead of leading it.

I do not think anyone noticed, but I also did not give the audience a long time to think about it. I will have to do another animation with the opposite effect, to see whether that looks better. But there's no time for that yet... Meanwhile, I hope you still enjoy the 'wrong farf', warped as it is.

Anonymous said...

The animations are pretty impressive, they show a lot of thought in the mechanics of the creatures you invent and the design in the last one is really neat, like an extraterrestrial butterfly. A little off topic but sense you did posts on possible leg movements of other organisms, what's your opinion on the leg moment and arrangement of the female MUTO from the new Godzilla movie? Her leg arrangement was pretty interesting though probably improbable for something that's 300ft tall (then again, the height alone is improbable).

Sigmund Nastrazzurro said...

Anonymous: Thank you. I never got a very good look at the MUTO, male or female, and the images on the internet seem to be mostly fan-based. As you said, the mass and size alone are improbable ('impossible' comes to mind). They are too large to suspend disbelief willingly, but that is a matter of taste.
Anyway, the overall shape is interesting, with the elongated wrists on the front legs and the knuckle walk. The MUTO looks rather like the animals people imagined could evolve if bats or pterosaurs were to return to a terrestrial way of life.

Anonymous said...

@ Sigmund Well you can see all the MUTO scenes here to study their movements: https://www.youtube.com/watch?v=tsy1iDIjMBQ

Another question out of curiosity, how big can an organism get in your opinion (either in earth gravity or lower gravity, say 0.5g)?

Anonymous said...

Also the MUTO's biological emp is interesting as well. Can you imagine any organism evolving that? I believe the explanation they give for the Godzilla film is that in disrupts the organ Godzilla uses to create his atomic blast.

Back on topic, can the Farfs or any of your four winged radial organisms crawl efficiently when not in flight?

Petr said...

I think the animation is fantastic, though! really well done!