Monday, 3 January 2011

Nereus (or how you can have radial flight with an odd number of wings)

As regular readers know, I am always on the lookout for creative projects concerning speculative biology. On places like Deviant Art you will find many interesting alien or alternate animals. Some feature new traits, others rework well-known themes; some are professionally drawn, others are less so. But what interests me most if there is a background: are there biotopes, is there a food web, do the predators match the prey, etc. That shortens the list considerably.

Some large projects have been in existence for very long times, and it does not feel entirely right to discuss them here. But there is one project, Nereus, that is relatively new. Its creator, Evan Black, does not mind, so that helps. Apparently Nereus received its name because humans first thought it was a water world (Nereus is a being from Greek mythology). The earliest post on the Nereus project on the Speculative Biology forum dates from May 2009. Evan has already produced 100 species and aims to achieve no less than 200 species. That is a lot or work: creatures have to be designed and described, and also drawn. I like the way Evan draws animals: while a bit stylised, they are very energetic, and as design they work: what you see are lively animals.

Click to enlarge (VERY much so!) Copyright Evan Black

Here is a start: a rather large cladogram of current Nereid species. Don't be surprised to find that the one on Evan's site differs from the one here, because he might have added a new species by the time you go there...

The Speculative Evolution pages contain discussions and comments on how Nereus develops, but I much prefer to see the result on Evan's own site. There, you can work your way through the menu, clicking on the Latin names of the various groups until you get to individual species, but you do not see what you are aiming for until you get to the species pages. Once there each species has two pages: one with text and a thumbnail, which leads to a much larger image with additional text. But there is another way to browse Nereus that I much prefer, and that is to choose 'world', and then 'cartography and climates'. That will take you to a list of 7 biomes, and clicking on them rewards you with an overview of that biome and small images of the species in it, that you can then pick and read at will.


Click to enlarge. Copyright Evan Black


As an example, here is the 'Sog Basin'. Sog "carpets the landscape like a thick tangle of spongy red veins", which sounds a bit like Well's Martian weeds. Luckily, there are no intelligent aliens around to regard Earth with envious eyes (or not yet). Sog sucks up water from the few available sources, and transports it across the otherwise dry biome. Leaks in the sog create watering holes, on which many species depend. Now that is why I prefer creations with a background: you immediately start to think how that works, how such species might look, etc.


Click to enlarge. Copyright Evan Black

Here is one such species: the kappa (Nothorana pratensis). It is a predator lying in wait in sog ponds, with just its dorsal eyes and its nostrils above the water. Take a good look: the kappa has three legs: two paired front ones and one unpaired jumping leg in the back. The illustration also contains a classification list containing the familiar Linnaean scheme, which starts at the species level and goes all the way up to the phylum Tetrabrachia (that would be 'four arms', if I remember my Greek correctly). One of the nicest things about Nereus creations is that it all fits together. Look up the Tetrabrachia, and you will find a page devoted to their anatomical Bauplan.


Click to enlarge. Copyright Evan Black

And here it is. The four arms in question concern four major nerve trunks emerging from the central brain. One trunks goes upwards, and that one deals mostly with sensory functions, which in modern Tetrabrachia has caused them to develop a head. The other three trunks control movement. In effect, what we are seeing here are radially organised animals, and I like the idea of taking radial animals rather further than they have managed to do on Earth (see the discussion on tetropters here, here, here and you can more on tetropters yourselves; here is something about radial symmetry; if that is not enough, just search for spidrids on this blog). But the kappa does not show radial symmetry; it is blatantly bilaterally symmetrical, and the legend includes information just when that happened.


Click to enlarge. Copyright Evan Black

I cannot resist showing one particular specimen, and that is because Evan and I discussed its s flight mode. Again, this is a radial life form. Most flying forms on Nereus are bilaterally symmetrical, resulting in flight plans that are superficially similar to the ones on earth. Not so the Cliff Whistler (Cadosmilos Aetopsis).


video

As you can see, it flies a bit like my tetropters. The tetropter discussions may have helped inspire the Cliff Whistler, which is flattering. Anyway, the Whistler flies by beating its three wings horizontally to and fro. Diehards out there may remember that I made extensive use of the 'clap-and-fling' principle to explain tetropter flight. The 'clap' involves two wings beating against one another at the end of their movement, then sweeping back to the other end of their range, where they then clap against another wing. Etcetera. That works with two wings (Terran insects and some birds), four wings (Furahan tetropters) and would work with more wings too, although no-one has yet invented any of those yet as far as I know. Besides offering increased lift through 'clap-and-fling', an even number of radial wings neatly solves the problem of torque: if a wing moves clockwise it pushes the body counter clockwise, which is useless. With two or four wings these forces even out.

Three-winged radial flyers run into problems. There is no clap-and-fling mechanism, and the wings move in unison: all three clockwise, and then all three counter clockwise. That leaves torque to be solved. Well, evolution, in the form of Evan, designed an adaptation of the Whistler's mouth parts at its bottom: these evolved into winglets beating in the opposite directions of the main wings, countering to a degree. Enough for the Cliff whistler to be a viable organism, or so Evan and I thought.

Recently I came up with a way to have a clap-and-fling mechanism with just three wings though. It would increase lift but introduce some new problems. Again, Evan and I thought that it might work, but not necessarily better than the Cliff Whistler approach. Perhaps one species will emerge on Nereus with this particular mechanism, we would have to ask Evan. I am not going to tell you how it works, merely that it can be done: each of the wings A, B and C claps against another wing on the extreme ends of its movement range. I wonder if anyone will take the bait...

9 comments:

j. w. bjerk said...

"Recently I came up with a way to have a clap-and-fling mechanism with just three wings though. It would increase lift but introduce some new problems."


As far as i can figure it out, with an odd number of wings you would have to do one (or both) of the following:

* give the different wings each different ranges of movement (I.E. one might move through 160º, while another 80º)
* make different wings move at different speeds, at different times.

Most plausibly (i think this is the one you thought of), is that one wing would move right and left at a constant speed, while the other two would switch between double speed or half speed at alternating times.

My intuition is that this (especially the first) would have dire aerodynamic repercussions, but i'm no aerodynamic expert.

I had thought about this problem before and come to no remotely satisfactory solution... but since you said there was a solution i had to try again.

tentaculus said...

Fantastic. Absolutely fantastic. Many, many thanks for sharing.

I suggest you to check out Purple-Plasmid's gallery in deviantart, if you haven't seen it yet.

http://purple-plasmid.deviantart.com/gallery/#Fentil

Evan Black said...

Thanks guys for your comments, and thanks Gert for the blog post! My website has had so much attention: more in the last month than in the year before!

A solution for three-winged flight that came to my mind involves the wing going faster in one direction than the other. This introduces stability issues, but perhaps not beyond what life forms can handle.

I've seen Purple-Plasmid's work as well. I'm very impressed with it.

Sigmund Nastrazzurro said...

Evan: my pleasure! Your message reminded me to respond to J,W.'s solution for triradial clap and fling. I wanted to wait for more responses and was then sidetracked... Sorry.

I will just repeat what I wrote to Evan a while ago. It seems that all three of us thought of the variable speed solution: "The trick proved to be simple: in my designs so far, the clockwise movement of a wing took just as long as its counter-clockwise movement. A wing's movement cycle is therefore divided into two halves. Say a cycle starts at 0 degrees and ends at 360 degrees, then the two points where the wings are at their furthest positions are 180 degrees apart. Where you start the cycle is arbitrary: suppose you define one clap position, the furthest in the clockwise direction of a wing, as occurring at 0 degrees, then the other clap position at the counterclockwise point will be at 180 degrees in the circle. All other wings will have to conform to this. This only works if there is an even number of wings. Now for a triradial design. Suppose it takes a wing one third of a cycle to move in the clockwise direction between the two clap positions, and two thirds of a cycle to move back in the counterclockwise direction. Do this for all three wings, and you will find that there will be claps at 0 degrees (wings 1 and 2), 120 degrees (wings 1 and 3) and 240 degrees (wings 2 and 3).
Is this a better solution than we one we had? I do not know really. Claps do not occur synchronously, but instead occur at intervals, and each clap would unbalance the beast a bit. What you would also need is to try to make the wing generate as much lift going one way as the other, even though it takes twice as long to do so (angle of attack?)."

Next weekend: my first digital Furaha painting will be revealed..

Evan Black said...

Digital painting? Awesome! I remember seeing one of the head of a centauroid you did some time back. I can't wait to see more!

Sigmund Nastrazzurro said...

RECTIFICATION

I was browsing and came upon one of Evan's comments from one year ago, on a post even older: http://planetfuraha.blogspot.com/2008/04/tetropters.html

On rereading that, it is perfectly clear that Evan had designed the 'differential speed' solution for odd-winged clap and fling flight at the time. I must have forgotten that, and when I sat down to attack the problem a year later, I thought of the same solution. Hidden memories? Independent thought? I honestly do not know, but credit where it is due: Evan thought of it before I did.

Evan Black said...

I had completely forgotten I had said that, so can I really claim anything? :)

In any case, I think the option is viable, and I may just implement it in a future species, but don't let that stop anyone from trying the idea out as well...

TalahRama said...

Nereus animals looke like pokemons.

Andrew Broeker said...

Wouldn't the walking gait from your page on cloakfish work with an odd number of wings?

Also, if the movement is totally sinusoidal with evenly arranged phases then you get no net torque on the body before considering aerodynamic effects, much like three-phase AC power.