Monday, 27 July 2009

Encyclopaedia of Furahan Life

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It's summer, there are many things to do, and writing this blog is not always one of them. But here is something to whet the appetite: just a preview random page of the new and great 'Encyclopaedia of Furahan Life'. Intriguing, isn't it? Mind you, at 930 pages it is not for the faint of heart. And those who have use for a coffee-table book better get themselves a sturdy coffee table.

It will be available soon through New Hades Publishers; just be warned that in backward areas of the Galaxy delivery may take up to a kiloyear.

Sunday, 19 July 2009

An experiment with digital 3D sculpting

Computers have created enormous changes in the creative arts, to the point where some artists never smell oil paints or India ink anymore, but instead merely hear the characteristic soft scratching sound of a stylus on a graphics tablet. I have not crossed over to the Digital Side yet, or at least not entirely. I am still hesitant to embrace Photoshop as the sole means for drawing and painting.

Then again, I have used computer graphics for many other things, from producing maps to depicting photorealistic planetary surfaces. The plant section on the Furaha site is in fact entirely computer-generated. I have now started using a bit of software that perhaps I should have considered much earlier. I had been looking for software to design 3D, that could then be depicted (in 2D) from any angle. The program Blender is completely free, but I found that the initial learning curve was very steep. I have now come across ZBrush, and while that has some odd quirks, it does allow you to more or less jump in and start sculpting. Mind you, it is not free at all, but at least there is a demo to play with. There are other similar programs (Mudbox), but ZBrush seems popular. Here are my very first and rather clumsy attempts to do something with it.

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The program allows you to produce a quick first outline of a shape using interconnected spheres. There are various symmetry options, useful if you want to draw two limbs at once. As you can also produce 8 radial limbs, I started drawing a spidrid (if you need information on spidrids, go to the land section of the Furaha site and select 'walking with...') . What you see above is its basic body pattern, all drawn with spheres.

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If you are happy with the spheres they can be turned into a mesh, which you can then push, distort, add to, etc., somewhat as if you are dealing with clay. And so, after some detailing, here is a spidrid in with some details added.


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Another attempt - a failed one-. The evolutionary history of 'Fishes' on Furaha needs to be detailed, so I can show the early evolutionary changes from six jaws to four, and the subsequent dwindling and specialisation of two of them, and the loss of two of the four eyes. Why not jump in with the head of a Sawjaw? (go to the water section of the Furaha site). It has four jaws. To detail their inside I needed good access, so I started working on them with the jaws in an impossibly wide gape. I then thought I could rotate them to close them somewhat, but rotation of entire body parts is something that I haven't mastered yet...

Will I be doing entire animals in Zbrush, and stop painting them altogether? I think not; I still like painted 2D images too much, digital or 'real'. There is a risk of losing vitality if uyou produce computer-generated scenes. It takes extraordinary skills to overcome that, I think. It is evidently possible to produce very detailed shapes with ZBrush, but it is something else to produce pleasing images with the result. There are people who can, and as an example I would like to draw attention once again to the work of Marc Boulay and Sylvia Lorrain: one does the ZBrush modeling, and the other does the texturing and produces the images. Here is a link to my last post on their work, and if you follow the links there, you will soon find what I mean.

Saturday, 11 July 2009

Mechanical and biological flight: heavier than air

While trying to find mechanical analogues for tetropters I stumbled upon some other technological innovations that might be transported to alien worlds as biological means of achieving flight. Some deal with heavier-than air flight, others with lighter than air. Let's start with the heavier than air designs, and leave the ballonts-like designs for another time.

On Earth, no animal has separate mechanisms for thrust and lift; instead, wings, and especially wing control, are subtle enough to combine thrust with lift. This holds for birds, bats, pterosaurs and insects, and of all these insect flight is in some aspects the most advanced, as insects can hover as well as fly forwards. Among vertebrates only hummingbirds are known to have evolved this ability. I suppose that this dual thrust-and-lift role is a typical example of biology performing much better than human creativity, and would not be surprised that advanced neural control is responsible for this superiority. But let us assume that separating thrust and lift can also work in the animal realm. In fact, I dreamed up such an animal once: the very first one I ever did on Furaha, in fact, Here it is: it has never before been shown on the site, and it is only a fragment of a larger painting.

Furahan Propulsor mechanicus

Its scientific name is 'Propulsor mechanicus', and I have forgotten its common name (a 'zummer'?). What you can see is that its front pair of wings does not flap, but the hind pair flaps very energetically, and provides thrust on the upstroke as well as the down stroke of the wings. As such, these wings are very much like an insects' wings in hovering flight, but rotated 90 degrees so the thrust is directed backwards instead of downwards.

Mechanical flying machines nearly always have a separation of thrust and lift, and most thrust mechanisms cannot be used as an inspiration for animal flight, as there are rotary parts involved. But people have been trying to design working 'ornithopters' for ages, and some of these are interesting.


video


For instance, the video above show a design wing a large lifting immobile wing, and two hind wings that provide thrust. The source is here. The two hind wings flap up and down rather like the fluked tail of a whale, but where a whale has only one tail, this design uses two such tails, one above the other. According to the text they flap in counter phase to provide balance. The design reminded me a bit of the Uther design for the Epona Project, if I understood correctly how Uthers were supposed to move: Steven Hanly once told me that the animation shown on the BBC documentary that you can find in an earlier post was not at all what he had in mind.

Eponan Uther by Steven Hanly

Uthers, one of which is shown here, have a large unpaired hind wing, and I think it provides the thrust while the paired front wings provide lift (Steven, please jump in if I got this wrong!).

If we leave the separation of thrust and lift behind, we can move on to more typical biological flight, in which each wings has both functions. But even then there are some interesting machines to be found. The typical body plan of a Furahan 'avian' involves a tetrapterate design with two paired wings. Some of you may have noticed that the first pair may overlap the second pair slightly, but in others, the two pairs are placed very far apart. he two images that follow illustrate the two variants.

Furahan Bulchouk

Furahan Seasoar

The idea behind the overlapping design was taken from sailing boats, in which sails that partially overlap work together to improve the boat's ability to make use of the wind. In aircraft 'canard' wings function similarly. I thought the same could be done with animal wings, hence the design. The other design also seemed fairly straightforward to me, in that the two pairs of wings allow great flexibility in how they are used: in unison or separately. I found ornithopter designs that I had never considered though, in which the two wings of one pair do not move up or down together, but instead one moves up while the other moves down. I do not think I like it, as this movement would cause asymmetrical stresses that seem impractical. Do not expect any Furahan animals to use this mode of flight. Still, people have built designs along such lines, and here is one:

video

This copy was taken from YouTube, but a much better quality can be seen on this page on the 'Entomopter' , which also shows a variant designed to fly on the planet Mars...

I will end with a design that I had not thought about and that I do find appealing. Take a tetrapterate avian like the bulchouk above, and move the first pair of wings even further aft so the two pairs are above one another. My first thought is that they would be in one another's ways, and they would. Still, if one pair moves up while the other moves down, you get a 'clap' effect, and those appear advantageous. In one of the previous posts on tetropters and micro air vehicles, two designs use exactly this type of wing plan: the Delfly and a Japanese design. Have a look again here; perhaps that is a design that one day will take to the skies as a fictional avian.

Saturday, 4 July 2009

"Go, tetropters, go!", or, "Tetropters III-bis"

Originally, I had wanted to include the following material in the previous post, but I could not get hold of the material in time. What I am referring to is a paper in the 'Journal of Aircraft' by Zdunich P, Bilyk D et al., entitled "Development and testing of the Mentor flapping-wing micro air vehicle" (J Aircraft 2007; 44: 1701-1711).

In the paper, the author describe the development of the Mentor air vehicle and elaborate on the radial 'body plan'. They did not use those particular words, probably because they did not have biological mechanism in mind. The text makes it abundantly clear that the two pairs of wings beat against one another and use the 'clap-and-fling' effect. Here is a quote from the paper (I omitted references):

"In 1998, however, the primary source and inspiration for the Mentor's configuration came from the "clap-fling" hypothesis of Weis-Fogh, which was developed by observing the behavior of small hovering insects. It was found that they produced extraordinarily high values of average lift coefficient, which was well beyond any explanation based on attached-flow aerodynamic theories. The hypothesis, based on observation of the wings' kinematics, was that the two wing surfaces clap together and then peel apart starting at the leading edge. At the instance just before the trailing edges come apart, both wings have strong equal and opposite bound vorticity. Further, because the trailing edges were joined during this peeling action, the strength of the vorticity is much greater than that produced from Kutta condition considerations. As the wings fling apart they carry this "super circulation," which thus produces a high value of lift."

J Aircraft 2007; 44: 1701-1711; Click to enlarge

Here is a computer sketch of the vehicle. The wings are at the top, and the three blades below are control surfaces.

The authors did some proper preliminary experiments as a proof of principle. The most important such principle was that the clap-fling design indeed augmented lift. To do so they clamped their wing set-up to a lab bench and measured how much thrust it provided. They did this once with the complete wing assembly, i.e., the two pairs moved to and fro produced the double clap and fling movement. They then repeated the experiment with just one pair of wings moving back and forth. These wings obviously had nothing to clap against, thereby eliminating the clap-and-fling contribution to thrust. Thrust was of course less because there was only one pair of wings in this particular experiment, but that was easily solved by doubling the measured thrust value. A comparison shows how much the clap-and-fling effect contributes:

J Aircraft 2007; 44: 1701-1711; Click to enlarge

The resulting graph shows that the thrust-to-power ratio is higher at all wing beat frequencies if there is a clap-and-fling effect than if there is not. Well, that settles that! I will stop discussing the tetropter wing design now, as I think the case has been proven. Future posts may deal with some other intriguing flight designs I came across searching for 'micro air vehicles'. These could well be used for alien life forms.

But I cannot help adding a final remark, even though I may be accused of vanity. The quote above makes it clear that the design of the Mentor took shape in 1998. I checked my Furaha design sketch book for the first sketches of tetropter flight plans. I had worked out three 'gaits' producing different amounts of lift, tilt and rotary effects over each wing cycle, and remember settling on the one discussed here because it balanced all these effects nicely. The page dates from April 30, 1996. Perhaps there are others who came up with such a design earlier, but for now, I like to think that I was the first to design a radial body plan using a double clap-and-fling with a vertical axis. I need a snappier name for that. Anyway, I doubt that this invention will make me a millionaire...