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What Scorpions Have To Teach Aircraft Designers
First time accepted submitter elloGov writes "The north African desert scorpion, Androctonus australis, is a hardy creature. Most animals that live in deserts dig burrows to protect themselves from the sand-laden wind. Not Androctonus; it usually toughs things out at the surface. Yet when the sand whips by at speeds that would strip paint away from steel, the scorpion is able to scurry off without apparent damage thanks to the unique structure of its carapace. Dr Han Zhiwu of Jilin University and colleagues have found that surface irregularities based on the scorpion's exoskeleton could substantially minimize atmospheric dust damage to aircraft."
They teach aircraft designers that "Rock You Like A Hurricane" fits perfectly at air shows.
I'm not sure but I think, not necessarily. They add dimples to golf balls to increase their flight distance and straighten their flight trajectories specifically to disrupt laminar flow, because over a sphere, turbulent flow actually can work better, if the dimples are just the right size and have just the right irregularity. I don't know for sure if it can be applied to aircraft though; maybe it only works on golf balls. Reference here.
Mythbusters did it to a car, and increased gas mileage. This was just using clay. If someone used decent materials, there is likely a huge gain to be had in performance. Of course, the surfaces on a plane NEED to interact with the air, so too much disturbance may not be a good thing.
Golf balls have dimples...
Doesn't seem to affect the flight characteristics of the F117A Nighthawk any... they use reinforced carbon-carbon laminate (which has a rough profile when the resin substrate sets) on its flight surfaces, not just for its physical properties (lightweight, immensely strong and very flexible), but also because that rough surface disperses RADAR and gives a fifty thousand pound strike aircraft the RADAR signature of a sparrow.
Operation Guillotine is in effect.
My guess would be (disclaimer: I am not an aerodynamicist) that surface irregularities of a certain size proportional to the overall aerodynamic characteristic would not affect it - much unlike the golf ball. Those turbulent areas immediately aft those dimples form a static bubble of high or low pressure (depending on the vector and position of the dimple relative to the centre of mass) which cause the desired effect. In a Stealth aircraft those irregularities are designed to not affect the aerodynamic behaviour in any way: what they do, is to reduce the RADAR signature of the aircraft, hence their size is calculated for maximum RADAR dispersion. We're talking bumps, curves and ridges of less than 1/64" high. Barely enough to detect even with bare fingertips.
On the other hand, you can make a brick fly. Look at the Rockwell Constellation series space shuttle orbiters.
Operation Guillotine is in effect.
Comment removed based on user account deletion
Actually, breaking up the surface is a well known technique for reducing drag. I know a company that makes a very finely etched plastic laminate for applying to the hulls of racing schooners specifically to reduce drag. It wasn't modeled on biomimetic material ( as far as I know) but it's the same idea.
Of course their current laminates wouldn't withstand dust. They're made for water.
John
...getting you over there.
Planes need a poison-tipped tail to fend of pterodactyl attacks. Until they get one of those they are simply flying coffins.
no, no it would NOT be cool if scorpions could fly D:
(stewardess) Just switch from Hard Rock to the Easy Listening channel.
Any insufficiently advanced magic is indistinguishable from technology.
Shark Skin is not smooth, but it has low friction in a fluid, in one direction.
I recall seeing a promo video from a company that applied such a surface to an Americas Cup boat hull.
Possibly what you are thinking of.
No brain, no pain.
When I was young a friend of mine, an aviation mechanic once told me the properties of how a plane flies. He then proceeded to say the armed forces ignore that and use the philosophy "put enough power behind it, anything can fly"
It doesn't? The F-117 can't even fly without a computer constantly making tiny adjustments. I'm not kidding either, it would literally crash if you tried to fly it manually. It's a flying brick.
The Nighthawk was still designed as much as possible like a true airplane; it's only unstable because they couldn't build a more aerodynamic stealthy shape using only flat surfaces (they used flat surfaces because the math for radar deflection depended on computer simulations, and computers couldn't do good enough calculations for curved surfaces in the late '70s).
Calling it a brick is really quite inaccurate. It had an amazingly narrow wingspan, but it's still a plane and it still produced sufficient lift to fly straight on a reasonable power budget. It wasn't stable without computer correction, but that doesn't mean it's a brick. It's not as if they simply strapped enough rockets onto a random shape to get it airborne.
There are a few types of drag, but for now let's just consider skin friction drag and pressure drag. For a smooth sphere the size golf ball, pressure drag (or wake drag, caused by the flow separation), is significantly higher than the skin friction because the surface area of the sphere is so small. The dimples introduce turbulence in the boundary layer (increasing skin friction) in order to delay flow separation (significantly reducing wake drag).
For an airplane, however, this situation is reversed. The surface area is enormous, and since the shapes of the wings and the fuselage are such that they delay flow separation as long as possible, the skin friction drag is significantly higher than the wake drag. Introducing dimples will decrease wake drag like a golf ball, but it will increase the skin friction more, causing a net increase in drag.
[snip] Ok I just scared myself into never going out again.
And if you are anything like me, that did not really change your life radically
They add dimples to golf balls to increase their flight distance and straighten their flight trajectories specifically to disrupt laminar flow, because over a sphere, turbulent flow actually can work better, if the dimples are just the right size and have just the right irregularity.
National Geographic's "Ultimate Crocodile" has a segment where the surface of a crocodile's skin is found to have similar properties. Seems that a fish's reaction time is more than sufficient to avoid a croc's bite if the fish is alerted. A cast of a crocodile head was used in a tank to measure the way water flows around a crocodile in motion, and it was proven that the bumpy irregularities on the crocodile's skin produce lower water pressure and the crocodile's body and help it maintain stealth.
I can't find the clip, but it's referenced here.
In addition to the fine qualities you listed, we Scorpios are also too smart to believe in astrology.
the Nighthawk is designed, like the F-16 Falcon, to be unstable in flight. That is what gives it the important characteristic of being able to turn on a dime hence makes it ideal for close proximity combat flying as well as improved avoidance of eg missiles, cannon shells. Such instability cannot be corrected in real time by a pilot who also has the usual other shit to do in the cockpit like watch where he's going, keep a bead on the RADAR, make flight decisions... it would be far too much of a distraction and besides, if he *could* think that fast he'd be teaching Hawking. That's why instead of a copilot they have a somewhat lighter computer dedicated to maintaining trim.
Operation Guillotine is in effect.
In this scorpion-skin situation I wouldn't be surprised if the surface drag is reduced.
Two reasons. The first is that the skin reduces erosion by the sand, which implies to me that the sand is kept away from the skin, again suggesting a thicker boundary layer, and that may decrease drag forces.
The second reason: the shark skin effect. A while ago there were these shark skin swimsuits, purportedly increasing the performance of swimmers by reducing surface drag. The shape of a shark (and most fish) are similar to aircraft in that they are highly streamlined and have little wake, making surface drag again dominant. If that works in water, it could also work in air.
Anyway it sounds like a straightforward experiment to test this: create two identical shapes (ball, wing, whatever), one with a polished surface and one with a dimpled/scratched surface, and put both in a wind tunnel. With or without sand.
Do you mean African or European sparrow?
Only dumb birds land downwind.
that's not important. A better question would have been, "What have the Romans ever done for us?"
Operation Guillotine is in effect.
My best guess: their equipment could not make it better than that.
This sounds a bit like a professor learned something interesting about how these scorpions are not affected by the sand storms, and out of curiousity tries to find out what causes it. They went for shopping in the local pet shops, got themselves a few scorpions, took samples of the armour, and went to work with that. Put it under a microscope, add UV light (both pretty standard equipment), then made a laser scan of the surface (not so standard equipment, but they likely have it for other purposes or asked another department in the university do do it for them), and then tried to recreate the surface as well as they could with their existing equipment for a sandblasting experiment.
Buying special equipment for a single experiment done out of simple curiousity is usually not worth it. You use what you have, make the best out of it, and now they have some positive, promising results that's the time to maybe find an industry partner to invest in the equipment that can make an exact replica and continue to do experiments.
at supersonic speeds (the nighthawk's max speed is only Mach 0.92, but at that speed the local airspeed over the upper surface of the wing would be transonic), things get a bit iffy. subsonic aerodynamics don't work at transonic and supersonic speeds. you get normal and oblique shockwaves, and supersonic nozzles behave like subsonic diffusers and vice versa. sharp corners produce less drag and heat than smoothly curving surfaces
Perhaps I'm wrong but scorpions, as living beings, are supposed to be able to fix possible carapace erosion, aren't they? I mean that an aircraft with an emulated scorpion surface would also be damaged in the long run. What would be really awesome is to create some sort of material with autoregenerating properties!
...and I have to admit I've never seen him suffer from atmospheric dust damage.
...if scorpions could fly.
G.
Exactly. How exactly does the scorpion using bumps on their skin to be less aerodynamic apply to airplanes? Planes already exist with "shark skin" texture to reduce drag, there was even a Mythbusters episode about it.
And why does the wikipedia article read exactly like this news story? "Androctonus australis is a hardy North African desert scorpion. Unlike Most other animals that live in deserts, Androctonus does not dig burrows to protect itself from a sandstorm. Instead, it can withstand sandstorms powerful enough to strip paint off steel, without any apparent damage."
Really? That's the best first three sentences for a encyclopedia entry of this creature? Other animals include a detailed description and locations they are found. Strange that the Wikipedia entry was created just 6 days ago.
Methinks slashdot and the economist has been duped by this "first time accepted submitter" elloGov
my karma will be here long after I'm gone
Hurm... I have a crazy idea...
Anyone have a VW Golf and a ball peen hammer they're willing to part with?
Random Thoughts From A Diseased Mind (Not For Dummies)
Aircraft designers call these Vortex Generators. Their purpose is to disrupt the laminar airflow. This helps the air streams to "stick" to the wing, improving control responsiveness and lowering stall speeds. The difference can be quite noticeable with some airfoil shapes, or almost unmeasurable in others, so one doesn't see them on all aircraft.
But what the article discusses here is NOT a vortex generator or anything of that ilk. It seems to be some sort groove that can mitigate the scratching caused by abrasives in the air stream. It might be interesting to see if such grooves could be integrated with Vortex Generators to improve not only wing performance but also longevity against abrasives, such as a dust or sand storm.
Nearly fifty percent of all graduates come from the bottom half of the class!
That's hardly scientific. Maybe the temperature changed, or the wind, or the driver's style, or whatever. One TV experiment does not good science make.
Nope, but before they did the "full scale" experiment, they did a small scale with a model car in a flow tank, with controlled temperature, and "wind" speed/direction. When they added dye to the flow, they saw that the "golf ball" car had a smaller eddy behind the car, which translates to less drag.
I agree that the Mythbusters aren't exactly a definitive scientific resource, but sometimes they actually do their due diligence and it gets cut because it doesn't make for good TV entertainment.
That being said, a divot is not the same as a bump, and the aerodynamics may be different. They do use a shark skin-like covering on some airplanes and boats to reduce drag, though, so there could still be some merit.
The surface irregularities mentioned are in microns. At that scale it's entirely possible that the research and application would involve material science to a great degree. The basic theoretical simulation work? Maybe not as much. The applied science, very much.
A fool throws a stone into a well and a thousand sages can not remove it.
http://xkcd.com/397/
you could add them starting at the transition point back on the airframe. Actually more than a few aircraft use vortex generators to already do this. It is usually a fix or is used where the extra lift is more important than the extra drag.
That is the big issue here. The last place you would want to add "bumps" to an airframe is the leading edge of the wing, props, turbines, and or rotors.
I can see the look on a gas turbine designers face now....
See my blog http://ilovecookes.blogspot.com/ for light hearted technical information.