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Flying Robots Made From Cellophane?
Roland Piquepaille writes "Researchers have discovered that ordinary cellulose is a piezoelectric and smart material that can flap when exposed to an electric field. ScienceNOW reports that electricity can give life to cellophane. When you put a very thin layer of gold on each side of cellophane, and that you apply electric current to the gold layers, one positive, one negative, the cellophane curved toward the positive side. If you switch the voltage fast enough, the cellophane starts to act as a wing. So it should be possible to use it to build lightweight flying robots carrying cameras, microphones or sensors for surveillance missions. Read more for additional references and pictures about this electroactive paper (EAPap)."
Cellophane isn't piezoelectric. It is just very amenable to carrying a lot of static charge, which is what is being employed in this case.
I am becoming gerund, destroyer of verbs.
Piezoelectric speakers are nothing new, but I don't think cellophane would have any advantages at all over the ceramic materials used currently. And as for electrostatic speakers (which is what I think you're referring to), they don't use a pizoelectric effect, so I don't think this would have any relevance there.
Oh no... it's the future.
Are not piezoelectric and do not use cellophane.
They work by putting an electrostatic charge on a mylar sheet, which is close to what the GP poster said.
And what you call cellophane wrap is not made of cellophane (or cellulose). It's regular petrochemical plastic based.
Cellophane (both wrap and tape) hasn't been in households for a long time now, at least 30 years.
http://lkml.org/lkml/2005/8/20/95
http://www.moller.com/skycar/
"The avalanche has already started. It's too late for the pebbles to vote." - Kosh
>An airplane wing does not produce lift because it is angled downwards,
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>it generates lift almost purely because of its shape.
Actually, you are quite mistaken.
I am an aerospace engineer. I have a BS in Aerospace Engineering and 16 years experience conducting flight test on a dozen aircraft ranging from Cessna- to 707-sized. I have also published papers on the process.
A wing produces lift according to this basic equation:
Lift = 0.5 * Coefficient of Lift * Density of the Air * Wing Area * Airspeed squared
This includes a few approximations since I can't type various symbols in plain test. You can look at the properly written equation here: http://www.aerospaceweb.org/question/aerodynamics
Coefficient of lift, part of that equation, is itself a direct function of Angle of Attack - the angle at which the chord of the wing meets the air. ("Chord" is defined, roughly, as a line between the front and back edges of the wing.)
The wing curvature, or camber as you correctly call it, is a contributor, but far from the only one, to the equation of lift coefficient versus angle of attack. A flat, or non-cambered, wing will produce zero lift at zero angle of attack. Increase the camber, up to a point, and you increase the lift at zero angle of attack. Or you can increase the angle of attack at zero camber to increase the lift. For that matter, you can spin a cylinder in an airflow and generate lift - zero camber, zero angle of attack (it's a circular cross section, so there's no angle!). So there are MANY factors influencing lift - any combination of these is possible; you just need to select which ones are most beneficial to a given design requirement.
As a matter of fact, the first documented equation to describe lift included only angle of attack and speed. It wasn't until decades later that careful observation of bird wing structure revealed the importance of camber. There's an intriguing story here about the Wright brothers and their development of the theory of lifting bodies, and how they overturned decades of established wisdom: http://www.first-to-fly.com/Adventure/Workshop/li
In a very simple and small wing (like most insects, which obviously can fly), it's almost ALL angle of attack, and no camber. Consider a dragonfly. The wings are perfectly flat. And the creature must create not only lift but also forward thrust with those wings. Quick and repetitive motions (as mentioned in this article) are perfect for this requirement. Camber has nothing to do with it, and camber, in fact, would impede the dragonfly, because the wing must also be capable of generating lift while moving backwards - and any effective camber is usually detrimental while going backwards. Finally, in the case of insects, the qualities of air are different at small scales (the so-called Reynolds Number effects) and lift operates somewhat differently from in large airplanes.
Consider also a dime-store balsa wood glider. In its cheapest form, the wing is completely flat. Yet it flies just fine. Or consider the paper airplane. It flies just fine with a slab of paper for a wing.
In short, you can take this article at face value regarding simple wings and lift. There are other wishful comments, but the aerodynamic description is quite fine.
--Brandon / Split Infinity Music