Could a very high surface area cape sufficiently slow a descent?

[wierdaaron]

We've heard of (http://www. technologyreview.com/advertisement.aspx?ad=computing&id=56&redirect=%2Fcomputing%2F21990%2F%3Fa%3Df) Gecko Tape, right? Rather than using some kind of chemical adhesive, it uses the same properties of a gecko's feet: it's covered by zillions of tiny fibers that split off into bojillions of tiny fiber ends that create so much surface area that it can stick to another surface just from the friction and/or the molecular attraction.

They say a piece of it the size of a sheet of paper can hold up 50 pounds or so, and this is still early prototype.

So I wonder if the same principal being used to stick to things could also be applied to drag. Say you had a large cape which was completely covered with these tiny fibers, each of which splits into more tiny fibers. This would total a tremendous amount of surface area. if you were to secure that cape to yourself and jump off a building, could all that surface area create enough drag to slow you down? It's hard to imagine, but isn't surface area kind of a big factor with drag?

[Chessic Sense]

IANAPhysicist, but doesn't it depend on how much is exposed to the air passing air? I think it would depend on how you design the cape. Are you holding it out with your hands? In that case, sure, you'd live. Are you attaching it to strings that are attached to your body? Then it's a parachute.

[wierdaaron]

Yeah, I should have specified that the cape is just dangling from you as a cape does. It's not being manipulated in any way to act as a parachute. Seemingly, the air would be in contact with both sides.

[Chronos]

Fluid dynamics isn't my strong point, but I imagine that what would happen would be that the cape would "stick" very tightly to the air immediately in contact with it, but there's no reason for that air to "stick" to other air. So you'll fall about as fast as you would with a cape of ordinary cloth, and take a thin boundary layer of air with you.

[billfish678]

If this extra stickiness caused the cape to flutter with much greater amplitude and frequency on a large scale then that might be a good thing overall.

Whether it does or would I have no idea and whether it is enough, I doubt it (unless the cape is REALLY big).

[Harmonious Discord]

Hope that you don't have it tied around your neck. Fluttering without the four corners attached to you it should act to slow you down, but not enough to save you.

[ZenBeam]

I think the problem is that however big the cape is, it won't stay spread out. Rather, it will all clump together, negating the benefit of the extra drag.

[Der Trihs]

I think the problem is that however big the cape is, it won't stay spread out. Rather, it will all clump together, negating the benefit of the extra drag.Perhaps if the little fibers are angled right, they can cause the cape to spread out farther than it would otherwise. Use the force of the drag to spread the cape.

[Harmonious Discord]

At what point do you call it a parasail or chute. Is it the point at which it works?

[billfish678]

At what point do you call it a parasail or chute. Is it the point at which it works?

Well, some model rockets use "streamers" which are basically long capes that are definitely different from parachutes.

[EdwardLost]

Fluid dynamics isn't my strong point, but I imagine that what would happen would be that the cape would "stick" very tightly to the air immediately in contact with it, but there's no reason for that air to "stick" to other air. So you'll fall about as fast as you would with a cape of ordinary cloth, and take a thin boundary layer of air with you.

Ditto

[Dahu]

It's already been tried. http://www.youtube.com/watch?v=BepyTSzueno

[billfish678]

[QUOTE=Dahu;11728789]It's already been tried. http:// www.youtube.com/watch?v=BepyTSzueno"

Ya know....a video cite, nearly a 100 years old, involving a tragic death really doesnt add much here IMO. YMMV.

[ianzin]

I guess Dahu didnt intend any harm, and I don't want to Junior Mod, but that link is to film of a man dying. Sure, it's from a century ago, but even so...?

We have two click rules about all kinds of stuff. I just wondered if this should be one of them. I'll refer it to the PTB.

[Dahu]

Sorry.

[[Undecided] Adrian]

Fluid dynamics isn't my strong point, but I imagine that what would happen would be that the cape would "stick" very tightly to the air immediately in contact with it, but there's no reason for that air to "stick" to other air. So you'll fall about as fast as you would with a cape of ordinary cloth, and take a thin boundary layer of air with you.

Exactly. The air in the boundary layer always has zero speed, and a cloth of tiny fibers won't change the thickness of it. A fluid simply has very little resistance to shear forces, unlike a solid.
Actually, a coarse wool cape would help you more than microfibers, since the boundary layer really would be thicker then. But it still wouldn't help.

[Miller]

Sorry.

I broke the link in your OP. Videos and pictures depicting actual death are a bit harsh to get to through a single link, and should be covered by the two click rule.

[pan1]

It's not the friction with the immediate layer of air that matters. It's the friction between that layer of air and the next that won't be enough to help you slow your fall.

[Chronos]

I broke the link in your OP. Videos and pictures depicting actual death are a bit harsh to get to through a single link, and should be covered by the two click rule.The link in the OP was just a technology review article about a newly-developed substance with extremely high surface area. It was the link in Dahu's post, which Dex already broke, that was the problematic one.

[ianzin]

The link in the OP was just a technology review article... Um, yes. The post I reported was Dahu's post containing the YouTube snuff dive, just in case anyone wanted to either impose a 2 click or break the link (again, no disrespect to Dahu, who I'm sure meant no harm). Not sure what happened behind the scenes or who dealt with it, but I didn't report the OP, nor was there any reason to AFAIK.

[Serenata67]

NO CAPES! (http://www.youtube.com/watch?v=M68ndaZSKa8)



(I promise this link isn't a snuff film, though it does have some cartoon violence.)

[Xema]

A mod should certainly restore the link in the OP, which is interesting and not a problem in any way.


As for the question, Chronos is correct: a surface that binds tightly to air molecules has limited potential to increase drag.

It may be worth noting that a technique of increasing surface area has potential to reduce drag. Ridges aligned with fluid flow have been shown to do this. Shark skin embodies this effect, and it has apparently been studied in bats.

Google "riblets" for further info.

[Machine Elf]

Your very large cape doesn't even need special materials; it just needs to be very large.

An extremely large flag on an extremely windy day can produce enough aero drag to seriously stress the flagpole upon which it's flying. Just increase the size of the flag until it produces enough drag to bear the weight of itself and a passenger at some reasonable descent speed, say 300 feet per minute (3.5 MPH).