Whale Flippers Make Better Airplane Wings

phreakmonkey writes "The bumpy, ridged surface on humpback whale flippers provide more lift, less drag, and exhibit better stall characteristics than traditional aircraft wing designs, according to Duke University, West Chester University, and the U.S. Naval Academy. This could help improve the design of airfoils used on everything from aircraft wings to underwater vehicles. The results were published in the May 2004 issue of Physics of Fluids and reported on Innovations Report."

Comments

Obligatory Douglas Adams...

[dustmote]

I don't think whales fly all that well, at least not according to Douglas Adams.

"I wonder if it will be my friend?" ***SPLAT*** :)

bumps

[OmniVector]

i'm not really an expert on the physics of aerodynamics but wouldn't bumps be completely contradictory to things like fluid dynamics? I can understand the whale flipper shape making a difference, but the bumps just seem like unnecessary drag.

Re:bumps

[MoeDrippins]

There have been a number of things where bumps (or otherwise non-flat/smooth) surfaces have helped aerodynamics; golf-ball dimples being the most recongizable example. If I recall correctly, some of the speed-skaters in the Olympics a few years back were wearing some whiz-bang body suit that had some "deformations" under the arms or somesuch for the same reason.

Here's one mention of something related.

Re:bumps

[Weh]

the strips on those suits are basically designed to 'trip' the flow so that it becomes turbulent (instead of laminar). Turbulent flow has more momentum which results in less pressure drag. The disadvantage of turbulent flow over laminar flow is that it gives more viscous drag.

Dimples in a golf ball are designed to increase the roughness so the amount of air being held to the surface of the ball is greater when the ball rotates. Higher air velocity (at the top) and lower velocity (at the bottom) create a pressure difference which gives lift.

Re:bumps

[M1FCJ]

Lift generated by a rotating body vs. lift generated by a rotating body generating turbulance. Interestingly enough turbulence helps. In high speeds laminar flows are not that good, in many aircraft sharp edges and slits on the wing are used to generate turbulance so that the shock wave won't be happening on the wing surface itself. It is not very good for lift. (When the aircraft is flying around 0.9M, the air flowing over the wing can move faster than sound).

Re:bumps

[ajax0187]

I would imagine it's just from a practical standpoint. An airplane wing can cause different effects depending on its airspeed (i.e. the most efficient airfoil shape at 150 knots is different than the most efficient shape at 1150 knots). Even though the dimples might create more lift at low airspeed, once you start approaching subsonic/supersonic conditions, the drag they produce would be more trouble then it's worth. And how exactly can you get rid of them? You can't (at least not at our present level of technology), and so we stick with more conventional flaps and spoilers.

Re:bumps

[John Hasler]

That's what the whales thought too, but after a few hundred thousand years of experimenting they decided that it really does work.

Damn whale hunters

[AtariAmarok]

I knew it all along. The skies used to be filled with whales before the whale hunters forced them to hide under the sea. Go get 'em, Greenpeace!

Re:Damn whale hunters

[patrick.whitlock]

personally, im not happy when a bird shits on my car.... can't imagine what i'd be like to have it shit on by a whale

Golf Ball Dimples

[joelparker]

Bumps and dimples tend to make things fly more reliably, by letting small eddies of air whirl. The same effect can be seen in golf balls-- a golf ball with dimples (like all the ones today) will fly farther and straighter than a perfectly spherical one.

Why does a golf ball have dimples?

Re:Golf Ball Dimples

[MachDelta]

Bumps and dimples tend to make things fly more reliably...

Oh! So THAT'S why geeks are always thrown farther by the bullies!
Here I thought it had something to do with reduced mass, but nope - its all aerodynamics!

Re:Golf Ball Dimples

[Alizarin Erythrosin]

Try reading this then. I play golf occasionally, and when it's obvious that the dimples do something. If you're ever hit a good shot off the tee you'll notice that the ball trajectory isn't parabolic, it curves up before coming back down.

Re:Golf Ball Dimples

[Weh]

your statement that 'things with dimples' tend to fly farther is not really true. An aeroplane doesn't have many dimples does it? A golf ball flies further when it is rotating (in the right direction) since the air velocity at the top is higher than at the bottom (creating a pressure difference). The dimples serve to increase the roughness which increases the amount of air being acelerated/decelerated. It is exactly the same effect as a flettner rotor

Experimentation?

[Dexx]

How, exactly, do you test something like that? Cessna with flippers? Drop whales from heights? Whale in a wind tunnel?

What conditions does this effect need?

[Retric]

The tests show that bump-ridged flippers do not stall as quickly and produce more lift and less drag than comparably sized sleek flippers.
...
The row of tubercles sheers the flow of water and redirects it into the scalloped valley between each tubercle, causing swirling vortices that roll up and over the flipper to actually enhance lift properties.

This sounds like the same effect that Honeybee's use, but I can't help but wonder what range of wind speeds this works for. My guess would be this is only useful for subsonic aircraft. Even if the effect were limited to say 1/2 the speed of sound there are plenty of aircraft that could benefit from this. If anyone can find a link which gives the conditions required for this effect that would be great until then I am going to assume it's not gong to work on a 747. Although some cessnas's might end up with bumpy wings.

Squishy bits?

[sithkhan]

Just out of curiousity, are the bumps and nodes alluded to in the article made of flesh? Isn't flesh compressable? Would this not have an effect upon the properties of the foil in question? I think it would be difficult to replicate these qualities. but I am not an aeronautical engineer, nor am I a rocket scientist. I'm only a humble chemist.

Learning from nature

[Gallowsgod]

I think science could do well learning more from nature. After all, nature have perfected lots of designs over millions of years.

Take bats for instance, only after spending years inventing sonars and radars we humans discover these little creatures had used the same solutions for quite some time.

Ricard Dawkins' brilliant book The blind watchmaker did a good job convincing me that we still have lots and lots to learn from nature.

Re:Learning from nature

[John Hasler]

"Learning from nature" is what science _does_.

Biased?

[Anonymous Coward]

I don't know about you but a study like this reported by a guy named Frank Fish sounds a little biased. I would even go as far as to say it sounds a little fishy...ok maybe that was a little too far.

Bumps are vortex generators

[Spamalamadingdong]

From the article:

As whales move through the water, the tubercles disrupt the line of pressure against the leading edge of the flippers. The row of tubercles sheers the flow of water and redirects it into the scalloped valley between each tubercle, causing swirling vortices that roll up and over the flipper to actually enhance lift properties. "The swirling vortices inject momentum into the flow," said Howle. "This injection of momentum keeps the flow attached to the upper surface of the wing and delays stall to higher wind angles."

This has been known to aerodynamicists for some time; there are vortex generators on many aircraft, including on the vertical stabilizers of many Cessnas (to improve the ability to resist turning forces during engine-out operations), on the leading edges of wings (to improve the attachment of airflow over the wings at high angles of attack and thereby increase the control effectiveness of the ailerons behind them), on the insides of the fan shrouds on the Boeing 757, and in other places.

This is not to say that this research doesn't show us anything we didn't already know, but it isn't exactly a huge revelation either.

Re:Bumps are vortex generators

[phreakmonkey]

Actually, I disagree. The increased low-speed handling (and higher angle of attack) characteristics of wings with vortex generators have been known for a long time. However, traditionally shaped vortex generators tend to increase drag, or at best leave it the same.

What appears to make this shape unique is that it actually increases the lift of the wing, increases the range of angle of attack (= lower stall speeds) AND reduces drag. This means it's more aerodynamically efficent overall, instead of trading one aerodynamic characteristic for another. (ie: increasing drag to lower the stall speed)

We haven't improved the overall efficency of wing design for some time. (That's why a 1967 Cessna 172 and a 2003 Cessna 172 have nearly identical wings.) This may change that.

- pm

Bumpy wings?

[Spamalamadingdong]

Most Cessnas are rivetted together, and already have bumpy wings....

What this says to me is that Ford may have had it more right than he knew, with the Trimotor. (The Trimotor's skins were corrugated with the ribs running parallel to the airflow.)

A quibble

[Spamalamadingdong]

We haven't improved the overall efficency of wing design for some time. (That's why a 1967 Cessna 172 and a 2003 Cessna 172 have nearly identical wings.) This may change that.

I'd put that down to the requirements for FAA type certification rather than limits of knowledge or design. You can buy all kinds of flap- and aileron-gap seals and other cleanup hardware for Cessnas, but you can't get them installed at the factory. If the company doesn't find those relatively simple additions worthy of inclusion in the aircraft as shipped, why would they redesign the wing and have to go through all the required testing and paperwork?

If Cessna really wanted to clean up their aerodynamics, they would have gone where the Stallion went. Looks like a Skylane, but goes one heck of a lot faster.

I look forward to experimenters trying to apply the knowledge learned from the whale investigators, though. If drag can be reduced by 8%, it means several percent less fuel required to cover the same distance (induced drag would not be reduced, only parasite drag).

Run a test on your memory, because....

[Spamalamadingdong]

You got it backwards.

TRIZ predicts this

[wjwlsn]

TRIZ is a step-by-step method for generating innovative solutions. That sounds stupid, I know, but bear with me. TRIZ is based on resolving contradictions between parameters... in classical TRIZ, there are 39 such parameters, mostly engineering focused. You have a contradiction when you have 2 parameters in conflict, where improving one of them makes the other worse. Your ideal solution would have BOTH improve.

Considering air flowing over an airfoil, I can see contradictions between lift (pressure, parameter 11) with speed (parameter 9) and energy spent (parameter 19). TRIZ then suggests inventive principles that might present a solution. Some promising hits appear to be:

• Spheroidality - Replace flat parts with curved ones. (principle 14)
• Vibration - Set an object into oscillation, or if oscillation exists, increase its frequency. (principle 18)

There are plenty of other ways to look at this, and possibly other principles might come into play. Combinations of principles might work as well... this seems to be the case with the principles found above.

For more info, check out the following site - TRIZ.

Please note that I have no connection with this site.

Reminiscent of Airbus trials with "shark skin"

[rv8]

Airbus was conducting trials many years ago with a covering that was striated like shark skin. They measured small drag reductions, but I haven't read anything about the concept in recent years. I suspect Airbus found that it was hard to keep the surface maintained properly.

http://www.spc.org.nc/coastfish/News/Fish_News/84/ Shark-skin-planes.htm
http://www.bio.davidson.edu/Courses/anphys/2000/Tu scano/Applications.htm