Whale tubercles for trailing edge?

[donee]

Hi FX...,

I am not sure using the whale tubercles on a canard aircraft is a good idea. The idea of the canard aircraft is that the canard is designed so that it stalls before the main wing, as speed decreases. This way the angle of attack of the main wing never increase into the stall regime.

So, if you put tubercles on the canard wing, it does not stall. And the angle of attack of the main wing can be reached where it does stall, and the aircraft falls out of the sky.

Maybe you could put turbercles on the main wing, and then thin up the section of the canard. All would have to be tested very carefully.

[aerohead]

Originally Posted by aerohead

Fun read! Guess we'll all see if it goes in the marketplace.Ease of manufacture may be an issue.Thats some very sophisticated architecture. Pressure and velocity distribution could affect dynamic balance,and resonance ( flutter ) may affect structural integrity with high velocity applications, as there are so many local areas of impact,channeling,redistribution and discontinuities of aft-trailing -edge flow .Super-turbulence!Whales can articulate their flippers while turning,changing angle of attack at will as they pirouette in the water.The fluke of the whale is responsible for propulsion.I'd be more impressed if the tubercles were present in the fluke where the real power is laid down .Since whales communicate at extremely low frequency,could it be that the tubercles are "heard" by other would-be mating-age male whales and fertile in-season females,as tail-feathers are "seen" on the male peacock? Yep,I'm losing it alright!

Well-well! I saw a Pacific Life Insurance Co. tv "ad" on PBS television,showing their mascot whale breaching.The fluke was clearly visible in the video footage,and the flukes trailing edge was festooned with the tubercules.-------------- Also,in a PBS Boeing "ad",their new jetliner is shown with the new GE turbofan engines which use the serrated trailing edge.---------------- It's been explained that the jet is using it for acoustic attenuation.Perhaps do to the nature of a whale's low-frequency long-distance undersea communications,the tubercules reduce local dynamic "noise",aiding their ability to distinguish songs over background chatter.Don't know!---------------- As an aside,I've noticed old-time wood fireplace chimney caps with serrated edges under the rain cap.My thought was that perhaps the serrations might help to entrain errant cinders within the rising heat plume,allowing time for the embers to self-extinguish before settling onto combustible materials below.Don't know.

[aerohead]

After many months,I located the NASA paper I believed would shed some light on the whale tubercles.The paper is entitled "Investigation of Acoustic Effects of Leading-Edge Serrations on Airfoils," by Alan S.Hersh,Paul T.Soderman,and Richard E.Hayden.The paper appeared in JOURNAL OF AIRCRAFT,Vol.11,No.4,April,1974,pp.197-202,Copyright,1974.

The report is pretty technical.15 references are listed,going back to 1928.The research stems from observations of the aero-acoustic behavior of the owl wing,with it's leading-edge "comb",downy wingtop,and serrated trailing edge.

The research was conducted at NASA's low noise BBN acoustic windtunnel.

The crux of the research is that the "tubercles" eliminate "tones" created by periodic vortex shedding, by blasting the flow into turbulent flow and random wake turbulence.

Early roughening of wings produced increased drag,but Soderman was able to tune the serrations so as not to aggravate lift or drag while elliminating noise.

The test data is basically about frequency and sound pressure level.Of note,is the fact that above 10-degrees angle of attack,the comb makes no difference,as the wing is stalled at that point,and turbulence is random and without "tones".

Since "hearing" is so important to both whales and owls,the adaptations appear to be less about aerodynamic or hydrodynamic efficiency,and more about feeding efficiency.

The paper is a good read and I thank Paul for sending me a copy.

P.S. I believe PBS Television has free Pod-Casts of it's programs available at PBS.ORG. If you haven't seen "Raptor Force" on NOVA,you're missing out!

[Otto]

Notice that the whale tubercles are on the leading edges, with the trailing edge smooth. Nature had plenty of time to refine the tubercles, and chose the leading edge.

That said, the barred owl has serrated edges on its feathers, for silent flight. These are not as efficient for speed, but worth the sacrifice for stealth, especially at night.