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Old Sep 06, 2011, 01:14 AM
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Originally Posted by Whiskers View Post
Further to this I searched 'vulture in flight' in Google Images.
There is nothing there that looks to me like a stepped wing section.
You know, when I read something like this it makes me wonder if I am crazy.

Take a look at the two images below. The first one shows the top of the vulture wing quite well. You can see the airfoil shape clearly. If you look at the wings you can see there are three different sets of feathers. The first set seem to stop at almost 50% of the chord. The nest set doesn't look like it gets much further than 60-65%. Each of these feathers have some kind of end. They make a scalloped shaped step, not very deep in height, sure, but a discontinuity all the same.

The last set of feathers is not even the least bit smooth. Can you see how they create ridges, call them fore-to-aft steps, that run the whole length of the wing, and slowly rotate out until they are almost aligned wingtip to wingtip before they stop?

Now look at the second photo. This one shows the underside of the wing while in flight. You can see that the leading edge of the underside of the wing has a short step, a row of dark feathers. In the photo it appears that some of them are lifting away from the primary feathers, possibly because they are in deep stall. Does that really not look like a discontinuity to you?


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Originally Posted by Whiskers View Post
But Dragonfly wings are another thing altogether:
http://jeb.biologists.org/content/203/20/3125.full.pdf
That was an excellent find. The wing cross sections are pretty wacky looking.
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Old Sep 06, 2011, 02:17 AM
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It's a matter of perception, isn't it?
You see a step; I see nature doing her best to eliminate a step given the problems of making a highly configurable and foldable wing.
Anyhow, I see your vulture and raise you an albatross
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Old Sep 06, 2011, 07:52 AM
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Like Whiskers, I see no step on the Vulture wing, only different colour feathers. Anyone who has seen these birds close up in zoos etc will have seen that in fact their wing surfaces are smooth, top and bottom.

In fact if you look at the photo showing the underside of the vulture wing posted by Tolladay, in that photo you can clearly see the profile of the wing upper surface of the wing nearest to camera.. The surface is a perfectly smooth curve much like any normal airfoil (see attached)... maybe a slight reflex but nothing even close to a step like discontinuity.

I also agree that insect wings are 'a different beast'.. They are full of ridges, that you might well call 'steps' of sorts.. But insect wings operate at an altogether different order of magnitude of Re numbers compared to R/C models.
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Old Sep 06, 2011, 09:45 AM
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Quote:
Originally Posted by Whiskers View Post
It's a matter of perception, isn't it?
Yes, I would say so.


Quote:
Originally Posted by Whiskers View Post
You see a step; I see nature doing her best to eliminate a step given the problems of making a highly configurable and foldable wing.
Forgive me for saying so, but isn't this an assumption on your part? Nature provides many perfectly smooth wings; bats for one. Mind you, this type of flight evolved from a different set of circumstances, but also is more recent then feathered flight.

Birds have been around long enough that I believe it is safe to assume an even smoother surface could have been realized if it provided a significant advantage. I don't know what the flying dinosaurs used, but I don't know if anyone thinks they were feathered.

Ever seen the surface of a feather?
http://www.daviddarling.info/images/feather_diagram.jpg

That is not a particularly smooth surface.


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Originally Posted by Whiskers View Post
Anyhow, I see your vulture and raise you an albatross
Like this?
http://www.independent.co.uk/multime...tr_137129s.jpg
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Old Sep 06, 2011, 09:52 AM
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Originally Posted by JetPlaneFlyer View Post
Like Whiskers, I see no step on the Vulture wing, only different colour feathers. Anyone who has seen these birds close up in zoos etc will have seen that in fact their wing surfaces are smooth, top and bottom.
Are you telling us the primaries lay against each other smoothly? Even you must see that the last portion of the wing is not smooth.

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Originally Posted by JetPlaneFlyer View Post
In fact if you look at the photo showing the underside of the vulture wing posted by Tolladay, in that photo you can clearly see the profile of the wing upper surface of the wing nearest to camera.. The surface is a perfectly smooth curve much like any normal airfoil (see attached)... maybe a slight reflex but nothing even close to a step like discontinuity.
How large a step does it need to be to be a discontinuity? I've seen turbulators which were about the thickness of two pieces of tape, and on a 50" wing. And again you seem to be missing the last 1/3 which is clearly not smooth.

Quote:
Originally Posted by JetPlaneFlyer View Post
I also agree that insect wings are 'a different beast'.. They are full of ridges, that you might well call 'steps' of sorts.. But insect wings operate at an altogether different order of magnitude of Re numbers compared to R/C models.
I totally agree. I don't know that I would call them steps, but they probably work in a similar fashion, and considering the thinness of the material likely add a huge amount of torsional strength over that of a flat shape or even an airfoil shape.
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Old Sep 06, 2011, 11:17 AM
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Amazing nature

Hi all, here is something from the nature which is near of KFm profiles, dragonfly wing profile. It is not smooth like the profiles on the bird wings, take a look.

AERODYNAMIC CHARACTERISTICS OF THE WINGS AND BODY OF A
DRAGONFLY

http://jeb.biologists.org/content/203/20/3125.full.pdf

http://jeb.biologists.org/content/199/2/281.full.pdf

http://www.public.iastate.edu/~huhui...-2007-0483.pdf

I think the dragonfly's wing profile is worth to try on a glider or even on a motorised rc-plane. I have little free flight glider which has a corrucated profile where the "waves" are crosswise (diagonally). This glider flies pretty good. It is not even near of the "odd" wing profile of the dragonfly, but it's not very conventional either.

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Old Sep 06, 2011, 11:25 AM
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Just thought I would add my findings to the mix...

Birds, when flying tend to incorperate two different KF type features. The first and most prominent is the KF step, which is created when one series of feathers overlaps the next, thus creating the vortices we have seen. One that has not been delved into as greatly yet, is the (KF Ridge) this is where the leading row of feathers does not set smoothly upon the next. You will normally see this when a bird is just taking off or hovering over prey. I have been doing some experimenting in this area and tests are showing that dependant upon the height of the ridge (just like the step) great lift can be found, dependant upon the length and depth of the undermined areas.

I have included a rough sketch to show what I mean.


ApachePilot
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Old Sep 06, 2011, 11:58 AM
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Bird flight

take a look here about "eddy flaps" it looks like KF airfoil to me:
http://www.bionik.tu-berlin.de/user/...rag/sld004.htm

take a look at the video here (at 20 minutes):
http://www.dailymotion.com/video/xjn...ement-1-4_news
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Old Sep 06, 2011, 01:47 PM
fix-it-up chappie
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Quote:
Originally Posted by Stra View Post
take a look here about "eddy flaps" it looks like KF airfoil to me:
http://www.bionik.tu-berlin.de/user/...rag/sld004.htm

take a look at the video here (at 20 minutes):
http://www.dailymotion.com/video/xjn...ement-1-4_news
22 minutes into this second link is a clear KF structure in use. Interesting. I wish I knew enough french to know what they are talking about.

Completely aside from all this airfoil talk, I think the good Professor Igno Rechenberg has the best hair I've seen on television this year. Incredible.
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Old Sep 06, 2011, 04:47 PM
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Quote:
Originally Posted by tolladay View Post
How large a step does it need to be to be a discontinuity?
That's a good point.. I'd add "how large does a discontinuity have to be before it's called a KF step?"

I guess 'smooth' is perhaps the wrong word to use in relation to a birds wing which by it's nature is cannot ever be perfectly smooth down to a sub millimeter level.. But equally the slight roughness of the feathers that make up a birds wing, and the microscopic discontinuity caused be the lapping of one feather over another, isn't what most reasonable observers would think of as a KF stepped airfoil.. is it

I'd be the first to support you if you claimed the feathers on a birds wing probably acted as turbulators to enhance low re performance.. But i still don't see anything in a birds wing that's even close to being what was described and depicted in the KF patent.

Or has KF now become a 'catch all' for any wing that has any form of turbulation device? If so had freeflight modelers already invented the KF airfoil when they glued pieces of thread along the upper leading edges of their glider wings decades before Dick ever made a paper airplane?
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Old Sep 06, 2011, 05:46 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post
I guess 'smooth' is perhaps the wrong word to use in relation to a birds wing which by it's nature is cannot ever be perfectly smooth down to a sub millimeter level.. But equally the slight roughness of the feathers that make up a birds wing, and the microscopic discontinuity caused be the lapping of one feather over another, isn't what most reasonable observers would think of as a KF stepped airfoil.. is it
TO take a slight tangent, years ago I read that owl feathers form very small "chevrons" that create vortices that muffle flight noise.

Not sure if this is in fact true, but it was interesting nonetheless.
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Old Sep 06, 2011, 06:21 PM
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Quote:
Originally Posted by JetPlaneFlyer View Post

Or has KF now become a 'catch all' for any wing that has any form of turbulation device? If so had freeflight modelers already invented the KF airfoil when they glued pieces of thread along the upper leading edges of their glider wings decades before Dick ever made a paper airplane?

Here's my point of view:

When I came up with the step back in 1964, it was to solve a problem.
I wanted to make a paper airplane that I could throw outside and have it climb up into the sky and then level off by itself and go into a nice long glide.

I was able to finally achieve this after many, many attempts. I did it by opening up pockets in the wings, thus creating a distinct step or discontinuity. I was able to reach the height of a telephone pole and then some. It was tricky in that the wings had to be equal. If one pocket was larger than the other it wouldn't fly straight. Or, if one wing was a little higher than the other it would not fly right.

When Fogleman and I patented this step concept, it did not exist anywhere as a patented idea. Today the step is being used all over the world in the RC in many different ways. I am proud of the fact that I made a contribution to this great RC hobby where people can build and fly their own designs without spending a fortune. To some people it is still a "Bastard" of an airfoil because it doesn't have the pedigree or nod from the official establishment as being a proper airfoil with scientific proof to back it up.

The point is that it works well in low Reynolds numbers. It works for many RC fliers. It has its place. That's good enough for me. If it didn't perform as well as it does it would be dead and buried by now.

What I attempted to do was create awareness of the stepped airfoil because it was seen as unworkable and ugly. It has been an uphill battle for almost forty years and it took a number of very creative RC people to demonstrate its possibilities by using the steps in different ways. I owe a great deal to many contributors to this idea.

About the time I was creating the step with my paper airplane, two gentleman working at Bell Labs in New Jersey made one of the greatest discoveries of all time. Arno Penzias and Robert Wilson saw something on a monitor that millions of other people had seen and thought nothing of it. What they saw was snow on their television set after their station went off the air. Penzias and Wilson paid more attention to the snow and made a startling discovery. The snow was from the microwave background of the universe and was produced by the big bang or singularity. This enabled people to trace the snow back to the very beginnings of the universe.

Many people had a chance to do something with this information, but it took these two gentleman to focus on it and make it a reality. The focus has to start somewhere and they did it.

My focus has been on a stepped airfoil and the term KF refers to this idea.
It's as simple as that.

Dick
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Old Sep 07, 2011, 01:57 AM
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Quote:
Originally Posted by JetPlaneFlyer View Post
That's a good point.. I'd add "how large does a discontinuity have to be before it's called a KF step?"

I guess 'smooth' is perhaps the wrong word to use in relation to a birds wing which by it's nature is cannot ever be perfectly smooth down to a sub millimeter level.. But equally the slight roughness of the feathers that make up a birds wing, and the microscopic discontinuity caused be the lapping of one feather over another, isn't what most reasonable observers would think of as a KF stepped airfoil.. is it

I'd be the first to support you if you claimed the feathers on a birds wing probably acted as turbulators to enhance low re performance.. But i still don't see anything in a birds wing that's even close to being what was described and depicted in the KF patent.
The feathers are right there. I think is presumptuous to assume they do not have an aerodynamic purpose. Perhaps you think it presumptuous on my part that I do. Lets call it a draw.

Quote:
Originally Posted by JetPlaneFlyer View Post
Or has KF now become a 'catch all' for any wing that has any form of turbulation device? If so had freeflight modelers already invented the KF airfoil when they glued pieces of thread along the upper leading edges of their glider wings decades before Dick ever made a paper airplane?
Not that I'm the expert on nomenclature, but I usually refer to them as turbulators when they appear in the first 1/3 or so of the airfoil, which is usually its max thickness. After that, then I am likely to call them KF steps, for lack of a better term. I also don't think the steps need to be perpendicular to the direction of travel, but others might.
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Old Sep 07, 2011, 01:59 AM
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Originally Posted by Cap_n_Dave View Post
TO take a slight tangent, years ago I read that owl feathers form very small "chevrons" that create vortices that muffle flight noise.

Not sure if this is in fact true, but it was interesting nonetheless.
IIRC it is barn owls, and they have some kind of special feather that has a fluffy leading edge to the wing.
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Old Sep 07, 2011, 06:47 AM
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Quote:
take a look here about "eddy flaps" it looks like KF airfoil to me:
http://www.bionik.tu-berlin.de/user/...rag/sld004.htm
I must say it does not look to me like any KF type wing-section I have seen on any plane or plan.
Of course, in my long time study of bird flight I have often observed feathers lifting in that way. It has always been when the bird was deliberately stalling, usually just before touchdown.
It's always the center section that stalls. The outer panels don't show this feather lifting, probably because the bird does not stall that part of its wing.
I think the feather-lifting is just an artifact of the stall. I don't believe its function is to delay the stall, given that the bird is intentionally stalling.
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