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Old Sep 17, 2011, 12:24 PM
fix-it-up chappie
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Originally Posted by maguro View Post
Those under wing feathers make great flow indicators. Did you notice how the airflow reversed under the wing when approached stall? ...
Yes they do. It makes me wonder to what purpose do those feathers exist. Are they nothing more than backflow, or stall indicators (which itself would be pretty cool)? Do they have another aerodynamic function? Are they purely ornamental, and if so, to what purpose?
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Old Sep 17, 2011, 04:03 PM
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Quote:
It makes me wonder to what purpose do those feathers exist. Are they nothing more than backflow, or stall indicators (which itself would be pretty cool)? Do they have another aerodynamic function? Are they purely ornamental, and if so, to what purpose?
We must understand that the bird, at the very end of that clip, is not using its wings for lift, just air-brakes.
The wings are super-stalled with the airflow at about 90 degrees to the surface so of course under-wing air will have a radial flow.
I am sure that lifting feathers are part of a bird's complex sensory system but I'm equally sure this bird didn't need a stall-warning in this situation. Everything there went exactly to plan.
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Old Sep 17, 2011, 04:37 PM
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Originally Posted by Whiskers View Post
We must understand that the bird, at the very end of that clip, is not using its wings for lift, just air-brakes.
The wings are super-stalled with the airflow at about 90 degrees to the surface so of course under-wing air will have a radial flow.
I am sure that lifting feathers are part of a bird's complex sensory system but I'm equally sure this bird didn't need a stall-warning in this situation. Everything there went exactly to plan.
Perhaps I used the wrong term. A stall warning is typically used in an airplane to help the pilot know he is about to stop experiencing more lift that weight. Obviously a bird does not need a stall warning, at least as humans would use one.

That being said, I can foresee the need for a bird to have a physical sense of how well the wing is controlling the bird's motion. This sense need not be up on the conscious level to work well. It could do just as well on a lower level like a reflex. In essence the bird need not "know" how well its braking as long as it has a "sense" of how well it is doing.

Humans do this kind of stuff all the time. For instance one can run pretty fast on uneven ground, and the feet will do a marvelous job of telling our legs when and where to exert force. If you step on the edge of a hole, in such a way that pushing hard might twist your ankle, your leg will automatically move that foot forward without exerting any backwards force, or it will redistribute the force so that only part of the foot is used.

These feathers may be providing crucial flight information to the bird as the wing develops backflow; telling the bird what shape the wing must take, and helping to control this delicate and taxing bit of flight. Conversely, they may not. For all we know, those small feathers might simply be for ornamentation.
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Old Sep 17, 2011, 05:02 PM
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Well, yes. I mentioned the "bird's complex sensory system" which would be providing constant air-flow and flight-load data.
Those small feathers most probably provide a smooth leading edge for normal flight and thermal insulation, which is a most important role as heat-loss in the fast-moving air flow is something the bird can not afford.
I think the way those feathers behave in this super-stalled situation is an artifact of the situation and do not provide any aerodynamic advantage.
Of course there is the remote possibility that I may be wrong.
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Old Sep 17, 2011, 05:57 PM
treefinder
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RE the David wing speed runs (first vid last page), I checked it with RCspeedo on the vid, and got 136.8 and147.4mph on the two runs that they noted. Interesting.
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Old Sep 18, 2011, 03:30 AM
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Originally Posted by tolladay View Post
Yes they do. It makes me wonder to what purpose do those feathers exist.
Their main function seems pretty obvious A bird need wing area to fly; sticking skinny 'arms' out and flapping would provide no lift (you can prove this by flapping your arms if you like).. The feathers are there to add area to the birds 'arms'. Bats use skin stretched between much extended finger bones but the principal is the same. Feathers have the advantage over skin of being more damage resistant.

The small feathers covering the fleshy parts of the bird probably have multiple functions but keeping the bird warm, like fur, is one of their main purposes.
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Old Sep 18, 2011, 10:12 AM
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Originally Posted by JetPlaneFlyer View Post
Their main function seems pretty obvious A bird need wing area to fly; sticking skinny 'arms' out and flapping would provide no lift (you can prove this by flapping your arms if you like).. The feathers are there to add area to the birds 'arms'. Bats use skin stretched between much extended finger bones but the principal is the same. Feathers have the advantage over skin of being more damage resistant.

The small feathers covering the fleshy parts of the bird probably have multiple functions but keeping the bird warm, like fur, is one of their main purposes.
The feathers we were speaking of are on the underside of the leading edge, a part of the wing already covered by flesh so they do not provide, as far as I can see, more surface area to the wing.

I am quite sure these feathers provide warmth to the bird, but their specific placement, length, shape, and action while the wing is spilling huge amounts of air, makes me wonder if they have another purpose.

It is possible, in fact highly likely, these feathers help shape the airfoil of the wing, especially upon the crucial first 1/4 length of it's chord, but if you watch the video you can see these feathers flap upwards, and totally expose the skin just before the bird lands. At this particular point of the wing's flight, a smooth airfoil shape on the leading edge is probably not all that useful as the wing not really flying as much as breaking the forward momentum like a drag chute.

Again, I can envision that being able to sense how the wing can spill air like this would help a good deal in it's control at this crucial point.
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Old Sep 18, 2011, 10:18 AM
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I'm with Tolladay. I don't think they have anything to do with adding area. Because form what I can tell only the shaft of a feather is on the LE. That will not add a significant amount of area


Remember guys, it may be a possibility, that the feathers just do that when he lands. Look at the structure of the wing and how the feathers are... When moving air hits them in a certain way they are going to move like that. Just like shingles on a roof top. Look at his legs right before he lands. these small hair like feathers are doing the same thing as the feathers on the wing.

It may be this complex feather changing wing, or it is just a possibility that this is just a bi- product of the wing design. Heck, it may be a both.
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Old Sep 18, 2011, 10:33 AM
fix-it-up chappie
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Originally Posted by anti-gravity View Post
I'm with Tolladay. I don't think they have anything to do with adding area. Because form what I can tell only the shaft of a feather is on the LE. That will not add a significant amount of area


Remember guys, it may be a possibility, that the feathers just do that when he lands. Look at the structure of the wing and how the feathers are... When moving air hits them in a certain way they are going to move like that. Just like shingles on a roof top. Look at his legs right before he lands. these small hair like feathers are doing the same thing as the feathers on the wing.

It may be this complex feather changing wing, or it is just a possibility that this is just a bi- product of the wing design. Heck, it may be a both.
Xactly. Well said.
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Old Sep 18, 2011, 01:49 PM
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The adding area comment was referring to the main flight feathers.
Like i said, the feathers on the fleshy parts of the wing will no doubt serve multiple purposes. I'm also pretty sure that they help shape the airfoil of the wing to some extent but I'm not so sure the fact that they stand up when the wing is stalled is so important. Heck my hair sometimes stands up if the wind blows in the wrong direction but I don't conclude that it's for any aerodynamic reason, I just decide it's time for a haircut

Bottom line is we are all just guessing.

Steve
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Old Sep 19, 2011, 02:35 PM
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Originally Posted by JetPlaneFlyer View Post
Bottom line is we are all just guessing.
Bird flight has been very well studied. The primaries and secondaries are the flight feathers and in flightless birds they are substantially reduced. All the other feathers provide insulation. Hummingbirds have as few as 10 flight feathers and albatross have up to 40.

In a more efficient wing (like an albatross) the feathers are very rigid. So much so that wear on an albatross flight feather has measureable effects on foraging efficiency. Hawks and owls, that must also be agile predators, have softer feathers which also helps to dampen noise (vortex generators).

There's no evidence that sensory feedback from feathers contributes to flight when there is so much stronger and more reliable information from muscles. You can imagine that windspeed effects on the hairs of your arm is ignored relative to muscle memory when you are gauging how hard to throw a baseball.

Rick, PhD (Zoology)
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Old Sep 19, 2011, 04:17 PM
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Well said, and I agree with most of it.
However in observing the Silver Gull (Chroicocephalus novaehollandiae) I have noticed the feathers, on the top of the wing at the center, reacting as the bird approaches a stalled condition.
The gull may not need a stall warning but those feathers would give one anyway and I'm sure it's part on the sensory system.
Getting to your hair on arm analogy, we humans use those hairs to detect slight wind changes.
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Old Oct 02, 2011, 08:05 AM
ApachePilot
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Very interesting conversation going on here gentlemen. Maybe we ought to ask the penguins at the zoo about their cousins......Nah, just kidding. You know, sitting on this end just reading what has been said here and what has been noted in books and films I think I can draw one conclusion. My arms are skinny, My fingers long; heck, I even add clothing that creates a larger mass/area. I flap my arms but yet I cannot fly.

Now, with the KF airfoil......

Most of the planes, wings and other flying contraptions that I have built using various KF airfoils have had one thing in common with their bird like cousins. The leading edges of the wing have all been tapered and/or rounded and left quite thin. We have left out steps rather thin also. Those that have build larger steps have reported back with less than favorable flight performance. I think we have to explore the very basic fundamental theory of what it is that actualy allows flight and how our KF airfoiled platforms fall into that theory. What forces are presented with each airfoil and what can we do to make that airfoil advance to the next step in the evolution of flight.

A bit off topic, I know....

But here is a question for you fellow, KF builders, designers and overall enthusiest. Has any one ever slid a pool noodle over the leading edge of their KF wing and seen what it does?

You might be in for a surprise here.....

I am getting off my soap box now, I have enjoyed what everyone has brought to the table. It is nice to see everyone submersed in such a topic.


ApachePilot
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Old Oct 02, 2011, 01:25 PM
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I have a set of thin steps to test along with thicker steps. I just need to get my airspeed recording working so I can finish with the KFM2 and move to KFM3 variants.

Roger
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Old Oct 04, 2011, 08:41 PM
Say Thea dyaoggh
Houston Tx
Joined Feb 2005
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Quote:
Originally Posted by tolladay View Post
The feathers we were speaking of are on the underside of the leading edge, a part of the wing already covered by flesh so they do not provide, as far as I can see, more surface area to the wing.

I am quite sure these feathers provide warmth to the bird, but their specific placement, length, shape, and action while the wing is spilling huge amounts of air, makes me wonder if they have another purpose.

It is possible, in fact highly likely, these feathers help shape the airfoil of the wing, especially upon the crucial first 1/4 length of it's chord, but if you watch the video you can see these feathers flap upwards, and totally expose the skin just before the bird lands. At this particular point of the wing's flight, a smooth airfoil shape on the leading edge is probably not all that useful as the wing not really flying as much as breaking the forward momentum like a drag chute.

Again, I can envision that being able to sense how the wing can spill air like this would help a good deal in it's control at this crucial point.

Ye this is what I was thinking right off when other dude said remote chance he could be wrong. Maybe I read him wrong. But ye they obviously do make technically more surface area because they exist and def add circumference also probably necessary circumference at that spot or there would be a divot and that being the case are also guilty of having to do with airfoil.

Anyways you guys are awesome. I just wish the strange cave dune people couldnt read all this./ you know this has become their new method for destroying something. This is their new misguided hobby. What a downer. I hate those btds. Cant they just live in there dirt and chill or move.
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