Talk:Bird flight
From Wikipedia, the free encyclopedia
 |
This article is within the scope of WikiProject Physics, which collaborates on articles related to physics. | |
| ??? | This article has not yet received a rating on the assessment scale. [FAQ] | |
| ??? | This article has not yet received an importance rating within physics. | |
|
Please rate this article, and then leave comments here to explain the ratings and/or to identify the strengths and weaknesses of the article. |
||
 |
Bird flight is part of WikiProject Birds, an attempt at creating a standardized, informative and easy-to-use ornithological resource. If you would like to participate, visit the project page. Please do not substitute this template. |
| B | This article has been rated as B-Class on the quality scale. |
| Top | This article has been rated as Top-importance on the importance scale. |
|
WikiProject Birds To-do:
|
|
|
|
|
Contents |
[edit] Adaptations for flight
To deal with the high metabolic demands of flight, birds have also developed a monodirectional pulmonary system, so that air flows in only one direction past the capillaries. --Eric Forste 00:23, 21 Jun 2005 (UTC)
[edit] Evolution is not purposeful
Several times in this article we are asked to believe that birds, or their body parts, changed purposefully. Evolution does not work this way. Neither the process of evolution, nor any animal body part, is goal-directed.
- JB Cassel
- It's bad wording on my part rather than intention. I'll try to change what I can find, feel free to change what I miss. Sabine's Sunbird 9 July 2005 19:10 (UTC)
[edit] Antioxidant Systems
Can anyone point me in the direction of finding out more about the advanced free radical fighting powers of birds?
- From [1] Uric acid (which is mostly formed from purine degradation) protects Vitamin C from oxidation by divalent ions and can act as an anti-oxidant. Uric acid also protects against free-radical catalysis by binding iron. Humans have higher levels of uric acid than monkeys and other mammals because humans lack the enzyme uricase. But birds typically have twice the plasma uric acid concentration as humans. Birds often live several times as long as comparably sized mammals despite over twice the metabolic rate, 2-6 times the plasma glucose and a 3ºC higher body temperature.
Mammals fed anti-oxidants show up to a 30% increase in average lifespan, but no increase in maximum lifespan. Anti-oxidants are most valuable for animals that are cancer-prone, or subjected to radiation or chemical toxins. There are evidently homeostatic mechanisms in cells that govern the amount of allowable anti-oxidant activity. For example, increased levels of Vitamin E in the diet correlates with reduced levels of glutathione peroxidase activity, and vice versa. Vitamin E was shown to increase catalase in banana fruit-flies -- with increasing doses of Vitamin E extending fruit-fly lifespan up to a dose of 5 micrograms/mL, above which increasing doses decreased lifespan [GERONTOLOGY 42:312-321 (1996)]. --Son of Paddy's Ego 00:23, 28 September 2005 (UTC)
[edit] Basic mechanics of bird flight
This paragraph was moved to the end so page can be read in sequence
Hi,
The lift section was just wrong. [2].
P.
Hello!! I was just about to say exactly the same, on coming here I realised someone else has pointed this out. Now the question for me is, how much exactly (or aproximately) does Bernoulli effect help birds fly? It's been already pointed out in the Wikipedia article for Wings that aircrafts fly mainly due to the Coanda effect, more or less the same says this excelent page on "http://jef.raskincenter.org/published/coanda_effect.html" - the page you point out mentions "Reaction lift" - I think it would be great to correct/expand the article mentioning this kinds of lift, too.
There are conspiracy theories everywhere from Kennedy's assassination to how a wing works. NASA is not hiding the truth! Occasionally a maverick comes along and challenges orthodoxy, like Wegener, but people who invoke the Coanda effect to explain normal aerodynamic lift are not prophets crying in the wilderness. 99.9% of professional aerodynamicists use the conventional explanation every day and in doing so produce successful aircraft, not by trial and error but with mathematics. (The other 0.1% are just eccentrics.) Unlike conventional aerodynamics, the 'Coanda theory' cannot be used to make further calculations, such as predicting the depth of the boundary layer. This is the ultimate test of any scientific theory, which it fails. The fact that a Wikipedia article states otherwise only proves that the majority do not understand aerodynamics.
There is a real Coanda effect, which has been used to generate lift using a jet blowing over a curved surface. However it needs the flow from high speed jet to produce enhanced lift, and it does it through turbulent mixing that does not occur above a normal wing.
The 'Coanda-ists' claim that the air “sticks” to the surface because of viscosity. This implies that if the viscosity of the fluid changes, the amount of lift an airfoil produces should change in proportion. Experiments show that the amount of lift produced by a real wing is independent of viscosity over a wide range. In fact the real Coanda effect requires turbulence, so it only occurs if the viscosity is sufficiently low.
The air speeds up the air above its upper surface. Coanda assume that the relative air-flow meets the wing at the same velocity as in free air and then follows the curve. This understates the pressure gradients by an order of magnitude.
There is an explanation on NASA's web site
It is sad when people who do not know a subject feel qualified to edit articles in Wikipedia. JMcC 10:33, 29 November 2005 (UTC)
Hello! After reading this guy's explanation on how flight is possible in [3], i kind of understand your nasty mood in your comments here. However, whoever wrote here "I think it would be great to correct/expand the article mentioning this kinds of lift, too." is an inteligent guy who wants to know more. Aerodynamics is a study that started with empiric observations. We should be greatfull for all the Coanda's out there that proposed (or not) the wrong theories! They paved the way to the more robust ones. Nowadays, we use the full blown Navier-Stokes to compute highly complex and non-linear flows. Not yet for practical uses like modelling an aircraft, but we'll get there soon. But to explain here Navier-Stokes is a bit too heavy, so the classic explanations are more suited. It happens though, that these classic explanations must be mentioned first to what conditions they apply. In effect, the bird flight is comparable to that of an aircraft only when the bird is not flapping the wings. When flapping occurs, the airflow around the wings in no longer steady but highly dynamic. Still today, the theory behind the modelling of modern subsonic aicraft uses models for predicting the boundary layer (which is very important to compute the drag, and every count of drag is measured in thousands of dollars or more) which assume a steady flight with a rigid non-flapping body. For years, the same theories that predicted successfully the aerodynamic behavior of an aircraft, failed to explain how come certain species of heavy bees could fly at all. Later on, research on insect wings saw that the flapping of the wings generates vortexes which change dramatically the airflow around the insect's body. You may hear sometimes someone saying that the insect flies on the vortexes he helps create, because these vortexes generate a pressure gradient across the insect's body which adds the lift that was missing out on the previous theories. Flapping flight is also very advantageous. Dynamic stall happens much later than steady stall, so birds can fly at much higher angles-of-attack. Plus, the flapping moves the wings through the air, so the body can actually be stopped. These two great advantages allow insects with a small brain to fly on with their own lives. Bees, when seen at slow motion, look like drunk drivers, bumping to the walls etc... because controlling flight is a heavy task, but if your flight engine will keep you up in the air no matter what you do, then even bees can do it :)
cheer up dude, the wikipedia is for everyone. The guys who built it believe on the law of the big numbers, i.e. if a lot of people edit this page, the contents will tend to the presently credited as correct version, no matter how many potential idiots change it.
Joao, 11 November 2006
[edit] Evolution of flight
From what I remember of my ornithology course several years back, ornithologists are still split on what triggered the evolution of flight. IIRC, the "top down" theory (gliding from trees) was postulated first, and the "ground up" theory (running/hopping after insects) was postulated as an alternative, but both have glaring problems. Kenneth Dial has suggested that rudimentary flappnig wings would have been an effective method to run up inclined surfaces.
Does anyone have any objections to a more complete write-up of this section? Ladlergo 16:58, 11 April 2006 (UTC)
[edit] Planform is not the same as aspect ratio
The article says, Elliptical wings are short and rounded, having a low aspect ratio. I don't understand this. There's no particular correlation between an eliptical shape and a high or low aspect ratio. You could have high aspect eliptical wings. I'm not sure what the original author was getting at here, so I'm not sure how to correct it. -- RoySmith (talk) 22:38, 11 December 2006 (UTC)
[edit] Minor Quibble -- Airspeed Vs Groundspeed
Shouldn't airspeed in:
"Take-off and landing" penultimate sentance: "If timed correctly, the airspeed once the target is reached is virtually nil. "
Be "groundspeed" instead?
DavesTA 23:10, 11 December 2006 (UTC)
