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    • UnderDawg

      A Few Simple Rules   05/22/2017

      Sailing Anarchy is a very lightly moderated site. This is by design, to afford a more free atmosphere for discussion. There are plenty of sailing forums you can go to where swearing isn't allowed, confrontation is squelched and, and you can have a moderator finger-wag at you for your attitude. SA tries to avoid that and allow for more adult behavior without moderators editing your posts and whacking knuckles with rulers. We don't have a long list of published "thou shalt nots" either, and this is by design. Too many absolute rules paints us into too many corners. So check the Terms of Service - there IS language there about certain types of behavior that is not permitted. We interpret that lightly and permit a lot of latitude, but we DO reserve the right to take action when something is too extreme to tolerate (too racist, graphic, violent, misogynistic, etc.). Yes, that is subjective, but it allows us discretion. Avoiding a laundry list of rules allows for freedom; don't abuse it. However there ARE a few basic rules that will earn you a suspension, and apparently a brief refresher is in order. 1) Allegations of pedophilia - there is no tolerance for this. So if you make allegations, jokes, innuendo or suggestions about child molestation, child pornography, abuse or inappropriate behavior with minors etc. about someone on this board you will get a time out. This is pretty much automatic; this behavior can have real world effect and is not acceptable. Obviously the subject is not banned when discussion of it is apropos, e.g. talking about an item in the news for instance. But allegations or references directed at or about another poster is verboten. 2) Outing people - providing real world identifiable information about users on the forums who prefer to remain anonymous. Yes, some of us post with our real names - not a problem to use them. However many do NOT, and if you find out someone's name keep it to yourself, first or last. This also goes for other identifying information too - employer information etc. You don't need too many pieces of data to figure out who someone really is these days. Depending on severity you might get anything from a scolding to a suspension - so don't do it. I know it can be confusing sometimes for newcomers, as SA has been around almost twenty years and there are some people that throw their real names around and their current Display Name may not match the name they have out in the public. But if in doubt, you don't want to accidentally out some one so use caution, even if it's a personal friend of yours in real life. 3) Posting While Suspended - If you've earned a timeout (these are fairly rare and hard to get), please observe the suspension. If you create a new account (a "Sock Puppet") and return to the forums to post with it before your suspension is up you WILL get more time added to your original suspension and lose your Socks. This behavior may result a permanent ban, since it shows you have zero respect for the few rules we have and the moderating team that is tasked with supporting them. Check the Terms of Service you agreed to; they apply to the individual agreeing, not the account you created, so don't try to Sea Lawyer us if you get caught. Just don't do it. Those are the three that will almost certainly get you into some trouble. IF YOU SEE SOMEONE DO ONE OF THESE THINGS, please do the following: Refrain from quoting the offending text, it makes the thread cleanup a pain in the rear Press the Report button; it is by far the best way to notify Admins as we will get e-mails. Calling out for Admins in the middle of threads, sending us PM's, etc. - there is no guarantee we will get those in a timely fashion. There are multiple Moderators in multiple time zones around the world, and anyone one of us can handle the Report and all of us will be notified about it. But if you PM one Mod directly and he's off line, the problem will get dealt with much more slowly. Other behaviors that you might want to think twice before doing include: Intentionally disrupting threads and discussions repeatedly. Off topic/content free trolling in threads to disrupt dialog Stalking users around the forums with the intent to disrupt content and discussion Repeated posting of overly graphic or scatological porn content. There are plenty web sites for you to get your freak on, don't do it here. And a brief note to Newbies... No, we will not ban people or censor them for dropping F-bombs on you, using foul language, etc. so please don't report it when one of our members gives you a greeting you may find shocking. We do our best not to censor content here and playing swearword police is not in our job descriptions. Sailing Anarchy is more like a bar than a classroom, so handle it like you would meeting someone a little coarse - don't look for the teacher. Thanks.
    • B.J. Porter

      Moderation Team Change   06/16/2017

      After fifteen years of volunteer moderation at SA, I will no longer be part of the moderation team. The decision to step aside is mine, and has been some time in the works but we did not wish to announce it in advance for a number of reasons. It's been fun, but I need my time back for other purposes now. The Underdawg admin account will not be monitored until further notice, as I will be relinquishing control of it along with my administrative privileges. Zapata will continue on as a moderator, and any concerns or issues can be directed to that account or to the Editor until further notice. Anyone interested in helping moderate the forums should reach out to Scot by sending a PM to the Editor account. Please note that I am not leaving the community, I am merely stepping aside from Admin responsibilities and privileges on the site.
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RKoch

How an airfoil works...maybe we've been wrong?

24 posts in this topic

As a kid (our car didn't have A/C back then) and sticking my hand out the window was pretty obvious how lift worked. I never understood why some people try to make things more complicated.

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we could always work on improving the wheel...

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Something I read recently, there are 4 theory's why wings work, therefore no one actually knows why aircraft fly. Scary but cool at the same time.

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Old old news at least for pilots. BTW, I used to rent an airplane with a symmetrical wing that flew as well inverted as upright :)

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https://en.wikipedia.org/wiki/Kutta_condition




The vorticity in the starting vortex is matched by the vorticity in the bound vortex in the airfoil, in accordance with Kelvin's circulation theorem.[1]:§ 2.14 As the vorticity in the starting vortex progressively increases the vorticity in the bound vortex also progressively increases and causes the flow over the topside of the airfoil to increase in speed. The starting vortex is soon cast off the airfoil and is left behind, spinning in the air where the airfoil left it. The stagnation point on the topside of the airfoil then moves until it reaches the trailing edge.[1]:§§ 6.2, 6.3 The starting vortex eventually dissipates due to viscous forces.

As the airfoil continues on its way, there is a stagnation point at the trailing edge. The flow over the topside conforms to the upper surface of the airfoil. The flow over both the topside and the underside join up at the trailing edge and leave the airfoil travelling parallel to one another. This is known as the Kutta condition.[5]:§ 4.8

When an airfoil is moving with a positive angle of attack, the starting vortex has been cast off and the Kutta condition has become established, there is a finite circulation of the air around the airfoil. The airfoil is generating lift, and the magnitude of the lift is given by the KuttaJoukowski theorem.[5]:§ 4.5


TL;DR lift force from airfoils is the caused by the downward deflection of air (fluid) resulting from circulation. There are other ways to create lift.

 

... or it's invisible gremlins. At some level either is a useful explanation. Neither is really a complete answer. At some level "nobody really knows" is the answer to all human understanding. Isn't it? I don't really know. Damn. Back to work.

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"Any sufficiently advanced technology is indistinguishable from magic" ;)

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As every Naval Aviator knows, you need Bernoullis to fly. The ones on the top of the wing "pull" the aircraft up, the ones on the bottom of the wing "push" the aircraft up. If the Bernoullis become detached, the plane enters the out of control flight regime.

 

So keep your Bernoullis happy and attached, and life is good!

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Old old news at least for pilots. BTW, I used to rent an airplane with a symmetrical wing that flew as well inverted as upright :)

 

Did it fly at the same relative angle of attack inverted and upright?

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Cambridge scientists have been wasting their time - this has been known for many decades. Bernoulli's principle does work, but is a weak force. A cambered airfoil produces some lift at zero angle of attack, but very little. A board produces nearly as much lift as a modern airfoil, the airfoil's main advantage is in lower drag.

 

The various theories of lift are simply mathematical models attempting to describe - not explain - the physical phenomenon. Ultimately it is just Newton's Third Law - air is pushed one way and the wing the other.

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FM

 

 

 

Fucking Magic

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The most important thing is to make sure the airfoil never leaves the environment.

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As a kid (our car didn't have A/C back then) and sticking my hand out the window was pretty obvious how lift worked. I never understood why some people try to make things more complicated.

 

They like A/C ??

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How an air foil works:

 

 

 

The real problem is the Ice Surface

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FM

 

Fucking Magic

 

This.

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A sail works because it changed the direction of the wind. It bends its path. Air enters the front edge at maybe 30 degrees and leaves at 180 degrees (or 0 degrees relative to its initial direction). That change in direction comes from the force of the sail and the reaction to that force moves the boat. It is much like the hand out the window. But if you try and move the air too fast, at too steep an angle, you get turbulence instead. Shape is very important.

 

If the "textbook" story about wings having the curved surface on top creating lift were correct, planes could not fly upside down, which they can. But upside down they are not as efficient and can stall quicker. It is the shape and turbulence of the airflow. But the lift is like the hand out the window.

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The important thing to remember here is that if you aren't confused you aren't thinking about the problem hard enough.

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Old old news at least for pilots. BTW, I used to rent an airplane with a symmetrical wing that flew as well inverted as upright :)

 

Did it fly at the same relative angle of attack inverted and upright?

 

I can't recall. The trim was way off upside-down though and it gave me a headache. This also depends on the angle of the wing chord line relative to the fuselage, so it would not be easy to tell one effect from the other just looking out the windshield.

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https://en.wikipedia.org/wiki/Kutta_condition

 

The vorticity in the starting vortex is matched by the vorticity in the bound vortex in the airfoil, in accordance with Kelvin's circulation theorem.[1]:§ 2.14 As the vorticity in the starting vortex progressively increases the vorticity in the bound vortex also progressively increases and causes the flow over the topside of the airfoil to increase in speed. The starting vortex is soon cast off the airfoil and is left behind, spinning in the air where the airfoil left it. The stagnation point on the topside of the airfoil then moves until it reaches the trailing edge.[1]:§§ 6.2, 6.3 The starting vortex eventually dissipates due to viscous forces.

As the airfoil continues on its way, there is a stagnation point at the trailing edge. The flow over the topside conforms to the upper surface of the airfoil. The flow over both the topside and the underside join up at the trailing edge and leave the airfoil travelling parallel to one another. This is known as the Kutta condition.[5]:§ 4.8

When an airfoil is moving with a positive angle of attack, the starting vortex has been cast off and the Kutta condition has become established, there is a finite circulation of the air around the airfoil. The airfoil is generating lift, and the magnitude of the lift is given by the KuttaJoukowski theorem.[5]:§ 4.5

 

... There are other ways to create lift.

 

...

Like a gentle rub

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The only myth they're seeking to be destroy is the one that says that two molecules of air separated at the leading edge of the wing somehow magically meet again at the trailing edge. But to a large extent I think its more of a "lie-to-children" than anything else, helping to provide a simplistic explanation of why flow over the top of the wing is important.

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Old old news at least for pilots. BTW, I used to rent an airplane with a symmetrical wing that flew as well inverted as upright :)

Did it fly at the same relative angle of attack inverted and upright?

I can't recall. The trim was way off upside-down though and it gave me a headache. This also depends on the angle of the wing chord line relative to the fuselage, so it would not be easy to tell one effect from the other just looking out the windshield.

 

Most competition acrobats are 0 degrees incidence. Add in a thrust line on the same axis and you don't need no stinking trim wheels....

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