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Those wingtip and flap effects on 2 are gnarly! I assume that those occur near dewpoint? or some other atmospheric conditions?
by csours 10y ago
Those wingtip and flap effects on 2 are gnarly! I assume that those occur near dewpoint? or some other atmospheric conditions?
- jacquesm 10y agoThey always occur. It's just that around the dewpoint you can visualize them. But they're all the more deadly for normally being invisible.
- phumbe 10y agoTo add to jacquesm's response, the footage in [2] is definitely from a humid day. That makes condensation happen very readily. If I remember correctly, the trails from the outboard edges of the flaps are just like wingtip vortices. The airfoil's geometry suddenly changes, acting like a wingtip and creating a vortex.
- cyberferret 10y agoIf you recall Boyle's Law from high school physics - Temperature is proportional to pressure. Aircraft wings generate an intense area of low pressure over the top of the wing (which is what essentially generates the lift). This low pressure area is magnified when flaps and slats are deployed. On a humid day, the lowering of the pressure over the wings can basically force the air temperature at that point to lower and reach dew point temperature, essentially forming temporary clouds that are whipped around by the moving air vortices. Once the aircraft has passed that point, the temperature generally stabilises and conforms to surrounding air temperature, which usually dissipates the temporary condensation. The 'twirly' bits on the wingtips is basically spillover from the high pressure under the wings to the low pressure above the wings, creating that mini tornado vortex. This is also the reason that many modern aircraft have those 'winglets' on the wingtips, to try and minimise these spillover vortices which can cause problems for trailing aircraft, as well as induce extra drag on the source aircraft.
- Zak 10y agoWings generate lift primarily by deflecting air downward. There is an area of low pressure over the wing where air is taking a longer path than under the wing, but that is only responsible for a small fraction of the lift.
- nether 10y ago"Longer path" has no bearing on reality. A flat plate can generate plenty of lift even with both sides the same. It's also hard to define "path," as the air starts convecting well ahead of the wing in subsonic flow.
- hexane360 10y agoAdditionally, the paths don't meet up/join at the trailing edge of the wing. There's no reason air above and below needs to separate and meet up into the same flow.
- xelxebar 10y agoWhile you're on point about flat wings, in wind tunnel tests on profiled wings, you do in fact see a velocity difference between top flowing and bottom flowing streams. It's not enough of a difference, however, to cause coincident streams on the leading edge to line back up at the trailing edge.
- teapot01 10y agoNASA has even published on this issue https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html https://www.grc.nasa.gov/www/k-12/airplane/wrong1.html
- ajross 10y agoFlat plates generate lift even in near vacuum conditions where the whole idea of Bernoulli flow is inapplicable, even.
- simion314 10y agoIf I remember right the "longer path" thing was in Encarta, there was a guy that used Encarta to prove to me that the theory is right and I believed it m it made sense I am wrong and not the encyclopedia.
- sgustard 10y agoEvery once in a while I have to re-realize how amazing this phenomenon is. The only thing in nature that flies are birds which weigh a few ounces. Nothing human-scale flies. Cars don't fly. Yet, the flying machines we decide to build weigh a million pounds and fly simply by going fast until the air lifts them up. That is some ludicrous black magic.
- Eduard 10y agobats and many insects can fly too.
- eCa 10y agoImagine seeing the quetzalcoatlus[1] fly... [1] https://en.wikipedia.org/wiki/Quetzalcoatlus https://en.wikipedia.org/wiki/Quetzalcoatlus
- subroutine 10y agoPossibly James Cameron's inspiration for Toruk Makto https://www.youtube.com/watch?v=M7NZERuFNEw https://www.youtube.com/watch?v=M7NZERuFNEw
- mcguire 10y agoThe size comparisons there don't do it justice. https://s-media-cache-ak0.pinimg.com/236x/09/de/53/09de530635ecb6731a6f71c4c23a6de0.jpg https://s-media-cache-ak0.pinimg.com/236x/09/de/53/09de53063... https://s-media-cache-ak0.pinimg.com/736x/0a/a1/80/0aa180ef69dddccffeda11d79a96d843.jpg https://s-media-cache-ak0.pinimg.com/736x/0a/a1/80/0aa180ef6... If you're near Austin, the Texas Memorial Museum on the UT campus had a mounted skeleton.
- chakalakasp 10y agoBTW the low pressure generating the lift thing is a myth. The lift is caused by the fact that the air is being deflected downward and good ol' Newton's Third Law.
- mannykannot 10y agoThe common explanation of lift for laypersons contains a number of non-sequiturs and even falsehoods, but this is not one of them. Newton's laws applied to the situation play out in complicated fluid dynamics, and result in a pressure difference over the wing, with a reduction above. That difference, summed over the wing, is the lift (and also the source of the induced drag, I believe, but that is a step beyond.)
- ashark 10y agoFun fact: One of the weirdest things about heavier-than-air flight is that upon posting any explanation for it online, several people will tell you you're wrong. Each of them will also disagree with one another. All will have sources. [EDIT] This also happens with the Oberth Effect.
- deleted 10y ago[deleted]
- mannykannot 10y agoTrue, though I think it's more of a fact about the Internet than about flight.
- snovv_crash 10y agoYes, but by making the air move you introduce a low pressure where it moved from, and a high pressure where it moved to. They are interconnected, just like how you can determine speeds through conservation of momentum or conservation of energy.
- thisrod 10y agoYou're both right. When Newton's third law is applied to a wing, the equal and opposite forces are pressure. No one tends to think about the pressure of the wing on the air, but it happens.
- ndonnellan 10y agoClose, but slightly backward. The saturation temperature (dewpoint) is lower at lower pressures. So the lower pressure air reduces the saturation point. The air is not being cooled by the wings. If the sat. point is close to the current air temperature, water vapor will condense. Similar phenomenon to boiling water at high elevations. Walking up the mountain isn't heating the water, but the boiling point drops as air pressure drops.
- Tloewald 10y agoActually both. When you reduce the pressure of a fluid its temperature goes down (you've used aerosol cans, right? Also that's how fridges work.)
- britPaul 10y agoOh boy, I can't wait to read the n-gate summary of all the wannabe fluid-dynamicists arguing about displacement vs. Bernoulli lift...
- mcguire 10y agoCheck out "See How It Flies": https://www.av8n.com/ https://www.av8n.com/