Hacker News Board Hacker News, browsed like a classic message board
Live data from Hacker News

Enroute Airbus A380 wake flips Challenger business jet upside down

flightservicebureau.org

Post reply on HN
Print view View original

311–320 of 376 posts

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#311

Post by Tloewald »

ndonnellan wrote: post #233
cyberferret wrote: post #36

Earlier quoted context omitted.

If 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…

Close, 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…

Actually 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.)

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#312

Post by dorfsmay »

baq wrote: post #139
dorfsmay wrote: post #128

Earlier quoted context omitted.

The shape of the wing makes a huge difference, so a plate or a piece of wood wouldn't make a good wing, but it is still able to fly. Proof? Inverted flight on low power aircraft and gliders.

Just stick your hand out of the window when you're on a highway. Plenty of lift or downforce depending how you tilt it.

Agreed, that's why I said it'd still work. But the shape does contribute to its efficiency, otherwise manufacturers wouldn't spend money trying out different shapes, adding winglet etc...

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#313

Post by Tloewald »

chakalakasp wrote: post #202
cyberferret wrote: post #36

Earlier quoted context omitted.

If 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…

BTW 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.

It's just another way of framing the same phenomenon (albeit one that makes much more sense to me than high school fluid dynamics). What gets left out of the pressure explanation is what pressure is, which is a statistical representation of Newton's third law applied over huge numbers of tiny things moving in random directions in a given frame of reference

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#314

Post by paulmd »

ghshephard wrote: post #171
webignition wrote: post #112

Earlier quoted context omitted.

Yes, you should absolutely wear a helmet when riding a bicycle at low speeds. Your skull is vulnerable to impacts at speeds that are relatively low compared to full-speed cycling. On a few occasions I've witnessed a cyclist panic and wobble after being passed far too closely by a car traveling far too fast for such a manoeuvre. This has caused such cyclists to wobble, inadvertently clip the curb and mount the pavemen…

To be clear - any cyclist crazy enough to ride a bicycle on the same road as cars definitely needs all the protection they can get, I think that goes without saying. But now you've moved from the "extraordinary low risk of accident" that comes from cycling to the "Probably one of the most dangerous things I can do" risk factor. And, pretty much 100% of the time I go snowboarding, I wear a helmet. What I'm trying to s…

> the "extraordinary low risk of accident" that comes from cycling

No, bicycling is fairly high-risk in general, like skiing, or any other sport that involves a human body travelling faster than the average set of legs can walk it around. Even just going around the block a few times there's always the chance of some random events leading to an unfortunate encounter with a tree.

Of course, it's not skydiving either. And life is a series of risks, I'm not saying don't do it.

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#315

Post by mcguire »

eCa wrote: post #153
sgustard wrote: post #136

Earlier quoted context omitted.

Every 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.

Imagine seeing the quetzalcoatlus[1] fly... [1] https://en.wikipedia.org/wiki/Quetzalcoatlus

The size comparisons there don't do it justice.

https://s-media-cache-ak0.pinimg.com/236x/09/de/53/09de53063...

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.

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#316

Post by Retric »

bdamm wrote: post #302
Retric wrote: post #277

Earlier quoted context omitted.

Fluid dynamics is a useful, but simplistic model. It's not actually true, but can accurately model truth.

Do you have a better model?

Better for what? Fluid dynamics is actually great for a huge number of stations. For pure realism you can use Quantum Mechanics, but good luck simulating that for a protean let alone a 747.

My point was you can still find a lot real world issues for example wing icing. So, that you need to be aware of what you are and are not simulating.

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#317

Post by smarx007 »

phumbe wrote: post #7

For anyone interested, there are several great youtube videos[1-4] that show the wakes (the wingtip vortices in particular) created by various aircraft. This incident brings the Reduced Vertical Separation Minima (RVSM)[5] into question. Strategic Lateral Offset Procedure (SLOP)[6] can be used used to avoid such incidents. [1] https://www.youtube.com/watch?v=E1ESmvyAmOs [2] https://www.youtube.com/watch?v=dfY5ZQDzC5s…

Reproduced on smaller planes: https://www.youtube.com/watch?v=KXlv16ETueU (from 0:46)

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#318

Post by vpribish »

Eduard wrote: post #144
sgustard wrote: post #136

Earlier quoted context omitted.

Every 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.

bats and many insects can fly too.

Very small rocks

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#319

Post by uzoodoo »

tempestn wrote: post #169
ajdlinux wrote: post #116

Earlier quoted context omitted.

That happens to be the justification that my country uses to make bicycle helmets mandatory (though there's significant debate about whether it's actually helped reduce injury rates, and it fairly clearly depresses overall rates of cycling versus other modes of transport). I think the cost of wearing an aircraft seatbelt while you happen to be seated is rather lower than the cost of having to wear a bicycle helmet, t…

What's the cost? Helmets aren't that expensive. Having to carry it around? Could always lock it to the bike. Helmet hair?

Wouldn't work if you're using a bike share.

It's actually the reason why I don't use the bike share program, even though I have a station right next to my apartment building. I could ride it to/from the train station or the grocery store, but I'm paranoid about not wearing a helmet, and hauling the bulky thing around all day is a massive inconvenience.

Re: Enroute Airbus A380 wake flips Challenger business jet upside down

#320

Post by britPaul »

cyberferret wrote: post #36
csours wrote: post #22

Earlier quoted context omitted.

Those wingtip and flap effects on 2 are gnarly! I assume that those occur near dewpoint? or some other atmospheric conditions?

If 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…

Oh boy, I can't wait to read the n-gate summary of all the wannabe fluid-dynamicists arguing about displacement vs. Bernoulli lift...
Post reply on HN