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Enroute Airbus A380 wake flips Challenger business jet upside down

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

#321

Post by conistonwater »

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.

Looking at https://www.grc.nasa.gov/www/k-12/airplane/wrong2.html it doesn't look like it's true that it's air being deflected that causes lift. There was a recent submission on HN explaining the theories of lift in sails: https://news.ycombinator.com/item?id=13829625. AFAIU air is not dense enough to make this deflection account for the magnitude of lift forces actually observed.

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

#322

Post by vpribish »

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 not the Bernoulli effect, but it is a pressure difference (from the 3rd law, as you say)

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

#323

Post by [deleted] »

ashark wrote: post #301
mannykannot wrote: post #208

Earlier quoted context omitted.

The 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.)

Fun 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]

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

#324

Post by tzs »

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.

There are myths related to low pressure (such as the infamous "equal transit time" theory), but low pressure generating lift is not one of them.

The pressure explanations and the Newton's Third Law explanations are not different theories of lift. They are just different ways of looking at the same thing underlying thing.

The motion of a wing through a fluid has to conserve mass, energy, and momentum. If you analyze lift by focusing on conservation of momentum, you get the Newton's Third viewpoint. If you analyze by focusing on conservation of energy, you get a pressure viewpoint.

See: https://www.grc.nasa.gov/www/K-12/airplane/bernnew.html

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

#325

Post by mcguire »

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…

The last video, the DR400 vs the Antonov, is an excellent demonstration.

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

#326

Post by mcguire »

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…

Check out "See How It Flies": https://www.av8n.com/

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

#328

Post by matsemann »

M_Grey wrote: post #292
matsemann wrote: post #107

Earlier quoted context omitted.

Not sure why you are calling off-piste skiing silly, a rich man sport and something one shouldn't do. It's an incredible feeling, lots of fun, and if you have to walk up the mountain first it's a nice nature experience as well. Yes, it can be dangerous, but it's a risk you can manage yourself. So it doesn't have to be very dangerous if one follows common advice and also don't ski where there is a high risk of avalanc…

Yes, it can be dangerous, but it's a risk you can manage yourself. Probably what Michael Schumacher thought to himself, back when he could still think.

Everything carries a risk, my point was that off-piste skiing doesn't have to be too much more dangerous than more mundane stuff, like driving a car.

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

#329

Post by School-Cotton »

lmm wrote: post #310
School-Cotton wrote: post #275

Earlier quoted context omitted.

Maybe I'm just a shitty cyclist but I've wiped out way, way more times on a bike than in a car. You can crash without it being a "collision".

Did you hit your head though? Even "low" speed for a car can be 20mph; you can hit a stationary object and be thrown around pretty severely. That said yeah if you're "wiping out" more than like once every few years you're doing something seriously wrong (or at least taking an unnecessary risk). I've only once had any kind of incident on my cycling commute.

The hardest I've wiped out on a bike was where a bike trail intersected a road. Everything was super wet and slick from rain. Despite bikes having right of way and my bright bike light being on, a truck with no headlights barreled across it without stopping.

Once I saw it, I had to slam on the brakes so hard my rear brake cable popped out of the handlebar, disabling the rear brake completely and I was putting full pressure on the front brake. I didn't have time to react and avoid going over the handlebars, and I hit my helmet on the pavement. (Thankfully, I did stop in time to avoid the truck hitting me).

Was I doing something seriously wrong? Yes -- I was riding a bike without a properly adjusted rear brake cable. However, this sort of mechanical issue (and any number of others) could happen to any riders who aren't much more hyper-diligent about maintenance than average.

Who knows if we'd even be having this conversation had I not been wearing a helmet that night.

From a public health perspective, evidence suggests making helmets mandatory is counter-productive, and so I don't support those laws. However, I still maintain that anyone who cycles without a helmet is fucking stupid.

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

#330

Post by School-Cotton »

monort wrote: post #279
School-Cotton wrote: post #270

Earlier quoted context omitted.

> The risk of a head injury that a helmet would prevent is much higher in a car What is this based on? My own intuition is that the risk is many times higher on a bike.

There are were 42000 brain injury-related hospitalizations for motor vehicle occupants per year, though this data is from before 2001. https://stacks.cdc.gov/view/cdc/13379/cdc_13379_DS1.pdf (Table 10)

Sure but you have to normalize it somehow. Americans drive way more than they bike. I imagine if you calculated this per-time or per-distance, driving would still come out much safer for the brain than cycling without a helmet.
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