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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

#331

Post by lmm »

School-Cotton wrote: post #329
lmm wrote: post #310

Earlier quoted context omitted.

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 pr…

Cycling in the rain is a risk. Cycling in the dark is a risk. Cycling across badly-designed intersections (and if it put you as a cyclist in the kind of danger it wouldn't have put a car in, it's a badly-designed intersection) is a risk. Being on the road without a helmet - indeed doing anything in your life without a helmet - is a risk. In all of these cases one weighs up the risk of doing it against the inconvenience of not doing it.

Maybe we're all "fucking stupid", but by the stats someone cycling without a helmet is less stupid than someone driving, at all. There's this weird, disproportionate cultural obsession with helmets for cyclists and cyclists only.

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

#332

Post by phumbe »

Zombieball wrote: post #142
phumbe wrote: post #37

Earlier quoted context omitted.

It's helpful to think of an aircraft's wake in two parts. The wing is deflecting air downward to provide lift; this creates a volume of downward-moving air behind the aircraft. There's higher pressure under the wing and lower pressure on top, so air from below tries to get above the wing at the wingtips. This causes circulatory motion, yielding wingtip vortices (see my top-level comment for some visualizations).

Great explanation! I think it's also interesting to point out this is also the explanation for the trend of adding winglets to the tip of the wings. They help reduce the wingtip vorticies, and in turn, reduce parasitic drag and improve fuel efficiencies.

Glad you brought up winglets. My favorite example are those on the new 737 MAX. Boeing's page[1] about them is top-notch.

[1] http://www.boeing.com/commercial/737max/737-max-winglets/

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

#333

Post by lutorm »

wallace_f wrote: post #191
lutorm wrote: post #44

This is a reminder that the announcement that you should "keep your seat belt fastened at all times when you're in your seat" isn't just something someone made up. It's a small price to pay in case you ever encounter severe turbulence en route, but it might be one of these things that most people don't realize until it happens to them. Hitting your head against the cabin ceiling can seriously put a damper on your tri…

Can we talk about this in terms of actual statistics? How dangerous is flying without a seatbelt relative to say, driving without one?

I'm not saying the risk is particularly large, at least in a large aircraft. However, the inconvenience of buckling your seat belt is practically nil, so the value proposition is pretty clear to me.

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

#334

Post by silverdrake11 »

danaliv wrote: post #55
taejavu wrote: post #49

Earlier quoted context omitted.

Yeah I'm pretty sure that's the first rule that goes out the window when you're on a private jet.

And it's the number one way you're going to get injured. Keep your seatbelt buckled, even when the sign is off.

I wonder if your head would actually hit the cabin ceiling though because of the centrifugal force. The plane might have flipped too quickly for that to happen

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

#335

Post by lutorm »

acallahan wrote: post #278
gingerbread-man wrote: post #211

Earlier quoted context omitted.

Per the FAA ( https://www.faa.gov/passengers/fly_safe/turbulence/ ): - Each year, approximately 58 people in the United States are injured by turbulence while not wearing their seat belts. - From 1980 through 2008, U.S. air carriers had 234 turbulence accidents, resulting in 298 serious injuries and three fatalities. - Of the 298 serious injuries, 184 involved flight attendants and 114 involved passengers. - At least…

Maybe it's safer /not/ to wear a seatbelt. It was hard to find good stats with quick googling, but this old source[1] suggests that blood clots during flights are the greater risk, killing at least 2,000 people in the UK per year. I suspect that keeping a seatbelt off while cruising lets you shift around more mid flight and would give a small decrease in the frequency of clots. [1] http://news.bbc.co.uk/2/hi/health/1…

You don't need to wear it tight (like you do with a car seat belt), we're not talking about tens of G accelerations like in a car crash. All you need is for it to prevent you from flying up out of your seat.

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

#336

Post by phumbe »

nb777 wrote: post #207
phumbe wrote: post #37

Earlier quoted context omitted.

It's helpful to think of an aircraft's wake in two parts. The wing is deflecting air downward to provide lift; this creates a volume of downward-moving air behind the aircraft. There's higher pressure under the wing and lower pressure on top, so air from below tries to get above the wing at the wingtips. This causes circulatory motion, yielding wingtip vortices (see my top-level comment for some visualizations).

Do you happen to know how arial refueling works then ? E.g. in this image [1] the jet is flying where I would expect a lot of deflected air to be moving to ? Or is it just deflected much more steeply ? [1]: https://upload.wikimedia.org/wikipedia/commons/d/d6/US_Navy_...

The other two replies covered your questions well, so I'll just add that wakes don't descend particularly fast. According to the FAA's Pilot's Handbook of Aeronautical Knowledge[1] (page 14-28), "Tests have also shown that the vortices sink at a rate of several hundred feet per minute, slowing their descent and diminishing in strength with time and distance behind the generating aircraft."

Considering the Challenger's encounter with the A380's wake, it took 1-2 minutes for the Challenger to hit the wake, so the wake probably had 1-3 minutes to make the 1000-foot descent. That very roughly fits the expected "several hundred feet per minute" descent rate.

Considering the case of refueling, the wake's motion downward is much slower than the aircrafts' horizontal motion, so it wouldn't have descended much by the time it's left behind entirely.

[1] Available for free at https://www.faa.gov/regulations_policies/handbooks_manuals/a...

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

#337

Post by lutorm »

wfunction wrote: post #56
lutorm wrote: post #44

This is a reminder that the announcement that you should "keep your seat belt fastened at all times when you're in your seat" isn't just something someone made up. It's a small price to pay in case you ever encounter severe turbulence en route, but it might be one of these things that most people don't realize until it happens to them. Hitting your head against the cabin ceiling can seriously put a damper on your tri…

While I agree with the general sentiment, to be honest there are easier solutions here. They could've just turned on the sign as soon as they saw the A380 so that people could fasten their seatbelts then. And then turned off the sign when the threat was gone. You don't need a cannon to kill a fly.

Does not work for Clear Air Turbulence, which can be severe enough to make people fly out of their seats, too. I've been in planes where the CAT was severe enough to have lifted me out of my seat if I hadn't been buckled in, and it happened with no warning.

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

#338

Post by lmm »

School-Cotton wrote: post #330
monort wrote: post #279

Earlier quoted context omitted.

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.

Again just from memory, driving is a lot worse per-time and per-commute, though a small factor better per-distance.

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

#339

Post by phumbe »

cjrp wrote: post #117
dingaling wrote: post #92

Earlier quoted context omitted.

The OP means that satnav ensures that two aircraft on a reciprocal or identical track will now pass over one another, whereas there used to be navigational slop that would give some unintentional but useful lateral displacement.

Ironic that you should use the term 'slop', since that's exactly how they avoid flying the same route across the Atlantic tracks for example (Strategic Lateral Offset Procedure).

Also worth noting for the transatlantic paths is the direction of traffic. When it's morning in North America, traffic is predominately westbound. When it's night, traffic is predominately eastbound.

Right now, it's the middle of the day (12:50p Central). There's a bit of a mix[1], but it's still predominately westbound.

The consequence of this is that most traffic will be separated by at least 2000 feet. Eastbound traffic will (generally) be at odd Flight Levels (so 29000 feet, 31000 feet, etc.) while Westbound traffic will be at even FLs (30000 feet, etc)[2]. This assumes RVSM airspace.

[1] I'm just looking at the transatlantic traffic on https://flightaware.com/live/

[2] https://www.law.cornell.edu/cfr/text/14/91.179

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

#340

Post by davrosthedalek »

School-Cotton wrote: post #266
danaliv wrote: post #55

Earlier quoted context omitted.

And it's the number one way you're going to get injured. Keep your seatbelt buckled, even when the sign is off.

Flying is already so incredibly torturously uncomfortable for me that the very slight risk of injury or death is worse it for the increased comfort of not having a seatbelt on.

It is worth the risk for the persons next to you or the row over when you get thrown through the plane and hit them in the head?
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