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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

#141

Post by jen729w »

sneak wrote: post #122
ghshephard wrote: post #96

Earlier quoted context omitted.

Using that philosophy, then anyone riding a bicycle, even if they aren't going at high-speed on road, should wear a helmet "just in case" there is an accident to protect their skull? There is a balance between annoyance and utility. I personally have no problem wearing a belt for the entire flight, including while sleeping. But I'm not to dismayed by those who leave it off, walk around the cabin, go hang out near the…

There is a pretty good statistical argument for wearing a helmet anytime one is near roads, sidewalks, moving walkways, bike lanes, or anywhere else objects are moving more than 0.5m/s, whether you are moving or not. You can even die relatively simply from falling from an otherwise motionless standing position and hitting your head on the paved ground. The brain is remarkably fragile. I kind of want the helmet-in-pub…

Here in Australia, where they're mandatory, us 'hipster' types get around this by wearing helmets that look like the sort of 'crash hat' that skateboarders wear: very dome-like, skull-shaped things rather than the traditional swept-back-vents-all-over helmets that your racing cyclist would wear.

Hotter in summer, but they look cooler. ;-)

FWIW, I thought it was weird at first having to wear a helmet. I'm from the UK. Now, though, it just seems bizarre that I wouldn't. It's my skull! My brain is in there. It only takes one idiot, and knocking my head off concrete from 6ft up at even 10km/h sounds like a terrible idea. Anything that cushions the blow, even if that blow is unlikely, now seems like the most obvious idea in the world.

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

#142

Post by Zombieball »

phumbe wrote: post #37
uptownfunk wrote: post #30

Had to google around to understand wake turbulence. If I read the wiki correctly, it's basically a horizontal tornado that emanates from the wings. That would explain the rolling that the aircraft encountered. On another note, I fly every week for work, can't imagine rolling five times and engines losing power with a drop of 10k feet. That's absolutely insane. I've had engines lose power before, but it was quickly re…

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.

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

#143

Post by Zombieball »

cr4ig_ wrote: post #46
jacquesm wrote: post #4

The wakes of large aircraft are such that even big passenger planes make sure to keep plenty of separation. https://en.wikipedia.org/wiki/American_Airlines_Flight_587 Is another example (though pilot error likely made a bad situation worse in that particular incident).

I was looking at FlightRadar24 and listening to ATC while an A380 took off from Dulles near DC. Not only did they warn for wake turbulence when the plane was already well away, they held other aircraft for a runway inspection after the plane took off. I'd imagine that kind of wake could kick up some significant debris on the ground as well.

I believe warning of wake turbulence is very common after take off of any large and heavy aircraft.

Wingtip vorticies can sit over a runway (or even drift over to parallel runways) for minutes after a takeoff. They are very dangerous to smaller aircrafts.

The key to avoiding vorticies is to take off at a point earlier than the previous aircraft and to climb at a steeper angle (vorticies travel behind and downwards from the aircraft that made them).

Example: http://www.boldmethod.com/images/learn-to-fly/aerodynamics/a...

Helicopters can also produce serious turbulence as well!

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

#144

Post by Eduard »

sgustard wrote: post #136
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…

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.

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

#145

Post by Zombieball »

goodcanadian wrote: post #27
NikolaNovak wrote: post #11

Earlier quoted context omitted.

Aviation thing (unfortunately, but it is what it is). You'll hear them referred to as Flight Levels or Angels as well (Angel 15 == 15,000feet).

Technically, the lowest flight level is FL200 or 20000'. Below that, altitudes are reported in feet. I'm not really familiar with the "angels" thing. I suspect that is specifically military. EDIT: there was a reply (since deleted) that indicated I may not be completely correct on stating FL200 as the lowest number used. I contend that I am still basically correct for North America, but there is some subtlety: https:/…

Could you clarify why you cite 20,000ft as the transition altitude? I've always been under the impression it is FL180.

From your wiki link:

> In the United States and Canada, the transition altitude is 18,000 ft.

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

#146

Post by ptaipale »

_ph_ wrote: post #120
ghshephard wrote: post #96

Earlier quoted context omitted.

Using that philosophy, then anyone riding a bicycle, even if they aren't going at high-speed on road, should wear a helmet "just in case" there is an accident to protect their skull? There is a balance between annoyance and utility. I personally have no problem wearing a belt for the entire flight, including while sleeping. But I'm not to dismayed by those who leave it off, walk around the cabin, go hang out near the…

I think the bicycle helmet comparison is valid here - one big point is, that the typical bicycle helmets are not protecting your head well, you would need a motorcycle helmet for good protection. I don't think one needs to be confined to the seat for the whole flight duration, but when sitting down, there is no good reason not to wear a belt either.

Bicycle helmets are a compromise of course; a heavier helmet would give better protection but would be very cumbersome. But even light helmets give a lot of protection against very simple, silly accidents, like not noticing a bump on the road, or failing to unclip when slowing down.

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

#147

Post by ptaipale »

jen729w wrote: post #141
sneak wrote: post #122

Earlier quoted context omitted.

There is a pretty good statistical argument for wearing a helmet anytime one is near roads, sidewalks, moving walkways, bike lanes, or anywhere else objects are moving more than 0.5m/s, whether you are moving or not. You can even die relatively simply from falling from an otherwise motionless standing position and hitting your head on the paved ground. The brain is remarkably fragile. I kind of want the helmet-in-pub…

Here in Australia, where they're mandatory, us 'hipster' types get around this by wearing helmets that look like the sort of 'crash hat' that skateboarders wear: very dome-like, skull-shaped things rather than the traditional swept-back-vents-all-over helmets that your racing cyclist would wear. Hotter in summer, but they look cooler. ;-) FWIW, I thought it was weird at first having to wear a helmet. I'm from the UK.…

Indeed. I feel naked if I start to cycle without a helmet (even though they are not strictly mandatory here, the law says you should wear one but there are no penalties for not wearing it.)

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

#148

Post by jonsen »

cyberferret wrote: post #137
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.

And as I have mentioned elsewhere on here - I have flown inverted a few times, and to do so take a tremendous amount of forward pressure on the control stick to even try and attempt to hold altitude while inverted, in order to counteract the wings natural (slight) positive AoA and the tendency for the wing to move towards it upper surface. In fact, most of the aircraft I have flown would not be able to sustain invert…

> I have flown inverted a few times, and to do so take a tremendous amount of forward pressure on the control stick to even try and attempt to hold altitude while inverted, in order to counteract the wings natural (slight) positive AoA and the tendency for the wing to move towards it upper surface.

I don't think that is right. The tail wing has a different angle of attack than the main wing. On the order of one degree I think. This is so to give a self stabilizing effekt. When flying upside down you have to compensate heavily to avoid what would be a destabilizing effect.

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

#149

Post by tajen »

webignition wrote: post #112
ghshephard wrote: post #96

Earlier quoted context omitted.

Using that philosophy, then anyone riding a bicycle, even if they aren't going at high-speed on road, should wear a helmet "just in case" there is an accident to protect their skull? There is a balance between annoyance and utility. I personally have no problem wearing a belt for the entire flight, including while sleeping. But I'm not to dismayed by those who leave it off, walk around the cabin, go hang out near the…

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…

Yours are anecdotal evidence of an extremely low risk. There are some bike accidents, which are already rare; Very few involve the head; and even fewer would be saved by a helmet. Whereas, requiring a helmet is a sufficient disincentive to biking that studies have shown that it increases the number of deaths in countries that made it mandatory, by making people drive instead and later die from cardiac diseases and obesity.

So yes you should wear a helmet while biking, but we should not make it mandatory.

In other counter-intuitive statistics about biking, passing at the red light is good for you.

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

#150

Post by CrowCrowCrow »

goodcanadian wrote: post #27
NikolaNovak wrote: post #11

Earlier quoted context omitted.

Aviation thing (unfortunately, but it is what it is). You'll hear them referred to as Flight Levels or Angels as well (Angel 15 == 15,000feet).

Technically, the lowest flight level is FL200 or 20000'. Below that, altitudes are reported in feet. I'm not really familiar with the "angels" thing. I suspect that is specifically military. EDIT: there was a reply (since deleted) that indicated I may not be completely correct on stating FL200 as the lowest number used. I contend that I am still basically correct for North America, but there is some subtlety: https:/…

Angels is a Nato standard brevity code for "thousands of feet". There's also Cherubs which is height of a friendly aircraft in hundreds of feet (https://en.wikipedia.org/wiki/Multiservice_tactical_brevity_...).

Generally, you'll use flight levels until either you hit the transition level specified in the approach plate or ATC clears you beneath that level, at which point they'll switch to using feet and give you the QNH (atmospheric pressure at sea level) to calibrate your altimeter.

For example, the ILS/DME approach for 26L at Gatwick has a transition of 6000 ft (http://www.ead.eurocontrol.int/eadbasic/pamslight-48EDD962FD...)

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