Enroute Airbus A380 wake flips Challenger business jet upside down • Hacker News Board

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

#171

Post by ghshephard » Fri, Mar 17, 2017, 9:38 AM UTC

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…

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 surface (apparently poorly) is that life, to some degree, is about managing risks. And we often respond carte blanche scenarios with exactly the same response, regardless of whether it's proportionally required.

Cycling - on road, moving fast, around anything else moving fast, at all treacherous conditions - sure, yes wear a helmet. But, casual cycling on a nice day, protected path - probably not required.

Another area of proportional risk response - portable devices on planes. At one time, end of the world if you had one on during takeout (seriously, other passengers would freak out if they thought yours was on) - and then, all of a sudden - every airport/airline in the United States lets you read your kindle, play games on your phone. People realized their responses were not proportionate to the risk.

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

#172

Post by samlittlewood » Fri, Mar 17, 2017, 9:38 AM UTC

jonsen wrote: post #148

cyberferret wrote: post #137

Earlier quoted context omitted.

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 degre…

As an aside, modern aerobatic aircraft are often rigged 0,0,0 (wing incidence, tail incidence, dihedral), so level flight will need equal elevator deflection in the appropriate direction.

Less efficient - but makes for symmetrical performance.

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

#173

Post by alkonaut » Fri, Mar 17, 2017, 9:38 AM UTC

goodcanadian wrote: post #26

nsgoetz wrote: post #20

I don't know much about aviation, but 1000ft seems kinda close to pass another aircraft. How normal is that distance?

By law, 5 (nautical) miles horizontal separation or 1000 feet vertical separation is required. When aircraft were smaller, that was probably more than sufficient. The A380 is another beast entirely, though.

The question is then - are there any systems that can ensure that two airraft aren't passing eachother at just 1000 feet if one of them is a behemoth? Will the corridors magically widen when an A380 enters it?

Will nearby aircraft be warned when crossing right under an A380 that they are basically on a collision course, while had it been a small aircraft it wouldn't be a problem?

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

#174

Post by Moru » Fri, Mar 17, 2017, 9:38 AM UTC

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.…

But a skateboard helmet doesn't work as well as a bicycle helmet when bicyckling. They are made for different falling types. They are better than nothing but not as good as the better bicycle helmets.

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

#175

Post by votingprawn » Fri, Mar 17, 2017, 9:41 AM UTC

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'd be interested to see in this thread, who here has actually studied aeronautical engineering

I studied Aerospace Engineering (PhD in Aerodynamics), and I stay out of internet conversations over "how" lift is generated. For me it is one of those topics that is just not worth debating. It seems that people get _really_ attached to their personally preferred theory of lift.

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

#176

Post by jabl » Fri, Mar 17, 2017, 9:41 AM UTC

M_Grey wrote: post #86

fulafel wrote: post #72

Earlier quoted context omitted.

Probably they have a different idea about risk management than more risk-averse people. Worrying a lot about very low probability events is not compatible with the risk-taking typically required to make a lot of money. After all millionaires are largely a "survivor club" filtered from high risk appetite workaholics.

I don't know about that. I think mostly it has to do with having the power to pick and choose critical service providers, bully them, etc. If Michael Jackson and Steve Jobs had not been as wealthy and powerful as they had been, they would also both probably be alive. Neither has much to do with being risk-takers, although you might be right that a higher arousal threshold desensitized them to risk. It may also be tha…

> ... Steve Jobs had not been as wealthy and powerful as they had been, they would also both probably be alive.

Steve Jobs got pancreatic cancer, IIRC. Which has a pretty low survival rate, per wikipedia 5% after 5 years from initial diagnosis. So most likely he'd be dead by now no matter what he would have done.

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

#177

Post by usrusr » Fri, Mar 17, 2017, 9:43 AM UTC

hbk1966 wrote: post #131

ajross wrote: post #77

Earlier quoted context omitted.

That's a meaningless correction, and technically not correct. Aircraft are lifted up by air molecules hitting the underside of the rigid body with more force than the top side, by definition. The net integrated instantaneous pressure at the surface of the aircraft IS the lift. The fact that air gets deflected downward is a necessary (c.f. conservation of momentum) effect too. So it's not incorrect to do the analysis…

No, the effect is negligible if it wasn't planes wouldn't be able to fly upside down. It's the pitch of the wing that generates most of the lift. That's why helicopters don't alter the rotor RPM they adjust the pitch of the blades to take a larger bite.

And the pitch of the wing causes one side of the wing to be hit harder by air molecules than the other, just like GP said. Maybe you hit reply on the wrong post?

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

#178

Post by Moru » Fri, Mar 17, 2017, 9:46 AM UTC

wfunction wrote: post #68

ekianjo wrote: post #66

Earlier quoted context omitted.

> They could've just turned on the sign as soon as they saw the A380 so that people could fasten their seatbelts then In a car you usually fasten your seatbelt all the time so that you don't have to guess when the risk is going to occur. In a plane there's no reason not to act the same way.

> In a car you usually fasten your seatbelt all the time so that you don't have to guess when the risk is going to occur. In a plane there's no reason not to act the same way. Sure there is. The chances of dying in a car accident are around 1% whereas the same in an air accident is, like, 100x less likely? It's like how you wear a helmet when you're in a construction zone but you don't wear a helmet when walking arou…

We are not only talking about dying in accidents, hitting your head on the ceiling can still hurt a lot. The risk does not only come from meeting planes, it can also be natural turbulence that you get no warning for.

The reasons there are less accidents in the planes is not because they are inherently more safe (ever read up how helicopters work?), it comes from the rigorous rules around everything flying. The rules exists mostly because something happened and the industry set rules to make it not happen again.

You wear helmets on construction sites because the risk of something falling on your head is so much higher when people are working with loose tools in high altitudes, hanging from ropes or whatever. (And the company is responsible for your safety so will protect their asses from getting sued.)

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

#179

Post by jabl » Fri, Mar 17, 2017, 9:46 AM UTC

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…

Huh? Over here at least, people (me included) cycle on the same road as cars all the time. Not freeways, of course, but normal city roads with a speed limit of up to 50 km/h. It's actually illegal to cycle on the sidewalk unless there's an explicit traffic sign allowing bicycles.

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

#180

Post by wayn3 » Fri, Mar 17, 2017, 9:46 AM UTC

E6300 wrote: post #100

ajross wrote: post #77

Earlier quoted context omitted.

That's a meaningless correction, and technically not correct. Aircraft are lifted up by air molecules hitting the underside of the rigid body with more force than the top side, by definition. The net integrated instantaneous pressure at the surface of the aircraft IS the lift. The fact that air gets deflected downward is a necessary (c.f. conservation of momentum) effect too. So it's not incorrect to do the analysis…

No, the correction is valid. The main component of lift is an upwards reactive force produced by pushing a mass of fluid downwards, in accordance with Newton's third law.

this is just an argument in whether you want to explain the phenomenon mechanically or in terms of thermodynamics.

pushing a mass of fluid downward is equivalent to creating a net downward pressure. its the same thing, just expressed in different terms. the unit of pressure is force per square inch, for you americans. by integrating over all the area, you get the force that you are talking about.