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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

#41

Post by nether »

Zak wrote: post #39
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…

Wings generate lift primarily by deflecting air downward. There is an area of low pressure over the wing where air is taking a longer path than under the wing, but that is only responsible for a small fraction of the lift.

"Longer path" has no bearing on reality. A flat plate can generate plenty of lift even with both sides the same. It's also hard to define "path," as the air starts convecting well ahead of the wing in subsonic flow.

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

#42

Post by [deleted] »

Zak wrote: post #39
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…

Wings generate lift primarily by deflecting air downward. There is an area of low pressure over the wing where air is taking a longer path than under the wing, but that is only responsible for a small fraction of the lift.

[deleted]

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

#43

Post by ams6110 »

JamilD wrote: post #12
paulannesley wrote: post #8

> one thousand feet above Are the imperial units of measurement an aviation thing, or an American thing, or a bit of both?

In aviation, feet are exclusively used, except in Russia and China.

So, not exclusively.

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

#44

Post by lutorm »

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 trip.

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

#45

Post by hexane360 »

nether wrote: post #41
Zak wrote: post #39

Earlier quoted context omitted.

Wings generate lift primarily by deflecting air downward. There is an area of low pressure over the wing where air is taking a longer path than under the wing, but that is only responsible for a small fraction of the lift.

"Longer path" has no bearing on reality. A flat plate can generate plenty of lift even with both sides the same. It's also hard to define "path," as the air starts convecting well ahead of the wing in subsonic flow.

Additionally, the paths don't meet up/join at the trailing edge of the wing. There's no reason air above and below needs to separate and meet up into the same flow.

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

#46

Post by cr4ig_ »

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.

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

#47

Post by goodcanadian »

ajross wrote: post #40
goodcanadian wrote: post #27

Earlier quoted context omitted.

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:/…

Technically , a flight level isn't a distance measurement at all. It's defined by atmospheric pressure, so that all planes use the same "ground" barometer by definition. The feet are expressed nominally relative to a standard sea level pressure.

That is absolutely correct. I thought about mentioning it, but did not. Flight levels are definitely expressed as "pressure altitudes" rather than absolute altitudes. The air pressure (or rather density) is the more important number when it comes to keeping an aircraft in the air, anyway.

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

#48

Post by cyberferret »

Zak wrote: post #39
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…

Wings generate lift primarily by deflecting air downward. There is an area of low pressure over the wing where air is taking a longer path than under the wing, but that is only responsible for a small fraction of the lift.

Well, the same Venturi principle applies if you look at it in terms of laminar airflow over the wing. The top of the wing (via curvature and downward deflection) is essentially creating a widening venturi tube, whereas the bottom of the wing is creating a closing venturi tube. (Oh, ok, it is planar rather than a tube, but the principle is essentially the same).

Hence the high pressure under the wing and the low pressure on top of the wing. The very act of 'deflecting' millions of cubic metres of airflow generates high/low pressure points. Hence at the end of the day, we could argue that the pressure differential is what is causing the lift?

Disclaimer: Not an aeronautical engineer, just a former commercial pilot.

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

#49

Post by taejavu »

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…

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

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

#50

Post by xelxebar »

nether wrote: post #41
Zak wrote: post #39

Earlier quoted context omitted.

Wings generate lift primarily by deflecting air downward. There is an area of low pressure over the wing where air is taking a longer path than under the wing, but that is only responsible for a small fraction of the lift.

"Longer path" has no bearing on reality. A flat plate can generate plenty of lift even with both sides the same. It's also hard to define "path," as the air starts convecting well ahead of the wing in subsonic flow.

While you're on point about flat wings, in wind tunnel tests on profiled wings, you do in fact see a velocity difference between top flowing and bottom flowing streams. It's not enough of a difference, however, to cause coincident streams on the leading edge to line back up at the trailing edge.
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