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The Boeing 747 begins its final descent

theatlantic.com

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Re: The Boeing 747 begins its final descent

#371

Post by jquery »

s1artibartfast wrote: post #358
kelnos wrote: post #240

Earlier quoted context omitted.

> what sense does it make to vote for an unpatriotic politician? I really dislike the concept of "patriotism". What does it even mean? I think you'll get different answers if you get different people. If people think that being critical of the US makes someone "unpatriotic", then that's their problem. If that makes a critical politician less electable, so be it. The alternative -- politicians censoring themselves and…

I think it mostly about perspective of history. For those that were attracted to it, Trump presented the idea that America and it's people are good at good at their core, and this can be brought back. Those same people view rhetoric from the other side as saying America is and was fundamentally evil and corrupt. They take this personally as a condemnation of them and their family.

He only presented that idea to a certain slice of Americans. If you were a Haitian American, you probably ate cats and dogs according to him.

Re: The Boeing 747 begins its final descent

#372

Post by dotancohen »

fransje26 wrote: post #368
dotancohen wrote: post #353

Earlier quoted context omitted.

Could you expand upon that for us interested laymen?

Ah. It was based on a series of performance graphs from Boeing, dating back to my aircraft-design days where that very question was discussed and I was baffled enough by the contradiction to ask for detailed clarifications to the presenting professor. Unfortunately, I don't have access to those old notes, and couldn't quickly find what I was looking for online. So for now, due to lack of proper supporting arguments,…

I remember hearing that the -300 cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres. But I have no idea what kind of drag the hump transition imparted on the upper fuselage. I kind of assumed that the low pressure zone above the rest of the aircraft would make up for most of the drag penalty of the transition (in general, not -300 specific). I'd love to hear your thoughts on the matter.

Assuming that the boundary layer is laminar for the entire length of the extended part of the fuselage during cruise - which is probably a good assumption, correct me if I'm wrong - then I wouldn't expect that the increased wetted area to add any significant drag. There is no additional frontal area, and no additional low pressure transition (just one moved back, obviously). But I'm not an aerospace engineer, just an interested laymen, so I'm just guessing. For all I know the straight staircase reduced drag compared to the classic spiral!

Re: The Boeing 747 begins its final descent

#373

Post by addaon »

dotancohen wrote: post #372
fransje26 wrote: post #368

Earlier quoted context omitted.

Ah. It was based on a series of performance graphs from Boeing, dating back to my aircraft-design days where that very question was discussed and I was baffled enough by the contradiction to ask for detailed clarifications to the presenting professor. Unfortunately, I don't have access to those old notes, and couldn't quickly find what I was looking for online. So for now, due to lack of proper supporting arguments,…

I remember hearing that the -300 cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres. But I have no idea what kind of drag the hump transition imparted on the upper fuselage. I kind of assumed that the low pressure zone above the rest of the aircraft would make up for most of the drag penalty of the transition (in general, not -300 specific). I'…

At transonic speeds, wave drag dominates both induced and parasitic drag. The hump reducing drag is about shape (area rule).

Re: The Boeing 747 begins its final descent

#374

Post by fransje26 »

dotancohen wrote: post #372
fransje26 wrote: post #368

Earlier quoted context omitted.

Ah. It was based on a series of performance graphs from Boeing, dating back to my aircraft-design days where that very question was discussed and I was baffled enough by the contradiction to ask for detailed clarifications to the presenting professor. Unfortunately, I don't have access to those old notes, and couldn't quickly find what I was looking for online. So for now, due to lack of proper supporting arguments,…

I remember hearing that the -300 cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres. But I have no idea what kind of drag the hump transition imparted on the upper fuselage. I kind of assumed that the low pressure zone above the rest of the aircraft would make up for most of the drag penalty of the transition (in general, not -300 specific). I'…

> [..] cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres.

In high-subsonic cases, it normally points to slightly better aerodynamics in the areas flirting with transonic regimes. The name of the game at those speeds is to try to delay the onset of drag-inducing shocks. These shocks will typically first appear on the wing, or in an area heavily influenced by the wing.

In the case of the -300, with the extended bubble coming down at about half the wing root chord, it is possible that the bubble downflow / low-pressure area positively influenced the flow over the wing to slightly delay the transonic onset and further effects.

Pulling the bubble further aft made things worse again.

> Assuming that the boundary layer is laminar for the entire length of the extended part of the fuselage during cruise

Mm. No, I would expect the flow to be turbulent well before that.

> and no additional low pressure transition (just one moved back, obviously).

Careful where you put your low pressure zones, the wing aerodynamics are critical and sensitive! :-) (see explanation above)

But to make things even more interesting, the 747- 300/400/8 cargo all use the short bubble. :-)

Re: The Boeing 747 begins its final descent

#375

Post by sbierwagen »

fransje26 wrote: post #278
bobthepanda wrote: post #257

Earlier quoted context omitted.

I would have to imagine that the newer 747-8 would have the much lower pressurization and other comfort standards of its generation of aircraft in the 2000s; the problem is that it didn't really sell so most people did not get to fly in one.

> I would have to imagine that the newer 747-8 would have the much lower pressurization Two small corrections: 1) If it would have had a change in internal pressurization, the -8 would have a higher pressurization to allow for a lower cabin altitude pressure. 2) The -8 does not have a higher pressurization, because they did not change the fuselage construction. Newer airplanes have lower cabin-altitudes thanks to the…

>thanks to the use of composite materials

Not always. 777X uses a conventional fuselage but has a 6,000 foot cabin compared to the 8,000 foot cabin on the legacy 777.

Re: The Boeing 747 begins its final descent

#376

Post by sidewndr46 »

dotancohen wrote: post #351
sidewndr46 wrote: post #198

Earlier quoted context omitted.

The Lockheed L-100 Hercules does exist and is apparently a civilian C-130

You're going to love the TU-114!

it had sleeping berths and a lounge I hear. As long as I can wear hearing protection, that sounds like a luxury travel experience.

Re: The Boeing 747 begins its final descent

#377

Post by dotancohen »

fransje26 wrote: post #374
dotancohen wrote: post #372

Earlier quoted context omitted.

I remember hearing that the -300 cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres. But I have no idea what kind of drag the hump transition imparted on the upper fuselage. I kind of assumed that the low pressure zone above the rest of the aircraft would make up for most of the drag penalty of the transition (in general, not -300 specific). I'…

> [..] cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres. In high-subsonic cases, it normally points to slightly better aerodynamics in the areas flirting with transonic regimes. The name of the game at those speeds is to try to delay the onset of drag-inducing shocks. These shocks will typically first appear on the wing, or in an area heavily…

Thank you.

  > But to make things even more interesting, the 747- 300/400/8 cargo all use the short bubble. :-)
I only recently noticed this on 3 minutes of aviation. Considering the 4 7 was originally designed for the passenger jets to be easily converted to cargo, I found it quite peculiar that the two -400 variants left the factory with different fuselages.

Re: The Boeing 747 begins its final descent

#378

Post by dotancohen »

addaon wrote: post #373
dotancohen wrote: post #372

Earlier quoted context omitted.

I remember hearing that the -300 cruised at a slightly higher Mach number, I assumed that was enabled by the center of pressure being moved back a few metres. But I have no idea what kind of drag the hump transition imparted on the upper fuselage. I kind of assumed that the low pressure zone above the rest of the aircraft would make up for most of the drag penalty of the transition (in general, not -300 specific). I'…

At transonic speeds, wave drag dominates both induced and parasitic drag. The hump reducing drag is about shape (area rule).

Thank you. I'll read about the different drag types.
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