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Glom
2005-Mar-14, 07:46 PM
You may have noticed a lot of civil aviation threads from me lately. This is because I've discovered the forum at airliners.net (http://www.airliners.net), which as a lot of good stuff but charges for posting privileges, so I take the issues I really want to discuss here. Besides, it's nicer here without all the nationalists (I'm American and I hate Airbus. I'm European and I hate Boeing.)

Anyway, 777 seating in economy (I've heard the term Y class used). There are two general arrangments: 3-3-3 and 2-5-2.

The problem with 2-5-2 is the dreaded middle seat in the middle of the 5. You have two people either side of you. However, some say that it's better than on 3-3-3, where there are two seat per row where you are seperated from the aisle by two people. I say that the window seat in 3-3-3 is not as bad as the middle seat in 2-5-2 because at least you have a window and bulkhead rather than more people on the other side.

I suggest an alternate seating plan: 3-4-2. This method has only one double-excuse-me seat per aisle like 2-5-2, but doesn't have the dreaded middle seat. It's the best of both worlds. For tourists flights it is good because it offers far more flexibility. You can have parties of 2, of 3, or of 4 and still give them their own little segment.

The only concern is balance, because now the seating is asymmetric. However, how much of a big deal would this be? It is the equivalent of moving the C seat an aisle's width inboard. Given how close to the longitudinal axis the C seat is anyway, I would be very surprised if this would require anything more than a minor bit of rudder trim.

Nicolas
2005-Mar-14, 07:51 PM
The assymetry would need some trim, which increases drag, which the companies don't want. At cruise, would it be rudder trim? Wouldn't you need direct roll compensation to stay en route?

BTW I'm european, I love the A380, I think 747, 777 and 787 are really cool, and I can't stand the commercial talks Boeing's commercial director aimed at us. :)

W.F. Tomba
2005-Mar-14, 08:40 PM
Could the balance problem be solved by alternating the orientation of the rows?

Tensor
2005-Mar-14, 08:42 PM
Could the balance problem be solved by alternating the orientation of the rows?

Wouldn't that lead to some weird looking aisles?

Doodler
2005-Mar-14, 08:47 PM
Could the balance problem be solved by alternating the orientation of the rows?

That would be an ergonomic nightmare for the flight attendants. Aisles need to run the full length of the compartment for the trays upon which they bring you the pseudo-food.

I suppose another reason for consistent seating arrangement is the interior ventilation. Long running rows of seats allow for very simply duct arrangements where a variable arrangement would require added weight for turns in the ducts. Plus those turns would cut the efficiency of the system down, either requiring a more powerful unit.

Candy
2005-Mar-14, 08:50 PM
Anyway, 777 seating in economy (I've heard the term Y class used). There are two general arrangments: 3-3-3 and 2-5-2.
I know at United, we call Economy Y class, Business is C class (meaning Connoisseur), and First is F class. :-k

W.F. Tomba
2005-Mar-14, 08:54 PM
Well, I've been on a couple of 777s, but I forget how wide the aisles were. If they're two or more seats wide, there will still be a straight passage that's always at least one seat wide.

Good point about the ducts, though.

Nicolas
2005-Mar-14, 08:56 PM
Straight aisles are a must for evacuation puposes as well, so I think that we'd need to solvethe imbalance differently.

A balance that sorts luggage according to density, accompanied by smart loading might be a solution. The problem is that most luggage has the same density.

Nicolas
2005-Mar-14, 08:57 PM
Well, I've been on a couple of 777s, but I forget how wide the aisles were. If they're two or more seats wide, there will still be a straight passage that's always at least one seat wide.

Good point about the ducts, though.

AFAIK they are not 2 rows wide. ANyway, an aisle with no constant width is a nightmare for evacuation, which is a nightmare with prismatic aisles already...

W.F. Tomba
2005-Mar-14, 09:03 PM
A balance that sorts luggage according to density, accompanied by smart loading might be a solution. The problem is that most luggage has the same density.
Maybe you could sort the passengers according to weight. :P

Candy
2005-Mar-14, 09:06 PM
A balance that sorts luggage according to density, accompanied by smart loading might be a solution. The problem is that most luggage has the same density.
Maybe you could sort the passengers according to weight. :P
Then it really would be widebody seating. :lol:

Nicolas
2005-Mar-14, 09:09 PM
I was thinking of passenger weight when posting that myself too! :)

Serious thought about it though: you'd get difficulties with children wanting to be with their parents etc. It might give rise to more inconveniences than it solves.

Evan
2005-Mar-14, 10:33 PM
The weight and balance wouldn't be much of an issue, at least for most of the flight. Fuel in the wing tanks could be used or pumped to compensate. Things like drop down oxygen masks would be a bigger problem. The big jets are pretty tolerant of CG changes. The later models of the 747-400 carry 12,490 liters of fuel in the horizontal stab.

Nicolas
2005-Mar-14, 10:54 PM
Ys, but uneven fuel distribution in the wings gives rise to wing root moments, plus shifting fuel costs energy and hence reduces efficiency.

I've never done X-axis center of gravity shift tests. I've done a test on longitudinal stbility however. In a 10 persons Cessna Citation2, a 86 kg person goes from the most rearward seat (modified plane version, but same rear row position) to the cockpit "door". I measured the change in horizontal stabilizer angle needed for stability, all other factors being (as far as possible) equal. It was between 1 and 2 degrees IIRC.

Shifting rows in a large plane has a relatively shorter moment arm, but the weight is more. So I don't know how large the effect would be of an assymetric layout. It looks less nice of course :).

Evan
2005-Mar-14, 11:10 PM
It only made a slight difference in roll trim on my Cessna 140 to have someone in the right seat vs solo. I think that would be proportionately a much bigger difference than a column of seats on a 777. On the 140 it was trimmed with an aileron tab so I trimmed it for just me as I usually flew solo.

They could also compensate via cargo loading.

Jpax2003
2005-Mar-14, 11:15 PM
I've never been in a wide-body but how much of a problem would an asymmetrical row create? I often fly in Super-80s and they have 2-3 asymmetry, IIRC. I think I was also in a plane that was 1-2 once.

Nicolas
2005-Mar-14, 11:15 PM
It only made a slight difference in roll trim on my Cessna 140 to have someone in the right seat vs solo. I think that would be proportionately a much bigger difference than a column of seats on a 777. On the 140 it was trimmed with an aileron tab so I trimmed it for just me as I usually flew solo.

They could also compensate via cargo loading.

You mean you used the very same trim tab setting (angle) as when flying alone, or you used the aileron trim tab?

About the cargo, if the cargo part of the fuselage is completey full with cargo boxes, there is little that can be done, as most cargo has the same density in a passenger jet.

Evan
2005-Mar-14, 11:40 PM
I mean I set the aileron trim tab to fly straight and level when solo. With a passenger it caused only a very slight right roll tendency that you could easily hold by the weight of your hand on the wheel.

Nicolas
2005-Mar-14, 11:45 PM
I mean I set the aileron trim tab to fly straight and level when solo. With a passenger it caused only a very slight right roll tendency that you could easily hold by the weight of your hand on the wheel.

OK I see. I think the roll tendency of the airliner would be rather small. The trim correction (constant manual force can be seen as a trim correction as well) will result in extra drag. I don't know how much it would be. ON long trips, it could become a drawback concerning the current fuel prices.

Designers would have to go through the effects of assymetric loading on the structure itself as well, especially under limit loading of course.

tmosher
2005-Mar-15, 01:22 AM
Well, I've been on a couple of 777s, but I forget how wide the aisles were. If they're two or more seats wide, there will still be a straight passage that's always at least one seat wide.

Good point about the ducts, though.

AFAIK they are not 2 rows wide. ANyway, an aisle with no constant width is a nightmare for evacuation, which is a nightmare with prismatic aisles already...

Typically, the aisles in coach section on a 777 are 17.5 (3-4-3) to 19.25" (2-5-2) wide (this is based on data gleaned from Boeing's 777 characteristics manual). Of course, there are other arrangements based on the airline's preference such as 3-3-3 in coach or 2-4-2 in the back of the aircraft.

Usually, there is symmetry in the seating arrangement to fit the seat tracks and the PSU's (passenger service units).

Glom
2005-Mar-15, 05:27 PM
Perhaps if the configuration was flipped in the different sections so the the F/As would only have to shift the trolley in the big gaps by the exits.

Nicolas
2005-Mar-15, 05:33 PM
Perhaps if the configuration was flipped in the different sections so the the F/As would only have to shift the trolley in the big gaps by the exits.

That would result in a torsional moment on the fuselage, but I don't think it would be a problem. I'd have to see a computer rendering of the layout with overhead compartments etc to see if everything would be feasible in reality (I'm a bit tired now, I can't portrait it completely in my mind; I do know what you mean though, don't get me wrong)

Glom
2005-Mar-15, 05:53 PM
Let me try this crude illustration:



|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
|(1)(2) (1)(2)(3)(4) (1)(2)(3)|
| |
| |
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|
|(1)(2)(3) (1)(2)(3)(4) (1)(2)|


Okay, so that looks pretty weird, but then it's hardly a scale drawing. I guess the problem on the 772 is that there are only two Y class sections. So the distribution in the back is different from the distribution in the front. I was counting on more smaller sections that would allow the difference to become more fudged throughout the aircraft. The 773 doesn't look much better either.

Nicolas
2005-Mar-15, 05:55 PM
Thanks for the drawing. That was the part I could visualize however, so sorry for the work :oops: . The drawing made me realize that there would be some design issues with the "central" overhead compartments, as they would have a different clearance left vs right.