BoeingBoy

You'd be surprised. Right after the US/PI merger blocking rear rows was common - US didn't have F/C and apparently it raised cain with the US W/B system for the PI planes. Plus it didn't help that PI loaded the belly bins to make the W/B work out while US loaded them depending on where the bags/cargo was going (destination in one bin, connecting in another) then moved passengers to make the W/B work. It wasn't unusual on the 727-200 to have up to 3 rows blocked off in the back of coach for the first couple of years after the merger, something I'd never seen at PI.

Just a FYI, if you're hand flying you can tell when someone walks toward the back or front of the plane. It's simple mechanical advantage. The larger the plane, the longer the arm that the weight of a passenger in the back can act through and the moment about a pivot point (in this case the pitch tendency about the CG) is the product of the weight and the square of the length of the arm. That squaring of the length of the arm means that the moment varies exponentially with the length of the arm - double the length of the cabin and the moment quadruples. It's the "Give me a lever long enough (the arm) and a place to rest it (the cg) and I can move the world" theory.

Jim

cwe84

Thats your opinion and you are entitled to it. Having flown the socalled worlds best airlines even in premo cabins all I have to say is they are just like US carriers. Its what your expectations are and what you believe service is.
Was it great service when a Singapore F/A told me I was fat and wouldnt let me have a glass of wine? Was it 5* service on Qatar when the crew ate my special meal? Was it service when the TAP F/A hit me in the head with a bottle of wine and spill it all over me and didnt appologize? Was it service when I was on SAA and my IFE didnt work and the purser told me I was a snot nose brat? Nope none of those were service and most of those were on revenue/miles tickets.

My best experiences so far have always been on US carriers. The attention to the finer details arent there I will admit. But I always feel like I am at home when I am onboard. To each his own experience.

747freightPilot

It's pretty clear that this wasn't done for balance.

I was an E145 pilot for 7 years and a captain for 5 and regularly had to instruct flight attendants to move people aft; I still deal with W&B prior to every flight in my current job as a 747 f/o. On the E145, needing to move people only happened when the plane was less than 2/3rds full and a disproportionate number of people are sitting in a particular section of the plane while other sections were empty.

The situation in the OP was done so that this F/A could have here own little kingdom on the last row for half the flight. Not that I can criticize because that's what I was trying to do too, then again I was on a paid ticket.

Also the F/A jumpseats on the airbus aren't bad. I've sat on many flight attendant jumpseats and would take them over packed-like-sardines middle seat any day of the week.

tommyleo

The plane had a whole lot of cargo?

747freightPilot

ORD-HKG is beginning to push the limit of a 744's range. On flights that long the weight of the fuel begins to limit the amount of passengers, bags, and cargo you can take. It's a 7500 NM trip and usually has significant headwinds; the 744 can usually do about 5000-6000 NM before payload starts to be limited.

tommyleo

Very cool description. So that means that six pax seated in the last row have the same W/B effect as, say, 20+ pax seated 10 rows forward?

BoeingBoy

I can't give an exact ratio of pax/row# but generally yes. Blocking a row at the CG would have no effect (except the new CG because the passengers were moved) while blocking the row that's the greatest distance from the CG would have the largest effect.

If you think of a plane being an arrow - the CG ahead of the feathers (tail) - it'll make more sense. Put an arrow in a bow backwards - feathers in front - and it won't fly straight. Having the CG in front of the controls (the feathers) adds stability. The further the CG is ahead of the controls, the greater the stability. However, you can also have too much stability if the controls don't have the authority to overcome the stability. You push the yoke forward or pull back and nothing happens. Thus airplanes are designed to have the CG within a certain range, usually measured as distance from some reference point like the nose. As long as the CG is within the design range the plane is stable without being too stable.

The last thing you want is for the CG to be so far aft that you run out of control authority to keep the nose up (or down) - the pitch moment of the elevator works through an arm whose length is measured by the distance to the CG. As the CG moves aft, the weight of the forward passengers exerts a greater pitch down moment because of a longer arm while the elevator exerts a smaller pitch up moment to counter the passengers because of a shorter arm. Because jet transports are designed with movable horizontal tails (based on findings in the X-1 tests), that movement can be used as a form of elevator input.

Remember the Express turboprop that crashed on takeoff from CLT a number of years ago? That was a combination of CG being aft of limits (due to the assumed passenger/baggage weights in use at the time) and bad control cable rigging which resulted in not having the full elevator authority. When the crew pitched up to take off, the CG problem caused dynamic instability which caused the nose to keep pitching up and the control cable mis-rigging reduced available elevator authority to the point that the crew was unable to stop the pitch up. The plane stalled and crashed, killing everyone on board I think.

The second worst situation is to have the CG so far aft that in the pitch axis the plane becomes dynamically unstable but is still controllable - if something causes a pitch up or down the effect gets worse as the pitch increases or decreases and elevator input in required to return the nose to where it should be. I made one flight in a DC 3 (a former life) where that was the case and it's a handful requiring constant attention.

So it's important to keep the CG within the design range. Which apparently has nothing to do with the OP's experience.

Jim

cwe84

I know that.... It was just a reference to tommyleo that even one person can make the difference for weight and for balance.

iztok

I wonder how this works on the flights to TLV (I flew CO back then) when over a dozen of people go to the back galley to pray in the morning.

I heard that LY didn't allow this thus many orthodox Jews flew CO that allowed such congregation. Not sure if new UA and US allow it.

CALMSP

UA couldn't find an extra 190lbs to put one more standby on when there was 100+ open seats? Something doesnt sound right.

CALMSP

^

aztimm

I'd like to remind everyone to both stay on topic and avoid any personal attacks.

For those who haven't looked at the Flyertalk Guidelines & Rules recently, here's the section on Personal Attacks:

http://www.flyertalk.com/help/rules.php#q87

Flyingfox

More power to you! We have had very different experiences indeed.

lougord99

You know a whole lot more than I do about this, but I believe you are wrong here.

http://en.wikipedia.org/wiki/Center_...of_an_aircraft

That is saying calculate the weight by the arms - not the arms squared.

http://en.wikipedia.org/wiki/Center_of_mass

No squaring here either

http://www.free-online-private-pilot...d_balance.html

The table noted here did not copy to this post, but again it was simply weight times arm length.

You were non-commuter plane pilot as best I can tell and so I assume you mean a non-commuter plane. Let's take a 737.

A reasonable assumption for take-off weight is in the neighborhood of 100,000 lbs. (http://en.wikipedia.org/wiki/Boeing_737_Classic)

A large ( 250 lb. ) man walks from the front of the plane to the back of the plane. So we take his weight times the distance walked and divide by the weight of the plane. So he has walked in the neighborhood of 100 ft. or 1200 inches. So he has moved the center of gravity of the loaded plane back about .3 inches.

Can you really feel a difference of .3 inches in the CG on your controls?

BoeingBoy

It could well be. The FAA has a funny attitude about weight & balance. The weight of the fuel, and cargo is known. The weight of the airplane is known but the "empty" weight used by airlines includes crew and their baggage, catering supplies (meals, beverages, etc) which can vary. Passengers and their checked baggage weight is based on an average weight per passenger or bag. Carry-on bags are included in the average passenger weight.

Given the average weights in the calculation, the loaded aircraft weight is only an approximation. For a 747 it's probably within 500 or 1000 pounds.

But if that calculated weight is one pound over the max weight allowable something or someone has to come off the plane.

US flies the A330-200 to TLV - the only plane in the fleet that has the range with a full load of passengers and crew. They could use an A330-300 - it can hold enough fuel for a non-stop flight but not enough fuel plus a full load of passengers and their baggage. To use the A330-300 for a non-stop flight means restricting the number of passengers and bags to less than the A330-200 can carry since the extra weight of the -300 also has to be offset.

Jim