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View Diary: How Airliners Work - Weight and Balance (160 comments)

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  •  Why oh why did I read this diary? (10+ / 0-)

    I'm nervous flying, and we're flying to Seattle this Saturday. Now I'm going to be looking at our fellow passengers and wondering whether their aggregate weight is within the estimated load.

    •  I don't like flying either (20+ / 0-)

      but unless your fellow passenger is the size of an army tank weight isn't something I worry about. turbulence is what I hate, regardless of the fact that turbulence rarely does anything bad.

      I just flew this weekend and happened to sit in front of a traveling pilot who was being grilled by the guy sitting next to him. He talked about the scale of the airline industry, and how many people are taking off at one airport within an hour, and multiplying that out. There's like 100,000 planes in the air over the United States on any given day.

      Then he started talking about birds hitting his engines, I didn't like that so much :(

    •  I wouldn't worry too much (26+ / 0-)

      The pilots want to get there as badly as you do.

      There's enough "slop" in the calculations that things would have to be pretty far off for it to be a problem.

      If the pilot's good, see, I mean if he's reeeally sharp, he can barrel that baby in so low... oh you oughta see it sometime. It's a sight. A big plane like a '52... varrrooom! Its jet exhaust... frying chickens in the barnyard!

      by Major Kong on Tue May 07, 2013 at 02:38:13 PM PDT

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      •  The good ole engineering adage (9+ / 0-)

        Design for 2x what you tell the user they can do, because they're going to push your plane/car/bridge/whatever hard.

        •  Often 1.5X "safety factor" is used for planes (13+ / 0-)

          so that it gives you a decent margin of safety, given the careful procedures Major Kong describes, while keeping the planes from being overly heavy.

          For other things like buildings, there aren't necessarily procedural controls and the weight isn't nearly as important, so the safety factor is often higher, as you say.

          Government and laws are the agreement we all make to secure everyone's freedom.

          by Simplify on Tue May 07, 2013 at 03:39:34 PM PDT

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          •  1.4 FOS against design load and environment (7+ / 0-)

            figure out the design loads, like landing weight, calculate
            forces from landing at max descent rate, then add in  1.4X

            now some real critical structures may be a bit more, but,
            in aircraft, 1.4 is a good working limit, but you do have to look at expected life and strength losses over time, so
            a brand new airplane may have 2.2 in the wing spars, but,
            things like the flaps may be 1.2 because they don't get used much, and they can be changed out during inspections if they are failing.

            but the control envelope?  Hard to manage against misloaded fuel or cargo.

            It's always interesting when they ask people to move forward because of the CG constraint.

            •  Into La Paz At Night in a Snowstorm (8+ / 0-)

              Once I was flying into Santiago, Chile via La Paz, Bolivia on a night flight.  As it turned out that night, La Paz was being hit with a very heavy snowstorm.  We were flying a Boeing 707 combo aircraft, part passenger/part cargo.  They removed the cargo and made sure the passengers were sitting close to wing spar.  It was a good thing too, because you couldn't see the wing tips because of the snow when we touched down in La Paz and the pilot never did apply the brakes, bringing the plane to a stop with the thrust reversers only.  I later found out that the La Paz runway was only about 7K feet long at 12K foot altitude - and the airport was closed for ten days after we departed for Santiago at 0-dark hundred that morning.  

              "Love the Truth, defend the Truth, speak the Truth, and hear the Truth" - Jan Hus, d.1415 CE

              by PrahaPartizan on Tue May 07, 2013 at 06:26:54 PM PDT

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            •  Don't ever figure on slop in airspeeds! (6+ / 0-)

              There's almost no slop in computed airspeeds in aircraft. They're designed for a maximum speed Vd (maximum dive speed), and Vne (never exceed speed) is 90% of that. During design flight testing, one aircraft is flown, usually once, at 95% of Vd.

          •  More structure (0+ / 0-)

            means more weight requiring more fuel to push it around, meaning more weight and more structure to support it. There's a point where over designing defeats its own purpose. 1.5X is what I've understood to be the norm, but it varies depending on who the aircraft is being designed for and it's purpose.

            You..ought to be out raising hell. This is the fighting age. Put on your fighting clothes. -Mother Jones

            by northsylvania on Wed May 08, 2013 at 03:38:03 AM PDT

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          •  Safety factors in buildings: (1+ / 0-)
            Recommended by:
            Simplify

            Large skyscrapers can cause a lot of damage if they fail, so they have pretty high safety factors.  For example:

            The late, lamented World Trade Center towers were built with a "tube within a tube" design (now widely used in modern skyscrapers).  The inner core was designed to handle the static weight of the building and had a safety factor of about 2:1.  The outer perimeter columns were designed to handle the dynamic stresses (loading due to wind, etc.) and had a safety factor of about 5:1.  And at the top of each tower was a hat truss structure that could transfer force between the inner core and the perimeter columns, so that they reinforced each other.  Overall, it was a very redundant structure, able to transfer loads in various ways in case any particular part failed.

    •  completely irrational. (7+ / 0-)

      Per mile you travel in a plane as opposed to driving, you are safer.

      You are excellent at fooling yourself if you imagine that you can drive "there" more safely than "professionally trained pilot" in a well maintained plane can get you "there".

      To those who say you prefer the feeling of having some control of your destiny...
      Get back to me after the dump-truck loaded with granite blows thru the red-light and uses your driver's side door as his alert system.

      I was raised by a tough s.o.b. that loved to have fun but was completely intolerant of fooling around when it came down to business.

      He became the FAA's Chief of Airworthiness the day after an engine fell of a plane climbing out of O'hare.

      I hated his guts at times. Tough way to grow up, or so I thought.
      He didn't raise kids... he raised young people that became responsible adults.

      Since becoming an adult, I've won awards for stuff I've built. I built a reputation for competence.
      I rarely let anyone else work on my vehicles (sailboats, planes, bicycles, or cars).

      Stop fooling yourself with irrational fears.
      There are some very capable people getting the job done.

      Enagaged activism wins elections. 100 million words on liberal/progressive websites gets beat by one new GOP voter casting their vote.

      by Nebraska68847Dem on Tue May 07, 2013 at 07:07:58 PM PDT

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      •  American 191 (5+ / 0-)

        I worked a day shift that day and turned on the TV an hour or so after I got home to see the coverage.

        For the record, although I had worked at ORD at one time, and was very familiar with the layout and procedures, I wasn't working there, then. I was at the ARTCC (ZAU) in Aurora.

        By the way, AA191 took off on 32R, which was where I once witnessed the longest takeoff roll I'd ever seen. It was a Korean Air 747 bound for Seoul nonstop, and apparently fully loaded. It used every bit of of that runway's 10,000'.

        I'm absolutely certain the Major has his own long takeoff roll tales to relate.

        •  There's a tiny golf course (0+ / 0-)

          and park lake off 32R (Lake Opeka).

          I worked in a tiny factory nearby and after work, fished at Lake Park... especially on hot summer evenings.

          Hot days, in low pressure... made for great fishing but terrible altitude density.

          More than once, I saw a 747 take forever to clear the treetops all the way out to the horizon!

          On the other hand, the day I took my SAT's, it was -19 degrees. I know exactly seeing take-offs all but straight up that January morning in 1974. Cold air with high pressure on the tarmac was a pilot's dream! Lots of air on the wing and cold fuel breathing the engines!

          The high school I went to and took my SAT's at... Maine South in Park Ridge.

          I graduated there... as did future POTUS Hilary Rodham Clinton!

          Enagaged activism wins elections. 100 million words on liberal/progressive websites gets beat by one new GOP voter casting their vote.

          by Nebraska68847Dem on Wed May 08, 2013 at 06:14:11 AM PDT

          [ Parent ]

      •  Neb - two office mates of mine (1+ / 0-)
        Recommended by:
        ER Doc

        were on American 191. It was tragic and unsettling. I had flown that flight from Chicago many times. At the time I was flying more than 100,000 miles a year.

        "let's talk about that"

        by VClib on Tue May 07, 2013 at 09:50:34 PM PDT

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      •  People don't think rationally about risk. (2+ / 0-)
        Recommended by:
        ER Doc, northsylvania

        It's really all about emotion.  

        I see this a lot in the very different context of HIV transmission.  People's attitudes and actions are not determined by actual risk.  They make decisions based on emotion, with sometimes unhappy consequences.

        "Ça c'est une chanson que j'aurais vraiment aimé ne pas avoir écrite." -- Barbara

        by FogCityJohn on Tue May 07, 2013 at 10:54:03 PM PDT

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        •  I understand. (1+ / 0-)
          Recommended by:
          FogCityJohn

          Most people play Russian roulette daily... with a two-shooter!

          On the other hand, people convey "fear" upon something that is safer than their logic process.

          We hate being lied to... and yet, we lie to ourselves and believe our own lies!

          Enagaged activism wins elections. 100 million words on liberal/progressive websites gets beat by one new GOP voter casting their vote.

          by Nebraska68847Dem on Wed May 08, 2013 at 06:17:14 AM PDT

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      •  Funny that you mention that (0+ / 0-)
        He became the FAA's Chief of Airworthiness the day after an engine fell of a plane climbing out of O'hare.
        That was American Airlines Flight 191 from Chicago to Los Angeles on May 25, 1979.

        I remember it because I was on that same flight two days earlier. I was going out to Los Angeles to spend the summer with my sister and her husband, working in their law office. Our plane had  "engine trouble" and had to head back to Chicago. As we were landing, I looked out the window and saw fire trucks racing to meet us on the tarmac. We landed without incident, and they switched us to a different plane.

        It was my first flight. I was only 21 at the time, and at that age you think you're immortal. We took off in the other plane and had a completely uneventful flight to Los Angeles.

        Two days later, that flight crashed and everyone on board died, including a relative of someone who worked in my sister's office.

        I still don't know whether the plane I was on that had "engine trouble" was the same plane that crashed two days later.

      •  What?! You want us to rely on actual data... (0+ / 0-)

        ...stats and evidence, instead of feelings?

        You will fail the litmus test, my friend...

        /snark

        Your hate-mail will be graded.

        by PavePusher on Thu May 09, 2013 at 08:21:55 PM PDT

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    •  elmo - commercial US air travel (2+ / 0-)
      Recommended by:
      ER Doc, northsylvania

      is like taking a bus.

      I have flown more than two million miles. It's a piece of cake.

      "let's talk about that"

      by VClib on Tue May 07, 2013 at 09:47:33 PM PDT

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