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

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  •  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:

      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.

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