|Quoting DLa320 (Thread starter):|
I know that planes can't be overweight when taking off so everything is distributed evenly to prevent being overweight, but how is the exact weight of the plane determined. Is it calculated manually or by some kind of scale.
You have a couple things going on here. While there are maximum weight limits for cargo compartments and such, the moving of passengers and bags has more to do with balance. All aircraft are designed to operate within a fore and aft limit. Imagine the aircraft being balanced on a nail. Moving the weight around makes that nail change places which affects the handling of the aircraft. Going too far one way or another can render controls ineffective, hence the limits.
As for the weight itself, an aircraft is only allowed to carry so much. Maximum ramp weight, maximum takeoff weight, and maximum landing weight are limiting factors on the aircraft itself. In some cases you may also see limits imposed by the strength of the runway and taxiways.
Calculations are something you learn from the first flight. When flying small GA
aircraft you add the total weights of your passengers and bags.
At the airlines, we use average weights. Since it's impractical to make everyone stand on a scale, we pretend every passegner boarding weights the same, let's say 190lbs. Bags are also counted at 30 pounds each, larger bags are 60 pounds. Our plane is divided into 3 zones for passenger seating and two bag compartments for balance computations. While it sounds very haphazard, it's very effective. These weights are also adjusted fairly often. In the 6 years I've been an airline pilot I've seen the weights increase 3 times as we as Americans get fatter.
After we find out the passenger and bag count, I enter this into the ACARS and it sends a text message to a performance computer. Once it's calculated, it tells us if our weight is within limits, what runways we can/can't use, our flap setting, thrust setting and our speeds for takeoff. If we are overweight or out of balance it tells us what to do to get within limits. Moving passengers is most common but in the extreme we may have to take a couple people off. All of this can (and used to be) done by hand but like anything, the computer makes it faster which saves the company money and improves on-time numbers (and limits mistakes).
Weight and balance, two things that are intertwined but not exactly the same.