dla320
Posts: 22
Joined: Wed Aug 10, 2011 7:48 pm

Weight Of Plane

Sun Aug 28, 2011 1:51 pm

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.
 
26point2
Posts: 816
Joined: Wed Mar 03, 2010 6:01 am

RE: Weight Of Plane

Sun Aug 28, 2011 4:08 pm

In the bizjet world the "empty weight" is measured on a scale. Three scales actually, one for each gear, then added. FAA required every 24 months and usually results in a slightly heavier plane each time it's weighed. Not sure about weighing airliners but likely the same thing?

Empty weight + fuel + payload = actual weight.

[Edited 2011-08-28 09:10:22]
 
BMI727
Posts: 11123
Joined: Mon Feb 02, 2009 9:29 pm

RE: Weight Of Plane

Sun Aug 28, 2011 4:52 pm

Quoting DLa320 (Thread starter):
Is it calculated manually or by some kind of scale.

For preflight purposes it is calculated by computer since weighing the plane before each flight is impractical. Just take the operating empty weight of the plane (which can vary greatly between airlines and often within one fleet) and then add the weight of the fuel, passengers, and cargo.
Why do Aerospace Engineering students have to turn things in on time?
 
rfields5421
Posts: 5638
Joined: Thu Jul 19, 2007 12:45 am

RE: Weight Of Plane

Sun Aug 28, 2011 5:49 pm

Quoting 26point2 (Reply 1):
Not sure about weighing airliners but likely the same thing?

I'm not sure of the exact procedures - but all aircraft are required to actually be weighed every so often.

The measured weight is listed for each aircraft - then they start adding weight.

Standard operational items, the food and beverages, the crew, the passengers, the baggage - and then the amount of fuel which can be legally carried.

For most weights - they use a standard average: passenger weight = x lbs per passenger times the number of passengers.

The same with baggage.

One of the issues with smaller regional type aircraft is that the 'standard' weight could be too low and the aircraft could easily be overloaded. Sometimes they actually have to weigh the bags and add up the totals.
 
pilotpip
Posts: 2820
Joined: Fri Sep 19, 2003 3:26 pm

RE: Weight Of Plane

Sun Aug 28, 2011 6:40 pm

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.
DMI
 
rfields5421
Posts: 5638
Joined: Thu Jul 19, 2007 12:45 am

RE: Weight Of Plane

Sun Aug 28, 2011 7:49 pm

Quoting pilotpip (Reply 4):
Calculations are something you learn from the first flight. When flying small GA aircraft you add the total weights of your passengers and bags.

For those who don't fly - it is often easier to deal with weights in a large aircraft than small ones.

I've got a couple friends that I cannot take flying at the same time. The weight of the three of us in that small GA aircraft would put it overweight with zero fuel onboard.
 
delta-flyer
Posts: 2631
Joined: Mon Jul 30, 2001 9:47 am

RE: Weight Of Plane

Sun Aug 28, 2011 8:18 pm

Quoting pilotpip (Reply 4):
Since it's impractical to make everyone stand on a scale, we pretend every passegner boarding weights the same

Hehe - this brings back memories .....

When I was a young lad, my mother and I emigrated to Canada and flew from Vienna to Moncton NB on a Maritime Central Airways chartered DC-4. Prior to boarding, every passenger had to stand on a scale with our total baggage (checked + carry-on) and our weights were recorded by one of the pilots. There was a large round scale - probably 75 cm diameter - displaying the passenger's weight, so there was no hiding your weight from the rest of the passengers, who were all gathered around awaiting their turns.

I was first, my mother was second, and all 70 or so passengers got weighed, in turn.

The flight left Vienna in the evening, stopped in Glasgow to refuel, then Reykjavik for breakfast and fuel, and arrived mid-afternoon, local time in Moncton. It took roughly 24 hours total.

Whatever we packed with us was all we had when we started our lives in Canada.

Here is a little tidbit of information about our flight ... http://books.google.com/books?id=K33...ada%20hungarian%20refugees&f=false
"In God we trust, everyone else bring data"

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