Problems Facing Flight: Weight

Weight and balance is an important factor in today aircraft. If you try to balance a ruler in your hand you notice that you have to place your finger somewhere in the center because that is where the center of gravity is. The center of gravity is a point where the weight of both sides is equal. If you hold something at the center of gravity, it will be totally balanced. Well The center of gravity is used similarly with aircraft.

The center of gravity on an aircraft is located close to the wing area. At this point everything is balanced. There is a range marked on aircraft where the center of gravity has to lie in. It is usually specified using the datum line as a reference. The Datum line is a set point where all measurements are taken from. If the center of gravity is out of range the aircraft becomes more and more difficult to control. It reaches the point where the aircraft can not stay in air. Balancing the aircraft takes place when there is an alteration on the craft. For example if a seat is taken out or if new radio equipment is installed.

FAA certified mechanics are the ones usually doing this task. Balancing an aircraft is not as difficult as it sounds. All we have to do is draw a table and list values. Below you will find a sample table with values to show how it is done.
ItemWeightARMMoment
Aircraft15000 lbs72 inches1080000
Radio15 lbs20 inches300
10 Seats400 lbs115 inches46000
Battery20 lbs20 inches400
TOTAL:15075 lbs1126700
Total Moment/Total Weight = new center of gravity.

In this case the center of gravity has moved from 72 inches to 36.9 inches from the datum line.

The way this works is the weight and arm are multiplied together and we get the moment as a result. The arm is simply the distance from the datum line. We first enter the aircraft and the current center of gravity known. This could be found in the aircraft log. Next we do the same for the other components that we are going to add. Except the Arm of the other components will be the distance from the datum line where the object will be placed. Then we add up all the values for the moment and weight and we divide. Moment/weight. This gives us the new center of gravity for the aircraft.

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