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Weight and Balance

The weight of the aircraft and how it is distributed influences every aspect of its performance. If it is too heavy structural damage may result due to turbulence, manoeuvring, or hard landings. The weight distribution or balance is important for stability and control considerations. The tail lifting surfaces must be able to keep the main wings in the normal lift producing angles of attack. If the weights are too far forward an excessive nose down attitude may result in high airspeeds on landing and the inability to round out the aircraft. If the load is too far aft then the tail surfaces may not be able to keep wings below the critical angle of attack and it may stall readily.

We describe this balance by multiplying weights by distances (called ‘arms’) from a known reference point on the aircraft (Reference Datum). A moment is the product of the weight of an item multiplied by its arm. When you divide the total all the moments of various weights of pilots and the aircraft, by the total weight, you are left with a distance from the reference point. This distance is the loaded centre of gravity of the aircraft. The aircraft designer sets a range for this that allows for safe operations.

For a 2-33 with Station 0 at nose and a all-up weight of 1040 lbs. If the weight properly distributed it will have a loaded centre of gravity between station 78.20" forward and station 86.10" rear(aft) limit. Given:

  1. Front pilot weight of 170 lbs at sta. 43.80"
  2. Rear pilot weight of 150 lbs at sta. 74.70"

                Weight X ARM = MOMENT
Sailplane Empty 612      96.12 58,825
Front pilot     170      43.80  7,446
Rear pilot      150      74.70 11,205
                ___            ______
Total Weight    932
Total Moment                   77,476


Total Moment/Total Weight = 77,476/932 = 83.13

The total weight of 932 pounds is less than the maximum all-up weight of 1040 pounds and the loaded centre of gravity is 83.13 inches which is within the design limits.