The weight of an aircraft influences more performance variables than any other single parameter during flight. Items such as acceleration, rate of climb, and maneuverability are heavily influenced by the aircraft weight. Changes to the weight over time, such as equipment additions, new paint or structural repairs and alterations are often overlooked as having a large impact on the performance and safety of the aircraft.
The primary reason for weighing an aircraft is to find out its empty weight and determining where the center of gravity is located. The pilot has the responsibility prior to every flight to know the maximum allowable weight of the aircraft and its center of gravity limits to comply with the certification limits established for the aircraft. Knowing the weight and center of gravity also ensures that the aircraft flies in a balanced, safe operation and consumes as little fuel as possible.
New weight and balance information is regularly required for all aircraft.14 CFR part 125 requires the current empty weight and center of gravity to be calculated from the values established by an actual weighing of the aircraft every 36 calendar months. Some aircraft are exempt from the 36-month requirement, however, all aircraft should not exceed 48 calendar-months since the last formal weighing.
Equipment for Weighing
There are two basic types of systems used to weigh aircraft: a Peries of electronic pressure sensitive Load Cells that are placed between the aircraft jack and the jack pads on the aircraft, and platform scales on which the aircraft is rolled upon so that the weight is taken at the wheels. The type of equipment selected for the weighing is determined based on the type of equipment available at the site and the recommendation of the aircraft manufacturer.
Aircraft Weighing System Calibration
Load Cell Aircraft Weighing Systems typically contain 3 Load Cells connected into a display console. The Load Cells are placed on aircraft jacks and the aircraft lifted until the weight of the aircraft is suspended by the Load Cells. The display console can provide the weight of each Load Cell individually and can also sum the Load Cell readings together to calculate the total aircraft weight.
The Load Cells typically have a range from 10,000 lbs. to 100,000 lbs. each, so a large load press with the capabilities of those forces is required for the calibration of the cells. The Load Cells can be checked against master Load Cells with higher accuracies, or used in the load press with precision weights.
Each Load Cell is calibrated using a minimum of 10 linear points throughout the full range of the Load Cell. The readings are typically plotted on a chart to produce a correction curve that displays the error of the linearity for the Load Cells.
Platform Scale Weighing Systems typically have capacities that range from 2,500 lbs. to 30,000 lbs. each. They are calibrated using large precision weights that are able to be placed on the top of the platform and the scale readout is compared to the value of the weight.
The Platform Scales can also be connected into a central display to provide the weight of each platform scale or the sum of the scales to display the total aircraft weight.