1383. Design, Fabrication, Calibration, Application, and Testing of Advanced Aircraft Weighing Systems

Paper

Abstract

The objective of this research effort was to apply the knowledge gained from the development of the individual load cell and read out system on the prior contract to a production weighing system consisting of on-top-of-jack load cells for level weighings and under tire platforms for ground attitude weighings. Part of the task requires development of a program for correction of c.g. from ground attitude to level position. The approach was to design, fabricate, assemble, calibrate, and demonstrate these two systems for accuracy, linearity, repeatability, and simplicity by weighing an aircraft. Also, the aircraft was weighed at various out-of-level positions and a program developed from which a curve can be plotted indicating out of level angle versus c.g. correction factor.
Significant results of this developmental program are that an aircraft can be weighed repeatedly to plus or minus one pound and can be weighed in the ground attitude and corrected to the level attitude with a high degree of accuracy. Vertical location of the vertical c.g. would aid in the accuracy of the calculations. It appears that an aircraft can be weighed more accurately on the platforms than with the on-top-of-jack load cells because of the numerous forces that enter the picture when using three or more jacks interfacing with the on-top-of-jack load cell which in turn interfaces with the jack pads on the aircraft and the bottom of the jack interfaces with the floor. The next most significant results noted in the development and application of the weighing system is the temperature effect, especially at temperatures below 60F (16C). Temperature profiles were conducted on both the newly developed load cells and platforms as well as one of the current weighing systems being used by USAF. The corrections for temperature change are significant. The systems exceeded the 0.1% requirement for accuracy.
The application resulting from this program is for weighing aircraft, either in a level position on-top-of-jacks or on platforms in a normal ground attitude to an accuracy of ~ one pound per platform or load cell or ~ 3 pounds (1.4 kg) per aircraft. It is recommended that all aircraft weighing systems employ a load cell with side load cancelling features. Due to the risk associated with the weighing of aircraft on top of jacks, it is recommended that the ground attitude weighing system be considered with development of the appropriate correction curves.