Estimation of Drag Coefficient from Flight Data of a Cargo Shell

Abstract

[Abstract] Two schemes to extract drag coefficient, CD, by processing radar tracked trajectories of artillery shell in motion have been proposed. Flight trajectories of artillery shell are considered. During design, development and validation of new artillery ammunition, a large number of these ammunitions are routinely fired to assess it’s range and accuracy characteristics. Trajectories traversed by these ammunitions in motion are tracked by a Doppler radar located at the firing site. The proposed schemes are applied on the radar tracked trajectory data of artillery shell to estimate the drag coefficient. The drag coefficient is strong function of Mach number. In order to simulate accurate flight dynamical model of artillery shell in motion, it is necessary to have accurate numerical values of CD at the corresponding Mach numbers. To capture the functional relationship between CD and Mach number, the drag coefficient CD of the ammunition was assumed to be a polynomial function of Mach number (separately for subsonic and supersonic). The coefficients of the assumed polynomial were estimated by minimizing the error between measured and estimated trajectories. In the second scheme, whole trajectory was split into different sets containing 50 or 100 data points. Each data set was processed using the proposed schemes to estimate numerical values of drag coefficient, CD corresponding to the average Mach number of the chosen data set. The proposed schemes were applied to estimate the drag coefficient by processing the measured trajectory data of artillery shell in motion. The estimated values of the drag coefficient (at different Mach numbers) have been presented along with its standard deviations. The difficulties encountered in processing the real trajectory data using the proposed schemes are also highlighted. It is observed that the proposed schemes could advantageously be applied to quickly estimate the numerical values of the drag coefficient at corresponding Mach numbers, by processing the trajectory data of artillery shell in motion.