A Critique of the Bell Helicopter Textron COBRA 2.75 Inch Rocket Ballistic Algorithm

摘要

The ballistic algorithm currently implemented on the AH-1S (Modernized) Cobra Helicopter for the 2.75-inch MK 40 rocket system is of interest due to ongoing efforts involving the Mk 66 rocket system. Additional interest arises due to past unresolved controversies centering on the issue of the adequacy and correctness of the mathematical formulation. The question is examined by comparison of the Bell Helicopter Textron (BHT) algorithm with a simple free flight model derived from basic ballistic equations. The analysis indicated the omission of a significant drag effect in the elevation equation and the lack of any compensation for wind effects in free flight. The BHT algorithms is shown to be deficient in the formulation of a component term which compensates for the ballistic influence of helicopter velocity normal to the line of site. The general inaccuracy of the 2.75-inch rocket has previously masked any chance of detection of a systematic bias that might be due to a poor ballistic algorithm. The insight provided by this critique leads one to focus on hover firings where analysis predicts a bias should be more clearly evident. The test data provides a dramatic confirmation of the theoretical inferences which imply a 60 mil elevation error bias at maximum range. (Author)