A SEMI-EMPIRICAL THEORY TO PREDICT THE LOAD-TIME HISTORY OF AN INFLATING PARACHUTE

Present parachute inflation theories are too complicated for design use and, though complex, still contain considerable simplifications in modelling the parachute structure and flow. This paper presents a theory to predict inflation loads which is more suitable for design calculations. Using empirical data extracted from limited field trials of a particular parachute system, the theory can predict inflation load-time histories for the system over its entire operational envelope. The method is used to calculate peak inflation loads for the C9 and Aeroconical parachute types over a wide range of experimental conditions and good agreement with trial results is obtained in almost every case. The shape of the inflation load-time curve for a particular parachute is shown to be determined principally by mass ratio. For a given mass ratio the magnitude of the peak inflation load is shown to be proportional to the square of the snatch velocity. The effects of altitude and canopy size are also investigated. An important new design feature emerges from the analysis in that it is demonstrated that if the suspended mass and operational deployment altitude of the parachute system are known, e.g. as in a barostatically operated escape parachute system, the canopy diameter may be selected to minimise the peak load factor.