COMPARISON OF ELECTROSTATIC AND AERODYNAMIC FORCES DURING PARACHUTE OPENING

The work reported here seeks to determine the conditions, if any, under which electrostatic effects become comparable to aerodynamic forces during parachute opening. A simple Bernoulli model is used to estimate the principal aerodynamic forces during the early stages of inflation. The electrostatic forces during this period are found by computing the Coulomb attraction between two folds of parachute cloth charged to opposite polarity. These attractive Coulomb forces produce an inward ''electrostatic tension'' that acts to oppose the outwardly directed tension caused by the Bernoulli pressure. The investigation involves theoretical analysis, small-scale wind-tunnel tests, and extrapolations to full-size parachutes. Our present estimates suggest that aerodynamic forces are two to three orders of magnitude larger than electrostatic forces for typical levels of air velocity and charge density. Typical levels of charge density are defined as those easily obtained in the laboratory via the process of triboelectrification (creation of static charge by friction).