As a parachute descends, its axis of symmetry oscillates about a vertical axis. This oscillation implies angular acceleration, with consequential linear acceleration developing. The significance of the acceleration terms in evaluating parachute performance has been long appreciated and commonly allowed for in dynamic stability analysis through introduction of appropriate apparent mass and apparent moment and inertia terms. This research, while dealing specifically with the aerodynamic performance of the parachute, considers the experimental technique to measure the total fluid resistance and apparent mass components of the parachute canopy which are related to the behaviour of any bluff body moving unsteadily through a fluid. Total fluid resistance and apparent mass components were evaluated by measuring forces and moments with strain gauges during the relative motion of parachute models submerged in water in a ship tank. While being towed by the motion of the carriage, a slider crank mechanism caused the sting-mounted canopies to be harmonically oscillated at a low frequency along any required line which was parallel to the tank bed. Results show that the apparent mass components depend on the shape of the canopy, its angle of attack and the acceleration modulus (the product of the acceleration of the canopy and its diameter divided by velocity squared) and, except at high values of the latter, can be considerably in excess of potential flow evaluations. A set of differential equations which describe the three-dimensional motion of the parachute canopy-store system during descent were developed. The non-linear equation of motions were solved numerically. The effect on dynamic stability due to the variation of system parameters was studied and appropriate stability criteria were developed. Results show that the resultant dynamic performance is highly sensitive to the chosen values of the apparent mass components.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:361007 |
| Date | January 1982 |
| Creators | Yavuz, T. |
| Publisher | University of Leicester |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/2381/34731 |
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