Quantification of Drag from Flat Suspension Line for Parachutes and the Influence of Flow Induced Vibrations

To increase the accuracy of autonomous parachute systems, the drag resulting from a common suspension line was quantified. 1000 pound flat Dacron parachute suspension lines were studied to assess its single line drag contributions and how flow induced vibrations affected the line’s profile drag. Current parachute models either neglect the drag caused by suspension lines or use circular cylinder geometry, leading to incomplete predictions of aerodynamic parameters and thus less-than-optimal performance. To quantify drag, the Jones technique, a modified momentum deficit wake profile technique, was validated against published data on a static 2:1 ellipse and then applied to both static and vibrating suspension lines. In experimental testing, the suspension lines were analyzed at three flow velocities and three tensions which closely simulated flight conditions. While the majority of testing involved the streamlined orientation, the effect of flow incidence angle was also investigated. The line has proved to be quite varied in response to fluid-structure interactions and resulting drag coefficients. When static, the line has coefficients of drag values of approximately 0.3 with uncertainty values of 0.02-0.07 at 0° angle of incidence. Drag coefficients increased to general values of 1.2±0.05 and 1.5±0.09 for 45° and 90°, respectively. The higher drag contributions for a majority of incidence angles make flat braided line suboptimal for higher glide slope parachute systems. Oscillation frequencies proved congruous with previously measured values and predictions, and the torsional vibrations had amplitudes with possibly some sensitivity to flow speed. Drag coefficients for vibrating lines, which only occurred for 0° angle of incidence, fell between 0.30 and 0.45 on the average.