Search

An experiment was conducted to evaluate approximate analytical methods for predicting the reduction in parachute drag due to forebody wake effects. The drag of a 20/sup 0/ conical ribbon parachute was measured at several axial stations behind an ogive-cylinder forebody with and without fins. The same parachute was tested in undisturbed flow (where wake effects were negligible) so that the effects of suspension line length on parachute drag could be separated from the drag losses caused by the turbulent wake. Total head pressure surveys were made across the forebody wake and integrated across the canopy skirt area to determine the effective dynamic pressure acting on the parachute. Experimental results confirmed the validity of the underlying physical model of the parachute/wake interaction: the ratio of parachute drag behind a forebody divided by wake-free parachute drag is equal to the ratio of effective dynamic pressure acting on the parachute divided by freestream dynamic pressure.

Kevlar-29, an aramid fiber manufactured by DuPont, is being used on parachute systems requiring high strength-to-weight ratios or resistance to sustained high temperatures. Tests of parachutes using Kevlar webbing, braided cords, ribbons, and thread have demonstrated that these Kevlar materials can be used successfully in ribbon parachutes with no detrimental effects on performance. A few changes must be made in the design of a ribbon parachute to accommodate Kevlar's high modulus. Examples of parachutes that use Kevlar suspension lines, radials, ribbons, reefing lines, bridles, and skirt bands are presented to show that they are much lighter and more resistant to aerodynamic heating than their all-nylon counterparts.

Results are presented for twenty-nine flight tests of a 22.2-ft (6.8-m) diameter ribbon parachute (reefed for 0.5 sec) with a nominal 2000-lb (907-kg) store. The design, fabrication, and packing of the parachute system are discussed. Low altitude drop tests were made with F-4 and A-4 aircraft at Mach numbers from 0.57 to 1.22, and rocket-boosted tests were made at Mach numbers from 1.62 to 1.70, the latter corresponding to a maximum dynamic pressure of 2720 psf (130 kN/m2). The maximum measured snatch load, reefed stage opening shock, and second stage opening shock were approximately 65 klb (289 kN), 165 klb (734 kN) and 150 klb (667 kN), respectively. The measured load data and sequence of parachute function times are relatively consistent and repeatable. There is no discernible effect of Mach number on the steady-state drag area of the reefed parachute at Mach numbers from 0.7 to 1.50. Nomenclature At,'Ae = effective canopy inlet and exit areas, respectively, during inflation process