COMPONENTS OF PARACHUTES

The design and construction of a parachute and its components are based on the old idea that a chain is only as strong as its weakest link. Every

component, or link from the jumper to the canopy must carry its share of the maximum load that is applied during the opening shock.

The five major parts of a standard service parachute, starting at the top and working down, are the pilot chute, main canopy, suspension lines, harness, and pack. These five major parts are shown in figure 1-3.

PILOT CHUTE

The pilot chute has the job of anchoring itself in the airstream, then pulling the remaining packed components out of the parachute pack. The order of deployment for most parachute

Figure 1-3.-The five major parts of a parachute. 1-5

Figure 1-4.-Pilot chute.

assemblies is the pilot chute, the canopy, the suspension lines, and the risers. A typical pilot chute is shown in figure 1-4.

CANOPIES

Five sizes of canopies are used in naval aviation. They are the 35-foot, 28-foot, 26-foot, 24-foot, and 17-foot sizes. The 28-foot canopy is the size dealt with in this chapter and is most commonly described as a polygon, having 28 sides, and a diameter of 28 feet plus or minus 1 inch. The 28-foot canopy contains approximately 796 square feet of nylon cloth, plus 2,400 yards of nylon thread. The sewing on a parachute varies from 8 to 10 stitches per inch. The cloth that is used in the construction of a parachute canopy is high-tensile strength, 1.1 ounce ripstop nylon. Ripstop nylon cloth must meet the following minimum requirements: tensile strength-42

pounds per square inch; tear strength -5 pounds; air permeability -80 to 100 cubic feet per minute.Tensile strength is the greatest stress cloth can withstand along its length without rupturing, expressed as the number of pounds per square inch. Tear strength is the average force, expressed in pounds, required to continue a tear across either the filling or the warp of the cloth. Ai r permeability is the measured amount, in cubic feet, of the flow of air through a square foot of cloth in 1 minute under a specific pressure.

The suspension lines are sewn into the canopy. These lines run continuously from the connector link on one side, through the canopy, and to the connector link on the other side (fig. 1-5). The material between any two suspension lines is called a gore. There are 28 gores in a 28-foot canopy. Each gore is composed of four sections identified

Figure 1-5.-Suspension lines on 28-foot canopy. 1-7

Figure 1-6.-Close-up view of a gore.

by the letters A, B, C, and D (fig. 1-6), starting with the bottom section. Figure 1-7 is a flat view of the entire canopy, and the note in the figure shows the relationship of the gore in figure 1-6 to the rest of the canopy.

Most woven cloth has two types of threads- warp and filling. These two types are identified by their relationship to the selvage edge. A selvage edge is a finished edge on two sides of a piece of fabric to prevent raveling. This finished edge sometimes has a narrow border of different threads or sometimes it may have a different weave. Warp thread runs parallel to the selvage edge of cloth and runs lengthwise down a roll of fabric. Filling thread runs perpendicular to the

selvage edge or crosswise across the width of the cloth.

The sections used in a parachute canopy are cut at a 45-degree angle to the centerline of the gore. This is called a bias construction and provides the maximum strength and elasticity. The radial and diagonal seams are double lapped for security. The suspension lines are enclosed in the channel produced by stitching the radial seams. Figure 1-7 shows a flat view of this bias construction of the 28-gore canopy. Stenciled on the top center gore (section A of gore 28) in letters one-half inch high and about 12 inches from the bottom of the canopy are the NAVAIRFAC order number, date of manufacture, serial number, and the manufacturer's mark or trademark. Stenciled on the diametrically opposite gore (section A of gore 14) is the date of manufacture and serial number.

If you should have to add markings to the canopy, the marking fluid you use should be in accordance with Specification MIL-I-6903A, Amendment No. 1.

Note the vent pictured in figure 1-8. This vent acts as a relief valve and relieves the high internal pressure within the parachute at the instant of opening. Without this vent, an opening at high speed could result in a dangerous rupture of the canopy. The skirt (not shown) and vent hems are reinforced with 1-inch tubular nylon webbing with a tensile strength (T/S) of 4,000 pounds, to aid in preventing tears from completely separating the canopy.

All machine stitching, except zigzag, should conform to Type 301, Federal Standard 751, and should be not less than 8 nor more than 10 stitches per inch. Ends of all tape, webbing, and lines must be seared to prevent fraying. No waxes should be used. For sewing diagonal seams, either size B or E nylon thread may be used. Use size E thread for all other seams, zigzag stitching, and repairs.

Removable connector links provide a quick attachment for the canopy and suspension lines to the lift webs.

Figure 1-7.-Flat view showing bias construction on a 28-foot canopy.

Figure 1-8.-Vent. 1-9

NOTE: To determine the service life of a parachute component, refer to the Maintenance Requirement Cards, NAVAIR 13-600-4-6-3.