Note: The term “plastic,” when used in conjunction for the materials
used as stiffeners in modern parachute containers, is a misnomer.
In reality, the composition of the material varies. The most
common material used today is MDS nylon, molydisulfide nylon.
In addition, Lexan®, a clear
polycarbonate material and HDPE,
high density polyethelyne, are also used. The most common thicknesses
used are .025", .040", and .060", which are standard commercial
thicknesses commonly available.
Stiffeners are used primarily as backing for grommets to spread the
load placed on closing flaps. Instead of focusing the load on the
diameter of the grommet, it is spread out across the length of the
stiffener, resulting in a smoother flap and container. Consequently,
replacing plastic stiffeners almost always requires replacing the
grommet as well. Usually the plastic breaks at the grommet location
because the hole for the grommet is the weak point. The following
procedure shows the replacement of the bottom main flap
stiffener of a Javelin container.
1.0 DISASSEMBLY:
1.1 Unpick the stitching that holds the binding tape to the bottom
flap [Figure A]. Remove the grommet.
1.2 Remove the stitching that holds the stiffener in position. Remove the stiffener.
2.0 REASSEMBLY:
2.1 Use the original stiffener as a template to cut a new stiffener [Figure B]. While many of the
older containers use HDPE or other materials, most of the newer designs use MDS nylon
because of its superior properties. Because of this, many riggers use MDS exclusively for
replacing any stiffeners.
2.1.1 Mark out the outline of the original stiffener on the MDS.
Mark the center of the hole for the grommet very precisely.
2.1.2 Use the basting tip to mark the center of the hole for the grommet.
Push the tip through the MDS until the shoulder of the tip
makes an indentation in the MDS [Figures C, D, E]. This
forms a pilot hole for the drill.
2.1.3 Using heavy shears or tin snips, cut the MDS nylon to shape.
Clip the corners to remove the sharp ends and if the edges are
sharp or rough, sand them with sandpaper.
2.1.4 Secure the MDS against a piece of wood and drill a 3/8" hole.
While this hole may seem big for the shank of the grommet,
when installed and the material is punched, it will be the right
size. A common mistake is to make the hole too small and
when the grommet is set, it cracks the plastic.
2.2 Insert the stiffener in between the layers of fabric of the bottom
flap and let it float inside.
2.3 Baste the two layers of fabric together with the single needle.
2.4 Restitch the binding to the bottom flap [Figure F].
2.5 Slide the stiffener to the edge of the flap and align the hole in the stiffener with the hole in the fabric. Use an “O” grommet to align the holes [Figure G].
2.6 Stitch the stiffener in place as per the original installation.
2.7 Insert the grommet with the correct orientation, and set with
the grommet set [Figure H]. Make sure that the grommet is
set sufficiently so there is no exposed edge to snag the lines
or material. Use the feeler gauge to check the gap under the
edge of the grommet [Figure J]. It should be no more than
.010". If more, hit the set again to tighten the grommet.
3.0 INSPECTION:
3.1 Verify the stiffener backing is resewn.
3.2 Check the grommet orientation.
3.3 The grommet must be set tightly and measured.
3.4 There should be no sharp edges on the inside of the grommet.
