Ram air parachute canopy with improved nose structure

Aeronautics and astronautics – Safety lowering devices – Parachutes

Reexamination Certificate

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Reexamination Certificate

active

06769649

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to ram air parachutes and more particularly to ram air parachutes having an improved canopy design.
2. Discussion of Related Art
Parachutes have evolved over the years into highly sophisticated systems, and often include features that improve the safety, maneuverability, and overall reliability of the parachutes. Initially, parachutes included a round canopy. A skydiver was connected via a parachute harness to the canopy by suspension lines disposed around the periphery of the canopy. Such parachutes severely lacked control. The user was driven about by winds with little mechanism for altering direction. Furthermore, such parachutes had a single descent rate based upon the size of the canopy and the weight of the parachutist. They could not generate lift and slowed descent only by providing drag.
In the mid-1960's the parafoil canopy was invented. Since then, variations of the parafoil canopy have replaced round canopies for most applications, particularly for aeronautics and the sport industry. The parafoil canopy, also known as a ram air canopy, is formed of two layers of material—a top skin and a bottom skin. The skins may have different shapes but are commonly rectangular or elliptical. The two layers are separated by vertical ribs to form cells. The top and bottom skins are separated at the lower front of the canopy to form inlets. During descent, air enters the cells of the canopy through the inlets. The vertical ribs are shaped to maintain the canopy in the form of an airfoil when filled with air. Suspension lines are attached along at least some of the ribs to maintain the structure and the orientation of the canopy relative to the pilot. The canopy of the ram air parachute functions as a wing to provide lift and forward motion. Guidelines operated by the user allow deformation of the canopy to control direction and speed. Ram air parachute canopies have a high degree of maneuverability.
Canopies are flexible and stretchable membrane structures, they distort based upon mechanical and aerodynamic tensions, stresses, airflows and pressure distribution. Although a cell is modeled as having a basically rectangular cross section, when inflated the shape distorts towards round with complex distortions. Under canopies of conventional design, the leading edge or nose of the ram air parachute is deformed during flight as is the top profile of the airfoil between the ribs. Additionally, with forward motion, the head-on wind overcomes the internal pressurization of the canopy, and deforms the nose of the canopy. This distortion blunts the nose of the airfoil or even indents it, impairing the aerodynamics of the parachute wing. The parachute flies less efficiently as a result. Therefore, a need exists for a ram air parachute canopy which reduces nose distortion and spanwise topskin distortion.
Inlets are required to inflate and pressurize the canopy to maintain its wing shape. However, the inlets are also the greatest source of drag on the wing which slows forward movement and reduces efficiency. The carrying capacity and glide ratio of the canopy would be improved if this drag could be reduced. Therefore, a need exists for a canopy with reduced drag from the cell inlets.
Typically, in a ram air parachute, suspension lines are attached to every other rib, thus creating loaded ribs (i.e., ribs to which suspension lines are attached) and non-loaded ribs (i.e., ribs which do not have suspension lines attached thereto). The different stresses on the loaded and non-loaded ribs also distorts the cell shape.
FIG. 1
illustrates a cross section of a portion of a typical ram air parachute canopy
500
during flight.
FIG. 1
shows two cells formed of parts
501
,
502
,
503
,
504
, with three loaded ribs
510
,
511
,
512
and two non-loaded ribs
521
,
522
. Suspension lines
541
,
542
,
543
are attached to the loaded ribs
510
,
511
,
512
. The top skin
530
and bottom skin
531
tend to arc between the ribs during inflation. Also, the non-loaded ribs
521
,
522
tend to be higher than the loaded ribs
510
,
511
,
512
, which provides a distortion along the span of the canopy. The distortion is aerodynamically undesirable and reduces the efficiency and performance of the canopy.
In order to keep the loaded and non-loaded ribs level and to improve upon the aerodynamics of the canopy, cross-bracing between ribs has been added to some canopy designs. Cross bracing is the use of diagonal ribs in addition to vertical ribs to create more loaded rib—top skin junctions without adding more lines which increase drag and possible deployment malfunctions. Perfection of the top profile of the airfoil is far more important aerodynamicly than the bottom profile. U.S. Pat. No. 4,930,927 illustrates such a design. Cross-braced designs suffers from a number of drawbacks. Cross-bracing results in very complicated construction, high manufacturing costs, and increased packing volume. The standard cross braced design is a ‘tri cell’ construction with a packing volume approximately 25% larger than an equivalent non-cross braced design. A cross section of a tri-cell canopy is illustrated in FIG.
2
. Furthermore, the increased rigidness induced by the cross-bracing creates higher opening forces for the pilot. Typically, large cross porting is used on all of the cells to reduce pack volume, which does nothing to slow the canopy's inflation on deployment. The opening forces can be so severe that they can jar the jumper's body causing discomfort and even injuries. Although designers have implemented “formed” noses, larger sliders, moved bridal attachment points and modified line trims to try to soften the openings of such cross-braced canopies, it has generally yielded limited improvement.
Sliders used to counteract the large opening forces on a cross-braced canopy often cause premature wear on the suspension lines of the canopy. A slider is a rectangular piece of material with a grommet at each corner. Grouped suspension lines pass through each grommet. When the parachute opens, the force of the opening canopy and separating suspension lines forces the slider down the suspension lines. Air resistance tends to slow movement of the slider and, hence, restrict opening of the canopy against the spreading force of the inflating canopy pushing the slider down. The most force on the slider comes from the lines to the outermost cells, which pushes the slider down rapidly caused friction heat. The heat changes the dimension of many standard types of lines (e.g., Spectra, dyneema brand lines). It is not uncommon for outer lines to change in dimension as much as five inches in only a couple of hundred jumps. Accordingly, cross braced canopies are almost exclusively supplied with Aramid based lines (e.g., Kevlar, Vectran, etc.). These lines do not change dimension with the generated slider-friction heat solving the problem stated above, but suffer from micro-fiber cracking. Accordingly, if over jumped, Aramid lines can break catastrophically with no warning.
Prior art canopies have included formed noses with shaped inlets to limit opening forces.
FIGS. 3 and 4
illustrate two prior art canopy designs having a formed nose.
FIG. 3
illustrates a tri-cell design with an formed nose having an oval inlet
801
by a loaded rib
802
. Reinforcing tape
803
is sewn around the oval shape of the nose.
FIG. 4
illustrates a formed nose created by extending the top skin
810
and bottom skin
811
around the nose of the canopy to create shaped inlets
812
. Again, reinforcing tape
813
is sewn to the inlet edges. While the fabric tape on the inlet edges of the formed noses in these designs limits wear, the canopy is still subject to span-wise stretching. The entire span of the canopy will stretch during flight and span wise distortion of the nose occurs due to the different stresses on loaded and non-loaded ribs. All prior art canopies with formed noses place the open inlets over a loaded rib. This creates a geometry wh

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