A low stretch fabric for use in inflatable devices that place pressure on body parts, such as anti-G garments. The novel design of the present invention allows it to inflate to a lesser volume, than conventional fabrics, while maintaining the same pressure. This results in faster response times and less bulk of the garment constructed of the present invention.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention relates to improved fabrics for use in anti-G 
garments worn by pilots of high performance aircraft. In particular, the 
present invention is a low stretch fabric, for use in an anti-G garment, 
with which the garment will inflate to a lesser volume, while applying 
appropriate forces to the wearer in order to counter the effects of G 
forces to which the wearer is exposed. The lower inflation volume allows 
the anti-G garment of the present invention to be less cumbersome and 
respond more rapidly to changes in G forces encountered by pilots than 
conventional anti-G garments. 
Description of Related Art 
When an aircraft is turned, the radial acceleration acting on the mass of 
the pilot is experienced as an increase in force in a direction 
perpendicular to the plane defined by the aircraft wings and fuselage. The 
passengers and pilot are pressed into their seats. The acceleration 
associated with this force is known as G forces, or simply G's. Modern 
fighter, and other high performance, aircraft which are very agile and can 
turn very sharply, commonly generate accelerations as high as 9 or more 
G's (9 times the acceleration of gravity). This acceleration creates 
hydrostatic forces in the pilot's cardiovascular system which tend to 
decrease the supply of blood to the eyes and brain, causing loss of 
vision, known as black-out, and even loss of consciousness (GLOC, G 
induced loss of consciousness). 
G induced loss of consciousness and degradation of aircrew performance 
under stress are very important, life threatening, problems faced in the 
employment of modern, high performance, aircraft. While pilots of these 
aircraft are trained to use muscular straining techniques to increase the 
flow of blood to the head, these straining maneuvers are inadequate and 
must be augmented by the use of anti-G garments. These garments are tight 
fitting inflatable devices commonly covering the abdomen and legs. The 
garment is attached to a compressed air supply in the aircraft and is 
automatically inflated through a "G-suit" inflation valve. The pressure 
level of the inflation is usually proportional to the G being experienced. 
Some of the most modern anti-G garment systems include a vest coupled with 
positive pressure applied to the pilots oxygen mask in addition to G-pants 
for the abdomen and legs. 
Two limitations to the useful performance of known anti-G garments are 
limited coverage over the surface of the body, and excessive inflation 
time. These limitations are being addressed by projects to design new 
garments with greater coverage areas, and to develop high flow and rate 
sensitive inflation valves to decrease response time. Both solutions can 
be complex and expensive. 
At the present time these garments are typically made from two fabrics. The 
first, inner layer, fabric is a coated or laminated fabric with the 
coating applied to make the garment air tight and to provide a medium for 
heat-sealing the assembly seams. The second, outer layer, fabric is 
typically made from Nomex, a high temperature resistant polyamide yarn. 
Its purpose is to protect the wearer and inner layer from fire in the 
event of an accident, and to mechanically transmit the loads developed 
through inflation of the garment. Neither of these fabrics is designed for 
low stretch and, in fact, both stretch extensively in use. 
SUMMARY OF THE INVENTION 
The present invention addresses these problems using some novel fabric 
designs to decrease fabric stretch in anti-G garments. Decreased fabric 
stretch would lead to decreased inflated volume, and therefore, to more 
rapid inflation of the garment. The invention provides a simple solution 
to some G-stress problems which could be rapidly implemented in the field 
without more expensive, and complex, aircraft modifications. 
It is anticipated that low stretch fabrics provided in accordance with the 
present invention will have other uses in other inflatable garments or 
devices which rely on fabric tension to transfer or transmit loads to a 
portion of the body, for example, M.A.S.T. (military anti-shock trousers) 
garments, and blood pressure measurement cuffs. Such devices could be 
designed for either human or animal use. 
Therefore, it is an object of the present invention to provide a low 
stretch fabric for use in inflatable garments that have a lower inflation 
volume, and thus faster response time, than conventional garments while 
applying adequate pressure to the wearer's body. It is another object of 
the present invention to provide inflatable garments that are less 
cumbersome and distribute pressure over the body more evenly than 
conventional garments. It is further an object of the present invention to 
provide a low stretch fabric for use in other inflatable devices that are 
utilized for applying pressure on body parts.

DETAILED DESCRIPTION OF THE PRESENT PREFERRED EMBODIMENT 
The present invention is achieved by the selection of a combination of yarn 
sizes, in both warp and filling, and yarn spacing (or count), in both warp 
and filling, and a type of weave which creates a condition of very low 
(nearly zero) crimp in either the warp or filling of the resulting fabric. 
It should be noted that it is not possible to achieve very low crimp in 
both directions simultaneously in the same woven fabric. Decreasing crimp 
in one direction necessarily will result in increased crimp in the other. 
A common error in textile design is to attempt to decrease the stretch of 
a fabric by using exotic, high performance, low stretch, yarn in an 
unsophisticated woven construction. The high performance yarn is then 
extensively crimped and its low stretch properties are essentially lost. 
The success of the design depends, in part, on the type of yarn chosen 
i.e., spun, filament, plied, core spun, and the fiber i.e., natural, 
synthetic, polyester, glass, nylon, aramid, blends and others. In addition 
composite yarns may be used such as a yarn with an inner glass core and an 
outer sheath of nomex, or the like. The yarn used must have a modulus 
which is high enough to achieve the low stretch desired, and must be of 
high enough tenacity to avoid breaking under load. In many applications 
high temperature resistant yarn must be used to prevent injury to the 
wearer in the event of an accident and fire. Inter yarn friction can be 
important in the design of fabrics considered under the invention to 
prevent ravelling and fraying. This is especially true when fire resistant 
yarns, such as aramid (an aromatic polymide), are used, because resins and 
finishing chemicals which might be employed to prevent raveling and 
fraying would compromise the fire resistant properties of the fabric. To 
this end spun yarns, or a combination of spun and filament yarns may be 
used to increase inter yarn friction. 
One of the most important yarn properties to be considered is bulk, or 
diameter. The diameter of the yarn in combination with the yarn count, or 
spacing, determines the packing density. The relative packing density 
between warp and filling can be used to control the distribution of crimp. 
For instance, a very tightly packed warp woven with a more loosely spaced 
filling will tend to promote crimp in the warp yarns and discourage crimp 
in the filling yarns. This effect can be enhanced if the diameter of the 
filling yarns is much larger than that of the warp. Fabric such a this 
would have its lowest stretch and therefore primary load carrying 
direction in the filling. It is important to consider these parameters and 
to orient the material properly- for each application. It is conceivable 
through adjustment of yarn weights, counts, and the other yarn parameters, 
to create a similar warp oriented fabric with the warp being the lowest 
stretch and therefore primary load carrying direction. 
The packing density of a yarn system (warp, filling) can be characterized 
numerically by multiplying the count by the square root of the yarn weight 
(expressed in any common units, e.g. denier, decitex, yarn count). By 
knowing, through experience, some empirical value of packing densities in 
both the warp and filling of a given fabric, and associated yarn weight 
(denier) ratios, filling/warp, it is possible to predict the approximate 
level of crimp in both warp and filling. Above certain values of warp 
density, the filling will not crimp even with low denier ratios. It has 
been found empirically, that a warp density greater than 1700 is 
desirable. Thus a fabric with the desired low stretch characteristics can 
be designed. 
The present invention includes the addition of air holding and/or 
heat-sealable coatings and laminated films applied to the special low 
stretch fabrics envisioned to facilitate the fabrication of inflatable 
garments and devices from these materials. 
EXAMPLE 1 
A polyester warp of 121 yarns per inch of 220 denier DuPont type 52 
polyester is woven in a plain weave with a filling of 38 yarns per inch of 
440 denier DuPont type 52 polyester. The warp is twisted to a level to 
promote efficient weaving on the type of loom selected. The high warp 
density of 1795 combined with the filling to warp yarn weight ratio of 2:1 
(440/220) places most of the crimp in the warp and very little in the 
filling. Therefore this fabric has relatively very low filling stretch 
under load. The resulting fabric weighs 7.15 ounces per square yard. This 
fabric, using non-fire retardant and non-high temperature yarn, would be 
more appropriate for non-aviation uses such as MAST garments, blood 
pressure cuffs, or the like. 
The fabric may be finished using standard procedures for polyester. The 
finishing steps might include scouring, resination with compounds such as 
urethane or melamine, heat setting, resin curing, and calendaring. 
The stress/strain characteristics of this fabric are presented in FIG. 4 
and a photograph is displayed in the upper left of FIG. 12. 
EXAMPLE 2 
A light weight Nomex yarn warp of very high count is woven in a plain weave 
with a heavier Nomex yarn filling of lower count. The warp is formed from 
200 denier type 433 sage green Nomex filament yarn with an end count of 
122 yarns per inch off loom. This yields a warp density of 1725. 
Experience tells that this density is high enough to pack the warp yarn 
together and prevent the formation of substantial crimp in the filling 
yarn. This warp yarn is typically twisted to a level high enough to 
facilitate efficient weaving. The filling is woven of 2 ply 200 denier 
type 433 sage green Nomex filament yarn. This gives an equivalent filling 
denier of 400 and a denier ratio of 2:1 (400/200). This ratio contributes 
further to the prevention of crimp in the filling yarn. Low filling crimp 
gives relatively very low filling stretch under load. The filling count is 
40 pics per inch, giving a filling density of 800. The resulting fabric 
weighs 5.85 ounces per square yard. This fabric is woven on a shuttle 
loom, although any type of loom which can process these yarns and counts 
would be appropriate. 
The fabric is then finished by the standard textile processes of, scouring, 
heat setting or autoclaving, calendaring, and application of anti-static 
chemicals. 
The stress strain characteristics of this fabric are presented in FIG. 5 
and a photograph is displayed in the lower left of FIG. 12. 
EXAMPLE 3 
The fabric from example 2 was combined with an air holding and/or 
heat-sealable coating. This resulting fabric could be used to replace both 
layers of the fabrics currently in use to manufacture anti-G garments. To 
accomplish this, a urethane, or the like, coating is laminated to one side 
of the fabric. The coating could also be applied by squeegee or other 
known methods. The resulting material weighs 7.8 ounces per square yard. 
The stress strain characteristics of this fabric are presented in FIG. 6 
and a photograph is displayed in the upper right of FIG. 12. 
EXAMPLE 4 
A 200 denier type 433 sage green Nomex filament yarn with an end count of 
122 yarns per inch is used as the warp. This warp is woven in a plain 
weave with a filling of 38 pics per inch of 40 four ply spun Nomex giving 
a filling density of 876. Again, the warp density of 1725 and warp to 
filling yarn weight ratio of 2.66:1 control the crimp distribution 
imparting most of the crimp to the warp, leaving the filling nearly crimp 
free. The resulting fabric weighs 6.3 ounces per square yard. Due to the 
use of spun yarn in the filling this fabric will have more internal 
friction and greater stability, and resistance to fraying and raveling. 
This fabric may be woven on a shuttle, or other suitable loom. 
Once woven this fabric is finished in much the same way as that of example 
1. 
The stress/strain characteristics of this fabric are presented in FIG. 7 
and a photograph is displayed in the lower left of FIG. 12. 
EXAMPLE 5 
Now a fabric as in example 4 above is combined with an air holding and/or 
heat-sealable coating or laminated film applied to facilitate the 
manufacture of inflatable garments and devices. To accomplish this, a 
Urethane, or the like, coating is laminated to one side of the fabric. The 
coating could also be applied by squeegee or other known methods. 
The prior art fabric used for comparison testing is known as MIL-C-83429A. 
This fabric was chosen because it is the fabric specified by the U.S. Air 
Force for use in anti-G garments. The majority of such garments in use 
today are constructed of MIL-C83429A. Its stress/strain characteristics 
are illustrated in FIG. 3. A standard test strip 2" wide and 20" long was 
used for all stress/strain tests. For example, the test strip made of the 
prior art fabric stretches about 0.47 inches under 30 lbs. of tension in 
the warp direction. 
By comparison, the fabrics of examples 1, 2, 3, and 4 exhibited much less 
stretch under the same test conditions. (See FIGS. 4-7, respectively.) The 
examples of the present invention also exhibit much less stretch in the 
fill direction. Because of their construction, the fabrics of the present 
invention do exhibit relatively large amounts of stretch in the bias. This 
is not a problem, however, in applications of the fabrics in anti-G 
garments, or other pressure devices, because the primary load directions 
are predictable and the fabric can be oriented with this in mind. 
FIG. 8 presents the resulting data from hoop stress testing of Examples 1, 
2, and 4 compared to the prior art. From this table it is evident that, as 
a percentage of total circumference, the examples tested stretch only a 
fraction of the amount that the prior art fabric stretches. Hoop stress is 
the major component of stress in an inflated cylinder and the bladders of 
an anti-G garment approximate an inflated cylinder when inflated. This 
same data is illustrated in graph form in FIG. 9. 
FIG. 10 represents the resulting data from actual measurements taken from 
inflated garments made of the prior art material, the example 1 fabric, 
and the example 2 fabric. It can be seen that the inflated volume of the 
prior art garment is significantly higher than that of the garments 
constructed of the materials of examples 1 and 2. Note that the pressure 
in the bladders, and thus the pressure exerted on the wearer, is the same 
in all cases, only the volume is less in the garments of the subject 
invention. Once again, less volume (due to less stretch) means shorter 
inflation times and quicker response. This results in less strain on the 
wearer during the onslaught of G forces. FIG. 11 presents the data of FIG. 
10 in graph form. 
FIG. 12 is a collection of electron microscope photographs of the fabrics 
of examples 1-4. From these photographs, the unique construction of the 
present invention is evident. In particular, it can readily be seen that 
there is very little, or no, crimp in the filling. This characteristic is 
the key to the low stretch qualities of the present invention. 
Fabrics envisioned under the present invention need not be woven in a 
particular weave. Although the examples specify plain weave, others such 
as twill or basket weave are certainly possible where appropriate. Many 
other yarn types such as nylon, acrylic, glass PBI, or the like, may be 
used as well. In addition the yarns may be constructed from a combination 
of materials. The key to the present invention is the selection of yarn 
weights and counts, through empirical knowledge, appropriate to the weave, 
loom, and yarn so as to control the distribution of crimp in either the 
warp or filling leaving one with very little crimp and therefore very 
little stretch. It is also important to orient the fabric correctly to 
take advantage of the anisotropic stretch characteristics. 
FIG. 13 illustrates a typical anti-G garment 10 constructed of the 
materials of the claimed invention.