V
`
`.1-
`
`TECHNICAL REPORT
`N ATICK/1-R-82/023
`
`AN INVESTIGATIO N;-O '
`INERTIAL PROPER~
`
`-IN VARIOUS CONFIGURA
`
`BY RICHARD, N
`
`jJ~Ill
`
`E9~'1AN2WU
`TEPENNSYLVANIA kAa1E UNJ1 W
`UNIVERSITY PARK, PENNSYLvANA
`
`UNITED STATES ARMY NATICK,"
`RESEARCH & DEVELOPMENT LABORATORIES'
`NATICK, MASSACHUSETTS 01760
`
`APPROVED FOR PUBLIC ?~ELEASE: DISTRIBUTION UNLIMITED.
`
`REPRODUCED FROM
`BEST AVAILABLE COPY
`
`IZ
`
`Petitioner Ex. 1082 Page 1
`
`

`
`01.
`
`A-n-.Toved f:)r puýbI-jc release; distribution unlimited.
`
`Citation of trade names in
`th~is report does not.
`constitute ani official indorsement or
`use of such Items.
`
`Destroy this report when no longer nneede.D
`return it
`to thae originator.
`
`o
`
`REPRODUCED FROM
`BEST AVAILABLE COPY
`
`Petitioner Ex. 1082 Page 2
`
`

`
`RECD
`PNSTRUCTIONS
`3. R'ECIPIENT'S CATALOG NUMBER
`*'c
`5. TYPE OF REPORT A PERIOD COVERED
`Final Report
`
`_ 6
`
`. PERFORMING ORG. REPORT NUMBER
`
`UNCLASSIFIED
`SECURITY CLASSIFICATION OF THIS PAGE (Whton Data Enttered)
`REPORT DOCUMENTATION PAGE
`1. REPORT NUMBER
`GOVT ACCESSION NO.
`I 4i'-2
`NATICK/TR-82/023
`
`.A
`
`.2.
`
`4. TITLE (ad Subtitle)
`AN INVESTIGATION OF THE INERTIAL PROPERTIES
`OF BACKPACKS LOADED IN VARIOUS CONFIGURATIONS
`
`__IPL-254
`
`7. AUTHOR(*)
`8. CONTRACT OR GRANT NUMBER(a)
`Richard N. Hinrichs, M.S.; Serge R. Lallemant, M.-.; DAAK60-78-C-0033
`and Richard C. Nelson, Ph.D.
`
`S. PERFORMING ORGANIZATION NAME AND ADDRESS
`Biomechanics Laboratory
`The Pennsylvania State University
`University Park, Pennsylvania
`16802
`II. CONTROLLING OFFICE NAME AND ADDRESS
`US Army Natick Research & Development Laboratories
`ATTN: DRDNA-ICCH
`01760
`Natick, Massachusetts
`4. "MONITORING AGENCY NAME & ADORES#i0 ditffernt Irco. Controlung Office)
`
`10. PROGRAM ELEMENT, PROJECT, TASK
`AREA & WORK UNIT NUMBERS
`6.2.,
`1G263747D669002
`
`12. REPORT DATE
`May 1982
`13. NUMBER OF PAGES
`74
`15. SECURITY CLASS, (of this report)
`UNCLASSIFIED
`
`IS.. DECL ASSI FICATION/DOWNGRADING
`SCHEDULE
`
`10. DISTRIBUTION STATEMENT (of thLi Report)
`Approved for public release; distribution unlimited.
`
`1,(cid:127) DISTRIBUTION STATEMEN'T (of
`
`,..bstact.€ an,.r.di Bl ock 20,: Idiff.r.n
`
`,,,= Report)
`
`-I
`
`18. SUPPLEMENTARY NOTES
`
`.aide
`
`.1n .ceey
`
`.nc Idntify by block nu.(cid:127)wbr)
`loads
`load carrying
`human backpack system
`loading configurations
`
`193. KEY WORDS (Continu. on rev.e.r
`backpacks
`backpack system
`military clothing
`military equipment
`inertial properties
`2i04 Alj!T`RACT rCcwaQ
`-
`.w r.
`"t evauy sitideulty by block numwber)
`In this study,
`the inertial properties of three, external-frame backpack
`systems were examined under six loading configurations.
`Two of the backpacks
`were developed by the Army and one was a commercially-available product. For
`each configuration, a 12.00-kg load, consisting of military clothing and equip-
`ment, was placed in
`the packs.
`The locations of the items were manipulated
`such that the densest were placed low, high, or in an intermediate position
`within the pack.
`In addition,
`two, 4.56-kg weights were strapped to the top,
`(Cont 'd.)
`
`e&,
`
`JOAN 731M
`
`EDtf'ION OF I NOV 6, IS, OBSOLETE
`
`UNCLASSIFIED
`SECURITY CLASSIFICATION OF THIS PAGE (When Data Entered)
`
`Petitioner Ex. 1082 Page 3
`
`

`
`UNCI ASSIFIED
`
`SECURITY CLASSIPICATION OF THIS PAGE(Phan Data
`
`neataod.)
`
`bottom, sides, or front of the pack and tested in combination with the inter-
`mediate position of the basic load.
`The mass, centers of mass, and inertia
`tensors of each backpack were obtained under each of the six loading configura-
`tions.
`The
`inertial
`properties of the backpacks and of the loading configura-
`tions were compared with respect to properties which are desirable in a back-
`packing system.
`
`I.I
`
`I.
`
`LINCLAS SIFIED
`
`SECURITY CLASSIFICATION OF THIS PAGgfW1ern Data EnIered)
`
`Petitioner Ex. 1082 Page 4
`
`

`
`Preface
`
`This is one of four studies comprising the final report of research
`performed under Contract Number DAAK60-78-C-0033 with the Individual Protection
`Laboratory, US Army Natick Research and Development Laboratories, Natick,
`Massachusetts.
`The work was formulated and directed by Drs. Carolyn K. Bensel
`and Richard F. Johnson, Human Factors Group, Individual Protection Laboratory.
`Dr. Bensel was the contract monitor and Dr. Johnson was the alternate.
`
`Ai/p
`
`12
`
`Petitioner Ex. 1082 Page 5
`
`

`
`Table of Contents
`
`Preface ..........................
`
`.................................
`
`Page
`
`.
`
`i1
`
`List of Figures .
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`.
`
`4
`
`List of Tables ...........................
`
`.............................
`
`Introduction ...........................
`
`..............................
`
`Basic Mechanical Considerations ..................
`
`.....................
`
`Procedures .........................
`
`...............................
`
`............
`
`Theoretical Basis Underlying the Methodology ........
`........................
`Center of mass ...................
`........................
`Inertia tensor ...................
`..........................
`Backpack Systems ....................
`.......................
`Loading Configurations ..................
`.................
`Configurations of basic load .............
`................
`Configurations of added weights ............
`..........................
`Backpack Holders ....................
`.......................
`Coordinate Axes System .................
`.........................
`Mass Determination ....................
`....................
`Center of Mass Determination ................
`..................
`Determination of Inertia Tensor .............
`...................
`Error Analysis and Validation ...............
`
`Results ............................
`
`.................................
`
`................................
`Mass ..........................
`...........................
`Center of Mass ....................
`...........................
`Inertia Tensor ......................
`
`Discussion ........................
`
`...............................
`
`References .........................
`
`...............................
`
`Appendices
`
`A. Clothing and Equipment Used in this Study .......
`
`...........
`
`B. Computer Program Used to Compute Inertial Properties .........
`
`6
`
`7
`
`8
`
`.. 12
`
`.. 12
`.. 12
`.. 15
`.. 17
`.. 18
`.. 18
`.. 19
`.. 19
`.. 19
`.. 25
`.. 25
`.. 27
`.. 31
`
`.. 39
`
`.. 39
`.. 39
`.. 44
`
`.. 46
`
`.. 49
`
`.. 51
`
`.. 69
`
`3
`
`Petitioner Ex. 1082 Page 6
`
`

`
`List of Figures
`
`Figure 1.
`
`A generalized rigid body showing three
`orthogonal coordinate axes through
`the CM ...............
`..........................
`
`Figure 2.
`
`An example of fixed rotation about a
`non-principal axis of inertia ...... ...........
`
`Figure 3.
`
`(FBD) of reaction
`Free body diagram
`.......................
`board ................
`
`Figure 4.
`
`(FBD) of reaction
`Free body diagram
`board with an object placed on it ... .........
`
`Figure 5.
`
`Pendulum system for determination of
`moments of inertia ...........
`.................
`
`Figure 6.
`
`ALICE backpack with weights attached to
`bottom ...............
`.......................
`
`Figure 7.
`
`Co~mnercial backpack with weights attached
`..................
`4) .............
`to top (L.C.
`
`Figure 8.
`
`1956 backpack with one weight attached to each
`side (L.C.
`5) .............
`...................
`
`Figure 9.
`
`Commercial backpack with weights attached to
`front (L.C.
`6) ............
`...................
`
`Figure 10.
`
`1956 and Commercial holders shown relative
`to 1-m stick .............
`....................
`
`Figure 11.
`
`Schematic diagram of holoer showing three
`coordinate axes
`(X, Y, and Z),
`three
`diagonal axes (XY,
`XZ, and YZ), and their
`andy ) ...
`.........
`orientation angles (
`,
`,
`
`Page
`
`9
`
`.. 11
`
`.. 13
`
`.. 14
`
`.. 16
`
`.. 20
`
`.. 21
`
`.. 22
`
`.. 23
`
`.. 24
`
`26
`
`Figure 12.
`
`1956 holder being weighed on balance ... ........
`
`.. 28
`
`Figure 13.
`
`Commercial composite (L.C. 1) being weighed on
`......................
`balance ................
`
`.. 29
`
`Figure 14.
`
`Reaction board apparatus set up to determine
`Z component of CM of ALICE composite (L.C.
`3)
`
`.
`
`.
`
`.
`
`30
`
`Figure 15.
`
`Oscillation stand from which holders and
`composites were swung ........
`...............
`
`.. 32
`
`-4
`
`Petitioner Ex. 1082 Page 7
`
`

`
`List of Figures (Cont.)
`
`Figure 16.
`
`1956 holder in place for moment of inertia
`measurement about YZ axis .....
`.............
`
`Figure 17.
`
`Photocell device for measurement of periods
`..................
`of oscil'ation ..........
`
`Figure 18. Modified holder and steel I-beam used to
`validate experimental data ...... ............
`
`Figure 19.
`Figure 20.
`
`I-beam mounted in holder .... .............
`Schematic drawing of I-beam showing dimensions
`
`in centimeters ..........
`
`..................
`
`Figure A-1. ALICE pack ............
`
`....................
`
`Figure A-2. ALICE frame .............
`
`....................
`
`Figure A-3.
`
`1956 frame ............
`
`....................
`
`Figure A-4. Commercial backpack ..... ... ................
`
`Page
`
`.. 33
`
`.. 34
`
`.. 35
`
`.. 36
`
`.. 37
`
`.. 53
`
`.. 55
`
`.. 59
`
`.. 63
`
`5
`
`Petitioner Ex. 1082 Page 8
`
`

`
`List of Tables
`
`Page
`
`Table 1. Dimensions and Mass of the Backpack Holders
`
`.....
`
`.. 19
`
`Table 2.
`
`Diagonal Axes Orientations for the Three
`Holders ...............
`......................
`
`Table 3.
`
`Deviation of Measured Inertia Tensor from
`Theoretical Values ..........
`.................
`
`25
`
`.. 38
`
`Table 4.
`
`Inertial Properties of ALICE Backpack ..........
`
`... 40
`
`Table 5.
`
`Inertial Properties of 1956 Backpack ... ........
`
`.. 41
`
`Table 6.
`
`Inertial Properties of the Commercial Backpack
`
`42
`
`Table 7.
`
`X Component of CM Expressed Relative to the Rear
`Edge of Holder ............
`...................
`
`.. 43
`
`Table 8.
`
`Z Component of the CM Expressed Relative to Each
`Backpack Frame where the Shoulder Straps Attach .
`
`44
`
`6
`
`Petitioner Ex. 1082 Page 9
`
`

`
`An Investigation of the Inertial Properties of Backpacks
`
`Loaded in Various Configurations
`
`Introduction
`
`One of the main goals of biomechanics research is
`to improve the effi-
`ciency of human movement.
`In situations where an external load is being
`carried, the inertial characteristics of the load may have a large effect on
`efficiency of movement.
`For example, a lighter load is usually easier to
`carry than a heavier one. This, however, may not always be the case.
`For
`example,
`it may be easier to carry two, 20-lb suitcases, one in each hand,
`than to carry one, 30-lb suitcase. With the former, even though the total
`weight is 10 lb more than with the latter, the center of mass of the load
`will fall in the sagittal plane of the body. Thus,
`the person may not evi-
`dence the substantial change in posture that is required to maintain balance
`when carrying the single, 30-lb suitcase.
`
`When movements involve rotation, the mass and center of mass
`(CM)
`are not the only inertial properties involved.
`Just as mass is
`the inertial
`property representing the resistance to change
`in linear motion, "moment
`of inertia," which describes the distribution of the mass about a particular
`axis of rotation, is
`the inertial property representing the resistance to
`change in angular motion.
`
`When quick changes in angular motion are desirable, so is a small
`moment of inertia. Examples of such quick changes are "hitting the dirt"
`and making a Rudden change
`in direction while running. A backpack with a
`relatively large moment of inertia about a given axis would be difficult to
`set into rotary motion. Likewise it would be difficult to stop the rotation
`once it had begun.
`
`Because a backpack can be loaded in a wide variety of ways,
`the soldier
`or recreational hiker has some control over the inertial properties of a
`particular backpack. There may also be substantial differences between packs
`of different design. A thorough investigation into the area of backpack
`inertial properties has not yet been done.
`It was the purpose of this
`study to manipulate the loading configurations of three backpacks of different
`design and to determine their inertial properties in each configuration.
`
`7
`
`Petitioner Ex. 1082 Page 10
`
`

`
`Basic Mechanical Considerations
`
`To understanrl the methods used in this study requires some knowledge
`of rigid body
`,'-namics. Although the reader should refer to any of the many
`texts on the subject (e.g., Synge & Griffith or Greenwood),
`this section
`outlines some of the basic mechanical considerations.
`
`In a parallel, uniform gravitational field, an object's mass and weight
`are proportional to each other, and its center of mass (CM)
`and center of
`gravity (CG)
`lie at the same point. Since the earth's gravitational field
`approximates chis condition, we can infer an object's mass by weighing it
`and can locate its CM by determining its CG. Weight and CG, however, are
`not fundamental quantities,
`they depend on the presence of a gravitational
`field.
`
`The inertial properties of a rigid body are its mass, CM, and moments
`of inertia. A certain moment of inertia is defined relative to an axis,
`one usually (but not necessarily) through the CM.
`In a three-dimensional
`body, an infinite number of axes can be passed through the CM, resulting in
`an infinite number of moments of inertia. Fortunately,
`these measurements
`are related in a regular manner,
`so that, by specifying only six parameters,
`the entire inertial system can be described.
`
`For a given set of three orthogonal axes drawn through the CM of the
`these six parameters are as follows (see Figure 1):
`
`body,
`
`-
`
`-
`
`-
`
`-
`
`-
`
`-
`
`I
`xx
`
`I
`yy
`I
`zz
`
`I
`xy
`
`I
`xz
`I
`yz
`
`the moment of inertia about the X-axis
`
`the moment of inertia about the Y-axis
`
`the moment of inertia about the Z-axis
`
`the product of inertia with respect to the XZ and NZ planes
`
`the product of inertia with respect to the XY and YZ planes
`
`the product of inertia with respect to the XY and XZ planes
`
`These six parameters form a symmetric matrix which is referred to as the
`"inertia tensor":
`
`xx
`
`II7xy
`
`yy
`
`xz
`
`yz
`zz
`1 Synge, J.L. and B.A. Griffith. Principles of Mechanics.
`York: McGraw-Hill, 1942.
`
`New York, New
`
`2Greenwood, D.T. Principles of Dynamics.
`Prentice Hall, Inc., 1965, pp. 362-401.
`
`Englewood Cliffs, New Jersey:
`
`8
`
`Petitioner Ex. 1082 Page 11
`
`

`
`'S.
`
`iU
`
`IIQI
`
`I
`
`Figure 1.
`
`A generalized rigid body showing three orthogonal
`coordinate axes through the CM.
`
`9
`
`Petitioner Ex. 1082 Page 12
`
`

`
`The diagonal elements are the moments of inertia and the off-diagonal ele-
`ments are the products of inertia.
`
`the X, Y, and Z axes chosen are "principal axes of inertia", the
`If
`products of inertia vanish, and the inertia tensor reduces to its diagonal
`form.
`
`I
`
`xx
`
`0I
`
`0
`
`Lz
`
`YY
`0
`
`1
`
`the presence of product terms indicates the principal axes
`Conversely,
`are rotated relative to the coordinate axes. Either way of expressing the
`inertia tensor, however, requires the specification of six parameters.
`One
`can specify either (1) the three moments and three products of inertia for
`a given axis system, or
`(2)
`the three principal moments of inertia and the
`orientations of the three principal axes of inertia relative to a given
`axis system.
`
`In order to get an intuitive feeling for the importance of principal
`moments and axes of inertia, consider a rigid axle with two masses posi-
`tioned in
`the X-Y plane as shown
`in Figure 2.
`The system rotates about
`the fixed axle which is coincident with the Y axis. The center of mass lies
`in
`the axle. Since the axle could balance in any static
`position, the
`system is said to be "statically
`balanced".
`
`The system is not, however, "dynamically balanced." There is a non-
`zero product of inertia, Iyz, which would produce shear forces tending
`
`to pull the axle out of its bearings when rotating. As can be seen in Figure
`2,
`two of the three principal axes (Y' and Z') are displaced from their
`corresponding coordinate axes by the particular placement of the masses.
`the masses were placed one above the other on opposite sides of the axle,
`
`If
`I yz
`
`The system could then rotate about a principal axis of inertia
`would vanish.
`and thus be dynamically balanced.
`An everyday example of this is a wheel of
`an automobile.
`It
`is
`important to have the axlc of the wheel coincide with
`!c principal axis. This avoids the vibration commonly encountered when dri-
`ving on a wheel that is not dynamically balanced.
`
`10
`
`Petitioner Ex. 1082 Page 13
`
`

`
`0.J
`o
`
`4.-)
`
`0
`
`.0
`
`(cid:127)
`
`.,.4"3
`
`I-)
`°*,,
`
`li)
`
`Petitioner Ex. 1082 Page 14
`
`

`
`Procedures
`
`The calculation of inertial properties requires the use of some fair-
`ly sophisticated procedures.
`In this study, a sensitive balance was used
`to determine mass, a reaction board was used to determine center of mass,
`and a pendulum was used to calculate the inertia tensor.
`The theory under-
`lying these methods will be discussed first followed by a detailed descrip-
`tion of the procedures.
`
`Theoretical Basis Underlying the Methodology
`
`Center of mass. Consider the free-body diagram (FBD) of a reaction
`board apparatus shown
`in Figure 3.
`The force measured at one end (B 1 ) is
`related to the mass of the board and the location of its CM
`in the following
`manner:
`m g d
`1 1
`£
`
`B1
`
`(1)
`
`where m1 is
`the mass of the board, g is
`the acceleration due to gravity,
`the distance to the CM of the board from the pivot point A, and £ is
`d
`is
`the distance between the points A and B.
`
`Shown in Figure 4
`is
`the FBD of the same apparatus with an object of
`mass m2 placed on the board with the projection on the board of its CM at
`an unknown distance d
`away from the pivot point A. The force measured at
`the other end (B2 ) reilects the contributions of both the board and the
`object in the following manner:
`
`B2
`
`m, g dl
`z.
`
`=B1
`
`+
`
`+
`
`m2 g d 2
`2
`
`+ m2 g d2
`
`(2)
`
`Solving Equation 2 for the CM distance d 2 yields
`
`(B 2 - B1 ) Y,
`
`d
`
`=2
`
`m2 g
`
`the object is placed on the board in
`If
`three different ways,
`location of its CM in
`three-dimensional space can be determined.
`
`the
`
`12
`
`Petitioner Ex. 1082 Page 15
`
`

`
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`
`13
`13
`
`Petitioner Ex. 1082 Page 16
`
`Petitioner Ex. 1082 Page 16
`
`

`
`0
`
`
`
`
`
`
`
`
`
`
`
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`
`Petitioner Ex. 1082 Page 17
`
`Petitioner Ex. 1082 Page 17
`
`

`
`Inertia tensors were determined here using3 a pendulum
`Inertia tensor.
`technique similar in theory to that described by Chandler et al.
`
`When an object is suspended in a pendulum (see Figure 5) and allowed
`to oscillate through small angles (@- 50), the period of oscillation (T)
`the effective pendulum length
`(m),
`is related to the mass of the pendulum
`and its
`the distance between the swing axis 0 and the pendulum CM),
`(d -
`moment of inertia about 0 (I1).
`
`where g is
`
`Io27r; gdý
`
`the acceleration due to gravity (9.81 m/sec 2).
`
`(4)
`
`is possible to me ;ure the mass, CM. and period of oscillation
`Since it
`of the pendulum, one can solve - r the moment of inertia I°. Rearranging
`terms in Equation 4 yields
`m g d T 2
`1o 0
`40 2
`
`(5)
`
`the pendulum consists of a composite system (e.g. a backpack fixed
`If
`inside a rigid holder) then the computed moment of inertia will reflect the
`contribution of both the pack and its holder. Since the object of concern
`the backpack, an additional measurement must be made on the holder alone.
`is
`Since moments of inertia are additive, the moment of inertia of the pack
`is
`(about the swing axis 0)
`
`10 (pack) = I° (composite) - I1 (holder)
`
`(6)
`
`One final step is needed to calculate the moment of inertia of the
`CM. This involves the parallel
`pack about one particular axis through its
`in Equation 7.
`shown
`axis theorem and is
`
`1CM (pack) - I1 (pack)
`
`- m
`
`d 2
`
`(7)
`
`the mass of the pack and d
`is
`where m
`P
`P
`axis 0 and the parallel axis through the CM of the 2ack (not the composite).
`
`the distance between the swing
`
`is
`
`Combining Equations 5, 6, and 7 yields
`=T2
`
`I CM(pack) mcg dcc
`4 2
`
`-
`
`mh g dh
`47T2
`
`T2
`h
`
`d2()
`P
`
`mp
`
`3 Chandler. R.F. C.E. Clauser, J.T. McConville, H.M. Reynolds, and J.W. Young.
`(Tech. Rep. AMRL-TR-
`"Investigation of Inertial Properties of the Human Body"
`74-137). Wright-Patterson Air Force Base, Ohio: Aerospace Medical Research
`(AD-A016-485)
`Laboratory, 1975.
`
`15
`
`Petitioner Ex. 1082 Page 18
`
`

`
`d
`
`0 I II I
`
`I
`
`I I
`
`I
`
`I I II
`
`II
`
`II I
`
`(cid:2)*A49
`
`Figure 5. Pendulum system for determination of moments of inertia.
`
`16
`
`-
`
`.
`
`---.-
`
`*,
`
`I
`
`U
`
`.4
`
`I
`
`I
`
`I
`
`Petitioner Ex. 1082 Page 19
`
`

`
`where the subscript c refers to the composite, h refers to the holder, and
`p refers to the pack.
`
`Three sets of measurements are taken to arrive at the moments of inertia
`of the backpack about the X, Y, and Z axes (I xx, Iyy, and
`I xz, and I yz), however,
`The products of inertia (I xy,
`three additional sets of
`To determine these terms,
`unknown.
`are still
`the XY
`measurements must be taken about the following axes: (1) an axis in
`the XZ
`(2) an axis in
`plane nonparallel to either X or Y (the "XY axis"),
`plane nonparallel to either X cr Z (the "XZ axis"), and (3) an axis in the YZ
`the orientations of
`If
`plane nonparallel to either Y or Z (the "YZ axis").
`the products of iner-
`these axes are known relative to the coordinate axes,
`tia can be computed using the following equations:
`2
`2
`(1 + tan
`+ I
`yy(9
`tan c
`
`) l()
`
`0
`
`I.., respectively).
`
`SIx
`
`xy xx
`= I
`
`2 tan
`
`Iz = I
`
`+ I
`
`tan 2Y-
`a
`
`-
`
`(I+tan
`
`2n
`
`) IY
`
`2 tan B
`
`I
`yz
`
`= I
`yy
`
`+1I
`
`zz
`
`2
`tan y-
`
`(il+tan
`
`2
`
`y)
`
`I
`
`'y7
`
`2 tan y
`
`(10)
`
`(11)
`
`the angle be-
`the angle between the X axis and the XY axis, 6 is
`is
`where u
`the angle between the Y axis and
`tween the X axis and the XZ axis, and y is
`are the moments of inertia about the XY, XZ,
`and I
`I O, I I
`the YZ axis.
`and YZ axes, respectlely.
`
`Backpack Systems
`
`The backpacks selected for this study were three, external-frame
`Two
`Each was tested without its shoulder straps or waist belt.
`systems.
`of the backpacks were developed by the Army (ALICE and 1956) and one was a
`in-
`commercially-available product. A brief description of each system is
`cluded here. Appendix A contains additional information on these items.
`
`It has shoulder
`a. ALICE. The frame is made of aluminum tubing.
`straps and a lower back strap made of a cloth spacer material covered with
`The ALICE
`nylon duck. The waist strap is constructed of narrow webbing.
`pack is a top-loading bag with a large main compartment and additional
`outside pockets.
`
`is contoured
`It
`1956. This frame is also made of aluminum tubing.
`b.
`is concave relative to the wearer's back. This frame
`such that the frame
`was outfitted with the ALICE pack.
`
`is
`The aluminum frame of the Camp Trails Astral Model
`c. Commercial.
`The shoulder straps
`comprised of two vertical and three horizontal components.
`The nylon pack contains two internal and five
`and waste band are padded.
`external compartments.
`
`17
`
`Petitioner Ex. 1082 Page 20
`
`

`
`Loading Configurations
`
`Army clothing and equipment constituted a 12.00-kg load which was put
`the main compartments of each pack. Further information on the components
`in
`of this basic load is presented in Appendix A. The particular items used
`and their individual weights are as follows:
`
`Item
`
`Weight (kg)
`
`1 pair
`
`1. Mattress
`2.
`Overshoe6,
`3.
`Poncho
`4. Waterproof clothes bag
`5.
`Sleeping bag
`6.
`Field coat with liner
`7.
`Field trousers with liner
`8.
`Cold weather underwear
`9.
`Socks, 1 pair
`10. Handkerchief
`11. Washcloth
`
`1.32
`2.31
`1.29
`.15
`3.08
`1.93
`1.18
`.60
`.08
`.02
`.04
`
`4
`
`Two, 4.56-kg weights were also used to simulate additional items, such
`as ammunition, which might be placed in outside pockets on a pack or strapped
`to some portion of the outside of a pack.
`
`Each backpack was tested under six loading configurations (L.C.). Two
`configurations consisted of all the items comprising the basic 12.00-kg load;
`four configurations consisted of the items in
`the basic load plus the two,
`4.56-kg weights.
`The six loading configurations were as follows:
`
`L.C. 1. Basic load low - no weights
`L.C. 2. Basic load high - no weights
`L.C. 3. Basic load intermediate - both weights on bottom of pack
`L.C. 4. Basic load intermediate - both weights on top of pack
`L.C.
`5. Basic load intermediate - one weight on each side of pack
`L.C. 6. Basic load intermediate - both weights on front of pack
`
`intermediate,
`In order to establish the low,
`Configurations of basic load.
`and high placements of the basic load within the packs, subjective judgments
`were made of the densities of the 11 icems of clothing and equipment which
`comprised the load.
`Since most of the items are compressible, actual measure-
`ment of their densities requires that a determination be made of the volume
`that each item occupies within the pack. This was not feasible. Thus, sub-
`jective judgments of densities were made.
`
`4
`
`4
`
`the
`For the low load configuration (L.C. 1), the items were placed in
`packs in order of decreasing density with the densest item (1-mattress) on the
`bottom and the least dense item (11 - washcloth) on the top. Therefore,
`the
`clothing and equipment was ordered from 1 (bottom)
`through 11 (top).
`For the
`this order was reversed; the least dense
`high load configuration (L.C. 2),
`item (11) was on the bottom and the densest (1) was on the top. Therefore,
`through 1 (top).
`the clothing and equipment was ordered from 11 (bottom)
`The positioning of the clothing and equipment for the intermediate configura-
`For the ALICE and the
`tions (L.C. 3-6) varied somewhat among the packs.
`
`18
`
`Petitioner Ex. 1082 Page 21
`
`

`
`from the bottom to the top of the
`the order of the items,
`1956 backpacks,
`6.
`It was necessary
`9, 10, 11, 4, 2,
`5, 1, 3,
`7,
`8,
`pack, was as follows:
`to modify this order for the Commercial backpack because, unlike the Army
`pack which had one main compartment,
`the Commercial pack had two separate
`compartments, and the lower of these two could not accomodate the sleeping
`bag (Item 5).
`The order in which the items were put into the Commercial
`pack was as follows:
`
`Lower compartment, bottom to top - 1, 3, 7
`Upper compartment, bottom to top - 5,
`8,
`9, 10, 11, 4,
`
`2, 6
`
`Configurations of added weights. The two extra weights,
`totalling 9.12 kg,
`were used in L.C. 3 through 6.
`They were attached firmly with shoelaces to
`the outside of the packs to create extreme loading conditions. For L.C.
`3 and
`L.C. 4,
`the weights were taped together and centered on the bottom and the
`top of the pack, respectively. Theie two configurations are pictured in Figures
`6 and 7.
`For L.C. 5, one weight was attached to the approximate center of
`each side of the pack (Figure 8), while, for L.C. 6, both weights were attached
`to the front of the packs (Figure 9).
`
`Backpack Holders
`
`Figures 6 to 9 show the backpacks inside their respective aluminum
`holders.
`The holders provided the rigidity necessary for testing the packs.
`Figure 10 shows the holders used for the 1956 and the Commercial packs.
`The same holder used for the 1956 was used for the ALICE with one modifica-
`tion; a crossbar was added to secure the top portion of the ALICE frame.
`The dimensions and mass of each holder are listed in Table 1.
`
`Table 1
`
`Dimensions and Mass of the Backpack Holders
`
`Holder
`
`ALICE
`
`1956
`
`Commercial
`
`Dimensions
`y
`
`(m)
`
`z
`
`.459
`
`.459
`
`.561
`
`.565
`
`.565
`
`.921
`
`x
`
`.408
`
`.408
`
`.330
`
`Mass
`(kg)
`
`3.865
`
`3.583
`
`6.735
`
`Coordinate Axes System
`
`A set of three orthogonal coordinate axes was defined relative to each
`holder. These axes are drawn schematically in Figure 11. The origin is
`at the geometric center of the holder.
`The X axis goes from back to front,
`the Y axis goes from side to side (right to left) and the Z axis goes from
`bottom to top.
`
`19
`
`Petitioner Ex. 1082 Page 22
`
`

`
`44
`
`
`
`Am.o..5aouuoncuvwzumuum3&3:Lawsxumaxuwn33¢.oauzmfim
`
`C-,
`
`
`
`
`
`200
`
`32e9aD.2801xEren.m...h.teD.
`
`Petitioner Ex. 1082 Page 23
`
`

`
`0
`
`0
`
`0
`
`S
`
`6
`
`Figure 7. Commercial backpack with weights attachedto top (L.G. 4).
`
`21
`
`Petitioner Ex. 1082 Page 24
`
`

`
`Figure 8.
`
`1956 backpack with one weight attached to each side (L.C.
`
`5).
`
`22
`
`Petitioner Ex. 1082 Page 25
`
`

`
`4
`
`0
`
`Figure 9.
`
`Commercial backpack with weights attached to front (L.C.
`
`6).
`
`23
`
`Petitioner Ex. 1082 Page 26
`
`

`
`C.)
`'-4
`4.1
`
`U
`
`I-
`
`0
`
`'.1
`
`1-.w
`'3
`-4
`0
`
`0C
`
`-,
`
`'3
`
`'0
`0%
`'-4
`
`'-.4
`a)
`3
`
`-- 4
`
`-. 4
`
`I
`
`I
`
`-U
`
`4
`
`4
`
`I
`
`I
`
`Petitioner Ex. 1082 Page 27
`
`

`
`The three nonparallel axes were defined approximately along the face
`diagonals of the holder. These are also shown in Figure 11 along with the
`angles defining their orientations. The values of these angles for each
`holder are listed in Table 2.
`
`Table 2
`
`Diagonal Axes Orientations for the Three Holders
`
`Holder
`
`ALICE
`
`1956
`
`Commercial
`
`%
`
`48.7
`
`48.7
`
`60.8
`
`Mass Determination
`
`(degrees',
`
`55.1
`
`55.1
`
`71.8
`
`y
`
`51.7
`
`51.7
`
`59.4
`
`A two-pan balance was used to measure the mass of each holder and
`of each composite,
`that is,
`each backpack in its holder. The balance is
`shown
`in Figures 12 and 13. Mass could be measured to the nearest gram.
`From repeated measurements, however,
`the accuracy was judged to be within
`10 grams.
`The mass of the backpack was calculated by subtracting the mass
`of the holder from the mass of the composite.
`
`Center of Mass Determination
`
`The reaction board used to locate the CM of each holder and each
`composite
`is shown
`in Figure 14.
`The board consisted of a piece of 3/4-
`inch plywood supported by the points of two wood screws on the left (which
`defined the "zero line") and the point of a third wood screw at the other
`end of the board, 110 cm away. This point was placed over one pan of the
`balance for measurement.
`The board was leveled by adjusting each screw.
`
`The following describes the protocol used
`to obtain the three compo-
`nents of the CM of each composite.
`(The holders were measured in
`the same
`way to determine their CM locations.)
`
`Six measurements were taken:
`two to determine the X component of the
`The composite was first placed with
`two for the Y, and two for the Z.
`CM,
`the edge of the holder on a line drawn 10 cm to the right of the "zero line"
`and the positive Y :irection pointing towards the balance. After the X
`distance from the -dge of the holder to the CM was calculated,
`the composite
`was rotated 180' so that the positive X direction pointed away from the
`balance.
`The X distanice from the opposite edge of the holder to the CM was
`then determined.
`
`25
`
`Petitioner Ex. 1082 Page 28
`
`

`
`z
`
`(XZ)
`
`(YZ)
`
`m
`
`Figure ]l.
`
`S~chematic diagram of holder showing three coordinate axes
`(X, Y, and Z), three diagonal axes (XY, XZ, and YZ), and
`their orientation angles (a, ý, and y).
`
`26
`
`Petitioner Ex. 1082 Page 29
`
`

`
`The sum of these two distances should, theoretically, equal the extent
`of the holder in the X direction, as they are both predicting the location
`The deviation of the actual sum from the theoretical
`of the same point.
`The two measure-
`was used as an indicator of the accuracy of the measurement.
`ments will, in general, not predict the same location due to possible errors
`The X component of the CM was considered
`arising in the measurement process.
`to be the average of the first and second measurements and was expressed re-
`lative to the geometric center of the holder.
`
`the measurements were repeated to determine the
`In a similar fashion,
`Figure 14 shows the ALICE composite being
`Y and Z components of the CM.
`The loading configuration of the pack consists
`measured for the Z component.
`the intermediate position and both 4.56-kg weights
`of the basic load in
`on the bottom of the pack (L.C.
`3).
`
`The accuracy of measurement referred to above was found to be very
`good; the average deviation in each direction was 1.5 mm for the composites.
`the deviation was considerably more, averaging
`For the holders, however,
`7 nun for the ALICE and 1956 holders, and 4 mm for the Commercial holder.
`
`It appears that the reaction board was very accurate for determining
`the composites ranging from roughly 18
`the CM of relatively heavy items,
`to 30 kg, but not as accurate for the lighter holders (3.5 to 6.7 kg).
`Perhaps a lighter, more delicate reaction board should be used in future
`work to measure the lighter items.
`
`For each load condition, the CM of each backpack without its holder
`was calculated by the following equat