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The title compound C18H20N2S is monoclinic, witha=10.256(2),b=7.470(4),c=21.377(4) Å,ß=101.52(2)°,z=4 and space groupP21/n. The structure was solved by direct methods, and refined by weighted full-matrix least squares. The refinement, based on 1373 reflections withI=2.5s (I), converged to a finalR of 0.062 (Rw=0.060). The conformation of the thiazine ring is a distorted half chair, and that of the pyrimidine ring is a distorted chair. All nonhydrogen intermolecular distances are greater than 3.5 Å.

The title compound C18H18N2O2S is monoclinic with unit-cell dimensionsa=8.849(10),b=9.185(11),c=20.257(9) Å,ß=109.28(10)°. The space group isP21/c, withZ=4. Data were measured by photographic methods. The structure was solved by direct methods. A full-matrix least-squares refinement converged toR=0.10. All atoms except sulfur were assigned individual isotropic thermal parameters. The conformation of the thiadiazepine ring system is distorted boat shaped, as indicated by torsion angle studies.

Performance of impact absorbers employing a pneumatic damper and a linear spring in parallel is analyzed. The governing nonlinear differential equations are derived and converted to nondimensional form. For case of a damper with fixed area orifice the equations are numerically integrated. Performance charts are presented in terms of three dimensionless parameters: mass, spring stiffness and orifice area ratio. Then, a second case is considered in which the damper orifice area is made to vary in two stages. During an initial portion of the stroke the orifice is closed and the air pressure rises to a certain value. In the second stage the orifice area varies in such a manner that a constant deceleration of the mass is achieved. A closed form solution of the governing equations is presented for the second case. The design and performance are compared with that of an impact absorber consisting of a spring only, and with those employing hydraulic dampers.

The paper presents the use of dimensional analysis as an aid in the design of dynamic systems. Basic theory of dimensional analysis is discussed. Two examples are given: (1) a two degree of freedom vibrating system and (2) a flexible rotor which is flexibly supported at its ends. Choice of suitable non-dimensional parameters is discussed. A digitial computer program is described which generates all of the possible sets of non-dimensional parameters for a given problem.

The application of a miniaturized energy absorbing mechanism to a light airplane occupant restraint system is presented. The mechanism absorbs energy through the continuous plastic deformation of a steel wire, closely approximating a constant force energy absorber. The design philosophy and the installation details for the aircraft are presented. A mathematical model is used for determining the occupant response during aircraft crash. The model considers plane motion of the aircraft and the human body, the latter being approximated by five rigid body segments. Occupant displacements and curves for accelerations and restraint forces are presented for a typical survivable light aircraft crash. The experimental results and the mathematical model response suggest that incorporation of the energy absorbing mechanism would produce a significant decrease in occupant injuries and fatalities. A parametric study of the occupant/restraint system is presented. Recommendations are made on steps towards improved crash protection and survival in general aviation.

A method for balancing a flexible rotor is developed which is based upon the dynamic response of the rotor in its normal modes as excited by the distributed mass unbalance. The balance corrections are determined by equating the modal components of the corrections to the modal components of the unbalance of the rotor. Methods of balancing individual modes as well as simultaneous balancing in any number of modes are presented. The suggested procedure requires calculation of the normal modes and critical speeds, and measurement of the dynamic amplitude at selected points along the rotor axis.