<DOC>
<DOCNO>
595
</DOCNO>
<TITLE>
the equilibrium piston technique for gun tunnel operation .
</TITLE>
<AUTHOR>
east,r.a. and pennelegion,l.
</AUTHOR>
<BIBLIO>
arc 22, 852, 1961.
</BIBLIO>
<TEXT>
  a modified technique for the operation of a gun tunnel is
suggested based on experimental results .  if the piston mass and the
initial barrel pressure are chosen correctly, then the peak pressures
associated with the gun tunnel may be eliminated .  under these
conditions the piston is brought to rest with no overswing .  some
measurements of the piston motion using a microwave technique are
reported which confirm this idea .
  the wave diagram associated with this mode of operation is
shown, and some calculations of the stagnation pressure are given which
show that during the suggested running time, the stagnation pressure
may be considerably greater than the driving pressure if the driving
chamber cross-sectional area is large compared with that of the driven
section .  for a uniform shock tube the stagnation pressure will always
be less than the driving pressure .  the use of air, helium and
hydrogen as driving gases has been considered .
  experiments in a gun tunnel are reported which show that the
equilibrium piston technique enables steady stagnation pressures to be
achieved over a time of approximately 15 ms using air as the driving
gas .  the expansion caused by the piston acceleration is shown to
interact with the stationary piston, but this is found to produce only a
small drop in stagnation pressure .
</TEXT>
</DOC>
