CHAPTER 7
PERFORMANCE EVALUATION
93. Instrumentation . a. General.
92. General. a. Propellant actuated devices are
evaluated to determine their compliance with design
(1) The instrumentation is to a large extent
requirements.
Design requirements may call for
determined by the design requirements, i.e., the
measurements of any or all of the following:
instrumentation is selected generally to measure
Velocity, acceleration, rate of change of acceleration,
the performance characteristics which the
thrust, stroke, and pressure.
device is designed to meet. It is desirable to
measure several parameters simultaneously to
b. In the experimental development of propellant
permit cross checking the data obtained. For
actuated devices, the task of obtaining an item with a
example, velocity may be measured directly
high degree of reliability, while firing relatively few
with magnetic pickups and the results can be
rounds, is a problem that is prevalent. For example, a
checked by integrating the acceleration-time
seat ejection catapult may be developed while firing
curve. Pressure-time or thrust-time data can be
only 20 to 30 rounds. It is, therefore, necessary to plan
converted to acceleration-time data for
the development program to give maximum statistical
comparison with experiments. In a properly
validity. Considerable success in this respect has been
designed, maintained, and calibrated system,
attained with the use of factorial techniques and analysis
there will be little differences in the results
in the design of experimental programs with physical
obtained by these various methods. (Pressure-
interpretations of data in terms of response surfaces. (A
time curves normally give greater values than
response surface gives a three-dimensional picture of
other methods because of internal friction.).
response parameters such as velocity, acceleration, and
rate of change of acceleration, as a function of ballistic
(2) If inconsistencies show up in the comparisons,
and physical parameters, such as charge weight
either the basic data, the method of data
composition, and temperature.).
reduction, or both are at fault. Performance
evaluation should be, so far as possible, based
on data obtained directly by use of
basic test fixtures used in the ballistic and performance
accelerometers, pressure gages, and the like
evaluation of propellant actuated devices, and presents
rather than on derived data, e.g., that obtained
sample evaluation programs. There are two basic
by differentiation or integration since some error
evaluation programs: (1) development and (2)
inevitably creeps in as a result of the derivation
qualification analysis. The development phase includes
methods, and this error in many cases may be
firings with workhorse and prototype models to establish
extremely large.
the charge and check newly designed components or
complete devices. Qualification and analysis firings are
(3) A simple block diagram of the instrumentation
conducted at the conclusion of the development
used
for
determining
performance
program to qualify the design as usable, after which the
characteristics in propellant actuated devices is
design is released to production.
shown in figure 86.
Several types of
transducers are used to obtain various types of
information.
(4) These transducers may be pressure gages of
either the piezoelectric or strain-resistance type,
load cells, or accelerometers. The coupling
network and calibrator will depend on the type of
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