26-04-2014, 04:18 PM
Aircraft flight fatigue Monitoring Device
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INTRODUCTION
When loads are repeatedly applied to a metal specimen, failure can be
Produced at load levels which would not cause failure with only a single
application. In aircraft, flight loads on the wing produced by maneuvers
and wind gusts cause the wings to be cyclically loaded through a random history,
making fatigue a matter of serious concern in aircraft design. In actuality,
structural fatigue is the factor that determines the life of the airplane
and is often the driver in establishing dimensions of structural components.
Each airplane of a given type flies such a completely different profile,
Although designed to perform the same mission, that the loading history is
quite unique. As a consequence, there is a need to monitor every airplane
and record the number, magnitude and sequence of the repeated loads. This
requirement can be nicely fulfilled through application of an onboard
microprocessor data acquisition system.
The system which was developed is comprised of two major subsystems:
the WRITE subsystem and the READ subsystem. The WRITE subsystem is tasked
with the airborne collection of data. It makes use of a microprocessor,
various components for signal processing, a magnetic tape recorder, and a
strain gage network to monitor strain-generated signals, identify significant
events, and record the collected data. The READ subsystem is tasked with
the retrieval of the data from the WRITE subsystem recorder. A desk-top
Calculator and cassette tape reader accomplish this task, which includes the
read-back of the magnetic tape, the pre-processing of data, and the operation
of a data file retrieval system.
THE WRITE SYSTEM
The WRITE subsystem of the fatigue life data acquisition system is
dedicated to the sensing of significant strain events which have been
experienced by the aircraft and the recording of those events. It includes
various hardware components used to monitor, digitize, process and record
signals, which are generated by strain gages, located at up to eight critical
points of interest. The software package of the microprocessor controls the
hardware components and monitors their functions. Screening, formatting,
Storing and recording of data are also functions performed by the software
package.
A/D Signal Processing Module
The analog signals from the strain gages must be digitized in order to
be analyzed and stored by the microprocessor. The module provides for multiplexer,
which is driven by a binary up-down counter. The counter provides
the channel number, and the multiplexer selects the channel. A sample and
hold component is used to stabilize the voltage of the input analog signal,
which allows signal digitization by the analog-to-digital converter (ADC).
The resultant output of the ADC is an 8-bit binary representation of the
Analog input.
THE READ SYSTEM
The READ subsystem of the fatigue life data acquisition system is dedicated
To the reading (or playback) of the magnetic tape created by the WRITE
subsystem. Its functions include reading, re-formatting, sorting, filing and
File retrieval of the data on the magnetic tape. These tasks are accomplished
with a minimum of hardware complexity and lengthy, but relatively uncomplicated,
Software.
The recorder employed is the Memo dyne Model 172 magnetic tape recorder.
The Model 172 is a read-only parallel data machine. The
Recorder reads the data in eight bit segments from the tape and assembles
the word into an 8-bit parallel format.
The Hewlett-Packard Model 9830 Calculator is the main computing component
of the READ system. The HP 9830 calculator may be equipped with various peripheral devices.
These devices include, among others, printers, x-y plotters, card readers,
Teletypewriters, paper tape readers and external cassette tape recorders.
Conclusion
The microcomputer is an ideal device for aircraft applications. There
are many highly complex operations on airplanes to be performed, monitored
or controlled, and size and weight are always at a premium. There is not
doubt there will be a large demand for them in a large variety of applications.