An Analysis of Current Interruption upon the Behavior of Light Bulb Filament during Initial Aircraft Impact in Support of Aircraft Accident Investigations
Date of Award
Thesis - Open Access
Master of Aeronautical Science
Dr. Marvin Smith
Dr. Eric v. K. Hill
Mr. Donald B. Hunt
The purpose of analyzing annunciator panels, warning, and indicator lamps is to determine the state ("on" or "off") of each light bulb immediately before the impact. Determination of the state of lamps may help investigators determine the probable cause of the accident. The information gained from the lamp's filaments may be used to infer the aircraft's operational parameters prior to impact and to a qualitative appreciation of the severity of the accident. It is generally agreed that upon impact the filament of an unlit bulb will fracture without deformation and the filament of a lit bulb will display plastic deformation (Ellis, 1984).
The main purpose of this study was to investigate the effects of current disruption as a result of initial impact forces upon light bulb filament behavior. One hundred and twenty commercially available T-1 five volt and T-1 twenty-eight volt aircraft light bulbs were subjected to inertial impact deceleration forces up to and including 90 times the force of gravity to investigate the effects of current disruption during the impact sequence. The age of the light bulbs ranged of from 50 to 1,600 hours. An air-cannon was used to accelerate the lamps along its horizontal barrel with impact occurring at a hydro-brake located 13 feet from the beginning of the barrel. The hydro-brake produced an inertial deceleration which neither broke the glass envelope nor destroyed the filament. Severance of power was accomplished through the use of a microswitch and a solid state relay.
It was hypothesized that there would be a noticeable combination of ductile and brittle deformation characteristics in the filaments as the result of these deceleration forces. The filament analysis of the #6839 lamps displayed brittle fractures along with a combination of plastic deformations. The #6839 double helix filament displayed stretching, uncoiling, entanglement, and general deformation of its secondary coil with localized areas of stretching and general deformation of its primary coil. The #718 lamps exhibited plastic deformation characteristics typical of a filament at its brittle or "off" state. The #718 lamps that were aged 1,600 hours displayed plastic deformations typical of a lamp that was illuminated or "on" prior to impact. The filaments exhibited coil stretching and general deformation.
The effects of aging had an important influence upon the behavior of the filaments in both lamp types. The on-set rate of notching depending upon the rated life of the lamp, the filament size, and rated current. Lamps with high rated life rates and low current requirements experienced a slower on-set of notching.
Transient indications of the #6839 lamp included a combination of stretching, local, resonance, slight, uncoiling, and general deformations accompanied by brittle fractures. The transient indications of the #718 lamps, aged 200 hours and older, included slight, local, stretching, and general deformations. Aging effects have a major influence upon the deformation behavior of the filament. The lamp's rated life, operating voltage, and filament diameter control the degree and onset of the notching effect which affects the deformation behavior.
Based on the results and conclusions obtained from this research, the following recommendations are suggested: (a) the development damage boundary curves for the T-1 series of lamps, (b) the investigation of resonance deformation in the T-1 lamp, and (c) additional testing of the T-1 lamp to better understand the relationship between the onset of notching and the lamp's rated life.
Scholarly Commons Citation
LaRow, Daniel J., "An Analysis of Current Interruption upon the Behavior of Light Bulb Filament during Initial Aircraft Impact in Support of Aircraft Accident Investigations" (1997). Master's Theses - Daytona Beach. 114.