Search Results

High levels of lightning current through carbon fiber composite material can result in local pyrolization of the resin due to heating of the carbon fibers. The loss of resin in the matrix can liberate the fibers resulting in a reduction or “knockdown” of structural performance. The gas produced during pyrolization can also cause delamination of the structural plies, further reducing the structural performance. Two areas of concern are the direct attachment point and fastener locations. To measure the effect of lightning current on structural performance, two coupon level configurations were employed. One test configuration was a standard, filled hole tension test specimen which had lightning current driven into the protruding head fastener in the center of the part while grounding two edges of the composite material. Different specimens were exposed to four levels of lightning current and then structurally tested for tensile strength.

Experimental studies of the mechanisms of lightning strokes to radome have shown that the protection efficiency can be related to the ability of diverter strips to initiate stable leaders before inception of energetic discharges take place inside the radome. A model based on a 3D code for electric field calculation is used to compute the threshold of these different processes and deduce the optimum strip height for a given internal electrode configuration. The results of this model are successfully compared to experimental estimation of optimum protection.

The main purpose of the experiments described here is the analysis of the mechanisms of radome protection with lightning diverters of various types and sizes. A high voltage arrangement and associated diagnostics have been implemented to perform a quantitative study of the inception and propagation mechanisms of the corona and leader discharges that precede the final breakdown. It is shown that ambient humidity plays a significant role on the discharge process and that the nature of the discharge initiated from the strip is very different depending on the strip type. Segmented strips are more likely to allow energetic discharges to propagate from an internal antenna leading to radome puncture.

A correlated high-speed image and E-field observation of natural lightning attachment process on a time scale of sub-microsecond has been performed. In one of the observed events, downward stepped leader pulses can be clearly identified either in E-filed or optical signals. When the stepped leader approaches within about three hundred meters of ground, optical pulses begin to appear in the lowest 40 m channel section. These pulses have larger amplitude than the pulses from the downward stepped leader. It appears that these pulses are produced by an upward connecting leader. These facts suggest that the upward connecting leader is also stepped and it could produce even stronger pulses than the corresponding downward leader. The downward stepped leader has a velocity of about 4x106 m/s, while the upward leader has the velocity of about 1.7x106 m/s. The return stroke pulses observed in the E-field and in the optical signal agree well in time but differ in fine structures.

Aircraft systems are designed with reliability, safety and cost effectiveness in mind. The certification of the aircraft is based on tests and results of theoretical analyses that show the compliance with the FAR/JAR requirements. Monitoring for safety for in-service aircraft is an important, critical and extremely complex process. The ultimate objective is to assure that the safety level is equal to the original estimate or better. The manufacturer of the aircraft is particularly responsible for overall monitoring and assessment of all safety related events and corrective actions. Many different philosophies were adopted for this purpose. The safety monitoring and audit strategy is generally based on experience, engineering judgment, event analysis and numerical quantification by using probability theory and statistical tools. The aircraft sequential entry in the service and the aging of their components lead to the non-homogeneity of the fleet.

Future technologies will enable carriers to collect additional flight data for Flight Operational Quality Assurance. This paper describes how analysis of these data using model-based activity tracking can automatically assess the causes of detected deviations to support safety-enhancement efforts. The paper describes the activity tracking methodology implemented in the Crew Activity Tracking System (CATS) using an example drawn from previous research in which CATS analyzed full-mission simulation data online. The paper also discusses current research on using CATS to analyze flight data from a Boeing 757 aircraft.

People at work are frequently distracted (“hijacked”) by a mix of in and out of workplace events, frequently including poor communications. As a result, they sometimes find themselves in situations in which they can be seriously injured or killed. An investigation into the “how” these situations were initiated led to list of six primary causes. Based on this list, an experiential program was developed to help people remain focused on their work, not get hijacked, and improve their communications.

There is nothing more frustrating and frightening to most pilots and flight instructors than to be the target of an FAA enforcement action. An enforcement action can result in anything from a warning letter to loss of flight privileges. The pilot who is subject to an FAA enforcement action must be aware of the various sanctions and enforcement procedures the FAA has at its disposal to prosecute and punish him. More importantly, the pilot must be made aware of his rights and privileges during an enforcement action.

What was always referred to as pilot error or human error is now considered to be an error by the organization that trained (or failed to train) the operator or front-line person. Although mistakes due to human error will never be completely eradicated, every attempt must be made to reduce these errors to their lowest possible number. Unfortunately, changing human behavior is difficult at best. The typical aviation safety training program does not use all available strategies to make these needed changes in behavior. Even one small omission can dramatically reduce the effectiveness of a training program. Instead of cranking out hour after hour of traditional lecture-type training, changes must be made in methodology and techniques. The training wheel is continually cranked, but whether it does any good is usually “hoped for” and guessed at. Aviation safety training is, for so much time and effort, a failure in motion.

System safety is taught as a discipline in some aeronautical programs. Such a course maybe designed to prepare career-minded aviation students with a solid background to face the technical intricacies of the commercial flight arena. Over the course of the past decade, the complexity of large modern transport category aircraft has grown, and along with that growth the command and control functions built into the avionics and flight control systems have become automatic. Most new pilots entering into the cockpits of these aircraft require an understanding of how to manage these new systems in light of the basic design principles used. One excellent method of providing education for students in aeronautical studies is through courses in system safety and operational risk management (ORM).

A comparison was done of the prediction capabilities for lightning indirect effects of two two-dimensional (2-D) computer codes using two graphite structural test fixtures. The two codes evaluated were an internal Boeing Method-of-Moments code and a commercially available Boundary Element method code. The codes were compared against each other and against test data. The purpose was to evaluate the prediction capabilities of both codes for use in predicting lightning indirect effects on internal components of graphite structure. Since 2-D codes are much easier to use than 3-D codes, they could be widely used in trade studies and design evaluations for lightning indirect effects protection of composite aircraft. The first code, REDIST, is a Method-of-Moments code developed in the 1980’s for use on the B-2. The REDIST code has short run times and is somewhat easier to use than the second code that was investigated.

The electromagnetic coupling between a conductor and a composite structure by wire-mesh techniques using method of moments is investigated. A three-bladed composite panel with an aluminum tube located above the panel is considered in this analysis. Computations are made of the current on the tube for various frequencies with height above the panel as a parameter. The numerical results compared reasonably well with the measurements. The technique proves to be useful in modeling the composite structures such as wings of an aircraft.

The certification of fuel systems is an important aspect of the overall certification of an aircraft against lightning hazards and embraces almost all disciplines needed to deal with the lightning interaction. Both direct and indirect effects are encountered and some understanding of the physics of fuel combustion and probability theory concerning ignition is also necessary to appreciate the factors influencing the safety or otherwise of a design. At one time the Western Air Forces were losing one aircraft every other year, due to lightning related fuel explosions. Similar accidents occur to Civilian aircraft, albeit less frequently. After a brief review of aircraft fuels and their flammability and some discussion of combustion processes, the paper considers factors affecting Minimum Ignition Energy (MIE) encountered during flight profiles, such as oxygen enrichment, temperature and pressure.

In the frame of the European project CATE (Composite and Advanced Aircraft Technologies Electromagnetic Protection), a full CFC mock-up has been designed and manufactured. Both measurements and computations have been carried out to investigate and to assess the coupling mechanisms throughout CFC structures. Different aspects have been covered: effects of apertures, effects of metallic devices, effects of protection on cables, … The understanding of the physical phenomena involved enables the formulation of general rules of protection which can be applied on very large aircraft at lower cost.

A three years analysis has been carried out inside the scope of the 4th framework programme driven by the European Commission. The objectives of this analysis were consisting of the development of three complementary tools required for the electromagnetic susceptibility analysis of a ground facility. - a new methodology approach based on critical coupling functions evaluation - a test equipment allowing a quantitative determination of these coupling functions - a numerical tool, based on the electromagnetic topology concept (ONERA CRIPTE code), which, by comparison with tests results, gives the evaluation of the full threat susceptibility of critical operational functions and conducts to the definition of pertinent electromagnetic protection to be applied on the ground facility. The definition and the characteristics of the three tools are presented. Experiments conducted on specific ground facilities are described.

The Finite Difference Time Domain (FDTD) method (as implemented in the commercial software package EMA3D) is used to model indirect lightning effects in a composite three bladed panel and a composite wing-box. The analysis is compared with low level continuous wave (LLCW) tests performed in the Boeing Lightning Effects Laboratory. Measured data include transfer functions for currents induced on metal tubing interior to the three-bladed-panel and wing-box. The thin wire and thin plate formalisms provided in EMA3D are used to model the composite surfaces and metallic conductors such as pipes in the wing-box. The wing-box is simulated both with and without apertures. The modeling results showed excellent agreement with measurements over a broad frequency range demonstrating the usefulness of FDTD as a predictive tool for lightning frequencies.

A lightning indirect effects analysis of a conductor over graphite composite structure was performed using a frequency domain analysis. An internal Boeing analysis code, EM_Model, was used to predict and model test data from two graphite composite test articles. The first was a simple graphite panel with an aluminum tube placed at various heights above the panel. The aluminum tube is representative of either hydraulic or fuel lines, or cable bundle shields. The second test article was the outboard section of a graphite wing-box with two aluminum tubes internal to the structure. A series of access panels in the wing skin provided a source of aperture coupling in addition to the diffusion currents. Both tests made low level CW (LLCW) measurements of the tube transfer function and were compared to model results with good agreement.

Small open shelters are common on athletic fields, golf courses, parks, roadside picnic areas, schoolyards, and elsewhere. Many of these shelters are built to protect against rain or sun, not lightning. What can be done to minimize risk/maximize safety for people inside them under direct and indirect lightning strike conditions? Although there is no such thing as a lightning-proof small outdoor shelter, a properly designed and installed lightning protection system may make a difference. Sometimes the difference is between life and death.

In an effort to determine the effectiveness of the sharp tipped lightning rods widely used in the U.S., we carried out a competition between sharp and blunt rods to determine which was preferentially struck by lightning. Over the past eight years, 12 blunt rods participated in cloud-to-ground discharges while none of the nearby rods with sharp tips were struck. Our analysis suggests that the emissions of point discharges from the tips of sharp rods associated with the rapid decrease of the electric field strength around the tips combine to make sharp rods poorer receptors for lightning than are moderately blunt rods.

Presented in this paper is a method to calculate the Franklin rod protection zone, through mathematical equations by considering the Franklin rod height and lightning stroke polarity impacts on striking distance[1]. The method was developed and analyzed for different cases with varied rod heights, and for positive and negative polarity. The calculated results of the protection zone were compared to the laboratory measured outcomes of several protected objects with varied heights.