Aircraft sampling

The Montreal Protocol of July 1987 resulted in an international treaty in which the industrialized nations agreed to halt the production of most ozone-destroying chlorofluorocarbons by the year 2000. This deadline was hastily changed to 1996, in February 1992, after a U.S. National Aeronautics and Space Administration (NASA) satellite and high-altitude sampling aircraft found levels of chlorine monoxide over North America that were 5i % greater than that measured over Antarctica. 

For use of these load-time functions for structural analysis, the impact area should be known. Figure 1-3 gives the area as a function of time during impact for a sample aircraft. The average values of the impact area chosen for the calculations were about 37 w for flat surfaces and about 18 m for spherical surfaces. 

Adhesives are not used Just for structural applications on modern aircraft. In fact, the number of non-structural applications of adhesives vastly outnumbers the structural applications. Adhesives are used for everything from assembling lavatory walls to attaching the No Smoking sign to cabin partitions. Just a sampling of adhesive types and applications are discussed below. 

According to a study by the World Health Organisation, viruses have been found to survive chemical treatment in aircraft toilets. Researches reported that up to half the samples of waste pumped from on-board toilets contained viruses despite the use of toilet sanitiser. All the viruses isolated from the waste were associated with enteric disorders. This indicates that other viruses such as those that cause hepatitis could also survive. As a consequence, future products will need to be even more effective as it is believed that between 1-10% of viruses survive to be potentially discharged into the environment. 

In Tajikistan when cotton plants are sprayed from aircraft during planting, the concentration of methylmercaptophos in the canal water reached 9.3 mg/l, and of thiometon reached 5 mg/l, hundreds and thousands of times higher than MPCs adopted in 1972 for bodies of water (MPC is 0.01 mg/l for methylmercaptophos, and 0.001 mg/l for thiometon). According to 1980 data, DDT, long banned by that time, was found in 27% of water samples from small canals [3, A86]. 

Aircraft turbines in jet engines are usually fabricated from nickel-based alloys, and these are subject to combustion products containing compounds of sulphur, such as S02, and oxides of vanadium. Early studies of the corrosion of pure nickel by a 1 1 mixture of S02 and 02 showed that the rate of attack increased substantially between 922 K and 961 K. The nickel-sulphur phase diagram shows that a eutectic is formed at 910 K, and hence a liquid phase could play a significant role in the process. Microscopic observation of corroded samples showed islands of a separate phase in the nickel oxide formed by oxidation, which were concentrated near the nickel/oxide interface. The islands were shown by electron microprobe analysis to contain between 30 and 40 atom per cent of sulphur, hence suggesting the composition Ni3S2 when the composition of the corroding gas was varied between S02 02 equal to 12 1 to 1 9. The rate of corrosion decreased at temperatures above 922 K. 

Recently, a method for predicting the remanent life of a reinforcing geotextile was proposed [1] in which the strain to failure of a sacrificial sample was divided by the current creep rate. This requires verification. However, very few methods have so far been proposed or used for monitoring plastics in service and at the same time providing a numerical prediction of their remaining life. The reason for this is not just that the methods are likely to be expensive and complicated, but that there are few applications of plastics which can compete in risk and replacement cost with a high temperature boiler or aircraft structure. 

Most of the atmospheric oxidant and ozone data—as well as the experimentally determined exposure data for v tation, animals, and humans—have been obtained with analyzers that sample and record the ambient concentrations almost continuously during the period of observation. The response times are usually acceptable for fixed-station monitoring, because data describing hourly averages are sufficient. Faster responses are needed, however, for studying chemical reaction rates, retention on inhalation, sampling while in motion (as from aircraft), and expediting calibrations. The response times required are therefore a function of the resolution needed. 

For any event to be accurately recorded, it must persist for the pulse time of the instrument. This time is equal either to the rise time or to the time to 100% response, depending on the design of the instrument. For accurate data from aircraft sampling plumes, for example, it is necessary to obtain rise times of a few seconds or less. This is a very fast response for an analyzer and has only recently become possible for ozone measurements. 

Substrate Characterization. Test coupons and panels of 7075-T6 aluminum, an alloy used extensively for aircraft structures, were degreased In a commercial alkaline cleaning solution and rinsed In distilled, deionized water. The samples were then subjected to either a standard Forest Products Laboratories (FPL) treatment ( 0 or to a sulfuric acid anodization (SAA) process (10% H2SO4, v/v 15V 20 min), two methods used for surface preparation of aircraft structural components. The metal surfaces were examined by scanning transmission electron microscopy (STEM) In the SEM mode and by X-ray photoelectron spectroscopy (XPS). 

Armstrong et al, (28) describe a unique approach of attaching sampling equipment to tethered balloons which are maneuvered from the ground into the plume of smokestack emissions. Aircraft sampling in plumes ( 9) has long been used, but it is expensive and difficult. 

Cahill, T. A., K. Wilkinson, and R. Schnell, Composition Analyses of Size-Resolved Aerosol Samples Taken from Aircraft Downwind of Kuwait, Spring, 1991, J. Geophys. Res., 97, 14513-14520 (1992). 

Field Sampling. An opportunity arose where actual field samples could be analyzed by both the infrared and gas chromatographic methods. At Robins AFB, Georgia, workers were inspecting and repairing the interior and exterior of C-141 aircraft fuel tanks. They were exposed only to JP-4 fuel fumes. Duplicate charcoal tubes or vapor monitors were attached to each worker, one on each lapel. Samples were drawn through the charcoal tubes at 0.20 to 0.26 1pm by portable pumps attached to the worker s belt. Because of slight variations, the total volumes collected for the duplicates were close, but not exactly the same in all cases. Samples were then labeled and shipped to our Laboratory for analysis by both methods. 

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