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86 For either case, the material type and thickness of the layer bogy test apparatus may prove sufficient to characterize the must be established. The material should be selected based on remaining unknown factors of the concept, such as the cover ultraviolet and weather durability. A material that can be layer, seam effects, and braking dynamics. dyed to a pavement gray color would be preferable, such as is currently in use for plastic EMAS tops. Paint application for yellow chevron markers would be required. 9.8. Summary After selection of a cover layer material that meets these Of the candidate systems evaluated, the glass foam arrestor general requirements, a moderate to full-scale test bed should concept is most similar to the current EMAS. It uses blocks of be constructed for overrun testing by a one-wheel bogy appa- crushable foam material that are installed on a paved surface. ratus or an aircraft. Such testing would ensure that the cover While the mechanical properties differ somewhat from cel- layer does not negatively impact the mechanical deceleration lular cement, the overall dynamic behavior proves analogous. performance of the bed. Consequently, the glass foam concept could be considered an equivalent to the existing EMAS technology, with the caveat 9.7.3. Seam Effect Characterization that bed thicknesses and material properties would not be identical. The research performed to date has identified that seams The material is closed-cell glass foam, which provides inher- between glass foam blocks should be investigated further. ent moisture and chemical resistance and improved handling Seams in the material have been observed to generate pulsed durability as compared with cellular cement. Manufacturer loads on a rigid tire form during testing; it is not presently information regarding past use indicates that long service known how substantial such loading pulses might be on life is possible, potentially eliminating the standard 10-year actual landing gear. replacement for an EMAS assumed in FAA Order 5200.9. One evaluation method could involve using a one-wheel Water immersion must be avoided, so drainage measures bogy apparatus fitted with a full-scale pneumatic tire that is would still be required for the bed. towed through the material. Direct comparisons could be made between fully glued test beds and those having un-glued seams. Installation of the system would rival the current EMAS design in terms of time and effort required. Repair of the bed after an overrun would be analogous to the current EMAS 9.7.4. Braking Dynamics requirements. Preparatory paving requirements would be The research performed has identified that braking in the identical. The cost to establish such a system would be nom- glass foam material may require further study. The current inally equal to, or greater than, EMAS; however, life-cycle costs modeling method of the APC makes simplifying assumptions could be reduced due to longer bed life. Maintenance needs regarding this phenomenon that are sufficient for a concept- could be reduced for a monolithic version of the concept, level evaluation. However, to ensure accuracy of design pre- which would have no joints to seal with tape or caulk. dictions, some additional tests may be beneficial. One method The APC predictions for the glass foam arrestor show fairly would involve using a one-wheel bogy apparatus fitted with constant deceleration throughout the arrestment with little brakes and a load measurement system that is towed through speed dependence, which are desirable characteristics. Arrest- the material. ing distances were comparable to the current EMAS. Of the three candidates evaluated, the multi-aircraft design case for the glass foam concept showed moderate performance. Arresting 9.7.5. Full-Scale Testing distances varied with the aircraft size. A full-scale aircraft overrun test of the glass foam arrestor Transition to a fielded system would require selecting a bed may or may not be critical to approve and field such a covering material and finalizing a set of foam densities that system. The mechanical nature of the system is very similar could be used for different arrestor applications. Additional to that of the current EMAS, which leaves fewer unknown investigation would be advisable to determine the impact of factors than for the other concepts evaluated. A one-wheel material seams in producing pulsed landing gear loads.