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132 Landing Gear Forces - MAIN STRUT 100 Main Gear Drag 80 Main Gear Limit Load Main Gear Ultimate Load Force (kip) 60 40 20 0 -150 -100 -50 0 50 100 150 200 250 300 Location [ft] Vertical Displacements - MAIN STRUT 20 10 Displacement [in.] 0 -10 Axle Displacement -20 Rut Depth Lower Bound of Bed Upper Bound of Bed -30 -150 -100 -50 0 50 100 150 200 250 300 Location [ft] Figure 11-26. Limit criterion aggregate foam arrestor--50-ft ramp-- design plots for B737-800 showing main-gear strut loading (top) and main strut axle and rut depth (bottom). First, the aggregate foam arrestor exhibits a depth-varying 11.6. Estimated System Cost strength property that is advantageous for arresting varied and Upkeep aircraft fleets. However, during a landing in an arrestor, the initial downward loads would be high, and this could cause a 11.6.1. Installation Process deep penetration and a corresponding drag-force overload to The loose aggregate solution offers the advantage of the landing gear. construct-in-place simplicity, which could produce instal- Second, the basin geometry of the arrestor concept would lation cost savings over a traditional EMAS. It reduces site force the aircraft to roll up the decline slope in the reverse preparation and eliminates block manufacturing, placement, direction from normal, acting as a ramp that would cause a and joint sealing. However, turf preparation and placement strong load to the landing gear. This issue could be eliminated would be additional tasks not required for the current EMAS. by only partially recessing the bed, as in the ideal EMAS The foam aggregate concept would require excavation of design cases. Mechanical performance was found to be nearly an arrestor bed basin with a depth nominally equivalent to equivalent with either version. However, the turf covering of that of an EMAS bed. This basin may or may not require the arrestor would be above grade in such cases, presenting paving before being filled with foam aggregate. However, the some construction and aesthetic complications. below-grade nature of the basin would require drainage from
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133 the bed to be included in the design using standard roadway install such a system, it is recommended that a detailed cost engineering practices. quote be sought from a firm qualified to undertake an instal- The basin would be filled with foam aggregate using earth- lation effort. Where possible, the methodologies used were moving equipment. Due to the crushability of the material and consistent with the prior survey information collected regard- the importance of maintaining the original gradation and den- ing the existing EMAS (Section 3.5). sity (Section 11.3.2), the foam aggregate would require care The costs may be broken into two major categories: site during installation. Bulldozers, or an equivalent, would reverse preparation and installation. The site preparation costs were fill the bed starting from the distal end and working backwards, estimated for two cases. The aggregate foam arrestor would such that they did not overrun previously deposited material. use a basin for the arresting materials rather than a flat Only vehicles with low ground pressure would be permissible runway-type surface as is used for the current EMAS design. on top of the bed material, such that the material was not com- The bottom of the basin could either be paved or earthen. pacted beyond design specifications. If a roller was to be used Drainage, excavation, and leveling would be required for for creating a level surface on top of the bed before applying either option. Assuming that a full paved surface is not pro- the turf cover layer, a prescribed degree of compaction would vided under the bed, the cost for site preparation was need to be pre-defined (Figure 11-27). However, grading the assumed to be reduced by half; this value was used for the bed could require a fairly manual process to obtain the desired lower-bound cost estimate for the system. If a full paved sur- results. face is provided, then the preparatory costs were assumed to Depending on the design of the reinforced turf layer, it be the same as for the current EMAS; this provided the upper- could be grown in place, or it could be grown in advance, then bound cost estimate. cut into segments and placed atop the bed. The latter alterna- The installation cost estimate was separated into specific tive would require the use of a front-end loader equipped to materials and general installation labor needs. Because these provide low ground pressure. costs were specific to the aggregate foam arrestor concept, they Once completed, the bed would permit normal traffic do not have a direct connection to any prior EMAS data. from grounds keeping vehicles and pedestrians. Vehicles with Discussions with the manufacturer produced cost estimates for high tire pressures, such as emergency vehicles and aircraft, the aggregate foam, reinforced turf cover layer, and geo-textile/ would be restricted from driving on top of the bed. geo-plastic layers. Where applicable, materials included freight costs for trans-Atlantic shipping. The labor costs were based on estimates from the manufacturer established from similar 11.6.2. Cost to Establish System installation efforts. A preliminary estimate was made for the cost to establish Finally, the site preparation and estimated EMAS costs an aggregate foam arrestor system. It must be noted that the were computed in two ways: (1) assuming average survey cost estimate from this section is only a basic approximation costs from this research, and (2) assuming FAA Order 5200.9 for the purposes of comparing the different arrestor alterna- costs. The final cost estimates for both options are given in tives. The cost estimate is based on a mixture of information Table 11-8 and Table 11-9, respectively. from the manufacturer, the airport survey, and FAA Order Using the survey cost assumptions of Table 11-8, a 300-ft 5200.9. To develop a more accurate estimate of the costs to arrestor bed would cost between 47% and 60% less than the current EMAS. If the Order 5200.9 costs are assumed, the cost advantage drops to between 37% and 44% (Table 11-9). Table 11-8. Estimated costs to establish aggregate foam arrestor, 150 x 300 ft, assuming survey average costs for current EMAS, units of millions USD. Cost Category Aggregate Foam Current System EMAS Lower Upper Bound Bound Site Preparation $ 1.08 $ 2.17 $ 2.17 Installation $ 2.16 $ 2.16 $ 6.03 Cost to Establish $ 3.24 $ 4.32 $ 8.19 Figure 11-27. Roller compaction of aggregate foam Percent of EMAS 40% 53% material during typical installation (43).