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103 The predicted stopping distances for the three aircraft are given in Table 10-5. All arrestment predictions assumed the following: 50-ft setback distance; 50-ft gradual decline to the maximum bed depth; 70-knot starting speed for the aircraft; No reverse thrust; Braking factor of 0.25 before and within the bed; and Arrestor bed loads based on interaction with tires, neglect- ing strut and axle components. Arrestor beds were designed for two different nose-gear loading criteria: 1. Limit Load Criterion, where the drag load applied to the nose strut cannot exceed the limit load for the nose gear (FAR Part 25.509); Figure 10-23. Tunneling of tire below turf surface. 2. Ultimate Load Criterion, where the drag load applied to the nose strut cannot exceed the ultimate load for the nose gear; Since the ultimate loading criterion permits higher loads on 10.5. Arrestor Performance the strut, deeper beds and shorter stopping distances resulted Predictions from those cases. 10.5.1. Scope of Simulations 10.5.2. Performance for Test Aircraft Using the APC, a separate optimal arrestor was designed for each of the three trial aircraft: CRJ-200, B737-800, and Table 10-5 lists best-case arrestor designs for each aircraft B747-400. Subsequently, an optimal mixed-fleet arrestor was taken individually. Each arrestor bed listed uses a different designed as a compromise best-fit for all three aircraft. material strength and depth that are optimized for the design All simulations assumed a turf-covered arrestor bed with aircraft. Generally, a range of acceptable strength and depth dry aggregate. If a drainage-type arrestor bed were used, the combinations was available. Compared with the similar aggregate would be intermittently wet and dry, and longer EMAS design cases on the right (provided by ESCO), the dis- arrestor designs would be required. tances are comparable if the ultimate loading criterion is used. It was determined through experimentation that the aggre- Table 10-6 shows the compromise design case with the best gate arrestor design functioned best as a fully recessed bed, with arrestor design for all three aircraft. The CRJ-200 controls the the top of the turf level with the runway, and the remainder of bed depth in this case, while the B737 controls the bed length. the material placed in a basin below grade. With the material strength and depth as specified, the B747 Table 10-5. APC predicted 70-knot stopping distances for engineered aggregate arrestor system. Nose-Gear Limit Nose-Gear Current EMAS, Load Criterion Ultimate Load Optimal Designs Criterion Arrestor Bed Depth Bed Depth Bed Depth Bed Design (in.) Length (in.) Length (in.) Length (ft) (ft) (ft) Single Aircraft CRJ-200 9.6 495 14.1 310 20 258 B737-800 13.5 462 19.5 361 20 287 B747-400 29.1 568 34.7 517 26 495