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23 Table 2-1. Literature review summary. dictability of the loads imparted to the landing gear: loadings that are too high can damage or fail the gear, and loadings that Document Type Topical Areas are too low will not efficiently arrest the aircraft. Accurate Government research Arrestor systems prediction of these loads cannot be obtained without also Government regulations Aircraft and landing gear capturing the dynamic response of the aircraft and landing dynamics Journal papers gear. Much like driving a car over speed bumps, the suspension Airport operations Patents response can dictate the overall degree of bounce and sub- Modeling and simulation sequent pitching, or "porpoising," that occurs. Inconsistent Manufacturer specifications and research Material science materials can lead to more porpoising, and hence higher loads Reference books on the landing gear. Magazine/newspaper/Internet articles While many documents have been reviewed, a few will be singled out here. Currey (14) provides a general text describing the fundamentals of design and analysis of landing gear, allow- a number of their product brochures. Active arresting systems ing for the general sizing of struts, tires, etc. Pritchard's (15) have seen the most widespread use for military aircraft with overview of landing gear dynamics provides a substantial array tail hooks. To arrest civilian aircraft, netting systems are of simulation options, which will be employed in the second used to either wrap over the aircraft wings or engage the main phase of the effort. Chester (16) outlines a modeling approach landing gear struts. The former approach presents hazards for for a generalized aircraft of varying size, with a focus on land- occupant emergency egress from the aircraft, as the netting ing gear dynamics and overall airframe response. Altogether, can block exit hatches. The latter approach has technical dif- we find that relevant variables to the current problem include ficulties due to widely varying landing gear geometries. strut stiffness and stroke length, tire pressure and dimensions, aircraft mass and moments of inertia, etc. Since these proper- 2.3. Recent Arrestor Research ties for an actual aircraft are proprietary manufacturer infor- mation, the information from these references will prove Due to some of the present concerns regarding the life-cycle beneficial for approximation. performance of the arrestors, MinneapolisSt. Paul Airport Experimental studies undertaken by the FAA have been (MSP) has conducted several limited research and testing reviewed. Micklos and DeFiore (17) discuss video analysis efforts. Stouffer (9) performed in-situ environmental tests techniques for determining aircraft parameters based on obser- on the arrestor bed and found a high relative humidity inside vations of aircraft landings. Tipps et al. (18) describe landing the bed, indicating the trapping of moisture inside the blocks. gear load factor statistical studies based on in-service aircraft Stehly (10) conducted testing on some older blocks of the measurements. These and similar reports focus on determining MSP 12R/30L arrestor, including fire-truck overruns and rough the level of loading that in-service aircraft actually experience, in-situ compression tests. Both tests indicated that performance often with a focus toward determining the appropriateness of degradation had occurred since the 1999 installation. the current Federal Aviation Regulations (FAR) requirements. Design reports for arrestor beds were reviewed (11), as well As such, they have less relevance to the current effort, where as relevant excerpts from airport certification manuals (12). The load limits for aircraft are the focus. design reports indicate that, in actual practice, the exit-speed performance of a given arrestor bed can vary widely across the aircraft fleet; some aircraft will be arrested at higher speeds 2.5. Airport Operations than others. Some literature was found pertaining to gravel truck In order to understand the implications of arrestor design arresting systems, typically used for arresting runaway trucks on airport operations, several sections of CFR Part 14 were on downhill roadways. Rogers (13) discusses cold-weather reviewed (19, 20). testing information that demonstrates the potential for aggre- FAA Order 5200.8 outlines the Runway Safety Area Pro- gate arresting beds to freeze over and become ineffective in gram (21). The intent of the program is to ensure that all Part harsh winter environments. 139 airports in the United States are brought into compliance with RSA requirements. Historical data shows that most overruns take place at speeds of 70 knots or less, and that 2.4. Landing Gear and aircraft typically come to rest within 1,000 ft of the end of the Aircraft Dynamics runway (Section 4.4.1). Consequently, a standard RSA has a Landing gear was studied by the project team following typical length of 1,000 ft. For airports not in compliance, five the review of soft-ground arrestors. A key performance metric remedial measures are described: relocating runways, reducing for soft-ground arresting systems is the consistency and pre- runway length, a combination approach, the use of declared