National Academies Press: OpenBook

Developing Improved Civil Aircraft Arresting Systems (2009)

Chapter: Chapter 13 - Summary of Passive System Candidates

« Previous: Chapter 12 - Depth-Varying Foam Material
Page 144
Suggested Citation:"Chapter 13 - Summary of Passive System Candidates." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 144
Page 145
Suggested Citation:"Chapter 13 - Summary of Passive System Candidates." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
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Page 145
Page 146
Suggested Citation:"Chapter 13 - Summary of Passive System Candidates." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
×
Page 146
Page 147
Suggested Citation:"Chapter 13 - Summary of Passive System Candidates." National Academies of Sciences, Engineering, and Medicine. 2009. Developing Improved Civil Aircraft Arresting Systems. Washington, DC: The National Academies Press. doi: 10.17226/14340.
×
Page 147

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144 Chapters 9 through 12 examined the passive system candi- dates on an individual basis. This brief chapter summarizes key findings for performance and cost on a side-by-side basis. 13.1. Overview The experimentation phase evaluated three passive arrestor candidate systems: 1. Glass foam arrestor 2. Aggregate foam arrestor 3. Engineered aggregate arrestor Each demonstrated relative strengths and weaknesses. All three options provide concepts with increased material dura- bility over cellular cement, which would likely result in longer life cycles and decreased maintenance requirements. 13.2. Performance Comparison The performance of the different candidates can be com- pared in two primary ways: based on (1) single-plane or (2) multi-aircraft bed designs. When comparing single- aircraft bed designs, the thickness of each bed and its mate- rial properties are optimized for the plane of interest. How- ever, the bed designs for the different aircraft may not be compatible with one another. For example, a best-case design for the B747-400 was typically found to overload the landing gear of the CRJ-200. When comparing multi-aircraft bed designs, a single bed is designed for best-case performance with all three of the subject aircraft simultaneously. A single bed thickness and material property are determined such that the overall performance is optimized for all three aircraft. The single-aircraft comparisons always produce the short- est feasible stopping distances. However, the multi-aircraft comparisons are more relevant to actual applications at air- ports, in which arrestor beds are designed as a compromise between the different aircraft serviced. Figure 13-1 compares the best single-aircraft bed designs for the three alternatives and compares them to the current EMAS technology. The four sets of bars show very similar trends in terms of relative stopping lengths for the different aircraft. The glass foam stopping distances are slightly shorter than those of the current EMAS, while the other two concepts would require slightly longer beds. The performance simi- larity of glass foam and the current EMAS is not surprising because both designs use crushable foam block material with similar mechanical behavior. However, this compari- son of single-aircraft performance is ultimately less relevant to real applications than the multi-aircraft comparisons that follow. Figure 13-2 compares the best multi-aircraft arrestor bed designs for the three alternatives. In each case, the B747-400 required the longest bed for arrestment from a 70-knot exit speed. It should be noted that performance predictions for the existing EMAS have not been included in the figure because the design cases did not apply to multi-aircraft bed designs. In general, the material could be assumed to follow a similar trend to glass foam, owing to the mechanical similarities just discussed. In comparing Figure 13-1 with Figure 13-2, the trend for leading and trailing concepts shifts considerably. The differ- ences illustrate how substantially the multi-aircraft perfor- mance deviates from aircraft considered individually. For the multi-aircraft case, bars of similar height indicate improved equality in the treatment of the three aircraft. Of the three concepts, the aggregate foam shows the most consistent per- formance, with dramatic reduction in the stopping distance for the B747-400. As an example, for a bed with a practical 400-ft length, the exit speeds for each aircraft are as shown in Table 13-1. The 400-ft bed would obtain a full 70-knot exit speed rating for the CRJ-200 with all arrestor concepts. Both the glass foam C H A P T E R 1 3 Summary of Passive System Candidates

145 and aggregate foam beds would further obtain a 70-knot rating for the B737-800, while the engineered aggregate falls behind at only 63 knots. For the B747-400, none of the beds obtain a full 70-knot rating; the aggregate foam leads at 56 knots and the engineered aggregate falls to below the minimum allow- able speed at 39 knots. Overall, the performance of the three concepts can be sum- marized as: • The aggregate foam concept provided the best overall mixed-fleet bed performance, showing the smallest spread in arrestor performance for the three aircraft. However, the bed design must be correctly specified to prevent oscillatory porpoising behavior. • The engineered aggregate produced speed-dependent land- ing gear loads. This would typically require designs to hedge against overloading by under-designing them, resulting in longer arrests than illustrated above. • The glass foam beds produced the most predictable and constant decelerations without speed dependence or por- poising effects. 13.3. Environmental Performance Comparison From an environmental performance standpoint, all three alternatives appear likely to offer superior performance to the current EMAS technology. The environmental perfor- 0 100 200 300 400 500 600 700 Current EMAS Glass Foam Engineered Aggregate Aggregate Foam St o pp in g D is ta n c e (ft ) CRJ-200 B737-800 B747-400 Figure 13-1. Comparison of single-aircraft bed performance for all candidates: distance travelled in bed for full arrest assuming 70-knot exit speed. 0 100 200 300 400 500 600 700 800 900 1000 Current EMAS Glass Foam Engineered Aggregate Aggregate Foam St op pi ng D is ta nc e (ft ) CRJ-200 B737-800 B747-400 D A TA N O T AV AI LA BL E Figure 13-2. Comparison of multi-aircraft bed performance for all candidates: distance travelled in bed for full arrest assuming 70-knot exit speed.

146 mance estimates are based on some test data, historical use of the materials, and engineering judgment. An exhaustive envi- ronmental test program has not been undertaken as part of this program. Life-cycle performance has been assumed to result from a combination of the core materials used and the protective measures taken to shield those materials from the elements. From a materials standpoint, the glass foam and aggre- gate foam concepts both use closed-cell glass foams that inherently resist water penetration. The engineered aggre- gate is composed of hard spherical pellets. All three of these materials appear to offer superior inherent resistance to gen- eral handling and moisture/chemical exposure when com- pared to cellular cement. Of the three, the engineered aggregate is the most durable material because it is not a crushable low-density foam. How- ever, the arresting properties of engineered aggregate can be affected by the dampness of the material in a manner that is unlikely to affect the glass and aggregate foams. The glass and aggregate foam materials showed degrada- tion if subjected to fully immersed freeze–thaw cycling con- ditions. Protection from standing water conditions would be required in all three cases, which is feasible using the pro- posed protective measures. Where such measures are taken, the materials have demonstrated a long service life. With regard to protective measures, methods for covering and sealing the three candidate materials against moisture, standing water, jet blast, and freezing conditions have been examined (see respective chapters). For the aggregate foam and engineered aggregate approaches, the use of geo-plastics and geo-textiles could render the beds essentially isolated from water entrainment and freeze–thaw damage. The glass foam material could be packaged in a manner similar to that of the current EMAS cellular cement or equipped with an alternative monolithic sealed top layer. Both the aggregate foam and engineered aggregate concepts propose using a turf layer atop the beds, which is novel for arrestor beds. While modeling predictions indicate that this is feasible, additional testing in wet and freezing conditions would be required to characterize that facet of environmental per- formance. Alternative cover layers are possible in the event of adverse performance. In all three cases, the proposed designs offer life-cycle poten- tial beyond the 10-year bed replacement interval that is assumed necessary for the current EMAS technology (29). 13.4. Cost Comparison The relative costs for the current EMAS and the candi- date systems are compared in Figure 13-3 and Figure 13-4 using survey cost assumptions and estimates from FAA Order 5200.9, respectively. The general trends appear similar in either case, with the aggregate foam concept pro- viding the least expensive alternative, and the glass foam Aircraft Glass Foam Engineered Aggregate Aggregate Foam CRJ-200 70+ 70+ 70+ B737-800 70+ 63 70+ B747-400 46 39 56 Table 13-1. Comparison of multi-aircraft bed per- formance: exit speeds for full arrest in 400-ft bed. $- $1 $2 $3 $4 $5 $6 $7 $8 $9 Co st to E st ab lis h ($M ) Installation Site Preparation Figure 13-3. Relative estimated cost comparison assuming survey costs (150 ft x 300 ft bed). $- $1 $2 $3 $4 $5 $6 $7 Co st to E st ab lis h ($M ) Installation Site Preparation Figure 13-4. Relative estimated cost comparison assuming FAA Order 5200.9 costs (150 ft x 300 ft bed).

147 providing the most expensive alternative. The costs in the figures denote the total cost to establish such a system and do not include life-cycle costs of bed replacement and maintenance. 13.5. Summary Comparison Glass foam provided equivalent dynamic behavior to the currently approved EMAS system. Its performance, cost, and construction are also similar to the current EMAS. However, use of glass foam with a monolithic construction offers reduced maintenance and a longer service life. Additionally, glass foam could be constructed using a stratified depth-varying layup, which would likely improve multi-aircraft bed performance (Chapter 12). Aggregate foam provided a novel approach that featured excellent multi-aircraft bed performance due to its depth- varying crushable material; this would effectively lead to shorter arrestor beds. Its cost was the lowest of the alternatives, combin- ing an inexpensive material with a simple installation process. Engineered aggregate features the most durable candidate arrestor material, much of which could be reused after an arrest- ing event. It has a cost that falls between the other concepts. Its speed-dependent nature produces weaker multi-aircraft per- formance, which would require longer arrestor beds to obtain the same exit speed ratings.

Next: Chapter 14 - Main-Gear Engagement Active System Concept »
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TRB’s Airport Cooperative Research Program (ACRP) Report 29: Developing Improved Civil Aircraft Arresting Systems explores alternative materials that could be used for an engineered material arresting system (EMAS), as well as potential active arrestor designs for civil aircraft applications. The report examines cellular glass foam, aggregate foam, engineered aggregate, and a main-gear engagement active arrestor system.

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