Developing Improved Civil Aircraft Arresting Systems (2009) / Chapter Skim
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Pages 46-59
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From page 46... ...
Following the identification of alternatives, taxonomy was developed to classify the different options and provide clarity of comparison. An initial assessment of the alternatives led to the selection of several promising candidates for detailed research in the experimentation phase of the effort.
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From page 47... ...
Yes Yes Phenolic foam Yes Metal foam Yes Glass foam Yes Yes Crushable foams Depth-varying foam Yes Yes Loose crushable fill Glass aggregate foam Yes Yes Pumice aggregate Yes Styrofoam aggregate Yes Hollow microspheres Yes Crushable Materials Crushable aggregates with binder Ceramic glass aggregate Yes Clay Soil Sand Yes Gravel Yes Loose aggregates Engineered aggregate Yes Yes Yes PA SS IV E SY ST EM S Displaceable Materials Fluids Water or Glycol pond Yes Hydraulic brake Yes Water impeller Textile Braking devices Eddy-current brake Over-wing barrier nets Cable/Net Systems Engagement devices Landing gear strut engagement Yes A CT IV E SY ST EM S Mechanical Surface Systems Surface of springsupported panels Yes Table 7-1. Classification of alternatives.
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From page 48... ...
Covering layers are often used to preserve the crushable or displaceable materials from the environment, jet blast, and so on. The current EMAS design uses such a "covering layer." The latest generation uses thin plastic tops, while the prior generation used cement board tops.
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From page 49... ...
UV sensitivity Arrestor beds that use covering layers (cement board, plastic, other) inherently protect the arresting materials from UV exposure.
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C Loose Crushable Fill Crushable aggregate foam Glass-based material that is chemically inert and has moistureresistant properties. Made of recycled glass, it offers potential cost savings over cellular glass foam.
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Engagement Devices Landing gear strut engagement Long-standing design option. Low-slung engine design on some current civil aircraft creates timing issues regarding deployment.
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Table 7-4 gives several sample pneumatic tire ground pressures, as well as the compressive strength of the current EMAS cellular cement. As may be seen, the internal pressure of the aircraft tire is greater than the strength of the EMAS material.
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7.5.4. Overall Aircraft Dynamics When overrunning the arrestor bed, the nose gear and main gear of the aircraft experience vertical and drag loads (Figure 7-4)
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7.5.7. Candidate 2: Aggregate Foam An aggregate foam arrestor concept has been proposed.
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This material is much like normal gravel in that the individual aggregate pieces do not Figure 7-6. Cellular glass foam material.
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7.6.1. Drag Load Dynamics Although a gravel-type arrestor bed appears to load the landing gear in a similar fashion as the current EMAS design, the dynamics involved are quite different.
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From page 57... ...
7.6.4. Summary of Mechanical Factors To summarize the dynamics of aggregate/gravel arrestor beds, the following factors have a direct impact on the overall performance: • Material properties – Particle size/gradation – Particle shape – Particle density • Inter-particulate properties – Internal angle of friction – Inter-particle friction – Inter-particle cohesion • Speed of travel • Material depth • Landing gear configuration • Pneumatic tire pressure • Limiting landing gear design loads, with special consideration for the nose gear – Vertical limit load – Longitudinal (drag-direction)
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From page 58... ...
Prior attempts have been made to adapt them for use with civil transport aircraft. To surpass these predecessors, any new attempts to adapt the active systems would require innovation and new sensor approaches.
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From page 59... ...
This maingear engagement approach circumvents the weakness of the crushable bed systems: it does not subject the nose gear to drag loads. Consequently, it would be possible to achieve higher decelerations and shorter stopping distances.
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