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OCR for page 153
153 Table 14-2. Path calculation data for active system there would be at least some aircraft for which this arrestor B737-800 landing gear capture. concept would not work. Lower Bound Optimal Launch Upper Bound Time to Launch 50 ms 80 ms 110 ms 14.4. Summary Tolerance 4.78 ms 7.80 ms 11.03 ms The main-gear engagement active system concept offered Initial Velocity 67.73 ft/s 42.33 ft/s 31.36 ft/s multiple advantages not available in surface-based arrestor Tolerance 3.08 ft/s 2.71 ft/s 2.22 ft/s beds. Feedback control offered the potential for ideal decel- Terminal Velocity 66.12 ft/s 39.75 ft/s 27.82 ft/s eration of aircraft. The friction brakes could adjust auto- matically to apply less load on a small plane than a large one, enabling one arrestor to treat all aircraft equally. The overall effect of these advantages would be shorter arrest- 14.3.3. Landing Gear Features ing distances for the entire design fleet of aircraft. One of the more problematic issues with this concept is The load calculations undertaken confirm that the essen- the varied nature of main landing gear features for different tial mechanics for the arrestor system would function as aircraft. On the main struts of many passenger aircraft, a anticipated. Tension regulation in the cable would be essen- variety of smaller hydraulic, electrical, and mechanical com- tial to prevent lateral overloading of the landing gear toward ponents are exposed on the front and outboard sides of the the end of the arrestment. struts. If the struts of these aircraft were engaged with a Despite these promising features, a number of complicat- cable or net and subjected to substantial load, these compo- ing issues remain for the active system concept: nents would likely be damaged. In the case of some aircraft, such as the A380, which has a secondary strut forward of the Aircraft identification and speed calculation would be main-gear strut, cable engagement could result in structural required for the system to function correctly. Systems failure of the main-gear assembly. Although it is possible to accomplish both could likely be developed, although that engagement geometries could be developed that reduce research of such facets has not yet been undertaken. the risk of structural damage to the landing gear, some Cable sizes are of concern because the thicker cables required degree of damage to the gear is likely under any arresting for rapidly arresting large planes could be heavy enough to conditions. damage smaller ones. The cable engagement process would likely result in dam- age to landing gear doors, actuators, wiring, and hydraulic 14.3.4. Infeasible Aircraft features on the front side of the main struts. During the investigation, it became apparent that some The window of time for deploying the system could be nar- aircraft would not have a deployment path solution as that row when the aircraft has low-slung engines because the discussed in Section 14.3.1. Figure 14-11 shows that the vertical path of the cable or net must miss the engine shorter B737-200 has engine locations that preclude engag- nacelles yet engage the main strut above the tires. ing the target point on the strut. Although a broad survey of Due to the longitudinal overlap of the engines and main infeasible aircraft was not undertaken, this case illustrates that struts, some aircraft would not have a feasible solution Infeasible Geometry: Target Point Blocked by Engine Figure 14-11. Infeasible geometry for landing gear engagement: B737-200.

OCR for page 153
154 path for cable deployment. These aircraft could not be offer the best overall engagement approach. Past activation engaged and arrested by a main-gear cable/net system. issues for the nets could be resolved using automation con- cepts as discussed, thereby eliminating the need for direct For these reasons, the active system approach is feasible for triggering by airport personnel. However, potential obstruc- stopping aircraft, but the main-gear engagement concept tion of aircraft exits and damage to the aircraft continue to should perhaps be eliminated from consideration. Barrier net remain obstacles to implementation. systems have been developed in the past, and they may still