Evaluation of Trapezoidal Shaped Grooves

Analysis of the friction data collected at ORD indicated that the trapezoidal runway grooves provide comparable friction values to the standard grooves, making it nearly impossible to separate the two purely on their friction data. Extensive amounts of rubber contamination were present at ORD, due to the high levels of aircraft operations, which likely caused the friction numbers to be lower. This was illustrated in the data readings, as the friction values closest to the runway centerline are lower than those that are 20 ft away, due to the closer proximity to where an air carrier aircraft’s main gear would be first touching down on the runway. Likewise, the friction numbers collected from the longer test section closest to the threshold of Runway 10 were generally higher than those collected from the shorter test section where the pavement was exposed to both aircraft landing on Runway 28 and aircraft that landed on Runway 10, which brake heavily before exiting the runway to taxi to the terminal. In all six figures, the standard grooves and trapezoidal-shaped grooves appear to offer comparable results, with a few small sections of trapezoidal-shaped grooves showing slightly higher values than the standard grooves. Researchers were not trying to identify specific numerical differences in the friction values but were trying to determine if the trapezoidal-shaped grooves provided comparable friction than the standard groove on the runway as a whole. Data Collection and Results—ORD. The average cutting time per cutting pass was the same for both the trapezoidal-shaped and standard grooves, with no identifiable differences in the cutting process. As with the NAPTF, ACY, and MCAF Quantico installations, the equipment, manpower, and supplies used for the airport installation were the same. The speed of installation was identical for both the standard and trapezoidal-shaped grooves. The costs for the trapezoidal-shaped grooves are calculated to be between 15% and 25% higher than the cost of the standard grooves but are expected to decrease as the blades cost come down with large-scale production. Continued analysis of the grooves at ORD showed some noticeable disfiguring, collapse, and closure of both groove designs, although the standard grooves experienced more significantly disfiguring and closure than the trapezoidal-shaped grooves. Within the first six months after installation, the trapezoidal-shaped grooves appeared to show a significant benefit in their ability to resist rubber contamination. After a prolonged period, the trapezoidal-shaped grooves showed evidence of rubber contamination, but were not filled in as much as the standard grooves. The trapezoidal-shaped grooves remained open enough for water to flow through them, providing the escape path needed for water to be displaced under an aircraft tire. Friction measurements taken on the asphalt runway at ORD indicate that the friction characteristics of the trapezoidal-shaped grooves are comparable, if not slightly higher, than the standard grooves. Phase Four—Test Site 2 Summary. In conclusion, the trapezoidal-shaped grooves performed satisfactorily at ORD. As with the previous effort at MCAF Quantico, the installation cost for the trapezoidal-shaped grooves was slightly higher than the cost of standard grooves. The trapezoidal-shaped grooves, however, appear to offer additional benefits that may offset the


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