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Jet Blast and Wake Turbulence Forces on Airport Signs
Final report: "Evaluation of Wind-Loading on Airport Signs"
Airport signs at certain critical locations at O’Hare International Airport and other major U.S. airports are being sheared off their mounting legs at the frangible coupling from aircraft jet engine blast and/or wake turbulence forces.This damage to the sign increases the chance of foreign object damage (FOD) as well as the loss of visual guidance for other aircraft. If much stronger couplings are installed, the advantages of frangibility are lost and the sign panel itself is subject to damage. Consequently, there is a need to better understand and to more precisely determine the forces at these locations. A study to investigate the forces exerted on airport runway signs caused by aircraft jet engine blast and wake turbulence was conducted. The project was divided into four individual tests. Two laboratory tests were conducted to determine the elastic/plastic limitations of the frangible couplings of an airport sign and to determine the strain on the sign (specifically the couplings) at various wind speeds with and without turbulence. The frangibility testing was conducted on a Material Testing System (MTS), and the strain/wind speed tests were conducted in the William J. Hughes Technical Center’s wind tunnel. Two field tests utilizing the current design criteria were also conducted at the Chicago O’Hare International Airport to investigate the load at which airport signs were structurally failing in the airfield environment and to measure the maximum forces experienced by these airport signs. A supplemental test was conducted to compare the effects on signs installed at the Federal Aviation Administration (FAA) maximum setback distance of 35 ft. from the runway edge and at the International Civil Aviation Organization (ICAO) outer limit of 49 ft. Since the end of March 1999, informal field tests have been conducted at Chicago O’Hare International Airport utilizing a slightly different sign design and stronger frangible couplings. To date, these signs have not failed. The results of these tests indicate that the current frangibility design criteria on airport signs installed at the FAA maximum setback distance is not adequate for signs installed on airports that service large transport aircraft; whereas the current frangibility design criteria is acceptable for the ICAO setback distances. Additionally, preliminary tests indicate that a more stringent frangibility requirement would accommodate the FAA maximum setback distances. Therefore, a modification to the frangibility requirements or maximum setback distance would appear to be a satisfactory solution to mitigate sign breakage. The former is recommended since it would appear to have no impact on the operational characteristics of the aircraft movement area. Contact Project Lead: Keith Bagot, AAR-411 Last Update:11/29/04 |
