TP 13579 PROCEEDINGS of the 2nd International Meeting ... - UQAC

IMAPCR ’99
97. Mr. van Es then recommended that the presented method instead of the JAA AMJ 25X1591
be used for predicting the rolling resistance due to dry snow. He added that this new method
should be validated, especially with larger aircraft with bogie landing gears.
98. An audience member was surprised at the perfect correlation produced by the model. He
inquired about the degree of correlation and accuracy. Mr. van Es offered the following
figures:
• standard deviation for the AMJ model: 50-100 percent;
• standard deviation for the NLR model: 20-30 percent;
• R 2 for the AMJ model: 0;
• R 2 for the NLR model: 0.6 – 0.9.
Hydroplaning of Modern Aircraft Tires
99. Mr. van Es stated that most of the current knowledge of hydroplaning was obtained in the
1960s by mainly NASA studies. Since then, new tire types like radials have been introduced
for civil aviation and, since hydroplaning of aircraft tires is often a contributing factor in
overrun and veer-off accidents, a fresh look at hydroplaning is needed.
100. A distinction was made between dynamic hydroplaning and viscous hydroplaning. Although
they can occur simultaneously, the focus of the study was on dynamic hydroplaning, because
it is the dominant one.
101. Hydroplaning can occur when the water depth is so high that both the tire tread and the
surface macrostructure cannot drain the water sufficiently and quickly.
102. A mathematical model was then presented and hydroplaning characteristics of three
different types of aircraft tires were analysed, i.e., bias-ply, type H, and radial belted, each
having different footprint dimensions for the same tire size, tire pressure, and load.
103. A comparison was made between the calculated and experimental hydroplaning speeds
(vs tire pressure) for the three types of tires.
104. Based on the results, Mr. van Es concluded that modern aircraft tires have lower hydroplaning
speeds than those predicted by the well-known and commonly accepted equation developed by
Mr. Horne of NASA. He stated that this was because of the differences in the footprint
dimensions of the newer tires as compared to the older bias-ply tires.
105. He recommended that these results be validated by conducting systematic tests on the
footprint characteristics of modern aircraft tires in combination with hydroplaning tests. He
suggested that the Aircraft Landing Dynamics Facility at the Langley Research Center
(NASA) be considered for these tests.
106. In response to a question, Mr. van Es added that aspect ratio was included in the model.
14