State of current knowledge regarding tyre braking performance of modern aircraft tyres on flooded runways Gerard van Es, NLR, Paris, 31st March / 1st April 2016
SAFETY | FUTURE SKY
DGAC-STAC Symposium Runway Surface Conditions Assessment and Reporting
Background q European Action Plan Prevention of Runway Excursions
provides recommendations to reduce runway excursions in Europe;
q Action Plan identified areas were research is needed to further reduce runway excursion risk, like:
q Braking performance of modern aircraft on flooded runways.
q Future Sky Safety Project addresses this topic amongst others:
q Presentation will discuss current state of knowledge.
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Definitions What is a flooded runway?
q Legal: A runway can be considered flooded when more than 25 percent of the runway surface area is covered by water that is more than 3 mm in depth;
q Alternative: A runway on which the water depth exceeds the ability of tyre tread and runway texture to prevent water film build-up below the tyre:
q Could be more or less than just 3 mm of water.
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Flooded runway
Wet runway
VERSUS
Braking friction-Dry, Wet, and Flooded
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Factors influencing friction on flooded runways q Runway texture (macro- and microtexture, runway
grooves); q Ground speed; q Tyre inflation pressure; q Tyre tread depth (dynamic hydroplaning); q Tyre type (bias-ply, radial, H-type):
q Impact on dynamic hydroplaning.
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Comparison of full dynamic hydroplaning speeds different tyre designs
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160
140
120
100
80
60
40
20
0
Hyd
ropl
anin
g sp
eed
(kt)
250200150100500Tire pressure (psi)
bias ply (new designs 1975-onwards) radial belted H-type bias ply (old designs 1960s)
9√p
6√p
Empirical equations for dynamic hydroplaning speed q Rotating wheel :
o Classical NASA ≈9.0√p o Modern bias-ply tyres ≈8.0√p o H-type tyres ≈7.5√p o Radial tyres ≈6.9√p
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q For spin-up dynamic hydroplane speed reduces by 15%;
q Note: dynamic hydroplaning speed also influenced by: water depth, macro texture, tyre grooves, and tyre footprint.
Review of experimental data on braking capabilities of aircraft tyres on flooded runways q Most data were from period 1959-1989;
q Data from full-scale aircraft tests as well full-scale traction facilities were collected;
q No friction data found for radial and H-type aircraft tyres (only for wet runways).
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Example of data sources
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NASA full-scale traction facility FAA CV-880 flight tests
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Full-scale aircraft data Flooded runways
Models for braking friction on flooded runways
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Final Remarks q Study summarises the state of current knowledge
regarding tyre braking performance of aircraft tyres on flooded runways:
q Full report available from the FSS website.
q Very limited data on flooded runway braking of aircraft with modern tyres and modern anti-skid systems:
q Flight tests in FSS project should partly fill this gap.
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Aircraft to be tested in FSS project
http://www.futuresky.eu/projects/safety