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