Dynamic Vs Viscous Hydroplaning

[concordino]

Hello All,

What is the difference between these two types of aquaplaning with their respective formulae and the differences in their speeds.

Many thanks !! :ok:

[Phil Squares]

Dynamic hydroplanning is 9 X square root of the tire pressure. I think viscous hydroplannng can occur at just about any speed and might be more dependent on temperature. Don't hold me to the last statement. However, trying to remember aero after 30+ years is a little difficult.

[safetypee]

See FLIGHT SAFETY AUSTRALIA, SEPTEMBER-OCTOBER 2000 “Slippery when wet” (http://www.casa.gov.au/fsa/2000/sep/FSA41-43.pdf)

[deeceethree]

You might find your answer here:

www.avweb.com/news/airman/184446-1.html

The intro to the article:

"........a new hazard emerges: hydroplaning. It might be great for surfboards, but it's no fun at all when it happens to an airplane on the runway. Bruce Edston explains the three different forms of hydroplaning and offers some prevention strategies."

[Alex Whittingham]

The classic research on dynamic hydroplaning was conducted by NASA, I think using a Caravelle. Quoting from the NASA Technical Memorandum (NASA-TM-85652):

The contact pressure between tire tread and pavement establishes the escape velocity of bulk water drainage from beneath the tire footprint. High pressure tires can expel surface water more readily from the footprint than low pressure tires. When the aircraft ground speed equals or exceeds the escape velocity of water drainage from the footprint, choked water flow occurs. The tire has now reached a state of total dynamic hydroplaning. Test results .... indicate that the critical aircraft groundspeeds required for this total hydroplaning condition to occur on a flooded (runway water depth is greater than tire tread groove depth) pavements with an unbraked tire are approximately:

Spin-down (rotating tire) speed, knots = 9 x square root of Infl. pressure, psi
Spin-up (nonrotating tire) speed, knots = 7.7 x square root of Infl. pressure, psi

......... It is important that pilots be aware that the lower hydroplaning spin-up speed, rather than the high hydroplaning spin-down speed, represents the actual tire situation for touchdown on flooded runways.