Hydroplaning

Question 1

Hydroplaning

Answer 1

● Hydroplaning occurs when the runway is wet and the tire no longer touches the surface of the runway
● A packed-snow or ice condition at a fixed temperature presents a relatively constant coefficient of friction with speed.
● This is not the case for a liquid (water or slush) state!
○ This is because water cannot be completely squeezed out from between the tire and the runway.

Question 2

Types of Hydroplaning

Answer 2

● There are three main types of hydroplaning:
○ Dynamic Hydroplaning
○ Viscous Hydroplaning
○ Reverted Rubber Hydroplaning

Question 3

Dynamic Hydroplaning

Answer 3

● This is due to standing water on the runway.
● In this case, the tire becomes completely supported by the water!
● As little as 3 mm of water on the runway combined with the “critical speed” of the tire will cause this

Question 4

Viscous Hydroplaning

Answer 4

● In this case, the tire ends up sliding on this thin film of water, instead of being completely lifted off of the runway by the water.
● It can occur at much slower speeds
● It usually only occurs on smooth surfaces.

Question 5

Reverted Rubber Hydroplaning

Answer 5

● During an emergency stop, the pilot may lock the brakes.
● The tire will then heat up, and the friction can cause the tire to become softer and more gummy like!
● Water will become trapped in the treads and the “melting tire,” which will then:
➢ Cause the water to boil and create steam
● This steam pressure will then lift the tire from the runway

Question 6

Formulas

Answer 6

● These equations give an approximation of the minimum speed necessary to hydroplane on a smooth, wet surface with tires that are bald or have no tread

Non-rotating tire:
○ 7.7 X √psi

● Rotating tire:
○ 9 X √psi

● For example, the minimum hydroplaning speeds for an aircraft with tires inflated to 49 PSI are calculated as:
● Non-rotating tire:
○ 7.7 X √49 = 54 kt;

● Rotating tire:
○ 9 X √49 = 63 kt

● Remember that the minimum speed at which a non-rotating tire will begin to hydroplane is lower than the speed at which a rotating tire will begin to hydroplane

Question 7

Hydroplaning-Antidotes

Answer 7

● If you suspect it is happening while on the roll, and you further suspect that the wheels have locked:
○ Release the brakes, and try to allow the tires to “spin up.”
○ This will increase the speed of the hydroplaning (remember the formula!) and,
○ It may give your anti-skid a chance to reset itself.
● When hydroplaning is encountered or expected, a pilot should also take full advantage of aerodynamic braking (spoilers, flaps, etc.) prior to using the brakes