road
A road is a linear way for the conveyance of traffic that mostly has an improved surface for use by vehicles (motorized and non-motorized) and pedestrians. Unlike streets, the main function of roads is transportation.
There are many types of ...
vehicle
A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses, mobility scooters for disabled people), railed vehicles (trains, trams), wa ...
,
aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air. It counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines ...
or other wheeled vehicle occurs when a layer of
water
Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as a ...
builds between the wheels of the vehicle and the road surface, leading to a loss of traction that prevents the vehicle from responding to control inputs. If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled
sled
A sled, skid, sledge, or sleigh is a land vehicle that slides across a surface, usually of ice or snow. It is built with either a smooth underside or a separate body supported by two or more smooth, relatively narrow, longitudinal runners ...
. Aquaplaning is a different phenomenon from when water on the surface of the roadway merely acts as a
lubricant
A lubricant (sometimes shortened to lube) is a substance that helps to reduce friction between surfaces in mutual contact, which ultimately reduces the heat generated when the surfaces move. It may also have the function of transmitting forces, t ...
. Traction is diminished on wet pavement even when aquaplaning is not occurring.
Causes
Every vehicle function that changes direction or speed relies on friction between the tires and the road surface. The grooves of a rubber tire are designed to disperse water from beneath the tire, providing high friction even in wet conditions. Aquaplaning occurs when a tire encounters more water than it can dissipate. Water pressure in front of the wheel forces a wedge of water under the leading edge of the tire, causing it to lift from the road. The tire then skates on a sheet of water with little, if any, direct road contact, and loss of control results. If multiple tires aquaplane, the vehicle may lose directional control and slide until it either collides with an obstacle, or slows enough that one or more tires contact the road again and friction is regained.
The risk of aquaplaning increases with the depth of standing water, higher speeds, and the sensitivity of a vehicle to that water depth.
Water depth factors
* Depth of compacted wheel tracks and longitudinal depressions: Heavy vehicles can cause ruts in the pavement over time that allow water to pool.
* Pavement micro- and macrotexture: Concrete can be preferable to hotmix asphalt because it offers better resistance to rut formation, though this depends on the age of the surface and the construction techniques employed while paving. Concrete also requires special attention to ensure that it has sufficient texture.
* Pavement
cross slope
Cross slope, cross fall or camber is a geometric feature of pavement surfaces: the transverse slope with respect to the horizon. It is a very important safety factor. Cross slope is provided to provide a drainage gradient so that water will run o ...
and
grade
Grade most commonly refers to:
* Grade (education), a measurement of a student's performance
* Grade, the number of the year a student has reached in a given educational stage
* Grade (slope), the steepness of a slope
Grade or grading may also ref ...
: Cross slope is the extent to which the cross-section of a road resembles an upturned U. Higher cross slopes allow water to drain more easily. Grade is the steepness of the road at a particular point, which affects both drainage and force exerted by the vehicle on the road. Vehicles are less likely to aquaplane while traveling uphill, and far more likely to do so at the trough of two connected hills where water tends to pool. The resultant of cross slope and grade is called
drainage gradient
Drainage gradient (DG) is a term in road design, defined as the combined slope due to road surface cross slope (CS) and longitudinal slope (hilliness). Although the term may not be used, the concept is also used in roof design and landscape arc ...
or "resulting grade". Most road design manuals require that the drainage gradient in all road sections must exceed 0.5%, in order to avoid a thick water film during and after rainfall. Areas where the drainage gradient may fall below the minimum limit 0.5% are found at the entrance and exit of banked outer curves. These hot spots are typically less than 1% of the road length, but a large share of all skid crashes occur there. One method for the road designer to reduce the crash risk is to move the cross slope transition from the outer curve and to a straight road section, where lateral forces are lower. If possible, the cross slope transition should be placed in a slight up- or downgrade, thereby avoiding that the drainage gradient drops to zero. The UK road design manual actually calls for placement of a cross slope transition in an artificially created slope, if needed. In some cases, permeable asphalt or concrete can be used to improve drainage in the cross slope transitions.
* Width of pavement: Wider roads require a higher cross slope to achieve the same degree of drainage.
* Roadway curvature
* Rainfall intensity and duration
Vehicle sensitivity factors
* The driver's speed, acceleration, braking, and steering
* Tire tread wear: Worn tires will aquaplane more easily for lack of tread depth. Half-worn treads result in aquaplaning about 3–4 mph (5–7 km/h) lower than with full-tread tires.
* Tire inflation pressure: Underinflation can cause a tire to deflect inward, raising the tire center and preventing the tread from clearing water.
* Tire tread aspect ratio: The longer and thinner the
contact patch
Contact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is commonly used in the discussion of pneumatic (i.e. pressurized) tires, where the term is used strictly to describe the portion of the tire’s ...
, the less likely a tire will aquaplane. tires that present the greatest risk are small in diameter and wide.
* Vehicle weight: More weight on a properly inflated tire lengthens the contact patch, improving its aspect ratio. Weight can have the opposite effect if the tire is underinflated.
* Vehicle type: Combination vehicles like semi-trailers are more likely to experience uneven aquaplaning caused by uneven weight distribution. An unloaded trailer will aquaplane sooner than the cab pulling it. Pickup trucks or SUVs towing trailers also present similar problems.
There is no precise equation to determine the speed at which a vehicle will aquaplane. Existing efforts have derived
rules of thumb
In English, the phrase ''rule of thumb'' refers to an approximate method for doing something, based on practical experience rather than theory. This usage of the phrase can be traced back to the 17th century and has been associated with various t ...
from empirical testing. In general, cars start to aquaplane at speeds above 45-58 mph (72–93 km/h).
Motorcycles
Motorcycle
A motorcycle (motorbike, bike, or trike (if three-wheeled)) is a two or three-wheeled motor vehicle steered by a handlebar. Motorcycle design varies greatly to suit a range of different purposes: long-distance travel, commuting, cruising ...
s benefit from narrow tires with round, canoe-shaped contact patches. Narrow tires are less vulnerable to aquaplaning because vehicle weight is distributed over a smaller area, and rounded tires more easily push water aside. These advantages diminish on lighter motorcycles with naturally wide tires, like those in the supersport class. Further, wet conditions reduce the lateral force that any tire can accommodate before sliding. While a slide in a four-wheeled vehicle may be corrected, the same slide on a motorcycle will generally cause the rider to fall. Thus, despite the relative lack of aquaplaning danger in wet conditions, motorcycle riders must be even more cautious because overall traction is reduced by wet roadways.
In motor vehicles
Speed
It's possible to approximate the speed at which total hydroplaning occurs, with the following equation.
Where is the tire pressure in psi and the result is the speed in mph for when the vehicle will begin to totally hydroplane. Considering an example vehicle with a tire pressure of 35 psi, we can approximate that 61 mph is the speed when the tires would lose contact with the road's surface.
However, the above equation only gives a very rough approximation. Resistance to aquaplaning is governed by several different factors, chiefly vehicle weight, tire width and tread pattern, as all affect the surface pressure exerted on the road by the tire over a given area of the contact patch - a narrow tire with a lot of weight placed upon it and an aggressive tread pattern will resist aquaplaning at far higher speeds than a wide tire on a light vehicle with minimal tread. Furthermore, the likelihood of aquaplaning drastically increases with water depth.
Response
What the driver experiences when a vehicle aquaplanes depends on which wheels have lost traction and the direction of travel.
If the vehicle is traveling straight, it may begin to feel slightly loose. If there was a high level of road feel in normal conditions, it may suddenly diminish. Small correctional control inputs have no effect.
If the
drive wheels
A drive wheel is a wheel of a motor vehicle that transmits force, transforming torque into tractive force from the tires to the road, causing the vehicle to move. The powertrain delivers enough torque to the wheel to overcome stationary for ...
aquaplane, there may be a sudden audible rise in engine RPM and indicated speed as they begin to spin. In a broad highway turn, if the front wheels lose traction, the car will suddenly drift towards the outside of the bend. If the rear wheels lose traction, the back of the car will slew out sideways into a skid. If all four wheels aquaplane at once, the car will slide in a straight line, again towards the outside of the bend if in a turn. When any or all of the wheels regain traction, there may be a sudden jerk in whatever direction that wheel is pointed.
Recovery
Control inputs tend to be counterproductive while aquaplaning. If the car is not in a turn, easing off the accelerator may slow it enough to regain traction. Steering inputs may put the car into a skid from which recovery would be difficult or impossible. If braking is unavoidable, the driver should do so smoothly and be prepared for instability.
If the rear wheels aquaplane and cause
oversteer
Understeer and oversteer are vehicle dynamics terms used to describe the sensitivity of a vehicle to steering. Oversteer is what occurs when a car turns (steers) by more than the amount commanded by the driver. Conversely, understeer is what occu ...
, the driver should steer in the direction of the skid until the rear tires regain traction, and then rapidly steer in the other direction to straighten the car.
Prevention by the driver
The best strategy is to avoid contributors to aquaplaning. Proper tire pressure, narrow and unworn tires, and reduced speeds from those judged suitably moderate in the dry will mitigate the risk of aquaplaning, as will avoidance of standing water.
Electronic stability control
Electronic stability control (ESC), also referred to as electronic stability program (ESP) or dynamic stability control (DSC), is a computerized technology that improves a vehicle's stability by detecting and reducing loss of traction ( skiddi ...
systems cannot replace defensive driving techniques and proper tire selection. These systems rely on selective wheel braking, which depends in turn on road contact. While stability control may help recovery from a skid when a vehicle slows enough to regain traction, it cannot prevent aquaplaning.
Because pooled water and changes in road conditions can require a smooth and timely reduction in speed, cruise control should not be used on wet or icy roads.
In aircraft
Aquaplaning, also known as hydroplaning, is a condition in which standing water, slush or snow, causes the moving wheel of an aircraft to lose contact with the load bearing surface on which it is rolling with the result that braking action on the wheel is not effective in reducing the ground speed of the aircraft.
Aquaplaning may reduce the effectiveness of wheel braking in aircraft on
landing
Landing is the last part of a flight, where a flying animal, aircraft, or spacecraft returns to the ground. When the flying object returns to water, the process is called alighting, although it is commonly called "landing", "touchdown" or ...
or
aborting
Abortion is the termination of a pregnancy by removal or expulsion of an embryo or fetus. An abortion that occurs without intervention is known as a miscarriage or "spontaneous abortion"; these occur in approximately 30% to 40% of pregnan ...
a
takeoff
Takeoff is the phase of flight in which an aerospace vehicle leaves the ground and becomes airborne. For aircraft traveling vertically, this is known as liftoff.
For aircraft that take off horizontally, this usually involves starting with a t ...
, when it can cause the aircraft to run off the end of the runway. Aquaplaning has been a factor in multiple aircraft accidents, including the destruction of
TAM Airlines Flight 3054
TAM Airlines Flight 3054 (JJ3054/TAM3054) was a regularly scheduled domestic passenger flight of TAM Airlines from Porto Alegre to São Paulo, Brazil. On the evening of July 17, 2007, the Airbus A320-233 serving the flight overran runway 35L a ...
which ran off the end of the runway in
São Paulo
São Paulo (, ; Portuguese for 'Saint Paul') is the most populous city in Brazil, and is the capital of the state of São Paulo, the most populous and wealthiest Brazilian state, located in the country's Southeast Region. Listed by the GaWC a ...
in 2007 during heavy rain. Aircraft which can employ
reverse thrust
Thrust reversal, also called reverse thrust, is the temporary diversion of an aircraft engine's thrust for it to act against the forward travel of the aircraft, providing deceleration. Thrust reverser systems are featured on many jet aircraft to ...
braking have the advantage over road vehicles in such situations, as this type of braking is not affected by aquaplaning, but it requires a considerable distance to operate as it is not as effective as wheel braking on a dry runway.
Aquaplaning is a condition that can exist when an aircraft is landed on a runway surface contaminated with
standing water
Water stagnation occurs when water stops flowing. Stagnant water can be a major environmental hazard.
Dangers
Malaria and dengue are among the main dangers of stagnant water, which can become a breeding ground for the mosquitoes that transmi ...
, slush, and/or wet snow. Aquaplaning can have serious adverse effects on ground controllability and braking efficiency. The three basic types of aquaplaning are dynamic aquaplaning, reverted rubber aquaplaning, and viscous aquaplaning. Any one of the three can render an aircraft partially or totally uncontrollable anytime during the landing roll.
However this can be prevented by grooves on runways. In 1965, a US delegation visited the
Royal Aircraft Establishment
The Royal Aircraft Establishment (RAE) was a British research establishment, known by several different names during its history, that eventually came under the aegis of the Ministry of Defence (United Kingdom), UK Ministry of Defence (MoD), bef ...
at Farnborough to view their grooved runway for reduced aquaplaning and initiated a study by the
FAA
The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
and
NASA
The National Aeronautics and Space Administration (NASA ) is an independent agency of the US federal government responsible for the civil space program, aeronautics research, and space research.
NASA was established in 1958, succeeding t ...
. Grooving has since been adopted by most major airports around the world. Thin grooves are cut in the concrete which allows for water to be dissipated and further reduces the potential to aquaplane.
Types
Viscous
Viscous aquaplaning is due to the viscous properties of water. A thin film of fluid no more than 0.025 mm in depth is all that is needed. The tire cannot penetrate the fluid and the tire rolls on top of the film. This can occur at a much lower speed than dynamic aquaplane, but requires a smooth or smooth-acting surface such as asphalt or a touchdown area coated with the accumulated rubber of past landings. Such a surface can have the same friction coefficient as wet ice.
Dynamic
Dynamic aquaplaning is a relatively high-speed phenomenon that occurs when there is a film of water on the runway that is at least 1/10 inch (2.5 mm) deep. As the speed of the aircraft and the depth of the water increase, the water layer builds up an increasing resistance to displacement, resulting in the formation of a wedge of water beneath the tire. At some speed, termed the aquaplaning speed (Vp), the upward force generated by water pressure equals the weight of the aircraft and the tire is lifted off the runway surface. In this condition, the tires no longer contribute to directional control, and
braking action
Braking action in aviation is a description of how easily an aircraft can stop after landing on a runway. Either pilots or airport management can report the braking action according to the U.S. Federal Aviation Administration. For an aircraft tire pressure of 64 PSI, the calculated aquaplaning speed would be approximately 72 knots. This speed is for a rolling, non-slipping wheel; a locked wheel reduces the Vp to 7.7 times the square root of the pressure. Therefore, once a locked tire starts aquaplaning it will continue until the speed reduces by other means (air drag or reverse thrust).
Reverted rubber
Reverted rubber (steam) aquaplaning occurs during heavy braking that results in a prolonged locked-wheel skid. Only a thin film of water on the runway is required to facilitate this type of aquaplaning. The tire skidding generates enough heat to change the water film into a cushion of steam which keeps the tire off the runway. A side effect of the heat is it causes the rubber in contact with the runway to revert to its original uncured state. Indications of an aircraft having experienced reverted rubber aquaplaning, are distinctive 'steam-cleaned' marks on the runway surface and a patch of reverted rubber on the tire.
Reverted rubber aquaplaning frequently follows an encounter with dynamic aquaplaning, during which time the pilot may have the brakes locked in an attempt to slow the aircraft. Eventually the aircraft slows enough to where the tires make contact with the runway surface and the aircraft begins to skid. The remedy for this type of aquaplane is for the pilot to release the brakes and allow the wheels to spin up and apply moderate braking. Reverted rubber aquaplaning is insidious in that the pilot may not know when it begins, and it can persist to very slow groundspeeds (20 knots or less).
Reducing risk
Any aquaplaning tire reduces both braking effectiveness and directional control.
When confronted with the possibility of aquaplaning, pilots are advised to land on a grooved runway (if available). Touchdown speed should be as slow as possible consistent with safety. After the nosewheel is lowered to the runway, moderate braking should be applied. If deceleration is not detected and aquaplaning is suspected, the nose should be raised and aerodynamic drag utilized to decelerate to a point where the brakes do become effective.
Proper braking technique is essential. The brakes should be applied firmly until reaching a point just short of a skid. At the first sign of a skid, the pilot should release brake pressure and allow the wheels to spin up. Directional control should be maintained as far as possible with the rudder. In a crosswind, if aquaplaning should occur, the crosswind will cause the aircraft to simultaneously weathervane into the wind (i.e. the nose will turn toward the wind) as well as slide downwind (the plane will tend to slide in the direction the air is moving). For small aircraft, holding the nose up as if performing a soft field landing and using the rudder to aerodynamically maintain directional control while holding the upwind aileron in the best position to prevent lifting the wing should help. However, avoid landing in heavy rain where the crosswind component of the wind is higher than the maximum demonstrated crosswind listed in the Pilot Operations Handbook.
See also
*
Road slipperiness
Road slipperiness is a condition of low skid resistance due to insufficient road friction. It is a result of snow, ice, water, loose material and the texture of the road surface on the traction produced by the wheels of a vehicle.
Road slipperin ...
*
Traction (engineering)
Traction, or tractive force, is the force used to generate motion between a body and a tangential surface, through the use of dry friction, though the use of shear force of the surface is also commonly used.
Traction can also refer to the ''maxim ...
, for effects similar to aquaplaning
*
Kugel fountain
A kugel fountain (also called a "floating" sphere fountain or by the pleonasmic name kugel ball) is a water feature or sculpture where a sphere sits in a fitted hollow in a pedestal, and is supported by aquaplaning on a thin film of water. Pres ...
References
;Inline
;General
*
Smart Motorist – ''Driving in the Rain'' * Airplane Flying Handbook, FAA Publication FAA-H-8083-3A, available for download from the Flight Standards Service Web site at http://av-info.faa.gov.