Hydroplaning (road vehicle)
Encyclopedia
Aquaplaning or hydroplaning by the tires of a road
vehicle
, aircraft
or sometimes roller coaster
occurs when a layer of water
builds between the rubber
tire
s of the vehicle and the road surface, leading to the loss of traction
and thus preventing the vehicle from responding to control inputs such as steering, braking or accelerating. If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled
.
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 and the sensitivity of a vehicle to that water depth.
There is no precise equation to determine the speed at which a vehicle will aquaplane. Existing efforts have derived rules of thumb from empirical testing. In general, cars aquaplane at speeds above 53 mph (72 km/h), where water ponds to a depth of at least 1/10 of an inch (2.5 mm) over a distance of 30 feet (9 meters) or more.
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.
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 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 begin to drift towards the outside of the bend. If the rear wheels lose traction, the back of the car will begin to 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.
If the rear wheels aquaplane and cause oversteer, the recovering occurs in the best possible way when the driver steers in the direction of the skid until the rear tires gain traction, and then rapidly steer in the other direction to straighten the car.
Electronic stability control
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.
or aborting a take-off, when it can cause the aircraft to run off the end of the runway. Aquaplaning was a factor in an accident to Qantas Flight 1
when it ran off the end of the runway in Bangkok
in 1999 during heavy rain. Aircraft which can employ reverse thrust 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, 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. This was initially developed by NASA for space shuttles landing in heavy rain. It 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.
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).
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. Remember that in a crosswind, if aquaplaning should occur, the crosswind will cause the aircraft to simultaneously weathervane into the wind as well as slide downwind.
Road
A road is a thoroughfare, route, or way on land between two places, which typically has been paved or otherwise improved to allow travel by some conveyance, including a horse, cart, or motor vehicle. Roads consist of one, or sometimes two, roadways each with one or more lanes and also any...
vehicle
Vehicle
A vehicle is a device that is designed or used to transport people or cargo. Most often vehicles are manufactured, such as bicycles, cars, motorcycles, trains, ships, boats, and aircraft....
, aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft 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.Although...
or sometimes roller coaster
Roller coaster
The roller coaster is a popular amusement ride developed for amusement parks and modern theme parks. LaMarcus Adna Thompson patented the first coasters on January 20, 1885...
occurs when a layer of water
Water
Water is a chemical substance with the chemical formula H2O. A water molecule contains one oxygen and two hydrogen atoms connected by covalent bonds. Water is a liquid at ambient conditions, but it often co-exists on Earth with its solid state, ice, and gaseous state . Water also exists in a...
builds between the rubber
Rubber
Natural rubber, also called India rubber or caoutchouc, is an elastomer that was originally derived from latex, a milky colloid produced by some plants. The plants would be ‘tapped’, that is, an incision made into the bark of the tree and the sticky, milk colored latex sap collected and refined...
tire
Tire
A tire or tyre is a ring-shaped covering that fits around a wheel rim to protect it and enable better vehicle performance by providing a flexible cushion that absorbs shock while keeping the wheel in close contact with the ground...
s of the vehicle and the road surface, leading to the loss of traction
Traction (engineering)
Traction refers to the maximum frictional force that can be produced between surfaces without slipping.The units of traction are those of force, or if expressed as a coefficient of traction a ratio.-Traction:...
and thus preventing the vehicle from responding to control inputs such as steering, braking or accelerating. If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled
Sled
A sled, sledge, or sleigh is a land vehicle with a smooth underside or possessing a separate body supported by two or more smooth, relatively narrow, longitudinal runners that travels by sliding across a surface. Most sleds are used on surfaces with low friction, such as snow or ice. In some cases,...
.
Causes
Every vehicle function that changes direction or speed relies on the friction between the tires and the road surface. If water comes between the tires and the road, friction may be reduced to the extent that the tires may slip, and the driver may lose control.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 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 rutsRut (roads)A rut is a depression or groove worn into a road or path by the travel of wheels or skis. Ruts can be formed by wear, as from studded snow tires common in cold climate areas, or they can form through the deformation of the asphalt concrete pavement or subbase material...
in the pavement over time that allow water to pool, negatively impacting draining.
- Depth of compacted wheel tracks and longitudinal depressions:Heavy vehicles can cause ruts
-
- 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 slopeCross slopeCross slope is a geometric feature of pavement surfaces; the transversal slope [%] with respect to the horizon. It is a very important safety factor. One task is to make water run off the surface to a drainage system, as Cross Slope is the main contributor to Pavement Drainage gradient. Very low...
and grade: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 the weight of the vehicle. 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 gradientDrainage gradientDrainage gradient is a term in road technology, defining the resulting vector of a road surface cross slope and longitudinal gradient .If the DG is too low, rain and melt water drainage will be insufficient...
or "resulting grade". Most road design manuals world wide 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 placing the 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.
- Pavement cross slope
-
- 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 patchContact patchContact patch is the portion of a vehicle's tire that is in actual contact with the road surface. It is most commonly used in the discussion of pneumatic tires, , where the term is strictly used to describe the portion of the tire’s tread that touches the road surface...
, the less likely a tire will aquaplane. Tires that present the greatest risk are small in diameter and wide.
- Tire tread aspect ratio: The longer and thinner the contact patch
-
- 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 from empirical testing. In general, cars aquaplane at speeds above 53 mph (72 km/h), where water ponds to a depth of at least 1/10 of an inch (2.5 mm) over a distance of 30 feet (9 meters) or more.
Motorcycles
MotorcycleMotorcycle
A motorcycle is a single-track, two-wheeled motor vehicle. Motorcycles vary considerably depending on the task for which they are designed, such as long distance travel, navigating congested urban traffic, cruising, sport and racing, or off-road conditions.Motorcycles are one of the most...
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
Sport bike
A sport bike, also written as sportbike, is a motorcycle optimized for speed, acceleration, braking, and cornering on paved roads, typically at the expense of comfort and fuel economy in comparison to less specialized motorcycles...
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.
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 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 begin to drift towards the outside of the bend. If the rear wheels lose traction, the back of the car will begin to 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
The recovering while traveling in a straight line occurs in the best possible way when the driver does not turn the steering wheel of the car or apply the brakes, and gently eases the pressure off the accelerator. The opposite of either of these actions could put the car into a skid from which recovery would be difficult or impossible. In such conditions when braking is unavoidable, the recovering most often occurs when the driver lightly pumps the brakes until aquaplaning has stopped.If the rear wheels aquaplane and cause oversteer, the recovering occurs in the best possible way when the driver steers in the direction of the skid until the rear tires gain 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
Electronic stability control is a computerized technology that may potentially improve the safety of a vehicle's stability by detecting and minimizing skids. When ESC detects loss of steering control, it automatically applies the brakes to help "steer" the vehicle where the driver intends to go...
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 may reduce the effectiveness of wheel braking in aircraft on landingLanding
thumb|A [[Mute Swan]] alighting. Note the ruffled feathers on top of the wings indicate that the swan is flying at the [[Stall |stall]]ing speed...
or aborting a take-off, when it can cause the aircraft to run off the end of the runway. Aquaplaning was a factor in an accident to Qantas Flight 1
Qantas Flight 1
Qantas Flight 1 is the flight number of the flagship Sydney to London route of Australia's Qantas, travelling via Bangkok.- Flight :Qantas flights travel between London and Australia on a route known as the "Kangaroo Route"...
when it ran off the end of the runway in Bangkok
Bangkok
Bangkok is the capital and largest urban area city in Thailand. It is known in Thai as Krung Thep Maha Nakhon or simply Krung Thep , meaning "city of angels." The full name of Bangkok is Krung Thep Mahanakhon Amon Rattanakosin Mahintharayutthaya Mahadilok Phop Noppharat Ratchathani Burirom...
in 1999 during heavy rain. Aircraft which can employ reverse thrust 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, 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. This was initially developed by NASA for space shuttles landing in heavy rain. It 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.
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 is nil. Dynamic aquaplaning is generally related to tire inflation pressure. Tests have shown that for tires with significant loads and enough water depth for the amount of tread so that the dynamic head pressure from the speed is applied to the whole contact patch, the minimum speed for dynamic aquaplaning (Vp) in knots is about 9 times the square root of the tire pressure in pounds per square inch (PSI). 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. Remember that in a crosswind, if aquaplaning should occur, the crosswind will cause the aircraft to simultaneously weathervane into the wind as well as slide downwind.
See also
- Traction (engineering), for effects similar to aquaplaning
External links
- NASA paper describing aquaplaning.