Aquaplaning or hydroplaning by tires of highway vehicles, aircraft or other wheeled vehicles occur when a water layer is formed between the wheels of the vehicle and the road surface, leading to traction loss preventing the vehicle responds to control inputs. If it happens to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled. Aquaplaning is a different phenomenon than when water on the road surface only acts as a lubricant. Traction is reduced on the wet pavement even when aquaplaning does not occur.
Video Aquaplaning
Cause
Any vehicle function that changes direction or speed depends on the friction between the tire and the road surface. The rubber tire groove is designed to disperse water from beneath the tire, providing high friction even in wet conditions. Aquaplaning occurs when the tire meets more water than it can disappear. The water pressure in front of the wheel forces the water slices under the leading edge of the tire, causing it to lift from the road. The tires then slide on a sheet of water with little, if any, direct road contact, and loss of control results. If multiple aquaplane tires, the vehicle may lose control of direction and shear until it collides with obstacles, or slow down enough so that one or more tires contact the ramp again and friction back.
The risk of aquaplaning increases with the depth of the puddle and the sensitivity of the vehicle to the depth of the water.
Water depth factor
- Depth of compacted wheel tracks and elongated pressure : Heavy vehicles can cause traces on the sidewalk over time that allow water to flow.
- Microscopic and makroteksure : Concrete can be preferred over hotmix asphalt because concrete offers better resistance to rut formation, although this depends on the age of the surface and the construction techniques used when paving. Concrete also requires special attention to ensure the texture is sufficient.
- Tilt slope and level : Cross slope is the extent to which the cross-sectional roads resemble higher upside U. Higher slopes allow water to flow more easily. Grade is the steepness of the road at a certain point, which affects both the drainage and the force provided by vehicles on the road. Vehicles tend to rise to aquaplane while traveling upwards, and are much more likely to do so in troughs of two connected hills where water tends to run. The result of slope and cross slope is called drainage gradient or "yield level". Most road design manuals require that drainage gradients in all road segments should exceed 0.5%, to avoid heavy water film during and after rain. The areas in which the drainage gradient may fall below the minimum 0.5% limit are found at the entrance and exit from the outer turns. This hot spot is usually less than 1% of the road length, but most of all skid crashes happen there. One method for road designers to reduce the risk of accidents is to move the cross-slope transition from the outer curve and to the straight-line portion, where the lateral force is lower. Where possible, cross-slope transitions should be placed slightly up or down, thereby avoiding that the drainage gradient drops to zero. The UK road design manual is actually requesting the placement of a cross-tilt transition in an artificial slope, if required. In some cases, permeable or concrete asphalt can be used to improve drainage in transition slope.
- Sidewalk width : Larger roads require a higher cross-dip to achieve the same level of drainage.
- Road arch
- Rainfall intensity and duration
Vehicle sensitivity factor
- Speed, acceleration, braking, and driver steering
- Wear tire tires : The tires used will make aquaplane easier for lack of depth of tread. Tread half wear produces aquaplaning about 3-4 mph (5-7 km/h) lower than with full tire tire.
- Tire inflation pressure : Underinflation can cause the tire to turn inward, increase the center of the tire and prevent the tread from clean water.
- Comparison of tire tread aspect : The longer and thinner the contact header, the less likely the tire will go up the aquaplane. Tires that provide the greatest risk of small diameter and width.
- Vehicle weight : The heavier on well-condensed tires will extend the contact patch, increasing the aspect ratio. Weight can have the opposite effect if the tire is underinflated.
- Vehicle type : Combined vehicles such as semi-trailers are more likely to experience uneven aquaplaning caused by uneven distribution of weight. A disassembled trailer will aquaplane faster than the taxi pulled. The pickup truck or the SUV trailer trailer also presents a similar problem.
There is no precise equation for determining the speed at which the vehicle will use aquaplane. Existing efforts have gained the practical rule of empirical testing. In general, cars start aquaplane with speeds above 45-58 mph (72-93 kph).
Motorcycles
Motorcycles benefit from narrow tires with canoe-shaped contact patches. Narrow tires are less susceptible to aquaplaning because heavy vehicles are distributed in smaller areas, and spherical tires are easier to push water sideways. This advantage is reduced on lightweight motorcycles with wide tires naturally, such as those in the supersport class. Furthermore, wet conditions reduce the lateral force that any tire can fit before sliding. While the slide in four-wheel vehicles can be repaired, the same slide on the motorcycle will generally cause the rider to fall. Thus, despite the relative lack of aquaplaning hazards in wet conditions, motorcyclists should be more careful because the overall grip is reduced by the wet road.
Maps Aquaplaning
In a motor vehicle
Response
What a driver experiences when a vehicle aquaplanes depends on which wheels lose traction and direction of travel.
If the vehicle is running straight, it may start to feel a bit loose. If there is a high road level under normal conditions, it may suddenly decrease. Small correction control input has no effect.
If the wheel is aquaplane, there may be a sudden increase in the engine RPM and show the speed as they start to spin. On the wide road, if the front wheel loses its grip, the car will suddenly drift toward the outside of the bend. If the rear wheel loses traction, the rear of the car will sag to the side. If all four wheels aquaplane at once, the car will slide in a straight line, again to the outside of the corner if the turn. When one or all of the wheels get back in the traction, there may be a sudden jerk in whatever direction the wheel indicates.
Recovery
Input control tends to be counterproductive during aquaplaning. If the car does not turn, reducing the accelerator can slow it enough to regain traction. Steering input can put the car into a slip where recovery will be difficult or impossible. If braking is unavoidable, the driver must do so smoothly and prepare for instability.
If the rear wheels are aquaplane and cause oversteer, the driver should aim toward the skid until the rear tire gets back in traction, and then quickly redirect in the other direction to straighten the car.
Prevention by driver
The best strategy is to avoid contributors to aquaplaning. Appropriate tire pressures, narrow and unloaded tires, and reduced speeds from moderately moderate grades in drying will reduce the risk of aquaplaning, as it avoids puddles.
The electronic stability control system can not replace defensive driving techniques and proper tire selection. This system relies on selective wheel braking, which depends on turn on the road contact. While stability control can help the recovery from slipping when the vehicle slows down enough to regain traction, it can not prevent aquaplaning.
Due to puddles and changing road conditions can require smooth and timely speed reductions, cruise control should not be used on wet or slippery roads.
On the plane
Aquaplaning can reduce the effectiveness of braking the wheels on a plane when landing or cancel off, when it can cause the aircraft to run from the end of the runway. Aquaplaning was a factor in the crash for Qantas Flight 1 when it ran from the end of the runway in Bangkok in 1999 when it rained heavily. Aircraft that can use upside-down braking have an advantage over a road vehicle in such situations, since this type of braking is unaffected by aquaplaning, but requires considerable distances to operate because it is not as effective as braking the wheels on a dry runway.
Aquaplaning is a condition that can exist when a plane lands on a runway surface contaminated with waterlogging, mud, and/or wet snow. Aquaplaning can have a serious adverse effect on soil control and braking efficiency. The three basic types of aquaplaning are dynamic aquaplaning, replaced rubber aquaplaning, and thick aquaplaning. One of the three can make the aircraft partially or completely uncontrollable at any time during the landing.
However this can be prevented by grooves on the runway. In 1965, the US delegation visited the Royal Aircraft Establishment at Farnborough to see their grooved runways to reduce aquaplaning and begin studies by the FAA and NASA. Grooving has since been adopted by most major airports around the world. A thin groove is cut in concrete that allows water to be lost and reduces the potential for aquaplane.
Type
Viscous
Thick aquaplaning is caused by thick water properties. A thin film of liquid no more than 0.025 mm is all that is needed. Tires can not penetrate fluid and tires spin on top of film. This can happen at a much lower speed than a dynamic aquaplane, but requires smooth or smooth surfaces such as asphalt or touchdown areas lined with accumulated rubber landing in the past. Such surfaces can have the same friction coefficient as wet ice.
Dynamic
Dynamic aeraplaning is a relatively high-speed phenomenon that occurs when there is a water film on the runway that is at least 1/10 inch (2.5 mm) deep. As the aircraft speed and water depth increase, the water layer builds an increasing resistance to displacement, resulting in the formation of water slices beneath the tire. At a velocity, called the aquaplaning velocity (V p ), the upward force generated by the water pressure is equal to the weight of the aircraft and the tire is lifted off the runway surface. In this condition, the tires no longer contribute to the directional control, and no braking action. Dynamic aeraplaning is generally associated with tire inflation pressures. Tests have shown that for tires with significant load and sufficient water depth for the number of treads so that the pressure of the dynamic head of the speed is applied to all contact fillings, the minimum speed for dynamic aquaplaning (V p ) at the node is about 9 times the square root of the tire pressure in pounds per square inch (PSI). For tire pressure of 64 PSI aircraft, aquaplaning speed is calculated at about 72 knots. This speed for wheels is rolling and not slipping; the locked wheel reduces V p to 7.7 times the square root of the pressure. Therefore, once the tire is locked by aquaplaning it will continue until the speed is reduced by other means (air resistance or back pressure).
Restore rubber
Reclaimed aquaplaning (steam) aquaplaning occurs during heavy braking that produces a protracted locked wheel skid. Only a thin layer of water on the runway is necessary to facilitate this type of aquaplaning. The tire slope generates enough heat to turn the water film into a steam pad that makes the tire take off. This side effect of heat causes rubber contact with the runway to return to its original uncured condition. Indication of an aircraft that has undergone a rubber aquaplaning recovery, is a typical 'steam-cleaned' mark on the runway surface and a patch of rubber that has returned on the tire.
Replaced rubber aquaplaning often follows a dynamic aquaplaning encounter, during which time the pilot may have a brake locked in an attempt to slow down the aircraft. Eventually the plane slowed down enough to where the tires made contact with the runway surface and the plane began to slip. The medicine for this type of aquaplane is for the pilot to release the brakes and allow the wheel to spin and apply moderate braking. Aquaplaning of replaced rubbers is dangerous because the pilot may not know when to start, and can withstand a very slow speed (20 knots or less).
Reduce the risk
Each aquaplaning tire reduces both the effectiveness of braking and directional control.
When faced with the possibility of aquaplaning, the pilot is advised to land on a grooved runway (if available). Touchdown speed should be as quiet as possible consistent with safety. After the nosewheel is lowered to the runway, moderate braking should be applied. If decelerations are not detected and aquaplaning is suspected, the nose should be lifted and aerodynamic pull is used to reduce speed to the point where the brakes are effective.
Proper braking technique is very important. The brakes should be applied firmly until they reach a point that only slips. In the first sign of the skid, the pilot must release the brake pressure and allow the wheel to spin upward. Direction control should be maintained as far as possible with the wheel. In a crosswind, if aquaplaning must occur, crosswind will cause the aircraft to simultaneously change the weather to wind (ie the nose will turn toward the wind) as well as the slide against the wind direction (the plane will tend to slide towards the moving air). For a small plane, hold your nose up as if doing a soft field landing and using the steering wheel to maintain aerodynamic direction control while holding the aileron against the wind in the best position to prevent lifting the wings should help. However, avoid landing in the pouring rain where the wind cross component is higher than the maximum wind wave shown in the Pilot Operations Handbook.
See also
- A slick path
- Traction (technique), for effects similar to aquaplaning
References
- Inline
- General
- B. N. J. Persson; U. Tartaglino; O. Album & amp; E. Tosatti (2004). "Sealing is the origin of rubber slipping on a wet road". Natural Materials . 3 (November 7): 882-885. arXiv: cond-mat/0412045 . doi: 10.1038/nmat1255. PMIDÃ, 15531886. < span>
- Smart Drivers - Driving in the Rain
- Airplane Flying Handbook, FAA-H-8083-3A Publication, available for download from the Standard Flight Services Web site at http://av-info.faa.gov.
External links
- NASA paper describing aquaplaning, TN D-2056 'Phenomenon pneumatic hydro conveyor'.
Source of the article : Wikipedia
0 Comments