Category: Test drive

The Enemy Does Not Sleep


Video: The Enemy Does Not Sleep

Отличия серверных жестких дисков от десктопных
Video: Archeage 2.9 / Враг не дремлет / The enemy does not sleep [Луций / Lucius] 2023, January
The Enemy Does Not Sleep
The Enemy Does Not Sleep







Carelessness is contraindicated to all of us, but it’s especially offensive to “fly away” to an experienced driver - a sort of “king” of the road. However, this often fails: an experienced one sometimes does not notice his own mistakes.

And so it happened with our reader Sh., Who replaced a good dozen cars in 30 years. In the May rain, he was driving to the country, the “nine” listened impeccably, and the driver, who knew every turn perfectly, walked them playfully, almost without touching the brake. The road turned smoothly to the left, and Sh., Having got into a protracted puddle, did not even slow down. But the steering wheel suddenly "felt better", and the car, as if not touching the water, whistled over the side of the road …. Landing in the shallow woods turned out to be rather hard …

Everything happened in a matter of moments, which the victim particularly complained about. And the fact that he, the master of winter driving on ice, the car refused to obey!

We have not talked about tire hydroplaning (this is what this phenomenon is called). One can only sympathize with the injured, especially the experienced ones, who are “really hurt” to “pierce” here: after all, insidious aquaplaning does not arise from scratch! To one degree or another, the driver himself is to blame. And if he is truly experienced, then danger must be foreseen.

What kind of "beast" is aquaplaning? Why can it be more dangerous than ice and easily catch an overconfident master of winter riding? Yes there is winter! Oh, pilots, “formulators” do not take skill, but how many of them flew off the track due to rain!

It is known for certain: the coefficient of adhesion of a car tire to clean, dry asphalt is about 0.8. With wet - one and a half to two times less. We’ll be more careful here … Even worse is the traction of tires with ice, where skillful management is generally unthinkable without special skills.

Aquaplaning is fundamentally different in that the tire, sliding on the water like a glider, has no direct contact with the road surface. Here, the adhesion coefficient is zero. So "control" here …

Studies have shown that as the speed increases, a water roller appears in front of the wheel, and a “water wedge” raises the tire from below, in front of the contact zone (Fig. 1). The stronger, the higher the speed. It is easy to calculate: if you substitute a flat plate for an air stream, then at a speed of 36 km / h the “high-pressure head” (additional pressure arising when the jet is braked) will be small - about 0.0006 kgf / cm2. Water is about 800 times denser - its high-pressure head will already be about 0.5 kgf / cm2. Do not rush to do a physical experience while sitting in a moving boat. In the palm of your hand will be a kilogram of silos … 70–80! And note: it grows "squared" in speed. At 72 km / h it will be four times more.

Each cubic centimeter of water is a tangible, solid gram of mass that needs to be dispersed in the tread slots and thrown out. In addition, water is not only a dense material, but also viscous. Fast movement along narrow, and even winding slots additionally resists. Thus, in order to throw out each “cube” of water, you need to apply more power to it, the faster we drive. In the end, in the "wedge" there is pressure that can lift the wheel. And it will completely lose contact with the road. This is aquaplaning.

If the puddle is deep enough, and the speed is only slightly higher than critical, then the resistance of the water rollers in front of the wheels is quite large - the speed drops rapidly, the slip stops. It is much more dangerous to enter a puddle at a speed at which the wheels hardly sink into the water, “gliding” along the surface. The water resistance is small … and such a “flight” threatens an accident. As happened with Sh.

So, aquaplaning belongs to the same category of hydrodynamic phenomena as gliding a glider or water skier on the surface of a reservoir - water resistance allows you to achieve high speed. A flat stone thrown along the “mirror” of the pond glides remarkably along it, even bouncing into the air … It is known that an artillery shell, having touched the surface of the water at a small angle, can bounce up - ricochet! Thanks for the high speed.

Back to the tire. Take a close look at her. Thoroughly worn out? There are two treads for a millimeter, and somewhere less … Many, saving, go on such. But is it always possible to save? On a dry road - please! On pure ice?.. Paradoxically, the height (depth) of the tread here is not so important - if only not completely bald! And in mud, snow or water, the requirements are completely different. The shallow depth of the grooves of the worn tread prevents water from quickly releasing the contact zone, contributing to the appearance of a “wedge”. And if the tire is too wide, with less load on the contact area and with less, respectively, pressure inside? An increase in the contact area is equivalent to an increase in the ski of a water sportsman - a wide wheel floats at a lower speed than a narrow one.

Even new tires behave differently depending on the design features, such as the carcass, the materials used, the tread pattern, its saturation, the number of slots for evacuating the water, their width, shape, etc. The problem is that the water (or and liquid mud, wet snowy “porridge”, etc.) were easily forced out of the contact zone. To this end, the tread is made directional when the main grooves resemble a herringbone (above - with the top forward). Then the top of this Christmas tree comes into contact with the coating first - and water (dirt, etc.) "does not lock" in the tread grooves or their intersections, but is gently (but persistently!) Forced out.

However, all directional tires have a natural flaw: they cannot be turned over. Otherwise, the water will flow back - from the sidewalls to the center. Many tires in the middle of the tread have a wide annular groove along which part of the water is dumped back, also destroying the "wedge".

The concept of "aquaplaning" applies not only to spring water, but also to dirty water - in half with clay, sand, etc. The density and viscosity of such a mixture is much greater, which many have been convinced more than once - the machine may stop obeying the mud even earlier, than in a clean puddle! Extremely treacherous snow, saturated with water. Indeed, self-cleaning of the tread - even the most outstanding - does not occur instantly.

Concluding the topic, we mention the road surface. If the wheels are smooth asphalt, the risk of aquaplaning is maximum. Here, a film of water just a few millimeters for the owner of bald tires can turn into a disaster. A rough, coarse-grained asphalt concrete eliminates aquaplaning until the water blocks the protruding pebbles by at least a few millimeters.

Summarize. Aquaplaning with a high speed and in a many-meter puddle is really dangerous for us: a sliding car is practically uncontrollable and almost devoid of brakes (more so than on ice). A car that does not have traction can turn sideways even from a gust of wind. And who knows how this will end?

What can be opposed to this? Own mind! First of all, do not "save" by riding on bald tires. But with the new in vain do not tempt fate. By the way, on a trip along a winding road with small puddles, it is easy to set your own “speed threshold”: if in puddles the wheels break into the axle boxes, slip, the car drives away, then it is unreasonable to drive into a large puddle at this speed. Leave it to inveterate "romantics." Slow down!

So there is aquaplaning: a - the speed is less than critical; b - the wheel “surfaced”.

This is how a tire works with directional tread (view from under the road surface).

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