How pilots stop airplanes from hydroplaning on wet runways?


How pilots stop airplanes from hydroplaning on wet runways?

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Large airplanes have anti-skid systems that function much like anti-lock brakes in passenger cars. However, you can’t fight the physics of standing water.

Airplanes require significantly more distance to stop on wet runways, and can easily hydroplane over standing water.

Above 60 knots of airspeed, much of an airplane’s braking acton is aerodynamic, and from engine thrust reversers (if equipped with them).

Spoilers add some drag, but their main effect is to kill lift to maximize friction between the wheels and the runway.

On a wet runway, pilots sometimes intentionally touch down harder to get better traction for the tire.

Having multiple wheels does help as the preceding wheel displaces the water for the following wheel.

Then there’s the a very good antiskid system.

Then you gonna anticipate the problem and plan to use a lot more thrust Reverser than normal.

There’s some pilot skill also, some plane require some pilot input to make the plane weigh more on the nose wheel to preserve steering authority.

Then there’s weight. Less weight, less braking effort. You can purposely take off lighter or you can burn all the reserve fuel before landing. Both of this will ease the braking.

The biggest factor is math. You land only if the math checks out. If not, divert to another place.

the tires treads are designed with channels for water to run through to make it easier for the tire to make contact with the ground

On top of the answers that focus on the airplane specifically, runways are not smooth asphalt like a highway. Runways are usually grooved to facilitate draining rain water.

[safety grooves](

One other thing that you don’t see so commonly anymore because propeller planes have gone out of favor commercially is some of them had a thing called “beta” which was reverse pitch on the blades. The pilot effectively is using the propeller(s) as a massive powered brake at that point instead of the tires.

What can you say on ELI5 that isn’t taken down for being concise and to the point?

Airplanes are designed to be controlled absent contact with the ground and contact with the ground does not obviate those controls such as rudder, flaps and ailerons. In short, it doesn’t matter as much in a plane if it does hydroplane because it has two system of control.

TLDR: They don’t

I once had a pilot explain it to me thus: “We land harder to break through the water”

I feel like that’s about as clear an ELI5 as there is.

Just a question to people who know more than me; could a high-pressure air hose be mounted in front of the wheels to blow the water away?

They use NASA developed technology to minimize hydroplaning on wet runways. Have you ever seen grooved roadways? Nasa design. Langley Research Center (NASA) has a [Aircraft Landing Dynamics Facility]( where aircraft tires and runway surfaces can be tested at race-car velocity. It was called Landing Loads Test Facility in the ’80s when I worked on their instrumentation. They were testing Space Shuttle tire designs while I was there.

The speed at which hydroplaning can occur is related to the tire pressure of the vehicle. (Horne’s Formula – speed in knots = 9 times the square root of the tire pressure in pounds per square inch) So, one thing that helps airplanes is having a much higher tire pressure than automobiles. A typical car will have a tire pressure of around 35 psi for a predicted hydroplaning speed of 53 knots (60mph). A typical large passenger plane has a tire pressure of around 200 psi resulting in a predicted hydroplaning speed of around 127 knots (146 mph). Of course, there are other things they do to reduce the effects of hydroplaning such as building the runways to better channel the water away.

Aircraft have spoilers on the wing that are set by the pilots to automatically deploy when the aircraft detects the wheels touching the ground.

This is really important to get proper braking as braking load is proportional to the weight on the wheels. Key factor in [this crash](

Another aspect that helps is the use of reverse thrust – this diverts engine power to go in reverse, and provides a braking force that’s independent of grip.

Other factors include the large grooves in the tyres and grooved runway surfaces (runway grooves tend to be perpendicular to the runway direction, tyre grooves are in line with the tyre – I suspect that’s to help with tyre wear and tread stiffness). Also, aircraft will usually land into wind to minimise ground speed, and can use different flap settings to change landing speed.

Also, pilots need to do landing distance calculations before landing considering many factors like weight and weather which includes if the surface is contaminated (such as water / snow / ice). If the calculations don’t work… they need to go for a longer runway / divert / slower landing speed.

All answers are correct, there is one additional important function of the spoilers.

Just as much as they increase drag, they push the aircraft downward.

You can apply brakes all you want but when a flight is touching down, its basically gliding and touching above the runway.

When spoilers are set, it puts a downward pressure on the airplane and thus the brakes become effective and thus slows the airplane PLUS prevents the airplane from hydroplaning PLUS pilots on a heavy rainy day slams the airplane to the runway so that the tires dont hydroplane.

Thats why you typically see a rough landing on a rainy day but smooth landing otherwise.

People have all mentioned various parts but the real answer is a combination of several things.

Runway design plays a huge part of it, they aren’t perfectly flat so water runs off of them instead of pooling and almost all large commercial runways are grooved with channels that are specifically engineered to remove water. Runway condition is also monitored and reported regularly to pilots before takeoff and landing.

Tire design is another huge part, airplanes don’t have racing slicks for tires, they have grooved patterns that are also specifically engineered to help remove water and prevent hydroplaning. Hydroplaning is also governed by basic physics, the speed at which a tire will hydroplane is 9*SqRoot(PSI) so it is known when both the main and nose gear are susceptible to it. This formula is also before the tire tread is factored in so real world will be better than that. As others have also said, airplanes have very smart antilock brake systems, far more advanced than anything you find on cars.

Finally, the way commercial planes land and stop helps with this. Thrust reversers are used for stopping, although they often do not have a huge impact because they take a second or so to deploy and then a bit longer to spool up in reverse. Either way, they do not need rubber on concrete contact to induce deceleration. More than anything the spoilers give a huge advantage to stopping. They dump lift and increase weight on wheels which helps to push the rubber through the water layer (that formula is also just for fighting gravity, not additional aerodynamic forces shoving the wheels downward). Add in that reverse thrust also points upwards and pushes down, the tires are designed for it, the ABS can account for it and the runway was designed to minimize it and it’s not that much of an issue anymore, especially when you calculate a unique landing distance for that specific airport’s current conditions and you know you have enough runway available for the aircraft’s ability to stop in those conditions.

You fly down the runway until your at a controllable speed then you use brakes very sparingly. If you have reverse capabilities you use that to help slow down and for centerline control.

God, this reminds me of my ex wife. She was always terrified of “hydroplaning” in the rain, but one day she was coming up to an underpass that was obviously flooded like 2′ deep. So she floored it, stalled out, flooded the intake and trashed the engine (in her freaking BMW). I said “what the hell were you thinking”, she said “I was going to hydroplane over it”. Yeah.

The real answer is we try to avoid landing on contaminated runways (>3mm standing water). Generally we just wait a few minutes for the storm to pass then land as that allows the water time to run off.

Landing on more than 3mm of water will almost guarantee Aquaplaning. In an aircraft, directional control isn’t hard because we have big aerodynamic control surfaces that work until we are slow enough for the tyres to break through and get grip. The most likely issue is tyre damage; when we aquaplane, sufficient heat is generated to melt the tyre rubber. You can see if it has happened if there are circular flat spots with little cracks running perpendicular to the tread.