How pilots stop airplanes from hydroplaning on wet runways?
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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.
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.
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.
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.
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.
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](https://en.wikipedia.org/wiki/American_Airlines_Flight_1420)
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.
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.
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](https://www.nasa.gov/vision/earth/improvingflight/aldf_demonstration.html) 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.
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?
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.
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