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Asked by: Mike Billman 1300 views General Aviation

What determines the speed at which hydroplaning occurs and how do you estimate or compute that speed?

Chris on May 20, 2012

9 times the square root of tire pressure

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John D. Collins on May 20, 2012

The speed that an aircraft tire will hydroplane is determined by the tire pressure. To calculate the speed, multiply the square root of the tire pressure in PSI times 9 to yield speed in Knots. This is the speed at which hydroplaning will commence. Assuming a tire pressure of 36 PSI, the square root is 6 and multiply this times 9 yields 54 Kts. You should keep your tires properly inflated to reduce the possibility of hydroplaning. Once hydroplaning starts, it can continue well below the minimum onset speed.

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Mike Billman on May 20, 2012

Thanks, John. I suspected as much. I also want to add that your answer pertains to wheels that are spinning. As I understand, there is a lower factor to multiply the square root of tire pressure by if the wheels are not spinning, as in a landing. I believe that factor is about 7.7. Is that the figure that you use?

Micah on May 21, 2012

Your wheels should begin spinning immediately upon contact with the runways surface; use the “spinning wheel” value, but most of all keep your tires properly inflated and fly the correct airspeed.

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