Hydroplaning

[hdaae]

Just pondering about the difference between hydroplaning speeds when taking off and landing.

Landing: V=7.7*Square(PSI)
T/O: V=8.6*Square(PSI)

What I would like to know is why there is a difference from a physics point of view.
I see the difference as far as you are starting rolling with the tires on the pavement when you take off, and when landing you are first entering the water, and therefore the speed will be higher.
But if anyone could give me a detailed explanation or direct me to a webpage that explains it 100% I would be greatful.

[411A]

Sorry hdaae, had a look, no reference on the NBAA website, altho it was there before, 'bout a year ago.
Only hydroplaned once...at the OLD Taipei airport, landing with a B707...and only "just" got stopped at the end. Good thing the reverse worked, and there was not much crosswind. Nasty business.

[FL310]

I can only assume that the difference is a result of the fact that when commencing a take off run the tyres have a good friction on the surface which they gradually lose during the progress, whereas during landing the friction only settles in after some time.
Taking this into account the different factors used may actually take care of this.

['%MAC']

When landing your wheels aren’t spun up, this is akin to water-skiing, hence you get a lower initial value for commencement of hydroplaning. During take-off, you are initially at zero speed, and the wheel is firmly planted on the ground with a fairly decent coefficient of friction. As you increase speed the wheel spins up slowly so the tire has minimal slip, and it has rotation when at the first onset of hydroplaning which ameliorates its effects, hence the higher speed for take-off. I would not view these equations as absolutes, they’re more heuristic. To wit, let’s say you have main wheels at 100 psi, that would lead you to believe that 77kts is your hydroplaning speed, well you might be at 75kts and experience hydroplaning, or you may never experience it. I noticed in a previous post that you like mathematical models, the data from hydroplaning was derived empirically by NASA, I think way back in ’66 (maybe earlier) see NASA TN-D 3515.

This is basically what FL said, again I prove my ability to interpret English into English