Not a tire engineer, even though that is a job title I had, and even though I have 20 years of vehicle dynamics experience, where as we say, 70% is in the tires.

With that perspective, meh. Doesn't make much sense to me.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

Tire engineer here! I worked in design, testing, quality, and application.

I agree with Greg. It doesn't seem to make sense.

First, the writer is obviously not a native English speaker, so there may be some confusion in the translation.

Second, there are things that just do not make sense. For example: "..... The rubber hydroplane causes significant reduction in tyre life. This just about more than normal wear. ...."

Some of this is the translation into English, but hydroplaning does NOT cause significant tire wear - just the opposite! In fact, some of the wear testing we used to do had an upper limit on how much wet weather miles we could put on. That's not exactly like hydroplaning, but it indicates that tire test engineers are aware that wet weather causes REDUCED tire wear.

I used your link and got to a discussion on 5G and aircraft, but I couldn't see anything about tires in the discussion. I only did a quick look. Could you help me out as to where in the long discussion this quote comes from. (maybe later I'll do a more detailed search, but it seems odd to be discussing tires in a 5G thread!)

The issue is at the end of the thread attached. It has to do with tire damage caused by some hydroplaning conditions. I didn't realise there were at least 3 types of hydroplaning. The fellows/gals had run out of explanations.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

I am Scottish so yes native english just rubbish at it, ex mecheng and commercial pilot.

The Reverted Rubber Hydroplaning is the damaging one.

https://boldmethod.com/blog/lists/2019/02/the-thre...

And this one has some pics of the damage

https://www.faasafety.gov/gslac/ALC/course_content...

I wouldn't class the soft touch down blisters as damage ..

The main issue is the weight on wheels not triggering the lift dump spoilers which also means the autobrakes are not triggered and reverse buckets released.

Oh and most aircraft tyres are remoulds if that makes any difference.

Quote (yes native english)

Your English is better than my Scottish.

Thanks Alistair... I thought Engineers and Disasters could use some help so took it to the guys/gals that should know. I had no idea that there were 3 or more types of hydroplaning.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

As I said in disasters I think tyres and our aircraft tyres are amazing engineering. And very much ignored and assumed they will work.

I've kept up with Formula 1 stuff for decades, so I'm vaguely aware of the technology involved... just vaguely, though.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Dik - you probably put this in the wrong forum - try aircraft engineering maybe?

The thing with tyres (spelt the English way) on cars is going to be different as you start from the basis that at 0mph, your tyre is in contact with the ground and then loses contact in deep water as you speed up or hit some water, but your car tyre is probably still moving or if not then you're sliding towards the crash barrier and there's nothing you can do...

This is a bit different - the tyre isn't moving but is "gliding" / sliding on top of a thin film of water generating friction and heat, but not enough downwards force to dispel the water and start turning or at leas that's my understanding of it. It's also going really quite fast and for a long way, much more so than a car tyre.

So it seems to be somewhere between a dry tarmac lock up which just literally burns rubber off the tyres and a moving tyre dispelling water and in contact with the ground. So maybe something more like a lock-up which is being cooled by the water film and generating steam to add to the mix? So I suppose it all depends on at what temperature does the tyre start to grain or de-laminate in this strange wet lock up situation?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

I figured automobile guys would be most up on tires... but may cross-post... I occasionally do. One big difference is that airplane tires start from stationary to moving very fast.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Quote (So it seems to be somewhere between a dry tarmac lock up which just literally burns rubber off the tyres and a moving tyre dispelling water and in contact with the ground. So maybe something more like a lock-up which is being cooled by the water film and generating steam to add to the mix? So I suppose it all depends on at what temperature does the tyre start to grain or de-laminate in this strange wet lock up situation?)

There appears to be at least three types of hydroplaning... one of the worst is related to vapourising the fluid under the tire and causing great damage.

https://www.faasafety.gov/gslac/alc/course_content...

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

i don't think it is hydroplaning

Quote (i don't think it is hydroplaning)

The FAA article refers to it as hydroplaning... I don't know... not my normal monkey.

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

Well maybe think of it like a large variation in speed between what it should be if in complete contact with the ground and what it might be with this thin film of water.

The start point as Alistair is describing it is that the tyre is not rotating due to inertial / static friction as the wheel approaches the runway. The pilot flares a bit too much and the wheel is now skimming along the runway rotating maybe a bit, say 25% to 50% of "full" speed and hence creating some heat, but not fully rotating and not fully locked up. Hence why the tyre overall all the way around suffers damage from all this steam and heat as opposed to a flat spot from a complete lock up / stationary tyre?

I didn't realise it but there are sensors on the plane which stop you trying to land with your feet firmly on the brakes as the tyres definitely wouldn't like that and I guess the airplane wouldn't either.

All a bit different to what a car tyre sees I suspect.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

i have no issues with the other three being that as described by the FAA. And i would imagine its exactly the same for cars.

This is a stationary tyre which has been cold soaked at -50 deg to -70 deg being brought into contact with a water surface doing 135 knts (150 mph) at a very slow rate.

People do land on water with tyres and don't sink. Its done as a circus stunt.

https://www.youtube.com/watch?v=6OAEGPVcvhU

But i would say that's viscous hydroplaning.

little inch the braking system is actually quite reasonably intelligent these days with redundancy, protection and backup.

Things have come a long way since Concorde.

Two thoughts:

Isn't there or can't there be an ABS system for airplanes?

If a problem is caused by a non-rotating tire as the airplane lands, and that is too slow to accelerate; why not use motors to kick them up to speed just prior?

Alistair?

Rather than think climate change and the corona virus as science, think of it as the wrath of God. Feel any better?

-Dik

ABS on aircraft is intended to produce identical levels of braking between the main gear - the spread is so large that if one suddenly loses traction due to ice or hydroplaning the torque from the other about the aircraft CG can quickly steer the plane off the runway. If all main gear is locked up the system cannot tell as it needs to function without nose wheel inputs. In addition it doesn't matter what happens with the nose wheel under that condition as it is on the centerline and if it is not aligned with the CG in the direction of speed change then things have already gone wrong.

It's possible there are some that do use the nose wheel to detect ground speed some of the time - but I would not expect all aircraft to do so.

The problem isn't that it doesn't accelerate quickly enough - there is plenty of torque to do that. The problem is that the brakes are not being released to allow that to happen. These are big tires and they would need to be brought up to a ground speed up to 150 mph in a few seconds; putting a motor large enough to do that is impractical (cost of fuel to carry them around all the time, for example) and not needed.

In the article is says the reverted rubber problem is from heavy braking following a period of dynamic hydroplaning, not from being at zero speed during landing. The steam is acting to pressurize the volume between the tire and the runway preventing enough friction to overcome the heavy braking - which the pilot is likely doing because the plane isn't slowing very much. The ABS system will keep the mains on both sides at the same RPM - zero - and not override the pilot. As far as it is concerned the plane has stopped.

It's a terminology thing. I haven't heard 'locked wheel in wet weather braking' described as hydroplaning before, although we certainly used to see that, and of course F1 commentators were always banging on about flat spotting.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm?

I believe ABS was first brought in for aircraft and Concord was one of the first to have it.

We used to have an analogue system on the jetstream which was a spinning thing in the hub matzarette? I am waiting for a mate to message me the proper name of it.

Modern stuff the A220 has 2 brake control units with 2 main protected channels in each and a third emergency channel. Which then drive the Electro mechanical Actuators (EMA'S) which there are 4 of them.

I haven't flown anything that is over 5 tons which doesn't have some form of antiskid.

The Jetstream you could land with the brakes on and the tyres lasted under a second before deflating after flat spotting. A220 you would need to be in down graded emergency braking mode for that to happen. If one channel out it would be normal brake mode you could land with your feet pushing hard on the brakes and it would not blow out. You would touch down and then there would be a 6 second pause reduced breaking as the nose comes down and then it would give you max breaking available for the surface conditions.

Auto break systems are all linked to a G meter and will brake to meet a G value depending what you have selected off/low/med/high. And as DAve says they keep everything symmetrical so if one side is slipping it reduces the other. There is a 4 th option which is RTO for take-off and its way way harsher than high. To be honest i have never landed with high selected in the real aircraft.

There is a system in development that will warn us if the achieved G deceleration is sufficient to stop before the end of the runway. But I suspect that's not going to appear for a a few more years.

What we are talking about though is the not so common event that the pilot gives an utterly silky smooth landing when people on board don't know they are even on the ground.

They tend not to happen by intention its usually weather related and the pilot actually wanted to thump it in to get the rubber onto the tarmac. But a gust has given you a bit of lift and killed the decent off.

Most aircraft OEM's recommend a positive landing so air ground logic kicks in and there is no messing about with lift dumps not deploying etc.

Apparently Maxaret has been around since the 50s Link

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

that's them Lou

Got a bit interesting when one side seized and the other side wasn't.

Apart from that it worked very well as described in the article. Don't remember any issues with the reservoir filling up.